JP2738281B2 - Hot rolling method of stainless steel slab - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for hot rolling a stainless steel slab which does not cause scale flaws during hot rolling and has excellent surface properties.

[0002]

2. Description of the Related Art In hot rolling of stainless steel, scale flaws are generated due to scale generated at the time of slab heating, and surface properties are remarkably deteriorated. Conventionally, various proposals have been made as measures for preventing scale flaws.

First, there is a measure for preventing scale flaws by considering that generation of scale is inevitable. Second, there is a measure for preventing scale flaws that suppresses the generation of scale itself. Among these preventive measures, one which is considered to be relatively effective in actual operation is disclosed in JP-A-61-1.
JP-A-11703, JP-A-62-13527 and JP-A-4-138803 can be mentioned. In any of these proposals, as a method of suppressing scale generation on the slab surface, the main point is to heat the slab in a relatively low temperature range for a short time.

[0004]

However, in the conventional method, the deformation resistance is increased by heating at a low temperature, and the rolling efficiency is reduced. Further, in the case of a thin material, the rolling temperature is lowered to cause ear cracks, and the manufacturable dimensions are limited. For this reason, it is difficult for the above-mentioned conventional technology to satisfy both of securing the productivity and improving the surface quality.

An object of the present invention is to provide a method for hot rolling a stainless steel slab which can improve descalability during hot rolling and can provide a product having excellent surface properties without scale flaws. I do.

[0006]

Means for Solving the Problems Conventionally, in the prevention of surface flaws of stainless steel, no study has been made from the viewpoint that no surface flaws will be generated if descale is performed completely even if scales are generated during slab heating. . Then, the inventors examined in detail the ease of descale and the properties of the scale.

As a result, it has been found that the descalability of the scale depends on the amount of metal contained in the Cr oxide layer formed on the surface layer of the slab, and that the amount depends on the temperature at which the scale is formed. In other words, the Cr oxide layer formed at a high temperature contains a mixture of metals, and therefore has good adhesion to metal and poor descalability, but the Cr oxide layer formed at a low temperature contains little metal and has a dense scale. Therefore, descalability is good.

[0008] In the hot rolling method for a stainless steel slab according to the present invention, the stainless steel slab is heated to 1000 ° C to 110 ° C.
The slab is soaked for 1 to 3 hours in a temperature range of 0 ° C., and the slab is soaked for 2 hours or more in a temperature range of 1150 to 1250 ° C., and then hot-rolled.

[0009]

In the hot rolling method for a stainless steel slab according to the present invention, first, a dense scale is formed on the slab surface in the first stage (low temperature stage) of slab heating. Since this scale does not contain metal, sufficient descaling property is secured to prevent surface flaws. After that, slab heating is performed for the purpose of ensuring rollability, but the resulting scale grows on the basis of scale with excellent descaling properties, so surface defects are prevented by descale work in the hot rolling process Shows sufficient descaling property.

That is, although it is well known that low-temperature / short-time heating is effective for preventing scale, the patentability of the present invention is that low-temperature heating is used as a scale material produced by slab heating performed to ensure rollability. It has been found that the fine scale layer generated by the above method may be used as a so-called protective film.

Next, the reason why the heating conditions in the first and second stages are limited will be described. In order to form a dense scale layer by heating at the first stage, if the temperature is lower than 1000 ° C., it takes a long time to generate the scale. , 1000-1100 ° C. Also,
The soaking time is 1 hour or more for the formation of the scale layer, and long-time heating causes a large loss in operation.
Limited to time.

As the final slab heating conditions, high-temperature heating is desirable from the viewpoint of rollability. However, if the temperature exceeds 1250 ° C., the reaction at the scale / metal interface proceeds, and a metal-mixed scale is newly formed. It was 1250 ° C. On the other hand, if the final slab heating temperature is lower than 1150 ° C., the additional element does not have a sufficient solid solution state required for the subsequent heat treatment, so the lower limit temperature was set to 1150 ° C.

The soaking time requires at least 2 hours in order to uniformly heat the slab. Incidentally, the hot rolling after slab heating in the present invention may be carried out in a normal operation, and does not require any special process.

[0014]

Hereinafter, various examples of the present invention will be described with reference to Table 1 in comparison with comparative examples. JIS standard S
Using three steel types of US304, SUS430 and SUS329J3L as test materials, the slab was heated under various heating conditions and then hot-rolled, and the occurrence of scale flaws at that time was examined. 100 slabs were rolled for each heating condition. After rolling, the slab was subjected to solution heat treatment, pickling, and the surface was visually observed. The results were evaluated and judged based on the scale flaw occurrence rate. Here, the “scale flaw occurrence rate” refers to an index expressing the number of scale flaws on the slab surface out of 100 pieces as a percentage (%).

