JPS6280252A - Warm-rolled sheet steel for working, excellent in ridging resistance and its production - Google Patents

Abstract

PURPOSE:To manufacture a sheet steel having superior ridging resistance obviating the necessity of cold rolling working or cold rolling-recrystallization annealing stage, by specifying a steel composition and by incorporating Ti and/or Nb under specific relations according to C and C content. CONSTITUTION:A steel stock has a composition containing, by weight, <0.01% C, <0.1% Si, <0.5% Mn, <0.1% P, 0.002-0.1% Al, <0.01% N and <0.003% O, containing further Ti and/or Nb according to C and N content so that relations in an inequality are satisfied and having the balance Fe with inevitable impurities. This steel stock is subjected to warm rolling at 200-800 deg.C by one or more passes and successively to annealing at 450-950 deg.C, so that warm-rolled sheet steel for working can be manufactured.

Description

Detailed Description of the Invention (Industrial Field of Application) This specification describes a cold rolling process or cold rolling and annealing process in relation to a working warm rolled thin steel sheet with excellent ridging resistance and a method for manufacturing the same. We will describe the results of our research and development efforts to advantageously avoid the complications of the process and eliminate the occurrence of ridging after press working.

Processing thin steel sheets with a thickness of approximately 2 mrrl or less used for applications such as building materials, automobile body materials, can stock, and various surface-treated original sheets are required to have the following properties.

(1) Mechanical properties In order to obtain good bending workability, stretching workability, and drawing workability, high ductility and high Lankford value (r value) are required, mainly in L7.

(2) Surface properties Since these materials are mainly used on the outermost side of the final product, not only the shape and surface beauty of the material but also various surface treatments are important.

The general manufacturing method for these thin steel sheets is as follows.

First, low-carbon steel is mainly used as the steel material, and after being made into a steel billet with a thickness of about 200 mm by ingot-making and blooming rolling, it is heated and soaked in a heating furnace, and then subjected to a rough hot rolling process to achieve a thickness of about 200 mm. Approximately 30
After forming a sheet bar into a hot-rolled steel strip with a predetermined thickness in a final hot rolling process at a finishing temperature of Ar3 transformation point or higher, the strip is then pickled and cold-rolled to a predetermined thickness (2 mm). , 0 mm or less), and then subjected to recrystallization annealing to produce the final product.

The biggest drawback of this practice is the extremely long process required to reach the final product. As a result, not only does the amount of energy, personnel and time required to produce the product increase, but additional disadvantages are added during these long steps which can cause problems with the quality of the product, particularly its surface properties.

As mentioned above, it has been essential to include a cold rolling process in the manufacturing procedure of thin steel sheets for processing.

This cold rolling process not only aims to reduce the desired thickness, but also utilizes the plastic strain introduced by cold working to produce crystals with (111) orientation, which is advantageous for deep drawability, in the final annealing process. Helps promote grain growth.

However, in cold working, the deformation resistance of the steel strip is significantly higher than in hot working, so the energy required for rolling is also significant, the rolling rolls are severely worn, and rolling problems such as slipping occur. Easy to occur.

On the other hand, if rolling can be performed in a relatively high temperature range (so-called warm range) of 200°C or above and below Ar=transformation point and particularly good workability can be obtained, the above problems can be eliminated and there are manufacturing advantages. can be said to be large.

In addition, as a method for manufacturing thin steel sheets for processing, a method of producing the final product through a hot rolling process is also considered.

According to this method, cold rolling and recrystallization annealing steps can be omitted, which is a great advantage.

However, the mechanical properties of a hot-rolled thin steel sheet are far inferior to those obtained through a cold rolling-annealing process. In particular, press-formed materials used for automobile bodies require excellent deep drawability, but hot-rolled steel sheets have a low r value of around 1.0, so their processing applications are extremely limited. Become something. This is because in the conventional hot rolling method, the finishing temperature is Ar, which is higher than the transformation point, and the texture becomes random during r-α transformation.

