JPH0748628A - Production of austenitic stainless steel sheet having high surface luster - Google Patents

Abstract

PURPOSE:To produce an austenitic stainless steel sheet in which, even by annealing in an economically controllable atmosphere, the intergranular erosion of a base sheet is hard to cause in the subsequent picking stage and thus having a high surface luster. CONSTITUTION:An austenitic stainless steel hot rolled sheet is preliminarily subjected to mechanical descaling treatment, is then subjected to continuous annealing of holding it in an atmosphere of 1 to 15% oxygen content and at 950 to 1300 deg.C and recrystallizing it, is thereafter subjected to picking and cold rolling and then subjected to bright annealing. Thus, the austenitic stainless steel sheet excellent in buffing properties can be obtd.

Description

Detailed Description of the Invention

[0001]

INDUSTRIAL APPLICABILITY The present invention has a good surface gloss because it has no surface defects such as intergranular corrosion.
The present invention relates to a method for producing an austenitic stainless steel sheet.

[0002]

It is generally known that the surface gloss of an austenitic stainless steel cold-rolled sheet is improved as the number of surface defects of a mother sheet (hot-rolled sheet after pickling) is reduced. One of the surface defects in this mother plate is intergranular corrosion that occurs when the hot rolled plate is pickled. This intergranular corrosion is usually caused by intergranular erosion in which the de-Cr layer at the intergranular boundary generated by oxidation during hot-rolled sheet annealing performed in an economical atmosphere is preferentially dissolved during subsequent pickling. Then, it is thought to occur.

As a method for suppressing the intergranular corrosion of a mother plate, Japanese Patent Laid-Open No. 177135/1985 discloses a method in which annealing is carried out for a short time in an inert gas, a reducing gas or a vacuum, followed by rapid cooling. Is disclosed. However, there is a disadvantage in that it is inferior in economic efficiency because equipment for maintaining a specific atmosphere or vacuum is required.

[0004]

SUMMARY OF THE INVENTION Therefore, the present invention has as its object to solve the problems of the above-mentioned prior art, and even after annealing in an atmosphere that is economically easy to adjust, Since it is difficult for the grain boundary erosion of the mother plate to occur in the pickling step, the surface defects are not revealed, and therefore, the surface gloss is excellent, and a method for producing an austenitic stainless steel sheet is proposed. .

[0005]

The inventors conducted various experiments on austenitic stainless steel in order to solve the above problems. As a result, the scales produced during annealing are (Fe, Cr) 203 type and (Fe, Cr) 304 type, and when the scale produced during annealing mainly consists of (Fe, Cr) 304 type It was found that the larger the layer, the greater the grain boundary erosion of the mother plate. The mechanism is not clear, but the growth rate of (Fe, Cr) 304 type scale is (Fe, C
r) It is considered to be significantly faster than the 203 type scale.

Further, the higher the oxygen content in the annealing atmosphere, the less likely the scale to be (Fe, Cr) 203 type main body and (Fe, Cr) 304 type main body, and the same oxygen content rate in the atmosphere. However, the more scale that remains during hot rolling on the surface of the steel sheet, the more scale (Fe, C
r) It was also found that the type 304 tends to be the main subject. Although this mechanism is not always clear at present, in the case of the (Fe, Cr) 203 type scale, it is mainly Fe203 in the early stage of oxidation, and it is necessary for this scale to generate. It is necessary to have a large amount of oxygen in the atmosphere, and if the scale produced during hot rolling remains, it is difficult to supply the amount of oxygen required for the production of Fe203 scale to the surface of the base steel. Are considered to be related.

The present invention was developed based on the above experimental results and a discussion of these results.
That is, according to the present invention, a hot-rolled austenitic stainless steel sheet is mechanically descaled in advance and then kept in an atmosphere of oxygen content: 1 to 15% and temperature: 950 to 1300 ° C for 1 to 240 seconds. It is a method for producing an austenitic stainless steel sheet having excellent surface gloss, which comprises performing continuous annealing for recrystallization, pickling, cold rolling, and bright annealing.

[0008]

[Function] FIG. 1 shows hot-rolled SUS304 sheets that have been subjected to descaling treatment by shot blasting in advance and those that have not been subjected to this treatment, at 1150 ° C. in annealing atmospheres of various oxygen contents. It is the result of investigating the grain boundary erosion depth in the mother plate subjected to pickling after annealing for holding for seconds and the glossiness when performing bright annealing by further cold rolling after annealing. For comparison, without descaling, the temperature was raised to 1150 ° C in an atmosphere with an oxygen content of 5%.
Grain boundary erosion depth in the mother plate subjected to pickling after performing annealing for 30 seconds, and also about the results of investigation of glossiness when performing bright annealing by further cold rolling after annealing, the above investigation It is shown in FIG. 1 in comparison with the results.

