JPS5941803B2 - Cold rolling method for thin steel strip for drawing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tandem mill cold rolling method for producing a thin steel strip with good processability.

Conventionally, the cold rolling method using tandem mills for thin steel sheets has no special restrictions, and the total rolling reduction rate is determined mainly from the product thickness, and the total rolling reduction rate is determined at each stand based on the capacity of the tandem cold rolling mill and the stability of operation. The distribution and rolling schedule (rolling reduction rate, rolling speed, tension) is determined.

For example, in the example of rolling reduction distribution in tandem mills on page 916 of the Steel Handbook (4th edition), when the total rolling reduction is 81 to 90%, the first stand is 19 to 34%, and the second stand is 41 to 47%.
, 3rd stand 38-45%, 4th stand 33-42
%, 5th stand 17-23%.

In general, a distribution method in which the rolling reduction ratio of the first stand is small, the rolling reduction ratio of the second stand and subsequent stands is very high, and the rolling reduction ratio of the final stand is small is preferred from the viewpoint of operational stability and is practiced.

The present inventors have conducted extensive research on the effects of rolling schedules such as rolling reduction, rolling speed, and tension distribution at each stand in a cold rolling method, that is, a tandem mill, on the material quality of thin steel sheets.

As a result, we have invented a rolling force method that dramatically improves the r-value and workability represented by elongation of thin steel sheets when the same material and total rolling reduction are used.

The present invention will be explained in detail below. The present invention is based on JIS G3141,
G3302 To provide good workability when manufacturing a thin steel sheet specified by G3303 and G3314 by rolling it with a tandem cold rolling mill at a plate thickness reduction rate before and after cold rolling, that is, a total reduction rate of less than 70 to 85%. It is a cold rolling method of 35% or more in the first stand of a tandem mill, or in the first and second stands of a tandem mill.
It is characterized by rolling at an average rolling reduction of 40% or more on the stand.

The purpose of the present invention is to manufacture a rolled steel sheet with excellent deep drawability.

Therefore, in order to form a recrystallized texture with good deep drawability, the total reduction ratio in cold rolling is specified to be 70% or more.

However, if the total reduction ratio is too large, it becomes difficult to obtain deep drawability, so the upper limit is set to less than 85%.

Next, the rolling reduction ratio for each pass, which is the most important in the present invention, will be explained.

A hot-rolled coil of low-carbon Al-killed steel manufactured in a normal process was annealed by changing the rolling reduction ratios of the first stand and the second stand in the cold rolling process (the mechanical properties thereof were investigated).

As shown in Figure 1, there is a good correlation between the rolling reduction rate of the No. 1 stand and the workability of thin steel sheets, and when the reduction rate exceeds 30%, the elongation of the thin steel sheet increases rapidly, and the Lankford value also improves. The properties become better.

The distribution of the rolling reduction after the second stand in Figure 1 is as shown in Table 1. When the rolling reduction at the first stand is 15 to 30%, the number of cold rolling passes is 5, and the number of cold rolling passes is 5. ,4. , 5
The rolling reduction ratio of the No. stand is 40-43% and 24-26%, respectively.
, 14-25%, and 11%.

If the reduction rate at the No. 1 stand is 35 to 45%,
The number of cold rolling passes was 4, and the rolling reduction ratios of the No. 2 and 3° No. 4 stands were 37 to 42%, 22 to 28%, and 11%.

Moreover, when the rolling reduction of the No. 1 stand was 50 to 60%, cold rolling was performed in three passes, and the rolling reduction of the No. 2 and 3 stands was 32 to 46% and 11%, respectively.

Therefore, the rolling reduction ratio of the No. 1 stand is specified as 35% or more, which is a significant difference in the improvement in workability.

The higher the rolling reduction rate (the better the material quality), so no upper limit is specified.

In addition, as shown in Figure 2, there is a good correlation between the average reduction ratio of the No. 1 and No. 2 stands and the workability of thin steel sheets, and workability improves rapidly when the average reduction ratio is 35% or more. do.

Table 2 shows the rolling reduction ratio distribution of each stand shown in FIG.

Therefore, 40% improvement in workability was recognized with a significant difference.
Let be the lower limit of the average rolling reduction of the No. 1 stand and the No. 2 stand.

The higher the average rolling reduction rate, the better the quality of the material, so the upper limit is not particularly defined.

