JPH0625752A - Manufacture of original sheet for surface treated steel sheet - Google Patents

Abstract

(57) [Summary] [Purpose] T3, T by continuous annealing line for general cold rolled steel sheet
Manufacture of 4th grade master plates. [Constitution] A method for producing a base plate for a surface-treated steel sheet, which comprises treating the material of (1) below in the process of (2). (1) Material:% by weight, C: 0.02-0.10%, Mn: 0.10-0.
40%, sol.Al: 0.030 to 0.100%, P: 0.020
% Or less, S: 0.020% or less, N: 0.0090% or less, and a continuous cast steel billet of low carbon aluminum killed steel with the balance being Fe and inevitable impurities. (2) Process (see Fig. 1): Hot rolling, winding in the temperature range of 500 to 700 ° C, and pickling. The cold-rolled steel sheet obtained by cold rolling is heated in the continuous annealing furnace at a temperature not lower than the recrystallization temperature and lower than the A ₁ transformation point for 5 seconds to 2 seconds.
Recrystallization annealing is performed by heating for 1 minute, and cooling is performed at a cooling rate of 10 ° C / sec or less to a temperature range of 300 ° C or less. Perform overaging treatment by holding in the temperature range of 200 to 300 ° C for 30 seconds to 10 minutes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a steel sheet used as a base sheet for T3 and T4 grade tinplate and a tin-free steel sheet specified in JIS G3303.

[0002]

2. Description of the Related Art Tinplate blanks are stipulated in JIS G3303 as being expressed as Rockwell T hardness (HR30T) values according to the refining degree, and T1 to T6 in order from the softest one.
It is divided into. Among them, HR30T is 54-60 T3
Similarly, T4 of 58 to 64 is used not only as a tin plate but also as a tin-free steel plate because it can be efficiently manufactured by continuous annealing and has a formability that can be processed into DI cans and the like. .

Conventionally, a soft plate of T3 or less is manufactured by long-time annealing by box annealing, and its production efficiency is low. Therefore, in order to improve the production efficiency in recent years, several methods of manufacturing by the continuous annealing method have been proposed. For example,
57-70227 discloses steel plates with different hardness, specifically T
Although there is a proposal for a method of separately manufacturing 4 and T5 by a continuous annealing method, this method is premised on production in a tin exclusive line without overaging treatment.

Further, Japanese Patent Application Laid-Open No. 4-80346 proposes a method of manufacturing a soft material of T3 or less by a continuous annealing method. The purpose is to cool the material after annealing at 40 ° C./sec.
It is intended to increase the amount of solid solution C immediately after quenching by increasing the speed as described above and to quickly reduce the amount of solid solution C in the overaging treatment in the next step to shorten the overaging treatment time.

The conventional method as described above is premised on that it is carried out in a continuous annealing line for exclusive use with tinning, which has no overageing zone or is short (usually 30 seconds or less). Therefore, when these methods are carried out in a continuous annealing line for a general cold-rolled steel sheet having a normal overaged zone, it is difficult to produce a stable original plate with a large variation in the tempering degree in the overaged zone.

[0006]

An object of the present invention is to use a conventional cold-rolled steel sheet having a conventional long (usually 1 minute or more) overaging zone without using a dedicated continuous annealing line for producing tin plate. Using a continuous annealing line, it is possible to inexpensively and stably manufacture a tin plate and tin-free steel plate (hereinafter simply referred to as "tin plate") having tempers T3 and T4. To provide.

[0007]

As will be described in detail later, the present invention provides a continuous annealing line dedicated to general cold-rolled steel sheets by appropriately combining the chemical composition of the materials used, hot rolling conditions, continuous annealing conditions, etc. Stable quality T3 and T4
It was made based on the knowledge that it is possible to manufacture a grade tin plate, and the gist of the material is (1) below.
This is a method for manufacturing a master plate for surface-treated steel sheet, which is characterized in that it is treated in the process (2).

(1) Material:% by weight, C: 0.02 to 0.10%,
Mn: 0.10 to 0.40%, sol.Al: 0.030 to 0.100%, P: 0.020% or less, S: 0.020% or less, N: 0.0090
% Or less and the balance of Fe and inevitable impurities in the low carbon aluminum killed steel continuously cast billet (2) Process (consisting of): After hot rolling and winding in the temperature range of 500 to 700 ℃ Pickle. The cold-rolled steel sheet obtained by cold rolling is heated in the continuous annealing furnace at a temperature not lower than the recrystallization temperature and lower than the A ₁ transformation point for 5 seconds to 2 seconds.
Recrystallization annealing is performed by heating for 1 minute, and cooling is performed at a cooling rate of 10 ° C / sec or less to a temperature range of 300 ° C or less.

