JPS61238919A - Manufacture of cold rolled deep drawing steel sheet having low anisotropy in plane - Google Patents

Abstract

PURPOSE:To manufacture the titled steel sheet without causing ear during deep drawing, by applying hot rolling, pickling, cold rolling to Al killed steel plate under specified conditions, and recrystallization annealing and overage treating the sheet in continuous annealing furnace. CONSTITUTION:A slab of Al killed steel contg. by weight %, 0.015-0.07% C, 0.05-0.50% Mn, 0.015-0.050% Al, <=0.0050% N is heated, soaked at <=1,150 deg.C, then hot rolled to plate under condition of finishing temp. of <=Ar3 point and it is wound at <=600 deg.C. Next, the plate is pickled to remove scale, the surface is neutralized, washed, cleaned, then cold rolled to the final thickness. The sheet is recrystallization annealed and overaging treated in continuous annealing furnace, to manufacture cold rolled steel sheet for deep drawing having low anisotropy in plane and without causing ear during deep drawing.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) What is described in this specification in relation to a method for manufacturing a cold-rolled steel sheet for drawing is, for example, when drawing a circular blank into a cylindrical or conical shape. This is the result of research and development into improving in-plane anisotropy, which should suppress the formation of localized protrusions, or so-called earings, on the edges of products within a practically acceptable limit.

(Prior art) Although no comprehensive explanatory literature has been found regarding the production of steel plates that do not produce selvages during drawing, in the past, rimmed steel was generally used as a material, and after heating and soaking to 1200°C or higher, the finishing temperature was A.
As an example, a method is used in which hot rolling is carried out to a temperature higher than the rs point, cold rolling is carried out at a comparatively small rolling ratio after pickling, and then box annealing is carried out. However, this method: ■ Because it is necessary to control the cold reduction rate to a small level,
The finishing thickness during hot rolling must be made thinner, and as a result, the hot finishing temperature often undesirably falls below the Arx point at the extreme end in the width direction or at the rear end during rolling, resulting in anisotropic There was a tendency for sex to increase.

■ In the case of box annealing, there was a problem with the temperature distribution inside the coil, making it difficult to reduce variations in anisotropy.

■ Since it is rimmed steel, there is a problem with non-metallic inclusions.
There was a risk of inducing cracks during pressing.

There were other problems.

(Problems to be Solved by the Invention) The difficulties associated with the manufacturing process of conventional cold-rolled steel sheets for drawing using rimmed steel as described above are advantageously overcome, and the in-plane anisotropy is small and the in-plane anisotropy is small. It is an object of the present invention to establish a method for stably manufacturing cold rolled steel sheets with good drawability.

(Means for solving the problem) This invention is made by Coo. 015-0.07% by weight, Mn:
0.05-0.50% by weight, SOI, AJ: 0
．． 015-0.050% by weight and N: 0.005
A steel containing 0% by weight or less, with the remainder substantially consisting of iron and unavoidable impurities, is heated to 1150°C or less, soaked, and hot rolled under conditions that result in a finishing temperature of Ar 3 or less, and then heated to 600°C. After winding with the following methods, pickling and cold pressing are carried out according to conventional methods, followed by recrystallization annealing and overaging treatment in a continuous annealing furnace. This is a method for manufacturing a rolled steel plate.

By the way, the above-mentioned problem of non-metallic inclusions in rimmed steel is solved by using Al quilt steel as the material. AI
Box-annealed materials of l-killed steel are manufactured for deep drawing, but materials that have deep drawability generally tend to have large in-plane anisotropy.

In order to improve the in-plane anisotropy here, although it is advantageous to set the finishing temperature during hot rolling to below the Ar= point and perform box annealing by controlling the cold rolling reduction rate to be high after pickling, Although this method can reduce anisotropy deterioration at the extreme end in the width direction and at the rear end during rolling, it is unavoidable that Eβ, which is important for drawability, decreases, and the anisotropy during box annealing cannot be avoided. Variations also cannot be reduced.

In order to solve this problem, the inventors conducted various experiments, and after setting the slab heating temperature to 1,150°C or lower and the finishing temperature during hot rolling to 3 points or less of Ar, the rolling reduction rate was controlled to be high and cold rolling was carried out. They found that by continuous annealing after rolling, it is possible to produce a steel plate with small in-plane anisotropy, little variation, and good El properties.

(for production) The gist of this invention is to use A1 killed steel. (1) In-plane anisotropy is small and its variation is small.

(2) Has good drawability.

The goal is to stably manufacture steel sheets that have both of these characteristics.

First, we will discuss in-plane anisotropy and its variation.

Figure 1 shows the anisotropy of the annealing furnace by heating a slab with the components shown in Table 1 to 1250°C and rolling it at several levels of finishing temperature and cold rolling reduction during hot rolling. This is a comparison of continuously annealed materials. The annealing conditions are shown in Figure 1, and the Ar content tends to decrease as the finishing temperature decreases for both box-annealed and continuous annealed materials. Continuously annealed material has a finishing temperature of A.
While Ar becomes almost O at the r3 point or below, there is a large variation in the box annealed material.

In addition, in the case of continuously annealed materials, even if the cold rolling reduction rate changes, the hot rolling finishing temperature is Ar, and if it is below the Ar point, the Ar is almost O, whereas in the case of the box annealed material, even if the cold rolling temperature is below the Ar point, the Ar is almost O. There is a significant variation in the finishing temperature at which Δr=0 depending on the rolling reduction rate.

Variations in box annealed materials are due to recovery and recrystallization during the heating process and AβN.
It is presumed that this is because the timing of precipitation differs within the coil, and the degree of integration of the (100) orientation, which provides good anisotropy, varies within the coil, but the difference in cold reduction rate dependence is unknown.

