JPH09137231A - Method for producing high-purity ferritic stainless steel sheet with excellent ridging characteristics - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To provide a manufacturing method of a highly pure ferritic stainless steel sheet with low ridging and stable. SOLUTION: Cr: 10 to 12%, C:
0.02% or less, N: 0.02% or less, Ti: 5 × (C
+ N) -0.8%, the balance is 1180 ° C. for a continuous cast slab of high-purity ferritic stainless steel with the balance being Fe.
Hot-rolling is performed by heating at the following temperature, and the hot-rolled steel strip obtained is wound at a temperature of 700 ° C or lower, and the obtained hot-rolled steel strip is 830 ° C to 870 ° C.
Hold in the temperature range of 2 hours or more, and then cold roll / anneal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a highly pure ferritic stainless steel sheet having low ridging and stable ridging characteristics.

[0002]

2. Description of the Related Art In order to reduce ridging of a ferritic stainless steel sheet, it is necessary to divide a so-called ferrite band in which coarse ferrite grain groups of a hot-rolled sheet annealing structure are extended in layers. Conventionally, as a method of dividing the ferrite band and utilizing the austenite phase to reduce ridging, a hot rolled steel strip of ferritic stainless steel is annealed in the austenite phase region from Ac ₁ point to 1000 ° C. Of producing an austenite phase in the ferrite band of JP-A-61-119
It is disclosed in Japanese Patent No. 5923.

[0003]

In the case of the ultra-low carbon and ultra-low nitrogen ferritic stainless steels (hereinafter referred to as high-purity ferritic stainless steels) targeted by the present invention, the hot-rolled steel strip has an Ac of ₁ point or more. Since the austenite phase is hardly generated even when heated to the above, it is difficult to apply the method for dividing the ferrite band by utilizing the austenite phase as described above.

[0004]

In order to reduce the ridging by dividing the ferrite band in the hot-rolled steel strip of high-purity ferritic stainless steel in which utilization of the austenite phase is not easy, the present inventors have proposed slab heating. By setting the hot rolling conditions such that the temperature is 1180 ° C. or lower and the winding temperature is 700 ° C. or lower, the ferrite band structure at the end of the hot rolling is made finer and the strain caused by the hot rolling is further reduced. Was conceived to accumulate. By subjecting such a hot rolled steel strip to annealing in a temperature range of 830 ° C. to 870 ° C. for 2 hours or more, the structure after annealing of the hot rolled sheet is completely recrystallized into fine grains and a coarse ferrite band is formed. The present invention has been completed based on the finding that the product sheet after being cut, cold rolled, and finally annealed has low and stable ridging.

That is, the gist of the present invention is as follows. % By weight, Cr: 10-12%, C: 0.0
2% or less, N: 0.02% or less, Ti: 5 × (C +
N) to 0.8% and the balance is Fe and unavoidable impurities. A continuously cast slab of high-purity ferritic stainless steel is heated to a temperature of 1180 ° C. or lower and hot-rolled to 700 ° C. or lower. Ridging characteristics characterized by being rolled at a temperature, subjected to hot-rolled sheet annealing in which the obtained hot-rolled steel strip is held in a temperature range of 830 ° C to 870 ° C for 2 hours or more, and then cold-rolled and annealed. The method for producing an excellent high-purity ferritic stainless steel sheet of

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In hot rolling a continuously cast slab, the slab heating temperature is set to 1180 ° C. or lower to prevent coarsening of the solidified casting structure, and the winding temperature is set to 700 ° C. or lower. The strain introduced by hot rolling is accumulated, and the band-like ferrite structure of the steel strip obtained after hot rolling is made finer, and it also serves as a driving force for recrystallization during annealing of the hot rolled sheet.

By such a method, the ferrite band is made into fine grains in advance, and the hot rolled steel strip in which strain is accumulated is annealed for 2 hours or more in the temperature range of 830 ° C to 870 ° C. , Completely recrystallize the structure after annealing,
Moreover, by making the recrystallized structure into fine grains, as a result, the ferrite band structure is finely divided. As a result, the structure after cold rolling and final annealing is uniformly fine grained, and a highly pure ferritic stainless steel sheet having low ridging and stable ridging characteristics can be obtained.

Next, the limited scope of the present invention will be described.
The reason for limiting the component content of the steel of the present invention is as follows. Cr: A basic element of stainless steel, and at least 10% or more is necessary to obtain the required corrosion resistance. If the content is more than 12%, the temperature required for recrystallization during hot-rolled sheet annealing rises and the time is extended, and under the hot-rolled sheet annealing conditions of the present invention, complete recrystallization becomes difficult, so the upper limit is set. It was set to 12%.

C: If contained in excess of 0.02%, Cr
Corrosion resistance deterioration of the weld heat affected zone occurs due to grain boundary precipitation of carbides. Since it is an interstitial solid solution element, it strengthens the steel and
If the content exceeds 02%, the workability deteriorates. For these reasons, the upper limit was made 0.02%. In order to reduce the cost of smelting steel, the lower limit of C content should be 0.0005.
% Is desirable.

