JPH10298658A - Manufacture of high purity ferritic stainless steel sheet excellent in ridging resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a high purity stainless steel sheet excellent in ridging resistance. SOLUTION: A high purity ferritic stainless steel, in which steel components are regulated so that the steel contains, by mass, <=0.015% C, <=0.020% N, <=1% Mn, 10.5-12% Cr, and 8×(C+N) to 0.4% Ti and further contains either of <=0.2% Si and <=0.03% Al and has the balance Fe with inevitable impurities, is used. This steel is held, in the course of hot rolling, at 970 to 1070 deg.C for >=5 min.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing 11% Cr high-purity ferritic stainless steel sheet having excellent ridging resistance.

[0002]

2. Description of the Related Art Ferritic stainless steel has corrosion resistance,
Since it is excellent in workability and does not add expensive Ni, it is inexpensive as compared with austenitic stainless steel. In particular, a high-purity ferritic stainless steel thin plate in which C and N are reduced and these elements are fixed by adding Ti or the like to reduce the amount of solute C and N in the steel is particularly suitable for press forming and deep forming. Excellent drawability.

[0003] In general, when a ferritic stainless steel sheet is press-formed, striped irregularities called ridging are produced along the rolling direction. Ridging not only impairs the aesthetics of the molded product, but also causes a polishing load to remove it, which is a problem when press-forming ferritic stainless steel.

Many reports have been made on the ridging mechanism of ferritic stainless steel. However, a layered coarse ferrite band structure (colonies) extending in the rolling direction existing in the solidification structure at the time of casting, hot rolling and hot rolling annealing structure. Structure) remains after the subsequent cold-rolling annealing, and there is a difference in the plastic anisotropy of each structure. The idea that unevenness occurs is the mainstream. That is, in order to improve the ridging resistance, it is necessary to finely cut a coarse ferrite band structure in a hot-rolled sheet and a hot-rolled annealed sheet, and many measures have been developed so far.

[0005] For example, Japanese Patent Application Laid-Open No. 4-160117 discloses a 17% C solution in which an austenite phase is precipitated at a high temperature.
Rough rolling of r ferritic stainless steel at 900 ° C to 11
The test was performed in a temperature range of 00 ° C.
A method is disclosed in which after the temperature is maintained in a temperature range of 1C to 1100C, finish rolling is performed. With this technology, ridging of 17% Cr ferritic stainless steel represented by SUS430 is greatly improved. However, as typified by this known technique, the conventional ridging reduction technology of ferritic stainless steel is mainly for 17% Cr ferritic stainless steel, and it is 11% Cr-low C as described in the present invention. The same effect cannot be obtained for N-Ti-added steel (high-purity ferritic stainless steel), and ridging resistance is not improved.

[0006]

The normal 11% Cr high-purity ferritic stainless steel does not produce an austenite phase in hot rolling that is effective in breaking the ferrite band. For example, C: 0.004%, N:
0.008%, Mn: 0.4%, Cr: 11.0%, T
i: 0.16%, Si: 0.5%, Al: 0.04%,
In a typical 11% Cr high-purity ferritic stainless steel whose balance is composed of Fe and unavoidable impurities, the austenite phase generated during hot rolling is at most about 5%.

[0007] Therefore, an object of the present invention is to increase the amount of austenite phase formed during hot rolling of 11% Cr high-purity ferritic stainless steel without adding a large amount of expensive alloying elements, and to cut the ferrite band. Accordingly, an object of the present invention is to provide a method for reducing ridging.

[0008]

Means for Solving the Problems The present inventors have proposed that 11% C
r A method was studied in detail in a laboratory to sufficiently generate an austenite phase during hot rolling of a high-purity ferritic stainless steel, thereby dividing a ferrite band and improving ridging resistance. As a result, by reducing the Si content and the Al content in the steel composition, an austenite phase is sufficiently formed in the hot rolling temperature range even in 11% Cr steel pure ferritic stainless steel, and the austenite phase is formed during hot rolling. The present inventors have found that a coarse ferrite band can be separated by the progress of recrystallization at the interface of the ferrite phase, and the ridging resistance can be improved, and the present invention has been completed.