In addition, it is extremely difficult to manufacture thin steel sheets with a thickness of 2.0 mm or less using only a hot rolling process. Moreover, in addition to the problem of dimensional accuracy, the decrease in steel plate temperature due to thinning forces the rolling of low carbon steel below the Ar3 transformation point, and the material (
ductility, drawability). Again analogy A
Even if the quality of the material can be ensured by rolling below r=transformation point, a new problem arises in that steel sheets rolled in the ferrite region are more likely to suffer from cringing.

Here, ridging is a defect in surface irregularities that occurs during the processing of a product, and is a fatal defect for this type of steel plate, which is mainly used on the outermost side of processed products.

In terms of metallurgy, ridging is caused by crystal orientation groups (for example, (100) oriented grain groups) that are not easily divided even after undergoing the annealing recrystallization process and remain stretched in the rolling direction. , generally tends to occur when processing is performed at a relatively high temperature in the ferrite (α) region, and this tendency is particularly strong when the reduction rate in the ferrite region is high, that is, when manufacturing thin steel sheets.

Recently, these thin steel sheets for processing have become more complex,
As materials become more sophisticated, they are often subject to more severe processing, and excellent ridging resistance is now required.

Incidentally, the manufacturing process of steel materials has changed significantly in recent years, and the case of thin steel sheets for processing is no exception.

In other words, in recent years, the introduction of a continuous casting process has made it possible to omit the blooming process, and the heating temperature of steel slabs has been lowered from the conventional 1200°C to around 1100°C or lower in order to improve material quality and save energy. There is a tendency. Furthermore, a process is being put into practical use in which a copper strip having a thickness of 50 mm or less is produced immediately from molten steel, thereby omitting the hot rolling heat treatment and rough rolling steps.

However, these new manufacturing processes are disadvantageous in that they destroy the structure formed when molten steel solidifies.
) It is extremely difficult to destroy the strong casting texture whose main orientation is <uVW>.

As a result, the final thin steel sheet was prone to the aforementioned jinging.

(Prior Art) Several warm-rolled thin plates for processing with controlled steel compositions have been disclosed. For example, in JP-A No. 58-9932, when the solid solution (C+N) is 13 to 142 ppm, 20°
After rolling at a reduction rate of 20% or more in the temperature range of C to 500 °C,
It is shown that (110) (001) strength increases by resintering and annealing. Also, JP-A-59-226
In Publication No. 149, C: 0.0025wt'A, N
: Steel with a composition of 0.0018 to 0.0021 50
It is disclosed that a thin steel sheet with excellent formability can be produced by rolling the steel sheet at 0 to 900'C with lubricating oil to 76 to 95% and then annealing or omitting the annealing.

In addition, some methods for manufacturing deep drawing steel sheets by warm rolling that omit the cold rolling process have been disclosed, for example,
No. 0809, JP-A-49-86214, JP-A-59-
No. 93835, JP-A-59-133325, JP-A-5
No. 9-185729, and JP-A-59-226149.
No. 8 is an example. Both methods are characterized by recrystallization treatment immediately after rolling in the warm region, and are innovative technologies that can omit the cold rolling step.

Furthermore, several methods have been proposed for manufacturing thin steel sheets for processing, which are formed into a thin steel sheet of a predetermined thickness in a relatively low temperature range below the Ar3 transformation point and then do not undergo cold rolling or recrystallization annealing steps.

For example, in Japanese Patent Application Laid-Open No. 48-4329, low carbon rimmed steel is rolled to 4 mm by 90% rolling at a temperature below the Ar3 transformation point.
Yield point: 26.1kg/mm by adjusting plate thickness
2゜Tensile strength 37.3kg/mm2. Elongation 49.7%,
A manufacturing example is shown that yields a property of r=1.29.

