JPH0669574B2 - Rolling method for stainless steel - Google Patents

Description

TECHNICAL FIELD The present invention relates to a stainless steel hot rolling method capable of preventing a flaw generated on the surface of a steel strip during rolling.

(Prior art) Hot rolling of stainless steel is continuously performed by a dedicated rolling machine such as a Steckel mill or planetary mill or a hot strip mill of ordinary steel. In the case of stainless steel, the surface of the stainless steel is flawed by hot rolling. If it occurs, it will not disappear easily even after cold rolling, and it will remain as a minute flaw, resulting in a defective product. However, since stainless steel is expensive, even if a small amount of defective products is generated, economic loss is large. Therefore, when the surface flaws generated by hot rolling are significant, the flaws are polished before the cold rolling for relief. However, even if such remedy measures are taken, it is not possible to remedy all and defective products cannot be avoided. Therefore, when surface defects occur, the yield and the production efficiency decrease.

By the way, as the work roll of the rolling mill during hot rolling, regardless of whether it is ordinary steel or stainless steel, generally the one whose surface is smoothed by mechanical polishing is used, but in the case of stainless steel, surface flaws occur. Then, since the problems as described above occur, great attention is paid to roll skin. Especially when rolling between ordinary steel rolling with a hot strip mill, if there is a rough surface on ordinary steel rolling, it becomes a problem, so when rolling stainless steel, replace all work rolls with smooth ones. , Stainless steel is rolled continuously in a batch.

(Problems to be solved by the invention) However, when a stainless steel having a Cr content of 10 wt% or more is rolled in such a state, the stainless steel to be rolled is welded to the work roll surface of the finish rolling mill, There has been a problem that so-called seizure occurs on the roll. This seizure is because when the Cr content of stainless steel is 10 wt% or more, an oxide scale layer is less likely to be generated on the surface, so the material to be rolled and the work roll come into direct contact during rolling, resulting in a metal touch state. It happens, but
When the seizure occurs on the work roll, the roll cannot be used unless it is re-polished. Therefore, when seizure occurs, it is necessary to suspend the rolling, replace the rolls, and re-polish the seizure-occurring roll. Therefore, there is a problem that, besides the reduction of the yield and the production efficiency, the roll unit and the rolling cost are increased.

As a measure for preventing the occurrence of seizure, conventionally, the rolling temperature during rolling is increased to reduce the rolling load, or the reduction ratio per pass is reduced, or rolling oil is used to separate the material to be rolled and the roll. We have taken measures such as improving the lubricity during this period, and further improving the roll material, but none of these methods can be completely prevented, which in turn reduces production efficiency and raises production costs. I was invited.

(Means for Solving Problems) The present invention, when hot-rolling a stainless steel having a Cr content of 10 wt% or more, has a width of at least the stainless steel to be rolled and a C content of 0.3 wt% or less of ordinary steel. To prevent the seizure of the material to be rolled onto the work roll by the method of rolling the stainless steel after forming the oxide scale layer on the work roll surface of the hot finish rolling mill by rolling it in advance with the hot rolling mill. I decided to do it.

When hot-rolling stainless steel by the above method, the occurrence of seizure is reduced because the oxide scale layer on the surface of the work roll is structurally stable, so when contacted with stainless steel, it gradually becomes finer than the surface. This is because it peels off in a granular form and becomes a lubricant.

This oxide scale layer may be formed by a method such as preheating before changing the work rolls, but after changing the work rolls, it is wider than the stainless steel width to be rolled or rolled with a normal steel of the same width. Then, the method of transferring the oxide scale on the surface to the work roll surface is easy. According to this method, the oxide scale layer can be uniformly formed on the entire surface of the work roll, and can be thickened by increasing the rolling amount of ordinary steel. For example, when rolling about 10 coils of ordinary steel with a coil weight of around 18 tons, C
Depending on the content, the oxide scale layer is
It becomes considerably thick with 80 μm and becomes stable.

