JPH09227999A - Ferritic stainless steel sheet excellent in ridging resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the ridging resistance of a ferritic stainless steel by prescribing the amt. and size of precipitates in a steel. SOLUTION: At first, this steel is incorporated with Cr by >=11wt.% from the viewpoint of corrosion resistance. Since Ti plays an important roll for suppressing the generation of ridging, the formation of the sulfide, carbide and nitride thereof is effective, and particularly, in the case of >=3Ti/(C+N+S), its ridging resistance is remarkably improved. Then, the carbide + nitride + sulfide having <=3μm grain size are present by >=1 piece per (dmean )<2> in the case the average grain size of the steel sheet is defined as dmean , and the volume ratio thereof is regulated to <=0.5%. This is because the precipitates having <=3μm grain size prevent the formation of (100) colonies and a band-shaped structure at the time of recrystallization after cold rolling suppresses the generation of ridging. Furthermore, by prescribing the number and volume ratio of the above precipitates, its ridging resistance can furthermore be improved.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a ferritic stainless steel sheet having excellent ridging resistance.

[0002]

2. Description of the Related Art Ferritic stainless steel is a material having excellent corrosion resistance and oxidation resistance and is widely used in various industrial fields. However, when deep drawing is performed by pressing or the like in the state of a steel sheet, it has a drawback that rough surface defects called ridging are likely to occur.
It was said to be unsuitable for applications that require severe processing such as deep drawing.

On the other hand, various techniques aimed at improving ridging resistance have been disclosed. They are roughly classified into (1) a technology focusing on component elements and (2) a technology focusing on manufacturing processes. (1) Regarding the technique focusing on the component elements, see Japanese Patent Laid-Open No.
No. 0-24913, C: 0.03 to 0.08 wt.
%, N ≦ 0.01 wt%, S ≦ 0.008 wt%, P ≦
0.03wt%, Si ≦ 0.4wt%, Mn ≦ 0.5w
t%, Ni ≦ 0.3 wt%, Cr: 15 to 20 wt%,
Disclosed is a ferritic stainless steel containing Al: N × 2 to 0.2 wt%, which is composed of the balance Fe and inevitable impurities and has excellent workability.

(2) Regarding the technique focusing on the manufacturing process, Japanese Patent Laid-Open No. 55-141522 discloses a ferritic stainless steel slab containing Al at 950 ° C. or higher.
A method for producing a ferritic stainless steel with remarkably little ridging, which is characterized by performing hot rolling after holding at a temperature of 00 ° C. or less, is disclosed.

[0005]

In these techniques disclosed heretofore, the effect of ridging resistance cannot be said to be sufficient, and the ridging resistance can be obtained only by the conventionally disclosed raw material components and hot rolling conditions. It was difficult to stably obtain a good ferritic stainless steel of In view of such a current situation, the inventors of the present invention have conducted extensive studies for many years, and as a result, it is very effective to control the amount and size of precipitates in steel for improving ridging resistance. I came to find a thing.

An object of the present invention is to provide a ferritic stainless steel sheet having excellent ridging resistance based on this finding.

[0007]

The present invention provides a ferritic stainless steel sheet containing 11 wt% or more of Cr with a weight ratio of Ti / (C + N + S) ≧ 3 and a grain size of 3 μm.
One or more of the following (carbide + nitride + sulfide) exists per (d _mean ) ² when the average grain size of the steel sheet is d _mean, and the volume ratio of these (carbide + nitride + sulfide) is Provided is a ferritic stainless steel sheet excellent in ridging resistance, which is characterized by being 0.5 wt% or less.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. Cr: Cr is a very effective element for corrosion resistance. Since the effect becomes remarkable at 11 wt% or more, the lower limit is 11 w.
t%. No upper limit is specified, but 50
If the content exceeds 50 wt%, not only the hot strength increases but also the cold ductility deteriorates, making it difficult to manufacture. Therefore, it is preferably 50 wt% or less.

Ti: Ti is a very important element in the present invention. As described below, the size and distribution of precipitates are controlled to prevent colonies and band-like texture growth that cause ridging phenomena that easily occur in ferritic single phase steel during recrystallization during annealing after cold rolling. Contribute to. In particular, the formation of Ti sulfides, carbides, and nitrides is effective. In FIG.
6.4 wt% Cr steel (Fe-16.4 wt% Cr-0.
4 wt% Si-0.2 wt% Mn-0.005 wt% C
-0.009 wt% N-0.003 wt% N-0.30
wt / P-0.50 wt% Mo) Ti / (C + N) which affects the ridging resistance when the Ti amount is variously changed.
Although the influence of + S) is shown, it can be seen that when Ti / (C + N + S) is 3 or more, the ridging resistance is remarkably excellent.

One (d _mean ) ² of (carbides + nitrides + sulfides) having a grain size of 3 μm or less is present per (d _mean ) ² when the average grain size of the steel sheet is d _mean, and their volume ratio is 0.5 wt. It is the technology that forms the basis of the present invention that the content is not more than%. This is because a precipitate having a particle size of 3 μm or less is prevented from forming a (100) colony or a band-like structure during recrystallization after cold rolling, and the occurrence of ridging is suppressed. At this time,
The size (particle size) of the precipitate must be 3 μm or less. This is effective at the time of recrystallization when it exceeds 3 μm (10
0) This is because the formation of colonies and band-shaped tissues cannot be prevented, and the effect of the present invention cannot be obtained.

