JPS6372829A - Manufacture of steel sheet for deep drawing having superior uniformity in internal quality of coil - Google Patents

Abstract

PURPOSE:To manufacture a steel sheet for deep drawing having superior uniformity in the internal quality of a coil by subjecting a steel contg. specified percentages of C, Si, Mn, P, S, sol. Al and N to hot rolling, coiling and cold rolling under specified conditions and by continuously annealing the resulting sheet. CONSTITUTION:A molten steel consisting of, by weight, >0.01-<0.02% C, <=0.30% Si, 0.05-0.50% Mn, <=0.10% P, 0.005-0.05% S, <=0.10% sol. Al, <=0.0080% N and the balance Fe with inevitable impurities is formed into a slab by continuous casting or other method. The slab is heated to 1,000-1,200 deg.C, hot rolled at a finishing temp. of the Ar3 point or above as usual and coiled at 700-<800 deg.C. The coil is descaled and cold rolled at >=40% draft and the resulting sheet is continuously annealed at the recrystallization temp. or below. Thus, a steel sheet for deep drawing having superior uniformity in the internal quality of a coil including both ends is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for producing a deep drawing steel plate with excellent uniformity of the material inside the coil.

(Prior art) When producing cold-rolled steel sheets for deep drawing by continuous annealing using low carbon aluminum guild steel, good deep drawability cannot be achieved unless the steel sheets are rolled at a high temperature of 700°C or higher after hot rolling. It is known that this cannot be done. This is achieved by winding at high temperatures.
This method utilizes the effect that cementite aggregates and AIN precipitates to become coarser. However, even in this method, good deep drawability cannot be obtained in the inner and outer circumferences of the coil where the cooling rate is high due to insufficient aggregation of cementite. Either cutting off the periphery, or inserting the coil into a heat-retaining furnace or covering it with a heat-retaining cover after winding it at a high temperature to improve the uniformity of the material inside the coil, as in JP-A-58-37128. There is a method to control the cooling rate. Cutting off both ends of the coil is a simple method, but it has the drawback of lowering yield, while placing it in a furnace or covering it with a heat insulating cover complicates the process and significantly increases costs. There are drawbacks.

(Problems to be solved by the invention) As mentioned above, in the conventional method, sufficient deep drawability (
High-temperature winding is essential in order to obtain a high r-value), but because the cooling rate at the inner and outer circumferences of the coil is fast, the cementite does not aggregate sufficiently coarsely, making it impossible to obtain the deep drawability required for a steel sheet for deep drawing. It has the disadvantage of lowering the yield, and the method of placing it in a furnace or covering it with a heat insulating cover has several problems, such as complicating the process and causing a significant increase in cost. Under these circumstances, when producing deep drawing steel sheets by continuous annealing using aluminum guild steel, there is a strong desire to develop a method for improving the material quality of the inner and outer circumferential parts of the coil.

That is, the problem to be solved by the present invention is that in a method of manufacturing a deep drawing steel plate using low carbon aluminum guild steel as a raw material by continuous annealing, the inner and outer peripheral parts of the coil are The disadvantage is that the material deteriorates.

(Means for solving problems) The gist of the present invention is as follows.

C: 0.01 XMO, less than 02X, Si: 0.
30X or less, Mn: 0.05-0.50%, P: 0.10X or less, S: 0.005-0.05%, sol, A1: 0.10X or less, N: 0.0
080X or less, steel consisting of balance Fe and unavoidable impurities 1000~
After heating to a heating temperature of 1200°C, it is hot rolled according to a conventional method, wound up at a temperature of 700°C or more and less than 800°C, then cold rolled at a reduction rate of 40% or more, and continuously annealed. A method for manufacturing a steel plate for deep drawing with excellent uniformity of the material inside the fill.

In order to improve the deep drawability (r value) by continuous annealing using aluminum guild steel, an important point is how to coarsely aggregate cementite during winding after hot rolling. For this purpose, a high temperature winding method has conventionally been adopted. However, even if it is wound at high temperatures, there are various disadvantages as described above.

The present inventors investigated a method that would not reduce the deep drawability of the inner and outer circumferential parts of the coil even when high-temperature winding was performed, and found that the heating temperature was The present invention was based on the new knowledge that by heating to 1000 to 1200°C and hot rolling, cementite becomes coarsely agglomerated and a high r value can be obtained even at a cooling rate equivalent to the inner and outer circumferential parts of the coil after winding. Completed.

That is, to describe in detail, by setting the C content to less than 0.02%, C is completely dissolved in the α phase in order to pass through the α single phase region during cooling after hot rolling. As the value decreases, cementite precipitates at the ferrite grain boundaries. At this time, the heating temperature before hot rolling was set to 1000 to 1
By aggregating and coarsely distributing existing precipitates such as MnS at 200°C, cementite nuclei are localized and the cementite becomes coarsely aggregated. MnS and AI
When existing precipitates such as N exist densely, cementite precipitates in large numbers, but when they are coarsely distributed, they preferentially precipitate from there, resulting in coarse agglomeration.The present invention solves this finding. This was done based on.

The present invention will be explained in more detail below.

The reason for limiting the chemical components is as follows.

If C is contained in an amount of 0.02% or more, even if the present invention is heated to 1000 to 1200°C and then hot rolled and coiled at a high temperature, cementite will not form at a high cooling rate corresponding to the inner and outer circumferential parts of the coil. Coarse agglomeration becomes insufficient, and r
Since the value becomes low, it is set to less than 0.02χ. Also, 0.0
1! If it is below, the solid solution C will increase rapidly and the aging property will deteriorate, so it is set to exceed o, otx.