Low dependence on cold rolling reduction is extremely advantageous in manufacturing products, and the in-plane anisotropy does not change even if the finishing temperature and hot-rolling finish thickness are the same and the cold-rolling finish thickness is changed. and allows material integration. In the case of continuously annealed materials, if the hot rolling finishing temperature is controlled below the Ars point, the cold rolling reduction can be brought to a range of 60 to 80 (χ), but
This is not possible for box annealed materials.

Therefore, considering the above-mentioned variation differences, it is necessary to apply continuous annealing.

If the hot rolling finishing temperature is controlled to be below the Ar3 point, the in-plane anisotropy will be good, but as mentioned above, El, which is important for drawability, will decrease. The inventors have discovered the usefulness of controlling the slab heating temperature as a method to solve this problem.

FIG. 2 shows the results of an investigation of the material properties after continuous annealing using steel having the composition shown in Table 1 above and following the same procedure as already described except for changing the slab heating temperature.

As is clear from FIG. 2, Ar hardly changes even when the slab heating temperature decreases, but EN rapidly increases when the temperature drops below 1150°C. In the figure, the ★ mark indicates data under the general conditions for manufacturing deep drawing steel sheets by continuous annealing, that is, when the finishing temperature is Ar1 point or higher and the coiling temperature is high, but the slab heating temperature is 1150 ° C. Below,
Even if the finishing temperature is below Ar and the winding temperature is low, there is no significant difference in the results.

Therefore, it is necessary to set the slab heating temperature to 1150°C or lower and the winding temperature to 600°C or lower.

Next, the reason for limiting the ingredients will be explained. ([%] is weight%) C: The lower C is, the more advantageous it is to drawability and ductility, but 0.0
If it is less than 15 (%), it will increase the cost during steel manufacturing, so it is 0.
．． 015 (%) was set as the lower limit.

Moreover, if it exceeds 0.07 C%, the workability deteriorates significantly, so the upper limit was set at 0.07 C%.

Mn: If it exceeds 0.50 C%, there will be problems with deterioration of workability and temper color, and if it is less than 0.05 [%], there is a risk of brittle cracking during hot rolling due to S, so the upper limit is set. was set at 0.50 C%], and the lower limit was set at 0.05 [%].

^1: Al combines with N to improve aging properties and drawability, but if it exceeds 0.050 C%, the amount of AIN precipitation increases, hindering grain growth during annealing, and causing material deterioration ( Moreover, if it is less than 0.015 (%), deoxidation will be insufficient and the problem of inclusions will occur.Therefore, the upper limit was set to 0.050 C%] and the lower limit was set to 0.015 C%].

If NUN is included in a large amount, it will cause material deterioration, so 0.00
50 C%] was set as the upper limit.

(Example) Example 1 After melting tli (A) to (K) shown in Table 2, a predetermined slab was manufactured by continuous casting. Thereafter, hot rolling was performed under the conditions shown in the same table, and after pickling under normal conditions, the sheet was finished to a thickness of 0.80 (in) at the rolling reduction ratio shown in the same table. After that, continuous annealing was performed under the conditions shown in Figure 1, and the rolling reduction was 0.8%.
Temper rolling was performed.

All compatible examples are YS: 19-23 (kgf/n
un”:l, TS:30~33 (kgf/mm”)
, EIl: showed a good value of 42 to 46 [%],
Δr is also almost 0.

Example 2 A blank with a diameter of 90 mm was prepared from a cold-rolled steel plate finished to a thickness of 1.5 mm according to the adaptation example of Example 1, and cylindrical drawing was performed under the conditions of a punch diameter of 50 mm and a drawing ratio of 1.8. The occurrence of selvage is compared with the case where rimmed steel is hot rolled according to the conventional technology at a soaking temperature of 1250°C and a finishing temperature of 1 point Ar or higher, cold rolled at a relatively low temperature, and then box annealed at 685°C for 8 hours. and is shown in Figure 3.

The Ea rate taken on the vertical axis of the figure is the average peak height at four points on the circumference of the cup after squeezing, H1l1mK+the average valley height as well.■1. ．． As, we used the evaluation using the value given by .

From these results, it is clear that in the cold rolled steel sheet obtained by the present invention, the occurrence of selvage during drawing is stably and significantly reduced.

(Effect of the invention) A cold-rolled steel sheet for drawing that has small in-plane anisotropy, little variation, and benign drawability can be produced stably using a heating furnace raw material under low-temperature heating of baka-slab. It has the added benefit of reducing costs by reducing the number of units and improving pickling efficiency after low-temperature winding.

[Brief explanation of drawings]

FIG. 1 is a graph comparing the relationship between hot rolling finishing temperature and Δr, FIG. 2 is a graph comparing the relationship between slab heating temperature, Δr, and El, and FIG. 3 is a graph comparing Ea ratio.

Claims (1)

[Claims] 1. C: 0.015-0.07% by weight, Mn: 0.05-0.50% by weight, Sol. Al: 0.015-0.050% by weight and N
: A steel containing 0.0050% by weight or less, with the remainder substantially consisting of iron and unavoidable impurities, is heated to 1150°C or less, soaked, and hot-rolled under conditions that result in a finishing temperature of Ar_3 points or less, Subsequently, the material is rolled up at 600°C or less, and then pickled and cold-pressed in accordance with conventional methods, followed by recrystallization annealing and overaging treatment in a continuous annealing furnace, which results in low in-plane anisotropy. A method for producing cold-rolled steel sheets for drawing.