JPS605362B2 - Temper rolling method for cold rolled steel strip - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for preventing fluctuations in skin pass efficiency due to changes (decrease) in ambient temperature, for example, during skin pass rolling of a cold rolled steel strip of ferritic stainless steel through a skin pass mill. The present invention relates to a skin pass rolling method that avoids (decrease) and improves the elongation rate in the skin fly process.

Cold-rolled steel strips, particularly cold-rolled steel strips of ferritic stainless steel, need to be passed through a skin pass mill and rolled at an elongation rate of about 1% in order to prevent yield point elongation during processing.

However, in this skin pass process, it has been found that when the ambient temperature drops, especially in winter, the yield strength of the rolled material increases and the elongation rate per pass decreases. Therefore, in order to obtain the required elongation rate, the number of passes must necessarily be increased, and the skin pass efficiency is inevitably reduced significantly. The purpose of the present invention is to prevent fluctuations (decrease) in skin pass efficiency due to changes (decrease) in ambient temperature. To improve skin pass efficiency by keeping it at the same or higher level. Ru.

To this end, the present invention provides a method in which the rolled steel strip is passed through a skin pass mill, and the temperature of the steel strip during passing through the skin pass mill is maintained at a certain temperature in the range of 30 to 70 oo. To provide a method for skin pass rolling of a cold rolled steel strip, which is characterized by heating the rolled steel strip in a coiled state to 30 to 70 mm before passing it through the skin pass mill. It is something. In order to uniformly heat a cold-rolled steel strip in a coiled state, it is preferable to insert a coil 1 of the cold-rolled steel strip into a flooded house 2 as shown in FIG. Warm air is used as heating means for the heating house 2. For example, warm air obtained by passing through a steam pipe heat exchanger (not shown) is guided into the heating house 2 by a fan 3. Make it. Figure 2 shows the results of one example of scorching heat heating of this coil, and shows the temperature change of the coil when the coil is inserted into the heating house 2 and warm air of about 80°C is introduced into the heating house 2. It shows. As is clear from Fig. 2, in carrying out the present invention, the blowing of hot air is stopped after a predetermined period of time after the temperature of the inner coil side and the outer coil side reach a certain temperature range. (Point A in Figure 2), instead of lowering the temperature inside the heating house 2, the temperature rise in the center of the coil due to the diffusion of the heat retained in the coil is waited until the temperature of the entire coil is equalized (point 2). It is best to take the coil out of the heating house at point B in the figure and immediately set it in a skin pass mill to perform skin pass rolling.This will ensure that the temperature remains at 30°C over the entire length of the steel strip that is unwound from the coil.
The sheet is passed through a skin pass mill and temper rolled while being maintained at a certain temperature in the temperature range of ~70q○. Third
The figure shows the results of an investigation to find out the causes of fluctuations in work efficiency in the skin pass process for cold-rolled steel strips, particularly the decline in work efficiency during winter, and the yield strength of the rolled material was identified as a significant factor. This figure shows the relationship between material temperature and yield strength of cold-rolled ferritic stainless steel strip.

According to FIG. 3, it can be seen that the yield strength increases as the material temperature decreases. Since the deformation resistance of the material to be rolled during skin pass rolling is proportional to the yield strength, the lower the material temperature and the higher the yield strength, the worse the skin pass rolling properties. Normally, in the skin pass process, in addition to preventing yield point elongation during processing, the work roll of the skin pass mill is designed to prevent stretcher strain (ferritic stainless steel), increase surface gloss, and correct shape. Since a relatively large one is used, the growth rate per pass is limited. In particular, as the material temperature decreases and the yield strength increases (as the deformation resistance of the material increases), the elongation rate per pass decreases, so in order to obtain the required elongation rate (usually around 1%), it is necessary to The number of passes will have to be increased. Therefore, the skin pass efficiency will be reduced. FIG. 4 shows the effect of the present invention in comparison with a conventional example when a skin pass is applied to a cold-rolled ferritic stainless steel strip.