That is, the gist of the present invention is as follows.
In mass%, C: 0.015% or less, N: 0.020% or less, Mn: 1% or less, Cr: 10.5 to 12%, Ti:
8 × (C + N) to 0.4%, and further containing Si: 0.
High-purity ferritic stainless steel that satisfies either 2% or less or Al: 0.03% or less, further contains B: 0.005% or less as necessary, and the balance is Fe and unavoidable impurities. The present invention relates to a method for producing a high-purity ferritic stainless steel sheet excellent in ridging resistance, wherein the steel is maintained at a temperature range of 970 ° C. to 1070 ° C. during hot rolling for 5 minutes or more.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The reduction of either the Si content or the Al content of a high-purity ferritic stainless steel increases the amount of austenite phase formed in the steel. FIG.
Are: C: 0.004%, N: 0.008%, Mn: 0.
4%, Cr: 11.0%, Ti: 0.16%, (a) Si: 0.5%, Al: 0.04%, (b) S
i: 0.06%, Al: 0.04%, (c) Si: 0.
850 ° C. to 1200% steel with 5% Al: 0.01%
It is the result of having measured the austenite phase ratio in the steel in the equilibrium state at the time of keeping for 30 minutes in each temperature range of ° C. The steel in which the amount of Si is reduced in (b) and the steel in which the amount of Al is reduced in (c) are:
An austenitic phase is formed below 1150 ° C,
The austenite ratio increases in the temperature range of -1070 ° C and reaches its maximum at 1000 ° C. The austenite phase ratio at 1000 ° C. is only 5% for (a), 80% for (b) and 45% for (c). By reducing the amount of Si or Al, the austenite phase ratio is reduced. It turns out that it becomes large. In addition, the effect of Si reduction is better for Al.
Greater than the effect of the drop. When the austenite phase is formed in the ferrite phase, the interface becomes a nucleation site for recrystallization, and the coarse ferrite band can be separated by the promotion of recrystallization during hot rolling, particularly at the later stage of rough rolling.
Ridging resistance can be increased.

Next, the limited range of the present invention will be described. The reasons for limiting the component content of the steel subject to the present invention are as follows. C: It is necessary to be 0.015% or less. 0.015%
When the content exceeds the range, the corrosion resistance of the weld heat affected zone is likely to be deteriorated due to the precipitation of Cr carbide at the grain boundary. Further, since it is an interstitial solid solution element, it strengthens steel, and if it exceeds 0.015%, the workability deteriorates. For these reasons, the upper limit is made 0.015%.

N: It is necessary to be 0.020% or less.
Since it is an interstitial solid-solution element, it strengthens the steel. If the content exceeds 0.020%, the workability deteriorates. Therefore, the upper limit is set to 0.020%.

Mn must be 1% or less. It is an element that is effective in deoxidizing steel and also enhances the austenite phase forming ability of steel.
Since the amount of S generated increases and deteriorates corrosion resistance, the upper limit is set to 1%.

Cr: 10.5% or more and 12% or less. It is a basic element of stainless steel, and must contain at least 10.5% or more in order to obtain necessary corrosion resistance. However, if the content exceeds 12%, the toughness and workability deteriorate, and the alloy cost further increases. Therefore, the upper limit is set to 12%.

[0015] Ti: It is necessary to be not less than 8 times and not more than 0.4% of C + N. By easily binding to C and N and substantially reducing the amount of C and N dissolved in the matrix,
Workability can be improved. However, this effect is 8 × (C
+ N) does not appear. Further, even if the content exceeds 0.4%, the hot workability of the steel is reduced, and this may cause flaws during hot rolling.
%.