Overageing treatment is performed by holding in the temperature range of 200 to 300 ° C. for 30 seconds to 10 minutes.

[0010]

The present inventors presume that a tempered T3 or T4 grade original plate is produced by a general continuous annealing line for cold-rolled steel sheets, and the chemical composition of the material used, from hot rolling to overaging treatment. The conditions were examined. The continuous annealing line for general cold-rolled steel sheets has a long overaging zone, and the normal processing conditions are 200-300.
Hold for 30 seconds to 10 minutes at a temperature of ° C. In order to obtain the stable strengths of the tempers T3 and T4 by receiving such overaging treatment, it is necessary to have the following basic conditions.
That is, (a) A suitable continuous annealing condition is selected with the aim of reducing precipitates in the overaging zone, and especially the cooling rate is slow cooling of 10 ° C / sec or less.

(B) In order to obtain strengths of T3 and T4 grades, the chemical composition of the material as described above for solid solution strengthening and fine grain strengthening, hot rolling conditions, and continuous annealing conditions are selected.

The object can be achieved for the first time by manufacturing under the conditions within a certain range set by appropriately combining the basic conditions of (a) and (b).

First, the reason why the chemical composition of the material is determined as described above will be explained. Hereinafter,% of the content of components means% by weight.

C: C is the most effective strengthening element for cold-rolled steel sheets, and a minimum of 0.02% is necessary for producing an original sheet having a temper of T3 or higher. However, if the content exceeds 0.10%, the hot-rolled sheet becomes hard and the efficiency and workability during cold rolling deteriorate. In addition, the flatness of the product original plate is also adversely affected.

Mn: Mn, like C, is a strengthening element that is harmless to the original plate, but if it is too much, the hot-rolled sheet becomes hard, so the upper limit is 0.40%, and in order to suppress hot brittleness. The lower limit was 0.10%.

Al (aluminum): Al is necessary for deoxidation during steel making, and is contained in an amount of 0.030% or more as sol.Al for fixing N (nitrogen) as AlN.
However, if the content of sol.Al exceeds 0.100%, inclusions in the steel sheet increase and press formability deteriorates, and there are disadvantages such as increased production costs.
It was 0.100%.

P: P is an element that has a strong strength improving effect, but it lowers the corrosion resistance when the original plate is a surface-treated steel plate such as tin plate, so the upper limit is 0.020% in order to keep it in a range without actual damage. did.

S: S impairs the workability of steel and produces MnS inclusions to deteriorate press formability, so the upper limit is 0.020.
%.

N: N is set to 0.0090% or less in order to suppress the age hardening in the overaging zone to a necessary amount or less and to keep the efficiency and workability in the cold rolling process.

Next, the reason why various conditions of the working process are determined will be described.

The hot rolling may be performed under usual conditions. But,
Winding after hot rolling shall be performed in the range of 500-700 ℃. If the coiling temperature is lower than 500 ° C, the crystals of the hot-rolled sheet will become fine and the hot-rolled sheet will become hard, making cold rolling difficult. On the other hand, if the coiling temperature exceeds 700 ° C, more C in the hot-rolled sheet precipitates during cooling after coiling and the solid solution C decreases,
In addition, the crystal grains become large, the hardness of the original plate decreases, and the strength of the grades T3 and T4, which is the object of the present invention, cannot be obtained.

After winding in the above temperature range, ordinary pickling is carried out and cold rolling is carried out to a predetermined plate thickness. There are no particular restrictions on these conditions.

Annealing is carried out in a continuous annealing line for general cold-rolled steel sheets, and the heat pattern is shown in FIG.

The soaking temperature is set to a temperature lower than the A ₁ transformation point because when the temperature is higher than the A ₁ transformation point, a lumped pearlite structure is formed and the corrosion resistance of the product after the surface treatment is deteriorated.
Further, the reason why the annealing time at this temperature is 5 seconds to 2 minutes is that
This is because it takes 5 seconds or more to cause recrystallization, and holding for 2 minutes or more saturates the effect.

After recrystallization annealing, stable tempers T3, T
In order to manufacture the tin plate and tin-free steel plate of No. 4, it is necessary to cool to a temperature of 300 ° C or less at a slow cooling rate of 10 ° C / sec or less. That is, by cooling at a slow cooling rate of 10 ° C / sec or less, cementite can be sufficiently precipitated during cooling, so that the hardness after overaging treatment is stable, and the original plate having the tempers T3 and T4 is prepared. It can be manufactured.