N: Steel is strengthened because it is an interstitial solid solution element, and if it exceeds 0.02%, the workability deteriorates, so its upper limit was made 0.02%. In addition, in order to reduce the melting and casting costs of steel, the lower limit of the N content is set to 0.003.
% Is desirable. Since Ti: C and N are easily combined with each other and have the effect of substantially reducing the amount of C and N dissolved in the matrix, the workability can be improved.
However, these effects do not appear at a content of 5 × (C + N) or less. Further, even if the content exceeds 0.8%, the hot workability of the steel is deteriorated, and it causes defects in hot rolling, so the upper limit was made 0.8%.

The slab heating temperature during hot rolling is 1180 ° C.
It is necessary to: This is because if the slab heating temperature exceeds 1180 ° C., the ferrite structure becomes coarse and the structure of the hot-rolled sheet also becomes coarse. If the slab heating temperature is too low, flaws may occur on the surface of the steel sheet during hot rolling, so the lower limit of the slab heating temperature is preferably 1080 ° C.

The coiling temperature of the steel strip after hot rolling is 700 ° C.
It is necessary to: This is because if the coil is wound at a temperature higher than 700 ° C., the strain introduced during hot rolling is released, and it becomes difficult to uniformly and completely recrystallize it during annealing of the hot rolled sheet. If the winding temperature of the steel strip is too low, the steel sheet may crack, so the lower limit of the winding temperature is preferably 450 ° C.

The temperature of hot-rolled sheet annealing is 830 ° C. or higher and 870 ° C.
Must be less than. At annealing temperatures below 830 ° C,
This is because the structure of the hot-rolled sheet is not completely recrystallized, and when the temperature exceeds 870 ° C., the structure undergoes coarse grain growth, resulting in ridging characteristics with large variations.
The reason for setting the time for hot-rolled sheet annealing to 2 hours or more is 2
This is because if the annealing time is shorter than the time, a uniform recrystallized structure cannot be obtained and the variation in the ridging characteristics becomes large. Further, the upper limit of the annealing time is 10 hours from the saturation point of the ridging characteristics and the economical viewpoint.

[0014]

EXAMPLE A highly pure ferritic stainless steel having the chemical composition shown in Table 1 was melted and continuously cast into a 250 mm thick slab. This slab was hot-rolled, hot-rolled sheet annealed, further cooled and finally annealed to obtain a 0.94 mm thick product.

[0015]

[Table 1]

The slab heating temperature prior to hot rolling is 116
It was carried out at 0 ° C, and the hot-rolled finish plate thickness was 3.2 mm.
It was wound up at 0 ° C. Subsequent hot-rolled sheet annealing is 750.
It carried out between 1 degreeC and 900 degreeC for 1 to 10 hours. Test pieces were cut out from 10 positions of each of the obtained product plates, and a ridging test was performed on each test piece. FIG. 1 shows the results of measuring the ridging height when the hot-rolled sheet annealing time after hot rolling was fixed at 8 hours and the hot-rolled sheet annealing temperature was changed between 750 ° C. and 900 ° C. The circles in the figure represent the average value of the ridging height measurement, and the error bars represent the maximum and minimum values of the measurement. When the hot-rolled sheet annealing temperature is less than 830 ° C and exceeds 870 ° C, the ridging is high and the variation is large, whereas 830 ° C to 870 ° C.
The ridging is low and stable between ℃.

FIG. 2 shows the results of measuring the ridging height when the hot-rolled sheet annealing temperature was fixed at 850 ° C. and the hot-rolled sheet annealing time was changed from 1 hour to 10 hours. ○ in the figure
The mark shows the average value of the ridging height measurement, and the error bar shows the maximum value and the minimum value of the measurement. When the hot-rolled sheet annealing time is less than 2 hours, the ridging is deteriorated and the variation is large.
On the other hand, when the hot-rolled sheet annealing time is 2 hours or more, the ridging is low and stable.

[0018]

According to the present invention, it has become possible to manufacture a high-purity ferritic stainless steel sheet with a stable and low ridging.

[Brief description of the drawings]

FIG. 1 is a diagram showing a result of measuring a ridging height when a hot rolled sheet annealing time is set to 8 hours and a hot rolled sheet annealing temperature is changed between 750 ° C. and 900 ° C.

FIG. 2 is a diagram showing the results of measuring the ridging height when the hot-rolled sheet annealing temperature after hot rolling was 850 ° C. and the hot-rolled sheet annealing time was changed between 1 hour and 10 hours.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Sumio Suzuki 1-1 Tobata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka Inside Nippon Steel Corp. Yawata Works

Claims (1)

[Claims] 1. By weight%, Cr: 10 to 12%, C: 0.02% or less, N: 0.02% or less, Ti: 5 × (C + N) to 0.
A continuous cast slab of high-purity ferritic stainless steel containing 8% and the balance Fe and unavoidable impurities
It is heated to a temperature of 80 ° C or lower and hot-rolled to 700 ° C.
It is wound at the following temperature and the hot-rolled steel strip obtained is 830
A method for producing a highly pure ferritic stainless steel sheet having excellent ridging characteristics, which comprises performing hot-rolled sheet annealing in a temperature range of ℃ to 870 ° C for 2 hours or more, followed by cold rolling and annealing.