On the other hand, in JP-A-52-44718, low carbon rimmed steel is hot-rolled to a thickness of 2.0 mm at a finishing temperature of 800 to 860°C (below the Arz transformation point) and coiled at a temperature of 600 to 730°C.
℃ has been shown to produce a low yield point steel plate with a yield point of 20 kg/mm2 or less, but the conical cup value, which is an index of drawability, is 60.60 to 62.
, about 18 mm, and in this respect the conventional example is 60.58 to 6.
Compared to 0.61, the drawability is the same or lower, and Japanese Patent Application Laid-open No. 53-22850 also describes a low carbon rimmed steel with a hot rolling temperature of 1.8 to 2.3 m at a finishing temperature of 710 to 750°C.
A method for producing a low carbon hot rolled steel sheet is shown in which the sheet thickness is 530 to 600°C, and the conical cup value of the product obtained by this method is listed in 1.
As in the case of Publication No. 2-44718, the drawing performance is higher than that of the conventional example and is inferior.

Furthermore, in Japanese Patent Application Laid-Open No. 54-109022, low carbon aluminum killed steel is rolled at a hot rolling finishing temperature of 760 to 820°C.
．． The yield point is 14.9 to 18.8 kg/mm2 by using a plate thickness of 6 mm and a winding temperature of 650 to 690°C. Tensile strength 27.7~29-8kg/mm" + elongation 39.0~
An example of manufacturing a low strength mild steel plate having properties of 44.8% is disclosed.

However, none of the above-mentioned known techniques give any consideration to improving the above-mentioned ridging resistance.

(Problems to be Solved by the Invention) The inventors previously disclosed in Japanese Patent Application No. 60-043981 that recrystallization annealing is performed after rolling at a temperature range of 800 to 300°C for at least one pass at a strain rate of 300 s-' or more. It was disclosed that by doing so, a thin steel sheet with excellent ridging resistance and workability can be obtained. Also, patent application No. 60-043971
As shown in the specification, excellent ridging resistance and processing can be achieved by rolling at least a pass in a temperature range of Ar + transformation point to 500°C at a strain rate of 300 s-' or more and a reduction rate of 35% or more. We have discovered a method for manufacturing azu-rolled thin steel sheets with high properties.

These manufacturing methods are revolutionary methods that make it possible to manufacture thin steel sheets with excellent ridging resistance and workability, but they all require the strain rate to be increased to 300 s-' or more, and due to the rolling technology, It is unavoidable that some difficulties will be involved.

As a result of repeated experiments, the inventors discovered that by regulating the steel composition, it was possible to manufacture 81a plates with excellent ridging resistance and workability without increasing the strain rate to 300 s-' or higher. be.

In other words, by developing a new process that does not involve a cold rolling process or a cold rolling-recrystallization annealing process, and which overcomes the constraints on strain rate during rolling, we can produce thin steel sheets with excellent ridging resistance and workability, and our manufacturing method. It is an object of the present invention to provide the following.

(Means for Solving the Problems) The above object can be advantageously achieved by a configuration based on the following matters.

C: 0.01 wt% or less, Si: 0.10 w
t% or less, Mn 20, 5 wtX or less, P: 0.1
wt% or less, Al: 0.002 to 0.10at
χ, N:, 0.01 t% or less, O: 0.003
wt% or less and at least one of Ti and Nb in a relationship according to the C and N contents, and the remainder is composed of unavoidable impurities and Fe, and has good ridging resistance. Excellent warm-rolled thin steel sheet for processing (first invention).

C: 0.01 wt% or less, Si: 0.10 i
+t% or less, Mn 20.5 wt% or less, P: 0.
1 wt% or less, A f ; 0.002 to 0.10
wtχ, N: 0.01wt% or less, O: 0.00
3 wt% or less, and further contains at least one of Ti and Nb satisfying the relationship according to the C and N contents.
A method for manufacturing a warm-rolled thin steel sheet for processing with excellent ridging resistance (second invention), characterized in that warm rolling is performed for at least one pass in a temperature range of 00° C., followed by rolling at a temperature of 450° C. to 450° C.

C: 0.01 wt% or less, Si: 0.10 w
t% or less, Mn: 0.5 wt% or less, P: 0.1
wt% or less, Al: 0.002-0.10gtχ
, N: 0.01 wt% or less, O: 0.003w
t% or less, and further contains at least one of Ti and Nb satisfying the relationship according to the C and N contents, 300"C
``Method for producing an as-rolled warm-rolled thin steel sheet for processing with excellent ridging resistance, characterized by performing warm rolling at least one pass at a reduction rate of 35% or more in the temperature range of the Arz transformation point (Third method) invention).

