JPS58224113A - Production of austenitic stainless steel plate with which earring hardly arises - Google Patents

Abstract

PURPOSE:To decrease the earring that arises during deep drawing, by subjecting austenitic stainless steel to hot rough rolling then to hot finish rolling at a specific draft and a biting temp. followed by cold rolling without annealing. CONSTITUTION:A steel ingot is subjected to hot rough rolling then to hot finish rolling at the draft and biting temp. in the range enclosed with the points A, B, C, D, E, A in the figure in the stage of deep drawing the plate or strip of austenitic stainless steel. The hot-rolled steel is bitten in a cold rolling mill in a -15-70 deg.C temp. range without annealing and is subjected to deep drawing by cold rolling. The deep drawn product is obtd. in a high yield without generation of earring in the product.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an austenitic stainless steel sheet or a copper strip (hereinafter simply referred to as a steel sheet) in which earrings generated during deep drawing are significantly reduced.

Conventionally, it is well known that deep drawability of ferritic steels such as ordinary steel sheets and chromium-based stainless steel sheets has a strong correlation with the plastic strain ratio (r value), and that the larger the r value, the better the deep drawability. There is. Furthermore, it is said that with regard to earrings in which the end portion of the cup exhibits a fan-like uneven shape when cylindrical deep drawing is performed, the smaller the in-plane anisotropy of the r value is, the smaller the earring becomes.

On the other hand, in austenitic stainless steel sheets such as SUS 301 and 8US 304, the deep drawability is mainly influenced by the behavior of the work hardening index (n value).

The increase or decrease in the n value depends on the generation status of deformation-induced martensite, and therefore the stability of the austenite phase, that is, Ni,
The balance of alloy components such as Mn+Cr, C, and N greatly influences workability. For this reason, conventional research on workability has focused on adjusting the alloy components in a well-balanced manner and finding a preferable n value for workability. For this reason, the deep drawing workability is not as good as the behavior of the r value, and little attention has been paid to the behavior of the r value, and in particular, the in-plane anisotropy of the r value and earrings have not been studied at all.

The object of the present invention is to significantly reduce earrings that occur during deep drawing of austenitic stainless steel sheets, and to improve yields in press working and the like.

The present invention achieves the above object by hot rough rolling an austenitic stainless steel and then hot finishing rolling at a reduction rate and biting temperature in the range of ABCDEA in Figure 3, without annealing. It is characterized in that it is rolled in a cold rolling mill at a temperature range of .degree. C. or higher and 70.degree. C. or lower.

The inventor believes that earrings occur due to the development of a strong texture unique to austenitic stainless steel, and that in order to make earrings smaller, it is necessary to reduce this unique texture, or to reverse the orientation of the earrings. We believe that this can be prevented if randomization of the texture is achieved, such as by preferentially developing secondary orientations that have an effect.

The results of a detailed study of the textures of various austenitic stainless steel sheets based on the above-mentioned ideas revealed that the formation of textures is strongly influenced by the biting temperature during cold rolling, and the rolling temperature is particularly important. It has been found that the cold-rolled texture and recrystallized texture when the rolling process is low are significantly different from the texture obtained from conventional rolling methods.

That is, when cold rolling an austenitic stainless steel plate, a target thickness is usually obtained by performing multi-noise rolling in 4 to 8 passes using a Sendzimir mill. At this time, the initial biting temperature of the P/'P during multiple passes of cold rolling is often the same as the temperature (room temperature) where the material was placed, but after the second pass The biting temperature generally rises to about 50 to 200°C due to the influence of processing heat in the initial pass. In multi-nos rolling, this phenomenon is repeated, so the temperature of the plate further rises, and generally, even though it is cold rolling, rolling is repeated in a considerably high temperature range.

The present inventor focused on the surface temperature of the steel plate when it is bitten in the rolling mill during cold rolling of austenitic stainless steel, and
? After careful cold rolling with the biting temperature controlled at a constant temperature for each step, the product was subjected to conventional annealing and pickling, and the texture of the product was examined.

A typical example of the texture obtained from SUS 304 is shown in FIG. The preferred orientation when the rolling temperature is high is (211)<i
11>, but in the case of low temperature rolling, (110)<001
＞ increases. (211) An increase in the <111> orientation produces a peak of the earrings at a position tilted by 45° to the rolling direction, and (1
10) Increase in <001> orientation produces earring ridges in the rolling direction and in the direction perpendicular to it. Therefore, if cold rolling is performed at a rolling temperature at which both textures are appropriately mixed, it is expected that the positions of the peaks and valleys of the earring will be averaged and the anisotropy will be reduced.

Therefore, in order to investigate the influence of the biting temperature of cold rolling on the anisotropy of cold rolled annealed sheets, SUS 304 (C: 0.0
7%, Si: 0.6%, Mn: 1.2%, P: 0.02
5%, S: 0.006%, Ni: 8.8%, Cr: 1
8.3'%, N: 0.035%), a hot-rolled plate with a thickness of 5 mm was obtained by hot rolling.

In hot rolling, after performing normal rough rolling, the material is held on a runout table, and when the surface temperature reaches 940℃,
Finish rolling started. According to the results of light microscopic observation, the structure after finish rolling was such that the crystal grains produced during rough rolling were expanded in the rolling direction. The hot-rolled sheet thus obtained was simply descaled without annealing, and then subjected to one-stage cold rolling (ICR) to form a cold-rolled steel sheet with a thickness of 0.7 m.

All the cold rolling at this time? The biting temperature of the steel is -20℃.
,0℃.