Si, Al: Si content of 0.2% or less, Al
It is necessary to satisfy one of the amounts of 0.03% or less. Each element is an effective element as a steel deoxidizer, but by reducing the content of these elements, 11%
The ability to form an austenite phase during hot rolling of Cr high-purity ferritic stainless steel can be enhanced. This effect appears when Si: 0.2% or less and Al:
0.03% or less.

B: For applications requiring higher secondary workability, it is effective to add it in an amount of 0.005% or less. B has the effect of repairing defects in the steel generated when processing the product and improving the secondary workability. However, B
If the content exceeds 0.005%, the hot workability of steel is significantly reduced, and cracks and flaws occur during hot rolling, so the upper limit was made 0.005%.

It is necessary to maintain the temperature in the range of 970 ° C. to 1070 ° C. during hot rolling for 5 minutes or more. By realizing a thermodynamic equilibrium state during hot rolling, an austenite phase ratio as shown in FIG. 1 can be obtained. By generating an austenite phase during hot rolling (temperature reduction, deformation), the ferrite band can be separated, and ridging resistance can be improved. If the holding temperature during hot rolling is less than 970 ° C. or exceeds 1070 ° C., the austenite phase is not so much formed, and as a result, the ferrite band is separated by recrystallization during hot rolling from the interface between the austenite phase and the ferrite phase. Almost no effect is obtained. If the holding time is less than 5 minutes, the austenite phase is not sufficiently formed, and there is no effect.

[0019]

EXAMPLES Three types of 11% C having the chemical components shown in Table 1
r High-purity ferritic stainless steels A to C were melted and continuously cast into 250 mm thick slabs. The slab was hot-rolled to a thickness of 3.2 mm under the conditions shown in Table 2, pickled, and further cold-rolled to a thickness of 0.94 mm to obtain a final annealed product. Table 2 also shows the results of measuring the ridging height when 16% tensile strain was applied to each product sheet in the cold.

[0020]

[Table 1]

In Table 2, No. 1 to 8 follow the method of the present invention. Steels B and C in which either the Si content or the Al content is reduced are 970 ° C to 1070 ° C during hot rolling.
By keeping the temperature for 5 minutes or more, the ridging resistance is greatly improved. The longer the holding time during hot rolling, the greater the effect of improving ridging resistance. Further, since the amount of austenite phase formation in the equilibrium state is maximum at 1000 ° C., when the holding time is equal, the holding temperature is 1000 ° C. and the ridging resistance is most improved.

On the other hand, the steel A in which neither the amount of Si nor the amount of Al has decreased is 5% at 970 ° C. to 1070 ° C. during hot rolling.
Even if it is held for more than one minute, the ridging resistance is not improved. Also, S
Steels B and C in which either the i content or the Al content is reduced
Regarding the above, when not held during hot rolling, when the holding temperature is not between 970 ° C. and 1070 ° C., and when the holding time is less than 5 minutes, the ridging resistance hardly improves.

[0023]

[Table 2]

[0024]

According to the present invention, 1 excellent in ridging resistance can be obtained.
Production of 1% Cr high-purity ferritic stainless steel sheet is possible.

[Brief description of the drawings]

FIG. 1 shows a sample of 11% Cr high-purity ferritic stainless steel having different amounts of Si and Al at 850 ° C. to 1200 ° C.
It is the result of having measured the austenite phase ratio in steel at the time of holding for 0 minute.

Claims (1)

[Claims] 1. Mass%, C: 0.015% or less, N: 0.020% or less, Mn: 1% or less, Cr: 10.5 to 12%, Ti: 8 × (C + N) to 0. 4%, and further satisfy either Si: 0.2% or less or Al: 0.03% or less, and further contain B: 0.005% or less as necessary, with the balance being Fe And a high-purity ferritic stainless steel having excellent ridging resistance, wherein the high-purity ferritic stainless steel is maintained at a temperature range of 970 ° C. to 1070 ° C. for 5 minutes or more during hot rolling. Steel plate manufacturing method.