Workability is further improved when the rolling reduction of the No. 1 stand is 35% or more and the average rolling reduction of the No. 1 and No. 2 stands exceeds 40%.

Note that the upper limit of the rolling reduction rate does not need to be specified based on the material, but the upper limit of the rolling reduction rate is determined by whether or not the plate fits into the rolls well.

The upper limit of the rolling reduction rate is not specified because the limit of biting varies depending on the cold rolling equipment and conditions.

Next, I will provide a supplementary explanation of the rolling reduction ratio distribution from the third stand onward.

The reduction rate at the final stand of cold rolling is determined by controlling the shape of the steel plate,
For hexagonal transfer, it is necessary to distribute the amount around 10 to 20%.

Therefore, in a conventional cold rolling mill consisting of 4 or 5 stands, if high pressure distribution is performed in stands No. 1 and No. 2,
After that, the rolling reduction rate of the intermediate stand will inevitably fall within the conventional distribution range.

Therefore, the rolling reduction ratio distribution from the third stand onwards may be the same as before.

This cold rolling method is JIS G3141.3302゜33
As long as it is a thin steel sheet specified by 03 and 3314, it is applicable without being restricted by its history up to the cold rolling process or by the method and conditions of annealing the cold rolled layer.

Further, the effects of the method of the present invention are not significantly affected by other conditions of cold rolling, such as rolling speed, rolling temperature, roll diameter, rolling tension, etc.

However, under these conditions, when the strain rate parameters of rolling such as the rolling speed are changed in the direction of increasing the strain rate, an effect similar to the effect of the method of the present invention is observed, albeit slightly.

Next, embodiments of the invention will be described.

Ladle component C: 0.035%, Si: 0.02%.

Mn: 0.21%, P: 0.013%, S: 0.016
%, Al: 0.045%, N: 0.0025% into a slab by continuous casting, and by hot rolling it
Manufactured hot-rolled coils.

In this case, the heating temperature of the slab was 1200°C, the hot rolling finishing temperature was 890-910°C, and the winding temperature was 620-650°C.

After pickling, this hot-rolled coil was unidirectionally rolled using a lindem mill and a reversing mill to achieve a total reduction of 80% under the conditions shown in Table 3.
, cold rolled to a plate thickness of 0.8 mrn.

The cold rolling symbols ■ and ■ indicate the case where the rolling reduction distribution is 50% or more in the first stand, and the cold rolling symbol ■ indicates the case where the average rolling reduction distribution between the first stand and the second stand is 45%. .

The cold rolled coil is box annealed and continuous annealed to 1.0
It was temper rolled at a rolling reduction of %.

The mechanical properties of the resulting product are shown in Figure 4. As is clear from the results in Table 2, the cold rolling method of the present invention (cold rolling condition I
, II, III) are cold-rolled using conventional rolling reduction distribution (cold-rolling condition ■).
Regardless of the annealing method, it is softer and has better deep drawability and stretchability than those manufactured by.

The effect of the method of the present invention, which can be called large reduction/pass rolling, generally becomes more pronounced as the rolling reduction rate for each pass is larger in the early stage of rolling, and as the large reduction/pass conditions are continued until the final pass of rolling. .

[Brief explanation of the drawings] Figure 1 shows capped steel manufactured by the usual method up to hot rolling, then cold rolled by the tandem mill method (rolling in the same direction).
007CX is a graph showing changes in material properties when the rolling reduction ratio of the No. 1 cold rolling stand (first pass) is varied when a product is produced by continuous annealing of 1 minute + 350° C. x 5 minutes. Figure 2 shows the process of cold rolling when aluminum quilt steel is manufactured by the usual method up to hot rolling and the hot rolling winding temperature is 700°C, and is cold rolled using a tandem mill method and then subjected to normal box annealing to produce a product. This is a graph showing changes in material properties when the average rolling reduction ratio of each stand No. 1 (first pass) and No. 2 stand (second pass) is varied.

Claims (1)

[Claims] 1. When cold rolling a copper strip with a tandem mill in a range where the total reduction rate, which is the plate thickness reduction rate before and after cold rolling, is in the range of 70% or more and less than 85%, the first Cold rolling of thin steel strip for drawing characterized by rolling at a rolling reduction of 35% or more in stand No. 2, or at an average rolling reduction of 40% or more in stands No. 1 and 2 in stand No. 2 and stand No. 2. Rolling force method.