JPH083685A - Nonageing deep-drawn steel pressurized in cold and its production - Google Patents

Abstract

PURPOSE: To impart an excellent deep drawing characteristic (a high plasticity- to-strain ratio r_m) to an aluminum killed steel by specifying the compsn. of the aluminum killed steel and regulating the hot rolling temp. thereof.

CONSTITUTION: The compsn. consists of, by weight, ≤0.08% C, ≤0.1% acid sol. Al and ≤0.2% Mn and the balance Fe and unavoidable impurities. The slab of such compsn. is rolled at ≤1260°C to form a hot rolled sheet contg. solid soln. nitrogen and thereafter the hot rolled sheet is subjected to cold rolling and annealing at a recrystallization temp. to stabilize the solid soln. nitrogen, by which the deep drawn steel sheet of an elongated grain structure having the r_m value of at least 1.8 is obtd. Further preferably, the product of the amt. of the acid sol. Al and the content of the total N in the compsn. is specified to ≤5×10^-4 and 0.03 to 0.08% acid sol. Al and 0.003 to 0.007% total N are incorporated into the steel, by which the steel sheet having r_m of ≥0.02, tensile strength of 29 to 32 kg/cm² and total elongation of ≥42% is obtd.

COPYRIGHT: (C)1996,JPO

Description

Detailed Description of the Invention

[0001]

This invention relates to cold-drawn, deep-drawn, non-aged, aluminum killed steel. In particular, the invention relates to low manganese, batch annealed steel produced from slabs having reduced hot rolling temperatures. This steel is characterized by an elongated grain structure and a very high mean plastic strain rate.

[0002]

BACKGROUND OF THE INVENTION It is well known that deep drawn steels require very high mean plastic strain (r _m ) of 1.8 or higher. The average plastic strain rate is defined by r _m = (r ₀ ° + r ₉₀ ° + 2r ₄₅ °) / 4. High r _m values can be determined, for example, by Ti,
This has been accomplished by adding various carbide and / or nitride formers such as Cd, Zr, B, etc. to the molten steel composition. However, the addition of such elements to produce deep drawn steels is not desirable because it increases the cost of the alloy. Also, similarly high r _m
It is also known that an aluminum killed steel having an equiaxial grain structure with a certain value can be produced by continuous annealing if aluminum nitride is precipitated before cold reduction. A batch annealed aluminum killed steel with an elongated grain structure can have aluminum nitride deposited during the slow heat up prior to the start of recrystallization in the annealing resulting in an r _m value of about 1.8. . Unlike batch anneal, aluminum nitride forms a high r _m value without precipitating before recrystallization in continuous anneal because of too fast heating rate. In order to produce a continuous annealed aluminum killed steel with a high r _m value, use of high coiling temperatures after hot rolling or precipitation of relatively cold slabs to precipitate aluminum nitride before cold reduction. This is done by reheating to a temperature sufficient to redissolve the aluminum nitride that precipitates during cooling of the slab following casting.

The following prior art discloses cold-killed aluminum killed steel produced by continuous annealing. U.S. Pat. No. 4,145,235 discloses a method of producing a low manganese aluminum killed steel having a high r _m value by hot winding the hot rolled steel at temperatures below 735 ° C. It has a r _m value up to 2.09 after continuous annealing. U.S. Patent No. 4,
478,649 discloses a method of directly hot rolling continuously cast aluminum killed steel slabs without reheating the slabs. The cast slab is hot-rolled before cooling to a temperature below Ar ₃ to avoid aluminum nitride precipitation. Aluminum nitride is deposited before continuous annealing by hot rolling the sheet after hot rolling at a temperature of at least 780 ° C.
U.S. Pat. No. 4,698,102 teaches that for aluminum killed steels, 12 so that the aluminum nitride deposited during cooling of the slab following casting does not remelt before hot rolling.
It is disclosed to use a slab temperature of 40 ° C. or less. It is disclosed that at a winding temperature after hot rolling of 620 to 710 ° C., the remaining dissolved nitrogen precipitates before continuous annealing. U.S. Pat. No. 4,116,729 discloses cooling a continuously cast aluminum killed steel slab to a temperature in the range of 650 ° C. to Ar ₃ for at least 20 minutes to precipitate aluminum nitride. The slab is then reheated to 950 to 1150 ° C. for hot rolling without remelting the aluminum nitride. R _m values after continuous annealing are disclosed those up to 1.6.

US Pat. No. 4,627,881 discloses that nitrogen should be 0.0
Production of continuously annealed aluminum killed steel with a high r _m value by adjusting the content of phosphorus to 025% or less, phosphorus to 0.010% or less, and the sum of phosphorus and 5 times nitrogen to 0.020% or less. The method of doing is disclosed. The slab is reheated in the temperature range of 1050 to 1200 ° C. and hot rolled. The hot rolled sheet was wound at temperatures below 650 ° C. Continuous annealing sheets cold reduced had r _m values up to 2.1. It is also known that continuous annealed aluminum killed steels with high r _m values can be produced by increasing the molten aluminum in the melt. U.S. Pat. No. 3,798,076 shows 0.13 after continuous annealing.
Disclosed is an aluminum killed steel having a molten aluminum of ˜0.33% and an r _m value of up to 1.91.

It is known that aluminum killed steels with similar high r _m values can be produced by batch annealing. U.S. Pat. No. 3,959,029 discloses performing conventional slab hot rolling with nitrogen kept in solution to prevent aluminum nitride from precipitating, i.e. prior to batch annealing. R _m up to 2.23 for non-aged aluminum killed steel by decarbonizing the sheet cold-rolled during annealing to less than 0.01% carbon.
The value is disclosed. U.S. Patent No. 4,473,411 discloses a having r _m values up to 1.85, batch annealed aluminum killed steel. Conventional (126
Sheets were produced from slabs having 0.12-0.24% manganese that were hot rolled without aluminum nitride precipitation using a hot rolling means (with a slab dropout temperature of 0 ° C.). Sheets hot rolled is cold reduced, and to increase the r _m values, the cooling point temperature was adjusted carefully during annealing.

[0006]

The addition of carbide and / or nitride forming elements to the melt to produce non-aging deep drawn steel is not desirable from an alloy cost standpoint. The melt processing techniques required to reduce residual carbon, nitrogen or phosphorus, ie vacuum degassing, tribe stirring, flux, etc., are expensive. To produce non-aged deep drawn aluminum killed steel, increasing the coiling temperature is not desirable due to uneven cooling rate, and hot rolling during cooling from elevated coiling temperature. It is very difficult to remove the scale formed on the formed sheet. Repeated special decarbonization anneals for the production of non-aged deep drawn aluminum killed steels are undesirable as they add cost. Therefore, there is a need to provide an inexpensive non-aging deep drawn aluminum killed steel. In particular, batch annealed aluminum having an r _m value of 1.8 or higher, which can be produced using conventional methods, or methods which add no more cost than conventional methods and are preferably lower cost. There is a need to provide killed steel.

The main object of the present invention is to stir or flux the melt without the use of melt alloying additives or without degassing to reduce the residual carbon, nitrogen or phosphorus to a very small amount. It is to produce aged deep drawn aluminum killed steel. Another object of the present invention is to produce a non-aged deep drawn aluminum killed steel without the use of elevated winding temperatures after hot rolling. Yet another object of the present invention is to produce a non-aged deep drawn aluminum killed steel without repeated special batch annealing such as decarbonization.

[0008]

SUMMARY OF THE INVENTION The present invention is a cold rolled, non-aging, recrystallized batch annealed steel characterized by an elongated grain structure having an r _m value of at least 1.8. Up to 08% by weight carbon, up to 0.1% by weight acid-dissolved aluminum, up to 0.2% by weight manganese, the balance essentially consisting of iron and inevitable impurities, about 1
It relates to a method for making sheeted steel with dissolved nitrogen from slabs hot rolled from temperatures below 260 ° C. More preferably, the steel is 0.05 wt% or less carbon, 0.03 to 0.08 wt% acid-dissolved aluminum, 0.02 wt% or less manganese, 0.003 to 0.
It essentially consists of 007% by weight of total nitrogen, but the product of the weight% of acid-dissolved aluminum and the weight% of total nitrogen is not more than 5 × 10 ^-4 . Particularly preferably, the steel is 5
After annealing at a temperature of thirty-eight to six hundred forty-nine ° C., has a r _m value of at least 2.0, 0.16 wt% manganese, 0.05 to 0.06 wt% acid soluble aluminum,
0.004 to 0.006% by weight of total nitrogen, but the product of the weight% of acid-dissolved aluminum and the total weight of nitrogen is 2 × 10.
^-4 in the range of to 4 × 10 ^-4, essentially consists in and about 1170 ° C. is hot rolled, is manufactured from a continuous cast slab.

