JPS5947011B2 - Manufacturing method of cold-rolled steel sheet for drawing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing cold-rolled steel sheets with excellent drawability with high productivity.

In general, the value of γ (in-plane average value of Lankford value) of cold rolled steel sheet decreases rapidly when the cold rolling reduction exceeds 70%.
It is known that drawability deteriorates.

On the other hand, if the cold rolling reduction ratio is increased, it is expected that the manufacturing capacity of cold rolled steel sheets will be significantly improved by increasing the thickness of the steel sheet in the hot rolling and pickling processes without causing a decrease in the rolling capacity in the cold rolling process.

Therefore, there has been a strong desire to develop a method for producing cold-rolled steel sheets for drawing having an excellent r value at a high cold rolling reduction.

The reason why the 〒 value decreases when the cold rolling reduction exceeds 70 factors is that when the cold rolling reduction exceeds 70 factors, the metastable (411) orientation (iron crystals parallel to the steel sheet surface) It is thought that this is because cold force meter energy is accumulated in crystal grains with (411) orientation, and the number of crystal grains with (411) orientation rapidly increases in the subsequent annealing process.

Conventionally, no method has been found to prevent the concentration of cold working energy on crystal grains with the (411) orientation, which occurs due to an increase in cold rolling reduction, without impairing productivity.

In addition, when the cold rolling reduction rate is increased, edge cracks occur at the edges of the steel sheet, and the quality of the cold rolled steel sheet deteriorates, which has also been an obstacle to increasing the cold rolling reduction rate.

Another disadvantage is that increasing the cold rolling reduction increases the power consumption of the rolling mill.

Therefore, until now, cold rolled steel sheets have been manufactured avoiding high cold rolling reduction rates.

In contrast, the present invention aims to produce a cold rolled steel sheet of excellent quality by using a high cold rolling reduction, that is, by increasing the productivity in the hot rolling and pickling steps.

The present invention will be described in detail below.

In this invention, the chemical components C and Mn of the steel sheet material must be contained in the ranges of 2.10% CS and 2.35% MnS, respectively.

When the amounts of C and Mn are contained in excess of the above ranges, it is not easy to stably obtain a cold rolled steel sheet with good drawability.

That is, it is desirable that the C and Mn contents are in the range of 2.05% CS and 2.25% MnS so that a product with good drawing properties can be obtained.

Within this range, a cold-rolled steel sheet with a high value can be obtained.

FIG. 1 shows an example of a cold rolling facility for carrying out the method of the present invention.The outline of the rolling process will be explained according to this drawing.A pickled hot rolled steel sheet 11 unwound from an unwinding machine 1 is shown in FIG. Primary cold rolling is performed by a rolling mill 2, for example a Sendzimer mill.

The rolled strip 12 is intermediately heated by a heating device 3, and then subjected to secondary cold rolling by a continuous cold rolling mill train 4 to a desired thickness.

The rolled strip 14 is wound up by a winder 5.

To explain the above-mentioned rolling process in more detail for each step, first, the rolling reduction ratio of the primary cold rolling by the rolling mill 2 must be 30 to 50%.

If the rolling reduction ratio is less than 30 coefficients, the deformation of the steel sheet during the primary cold rolling is small, so that the effect of improving the 7 value by the intermediate heating is not sufficient.

On the other hand, if the rolling reduction ratio exceeds 50%, the deformation of the steel sheet during the primary cold rolling will be so large that the harmful (411) orientation can no longer be removed by intermediate heating, which is inappropriate.

Regarding the number of passes, it is preferable to reduce the number of passes in primary cold rolling and to increase the rolling reduction ratio of the passes.

In order to maintain good surface quality, cold rolled steel sheets are pickled prior to cold rolling.

The strip temperature after passing through the pickling process is usually 100°C or less.

The intermediate heating temperature of the primary cold-rolled strip 12 is 200
It must be maintained at a temperature of 650°C or higher for a period of time that does not cause recrystallization.

If the intermediate heating temperature is less than 200° C., a desired lower value cannot be obtained depending on the magnitude of the total rolling reduction (rolling reduction through primary and secondary cold rolling).

FIG. 2 is a graph showing an example of the relationship between intermediate heating temperature and average r value.

According to the same figure, it can be seen that when the total rolling reduction ratio is 90 parts, the intermediate heating temperature must be 200° C. or higher in order for the lower value to be 1.0 or higher.

In addition, as mentioned above, during cold rolling by intermediate heating (4
11) Cold working energy concentrated in an oriented crystal flow is dispersed, but if recrystallization occurs during intermediate heating, the texture changes and the energy dispersion effect becomes meaningless.