According to the figure, when the hot-rolled sheet of SUS304 is descaled in advance and the oxygen content in the annealing atmosphere is 1% or more, the grain boundary erosion of the mother sheet becomes extremely small, and It can be seen that the glossiness after rolling is significantly improved. Further, this effect is exhibited even when the oxygen content is 15% or more, but if the oxygen content is increased more than this, the thermal efficiency is deteriorated and a large amount of NO _X is generated. On the other hand, if descaling is not performed in advance, even if the oxygen content in the annealing atmosphere changes, the size of the grain boundary erosion of the mother plate and the glossiness after cold rolling have almost no difference from those after the normal process. .

When the hot-rolled sheet of austenitic stainless steel is descaled in advance and then annealed in an atmosphere having an oxygen content of 1 to 15% as in the present invention, the annealing temperature and time are set to the mother plate. Has little effect on the grain boundary erosion depth and the glossiness after cold rolling. Therefore, the annealing temperature and time may be regulated by the recrystallization conditions of the hot rolled austenitic stainless steel. By the way, recrystallization is 95
It does not occur at a holding temperature of less than 0 ° C or less than 1 second. Also, 13
Holding above 00 ° C or above 240 seconds is economically disadvantageous.

Here, the descaling of the hot rolled sheet is limited to the mechanical treatment because the method of dipping the steel sheet in sulfuric acid or nitric hydrofluoric acid, which is usually used as a chemical treatment, is different from the case of the annealed sheet. Since there is almost no de-Cr layer on the surface of the plate, the dissolution of the base iron does not proceed, it takes a long time to de-scale and the productivity is inferior. Strain was introduced into the surface layer of
The reason is that the effect of facilitating the generation of the (Fe, Cr) 203 type Cr ₂ O ₃ scale can be expected because it promotes the diffusion of Cr. As this mechanical treatment, in addition to shot blasting, it is advantageous to introduce a crack into the scale with a skin pass, a leveler or the like.

As described above, in the present invention,
A hot-rolled austenitic stainless steel sheet was mechanically descaled in advance, and then continuously annealed by holding it at 950 to 1300 ° C for 1 to 240 seconds to recrystallize it in an atmosphere with an oxygen content of 1 to 15%. Then, by performing pickling, cold rolling, and bright annealing, it becomes possible to manufacture an austenitic stainless steel sheet having excellent surface gloss.

[0013]

[Examples] Hot-rolled sheet conforming to SUS304 having a plate thickness of 4 mm, subjected to descaling treatment by iron ball shot blasting with a projection density of 50 kgf / m ² and a projection speed of 50 m / s, and a descaling treatment In the butane gas atmosphere with various oxygen contents, 950 to 1300 ° C and 1 to 240 sec.
After descaling by iron ball shot blasting with a projection density of 60 kgf / m ² and a projection speed of 60 m / sec, the sample was immersed in 80 g sulfuric acid: 200 g / l aqueous solution for 60 seconds. Then 60 ℃ nitric acid: 150g / l and hydrofluoric acid: 30g
The intergranular erosion depth when immersed in an aqueous solution of 1 / l for 60 seconds was investigated. Furthermore, the glossiness when the bright annealing was performed at 1150 ° C. for 1 second in an ammonia decomposition gas after finishing to 0.7 mm thickness by ordinary cold rolling was also investigated.

In addition, as a comparative example, the grain boundary in the case where the same treatment as described above was performed after performing the annealing at 1150 ° C. for 30 seconds in an atmosphere having an oxygen content of 5% without performing the descaling treatment The erosion depth and gloss were also investigated. The results of these investigations are shown in Table 1.

[0015]

[Table 1]

As shown in the table, sample Nos. 5 to 7 in which the oxygen content in the annealing atmosphere was less than 1% even if the descaling treatment was performed before the annealing, and the descaling treatment was not performed before the annealing. Sample Nos. 8 to 14 showed almost the same results as the steel sheets obtained by the conventional method with respect to the grain boundary erosion depth and the glossiness. On the other hand, sample Nos. 1 to 4 obtained according to the present invention have a grain boundary erosion depth of Comparative Example (Sample Nos. 5 to 1).
It was less than half that of 4) and the glossiness was more than 1.5 times.

[0017]

EFFECTS OF THE INVENTION According to the present invention, since a highly protective scale can be generated during annealing to suppress the growth of the Cr-free layer, grain boundary erosion hardly occurs even if pickling is performed. By cold rolling and bright annealing the mother plate, austenitic stainless steel having excellent surface gloss can be manufactured at low cost. Further, according to the manufacturing method of the present invention, collapse of the grain boundary erosion grooves and the like are reduced, so that an austenitic stainless steel sheet having excellent corrosion resistance can be obtained. Further, by cold rolling, annealing, pickling and skin-passing the mother plate, it is possible to manufacture an austenitic stainless steel plate having excellent buff polishing properties.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between an oxygen content rate in an annealing atmosphere, a grain boundary erosion depth, and a glossiness.

Claims (1)

[Claims] 1. A hot-rolled austenitic stainless steel sheet is mechanically descaled in advance, and then the oxygen content is:
1 to 15% and temperature: 1 to 24 in the atmosphere of 950 to 1300 ° C
A method for producing an austenitic stainless steel sheet having good surface gloss, which comprises performing continuous annealing for holding for 0 second to recrystallize, followed by pickling, cold rolling, and bright annealing.