A feature of the present invention is characterized by an elongated granular structure and an r _m value of at least 1.8, with up to 0.08% carbon by weight, less than 0.1% by weight acid-dissolved aluminum,
Manganese up to 0.20% by weight, the balance essentially consisting of iron and unavoidable impurities, produced from slabs hot-rolled from temperatures below about 1260 ° C. by forming sheets with dissolved nitrogen, It is in cold rolled, non-aging recrystallized batch annealed steel sheet.

Another feature of the invention is characterized by an elongated grain structure and an r _m value of at least 2.0, 0.05%.
Less than carbon by weight, 0.02-0.1% by weight acid-dissolved aluminum, less than 0.20% by weight manganese, the balance essentially consisting of iron and unavoidable impurities, hot rolled from temperatures below about 1175 ° C. Cold-rolled, non-aged recrystallization batch-annealed steel sheet produced by forming a sheet with molten nitrogen from a continuous cast slab.

Yet another feature of the present invention is characterized by an elongated granular texture and an r _m value of at least 1.8,
Carbon less than 08% by weight, less than 0.01% by weight of acid-dissolved aluminum, less than 0.20% by weight of manganese, nitrogen as impurities, the product of the% by weight of acid-dissolved aluminum and the total% of nitrogen being Is less than 5 × 10 ⁻⁴ , and the balance consists essentially of iron and unavoidable impurities.
In cold-rolled, non-aged recrystallization batch annealed steel sheets produced by forming sheets with molten nitrogen from continuously cast slabs hot rolled from the following temperatures.

Yet another feature of the present invention is characterized by an elongated granular texture and an r _m value of at least 2.0,
05% by weight or less of carbon, 0.03 to 0.08% by weight of acid-dissolved aluminum, 0.20% by weight or less of manganese,
It contains 0.003 to 0.007% by weight of total nitrogen, the product of the weight% of acid-dissolved aluminum and the total weight of nitrogen being not more than 5 × 10 ⁻⁴ , the balance being iron and inevitable impurities. A cold-rolled, non-aged, re-crystallized batch annealed steel sheet made by forming a sheet with molten nitrogen from a continuously cast slab that becomes essentially and is hot rolled at a temperature of about 1175 ° C. or less. It is in.

Yet another aspect of the invention is characterized by an elongated granular texture and an r _m value of at least 2.0,
05% by weight or less of carbon, 0.05 to 0.06% by weight of acid-dissolved aluminum, 0.16% by weight or less of manganese,
It contains 0.004 to 0.006% by weight of total nitrogen, the product of the weight% of acid-dissolved aluminum and the total weight of nitrogen being 2 × 10 ⁻⁴ to 4 × 10 ⁻⁴ , the balance being iron. And cold-rolled, non-aged recrystallized, which consists essentially of unavoidable impurities and is made into a sheet with molten nitrogen from a continuously cast slab that is hot-rolled from a temperature of about 1175 ° C. or less. Located on a batch annealed steel plate.

Another feature of the present invention is 0.08% by weight or less of carbon, 0.1% by weight or less of acid-dissolved aluminum, 0.
Providing a slab consisting essentially of 20 wt% or less manganese, the balance being iron and unavoidable impurities, hot rolling the slab having a temperature of less than about 1260 ° C., descaling the hot rolled sheet, Cold depressing the descaled sheet and recrystallizing batch annealing the cold reduced sheet, the annealed sheet being non-aged and having an elongated grain structure and at least 1.8.
And the r _m value of the sheet steel.

Another feature of the present invention is 0.08% by weight or less of carbon, 0.1% by weight or less of acid-dissolved aluminum, 0.
Prepare a melt consisting essentially of 20% by weight or less of manganese, and the balance of iron and unavoidable impurities.
Cast into a slab having the following thickness, hot rolling the slab at a temperature of less than about 1260 ° C. into a sheet with molten nitrogen, descaling the hot rolled sheet, and descaled sheet Cold-reducing, and re-crystallizing batch annealing the cold-reduced sheet, the annealed sheet being non-aged and characterized by an elongated grain structure and an r _m value of at least 1.8. It is in the method of manufacturing sheet steel.

Another feature of the present invention is 0.05% by weight or less of carbon, 0.02 to 0.1% by weight of acid-dissolved aluminum, 0.20% by weight or less of manganese, and the balance of iron and inevitable impurities. Prepare a melt that becomes essentially, cast the melt into a slab, hot roll the slab at a temperature of less than about 1175 ° C. into a sheet with melted nitrogen, and hot roll the sheet. Descaling, cold rolling the descaled sheet, and recrystallizing batch annealing the cold rolled sheet, wherein the annealed sheet is non-aged and has an elongated grain structure and at least 2. A method for producing sheet steel characterized by an r _m value of 0.

Another feature of the present invention is 0.08% by weight or less of carbon, 0.01% by weight or more of acid-dissolved aluminum,
Manganese up to 0.20% by weight, and nitrogen as an impurity, provided that the weight% of acid-dissolved aluminum and the weight% of total nitrogen
And a slab consisting essentially of 5 × 10 ⁻⁴ or less is prepared, and the slab having a temperature of about 1260 ° C. or less is hot-rolled into a sheet having molten nitrogen, and hot-rolled. Descaled sheet, cold rolled the descaled sheet, and recrystallized batch annealed the cold rolled sheet, the annealed sheet being non-aging and having an elongated grain structure. At least 1.
A sheet steel manufacturing method characterized by an r _m value of 8.

Another feature of the present invention is 0.05% by weight or less of carbon, 0.03 to 0.08% by weight of acid-dissolved aluminum, 0.20% by weight or less of manganese, 0.003 to 0.
A melt containing 007% by weight of total nitrogen, the product of the weight% of acid-dissolved aluminum and the weight% of total nitrogen being not more than 5 × 10 ⁻⁴ , the balance being essentially iron and inevitable impurities. Is prepared, the melt is cast into a slab, the slab is cooled to a temperature of Ar ₃ or lower to precipitate aluminum nitride, and the slab is reheated to a temperature of 1175 ° C. or lower to remelt the aluminum nitride. The slab with at least Ar ₃
Hot rolling into a sheet having a finishing temperature equal to and a cooling temperature of 593 ° C. or less, the hot rolled sheet having dissolved nitrogen, descaling the hot rolled sheet and descaling Cold rolled the sheet,
A method of making a sheet steel comprising recrystallizing batch annealing a cold rolled sheet, the annealed sheet being non-aged and characterized by an elongated grain structure and an r _m value of at least 2.0. It is in.

Other features of the present invention are: 0.05% or less carbon, 0.05 to 0.06% by weight acid soluble aluminum, less than 0.20% manganese, 0.004 to 0.
006% by weight of total nitrogen, the product of the weight% of acid-dissolved aluminum and the total weight of nitrogen being 2 × 10 ⁻⁴ to 4 ×.
Providing a melt consisting essentially of iron and unavoidable impurities, the balance being in the range of 10 ⁻⁴ , casting the melt into a slab, cooling the slab to a temperature of Ar ₃ or lower, to remove aluminum nitride. Precipitating, reheating the slab to a temperature of 1175 ° C. or lower to redissolve the aluminum nitride, hot rolling the slab to a sheet having a finishing temperature at least equal to Ar ₃ and a cooling temperature of 593 ° C. or less, Hot-rolled sheet having dissolved nitrogen, descaling the hot-rolled sheet, cold-rolling the descaled sheet, re-crystallizing batch annealing the cold-rolled sheet And the annealed sheet is non-aged and is in a process for making sheet steel characterized by an elongated grain structure and an r _m value of at least 2.0.

Another feature of the present invention is 0.05% by weight or less of carbon, 0.05 to 0.06% by weight of acid-dissolved aluminum, 0.16% by weight or less of manganese, 0.004 to 0.
006% by weight of total nitrogen, the product of the weight% of acid-dissolved aluminum and the total weight of nitrogen being 2 × 10 ⁻⁴ to 4 ×.
In the range of 10 ⁻⁴ , the balance providing a melt consisting essentially of iron and unavoidable impurities, casting the melt into a slab, cooling the slab to a temperature of Ar ₃ or less to remove aluminum nitride. Precipitating, reheating the slab to a temperature of 1175 ° C. or lower to redissolve the aluminum nitride, hot rolling the slab to a sheet having a finishing temperature at least equal to Ar ₃ and a cooling temperature of 593 ° C. or less, Hot-rolled sheet having dissolved nitrogen, descaling the hot-rolled sheet, cold-rolling the descaled sheet, re-crystallizing batch annealing the cold-rolled sheet The annealed sheet is non-aging, with an elongated grain structure and at least 2.
A method for producing sheet steel characterized by an r _m value of 0.

The advantages of the present invention are produced by hot rolling a slab of reduced temperature, which results in reduced energy costs, improved yield and productivity and extended slab furnace life. , An elongated grain structure and a cold-rolled, non-aged recrystallization batch annealed aluminum killed steel characterized by an r _m value of at least 1.8. Further advantages of the present invention include producing steel from thin continuously cast slabs. Further additional advantages of the invention include the production of steel using reduced annealing temperatures, thereby reducing annealing time and energy. The above as well as other objects, features, and advantages of the present invention will become apparent in view of the following detailed description.

