JPS61250113A - Manufacture of delayed aging steel sheet for slight working having burning hardenability - Google Patents

Abstract

PURPOSE:To obtain a delayed aging steel sheet for slight working having superior burning hardenability by regulating the composition of a steel and controlling the hot rolling, coiling and annealing temps. CONSTITUTION:The composition of a steel contg., by weight, 0.02-0.12% C, <=0.02% S and 0.002-0.006% N is regulated so that the amounts of Mn, S, O and Al in the steel satisfy formulae I, II. A slab of the steel is heated to >=1,100 deg.C, hot rolled, coiled at 300-600 deg.C and cold rolled. The resulting cold rolled steel sheet is continuously annealed by heating to the recrystallization temp. - 750 deg.C and soaking for <=1min.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for manufacturing a slow-aging cold-rolled steel sheet for light working that has bake hardenability by continuous annealing.

(Prior art) Conventionally, as a method for producing non-aging high-grade cold rolled steel sheets with excellent press formability using a continuous annealing method, a C content of 0.0 was used.
8% or less, Mn, AL and 8.0% as unavoidable impurities. N content is 32s &I)≦Mn(%)≦0.25%・27
27X2 -N(a)+□0(5)≦AL(a)≦0.2%14
Steel whose composition has been adjusted to satisfy 16X3 is hot-rolled at a finishing temperature of 650
~980 C, hot rolling at a winding temperature of 300 to 600 C, followed by cold rolling, and by continuously annealing the obtained cold rolled steel sheet, it is necessary as a cold rolled steel sheet for press forming of four automobile bodies, etc. Japanese Patent Publication No. 53-38690 discloses a method for producing a cold-rolled steel sheet having excellent deep drawing properties, stretchability, and anti-aging properties, which are required as properties. However, deep drawability is not required for cold-rolled steel sheets for light processing, which are used for drums, home appliances, desks, shelves, etc.
Steel plates with good shapes are required.

Cold-rolled steel sheets for light processing are manufactured by box annealing continuous cast steel with little variation in the longitudinal direction of the coil, but since the desired shape cannot be obtained by box annealing, skin pass, tension leveler, etc. Shape correction is being carried out.

(Problems to be Solved by the Invention) However, during box annealing, there is a skin pass because there is a material difference in the rolled material due to the temperature difference between the outer and inner windings.

It is difficult to correct the shape with correction methods such as tension levelers.
The straightening conditions had to be changed each time in the longitudinal direction. In addition, cold-rolled steel sheets for light working are baked during painting, but whereas conventional rimmed steel has bake hardenability due to solid solution N, it is now manufactured using a continuous casting method.
N was fixed at ht, and no improvement in strength could be expected by baking treatment. Therefore, in order to improve the strength of the final product, it was necessary to increase the thickness of the board or to reinforce it with reinforcing materials. For this reason, methods have been proposed such as adding N to the steel to give it bake hardenability and reducing steel as much as possible, but the former causes significant aging deterioration if the amount of N is not controlled, while the latter Practical use has not progressed much due to problems such as blowholes occurring on the surface.

Measures to solve problem C) The present invention eliminates the drawbacks and problems of the prior art.

The object of the present invention is to provide a method for producing a steel plate for light working that has bake hardenability and slow aging properties that can be improved, and the present invention aims to provide a method for manufacturing a steel plate for light working that has bake hardenability and slow aging properties that can be improved. The above object can be achieved by providing a complete method of manufacturing a steel plate for light processing. In other words, this invention is 0.
02%≦C≦0.12% steel, Mn, Azs S,
0. N content is 7×S (%)≦Mn≦0.25
%, and S≦0.020% and 0.002%≦N≦0.006%, the steel was heated at a slab heating temperature of 1100 C.
Above, hot rolled, then hot rolled coiling temperature 300C~
Bake hardenability characterized by rolling up at 600C, then cold rolling, and continuously annealing the obtained cold rolled steel sheet at a soaking temperature higher than the recrystallization temperature and lower than 750C and for a soaking time of 1 minute or less. The present invention relates to a method for producing a steel plate for light working that has slow aging properties.

Hereinafter, the method for producing a light working steel plate having bake hardenability and slow aging properties according to the present invention will be explained in detail.

The present invention aims to provide, at low cost, a steel plate for light processing that has excellent production efficiency, has hardening ability during annealing by a continuous annealing method, and has little aging deterioration even if the base plate is left for a certain period of time.

In order to achieve both bake hardenability and slow aging properties, it is necessary to control the amount of solid solution C2 and solid solution N remaining in the final product.