Now, I will start by explaining the research results that formed the basis of this invention.

The sample steel had Si: 0.01 to 0.04wtχ, Mn
: 0.06-0.19wtχ, P: 0.007
~0.018wtχ, SF 0.002~0.009
wtχ, A 1: 0.009-0.059 Tsubatχ, O
: 0.001~0.012wtχ, Ti: O~0
．． 026wtχ, Nb: 0 to 0.035wtχ□)
The value of is o, oooυ8～υ, υUlbwtX (D dry W
It is a hot-rolled steel plate with a circular composition.

This hot-rolled steel plate was heated and soaked at 600° C. and rolled at a rolling reduction of 30% in one pass.

FIG. 1 shows the relationship between the value of and the lower value and ridging index after annealing (soaking temperature 800° C.).

It can be seen that by regulating the steel composition so that O≦0.003wtχ, the lower value and ridging resistance are significantly improved.

In addition, a similar hot-rolled sheet was heated to 700℃ and soaked for 1 pass and 2
Rolling was carried out at rolling reductions of 0%, 40% and 60%.

Figure 2 shows the relationship between the value of , the lower value of the steel plate after rolling, and the ridging index.

C (匈tX) Lower value and ridging resistance strongly depend on (□+,
0.0001wtχ≦(wtχ
), by regulating the steel composition to 0≦0.003wtχ and setting the rolling reduction to 35% or more, the lower value and ridging resistance are significantly improved.

As a result of repeated research based on these basic data, the inventors confirmed that a thin steel plate with excellent ridging resistance and workability can be manufactured by regulating the steel composition as described below.

(1) Steel composition In this invention, the steel composition is the most important, and C, N, and ^1. O is C50,01wtχ,N respectively
≦0.01wtχ, 0.002wtχ≦Af≦0.1
It is important that 0%1tχ, 0≦0.003wtχ and the content of C and N satisfy the relationship of the following formula with the content of one or both of Ti and Nb. If the steel composition does not satisfy the above relationship, normal rolling conditions (strain rate 300
s-' or less), it is not possible to obtain excellent ridging resistance and workability.

Of course, in order to obtain high strength, P: 0.1 wt% or less.

Si: 0.1wt! and Mn: 0.5wt
% or less depending on the desired strength.

In this invention, the unavoidable impurity mainly refers to S, and the less S there is, the more a texture is formed which is advantageous for workability, but if it is 0.01 wt% or less, there is no significant deterioration in workability.

(2) Manufacturing method of rolled material Steel slabs obtained by conventional methods, ie, ingot-blowing or continuous casting methods, can of course be applied.

The heating temperature of the steel piece is suitably 800 to 1250°C, and preferably less than 1100°C from the viewpoint of energy saving.

Of course, the so-called CC-DR (continuous casting-direct rolling) method, in which rolling is started without reheating the steel billet after continuous casting, is also applicable.

On the other hand, the methods of immediately casting rolled materials of 50 Tsuru or less from molten steel (sheet bar caster method and strip caster method) have great economic merits from the viewpoint of energy saving and process saving, and are particularly advantageous as methods for manufacturing rolled materials. be.

(3) Rolling process In the process where the cold rolling process can be omitted, at least one bath is
It is essential to roll in a temperature range of 800°C. In a high temperature range where the finish rolling temperature exceeds 800° C., no matter how much the steel composition is controlled, only a product with poor ridging resistance and processing properties can be obtained. On the other hand, if it is less than 200°C, the deformation resistance will significantly increase, causing problems specific to cold rolling, so the finish rolling temperature was limited to a range of 200 to 800°C.

In addition, in the process where cold rolling-recrystallization annealing can be omitted, at least one bath is
It is essential to roll with a rolling reduction of 5% or more. If this rolling temperature exceeds the Ar3 transformation point, there is concern that no matter how much the steel composition is controlled, the ridging resistance and workability will be poor.
If the temperature is less than 300°C, recrystallization after rolling will not proceed sufficiently.