[0022]

DETAILED DESCRIPTION OF THE INVENTION Sheet in the present invention is understood to mean both cold-rolled strips of indefinite length and cold-rolled strips of a certain length. In addition, the cold rolled sheet of the present invention,
It can be produced from continuously cast slabs from ingots or melts rolled in a slab mill. The chemical composition of the steel of the present invention consists essentially of carbon 0.08% or less, acid-dissolved aluminum 0.1% or less, manganese 2% or less (all by weight), and the balance iron and inevitable impurities. It is a thing.

As will be described in more detail below, the composition of aluminum, nitrogen and manganese is important for flexibility and good drawability individually during processing.
Equally important is the product of aluminum and nitrogen, ie wt% aluminum dissolved in the acid × wt% total nitrogen. The composition of aluminum and nitrogen, the product of which is preferably 5 × 10 ⁻⁴
It was determined below that it is more preferably adjusted to be in the range of 2 × 10 ⁻⁴ to 4 × 10 ⁻⁴ . When the hot rolling needs to be performed for a relatively long time, it is extremely important to control the product of aluminum and nitrogen.

The manganese should be at least 0.05% by weight to prevent hot embrittlement due to sulfur during hot rolling. If manganese is not low and about 0.24
Beyond weight percent, insufficient nitrogen remains dissolved in the hot rolled sheet made from the reduced temperature slabs of the present invention. For the lowest slab and batch anneal temperatures and the highest r _m values, manganese is preferably less than 0.20 wt%, more preferably less than 0.2.
It should be below 16% by weight.

For aluminum killed steel, at least 0.01% by weight of acid-dissolved aluminum is required to deoxygenate a melt having a ratio of acid-dissolved aluminum to total nitrogen of at least 2: 1. Maintaining this ratio ensures that residual nitrogen is present as aluminum nitride so that the recrystallized batch annealed steel is non-aged. For this reason, the acid-dissolved aluminum should be at least 0.02% by weight. Since annealed steels have excessive hardness, reduced drawability and excessive alloy cost, acid-dissolved aluminum is less than 0.1%.
It should not exceed 01% by weight. To minimize slab and batch anneal temperatures and maximize r _m values, the acid-dissolved aluminum should be 0.08 wt% or less. More preferably, the acid-dissolved aluminum is 0.
03-0.08% by weight, most preferably 0.05-0.
It should be 06% by weight.

Normal residue amount, ie 0.01% by weight of total nitrogen
Impurities of less than, less than 0.02% by weight phosphorus and less than 0.018% by weight sulfur are acceptable. For maximum drawability, total nitrogen should preferably be less than 0.008% by weight. More preferably, the total nitrogen is 0.003-0.
007% by weight, most preferably 0.004 to 0.006
It should be wt%. The carbon should not exceed 0.08% by weight as it causes excessive hardness in the batch annealed steel. Carbon is preferably 0.03 to 0.05% by weight.

A slab with a normal thickness of 150-250 mm is hot-rolled to a gradual reduction in thickness, with a series of roughing stands to a thickness of about 30 mm, and with a series of finishing stands. About 2.5m
made into steel with a thickness of m. The hot rolled steel is then coiled, descaled, cold reduced and recrystallized batch annealed. Non-aged, batch annealed aluminum killed steel requires that nitrogen be retained in the solid solution (not precipitated as aluminum nitride) in the hot rolled sheet after hot rolling. Prior to hot rolling, the slab is reheated due to the slab being cooled to a temperature below Ar ₃ and the hot rolled sheet serves to form the recrystallized structure required for good r _m values. Sufficient aluminum nitride must be redissolved so that it has dissolved nitrogen. For slabs that have been hot rolled directly after continuous casting or from slabs for plate rolling, nitrogen will not precipitate as aluminum nitride if the slab is not cooled to a temperature below Ar ₃ .
Therefore, it is not necessary to reheat the directly rolled slab. Since the directly rolled slab does not need to remelt the aluminum nitride, it does not need to raise the temperature of the pre-cooled slab to below Ar ₃ .

The precipitation of aluminum nitride during the heating stage of the batch anneal cycle causes the formation of the desired strong [111] recrystallized structure which gives the r _m value required for good draw performance. For cold rolled and recrystallized batch annealed steels, thermal machining of the slab during hot rolling is performed in such a way that the amount of aluminum nitride in the hot rolled sheet is minimized. Done. "SOLUTION
AND PRECIPITATION OF ALUMINUM NITRIDE IN RELATION
TO THE STRUCTURE OF LOW CARBON STEELS, Trans.ASM, 46
(1954) 1470-1499 ”, the paper by WCLeslie stated that the melting temperature of aluminum nitride during hot rolling is a function of the weight percent product of total nitrogen and acid dissolved aluminum present in the steel. ing. Whether continuously cast or manufactured from an ingot, a slab of normal thickness cooled to below Ar ₃ is at least due to the complete remelting of the aluminum nitride formed during cooling of the slab after casting. 126
It is reheated to a temperature of 0 ° C. before hot rolling.

Following reheating, the thick slab was hot rolled through a roughing stand where the slab temperature was 3.2.
The temperature is reduced from about 1260 to about 1040 ° C in 5 to 3.75 minutes. Steel at a thickness of 25-30 mm at about 1040 ° C is further reduced to a thickness of about 2.5 mm by passing it through a multi-stand finishing mill. The temperature of the steel is lowered from about 1040 ° C to the steel outlet temperature (finishing temperature) of about 870 ° C in about 10 seconds or more. The slab is preferably processed to a finishing temperature of at least 870 ° C. in order to control grain size as well as avoid aluminum nitride precipitation. Also, the cooling temperature is adjusted to minimize aluminum nitride precipitation. At the finish rolling exit, the steel is 650 ° C or less, more preferably 593 ° C or less, most preferably 56 ° C or less, before being wrapped into the coil.
Water quench to a temperature below 6 ° C. This is a suitable temperature for initiating the long-term process of cooling the hot rolled steel into coil form and avoiding the precipitation of large amounts of aluminum nitride. Thus, a large amount of nitrogen is retained in solution in the hot rolled steel prior to cold reduction. About 7
At coiling temperatures raised above 00 ° C., precipitation of excess aluminum nitride, which guarantees practical drawbacks in order to obtain good deep drawability and a high r _m value by subsequent cold reduction and batch annealing. Will result.

If manganese was reduced and aluminum and nitrogen were adjusted, it was determined that the slab should not be at a high temperature of 1260 ° C. or higher after batch annealing to obtain a high r _m value. Was done. The slab is at a temperature below 1175 ° C, most preferably about 1149
It is preferably reheated to ° C and hot rolled from that temperature.

[0031]

EXAMPLE Aluminum killed steel was produced in the laboratory by vacuum melting. Steel A-E is 28.6mm thick and 102m wide
It was cast into a slab ingot measuring m and 178 mm in length and cooled to ambient temperature. Four slabs of each steel composition were heated from ambient temperature to 1093 ° C, 1149 ° C, 1
Reheated to 204 ° C and 1260 ° C. The residence time of the slab in the heating furnace was 1 hour. The slab is hot rolled into a 3.6mm thick sheet in about 5 minutes, finished at a temperature of 927 ° C, cooled to 566 ° C with water imitating the cooling temperature,
The furnace was then gradually cooled to ambient temperature. The hot rolled sheet was then descaled by pickling and cold rolled 70% to a thickness of 1.07 mm.
The cold-pressed sheet is (simulated in batch annealing)
It was heated to a temperature of 649 ° C. at a rate of 28 ° C./hour, soaked at this temperature for 4 hours and then cooled at a rate of 28 ° C./hour. The annealed sheet was 1% temper rolled. The wt% composition and r _m values of the temper rolled sheets of Steels AE are shown in Table 1.

[0032]

[Table 1]

The results in Table 1 show that the conventional slab temperature 126
Sheets of all manganese compositions are shown to have r _m values of at least about 1.8 when using 0 ° C. Steel A with a manganese composition of less than 0.22% by weight
-D had high r _m values when the slab was reheated to the reduced temperatures of 1149 ° C and 1204 ° C. In fact, the use of a slab temperature of 1149 ° C.
For r., A very high r _m value of 2.30 or more was exhibited. However, further lowering the slab temperature to 1093 ° C. is very low for all manganese compositions, indicating that the nitrogen retained in solution in the hot-rolled sheet prior to cold reduction is clearly not sufficient. The r _m value was 1.32. Steel E had an r _m value of 1.8 or less when hot-rolled from a slab with reduced temperatures of 1149 ° C and 1204 ° C. Obviously manganese content is 0.2
The reduction from 2% to 0.16% by weight has a significant effect on the amount of nitrogen retained in solution in the hot-rolled sheet rolled from the slab having the reduced temperature. By adjusting the manganese content, it is possible to have clearly enough nitrogen present in the hot-rolled sheet for the formation of the recrystallized structure necessary for good r _m values after batch annealing.