As for the ordinary steel to be rolled, the smaller the C content, the more the oxide scale can be formed on the work roll. In general, in the case of carbon steel, the higher the C content, the higher the hardness, and the higher the deformation resistance during rolling. Therefore, the rolling load also increases. As a result, the lubrication conditions on the roll surface become severe, and This is because it causes rough skin and scale banding (a type of light roll flaw), making it difficult for oxidized scale to form. Therefore, it is preferable to roll the ordinary steel having a C content of 0.3 wt% or less.

However, since the oxide scale layer of the work roll is peeled off little by little as the stainless steel is rolled as described above, seizure occurs when the rolling is continued. Therefore, if the stainless steel is rolled to a certain extent, this time, the ordinary steel is rolled by a predetermined amount, the oxide scale layer is formed again on the work roll surface, and then the stainless steel is rolled again. Occurrence can be prevented.

(Example) Example 1 In a hot strip mill in which the surface of a work roll remains mechanically polished, ordinary steel and stainless steel were hot rolled under the hot rolling conditions shown in Table 1. As the ordinary steel, a slab having a C content of 0.05 to 0.11 wt% and a weight of about 20 tons,
For stainless steel, the Cr content is 10.91, 13.0.
Slabs of steel grades of 6, 17.35, 19.87, 22.61 wt% and a weight of about 15 tons were used.

At the time of rolling, first, 70 coils of ordinary steel is continuously rolled before rolling each stainless steel of the above steel types to form an oxide scale layer on the work roll surface of the finishing rolling mill, and then stainless steel is classified into steel types. Multiple coils were continuously rolled.

As a result, seizure did not occur up to 3 coils in each stainless steel, but surface flaws due to seizure were recognized from the 4th coil.

Example 2 Under the same hot rolling conditions as in Example 1, ordinary steel having a C content of 0.08 wt% was continuously rolled by 8 coils, and then stainless steel was continuously rolled by 3 coils. However, surface flaws were observed in all types of stainless steel. I couldn't do it.

Example 3 Under the same hot rolling conditions as in Example 1, plain steel having a C content of 0.08 wt% was continuously rolled by 3 coils, and then stainless steel was continuously rolled by 19 coils. Admitted.

Example 4 70 coils of ordinary steel having a C content of 0.05 to 0.11 wt% was continuously rolled under the same hot rolling conditions as in Example 1, and then stainless steel and ordinary steel were alternately rolled one coil at a time. The stainless steel having the Cr content rolled in Example 1 was used, and the stainless steel having a lower Cr content was rolled in order. As a result, no surface flaw was observed in any of the stainless steels.

Example 5 In the same manner as in Example 4, one coil of ordinary steel was rolled and then two coils of stainless steel were rolled, but no surface flaw was observed in each steel type.

(Effects of the Invention) As described above, according to the present invention, since seizure of stainless steel does not occur on the work roll, the roll unit and rolling cost do not increase. As a result, surface defects do not occur in the rolled stainless steel, and the yield and production efficiency do not decrease.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuki Tsuchiya 11-1 Showa-cho, Kure-shi, Hiroshima Inside the Kure Works, Nisshin Steel Co., Ltd. Steelmaking Co., Ltd. Hanshin Works (72) Inventor Akiyuki Kataoka 1-13-2 Tenjin, Chuo-ku, Fukuoka-shi, Fukuoka Nisshin Steel Co., Ltd. Fukuoka Sales Office (56) Reference JP-A-60-170503 (JP, A) )

Claims (1)

[Claims] 1. When hot rolling stainless steel having a Cr content of 10 wt% or more, ordinary steel having a width of at least the stainless steel to be rolled and having a C content of 0.3 wt% or less is previously rolled by a hot rolling mill. A method for rolling stainless steel, comprising forming an oxide scale layer on the surface of the work roll of the hot finish rolling mill, and rolling the stainless steel.