JPH0820844A - Ferritic stainless steel sheet excellent in workability and its production - Google Patents

Abstract

PURPOSE:To inexpensively produce a ferritic stainless steel excellent in wear resistance and workability while obviating the necessity of large amounts of alloying elements by incorporating specific amounts of C, Cr, Si, Mn, and Fe. CONSTITUTION:A steel, which has a composition consisting of, by weight, 0.07-0.1% C, 16-18% Cr, 0.5-0.75% Si, <=0.3% Mn, and the balance essentially Fe and satisfying Mn/Si <=0.5, is used. After a hot rolled plate is cold-rolled, the resulting sheet is annealed and temper-rolled at 6-15% draft. By regulating Mn content to <=0.3% and further regulating Mn/S to <=0.5, the formation of MnO-SiO2 inclusions extending in a rolling direction can be inhibited and the form of the inclusions can be formed into SiO2 hard to receive adverse effect on workability. By regulating the draft at temper rolling to 6-15%, elongation in the C direction becomes 6-12% and also desired Hv can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferritic stainless steel sheet having excellent workability, which is suitable as a material for a floppy disk center core, and a method for producing the same.

[0002]

2. Description of the Related Art The characteristics required for a floppy disk center core are (1) excellent wear resistance,
(2) Good magnetic properties (a ferromagnetic material)
, (3) excellent press formability, and (4) good corrosion resistance. Conventionally, as a material for such a floppy disk center core, SUS43 is generally used.
0 hard finishes have been used. However,
Since this type of core is subjected to severe drawing in the manufacturing process, when the above-mentioned SUS430 steel plate is used, cracks in the direction perpendicular to the rolling direction as shown in FIG. 1 often occur during press forming. .

As a solution to the above problem, Japanese Patent Laid-Open No. 63-143 has been proposed.
No. 87 discloses a steel structure of ferrite-martensite 2
A method has been proposed in which the phase structure (martensite content: 30 to 95%) is used and the ductility is improved with a predetermined hardness. Further, JP-A-64-19570 discloses a method for ensuring ductility by increasing the Si and Ni contents to reduce the reduction rate of hard rolling after cold rolling-annealing treatment. 240936
In the publication, there is proposed a method of increasing the Si, Mn, Cr, and Ni contents and similarly reducing the reduction rate in hard rolling after cold rolling-annealing treatment to secure ductility.

[0004]

However, although the former method in which the steel structure has a ferrite-martensite two-phase structure improves workability, the amount of martensite is as large as 30 to 95%, and therefore corrosion resistance is high. There was a problem that it was inferior to. In addition, the latter method of adding alloy elements such as Si, Ni, and Cr, etc., has a problem in that cost is increased because a large amount of expensive alloy elements are required. Therefore, an object of the present invention is to solve the above-mentioned problems in an advantageous manner, it is inexpensive and has corrosion resistance equivalent to that of SUS430 series.
Moreover, it is to propose a ferritic stainless steel sheet having excellent wear resistance and workability together with its advantageous manufacturing method.

[0005]

[Means for Solving the Problems] The floppy disk center core has a Vickers hardness (H
In v), a high hardness of 220 ± 10 is required. As a means for obtaining this hardness, there are methods such as (1) increasing the alloying element to harden the material, and (2) increasing the rolling reduction in temper rolling. However, if the reduction ratio of the temper rolling is increased to make it harder, the ductility decreases, so that cracks, particularly in the direction perpendicular to the rolling direction, are likely to occur during press molding of the floppy disk center core.

Therefore, in order to achieve the desired purpose,
It is important to design the alloy and set the rolling reduction considering the above (1) and (2). Therefore, with the above points in mind, the inventors have conducted extensive research to develop new materials, and as a result, Mn
It has been found that by limiting the amounts of Si and Si and their ratios within a predetermined range, a particularly large amount of alloying elements is not required and a desired hardness can be secured at a relatively low pressure ratio. The present invention is based on the above findings.