Therefore, it is preferable that at least one bath with a rolling reduction of 35% or more be in the range of 300° C. to Ar3 transformation point.

Regarding the strain rate, the inventors disclosed in Japanese Patent Application No. 60-0439
No. 71, Japanese Patent Application No. 60-043981, each specification 8a00
It is disclosed that a thin steel plate with excellent ridging resistance and workability can be manufactured by setting the steel composition to s-' or more, but in this invention, it is possible to produce a thin steel plate with excellent ridging resistance and workability by simply regulating the steel composition. Therefore, in this invention, the strain rate may be arbitrary.

The number of rolling passes and the distribution of the rolling reduction ratio may be arbitrary as long as the above conditions are satisfied.

The arrangement, structure, roll diameter and tension of the rolling mill, presence or absence of lubrication, etc. have no essential influence.

(4) Annealing process The annealing method may be either a box annealing method or a continuous annealing method, but the latter is advantageous from the viewpoint of homogeneity and productivity.

The heating temperature is 400 to 950°C.

In principle, annealing is not necessary for products where the recrystallization annealing process can be omitted, but due to material requirements, heat retention is performed on the runout table after rolling and during the winding process.
It is not prohibited to perform soaking treatment or, if necessary, to perform some heat treatment after rolling.

(5) Pickling and temper rolling The steel strip obtained by the above-mentioned procedure is rolled at a lower temperature than conventional methods, so the oxidation layer is thin and the pickling property is extremely good, so no pickling is required. It can also be used for a wide range of purposes. In addition to conventional acid removal, mechanical removal can also be used for descaling. Furthermore, for the purpose of shape enforcement, surface roughness adjustment, etc.
Temper rolling of 10% or less can be added.

(6) Surface treatment The steel strip thus obtained is galvanized (including alloy-based)
It has excellent surface treatment properties such as tin plating and enameling, so it can be used as a base plate for various surface treatments.

(effect) The reasons for limiting the steel composition and its effects are as follows.

It was found that Ti and Nb are precipitated and fixed as carbon and nitride.

Furthermore, about 1 to 10 ppm of interstitial solid solution C during warm rolling.
, N, the effect of dynamic strain aging forms a texture with a crystal orientation that is advantageous for ridging resistance and workability.

It was also found that such an effect is effective when the O content in the steel is only 30 p, □ or less. Therefore, limitations were placed on C, N, Ti and/or Nb.

Although the effect of zero in steel is not clear, it is thought to have an influence on changes in processing strain.

In addition to the above, the reasons for limiting the components in the steel are as follows.

■C≦0.01wtχ The smaller the C component, the better the workability;
If the content exceeds χ, the amount of carbide precipitated becomes too large and the workability of the final product deteriorates, so C50,
01ivtχ.

■N≦0.01wt% The lower the N content, the better the workability;
If N≦0.
01wtX.

■0.002wtx
, 003w tχ becomes difficult to realize.

On the other hand, even if it is added in excess of 0.10wtχ, further deoxidizing effect cannot be obtained and the cost is high.
02wtX≦Aj2≦0.10wtχ.

■St≦O, Iwtχ The Si component has the effect of strengthening steel, but 0.1wtχ
If it exceeds this value, it becomes difficult to form a texture that is advantageous for workability, so SiS2.1wtX was selected.

■Mn≦0.5wtχ The Mn component has the effect of improving the toughness of steel, but 0, Si
If mtX is exceeded, it becomes difficult to form a texture that is advantageous for workability, so Mn≦0.5wtχ was set.

■P≦0.1 How many tχ The P component has the effect of strengthening the steel, but if it exceeds 0.1wtχ, recrystallization becomes difficult and ductility deteriorates, so P≦O, 1wtχ.

(Example) Molten steel whose composition was adjusted to the composition shown in Table 1 was made into a sheet bar with a thickness of 30 to 40 m by the methods shown in Tables 2 and 3, respectively. 0.8~
A 1.5u+ thin steel plate was used.