FIG. 3 shows a graph showing an example of the relationship between recrystallization time and recrystallization temperature.

If the intermediate heating time is not in the lower range of the curve in the same graph, the above-mentioned recrystallization will occur.

Note that when the intermediate heating temperature is set to 300° C. or higher, the margin for improving the lower value becomes significantly large.

The holding time for intermediate heating varies depending on the heating temperature, but for example, in the range of 300° to 500°C, the holding time is 2 seconds or more (preferably 1
0 seconds or more), a 7-value improvement effect occurs.

In order to prevent edge cracking and save power, secondary cold rolling after intermediate heating is performed at a temperature of 200° to 4, which reduces the resistance to change of the strip.
It is desirable to carry out the process at a temperature of 00°C or 600°C or higher.

Further, the intermediate heating temperature needs to be 650°C or less.

The reason for this is, as shown in FIG. 3, that if the temperature exceeds 650° C., the recrystallization time, which is the upper limit of the intermediate heating time, becomes shorter, making it difficult to perform stable intermediate heating treatment.

The rolling reduction ratio of the secondary cold rolling by the continuous cold rolling mill row 4 is preferably such that the total rolling reduction ratio of the primary and secondary cold rolling is 70 parts or more, preferably 80 to 98 parts.

This is because, in order to increase the thickness of the hot-rolled steel sheet and reduce the total cost of manufacturing the steel sheet, a total reduction ratio of the above level is required.

In the conventional manufacturing method, when the total rolling reduction exceeds 70%, as mentioned above, a decrease in the bottom value and occurrence of edge cracking occur, resulting in a decrease in quality.

However, in the present invention, such a problem is solved by intermediate heating, and even if the total rolling reduction ratio is 90 factors, the above-mentioned quality deterioration does not occur.

The secondary cold-rolled IJ tube normalizes its structure,
Annealing is performed to remove processing strain, and the annealing may be continuous annealing or box annealing.

When continuous annealing is performed, it may be performed on the same line as a continuous rolling mill.

Next, embodiments of this invention will be described.

C: 0.041% and Mn: 0.04% melted in a converter.
Rimmed steel ingots containing 22% (referred to as steel ingots A) and C:
Rimmed steel ingot containing 0.065 and Mn: 0.32% (
After blooming, a steel ingot (referred to as steel ingot B) was hot-rolled to a thickness of 10 mm and wound at a temperature of 550°C.

The hot-rolled steel sheets were cold-rolled by the method of the present invention, comparative methods A-G, and conventional method Z as shown in Table 1 to produce strips having a thickness of law (i.e., total reduction ratio of 90 factors). .

Table 1 shows the occurrence of edge cracking at this time and the motor power ratio of the secondary cold rolling mill (the conventional method is set to 1.00).

Furthermore, after box annealing the manufactured strip for 4 hours at 700°C and temper rolling at 1%, the average r
The values were measured and the results are also shown in Table 1.

According to the results in Table 1, edge cracking occurred in the conventional method Z, but with the method of this invention, except for D, which slightly occurred.
No ear cracking occurred at all.

The average value obtained by the method of the present invention is significantly improved compared to that obtained by the conventional method.

Further, in the case of this invention, the rolling mill motor power is reduced by a maximum of about 20 factors compared to the conventional method.

As is clear from the above detailed explanation, according to the present invention, it is possible to manufacture high-quality strip with high drawability and no edge cracks with high productivity at a high reduction rate exceeding 70%. , and the power consumption in the secondary cold rolling mill can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing an example of rolling equipment for carrying out the method of the present invention, Fig. 2 is a graph showing the relationship between intermediate heating temperature and average r value, and Fig. 3 is a graph showing the relationship between recrystallization time and recrystallization temperature. This is a graph showing the relationship between 1: Unwinding machine, 2nd primary cold rolling machine, 3: Heating device, 4:
Secondary cold rolling mill row, 5: Winding machine, 11: Hot rolled steel plate, 12
~14 strips.

Claims (1)

[Claims] IC: A hot rolled steel sheet containing 0.1% or less and Mn 0.35% or less is subjected to primary cold rolling at a reduction ratio of 30 to 50%, and then heated to a temperature of 200°C or more and 650°C or less for a period of time during which recrystallization does not occur. 2. A method for manufacturing a cold-rolled steel sheet for drawing, characterized in that the steel sheet is held and subsequently subjected to secondary cold rolling and annealed so that the total reduction ratio of the primary and secondary cold rolling becomes 70 coefficients or more.