It is well known that non-aging, cold rolled, batch annealed aluminum killed steel is characterized by a grain structure having an elongation of 2.0 or greater. Such grain elongation indicates that aluminum nitride was precipitated during the slow temperature rise prior to recrystallization during annealing. It is also known that the melting temperature of aluminum nitride is a function of the product of nitrogen in the steel and the weight percent of aluminum. According to Leslie et al., The nitrogen and aluminum compositions of Steels AD imply an "apparent" melting temperature of aluminum nitride before hot rolling at 1284 ° C or higher. However, the grain structure of Steels A-D after cold reduction and batch annealing was 1149 ° C and 12 ° C.
With a reduced slab temperature of 04 ° C, the normal elongation, ie
It had a very high elongation of 2.0 or more.

For example, FIG. 1 shows a r of 2.38 for steel cold annealed and batch annealed at 649 ° C. for 4 hours.
₃ shows the very elongated grain structure of Steel B with _m value. The sheet was reheated to 1149 ° C. and made from a slab with a pseudo coiling temperature of 566 ° C. after hot rolling. FIG. 2 shows the equiaxed grain structure of Steel B having an r _m value of 1.26, which was treated as in FIG. 1 except that the slab was reheated to 1093 ° C. Figure 1
It demonstrates that a slab temperature of 093 ° C. does not result in sufficient nitrogen dissolved in the hot rolled sheet to create an elongated grain structure after cold reduction and batch annealing.

FIG. 3 shows the typical partially elongated grain structure of Steel E, which has a low r _m value of 1.44. Steel E in FIG. 3 was processed in the same manner as steel B in FIG. A significant difference between Steel E of FIG. 3 and Steel B of FIG. 1 is that the steel of FIG. 3 has 0.22 wt% manganese, while the steel of FIG. 1 has 0.10 wt% manganese. Was that. Note that the grain structure elongation of the steel of FIG. 3 is not only significantly smaller than that of the steel of FIG. 1, but that the grain structure of FIG. 3 contains a significant number of equiaxed grains. Should be. FIG. 4 shows the normal elongation grain structure of Steel E having an r _m value of 1.79. Steel E in FIG. 4 was processed as Steel B in FIG. 1 except the slab was reheated to 1260 ° C. The grain structure of the steel of FIG. 4 having a normal hot rolling slab temperature had grain elongation close to that of the steel of FIG. Unlike the grain structure of Steel E of FIG. 3 due to the use of reduced hot rolling temperatures, the grain structure of FIG. 4 using normal slab hot rolling temperatures had very few equiaxed grains. .

The remaining steels A, C and D with the reduced slab temperatures of 1149 ° C. and 1204 ° C. had grain elongations similar to those shown in FIG. Steels A, C and D with a reduced slab temperature of 1093 ° C. had a grain structure similar to that shown in FIG. Steels A, C and D having a normal slab temperature of 1260 ° C. had a grain elongation similar to that shown in FIG. Steel A-D
In order to obtain an elongated grain structure and a high r _m value after cold reduction and batch annealing, it was sufficiently melted in the sheet hot-rolled from the slab at a reduced temperature of 1149 ° C. and 1204 ° C., in particular 1149 ° C. Leslie et al. Teach that they did not have nitrogen. Contrary to such teachings, cold rolled and batch annealed made from slabs having less than 0.22 wt% manganese and reheated to temperatures of 1149 ° C and 1204 ° C. It was found that each of the steels A to D produced had a grain elongation larger than the normal elongation. The reason why such elongation grain structure is obtained at the lowered slab heating temperature is not known. Steel AD, although not proven by analysis
This unpredictable result of is that the classical elongated particles (exceptionally high r _m values) after cold reduction and quasi-batch annealing.
This can be explained by the fact that the steel clearly has enough nitrogen dissolved and retained in the hot-rolled sheet. In other experiments 704 instead of 566 ° C
Steels A-E were manufactured by working in the same manner as the examples described in Table 1, except that the pseudo-winding temperature was raised to 0 ° C. The r _m values are shown in Table 2.

[0038]

[Table 2]

At all compositions and slab reheat temperatures, the r _m values of these batch annealed sheets decreased to 1.41 or less. This implies that elevated pseudo-winding temperature causes precipitation of nitrogen as aluminum nitride before cold reduction. Conversely, these results confirm that for steels A-D in Table 1 having reduced slab temperatures of 1149 ° C and 1204 ° C, the aluminum nitride has dissolved after hot rolling.

The r _m values in Tables 1 and 2 are shown graphically in FIG. The upper curve 10 is 1149
° C. When it is cold reduction and batch annealing than sheet produced from a slab having a coiling temperature of hot rolled and 566 ° C. at reduced temperature of 1.8 or more r _m
3 shows low manganese steels A-D with values. The r _m value of similarly processed steel E dropped to 1.44. When the slab temperature of Steel E is raised to the normal temperature of 1260 ° C, r
_{The m} value rises to 1.79. Steel A-E slab is 114
Although heated to 9 ° C, when the pseudo-winding temperature was raised to 704 ° C, it decreased to 1.28 or lower as shown in the curve 12. If the steel AE slab was reheated to 1093 ° C. and a cooling temperature of 566 ° C., then all r _m
The value was 1.30 as shown in the bottom curve 14.

In an additional experiment, the slab was 1093
It can be rolled from temperatures on the order of 0 ° C. and, by careful control of manganese, total nitrogen and acid-dissolved aluminum, an r of at least 1.8 after batch annealing.
It was found that the _m value was obtained. Additional aluminum killed steels F-I were melted, cast into slab ingots, hot rolled into sheets in about 0.5 minutes, pickled, cold reduced, batch annealed, then in Table 1. Temper rolled in the same manner as Steels A-E in the described examples. The composition by weight% and r _m value of steel F~I shown in Table 3.

[0042]

[Table 3]

The results of Table 3 has the effect of manganese, decrease of total nitrogen and acid soluble aluminum to further increase the r _m values after further reduced and batch annealed slab temperature required before hot rolling It is shown that. Comparison of Steel F and Steel G shows that Steel G has a higher r _m value than the corresponding r _m value of Steel F at all slab temperatures. Similarly, comparison of the steel H and steel I shows that it has a high r _m values than the corresponding r _m value of steel H steel I in all the slab temperature. This means that if the total nitrogen was reduced from about 0.009 wt% to 0.003 wt% and the acid-dissolved aluminum was reduced from 0.08 wt% to 0.04 wt%,
It clearly demonstrates the beneficial effect of increasing the r _m value. Similar comparisons demonstrate that there is a beneficial effect of increasing the r _m value when manganese is decreased. The total r _m value for steel H is higher than the corresponding r _m value for steel F at each slab temperature. For Steel G and Steel I,
The total r _m values for Steel I are 1149 with substantially the same r _m value.
℃ except was higher than the corresponding r _m value of G steel at each slab temperature.

Finally, Steel I, which has a low composition for each of acid-dissolved aluminum, total nitrogen and manganese, has a high acid-dissolved aluminum and total nitrogen and / or manganese at all slab temperatures (except for Steel G at 1149 ° C.). Was much higher than the corresponding r _m values for steels F, G and H with. Further, Steel I has a slab temperature of cold rolled and batch annealed without deterioration of the drawability of the sheet,
It has been demonstrated that at least about 170 ° C. (1260 ° C. or higher to 1093 ° C. or lower) can be lowered, which reduces energy costs.
Surprisingly, the drawability of the steel sheet can be expected to improve substantially (to high r _m values) with this reduction in cost.

The results from Table 3 are shown graphically in FIG. Steel F, shown in curve 16, generally had an r _m value of 1.8 or less at all temperatures. Steel H, shown by curve 18, has a slab temperature of about 1.49C at a reduced slab temperature of 1149 ° C.
It had an r _m value of 8 or greater. This is, r _m value increases,
It also demonstrates the advantageous effect of being able to reduce the required slab temperature when manganese is reduced from 0.22% to 0.12% by weight. Steel G of curve 20 demonstrates the beneficial effect of increasing the r _m value and the slab temperature required when acid dissolved aluminum and total nitrogen are reduced. r _m value was at least 1.8 at the slab temperature of about 1093 ° C.. Finally, Steel I of Curve 22 has good or improved drawability and has the beneficial effect of reducing energy costs during hot rolling if the composition of acid-dissolved aluminum, total nitrogen and manganese is carefully adjusted. Had better r _m values than any of the other three steel compositions. The highest slab temperature was 1149 ° C. First
Although not shown in the table, steels G and I, which are relatively acid-dissolved aluminum and low in total nitrogen, have an r _{m of} about 1.8 or more even when the slab is reheated to 1093 ° C.
Had a value. The r _m value was also evaluated as a function of annealing temperature. In the following examples, aluminum killed steels JQ were produced and their composition weight percentages are shown in Table 4.

