JPH0637671B2 - Manufacturing method of stainless steel sheet with excellent strength and corrosion resistance by hot controlled rolling - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a stainless steel sheet having excellent strength and corrosion resistance by hot controlled rolling.

(Prior Art) Ni—Cr-based austenitic stainless steel represented by 18Cr-8Ni is hot-rolled and air-cooled, then at a temperature of 1
It is manufactured by the steps of recrystallizing the working structure and growing the crystal grains in a heat treatment furnace maintained at 000 ° C. or higher, and performing heat treatment for melting and solidifying carbides.

It is also well known that this solution heat treatment is performed in order to prevent the problem that chromium carbide and the like are precipitated at the grain boundaries, which significantly deteriorates the corrosion resistance of this part, and consequently makes stainless steel easily corroded. ing.

As a method of controlling the strength level of a material in this manufacturing process, conventionally, there is an addition of a solid solution strengthening element, for example, strength improvement by increasing N content.

(Problems to be Solved by the Invention) Recently, while the development of stainless steel manufacturing technology at a low manufacturing cost has been sought, the above-mentioned solid solution is cooled to room temperature after hot rolling and heated to a high temperature again. The manufacturing method of heat treatment requires enormous heat energy and a long time, and has a problem in productivity.

Due to such a problem, recently, as a manufacturing method in which the solution heat treatment after hot rolling is omitted, JP-A-55-107729, JP-A-60-26619 and JP-A-60-1 are available.
As described in Japanese Patent No. 97817, a manufacturing technique of an austenitic stainless steel sheet which is rapidly cooled from a high temperature after hot rolling has been developed.

The method described in JP-A-55-107729 is 850.
After performing hot rolling at a cumulative rolling reduction of 50% or more in a temperature range of ˜1150 ° C. and at a finishing temperature of 850 ° C. or more, at a cooling rate determined by the C content in steel at a temperature of 850 to 550 ° C. or more. It is a manufacturing method in which it is rapidly cooled,
The method described in Japanese Patent No. 6619 is a method in which after hot rolling, a temperature between 800 ° C. and 500 ° C. is cooled at a rate higher than that determined by the C, N and Mo contents. In addition, JP-A-6
The method described in JP-A 0-197817 is 850 to 950.
Cumulative reduction of 30% or more in the temperature range of ℃, followed by 2 ℃
It is a method of cooling to at least 550 ° C. at a cooling rate of not less than / sec.

In the hot strip method, a method for omitting the solution heat treatment has been developed for hot rolling and cooling.

However, as a characteristic of the manufacturing method of the thick plate, there is a problem that the manufacturing method cannot be patterned like the hot strip because the plate thickness and the plate width to be manufactured are various.

The present invention, after hot rolling, without undergoing solution heat treatment to reheat, excellent corrosion resistance equivalent to the solution heat treated material, and,
We have found that a stainless steel plate with controllable strength can obtain stable material even in various rolling dimensions by controlling the final 1-pass pre-finishing temperature, final 1-pass start temperature, cooling start temperature, etc. during hot rolling. It is configured as.

(Means for Solving the Problem) The gist of the present invention is to make a stainless steel piece heated to a high temperature have a final 1-pass pre-finishing temperature of 980 ° C. or higher during hot rolling and a final 1-pass starting temperature of 900. Hot rolling at a final 1-pass reduction of 20% or less at a temperature of ℃ or more, and then the temperature during cooling is related to the C content in the steel by water cooling at ab line or more in FIG. A method for producing a stainless steel sheet having excellent strength and corrosion resistance by hot controlled rolling, which comprises cooling from a starting temperature to 500 ° C at a cooling rate of 2 ° C / sec or more and then at an arbitrary cooling rate. It is in. In the present invention, it is also possible to extend the control range of strength by applying the conventional control of the component system.

Hereinafter, the present invention will be described in detail with reference to the drawings.