After that, recrystallization annealing (soaking temperature 600℃~820℃)
Table 2 shows the material properties after pickling and temper rolling (reduction ratio of 0.5 to 1%). In addition, after rolling, recrystallization annealing is omitted and pickling is performed.
Table 3 shows the material properties after temper rolling (reduction ratio of 0.5 to 1%). The tensile properties were determined using a JIS No. 5 test piece.

In addition, the ridging property was evaluated using a JISS No. test piece cut out from the rolling direction and subjected to 15% tensile strain by visually observing the surface unevenness from 1 (good) to 5 (poor). . No evaluation criteria have been established for this evaluation because ridging did not appear when conventional low-carbon cold-rolled steel sheets were manufactured. Therefore, in this invention, the index evaluation criteria based on the visual method for conventional stainless steels are applied as is. An evaluation of 1.2 indicates ridging properties that pose no problem in practical use.

The fH plates produced according to the present invention exhibit better ridging resistance and workability than the comparative examples.

(Effects of the Invention) According to the present invention, by simply regulating the steel composition and omitting the cold rolling process or the cold rolling-recrystallization annealing process,
It is possible to obtain thin steel sheets with good workability and excellent ridging resistance, and the rolled material is compatible with the sheet bar caster method, strip caster method, etc., which greatly simplifies the manufacturing process of thin steel sheets for processing. can be realized.

[Brief explanation of drawings]

They are a graph showing the relationship between the weighting index and the T value, and a graph showing the relationship between the weighting index and the T value. Figure 1 (Goji Garina @t/'%) - (-Cucumber '7B (wt%)
)) Figure 2 (%m) Door construction)) - (7911%) + @ Chung Nora Proceedings Amendment Book December 28, 1985 Director General of the Patent Office Uga Michibe 1, Indication of the case 1985 Patent Application No. 219997 2, Title of Invention: Warm-rolled thin steel sheet for processing with excellent ridging resistance and its manufacturing method 3, Intermediary with the amended case Patent applicant (125) Kawasaki Steel Corporation 4. Agent

Claims (1)

[Claims] 1. C: 0.01 wt% or less Si: 0.10 wt% or less Mn: 0.5 wt% or less P: 0.1 wt% or less Al: 0.002 to 0.10 wt% N: 0. 01wt% or less O: 0.003wt% or less and at least one of Ti and Nb, C and N
Depending on the content, 0.0001 (wt%) ≦ (C (wt%) / 12 + N (
wt%)/14)-(Ti(wt%)/48+Nb(w
t%)/93)≦0.0010 (wt%), and the remainder has a composition of unavoidable impurities and Fe, and has excellent ridging resistance. 2. C: 0.01 wt% or less Si: 0.10 wt% or less Mn: 0.5 wt% or less P: 0.1 wt% or less Al: 0.002 to 0.10 wt% N: 0.01 wt% or less O: 0 .003 wt% or less, and further contains at least one of Ti and Nb,
0.0001(wt%)≦(C(wt%)/12+N(
wt%)/14)-(Ti(wt%)/48+Nb(w
A steel material having a composition satisfying the relationship of t%)/93)≦0.0010 (wt%) is subjected to at least one pass of warm rolling in a temperature range of 200 to 800°C, and then 45
Characterized by annealing at a temperature range of 0 to 950°C,
A method for producing a warm-rolled thin steel plate for processing that has excellent ridging resistance. 3. C: 0.01 wt% or less Si: 0.10 wt% or less Mn: 0.5 wt% or less P: 0.1 wt% or less Al: 0.002 to 0.10 wt% N: 0.01 wt% or less O: 0 .003 wt% or less, and further contains at least one of Ti and Nb,
0.0001(wt%)≦(C(wt%)/12+N(
wt%)/14)-(Ti(wt%)/48+Nb(w
t%)/93)≦0.0010 (wt%), the steel material is subjected to at least one pass in the temperature range of 300°C to Ar_3 transformation point at a temperature with a reduction rate of 35% or more. A method for producing an as-rolled warm-rolled thin steel sheet for processing, which is characterized by performing inter-rolling and has excellent ridging resistance.