[0046]

[Table 4]

Steels J-Q were cast into slab ingots, hot rolled into sheets, pickled, cold reduced, batch annealed, then steels A-E in the examples given in Table 1. It was temper rolled as well. 11
The slab with a hot rolling temperature of 49 ° C was hot rolled for about 0.5 minutes and the slab with a hot rolling temperature of 1260 ° C was hot rolled for 0.7 minutes. With soaking time of 4 hours,
A batch anneal temperature of 566-732 ° C was used.
r _m values, yield strength, shows a total elongation% after tensile strength and temper rolling in Table 5, shows the graph in Figure 7-9.

[0048]

[Table 5]

Steels N and O with 0.007, 0.008 to 0.009 and 0.22% by weight of relatively high acid dissolved aluminum, total nitrogen and manganese (curve 3 in FIG. 7).
0) indicates that the use of a slab temperature below 1260 ° C is an acceptable r _m for batch annealed aluminum killed steel.
Relatively consistent with the teaching of Leslie et al.
Steels P and Q (curve 28) hot rolled at a normal slab temperature of 1260 ° C. show that they have the usual r _m values of batch annealed aluminum killed steels, ie generally less than 1.8. There is. Curves 26 of steels L and M hot rolled at a normal slab temperature of 1260 ° C. have an improved r _m value demonstrating the beneficial effect of very low manganese of 0.12 wt%. It was Steels J and K (curve 24) had good r _m values of 2.0 and above when hot rolled at a reduced slab temperature of 1149 ° C. Surprisingly, the r _m values of steels J and K hot-rolled at low slab temperatures have the same composition, but 1260
Was substantially higher than the r _m values of hot rolled steels L and M from ° C. Aluminum killed steels having a normal manganese composition and hot rolled from slab temperatures of 1260 ° C. or higher generally have batch anneal temperatures above 649 ° C. to develop normal r _m values and mechanical properties. Is required. Amazing thing is
Steels J and K also have good r at an annealing temperature of about 566 ° C.
was to have an _m value. In addition to improved drawability and reduced energy costs during hot rolling, the present invention can save time and energy costs during batch annealing.

The preferred tensile strength for deep drawn steel is about 3
2 kg / mm ² or less, most preferably about 29 to 32 kg / m
m ² . Curves 32 and 34 in FIG.
For steels J, K and N, O with a reduced slab temperature of 49 ° C. The annealing temperature is preferably below about 650 ° C. to obtain the desired tensile strength. In contrast, the steels L, M and P, Q (curves 36 and 38), each with a normal slab temperature of 1260 ° C, were increased compared to the steel hot rolled from the slab temperature of 1149 ° C. It had a tensile strength. Curves 32 and 34 show that the batch anneal temperature can be reduced for hot rolled steel from a reduced slab temperature.

Curves 40 and 42 in FIG. 9 correspond to steels J, K and N, O, respectively, and show% total elongation as a function of batch annealing temperature. Steel J rolled from 1149 ° C. with very low manganese of 0.12% by weight
And K have excellent total elongation at all batch annealing temperatures, while 0.2 rolled from 1149 ° C.
Steels N and O with 2% by weight manganese (curve 42)
Had a good total elongation at an annealing temperature of 600 ° C. or higher. Curves 44 and 46 are 1 each
Corresponds to steels L, M and P, Q rolled from 260 ° C. Steels L, M and P, Q had poor total elongation at annealing temperatures below 650 ° C.

In the laboratory experiments described above, the total hot rolling time was 0. 0 for steels with reduced slab temperatures.
It was 5 minutes. Total hot rolling time means the elapsed time required to roll the slab through the roughing stands and the finishing stands present in the hot rolling mill. Conventional hot strip mills generally require long rolling times of about 4 minutes or more for slabs having a thickness of 200 mm or more. In another experiment, the r _m value was determined as a function of total hot rolling time and aluminum and nitrogen contents. Steels R-BB were cast into slab ingots, hot rolled into sheets, pickled, cold reduced, batch annealed, then about 0.
It was temper rolled in the same manner as the examples described in Table 1, except that hot rolling times of 5, 2 and 4 minutes were used. Slab ingot at room temperature to 1149 ℃
Was reheated in a furnace, held for 1 hour and then hot rolled in three rolling passes into a sheet having a thickness of 3.6 mm. The steel hot-rolled for 0.5 minutes, after passing the second pass,
It was held until the temperature had dropped to 949-943 ° C before passing through the third path. Finishing temperature after passing the third road is 90
It was 4 ° C. The steel is immediately cooled with water and then 5 in the furnace.
Cooled slowly from 66 ° C to ambient temperature. The hot rolled steel for about 2 minutes was treated as before, except that it was maintained in a furnace maintained at 982 ° C. for 80 seconds after passing the second pass. Steel rolled for about 4 minutes, after passing the second road,
It was hot rolled as before except that it was held for 200 seconds in a furnace maintained at 982 ° C. Table 6 shows the compositional weight percentages of steels R to BB, the product of aluminum and nitrogen, and the calculated fractions and mechanical properties of aluminum nitride dissolved in the slab at the reheating temperature of 1149 ° C.

[0053]

[Table 6]

Even though the compositions of aluminum and nitrogen with only 2 and 3 significant digits respectively are shown in this table, the composition of aluminum and nitrogen with 3 and 4 significant digits respectively is the product of aluminum and nitrogen. And 1149 ° C
It was used for the calculation of the aluminum nitride fraction dissolved in. The r _m values, tensile strength and% total elongation are for the steel after 70% cold reduction, batch annealing and temper rolling. FIG. 10 shows r _m
Figure 3 is a graph of values as a function of hot rolling time for steels R-Z and BB hot rolled from slabs reheated to 1149 ° C and batch annealed at 649 ° C for 4 hours. The curve for steel AA is omitted from Figure 10 because the r _m value is essentially the same as that of steel BB. Steel R with a relatively high concentration of nitrogen, aluminum and manganese (curve 46) had low r _m values for hot rolling times of 2 minutes or more. Steel S (curve 48) had the same composition as Steel R except Steel S had a very low manganese. Steel S has improved r _m values at all hot rolling times, but the r _m values were still unacceptable at times of 2 minutes or more. Steel T (curve 50) had a composition similar to Steel S, except that the nitrogen was substantially reduced. Steel T
Significantly improved the r _m value for all hot rolling times and was about 2.0 for 2 minutes or more.

Steel U, shown by curve 52, had similar composition and r _m value to Steel T at hot rolling times of 0.5 and 2 minutes. Remaining steels V-Z and BB (curve 5 respectively
4-64) had low aluminum, nitrogen and manganese except steel Y had 0.23 wt% manganese and steel Z had 0.07 wt% acid-dissolved aluminum. Steels VZ and BB had good r _m values at all hot rolling times. Steel Y with 0.23% by weight manganese (curve 60) has an acceptable r _m value for all hot rolling times, of about 2.0 for hot rolling times of 0.5 and 4 minutes. had an r _m value. Curves 62 and 6, each with 0.003 wt% total nitrogen
Steels Z and BB designated 4 had acceptable r _m values of about 1.9 or higher at all rolling times. Surprisingly, steels Z and BB had the highest calculated fraction of aluminum nitride (100%) dissolved in the hot rolled sheet, but the highest r _m values were I didn't have it. Steels T, U, V and W were about 40%, 49%, 56% and 67% aluminum nitride, respectively, which were clearly melted at the reheating temperature of 1149 ° C. before hot rolling.
% Of r for steels Z and BB at all hot rolling times
It had a high r _m value than the _m value. Steel T, U, V and W
Removes 0.002 of nitrogen that is melted and retained after hot rolling.
It had more than weight%. This demonstrates that for batch annealed aluminum killed steels low in manganese, the aluminum nitride need not be completely melted during slab reheating before hot rolling. The absolute amount of nitrogen retained in solution after hot rolling appears to be more important than the retained fraction. For optimum r _m values, nitrogen that is melted and retained after hot rolling should be at least 0.00
Table 6 and FIG. 10 clearly show that the total nitrogen is preferably 0.004 to 0.006% by weight together with 2% by weight.

As shown in the graph of FIG. 10, the r _m value of the batch-annealed aluminum killed steel is
It appears to be a function of nitrogen, aluminum and manganese as well as the total time of hot rolling. Even by adjusting the manganese less than 0.02 wt%, batch annealed after at least about 1.8 relatively long heat more than 2 minutes when using slab temperatures less than 1260 ° C. in order to obtain r _m values of Controlling aluminum and nitrogen appears to be important when interroll times are required. When the hot rolling time is 2 minutes or more and manganese is adjusted to 0.16 wt% or less, if the product of acid-dissolved aluminum% and total nitrogen% is about 5 × 10 ^-4 or less, acid-dissolved aluminum is It is at most 0.08% by weight and total nitrogen is at most 0.007% by weight. Hot rolling time is 2 minutes or more, and acid-dissolved aluminum and total nitrogen are about 0.05 and 0.005% by weight, respectively.
Manganese is at least 0.2 when adjusted below.
It is 3% by weight.

