JPS6119689B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a ferritic stainless thin steel sheet, and particularly to a method for manufacturing a ferritic stainless thin steel sheet that can simplify the manufacturing process, has less ridging, and is free from surface flaws. Conventionally, ferritic stainless thin steel sheets (SUS430) have been produced by box annealing hot-rolled steel strips at a temperature range of 800 to 850°C for 2 hours or more, or by box annealing them at 900°C to 1100°C.
It is manufactured by a method of continuous annealing for a short period of time in a temperature range of 100 mL, followed by cold rolling. One of the metallurgical meanings of hot-rolled sheet annealing is that this annealing actively promotes recrystallization, finely randomizes the hot-rolled structure, and reduces ridging in the final product. In order to effectively perform this recrystallization, it is necessary to impart strain to the hot-rolled sheet by lowering the slab heating temperature or lowering the finish rolling temperature. When rolling is performed to impart surface defects, surface defects called scale defects are likely to occur. The present invention provides a method for manufacturing a ferritic stainless thin steel sheet that does not require such strain imparting hot rolling, and also omits the conventionally necessary hot-rolled sheet annealing step, thereby causing no surface defects and less ridging. It is something. In other words, after rough rolling, the rough rolled piece is heated to 1100℃ or higher.
We have discovered that stainless steel sheets with no surface flaws and small ridging can be produced without hot-rolled sheet annealing by holding the sheet at a temperature of 1150°C or lower for at least 1 second and no more than 10 minutes, or by finishing rolling immediately after heating.
This completes the present invention. The metallurgical reason why ridging is reduced by heat treatment under such conditions after completion of rough rolling is not necessarily clear, but the inventor of the present invention thinks as follows. In other words, in SUS430 stainless steel, the γ phase reaches its maximum near 1100℃, so by holding it for a short time at a temperature between 1100℃ and 1150℃, the γ phase is finely precipitated and dispersed. We believe that this is because recrystallization is promoted by being held in Therefore, as a ferritic stainless steel that exhibits the effects of the present invention, a ferritic stainless steel having a component system such as α+γ two phases in the temperature range of 1100°C to 1150°C is suitable. When the γ phase is reprecipitated after rough rolling, γ
Since the phase preferentially precipitates on the grain boundaries of grains that have been made ultra-fine through rough rolling and on areas where strain has accumulated, the number of precipitated sites is overwhelmingly greater than when the phase is precipitated and dispersed during casting. This enables fine dispersion. In the case of ferritic stainless steel, which has a single α phase in the temperature range of 1100°C to 1150°C, there is no effect of fine dispersion of the γ phase, so the ridging reduction effect of the present invention cannot be expected, and it is a mere static Since it is only a recrystallization effect, the ridging reduction effect is α
Needless to say, the effect is smaller than that of steel with +γ2 phase. Furthermore, it goes without saying that the so-called martensitic stainless steel, which has a single γ phase from the slab heating temperature to the temperature of 1100° C., is not within the scope of the present invention. In other words, the ferritic stainless steel that is the subject of the present invention has α+
A ferritic stainless steel having a γ2 phase, such as the SUS430 stainless steel mentioned above, is most suitable. In the present invention, the reason why the heating holding temperature is set to 1100°C or higher is because the effect of improving ridging is relatively small at a temperature lower than this, and the reason why the heating holding temperature is set to 1150°C or lower is that the effect of improving ridging is recognized even at a temperature higher than this. However, in order to maintain the slab at such a high temperature, it is necessary to raise the slab heating temperature to a significantly high temperature or actively heat the rough rolling, which requires a large amount of thermal energy and is not economical. Also, the holding time was set at 1 second or more because it is effective if the temperature reaches 1100°C, so the holding time was set at 1 second or more as the minimum necessary time. This is because the effect is saturated. The present invention will be explained below based on examples. SUS430 stainless steel slabs with a thickness of 200 mm shown in Table 1 were heated at three temperatures: 1000℃, 1100℃, and 1200℃.
After heating under the following conditions, it was roughly rolled to a thickness of 20 mm.

[Table] Then, after holding at a temperature of 1100℃ for 1 second, 5 minutes, and 10 minutes, finish rolling was performed to make a hot-rolled sheet with a thickness of 3.7 mm.
For comparison, a hot rolled sheet was also prepared by finish rolling immediately after rough rolling. These hot rolled plates are
Hot rolled plate cold rolled without annealing to a thickness of 0.7mm
After forming a cold-rolled sheet, annealing was performed at a temperature of 820°C. Figure 1 shows the ridging characteristics of these materials, and after rough rolling according to the conditions of the present invention, 1100
The slab heat treated at a temperature of 30°F showed good ridging properties regardless of the slab heating temperature. Furthermore, since finish hot rolling was carried out at such a high temperature, the deformation resistance in the finish hot rolling process could be reduced, and a hot rolled sheet with a good surface free from scale flaws was obtained. If heating is not performed as in the present invention, the resulting product will have poor ridging properties, especially if the slab heating temperature is low, and the finishing hot rolling temperature will be low.
Surface flaws called so-called scale flaws occurred. As is clear from the above examples, by hot rolling according to the method of the present invention, a ferritic stainless thin steel sheet with no surface flaws and small ridging can be produced in a process that omit hot-rolled sheet annealing. Therefore, the present invention greatly contributes to industry. Furthermore, although the above embodiments have been explained using SUS430 steel as an example, it goes without saying that the present invention includes ferritic stainless steels in which the γ phase precipitates in the temperature range of 1100°C to 1150°C.

[Brief explanation of the drawing]

FIG. 1 shows the influence of heating conditions after rough rolling on the ridging properties of the finished product.

Claims (1)

[Claims] 1. When hot rolling a ferritic stainless steel slab, after hot rough rolling, the temperature is 1100°C or higher and 1150°C or higher.
℃ or less for 1 second or more or less than 10 minutes or heated to reprecipitate the austenite phase, hot finish hot rolling is performed, and then cold rolling is performed without annealing the hot rolled sheet. There are no surface scratches,
A method for manufacturing ferritic stainless thin steel sheets with small ridging. 2. The method according to claim 1, characterized in that SUS430 stainless steel is hot rolled.