JPS5980753A - Ferritic stainless steel plate producing no stretcher strain - Google Patents

Abstract

PURPOSE:To obtain the titled low-cost steel plate producing no stretcher strain even in a multi-step drawing stage by providing a specified composition consisting of C, Si, Mn, Cr, N, Fe and inevitable impurities and having specified relation. CONSTITUTION:A ferritic stainless steel plate producing no stretcher strain is obtd. by providing a composition consisting of, by weight, <=0.08% C, <=0.70% Si, <=1.00% Mn, 15-20% Cr, 0.04-0.12% N (C+N=0.08-0.15%) and the balance Fe with inevitable impurities. >0.08% C deteriorates the corrosion resistance and toughness and hardens the material. >0.70% Si hardens the material and reduces the elongtion. >1.00% Mn hardens the material. <15% Cr does not give the desired corrosion resistance, and >20% Cr makes looping remarkable. N and C+N prevent the production of a stretcher strain in said ranges, yet more than the uppr limits of N and C+N harden the material.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ferritic stainless steel sheet that does not generate stretcher strain even in a multi-stage drawing process.

In recent years, 5US304.5US301. and 5US43
The demand for thin stainless steel sheets, represented by 0, continues to increase9, and in particular, their use as materials for general durable consumer goods is expanding.

In particular, 5US430 steel is similar to 5US304 and 5US3
Since it is cheaper than 01 Chime, it is used over a wide range of areas.

By the way, in most cases, these stainless steel plates require press working when used, but in this case, 5US430 steel cannot be used with other 5US304 or 5US
Unlike 301 steel, L/X 7111 exhibited an inconvenient phenomenon in which stretcher strain occurred during machining, impairing the appearance of the product. However, in reality, when producing 5US430 steel plate, the occurrence of stretcher strain can be prevented by applying temper rolling after the cold rolling, annealing, and pickling processes, so there is no problem with normal pressing. There wasn't.

However, in the case of multi-step drawing that requires intermediate annealing, the material hardens during processing, so if intermediate annealing is performed in the middle of pressing, the effect of skin pass rolling applied to the material will disappear. There is a problem in that a noticeable stretcher is generated and a large amount of polishing cost is required to remove the stretcher.

From the above-mentioned viewpoint, the present inventors aimed to obtain a stainless steel sheet that does not generate stretcher strain even in a multi-stage drawing process and is inexpensive. As a result of repeated basic studies and research on the effects of

In other words, stretcher strain is mainly caused by C and N, especially N, dissolved in the steel, and can be completely explained from a dislocation theory.To prevent this, Al+
Although it is known that methods of fixing N by adding Ti or reducing N as much as possible by limiting the manufacturing atmosphere are effective,
They discovered a new fact that when more than a certain amount of N is added, the elongation at yield point decreases and stretcher strain is eliminated, contrary to the conventional wisdom.

Figure 1 shows the relationship between the amount of N in ferritic stainless steel and stretcher strain (yield point elongation).
As shown in Figure 1, N
If the amount is about 0.3% (hereinafter, the percentage indicating the component ratio is 9% by weight) or less, the conventional wisdom is that i-, fl
) The yield point elongation increases as N it increases, but
It can be seen that when Nff is further increased, the yield point elongation decreases and the stretcher strain is eliminated, contrary to the conventional wisdom.

Therefore, this invention was made based on the above knowledge, and the composition of the ferritic stainless steel copper plate is as follows: C: 0.08% or less, St: 0-709b or less.

Mn: 1.00% or less, Cr: 15-20%, N:
0.04-0.12% (however, C+N: 0.08-0.15%), F
e and unavoidable impurities: the remainder, and is characterized in that the generation of stretcher strain is prevented by forming the following.

Next, in the ferritic stainless steel of the present invention,
The reason why the amounts of each component are limited to the above ranges will be explained.

(Al C The C component is one of the inevitable impurities accompanying steel, and is an element that has a large effect on the corrosion resistance and toughness of ferritic stainless steel, but if its content exceeds 0.08%, the corrosion resistance and toughness will deteriorate. Since the toughness deteriorates and the material hardens, making it unsuitable for use as a steel plate for press working, the content was set at 0.08% or less.

(bl 5i Si component is an element necessary to improve the cleanliness of steel as a deoxidizing agent. Although it is desirable to have a large amount of Si dispersion in order to recover Cr, it is not necessary to contain more than 0.70%.) Since this would cause the material to harden and reduce its elongation, the content was set at 0.70% or less.