The relationship between aluminum and nitrogen and the r _m value can be expressed as a function of the product of aluminum and nitrogen, that is,% by weight of acid-dissolved aluminum x% by weight of total nitrogen. Steels C, H, I, J, S, T, U, V, W, X, Z, AA and BB all had low manganese levels of 0.11 to 0.13% by weight. Two samples of each of these steels (Steel C,
(Except H, I and J) were hot rolled for a time of about 0.5 minutes and 2 minutes and batch annealed at 649 ° C. for 4 hours. Steels C, H, I and J were hot rolled for a time of about 0.5 minutes. R _m as a function of the product of aluminum and nitrogen
Values are shown in FIG. In both hot rolling time,
The r _m value increases with increasing product of aluminum and nitrogen,
Optimal r at a product of aluminum and nitrogen of about 3 × 10 ^-4
_{The m} value was obtained. As the product of aluminum and nitrogen increased further, the r _m value decreased as shown by curve 66 for hot rolling time of 0.5 minutes and curve 68 for hot rolling time of 2 minutes. The result of the hot rolling time of 4 minutes was substantially the same as the hot rolling time of 2 minutes (see Table 6).

The low manganese steel with a short hot rolling time of 0.5 minutes had an acceptable r _m value for all aluminum-nitrogen products. However, at a long hot rolling time of 2 minutes, the product of aluminum and nitrogen is about 5 × 10 ^−4.
1.8 or more acceptable r unless
_{The m} value was obtained. For example, in a steel with 0.11 to 0.13 wt% manganese and 0.08 wt% acid-dissolved aluminum, the total nitrogen should not exceed about 0.006 wt%. Interestingly, the left half of curves 66 and 68 implies that the product of aluminum and nitrogen should not be less than about 1 × 10 ⁻⁴ . That is, 0.03% by weight
For steel with acid-dissolved aluminum, total nitrogen should be at least 0.004% by weight. On the other hand, for steels having total nitrogen of 0.003 or less, the acid-dissolved aluminum must be at least 0.04% by weight. In all cases, the total nitrogen should not be less than 0.003% by weight. Otherwise, not enough dissolved nitrogen will be utilized in the hot band stage after hot rolling and will precipitate during heating in batch annealing after cold rolling. At the optimum r _m value, the product of aluminum and nitrogen is 2 × 10 ^-4
It should be ~ 4x10 ^-4 .

Steels R-BB hot rolled from the slab reheated to 1149 ° C for 4 minutes were batch annealed at temperatures of 649 ° C, 607 ° C and 566 ° C. Steels V, W and X were also batch annealed at 538 ° C. The r _m values as a function of annealing temperature for steels R, V, X and Y are shown in FIG. Steel R with relatively high concentrations of nitrogen, aluminum and manganese
(Curve 70) does not appear to have good r _m values at any annealing temperature if a long hot rolling time of 4 minutes is required. Steel Y containing a small amount of nitrogen and aluminum but a relatively high manganese content of 0.23% by weight Y
The (curve 72) has a good r _m value at an annealing temperature of about 600 ° C., which is higher than that of the rolling time of 4 minutes. Steels V and X with low nitrogen, aluminum and manganese
(Curves 74 and 76) gave excellent r _m values at all annealing temperatures. Surprisingly, Steels V and X had excellent r _m values at an annealing temperature of 566 ° C. with 4 minutes of hot rolling. Also steel V, W and X
Was batch annealed at 538 ° C. for 8 hours instead of 4 hours. When batch annealed at 538 ° C., Steels V and X had excellent r _m values and mechanical properties, while Steels V, W and X had acceptable r _m values. Steel W was not completely recrystallized after batch annealing at 538 ° C. The r _m value of Steel W was good at 1.8, but its tensile strength was unacceptable.

In order to clearly explain the interdependence of hot rolling time, manganese, and aluminum-nitrogen product for slabs rolled from temperatures below 1260 ° C., some results of the above steels are described below. It is shown in Table 7. Table 7 shows
0.12 to 0.13 wt% or 0.22 to 0.23 wt% manganese and a product of aluminum and nitrogen in the range of about 1.4 × 10 ^{−4 to} 7.5 × 10 ⁻⁴ ; about 1149 was hot rolled from ° C. of the temperature of the slab, indicating a r _m value but was annealed 4 hours times the 0.5 or 2 minutes of the hot rolling time of the steel at 649 ° C.. Table 7 is classified into two steels having the same manganese composition and having the aluminum and nitrogen product values as close as possible within the above range. The results are shown graphically in FIG.

[0061]

[Table 7]

The curve 78 shows that the product of aluminum and nitrogen is 1.4 × 10 ^{−4 to} 6.3 × 10 in a low rolling time of 0.5 minutes and low manganese of 0.13% by weight or less.
^In the range of ^-4 , the r _m value is very high, that is, 2.0 or more. Curve 80 has a relatively long rolling time of 2 minutes and a low manganese content of 0.13% by weight, and the product of aluminum and nitrogen is up to about 5 × 10 ⁻⁴ , r
It shows that the _m value is very high. When the product of aluminum and nitrogen was about 5 × 10 ⁻⁴ or more, the r _m value was substantially 1.8 or less (steel S). Curve 82 is about 0.5
With a rolling time of 1 minute and a relatively high manganese content of 0.22 to 0.23% by weight, when the product of aluminum and nitrogen increased to about 6.3 × 10 ⁻⁴ , the r _m value was very low, That is, it represents 1.4 (steel N). This is as shown by curve 78 for a rolling time of about 0.5 minutes, 0.12 wt% manganese and about 6.3 × 10 ^-4.
In contrast to Steel S, which has a relatively high aluminum-nitrogen product. Curve 82 also shows steel Y having a relatively high manganese content of 0.22 to 0.23% by weight and a low aluminum and nitrogen product of less than about 2.2 x 10 ^-4 at a rolling time of about 0.5 minutes. The r _m values for G and G are very high, but are somewhat lower than the r _m values for steels X and I with 0.12 wt% manganese and the same aluminum-nitrogen product.

Further, the curve 82 shows that when the product of aluminum and nitrogen is about 1.4 × 10 ⁻⁴ , the r _m value at a rolling time of about 0.5 minutes is very high regardless of the manganese composition. It means essentially the same, for example 2.3. Comparing curve 82, which has the same manganese but rolling time of 0.5 minutes, with relatively high manganese of 0.22 to 0.23 wt% and rolling time of 2 minutes, curve 84, It can be seen that at relatively high values, i.e. above 0.02% by weight, the r _m value is less affected by rolling time. In contrast, comparing curve 78, which has the same manganese and rolling time of 0.5 minutes, with manganese of 0.13 wt% or less and rolling time of 2 minutes, manganese is It can be seen that at very low levels, i.e. below 0.02% by weight, the r _m value is significantly influenced by rolling time. Even so, when the product of aluminum and nitrogen is about 2 × 10 ^{−4 to} 5 × 10 ⁻⁴ in a rolling time of 2 minutes,
0.12 to 0.22 to 0.23% by weight of manganese
Steels with up to wt% manganese have very good r _m
It was a value.

All the features of the present invention are that the aluminum and nitrogen contents are 0.05 wt% and 0.005 wt% respectively, and the optimum aluminum-nitrogen product is about 2.5 × 1.
The r _m values for steel CC with a normal total hot rolling time of 0 ⁻⁴ , about 4 minutes and a low manganese composition of 0.11 wt. Steel CC r _m
The values are compared with the r _m values of steel DD with the same optimum composition, except for the relatively high manganese content of 0.21% by weight. Steel C
C and DD were cast into slab ingots, hot rolled into sheets, pickled, cold reduced, batch annealed, then 4 minutes hot rolling time 1149 ° C, 1
Temper rolled in the same manner as the examples shown in Table 6, except used for slab reheat temperatures of 204 ° C and 1260 ° C. Samples of each steel are 649 ° C, 6
It was batch annealed for 4 hours at temperatures of 07 ° C and 566 ° C. The result indicates that the eighth shown in Table not negatively influenced if r _m values were used reduced slab reheating temperature and reduced by the annealing temperature. In fact, the r _m value at the reduced slab reheat temperature of 1149 ° C. was generally equal to or greater than the r _m value of steel CC and DD at the normal reheat temperature of 1260 ° C. R _m values at reduced been annealing temperature of 566 ° C. is was slightly smaller than r _m value of annealing temperatures of 649 ° C.. As shown in Table 7 above, manganese and r _m values are clearly interdependent. The r _m values of the low manganese steel CC exceeded the r _m values of the relatively high manganese steel DD at all annealing temperatures. Nevertheless, even with the relatively high manganese of 0.21% by weight, the reduced slab reheat temperature of 1149 ° C and 566 ° C when aluminum, nitrogen and the product of aluminum and nitrogen were all carefully adjusted. At the use of reduced annealing temperatures of, the r _m values were good, ie at least 1.8.

