JPS5849622B2 - Manufacturing method of cold-rolled steel sheet for ultra-deep drawing by continuous annealing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a cold-rolled steel sheet for ultra-deep drawing by continuous annealing.

In recent years, technology for manufacturing cold-rolled steel sheets for processing by continuous annealing has been put into practical use, and large-scale production is being carried out using actual equipment.

However, the most important technology in the current production of cold-rolled steel sheets by continuous annealing requires that the winding temperature after hot rolling be as high as 680° C. or higher, especially for cold-rolled steel sheets for drawing.

However, this high-temperature winding has several problems in addition to reduced pickling properties and deterioration of ductility due to lumpy carbides.

Therefore, as a method for manufacturing cold-rolled steel sheets with excellent drawability without high-temperature rolling by continuous annealing, for example,
A method described in Japanese Patent No. 29696 has been proposed.

According to the above-mentioned patent publication, a soft cold-rolled steel sheet can be produced by continuously annealing a steel obtained by adding boron (B) to AA killed steel even when rolled at a low temperature of about 650°C.

However, as stated in the above-mentioned patent publication, the addition of B lowers the r value of the product.

Therefore, the present inventors conducted various studies on the manufacturing method of ultra-deep drawing cold-rolled steel sheets using B-added steel, and found that the reason why the r value deteriorates due to the addition of B is due to the B precipitated by the reaction between B and C. This is due to the harmful effects of carbides. Therefore, if the C content is kept low, the B/N ratio is controlled within an appropriate range, and the hot rolling conditions are specified, the precipitation of B carbides can be suppressed, and even B-added steel can have a low r value. We have discovered that high-quality cold-rolled steel sheets can be manufactured by continuous annealing.

The present invention will be explained in detail below.

The steel of the present invention has c2o. Less than oi%, Mn: 0.40φ
Below, acid-soluble Al: 0.005 to 0.06, N:
0.0010 to 0.0060, B:B/N ratio is 0
．． 5 or more and 2.5 or less, with the remainder consisting of iron and inevitable impurities.

C is an important component in the present invention, and since B carbide that reacts with B and precipitates lowers the r value, in order to achieve the purpose of the present invention, the upper limit should be set to o. o Less than 1%.

C is reduced by vacuum degassing during the steelmaking process, but
Conventionally, O. It was not easy to reduce C to 6% or less.

However, with recent advances in technology, o. Although it is possible to easily reduce C to about 1%, the preferable range from the viewpoint of manufacturing cost is 0.004 to 0.007.

Mn is an element necessary to prevent brittle fracture induced by S during hot rolling, but a large amount of Mn reduces workability, so the upper limit is set at 0.40.

Although AA is an element necessary only for deoxidizing steel in the present invention, in order to perform stable deoxidation treatment and eliminate surface flaws on steel sheets, the amount of acid-soluble Al should be at least o. oo5% is required.

Another large amount of AJI? containing A6N due to the precipitation of BN.
The upper limit is set at 0.06, since the precipitation of B carbide takes precedence and the object of the present invention cannot be achieved.

Preferred acid-soluble Al! The range is 0.01-0.04%.

In addition to Al, Si is usually considered as a deoxidizing agent, but Si has a weak deoxidizing power, and when B is added, an oxide of B is formed, which deteriorates workability. Therefore, in the present invention, Si is used as a deoxidizing agent. Do not include it as an agent.

Too much N reduces workability, so it is added o. oo6o
% or less.

On the other hand, o. oo1o
The lower limit is %.

The weight percent ratio of B and N, B/N, is the most important component in the present invention, and if B/N is less than 0.5, precipitation of klN takes priority and the r value does not become high.

Moreover, when it exceeds 2.5, boride precipitates in ultra-low carbon steels such as those of the present invention, causing surface cracks during solidification and deteriorating the stretchability of the product.

Most preferably, B/N is in the range of 0.9 to 1.5.

Note that B is preferably added after the fi by kl has been sufficiently performed.

Since P, S, etc. mixed as unavoidable impurities deteriorate workability, it is preferable to reduce their content as much as possible.

Since Si is an element that deteriorates the surface characteristics of the steel sheet, the smaller the Si, the better the Si is set to 0.03φ or less.

Molten steel having the steel components as described above is made into a steel billet by ingot formation or continuous casting, and then hot rolled.

The finishing temperature during hot rolling is set to be higher than the Arg point in order to ensure high 7 value (deep drawability).