(bl Mn The Mn component also has a deoxidizing effect like the Si component,
Furthermore, it also has the effect of removing mud from the mud, but 1
．． If the content exceeds 0.00%, the material will harden and become unsuitable for press forming steel sheets, so the content should be reduced to 1.00%.
I concluded that it was less than 00%.

(di Cr The Cr component is an important element that determines the corrosion resistance of stainless steel, but if its content is less than 15%, the desired corrosion resistance cannot be obtained; on the other hand, if it is contained more than 20%, Since roving (also called ridging, wrinkle-like unevenness that occurs in the rolling direction after press working) becomes noticeable, the content was increased to 15 to 20%.

(el N As mentioned above, when the N content is less than 0.04%, the yield point elongation of the steel increases as the N content increases, causing strain strain. %
Above this, the yield point elongation decreases to such an extent that stretcher strain does not occur. However, if the N content exceeds 0.12%, the steel will harden significantly and
Since it causes blowholes, its content is set at 0.04 to 0.12%.

lf+c+N Figure 2 is a diagram showing the relationship between the (C+N) content and elongation of ferritic stainless steel.As is clear from Figure 2, (c+N)1 is less than 0.08%. If the amount exceeds 0.15%, roving becomes noticeable, and the elongation deteriorates significantly even if the amount exceeds 0.15%. For the above reasons, (C+
N) The amount was added to 08 to 0.1596.

It goes without saying that the steel sheet of the present invention can be manufactured by ordinary processes such as @casting, hot rolling, and cold rolling.

Next, the present invention will be explained by examples and in comparison with comparative examples.

Examples First, steel plates 1 to 1 were finished to a plate thickness of 'Q, 7 m, having the compositions shown in Table 1, respectively, by ordinary mm casting, hot rolling, cold rolling and annealing. 13 were manufactured.

Then, the yield point elongation of each of these steel plates was measured, and the results are also shown in Table 1. The yield point elongation was measured by automatically drawing a load-elongation curve in a commonly performed tensile test, and measuring the permanent elongation until yield completion based on the obtained curve diagram.

Furthermore, the results of performing a multi-stage patterning process on each of the blunt roots and training the occurrence of stretcher strain are also shown in Table 1 above.

In the drawing 9 caloe test, the press drawing ratio of the first step: 0.55%, the press drawing ratio of the second step: 0.89%, and the press drawing ratio of the third step: 0.90%.

Press squeeze! After performing 11, intermediate annealing was performed by holding at 830°C for 1 minute and then cooling, and then in the fourth step, a four-step drawing with a breath drawing ratio of 0.92% was performed, as shown in Figure 3. This was done by creating a spray gun. Incidentally, FIG. 3 also schematically shows the state in which the stretcher strain appears. ! Furthermore, in Table 1, the occurrence status of stretcher strain is indicated by ○ if no stretcher strain occurs and fc, and by X if it occurs significantly.

From the results shown in Table 1, all of the steel plates 1 to 9 of the present invention had an elongation at yield of 1.0% or less.

It is said that if the yield point elongation is about 1% or less, stretcher strain, which becomes a practical problem, will not occur, and it can be seen that satisfactory results were obtained even in the 1 stretcher strain occurrence condition test.

On the other hand, in the conventional steel sheet in which both the N and M contents were lower than the range of the steel sheet of the present invention, the elongation at yield point was significantly higher, and significant stretcher strain occurred.

As described above, according to the present invention, it is possible to obtain a ferritic stainless steel sheet that effectively prevents stretcher strain by simply increasing the N content in the steel. Even in the case of process drawing, industrially useful effects such as eliminating the need for polishing to remove stretcher strains are brought about.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between Ni in ferritic stainless steel and elongation at yield point, Figure 2 is a diagram showing the relationship between Ni in ferritic stainless steel and elongation at yield point.
Fig. 3 is a schematic diagram showing the spray gun obtained by four-step press drawing and its stretcher strain generation situation. Applicant Nippon Stainless Co., Ltd.

Claims (1)

[Claims] C: 0.08% or less, St: 0.7Q qb or less, Mn: 1.00% or less, Cr: 15-2'O%,
A stretcher characterized by containing N: 0.04-0612% (however, C+N: 0.08-0.15%), Fe and unavoidable impurities: the remainder (% in the above mold) Ferritic stainless steel plate that does not generate strain.