[0065]

[Table 8]

Those skilled in the art will appreciate that a slab with a typical thickness of 150-250 mm is hot rolled to a thickness of about 2.5 mm and has a finishing temperature of at least 870 ° C.
It will be appreciated that an initial temperature of 0 ° C is required. About 1
The most preferred slab temperature of the present invention below 149 ° C is 2
It was actually applied to thin continuously cast slabs with a thickness of 5 to 50 mm. An additional cost reduction is possible by casting the melt into a thin slab rather than a thick slab with a typical thickness of 150 mm. Casting into a thin slab minimizes the time and energy to hot roll into a sheet. For example, thin slabs eliminate or minimize reduction using roughing stands. In addition to saving time and energy during rolling, further energy savings can be made because the initial slab temperature is well below that required for thick slabs. At least 1
Instead of 260 ° C., the thin slab can be heated to around 1093 ° C. and can be hot rolled into non-aged, batch annealed, aluminum killed steel with very high r _m values.

Various modifications can be made to the present invention without departing from the scope and spirit thereof. For example, the steels of the present invention can be manufactured from continuously cast thin or thick slabs and from slabs made from ingots. Various reduced slab temperatures can be used as long as the hot rolling finish temperature is above Ar ₃ and the coiling temperature is preferably below 593 ° C. Accordingly, the limitations of the invention will be determined from the appended claims.

[Brief description of drawings]

FIG. 1 is a photograph in which a grain structure of a cold-rolled recrystallization batch-annealed steel according to one embodiment of the present invention is magnified 100 times.

FIG. 2 is a 100 × magnified photograph of the grain structure of steel having the same composition as in FIG. 1 but having a grain structure outside the invention.

FIG. 3 is a photograph of a grain structure of a steel manufactured by using the method of the present invention, which has an r _m value outside the scope of the present invention, magnified 100 times.

FIG. 4 shows a grain structure of a cold rolled recrystallized batch annealed aluminum killed steel having a conventional composition and produced from a slab hot-rolled from a conventional temperature.
It is a photograph magnified 0 times.

In Figure 5 the various slab temperature and various hot rolling coiling temperature and the manganese composition as a function, a graph showing the r _m values of cold reduced been batch annealed aluminum killed steel.

[6] Various acid dissolution aluminum, in total nitrogen and manganese compositions, the slab temperature and function, is a graph showing the r _m values of the cold reduced batch annealed aluminum killed steel.

[7] and batch annealing temperatures, slab reheat between temperature and function manganese composition is a graph showing the r _m values of cold reduced aluminum killed steel.

8 is a graph showing the tensile strength of the steel of FIG. 7 as a function of batch annealing temperature, slab reheat temperature and manganese composition.

9 is a graph showing the total elongation of the steel of FIG. 7 as a function of batch annealing temperature, slab reheat temperature and manganese composition.

[10] Various acid dissolution aluminum, in total nitrogen and manganese compositions, the hot rolling time a function is a graph showing the r _m values of the cold reduced batch annealed aluminum killed steel.

FIG. 11: Acid-dissolved aluminum in cold-killed aluminum-killed steel from a slab having a temperature of 1149 ° C., hot rolled at two different hot rolling times and batch annealed at 649 ° C. for 4 hours. 3 is a graph showing the r _m value as a function of the product of γ and total nitrogen.

[12] 1149 ° C. Various acid dissolution aluminum when it is hot rolled from the slab having a temperature of, r _m of total nitrogen and in manganese compositions, batch annealing temperature cold reduced aluminum killed steel as a function It is a graph which shows a value.

FIG. 13: Cold rolling as a function of manganese, hot rolling time, and product of aluminum and nitrogen in steel hot rolled from a slab having a temperature of about 1149 ° C. and annealed at 649 ° C. for 4 hours. It is a graph which shows the r _m value of the rolled aluminum killed steel.

Claims (36)

