JPH06198305A - Production of austenitic stainless steel strip excellent in surface property - Google Patents

Abstract

PURPOSE:To provide a method for manufacturing an austenitic stainless steel strip minimized in surface flaws. CONSTITUTION:A cast billet is manufactured by continuously casting of an austenitic stainless steel contg., by wt.%, <=0.001% S, <=0.0005wt.% Pb, <=0.0005wt.% Bi, 5 0.0010wt.% Zn. Successively, after heating the cast billet, a 1st pass of hot rolling at a biting temp. of 1210-1270 deg.C and draft of <=20% is executed and a hot rolled steel strip is made by hot rolling the cast billet to a prescribed thickness, the surface and back faces of the hot rolled steel strip are scarfed at the cutting quantity of >=10mum per one face and cold rolling at the total draft of >=40% and annealing are executed.

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 an austenitic stainless steel strip with few surface defects.

[0002]

2. Description of the Related Art Conventionally, in the production of austenitic stainless steel strip, melting is performed by an electric furnace mainly using scrap, and a slab is produced by continuous continuous casting (CC). Next, surface grinding is performed by a grinder to remove surface defects of the slab, and hot-rolled steel strip (hereinafter simply referred to as hot-rolled steel strip) is manufactured by hot rolling. At this time, the width of 0.5 mm on the front and back of the hot rolled steel strip
Hereinafter, since linear fine flaws having a length of about 5 to 100 mm are likely to occur, it is necessary to perform surface grinding again to remove these surface defects in a subsequent process, which is a major factor for increasing manufacturing cost. It was.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for obtaining an austenitic stainless steel strip which can omit surface grinding of a slab and a hot rolled steel strip and has few surface defects. is there.

[0004]

In order to solve the above problems, the present invention provides a chemical composition of austenitic stainless steel,
In particular, the impurity element, the trapping temperature and the rolling reduction in the initial pass in hot rolling are specified, and the amount of surface ablation for removing the surface flaw of the hot rolled steel strip is regulated.

That is, the gist of the present invention is
% By weight, C: 0.15% or less, Si: 2.0% or less,
Mn: 5.0% or less, P: 0.04% or less, S: 0.0
01% or less, Cr: 15 to 25%, Ni: 5 to 20%,
Pb: 0.0005% or less, Bi: 0.0005% or less, Zn: 0.0010% or less, and if necessary,
Mo: 5% or less, Cu: 5% or less of 1 type or 2 types, the balance is Fe and unavoidable impurities and the austenitic stainless molten steel is continuously cast to produce a slab, which is subsequently cast. After heating the piece, the biting temperature is 1210-1
Hot rolling of the first pass at 270 ° C. and a reduction rate of 20% or less is performed, followed by hot rolling to a predetermined plate thickness to form a hot rolled steel strip, and subsequently the hot rolled steel strip The surface properties are characterized in that the front and back surfaces are subjected to fusion cutting with a cutting amount per surface of 10 μm or more, followed by cold rolling with a total reduction of 40% or more, and subsequent annealing. The method of manufacturing an excellent austenitic stainless steel strip of.

The present invention will be described in detail below along with its operation.

[0007]

First, the reason why the chemical composition of steel is limited as described above in the present invention will be explained. Although C is harmful to the corrosion resistance of stainless steel, it is the most effective component for increasing the strength, and is set to 0.15%. If it exceeds 0.15%, chromium carbides are likely to be formed significantly,
Corrosion resistance is significantly deteriorated.

Si is necessary as a deoxidizing agent in steel making, but if it exceeds 2.0%, the ferrite forming ability becomes strong,
It deteriorates hot workability. Therefore, the upper limit is 2.0%. Mn is a component that stabilizes the austenite phase and is effective as an inexpensive Ni substitute component, but it deteriorates corrosion resistance and oxidation resistance. Therefore, the upper limit is set to 5.0%.

The lower the content of P is, the better it is in terms of corrosion resistance and hot workability. However, the reduction is accompanied by an increase in cost, so the upper limit was made 0.04% from the viewpoint of industrial economic efficiency. S is
It is an important component for preventing surface defects of the present invention. From the detailed investigation of the surface flaw generation process, it was found that the flaw was generated in the initial pass of the hot rolling, and that this flaw originated from the grain boundary crack of the continuously cast slab. It is widely known that when sulfides are precipitated at the austenite grain boundaries, the grain boundary strength is reduced and cracks tend to be the starting points.
Therefore, it is considered that lowering S is effective for preventing sulfide precipitation at grain boundaries.
It was found that the content of 0.001% or less makes it possible to reduce fine linear surface flaws in combination with the hot rolling conditions described later, and the upper limit was determined.

Cr has a great effect on corrosion resistance and ferrite formation. If it is less than 15%, the corrosion resistance deteriorates to 25
%, The amount of ferrite increases and the workability deteriorates.
Therefore, the range of Cr is limited to 15 to 25%. Ni
Is a component that stabilizes the austenite phase and improves drawability. If it is less than 5%, the austenite phase is unstable and the drawability deteriorates. However, if it exceeds 20%, it becomes very expensive, so the range of Ni is limited to 5 to 20%.

Pb, Bi and Zn are important components for preventing surface defects of the present invention, and are highly purified to 0.0005% or less, 0.0005% or less and 0.0010% or less, respectively. Similar to S, Pb, Bi, and Zn easily segregate at the grain boundaries of steel, form a low-melting-point phase, and significantly reduce the grain boundary strength, causing intergranular cracks in hot rolling and causing frequent surface defects. . Therefore, particularly strict control is required, and each is limited as described above.