Table 1 shows Examples 1 to 8 and Comparative Examples 1 to 7 as examples. Examples 1 to 8 correspond to the results of examining the slab surface which was hot-rolled under the conditions included in the method of the present invention. On the other hand, Comparative Examples 1 to 7 correspond to the results of examining the slab surface which was hot-rolled under conditions of the conventional method and conditions deviating from the conditions of the method of the present invention, respectively. Hereinafter, each condition and result will be described. Example 1 A SUS304 slab having a thickness of 300 mm was soaked in a soaking furnace at a temperature of about 1000 ° C. for about 1 hour. Further, it was kept in a soaking furnace at a temperature of about 1150 ° C. for about 5 hours. The inside of the soaking furnace is adjusted to a gas atmosphere containing oxygen gas (blast furnace gas is introduced into the furnace). Next, the slab was unloaded from the furnace, and was hot-rolled in a rolling line to finally obtain a 50 mm product.

When 100 slabs were examined, the scale flaw occurrence rate was 1%. Example 2 A SUS304 slab having a thickness of 300 mm was kept in a soaking furnace at a temperature of about 1000 ° C. for about 3 hours. Further, it was kept in a soaking furnace at a temperature of about 1250 ° C. for about 5 hours. Next, the slab was unloaded from the furnace, and was hot-rolled in a rolling line to finally obtain a 50 mm product.

Examination of 100 slabs revealed that the scale flaw occurrence rate was 3%. Example 3 A SUS304 slab having a thickness of 300 mm was soaked in a soaking furnace at a temperature of about 1050 ° C. for about 1 hour. Further, it was kept in a soaking furnace at a temperature of about 1150 ° C. for about 5 hours. Next, the slab was unloaded from the furnace, and was hot-rolled in a rolling line to finally obtain a 50 mm product.

When 100 slabs were examined, the scale flaw occurrence rate was 1%. Example 4 A SUS304 slab having a thickness of 300 mm was kept in a soaking furnace at a temperature of about 1050 ° C. for about 3 hours. Further, it was kept in a soaking furnace at a temperature of about 1250 ° C. for about 5 hours. Next, the slab was unloaded from the furnace, and was hot-rolled in a rolling line to finally obtain a 50 mm product.

When 100 slabs were examined, the scale flaw generation rate was 3%. Example 5 A SUS304 slab having a thickness of 300 mm was soaked in a soaking furnace at a temperature of about 1100 ° C. for about 1 hour. Further, this was kept in a soaking furnace at a temperature of about 1200 ° C. for about 5 hours. Next, the slab was unloaded from the furnace, and was hot-rolled in a rolling line to finally obtain a 50 mm product.

When 100 slabs were examined, the scale flaw occurrence rate was 2%. Example 6 A SUS304 slab having a thickness of 300 mm was soaked in a soaking furnace at a temperature of about 1100 ° C. for about 3 hours. Further, it was kept in a soaking furnace at a temperature of about 1250 ° C. for about 5 hours. Next, the slab was unloaded from the furnace, and was hot-rolled in a rolling line to finally obtain a 50 mm product.

Examination of 100 slabs revealed that the scale flaw occurrence rate was 4%. Example 7 A SUS430 slab having a thickness of 150 mm was kept in a soaking furnace at a temperature of about 1050 ° C. for about 2 hours. Further, it was kept in a soaking furnace at a temperature of about 1200 ° C. for about 3 hours. Next, the slab was unloaded from the furnace, and was hot-rolled in a rolling line to finally obtain a 12 mm product.

When 100 slabs were examined, the scale flaw occurrence rate was 1%. Example 8 A SUS329J3L slab having a thickness of 150 mm was kept in a soaking furnace at a temperature of about 1050 ° C. for about 2 hours. Further, it was kept in a soaking furnace at a temperature of about 1200 ° C. for about 3 hours. Next, the slab is unloaded from the furnace and hot-rolled on a rolling line.
Finally, the product was finished to 12 mm.

When 100 slabs were examined, the scale flaw occurrence rate was 1%. Comparative Example 1 A SUS304 slab having a thickness of 300 mm was kept in a soaking furnace at a temperature of about 1150 ° C. for about 5 hours. Next, the slab was unloaded from the furnace, and was hot-rolled in a rolling line to finally obtain a 50 mm product.

When 100 slabs were examined, the scale flaw occurrence rate was 15%. Comparative Example 2 A SUS304 slab having a thickness of 300 mm was held in a soaking furnace at a temperature of about 1250 ° C. for about 5 hours. Next, the slab was unloaded from the furnace, and was hot-rolled in a rolling line to finally obtain a 50 mm product.

Examination of 100 slabs revealed that the scale flaw generation rate was 16%. Comparative Example 3 A SUS304 slab having a thickness of 300 mm was soaked in a soaking furnace at a temperature of about 1050 ° C. for about 30 minutes. Further, it was kept in a soaking furnace at a temperature of about 1150 ° C. for about 5 hours. Next, the slab was unloaded from the furnace, and was hot-rolled in a rolling line to finally obtain a 50 mm product.