On the other hand, although there is no need to limit the upper limit due to the material, it is set to 960° C. or less in relation to the manufacturing process.

The winding temperature is set to 680° C. or lower because if it is too high, precipitation of B carbides becomes noticeable and the r value decreases.

The lower limit of the winding temperature does not need to be specified in terms of the material, but is set at 5000C due to the manufacturing process.

After pickling, the hot rolled coil is cold rolled, and the rolling reduction is set to 60% or more in order to obtain a high r value.

On the other hand, if the reduction wheel is too high, the r value will decrease, so the upper limit is set at 90%.

Continuous annealing is then performed at a temperature above the recrystallization temperature to ensure a high r value.

However, if the AC3 point is exceeded, the recrystallized texture becomes disordered (randomized) and the r value decreases, so the upper limit is set at the AC3 point.

Examples of the present invention will be described below.

Example 1 A steel billet was melted with the ingredients shown in Table 1 by continuous casting, and the plate thickness was 4.5 mm at the hot rolling temperature shown in Table 1. After hot rolling to Omrn, it is pickled and the plate thickness is 0. Cold rolled to 8 myn, then 70 myn
After soaking at 0° C. for 1 minute and at 850° C. for 1 minute, it was cooled in air and subjected to temper rolling at a rolling reduction of 0.8.

The mechanical properties of the steel sheet are shown in Table 2, and the cold rolled steel sheet obtained by the method of the present invention is extremely superior in deep drawability and stretchability compared to the cold rolled steel sheet of the comparative example.

The steel sheet according to the present invention exhibits extremely excellent elongation properties of 50 degrees or more even when annealed at a low temperature of 700° C. and without any over-aging treatment.

Furthermore, by increasing the annealing temperature, a cold-rolled steel sheet with extremely excellent deep drawability as well as stretchability can be obtained.

Example 2 C: 0.004-0.006%, Si: 0.01-0.
02%, Mn: 0. 1 2 ~0.23%, P<
0. 0 2%, skuo. o1s%, soAAl: 0
．． 015~0.025%, N:0.0018~
A large number of B-added ultra-low carbon steels with different B/Ns of 0.0036% were melted and heated to a plate thickness of 4.0 with a finish rolling temperature of 890°C to 910°C and a winding temperature of 600 to 660°C. After stretching, pickling and 0. Cold rolled to 8 mm thickness, then 700℃ x 1
After continuous annealing at 850°C for 1 minute, the rolling reduction was o. s % temper rolling was performed.

The mechanical properties of the steel plate were organized in terms of the relationship between the weight ratio B/N of the amount of B and the amount of N, and FIG. 1 was obtained.

From this figure, it can be seen that when the B/N ratio satisfies the condition of 0.5 or more and 2.5 or less, extremely excellent deep drawing workability and stretch workability are exhibited.

As shown in the above examples, the B-added ultra-low carbon AA killed steel sheet manufactured by the method of the present invention has extremely excellent drawability and stretchability, and it can be rolled at low temperature and subjected to over-aging treatment. The fact that cold-rolled steel sheets for ultra-deep drawing can be produced without drawing is extremely valuable industrially.

In addition, the cold-rolled steel sheet produced by the method of the present invention can be used as a material for surface-treated steel sheets that are plated with zinc, tin, aluminum, chromium, tin-lead alloy, etc., and has a surface treatment for deep drawing that provides excellent drawing stretchability. It is also possible to manufacture steel plates using a continuous annealing method.

[Brief explanation of drawings]

FIG. 1 is a chart showing the total elongation and Y value when B-added ultra-low carbon killed steels having various B/N ratios are continuously annealed.

Claims (1)

[Claims] 1 As a heavy rice cake, c:o. o Less than 1%, Mn: 0.4
0 or less, acid soluble 1? : 0.005~0.06, N2 0.0 0 1 0-0.0 0 6 0, B:
A steel billet with a B/N ratio of 0.5 or more and 2.5 or less and the balance consisting of iron and unavoidable impurities is heated at a finishing temperature of 3 Ar points or more and 960°C or less and a winding temperature of 500°C or more and 680°C or less. A method for producing a cold-rolled steel sheet for ultra-deep drawing by continuous annealing, characterized by performing inter-rolling, cold rolling at a reduction rate of 60 to 90, and then continuous annealing at a temperature between the recrystallization temperature and Ac3 points. .