The overaging treatment is carried out by holding at 200 to 300 ° C. for 30 seconds to 10 minutes. Generally, the tin plate has a small thickness and is likely to cause a flatness defect called a heat buckle. To avoid this, the overaging temperature was set to a low temperature of 200 to 300 ° C. A hold of at least 30 seconds is required to reduce the solid solution C at this temperature. On the other hand, in order to hold for more than 10 minutes, it is necessary to modify the continuous annealing equipment, which goes against the purpose of the present invention of using a general continuous annealing line for cold-rolled steel sheets.

The steel sheet after the overaging treatment is subjected to ordinary temper rolling to obtain a raw material for tinplate and tin-free steel sheet.

[0028]

Example 1 For the purpose of producing a T4 grade tin plate,
A molten steel having the components shown in Table 1 was made into a 220 mm thick continuously cast slab, heated to 1000 to 1200 ° C, finished in the temperature range of 850 to 900 ° C, wound at a temperature of 500 to 650 ° C, and then acidified. Wash,
Then, cold rolling was performed by a conventional method. This cold rolled steel sheet
After recrystallization annealing, heating to 80 ℃ and holding for 40 seconds,
Continuous annealing was performed by cooling at a cooling rate of 0 ° C / sec, and then overaged at 250 to 500 ° C for 5 to 180 seconds.
Then, temper rolling with a reduction rate of 0.8% was performed.

The hardness of the original plate obtained in the above steps was measured, and the hardness after forced aging (100 ° C. × 60 minutes) was measured to examine the change. This forced aging is a treatment that is performed under the assumption of the heating conditions, because when the tin plate is applied to the original plate, it may be heated and aged to deteriorate the characteristics. Table 2 shows the hardness (HR30T) before and after forced aging.

As can be seen from Tables 1 and 2, the cooling rate after recrystallization annealing was slow (10 ° C./sec or less):
The increase in hardness after forced aging is smaller than that with a high cooling rate. This is because the cementite was sufficiently precipitated during the cooling after the recrystallization annealing, so that the cementite, which causes age hardening by the forced aging, does not exist in the steel.

[0031]

[Table 1]

[0032]

[Table 2]

FIG. 2 shows No. 1 which is an example of the present invention in Tables 1 and 2.
4 and No. 4 and comparative examples No. 5 and No. 6 show hardness before and after forced aging. As shown in the figure, the cooling rate after annealing is 7 ℃ / se, whether the overaging temperature is 250 ℃ or 300 ℃.
In the present invention example (○) having a small c, the increase in hardness due to forced aging is small at 2 points or less and stable.

On the other hand, the cooling rate after annealing is 100 ° C.
In the comparative example (●), which is large as / sec, the amount of solid solution C is large,
There is not sufficient precipitation of C even in overaging treatment, and solid solution C remains, so that it is precipitated during forced aging and the hardness is greatly increased. That is, the quality of the original plate is not stable.

[0035]

According to the method of the present invention, an original plate having a stable quality of tempers T3 and T4 can be easily manufactured by a continuous annealing line for general cold-rolled steel plates. This original plate can be used as a material for tinplate and tin-free steel plates.

[Brief description of drawings]

FIG. 1 is a view showing a heat pattern in a continuous annealing step in the method of the present invention.

FIG. 2 is a diagram showing the relationship between the conditions of overaging treatment and the hardness of the original plate before and after forced aging.

Claims (1)

[Claims] 1. By weight%, C: 0.02 to 0.10%, Mn: 0.10 to
0.40%, sol.Al: 0.030 to 0.100%, P: 0.02
Continuous casting of low carbon aluminum killed steel containing 0% or less, S: 0.020% or less, N: 0.0090% or less and the balance of Fe and inevitable impurities was hot-rolled in a temperature range of 500 to 700 ° C. A cold-rolled steel sheet obtained by winding, pickling, and then cold rolling is placed in a continuous annealing furnace at a recrystallization temperature or higher.
Recrystallization annealing is performed by heating for 5 seconds to 2 minutes at a temperature lower than the A ₁ transformation point, and after cooling to a temperature range of 300 ° C or less at a cooling rate of 10 ° C / sec or less, a temperature range of 200 to 300 ° C. 30 seconds to 10
A method for producing an original plate for a surface-treated steel sheet, which is characterized by holding for minutes and performing an overaging treatment.