Heat a high temperature heat-bearing stainless steel piece produced from molten steel of stainless steel through an ingot, slab or continuous casting method, or heat a stainless steel piece heated to a high temperature from a low temperature. Rolling for a while. The components of the stainless steel piece as the starting material of the present invention are not particularly limited, but C: 0. 0 from the strength and corrosion resistance required for stainless steel.
008-0.10%, Si; 0.08-4.4%, M
n; 0.09 to 8.3%, P; 0.04% or less, S;
0.01% or less, Cr; 16.1-26.0%, Ni;
4.2 to 22.0%, N; 0.01 to 0.38%, A
l; 0.3% or less, and if necessary Mo: 4.5
~ Or less, Cu; 3.7% or less, Ti; 0.9% or less, N
b; 0.9% or less can be included. Stainless steel pieces heated to high temperature are rolled several times to finish to product size, but the final 1-pass pre-finishing temperature during hot rolling is 980 ° C or higher, and the final 1-pass start temperature is 900 ° C.
Rolling at above (preferably below 1100 ° C),
If the final 1-pass starting temperature is less than 900 ° C., the control of the final rolling reduction and the cooling starting temperature will not be stable and the material will be unstable. Further, hot rolling with a final 1-pass rolling reduction of 20% or less is performed to control the strength level. Further, when the final rolling reduction exceeds 20%, recrystallization occurs and the strength decreases, so an upper limit is set for the rolling reduction.

That is, the final reduction rate and the final 1-pass start temperature are controlled to control the strength level, and the final reduction rate is 2
The larger the value is within 0%, the final 1-pass start temperature is 90.
The strength level improves as the temperature decreases above 0 ° C. The rolling method as described above is summarized in FIG.

In the stainless steel sheet that has been hot-rolled in this way and rolled into a product of a predetermined size, carbide precipitation is observed from the temperature above the line ab in FIG. 1 in relation to the C content in the steel. Cooling is performed at a cooling rate of 2 ° C./sec or more between temperatures up to 500 ° C. At a slow cooling rate of less than 2 ° C./sec, carbide precipitates at the grain boundaries and the surface corrosion resistance deteriorates.

Next, a production example of the present invention will be described. A stainless steel having a chemical composition shown in Table 1 was melted and continuously cast (CC) and ingot / agglomerated (IC) to form a slab having a thickness of 150 to 200 mm.

The slab was heated to 1200 ° C. in a heating furnace and rolled into a plate.

The final 1-pass rolling reduction was set from 2% to a maximum of 40%, and the rolling reduction up to that point was not particularly restricted.

The steel sheets had plate thicknesses of 19 mm, 30 mm, 35 mm, and 40 mm, and rolling was performed by setting the final finishing temperature before the first pass and the starting temperature of the final one pass.

Table 2 shows the final 1-pass rolling reduction and temperature conditions from rolling to cooling of each test material.

As comparative examples, examples in which the water cooling start temperature is low and the corrosion resistance fails, and those in which the final 1-pass rolling reduction exceeds 20% show examples in which the strength decreases.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between steel plate surface temperature and C content in steel in terms of corrosion resistance, and FIG. 2 is a diagram showing the relationship between each step of the present invention and temperature.

Continued Front Page (72) Hiroki Yamamoto 1-1-1 Emitsu, Hachimanto-ku, Kitakyushu, Kitakyushu, Fukuoka 1-1-1 Inside Nippon Steel Co., Ltd. Yawata Works (72) Inventor, Katsuhiko Yamada Emitsu, Hachiman-ku, Kitakyushu, Fukuoka 1-1-1 Inside Nippon Steel Co., Ltd. Yawata Works (72) Inventor Masamitsu Machinaga 1-1-1 Edamitsu, Hachiman-Higashi-ku, Kitakyushu, Kitakyushu, Japan 1-1-1 Nippon Steel Co., Ltd.

Claims (1)

[Claims] 1. A stainless steel piece heated to a high temperature has a finishing temperature before the final 1-pass during hot rolling of 980 ° C. or higher, a starting temperature of the final 1-pass is 900 ° C. or higher, and a final 1-pass rolling at that time. The rate of 20% or less is hot-rolled, and then the temperature in the course of cooling is related to the C content in the steel.
-2 ° C between the water cooling start temperature above line b and 500 ° C
A method for producing a stainless steel sheet having excellent strength and corrosion resistance by hot controlled rolling, which comprises cooling at a cooling rate of at least 1 sec / sec and then cooling at an arbitrary cooling rate.