The heating coil (marked with an x) in Figure 4 is a coil made of cold-rolled steel strip whose material temperature is 10 degrees Celsius or less during the period when the ambient temperature is 10 degrees Celsius or less (winter). and heated, and taken out from heating house 2 at point B in Figure 2.
The coil, which had been uniformly heated to 40°C, was immediately set in a skin pass mill, and the skin pass process was carried out.

In addition, in the winter period (marked 0) in Figure 4, the coil whose material temperature was 10 qo or less in the winter season was set in the skin pass mill as it was and the skin pass process was carried out, and in the summer period (△ mark), the material temperature was lower than 10 qo in the summer season. Temperature is 20-30qo
The coil, which has a relatively high height, was directly set in the skin pass mill and the skin pass process was performed.
From FIG. 4, it can be seen that when using the method of the present invention, the average number of passes per coil (P
/C) was significantly reduced for all plate thicknesses, and the skin pass efficiency (T/H) was greatly improved, and the work efficiency was improved to the same level or higher than the conventional level in summer (△ mark). I understand that.

This also shows that if the temperature of the steel strip passed through the skin pass mill is at least 30:00 or higher, the work efficiency will be improved compared to the summer level. Therefore, in carrying out the present invention, the cold rolled steel strip is coiled before passing through the skin pass mill so that the temperature of the cold rolled steel strip passing through the skin pass mill is a certain temperature of 30 qo or more. It is important to uniformly heat the product to 30 qo or more in advance.

Furthermore, as shown in Figures 1 and 2, the temperature at which the coil can be uniformly heated accurately and economically using the heating house 2, which can be easily and inexpensively constructed using a steam heating source, is 30. A range of ~70°C is suitable. At a low temperature of less than 30 qC, it is difficult to uniformly heat the entire coil accurately and stably.

Further, there is no need to heat it to a very high temperature, and heating to a temperature exceeding 70 qo does not produce any particular effect. For these reasons, in the method of the present invention, the cold-rolled steel strip is uniformly heated to a temperature of 30 to 7,000 degrees Celsius before passing it through the skin pass mill. Then, by setting the coil that has been uniformly heated to this temperature in a skin pass mill, the skin pass process is carried out in a state where the temperature is maintained at a certain temperature in the range of 30 to 70 oo. There is a concern about cooling during the time between taking it out of the heating house and setting it on the skin pass mill, but since the cooling rate is very slow when it is wrapped in a coil and the difference from the ambient temperature is not large, during this time There is no need to worry too much about cooling the steel strip, and if it is uniformly heated to 30 to 70 q0 in a heating house and set in the skin pass mill, the steel strip passing through the skin pass mill will have a temperature of 30 to 7000 q0 over its entire length. Able to maintain temperature. In this way, the present invention clarifies the cause of the decrease in work efficiency during the winter in the skin pass process, which has never been seen before, and also allows the cold rolled steel strip to be used as a coil in a heating house. 30~7000
This problem was solved by a process in which the cold-rolled steel strip was uniformly heated to a temperature of This eliminates fluctuations in work efficiency during the skin pass process and achieves economical rationalization of the skin pass process.

[Brief explanation of drawings]

Fig. 1 is a perspective view of the entire notch of a heating house suitable for carrying out the method of the present invention, Fig. 2 is a relational diagram showing the temperature change of the coil during operation of the heating house of Fig. 1, and Fig. 3 Figure 4 shows the relationship between yield strength and material temperature of cold-rolled ferritic stainless steel strip, and Figure 4 shows the effect of improving operability in the skin pass process when the method of the present invention is applied to cold-rolled ferritic stainless steel strip. FIG. 1...Cold rolled coil, 2...Heating house, 3
...Juan. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. When passing a cold rolled steel strip through a skin pass mill, the temperature of the steel strip being passed through the skin pass mill is maintained at a certain temperature in the range of 30 to 70°C. Before passing through this skin pass mill, the cold-rolled steel strip is pre-coiled at 30 to 7
A method for temper rolling a cold rolled steel strip, characterized by soaking and heating to 0°C. 2. The method according to claim 1, wherein the cold rolled steel strip is a cold rolled steel strip of ferritic stainless steel. 3. Heat the coil of cold-rolled steel strip to 30-70℃ in a hot air heating house.
The method according to claim 1 or 2, wherein the method is subjected to uniform heating.