Mo and Cu improve the corrosion resistance.
One type or two types are contained in the range of 5% or less.
If it exceeds 5%, the workability deteriorates, so 5% was made the upper limit. Next, the relationship between the bite temperature of the first pass and the surface flaw in the hot rolling of the slab, which is another feature of the present invention, will be described. In the present invention, the bite temperature in the first pass was limited to 1210 to 1270 ° C. in the hot rolling of the slab, but the upper limit temperature was set to 1270 ° C. When the temperature exceeds the same, scale formation is rapidly accelerated. The reason is that the surface roughness after hot rolling is caused, and the lower limit temperature is set to 1210 ° C., because if it is lower than the same temperature, the deformation resistance in hot rolling becomes high and the linear surface defects are increased. is there. The rolling reduction in the first pass in hot rolling was limited to 20% or less, but the upper limit of the rolling reduction was 20%.
% Means that when the rolling reduction exceeds the same, grain boundary cracking increases rapidly,
This is because linear surface defects frequently occur after hot rolling.

After the hot rolled steel strip is wound,
Alternatively, after performing annealing as necessary, descaling is performed by a combination of mechanical and chemical methods. The amount of surface ablation by descaling for removing surface defects requires a depth of 10 μm or more. When the amount of fusing is less than this, extremely fine linear flaws during hot rolling remain on the surface of the steel strip, deteriorating the surface quality after cold rolling. Although the total reduction ratio of cold rolling was regulated to 40% or more, this value is a necessary condition for ensuring the surface gloss as a stainless steel plate.

[0014]

EXAMPLES Next, the superiority of the present invention will be specifically described with reference to Examples and Comparative Examples. Table 1 shows the chemical compositions of the present invention and comparative examples, and Table 2 shows the biting temperature of the first pass of hot rolling, the rolling reduction, the amount of hot-rolled steel strip, and the linear surface after cold rolling and annealing. Indicates the occurrence status of defects.

All materials were melted in an electric furnace, which is a normal refining process for stainless steel, and then refined by an argon / oxygen decarburization treatment, and continuously cast to obtain plate widths 1230 to 15
It was a 60 mm cast piece. The surface of the slab was not ground, and after soaking, hot rolling was performed under the conditions shown in Table 1, shot blasting and descaling with a hydrofluoric acid solution, and the amount of fusing was measured by a gravimetric method. The amount of smelting was adjusted by changing the pickling time. Then, cold rolling and annealing were performed, and the linear surface flaws of the steel strip were observed. The evaluation of linear surface flaws was performed by cutting out the top and bottom of the steel strip to a length of 0.5 m, counting the total number of flaws on the surface, summing them, and expressing the number of occurrences per 1 m of length.

Inventive Example No. In Nos. 1 to 8, no linear surface flaws were observed on the surface of the steel strip after cold rolling and annealing, indicating extremely good surface properties. No. 1 with Mo or Cu added. Nos. 1, 5 and 8 were not added. 2, 3, 4, 6 and 7. Comparative Example No.
In Nos. 9 to 12, the impurity elements Pb, Bi, Zn, and S were beyond the scope of the present invention, and the initial pass trapping temperature of hot rolling, the rolling reduction, and the descaled ablation amount of the hot-rolled steel strip were true. It is outside the scope of the invention, and surface defects frequently occur in cold-rolled and annealed sheets.

[0017]

[Table 1]

[0018]

[Table 2]

[0019]

EFFECTS OF THE INVENTION By controlling the main components and impurity elements of austenitic stainless steel, and further by controlling the hot rolling conditions and the descaling conditions of the hot rolled steel strip as described above, surface treatment of the slab and hot rolled steel The surface maintenance of the strip can be omitted, and a cold-rolled / annealed steel strip having a good surface property can be stably obtained at low cost, and an industrially effective effect is brought about.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuro Takeshita 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Co., Ltd. Technology Development Division (72) Kenji Yamada 20-1 Shintomi, Futtsu-shi, Chiba Made by Shinnihon Iron & Steel Co., Ltd.

Claims (2)

[Claims] 1. By weight%, C: 0.15% or less, Si: 2.0% or less, Mn: 5.0% or less, P: 0.04% or less, S: 0.001% or less, Cr : 15 to 25%, Ni: 5 to 20%, Pb: 0.0005% or less, Bi: 0.0005% or less, Zn: 0.0010% or less, the balance being austenitic stainless molten steel composed of Fe and unavoidable impurities Is continuously cast to produce a slab, and the slab is subsequently heated, and the biting temperature is set to 1210 to 127.
Hot rolling of the first pass at 0 ° C. and a rolling reduction of 20% or less is performed, and then hot rolling is performed to a predetermined plate thickness to form a hot rolled steel strip. The surface properties are characterized in that the front and back surfaces are subjected to fusion cutting with a cutting amount of 10 μm or more per one surface, followed by cold rolling with a total reduction of 40% or more, and subsequent annealing. Of excellent austenitic stainless steel strip. 2. The composition of molten austenitic stainless steel is characterized in that the composition according to claim 1 further contains 1% or 2% by weight of Mo: 5% or less and Cu: 5% or less. A method for producing an austenitic stainless steel strip having excellent surface properties.