That is, the gist of the present invention is as follows. (1) C: 0.07 to 0.10 wt%, Cr: 16 to 18 wt%, Si: 0.50 to 0.75 wt%, Mn: 0.30 wt% or less is Mn / Si
Ferritic stainless steel sheet with excellent workability, characterized in that it is contained in the range of ≤0.50, and the balance is Fe and inevitable impurities.

(2) C: 0.07 to 0.10 wt%, Cr: 16 to 18 wt
%, And Si: 0.50 to 0.75 wt%, Mn: 0.30 wt% or less in the range of Mn / Si ≤ 0.50, the balance being Fe and inevitable impurities. A method for producing a ferritic stainless steel sheet having excellent workability, which comprises rolling, annealing, and temper rolling with a rolling reduction of 6 to 15%.

[0009]

In the present invention, the composition of ingredients and the production conditions are limited to the above ranges for the following reasons. C: 0.07 to 0.10 wt%; C is an element effective for strengthening the material, and if the content is less than 0.07 wt%, the mechanical strength is not sufficient, while if it exceeds 0.10 wt%, it becomes a grain boundary. Since the precipitation amount of carbides increases, causing deterioration in toughness and corrosion resistance, the range was limited to 0.07 to 0.10 wt%.

Cr: 16-18 wt% Cr is an element necessary for improving the corrosion resistance. To obtain this effect, at least 16 wt% or more is required, but if it exceeds 18 wt%, the cost of the material will increase, so the amount of Cr added is
It was limited to the range of 16-18 wt%.

Si: 0.50 to 0.75 wt%; Si is an extremely effective element as a strengthening component, but if the content is less than 0.50 wt%, sufficient strength cannot be expected, while 0.75 wt%
%, There is a disadvantage of increasing the cost of the material, so the content of Si is limited to 0.50 to 0.75 wt%.

Mn: 0.30 wt% or less; Mn, like Si, is an element effective for strengthening the material, so in the present invention, 0.30 wt% or less (preferably 0.10 to 0.
(30 wt%).

Mn / Si ≦ 0.5; By the way, Mn is an element that plays an important role in the morphology of inclusions, but the morphology of these inclusions has an extremely large effect on workability and extends in the rolling direction. The presence of A-type inclusions significantly deteriorates workability.
In this respect, the Mn content is suppressed to 0.30 wt% or less, and the Mn / S
When the ratio is 0.50 or less, the formation of MnO—SiO ₂ inclusions extending in the rolling direction can be suppressed, and the form of the inclusions can be changed to SiO ₂ with less adverse effect on the workability to improve the workability. Therefore, in the present invention, the amounts of Mn and Si satisfy the above-mentioned ranges and are contained within the range of Mn / Si ≦ 0.50.

In the present invention, as impurities, P,
S, Cu, Ni, Al, N, and O are allowed to be contained, but their contents are P ≦ 0.040 wt% and S ≦ 0.030 wt, respectively.
%, Cu ≦ 0.50 wt%, Ni ≦ 0.50 wt%, Al ≦ 0.150 wt%, N
It is desirable that ≦ 0.050 wt% and O ≦ 0.080 wt%.

-Quench reduction ratio: 6 to 15%; Fig. 2 shows the reduction ratio and the Hv of the steel plate during temper rolling for hardening when a steel plate satisfying the above-mentioned preferable composition range is manufactured. The relationship, and FIG. 3 shows the results of examining the relationship between Hv and elongation in the C direction in comparison with the conventional material. The chemical compositions of the test materials for these experiments were as follows: C: 0.08 wt%, Cr: 1
6.22wt%, Si: 0.64wt%, Mn: 0.30wt%, P: 0.033wt%,
S: 0.005 wt%, Ni: 0.06 wt%, Al: 0.001 wt%, Mn / Si: 0.47
, C: 0.06 wt%, Cr: 16.25wt%, Si: 0.32wt%
, Mn: 0.65 wt%, P: 0.035 wt%, S: 0.007 wt%, Ni: 0.08
It was wt%, Al: 0.001 wt%, Mn / Si: 2.03. From FIGS. 2 and 3, in the conventional material, Hv: 220 which is required as a floppy disk center core from the viewpoint of its wear resistance.
To obtain ± 10, rolling must be carried out at a reduction rate of 25 to 45%, but the elongation in the C direction of the steel sheet obtained at such a reduction rate is
It can be seen that it is extremely small at 1.0%. On the other hand, in this invention material, the rolling reduction required to obtain the desired Hv is 6 to 15
%, And the elongation in the C direction obtained at this time reaches 6 to 12%.