If C is less than 0.02%, the strength of the base metal will be insufficient, making it unsatisfactory as a steel plate for light processing, and increasing the plate thickness to increase the strength will increase the price. On the other hand, if it exceeds 0.12%, a large amount of fine carbide precipitates during the hot rolling stage, which is not only disadvantageous for leaving solid solution C, but also deteriorates weldability. It is necessary to keep it within the range of .12%.

For pigeons, if there is not a sufficient amount to fix the impurity S as MnS, red heat brittleness will occur due to excess S, so seven times the amount of S (material) is required. Furthermore, MnS acts as a precipitation nucleus for C in steel, and if the amount of MnS is large, it becomes difficult to leave an appropriate amount of solid solution C. -1 Too many storms tend to harden the material, and it is necessary to suppress the upper limit of Mn, 8, so Iori is 8
% or more and 0.25% or less.

S needs to be 0.020% or less.

Red works to fix O and N in steel. The amount of 0 in molten steel is usually reduced to about soppm before continuous casting, but if this remaining 0 is not fixed as Beni 203 with Beni 203, blowholes will occur on the slab surface. is necessary.

Furthermore, red has the function of fixing N=iz as l'd and N in a certain temperature range, but in order to improve the bake hardenability of steel, it is necessary to leave a certain amount of N as solid solution N.

Furthermore, if Asahi is present in large quantities, Ω itself must become a harmful impurity.

It is sufficient that a certain amount of N remains as solid solution N, 0.002
If the amount is less than 0.0%, the upper limit is set to 0.006%, and the lower limit is set to 0.006%, since it easily sticks to red during the rolling and continuous annealing stages.
It is necessary to keep it within the range of 0.002%.

Next, the steel whose composition has been adjusted within the above-mentioned range is subjected to a refining operation by hot rolling and continuous annealing.

Raise the heating temperature of the slab to 1100 C or higher and
It is melted and hot rolled. If the coiling temperature exceeds 600C, AzN will coarsely precipitate during the winding diameter slow cooling, making it impossible to adjust the properties of the steel sheet, and if the coiling temperature is lower than 300C, the shape of the hot rolled sheet will deteriorate. The hot rolling coiling temperature needs to be in the range of 300C to 600C since root permeability in the next step will be inhibited.

Next, the material is adjusted by continuous annealing, but controlling the soaking conditions is important in continuous annealing. If kept at high temperature for a long time, N will become coarse A1. It precipitates as N and the bake hardenability deteriorates. Therefore, it is necessary to set the upper limit of the annealing temperature to 750 C%, preferably 700 C or less, and to pass the sheet within a soaking time of 1 minute.

Next, the present invention will be explained in more detail with reference to examples.

(Example) Steels with various components shown in Table 1 were melted by a continuous converter casting process, and the slab heating temperature was 1200 C, and the hot rolling coiling temperature was 450 C.
After making it into a 3.5m hot-rolled plate at C~640C,
1, Qss cold-rolled sheet, continuous annealing under the soaking conditions shown in Table 1, aging treatment at 400C to 350C for 2 to 3 minutes, and 1% skin bath treatment f! In the steels of samples 1 to 4 treated within the conditions of the present invention, all B
It has excellent properties with H (bake hardening fjk) of 5 KPf/m" or more, and after being held at 30C for one month, the Y and E (yield point elongation) values, which are indicators of moss stretcher strain, are low and show slow aging. On the other hand, the steel of sample 5 has a high coiling temperature, the steel of sample 6 has a high MnS content, the steel of sample 7 has a high red content, and the steel of sample 8 has a high coiling temperature. Because the temperature is high, the BH (bake hardening) is low in all of them.The steel of sample 9 has a high N content, so the Y and E (yield point elongation) values are high.

(Effects of the Invention) As described above, according to the present invention, by adjusting the components of the steel and controlling the hot rolling temperature, hot rolling coiling temperature, and annealing temperature, a slow aging process with excellent bake hardenability is achieved. A steel plate for light processing with high strength can be obtained, and the effect is extremely large.

Claims (1)

[Claims] 1. Steel with 0.02%≦C≦0.12%, Mn, Al,
The content of S, O, and N is 7×S(%)≦Mn≦0.25%, and S≦0.020% [(27×2)/(16×3)]×O(%)≦Al ≦［
(27×2)/16×3]×O(%)+0.03% and 0.002%≦N≦0.006% Steel was heated at a slab heating temperature of 11
Hot rolling at 00°C or higher, then hot rolling winding temperature 300°C
The steel sheet is coiled at ~600°C, then cold rolled, and the obtained cold rolled steel sheet is continuously annealed at a soaking temperature of not less than the recrystallization temperature and not more than 750°C, and for a soaking time of 1 minute or less. A method for producing a light working steel plate that has bake hardenability and slow aging properties.