In FIG. 2, Fe-18.1 wt% Cr-0.4
wt% Mn-0.009 wt% C-0.012 wt% N
The ridging score for (0.003 wt% S-0.20 wt% Ti) (carbide + nitride + sulfide) number / (d _mean ) ² was shown. As shown in FIG. 2, from the viewpoint of improving the ridging resistance, the number of precipitates should be 1 or more per (d _mean ) ² when the average crystal grain size is d _mean . If it is less than that, the precipitate does not effectively act to improve the ridging resistance.

The volume of these precipitates is 0.5.
Must be below wt%. This is because if it exceeds 0.5 wt%, the corrosion resistance, especially the pitting corrosion resistance, tends to deteriorate. Here, for the precipitate, carbide, nitride,
There is no limitation as long as the conditions of the present invention are satisfied regardless of whether sulfides are used alone or in combination.

The ferritic stainless steel contains Si, Mn, Al, Mo, Ni, Cu, Nb, V, in order to improve various properties such as corrosion resistance, oxidation resistance and mechanical properties.
Various elements such as W, Ca, Mg, B, P, Ta and Zr are added, or these elements and O, As, Bi, Sb and the like are mixed as unavoidable impurities. Basically, if the conditions of the present invention are satisfied, there is no problem in adding or mixing these components, and therefore there is no limitation.

The ferritic stainless steel sheet excellent in ridging resistance of the present invention is generally manufactured industrially by the following method. After smelting, a slab having a thickness of about 160 to 260 mm is obtained by a continuous casting method. At this time,
From the viewpoint of the precipitation morphology (size, distribution) of carbides, nitrides, and sulfides, preferably high speed casting (for example, casting speed is 0.7 m
/ Min or more) is preferable. After that, the slab is hot-rolled into a hot-rolled steel strip having a plate thickness of about 1.5 mm to 6 mm.
At this time, the slab soaking temperature is preferably 1200 ° C. or lower from the viewpoint of the size and distribution of the deposits, which is the point of the present invention. From the viewpoint of fine precipitation of TiC and TiN, the finish temperature of rough rolling during hot rolling is from 1050 ° C to 950 ° C.
Is preferable, and the rolling reduction is preferably 30% or more for at least one pass in rough rolling. Generally, the hot-rolled steel strip obtained is subjected to recrystallization annealing. Although the temperature varies depending on the amount of alloying elements, in order to obtain the effect of the present invention, if it exceeds 1150 ° C, The temperature is preferably 1150 ° C. or lower because coarsening or re-dissolution of carbon / nitride precipitated during hot rolling tends to occur. The annealing of the hot-rolled steel strip is not essential, and the present invention can be achieved by performing cold-rolling as it is. When it is used as a cold rolled steel sheet, it is further subjected to cold rolling and recrystallization annealing. In particular, regarding recrystallization annealing, from the viewpoint of precipitate morphology (size and distribution), which is the effect of the present application, 105
The temperature is preferably 0 ° C. or less, and the average crystal grain size is preferably 150 μm or less.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments.
30 kg of various alloys shown in Table 1 were melted in a laboratory, and a hot-rolled plate having a plate thickness of 4 μm was formed by known hot rolling. The hot-rolled sheet thus obtained was annealed after recrystallization and then descaled to a sheet thickness of 0.7 μ
After cold rolling to m, recrystallization annealing was performed to produce a cold rolled annealed plate.

The ridging resistance was evaluated by 20w in the rolling direction.
The degree of ridging generated on the surface of the steel sheet after applying t% tensile strain was evaluated. Observation of precipitates is performed by SEM, and
The number of observations was measured by observing 00 fields. The average crystal grain size was determined by a cutting method using an optical microscope. From both
(D _mean ) ^{2 The} number of precipitates having a particle size of 3 μm or less per area was determined. Table 2 shows the ridging resistance evaluation results. It can be seen that the invention examples are remarkably excellent in ridging resistance in any case. On the other hand, it can be seen that the ridging resistance is inferior when the number of precipitates having a size of 3 μm or less is small or when Ti / (C + N + S) is less than 3.

[0017]

[Table 1]

[0018]

[Table 2]

[0019]

According to the present invention, Ti / (C + N + S)
Is 3 or more and the average crystal grain size is d_meanAnd
When carbides, sulfides and nitrides with a particle size of 3 μm or less
_mean) ^Two Blow by having more than one per
It can significantly improve the resistance to ridging of stainless steel.
Now you can do it.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between Ti / (C + N + S) and ridging scores.

[Fig. 2] (Carbide + Nitride + Sulfide) Number / (d _mean )
⁶ is a graph showing the relationship between ² and the ridging score.

Claims (1)

[Claims] 1. A ferritic stainless steel sheet containing 11 wt% or more of Cr, in a weight ratio of Ti / (C +
In N + S) ≧ 3, particle size 3μm following when the average crystal grain size of the steel sheet and d _{me an,} is (carbides + nitride + sulfide) (d
_mean ) 1 or more per ^{2 and} a volume ratio of (carbide + nitride + sulfide) is 0.5% or less, a ferritic stainless steel sheet excellent in ridging resistance.