As described above, the invention material can obtain a desired Hv under a light pressure, and the El in the C direction at this time is remarkably excellent as compared with the conventional material, so that it cracks even in severe press forming. Can be eliminated. Therefore, in the present invention, the rolling reduction in temper rolling for hardening is limited to the range of 6 to 15% during the manufacturing process.

Other manufacturing conditions may be in accordance with ordinary methods and are not particularly limited.

Thus, it is possible to obtain a ferritic stainless steel sheet having excellent wear resistance and workability, but this steel sheet is not limited to the use only for floppy disk center core materials, but requires severe forming processing. Needless to say, it is suitable for all uses.

[0019]

Example A hot rolled sheet having the composition shown in Table 1 was cold-rolled at a rolling reduction of 67% to a sheet thickness of 0.36 mm, and then 780-
After annealing at 850 ° C, temper rolling for hardening was performed at various reduction ratios. Table 1 also shows the results of the examination of the hardness and the elongation in the L direction and the C direction of each of the obtained steel sheets. The test piece used was JIS Z2201 13B.
No.

[0020]

[Table 1]

As is clear from the table, all of the steel sheets obtained according to the present invention have an appropriate hardness of Hv of about 220, and further, not only the elongation in the L direction but also the elongation in the C direction.
It has a high value of 6.4% or more. On the other hand, the amount of C
No. 6, which is less than the proper range of this invention at 0.05 wt%, had a high C-direction elongation of 9.7%, but had a slightly low Hv of 198. Further, No. 8 having a large amount of Mn and thus having an Mn / Si ratio of 0.67, which exceeds the upper limit of the appropriate range, had a good Hv of 223, but C
Directional elongation is low at 3.6%. Furthermore, the amount of C is large, and Mn
Nos. 9, 10 and 11 having a large amount and therefore a high Mn / Si ratio are not only able to obtain an appropriate Hv, but also have an elongation in the C direction of 1.5 to 2.0%, which is extremely low.

[0022]

As described above, according to the present invention, it is possible to inexpensively obtain a ferritic stainless steel excellent in wear resistance and workability without requiring a large amount of alloying elements, and particularly for a floppy disk center core. It has a great effect as a material.

[Brief description of drawings]

FIG. 1 is a diagram showing a state of occurrence of cracks in a floppy disk center core.

FIG. 2 is a graph showing the relationship between the temper rolling reduction and Hv.

FIG. 3 is a graph showing the relationship between Hv and elongation in the C direction.

Claims (2)

[Claims] 1. C: 0.07 to 0.10 wt%, Cr: 16 to 18 wt%, Si: 0.50 to 0.75 wt%, Mn: 0.30 wt% or less in the range of Mn / Si ≤ 0.50, The balance is Fe and inevitable impurities, and is a ferritic stainless steel sheet with excellent workability. 2. C: 0.07 to 0.10 wt%, Cr: 16 to 18 wt%, Si: 0.50 to 0.75 wt%, Mn: 0.30 wt% or less in the range of Mn / Si ≦ 0.50, The balance is Fe and the composition of unavoidable impurities, hot-rolled sheet, after cold rolling,
A method for producing a ferritic stainless steel sheet having excellent workability, which comprises performing annealing and then temper rolling at a rolling reduction of 6 to 15%.