Si is 0.30! The upper limit is set to 0.302 since the chemical conversion treatment properties and hot-dip galvanizing properties will deteriorate if the content is larger.

If Mn is less than 0.05%, flaws will occur due to hot embrittlement and the surface quality of the steel plate will be impaired, so 0.05χ is set as the lower limit.
If it is more than 0.50%, deep drawability will deteriorate, so 0.50%
The upper limit is %.

P can be effectively used to increase strength, but if it exceeds 0.101, the risk of secondary processing embrittlement increases, so the upper limit is set at 0.10%.

S is precipitated and fixed as MnS and is used as the nucleus of cementite during winding. However, if it exceeds 0.05%, the number of nuclei will increase unnecessarily and the cementite will not aggregate, so the upper limit should be set to 0.05%.
05%. Furthermore, if it is less than 0.005%, the nucleus will not have an appropriate size, so the lower limit is set to 0.0051.

AI and N are each 0.10! O and 0.008
If more than 0.02 is contained, the deep drawability will be lowered, and the coarse agglomeration of recementite, which has an unnecessarily large number of cementite nuclei, will not occur, so the upper limit is set at 0.0080%.

The other components are Fe and unavoidable impurities.

A hot rolling method in which molten steel whose chemical composition has been adjusted to fall within the above chemical composition range is made into a slab by continuous casting or ingot forming is heated to a heating temperature of 1000 to 1200°C to achieve a finishing temperature of Ar3 or higher. If the heating temperature is lower than 1000°C, the finishing temperature cannot be ensured, so 1000°C is the lower limit.

The upper limit is determined by the solution temperature of MnS. If the temperature is higher than the solution temperature, coarse MnS will be dissolved once, so that a large number of fine MnS will be present during winding. Therefore, recementite, which has a large number of nuclei, does not aggregate coarsely. However, even if the amount of Mn and S is increased to raise the solution temperature, the number of MnS increases, so even if the temperature is below the solution temperature, the temperature is 1200℃.
If it exceeds Mn, cementite will not coarsely aggregate;
When the number of MnS is reduced by lowering the amount of S and the amount of S, cementite coarsely aggregates up to 1200° C. even at temperatures higher than the solution temperature. Therefore, within the range of Mn amount and S amount of the present invention,
The upper limit of the heating temperature is a constant 1200℃ regardless of the amount, and if it exceeds 1200℃, the r value decreases, so 120℃
The upper limit is 0°C.

There is no upper limit to the winding temperature from the viewpoint of the material, but 80
If the temperature is higher than 0℃, the grains will become coarser and roughness will occur, so the temperature should be lower than 800℃, and if the temperature is lower than 700℃, the level of deep drawability of the steel sheet as a whole will decrease.
00℃ or higher. The hot rolled coil obtained by this method is descaled and then cold rolled at a rolling reduction rate of 4.
If the thickness is less than 0, sufficient deep drawability cannot be obtained, so the lower limit of the cold rolling rate is set at 40%.

Next, recrystallization annealing is performed, and the annealing method is continuous annealing. As continuous annealing, any process for manufacturing various types of cold-rolled steel sheets, galvanized, tin-plated, chrome-plated, etc. can be adopted. As a condition for continuous annealing, there is no need to specify the annealing temperature as long as the steel plate temperature is above the recrystallization temperature, and over-aging treatment for the purpose of improving the aging properties of the steel plate may be performed as necessary. , skin pass rolling after annealing, rust prevention treatment, application of lubricant, etc. may be performed as necessary.

(Example) Steel having the components shown in Table 1 is melted, made into a slab by continuous casting, heated to a temperature range of 1000 to 1250°C, hot rolled at a temperature of 890°C or higher, 82
It is wound up to form a coil at a temperature of 0°C, pickled, cold rolled at a rolling reduction of 8 oz, and then continuously annealed by soaking at 750°C for 60 seconds and subsequently overaging at 350°C for 3 minutes. A cold-rolled steel sheet was obtained.

Samples were cut from the obtained cold-rolled steel sheet from the stirrups corresponding to the innermost and outer peripheral parts and the center part of the coil at the time of winding, and the r value, which is an index of deep drawability, was measured.

In addition, specimens were cut out at the hot-rolled coil stage and the occurrence of coarse grains, which cause rough skin and reduced deep drawability, was investigated. Table 2 shows the manufacturing conditions, the measurement results of the r value, and the investigation results for the presence or absence of coarse particles.

From Table 2, it can be seen that in the method of the present invention, 1.7
It can be seen that a high r value as above can be obtained, and a steel plate for deep drawing with excellent uniformity of the material inside the coil without the generation of coarse grains can be obtained.

(Effects of the Invention) According to the present invention, it is possible to manufacture a steel plate for deep drawing with excellent uniformity of the material inside the coil including the outermost ends of the coil,
This method is extremely advantageous because it can solve the problem of reduced yield due to material deterioration at both ends of the coil in the conventional method.

Claims (1)

[Claims] C: more than 0.01% and less than 0.02%, Si: 0.30% or less, Mn: 0.05 to 0.50%, P: 0.10% or less, S: 0. 005-0.05%, sol. Steel consisting of Al: 0.10% or less, N: 0.0080% or less, balance Fe and unavoidable impurities at 1000~
After heating to a heating temperature of 1200°C, it is hot rolled according to a conventional method, wound up at a temperature of 700°C or more and less than 800°C, then cold rolled at a reduction rate of 40% or more, and continuously annealed. A method of manufacturing a steel plate for deep drawing with excellent uniformity of material inside the coil.