When 100 slabs were examined, the scale flaw occurrence rate was 14%. Comparative Example 4 A SUS304 slab having a thickness of 300 mm was kept in a soaking furnace at a temperature of about 1150 ° C. for about 2 hours. Further, it was kept in a soaking furnace at a temperature of about 1250 ° C. for about 5 hours. Next, the slab was unloaded from the furnace, and was hot-rolled in a rolling line to finally obtain a 50 mm product.

When 100 slabs were examined, the scale flaw occurrence rate was 18%. Comparative Example 5 A SUS304 slab having a thickness of 300 mm was kept in a soaking furnace at a temperature of about 1050 ° C. for about 2 hours. Further, it was kept in a soaking furnace at a temperature of about 1300 ° C. for about 5 hours. Next, the slab was unloaded from the furnace, and was hot-rolled in a rolling line to finally obtain a 50 mm product.

When 100 slabs were examined, the scale flaw occurrence rate was 23%. Comparative Example 6 A SUS430 slab having a thickness of 300 mm was kept in a soaking furnace at a temperature of about 1150 ° C. for about 5 hours. Next, the slab was unloaded from the furnace, and was hot-rolled in a rolling line to finally obtain a 50 mm product.

When 100 slabs were examined, the scale flaw occurrence rate was 30%. Comparative Example 7 A SUS329J3L slab having a thickness of 300 mm was kept in a soaking furnace at a temperature of about 1200 ° C. for about 5 hours. Next, the slab was unloaded from the furnace, and was hot-rolled in a rolling line to finally obtain a 50 mm product.

When 100 slabs were examined, the scale flaw occurrence rate was 33%. As is clear from the results of Comparative Example 1 and Comparative Example 2 (SUS304), if the slab is heated to a temperature range of 1150 ° C. or more without heating at a low temperature (first stage heating at 1000 to 1100 ° C.), the scale becomes large. The flaw generation rate reaches as much as 15-16%.
On the other hand, as is clear from the results of Examples 1 to 6,
When the slab was heated under appropriate conditions in the first and second stages, the scale flaw occurrence rate was reduced to 1-4%.

Further, as is apparent from the results of Comparative Example 3 (SUS304), if the first-stage heating holding time is too short, that is, 30 minutes, even if heating is performed under appropriate conditions in the subsequent second-stage heating, scale flaws will occur. The incidence can be as high as 14%. On the other hand, as is clear from the results of Examples 1 to 6, when the slab was heated under appropriate conditions in the first and second stages, the scale flaw occurrence rate was reduced to 1 to 4%.

Further, as is apparent from the results of Comparative Example 4 (SUS304), the temperature in the first stage heating was 11
If the temperature is too high at 50 ° C., the scale flaw generation rate will be 1 even if heating is performed under appropriate conditions in the subsequent second stage heating.
Increase to 8%. On the other hand, as is clear from the results of Examples 1 to 6, when the slab is heated under appropriate conditions in the first stage and the second stage, the scale flaw generation rate becomes 1 to 4%
Reduced to

Further, as is clear from the results of Comparative Example 5 (SUS304), even if the first stage heating was performed under appropriate conditions, if the heating temperature in the subsequent second stage heating was too high, the scale flaw generation rate was high. Increases to 23%. On the other hand, as is clear from the results of Examples 1 to 6, when the slab was heated under appropriate conditions in the first and second stages, the scale flaw occurrence rate was reduced to 1 to 4%.

Further, as is apparent from the results of Comparative Example 6 (SUS430), when the slab is heated to a temperature range of 1150 ° C. or higher without heating in the first stage, the scale flaw generation rate increases to 30%. On the other hand, as is apparent from the results of Example 7, when the slab was heated under appropriate conditions in the first and second stages, the scale flaw occurrence rate was reduced to 1%.

Further, Comparative Example 7 (SUS329J3L)
As is clear from the results, when the slab is heated to a temperature range of 1200 ° C. or more without heating in the first stage, the scale flaw generation rate increases to 33%. On the other hand, as is apparent from the results of Example 8, when the slab was heated under appropriate conditions in the first and second stages, the scale flaw occurrence rate was reduced to 1%.

As described above, according to the embodiment of the present invention, the scale flaw generation rate is increased in any of austenitic stainless steel (SUS304), ferritic stainless steel (SUS430), and duplex stainless steel (SUS32J3L). Was significantly reduced, and extremely good surface properties could be obtained.

[0037]

[Table 1]

[0038]

Conventionally, when scale flaws are generated on the surface of stainless steel, the surface properties are remarkably impaired by flaw care, and the production period and production cost are increased. In addition, when the slab is heated at a low temperature for a short time to suppress scale flaws, a reduction in the rolling temperature limits the manufacturable dimensions. ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to manufacture a stainless steel plate without scale flaws without restriction of hot workability, and an industrially advantageous effect is obtained.

Claims (1)

(57) [Claims] 1. A stainless steel slab of 1000 ° C. to 1 ° C.
A stainless steel, which is soaked in a temperature range of 100 ° C. for 1 hour to 3 hours and further soaked in the temperature range of 1150 ° C. to 1250 ° C. for 2 hours or more, and then hot-rolled. Hot rolling method of slab.