JP2505579B2 - Manufacturing method of cold-rolled steel sheet for hollows having excellent resistance to tabs and its uniformity in the coil - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a cold-rolled steel sheet for enamel, which is excellent in dent resistance.

More specifically, it relates to a method for manufacturing a cold-rolled steel sheet for enamel, which is excellent not only in resistance to tabulation but also in coil uniformity of resistance to tabulation.

(Prior art) Conventionally, capped steel has been used as a cold-rolled steel sheet for enamel that has excellent knuckle resistance, but in order to reduce manufacturing costs, a manufacturing method from the ingot method to the continuous casting method has been investigated, and already Several methods have been disclosed. The first is a method in which the oxygen content in the steel is contained more than in the capped steel as disclosed in JP-A-62-270727, but this method is very strict control in steelmaking work in order to eliminate surface defects. However, this is not an easy manufacturing method. There is also a problem in terms of workability. The second is a method of adding a carbide-forming element such as Ti or Nb as disclosed in, for example, Japanese Patent Laid-Open No. 60-110845. This method uses a vacuum degassing treatment method to improve workability. It is necessary to reduce carbon, which significantly increases the manufacturing cost. Third,
This is a method of agglomerating carbides by high-temperature winding in hot rolling, but this method does not improve the ends of the coil.

(Problems to be Solved by the Invention) The present invention solves these problems in view of the difficulty of steelmaking work, the necessity of vacuum degassing treatment, the variation in the quality of the coil, etc. An object of the present invention is to provide a method for manufacturing a cold-rolled steel sheet for enamel that is inexpensive, has excellent dent resistance, and has no variation in the steel sheet.

(Means for Solving the Problems) The present invention includes C: 0.02 to 0.08%, Mn: 0.08 to 0.50%, and sol.A.
l: 0.005-0.06%, N: less than 0.0030%, Of 0.0010% or more to -0.0010% or more, with the balance being iron and inevitable impurities, continuously cast slabs at 900 ° C
After cutting as above, direct heating hot rolling is started within 40 minutes after applying auxiliary heating, and after finish rolling, it is wound at over 650 ° C and 700 ° C or less, cold rolled, and then continuously annealed. It is a method for producing a cold-rolled steel sheet for enamel that is excellent in tabularity and uniformity in the coil.

 Hereinafter, the present invention will be described in detail.

C is required to be 0.02% or more in order to use the carbide in steel for improving the rust resistance. However, if it is too large, the workability deteriorates, so the content is made 0.08% or less.

Mn is set to 0.08% or more to prevent hot embrittlement and improve slab resistance. On the other hand, if the amount is too large, the effect of improving the wing resistance is weakened and the workability is also reduced, so the content is made 0.50% or less.

Al is 0.005% or more as heat-soluble Al for deoxidation, but if it is too much, the workability is deteriorated, so 0.06% or less.

Since N is an element harmful to the workability, it is preferably less than 0.0030% from the viewpoint of workability.

B is for fixing N easily and for improving the wing resistance. As such, it is important to regulate the content, and the amount is set to 0.
0010% or less. However, if a large amount of B is contained, the workability is deteriorated, so the content is made 0.0010% or more.

After continuously casting the above component steel, hot rolling is started by supplementary heating by a so-called direct feed rolling method, and direct feed hot rolling is started within 40 minutes after cutting the slab at 900 ° C or higher. This is because the surface temperature of the slab, especially the length and length of the slab, and the slab at the tip end and the slab, respectively, when cut below 900 ° C or after cutting above 900 ° C for more than 40 minutes. This is because the temperature drop at both ends in the width direction becomes large and it becomes difficult to obtain the effect of improving the slab resistance, and the slab resistance varies in the steel sheet coil.

The finishing temperature of hot rolling is preferably set to an Ar ₃ point transformation point or higher from the viewpoint of ensuring workability. The coiling temperature is set to more than 650 ° C from the viewpoint of resistance to tabulation and workability, but if it is too high, the pickling property is significantly reduced, so the upper limit is 700 ° C.

Cold rolling has a rolling reduction of 60% or more to improve the tubing resistance, but if it is too high, it will have the opposite effect, so it will be 85% or less.

Next, recrystallization annealing is performed by continuous annealing. This is because continuous anneal provides more uniform resistance to crushing in the coil than the conventional box anneal method. The annealing temperature is preferably as high as possible for improving the workability, but if it is too high, the rust resistance is lowered, so that it is preferably 700 to 800 ° C. After annealing, temper rolling of about 1% is usually performed.

(Examples) The component steels shown in Table 1 were continuously cast, and then hot-rolled by direct feed rolling and ordinary post-reheating rolling (reheating temperature 1150 ° C). In direct rolling, the heat history up to the start of hot rolling was changed. The finishing temperature of hot rolling was 900 ℃ and the coiling temperature was changed between 600 and 750 ℃ after finishing the plate thickness to 2.8 mm. After pickling 0.
After cold rolling to 8 mm, continuously anneal at 750 ℃, 1.0%
Was temper-rolled. The tabularity of the obtained steel sheet was evaluated at the front, middle, and rear positions of the coil, and the mechanical properties were also investigated.

The results are shown in Table 2 together with the production conditions. In the route of the slab described in the same table, direct hot rolling is described as DR, and conventional hot rolling after reheating is described as CCR. The steel sheet produced by the method of the present invention has a longer hydrogen permeation time than a conventional steel sheet obtained by rolling after reheating, has less variation in the coil, and exhibits excellent dent resistance in uniformity. Further, although there is generally the fact that continuous annealing of a straight rolled material is considerably inferior to the conventional reheat rolled material, the steel sheet according to the present invention exhibits the same mechanical properties as the conventional method.

(Effects of the Invention) The cold-rolled steel sheet for enamel manufactured by the method of the present invention has uniform enamel characteristics in the coil without adding expensive alloy elements, and has a direct feed rolling method and a continuous annealing method. The industrial significance of greatly reducing the manufacturing cost by simplifying the omission is significant.

Claims (1)

(57) [Claims] 1. C: 0.02-0.08%, Mn: 0.08-0.50%, sol.A
l: 0.005-0.06%, N: less than 0.0030%, Of 0.0010% or more to -0.0010% or more, with the balance being iron and inevitable impurities, continuously cast slabs at 900 ° C
After cutting as above, direct heating hot rolling is started within 40 minutes after applying auxiliary heating, and after finish rolling, it is wound at over 650 ° C and 700 ° C or less, cold rolled, and then continuously annealed. A method for producing a cold-rolled steel sheet for enamel, which is excellent in toughness and uniformity in the coil.