[Claims] 1. A having r _m values characterized and at least 1.8 by elongated grain structure, it is cold reduced to a aluminum killed steel consisting of non-aging sheet annealed recrystallization batch, the sheet Is 0.08% by weight
The following carbon, 0.1% by weight or less of acid-dissolved aluminum,
Up to 0.20% by weight of manganese, the balance essentially consisting of iron and unavoidable impurities, the sheet being produced from a slab having a hot rolling temperature below 1260 ° C., the slab having dissolved nitrogen Aluminum killed steel hot rolled into sheets. 2. An aluminum killed steel consisting of a cold rolled, recrystallized batch annealed non-aged sheet characterized by an elongated grain structure and having an r _m value of at least 2.0. Is 0.05% by weight
The following carbon, 0.02-0.1 wt% acid-dissolved aluminum, 0.20 wt% or less manganese, the balance consisting essentially of iron and unavoidable impurities, the sheet being 1175 ° C.
An aluminum killed steel produced from a continuously cast slab having the following hot rolling temperatures, wherein the slab is hot rolled to a sheet having molten nitrogen. 3. The aluminum killed steel according to claim 1, wherein the slab is continuously cast to a thickness of 25 to 50 mm. 4. The slab is Ar before hot rolling.
A continuously cast slab cooled to a temperature of ₃ or less, wherein the cooling causes precipitation of aluminum nitride and is reheated to 1260 ° C. or less before hot rolling the slab to redissolve the aluminum nitride. The aluminum killed steel according to claim 1. 5. The aluminum killed steel of claim 1, wherein the hot rolled sheet has a hot rolling coiling temperature of 593 ° C. or less. 6. The batch annealing is at least 64.
The aluminum killed steel according to claim 1, which has a temperature of 9 ° C. 7. having r _m values characterized and at least 2.0 by elongated grain structure, it is cold reduced to a aluminum killed steel consisting of non-aging sheet annealed recrystallization batch, the sheet Is 0.05% by weight
A slab in which the sheet is continuously cast, consisting essentially of the following carbon, 0.02-0.1 wt% acid-dissolved aluminum, 0.20 wt% or less manganese, the balance iron and inevitable impurities. A sheet having nitrogen dissolved therein, the slab being cooled to a temperature of Ar ₃ or less before hot rolling and being reheated to a temperature of 1175 ° C. or less before hot rolling. An aluminum killed steel that is hot rolled to a hot rolling temperature that includes a finishing temperature of Ar ₃ or higher and a coiling temperature of 593 ° C. or lower. 8. The aluminum killed steel according to claim 7, wherein the slab is continuously cast to a thickness of 50 mm or less. 9. A slab consisting essentially of 0.08% by weight or less of carbon, 0.1% by weight or less of acid-dissolved aluminum, 0.20% by weight or less of manganese, and the balance of iron and inevitable impurities is prepared. Hot-rolling the slab having a hot-rolling temperature of 1260 ° C. or less into a sheet having melted nitrogen, winding the hot-rolled sheet, and descaling the hot-rolled sheet. Comprising cold rolling the descaled sheet and recrystallizing batch annealing the cold rolled sheet, the annealed sheet being non-aged, characterized by an elongated grain structure and A method of making an aluminum killed steel having an r _m value of at least 1.8. 10. Carbon up to 0.05% by weight, 0.02
~ 0.1 wt% acid-dissolved aluminum, 0.20 wt%
The following manganese, the balance is prepared a melt consisting essentially of iron and unavoidable impurities, cast the melt into a slab,
Hot-rolling the slab having a hot-rolling temperature of 1175 ° C. or less into a sheet having melted nitrogen, winding the hot-rolled sheet, descaling the hot-rolled sheet, Cold depressing the descaled sheet and recrystallizing batch annealing the cold reduced sheet, the annealed sheet being non-aging, characterized by an elongated grain structure and at least A method of making an aluminum killed steel having an r _m value of 2.0. 11. The manufacturing method according to claim 9, further comprising a continuous casting of the slab and an additional step of cooling the slab to a temperature of Ar ₃ or lower after casting. 12. The method of claim 9 including the additional step of continuously casting the slab having a thickness of 25 to 50 mm. 13. The finishing temperature of the hot rolled sheet is Ar ₃ or higher, and the winding temperature of the sheet is 593.
The production method according to claim 9, which is not higher than ° C. 14. The batch annealing is at least 64.
The method according to claim 9, wherein the temperature is 9 ° C. 15. 0.05% by weight or less of carbon, 0.02
~ 0.1 wt% acid-dissolved aluminum, 0.20 wt%
The following manganese, the balance is prepared a melt consisting essentially of iron and unavoidable impurities, cast the melt into a slab,
The slab is cooled to a temperature below Ar ₃ and the slab is cooled to 11
Reheating to a temperature of 75 ° C. or lower and hot rolling the slab into a sheet having a finishing temperature of Ar ₃ or higher, winding the hot rolled sheet at a temperature of 593 ° C. or lower, where The sheet comprises dissolved nitrogen, comprising descaling the hot rolled sheet, cold reducing the descaled sheet, and recrystallization batch annealing the cold reduced sheet, A method of making an aluminum killed steel, wherein the annealed sheet is non-aged, characterized by an elongated grain structure and having an r _m value of at least 2.0. 16. Cold reduction, characterized by an elongated grain structure and having an r _m value of at least 1.8,
An aluminum killed steel consisting of a recrystallization batch annealed non-aged sheet, wherein the sheet comprises 0.08 wt% or less carbon, 0.01 wt% or more acid-dissolved aluminum, 0.24 wt% or less manganese. , Containing nitrogen as an impurity, wherein the product of the weight% of aluminum dissolved in acid and the weight% of total nitrogen is 5 × 10 ⁻⁴ or less, and the balance consists essentially of iron and inevitable impurities, and the sheet is 1260 ° C. An aluminum killed steel produced from a slab having the following hot rolling temperatures, wherein the slab is hot rolled into a sheet having molten nitrogen. 17. The aluminum killed steel of claim 16 wherein said sheet has 0.03 to 0.08 wt% acid-dissolved aluminum and said r _m value is at least 2.0. 18. The sheet has a thickness of 0.003 to 0.007.
With wt% total nitrogen, said r _m value being at least 2.0
The aluminum killed steel according to claim 16, which is 19. The aluminum killed steel of claim 16 wherein the sheet has no more than 0.20 wt% manganese and the r _m value is at least 2.0. 20. The sheet has a tensile strength of 29 to 32 kg / cm ² and a total elongation of at least 42%.
Aluminum killed steel described. 21. The sheet has 0.05-0.06 wt% acid-dissolved aluminum, 0.004-0.006 wt% total nitrogen, and the product of acid-dissolved aluminum wt% and total nitrogen wt%. Is in the range of 2 × 10 ⁻⁴ to 4 × 10 ⁻⁴ , and the r _m value is at least 2.0. 22. Cold reduction characterized by an elongated grain structure and having an r _m value of at least 2.0,
An aluminum killed steel consisting of a recrystallization batch annealed non-aged sheet, wherein the sheet comprises 0.05% by weight or less of carbon, 0.03 to 0.08% by weight of acid-dissolved aluminum, 0.003 to 0. 0.007% by weight total nitrogen,
The sheet contains not more than 0.24% by weight of manganese, the product of the weight% of aluminum dissolved in acid and the weight% of total nitrogen being not more than 5 × 10 ⁻⁴ , the balance consisting essentially of iron and inevitable impurities. An aluminum killed steel produced from a continuously cast slab having a hot rolling temperature of 1175 ° C. or less, wherein the slab is hot rolled to a sheet having molten nitrogen. 23. Cold reduction characterized by an elongated grain structure and having an r _m value of at least 2.0,
An aluminum killed steel consisting of a recrystallization batch annealed non-aged sheet, wherein the sheet comprises 0.05% by weight or less carbon, 0.05-0.06% by weight acid-dissolved aluminum, 0.004-0. 0.006% by weight of total nitrogen and 0.24% by weight or less of manganese, the product of% by weight of acid-dissolved aluminum and% by weight of total nitrogen being 2 × 10 ⁻⁴ to 4
X 10 ^-4 , the balance consisting essentially of iron and unavoidable impurities, the sheet being produced from a continuously cast slab having a hot rolling temperature of 1175 ° C. or less, the slab having dissolved nitrogen. Aluminum killed steel hot rolled into sheets. 24. 0.08% by weight or less of carbon, 0.01
It contains more than wt% acid-dissolved aluminum, less than 0.24 wt% manganese and nitrogen as an impurity, where the product of acid-dissolved aluminum wt% and total nitrogen wt% is 5 × 10 ^-4.
The slab consisting essentially of iron and unavoidable impurities as the balance is prepared, and the slab having a hot rolling temperature of 1260 ° C. or less is hot rolled into a sheet having dissolved nitrogen, Rolling a hot rolled sheet, descaling the hot rolled sheet, cold rolling the descaled sheet, and recrystallizing batch annealing the cold rolled sheet, A method of making an aluminum killed steel, wherein the annealed sheet is non-aged, characterized by an elongated grain structure and having an r _m value of at least 1.8. 25. The batch anneal is at least 64.
The method according to claim 24, wherein the temperature is 9 ° C. 26. The batch anneal is at least 53.
The method according to claim 24, wherein the temperature is 8 ° C. 27. The method of claim 24, wherein the slab has 0.03 to 0.08 wt% acid-dissolved aluminum and an r _m value of at least 2.0. 28. The slab has a thickness of 0.003 to 0.007.
25. The method according to claim 24, having a total weight% of nitrogen and having an r _m value of at least 2.0. 29. The method of claim 24, wherein the slab has 0.20 wt% or less manganese and an r _m value of at least 2.0. 30. The slab comprises 0.05 to 0.06 wt% acid-dissolved aluminum, 0.004 to 0.006 wt% total nitrogen, acid-dissolved aluminum wt% and total nitrogen wt%.
^{25. The process according} to claim 24, wherein the product of is in the range 2 × 10 ⁻⁴ to 4 × 10 ⁻⁴ and the r _m value is at least 2.0. 31. The batch annealed sheet is 2.
25. The method of claim 24 having a tensile strength of 9 to 32 kg / cm < ² > and a total elongation of at least 42%. 32. The method according to claim 24, wherein the slab is continuously cast to a thickness of 25 to 50 mm. 33. The slab is cooled to a temperature of Ar ₃ or lower to precipitate aluminum nitride, and the slab is reheated to a temperature of 1260 ° C. or lower to remelt the aluminum nitride before hot rolling. 25. The manufacturing method according to claim 24, which includes a step. 34. 0.05% by weight or less of carbon, 0.03
~ 0.08 wt% acid-dissolved aluminum, 0.003 ~
It contains 0.007% by weight of total nitrogen and 0.24% by weight or less of manganese, the product of the acid-dissolved aluminum weight% and the total nitrogen weight% being 5 × 10 ^-4 or less, the balance being iron and unavoidable. A melt essentially consisting of impurities is prepared, the melt is cast into a slab, and the slab is cooled to a temperature of Ar ₃ or lower to precipitate aluminum nitride.
The aluminum nitride is re-melted by reheating to a temperature of ℃ or less, and the slab is hot-rolled to form a sheet having melted nitrogen, the hot-rolled sheet is wound, and the hot-rolled sheet is rolled. Descaling the sheet, cold rolling the descaled sheet, and recrystallizing batch annealing the cold rolled sheet, the annealed sheet being non-aging and elongated particles. A method of making an aluminum killed steel that is characterized by a texture and has an r _m value of at least 2.0. 35. 0.05% by weight or less of carbon, 0.05
~ 0.06 wt% acid-dissolved aluminum, 0.004 ~
It contains 0.006% by weight of total nitrogen and 0.24% by weight or less of manganese, wherein the product of the acid-soluble aluminum weight% and the total nitrogen weight% is 2 × 10 ⁻⁴ to 4 × 10 ⁻⁴ , the balance being Prepares a melt consisting essentially of iron and inevitable impurities,
The melt is cast into a slab, the slab is cooled to a temperature of Ar ₃ or less to precipitate aluminum nitride, the slab is reheated to a temperature of 1175 ° C. or less to remelt the aluminum nitride, and the slab Hot-rolled at least Ar
Forming a sheet having a finishing temperature equal to ₃ and winding the hot-rolled sheet at a temperature of 593 ° C. or less, wherein the sheet has dissolved nitrogen and descaling the hot-rolled sheet. Cold depressing the descaled sheet, the cold pressed sheet 538-64
Consisted of recrystallization batch annealing in the range of 9 ° C,
A method of making an aluminum killed steel, wherein the annealed sheet is non-aged, characterized by an elongated grain structure and having an r _m value of at least 2.0. 36. 0.08% by weight or less of carbon, 0.01
It contains more than wt% acid-dissolved aluminum, less than 0.24 wt% manganese and nitrogen as an impurity, where the product of acid-dissolved aluminum wt% and total nitrogen wt% is 5 × 10 ^-4.
The following is provided, and the balance is prepared by preparing a melt consisting essentially of iron and unavoidable impurities, and continuously casting the melt.
To form a slab having a thickness of ˜50 mm, cooling the slab to a temperature of Ar ₃ or lower to precipitate aluminum nitride, and reheating the slab to a temperature of 1175 ° C. or lower to redissolve the aluminum nitride. Hot-rolling the slab into a sheet with molten nitrogen, winding the hot-rolled sheet, descaling the hot-rolled sheet, and cold-rolling the descaled sheet. Roll down,
Comprising recrystallizing batch annealing the cold rolled sheet, the annealed sheet being non-aged, characterized by an elongated grain structure and at least 2.
A method of making an aluminum killed steel having an r _m value of 0.