Rolling was performed while maintaining constant temperatures of 20°C, 40°C, 60°C, and 80°C. The rolling reduction ratio in both cases is 86. %. These cold-rolled sheets were annealed at 1100° C. for 10 seconds and air-cooled, then pickled, and then the anisotropy was examined by an earring test.

The earring test was performed using cold rolled annealed sheets. A blank of Owφ was cut out and deep drawn using a punch of 40.0++lff1φ, and the earring ratio was determined from the unevenness of the cup end.

The earring rate used here is defined by the following equation.

h, is the height measured from the bottom of the cup to the top of the mountain on the rim of the cup, and h! indicates the height to the valley of the cup edge. The results are shown in Figure 2.

Regardless of whether hot-rolled sheets are annealed or not, the earring ratio changes depending on the rolling temperature, and there is a temperature at which the earring ratio becomes minimum. It was confirmed that when the rolling temperature is higher than the minimum temperature, the ridges of the earrings occur at a position inclined at 45° from the rolling direction, and when the rolling temperature is lower, they occur in the rolling direction and in a direction perpendicular to this.

The basis for limiting the present invention will be described below.

The influence on the earring properties of austenitic stainless steel thin sheets is largely due to the rolling temperature during cold rolling, and when the rolling temperature is high, the earrings form ridges at a 45° angle to the rolling direction, and conversely, the temperature is too low. At high temperatures, ridges of earrings occur in the rolling direction and in the perpendicular direction, resulting in a high earring ratio in both cases, which is undesirable. When a hot-rolled austenitic stainless steel sheet is roughly rolled under normal conditions and then finished hot-rolled at the reduction ratio and biting temperature shown in Figure 3, and then cold-rolled without solution heat treatment. teeth,
If the rolling temperature exceeds 70°C or falls below -15°C, the earring ratio will be equal to or higher than that of the conventional manufacturing method, and the anisotropy will not be improved.

Therefore, the biting temperature during cold rolling must be in the range of -15°C to 70°C, but at the same time, the finish rolling conditions during hot rolling must satisfy the reduction rate and biting temperature in the ABCDEA range shown in Figure 3. There is a need.

The range ABCDEA in FIG. 3 indicates conditions under which recrystallization does not occur during rolling. Generally, rough rolling is completed at a high temperature of 1050°C or higher, so the structure after rolling becomes coarse grains that have completed recrystallization. However, if several passes of finish rolling are performed subsequently, recrystallization occurs repeatedly during rolling. As a result, the structure of the hot-rolled sheet has extremely small crystal grains.

When a hot-rolled sheet with a fine grain structure is simply descaled, cold rolled, and annealed, the grain boundary area that becomes the starting point for recrystallization is large, promoting preferential growth of the recrystallization texture, and (211) <
111> increases extremely and anisotropy becomes noticeable. Therefore, it is desirable to perform finish rolling at a low temperature to reduce anisotropy, and the conditions in the range ABCDEA in Figure 3 do not cause recrystallization, that is, the grains after rough rolling are simply expanded to reduce the grain boundary area. This shows the rolling conditions that can be maintained at the minimum. 'In Figure 3, the upper limit of the biting temperature is regulated by AB and BC,
If finish rolling is started at a higher temperature than this, recrystallization occurs during hot rolling and the structure becomes fine grained. Also, the biting temperature is DE
When it is lowered further, deformation resistance increases, surface flaws rapidly increase, and productivity is inhibited.

If the rolling reduction ratio is greater than C, surface flaws will increase and at the same time, edge cracks will begin to occur. When the rolling reduction rate is lower than EA, the finished plate thickness becomes extremely thick, or the number of times of rolling increases, and the rolling effect decreases. Therefore, the conditions for finish rolling are AB and B shown in Figure 3.
The rolling reduction rate and biting temperature must be within the shaded range of CDgA.

The present invention will be explained in detail below using examples.

Austenitic stainless steel having the components shown in Table 1 was melted using an electric furnace-AOD method to obtain a 160-fi thick CC slab. After that, it was heated to 1230℃ in a heating furnace, and then the first
Hot rolling was performed under the conditions shown in the table. The finished thickness of the hot rolled plate is 2.
Finished between 7 dew and 4.0.

These hot-rolled plates were not subjected to solution heat treatment, but were immediately descaled and cold-rolled at the biting temperature shown in Table 1 to a plate thickness of 0.8 m.

The final annealing was performed by rapid cooling at 1100° C. for 55 seconds in a furnace, and the 0.2 inch proof stress, tensile strength, elongation, and earring ratio of the product plate were determined. These results are shown in Table 2.

When the hot rolling conditions satisfy the rolling reduction and biting temperature shown in Figure 3, and the cold rolling temperature range is between 115°C and 70°C, the earring ratio decreases and the anisotropy is improved. It turns out that

On the other hand, the tensile properties are almost unaffected by the rolling temperature of cold rolling, and values equivalent to those of conventional products can be obtained.

Table 2: Tensile properties and earring ratio of the product sheet The manufacturing method of the present invention described above is applicable not only to SUS 304 but also to any austenitic stainless steel with deformation-induced martensitic transformation.

By applying the present invention, it is possible to significantly reduce the amount of earrings generated by deep drawing, resulting in many effects such as a reduction in the amount of cut off after pressing and a reduction in the required blank size before deep drawing.

[Brief explanation of drawings]

Figure 1 shows the influence of cold rolling temperature on the texture of SUB 304 cold rolled annealed plate (100) pole figure ((a) rolling temperature θ℃, (b) rolling temperature 80℃), Figure 2 Figure 3 shows the effect of cold rolling temperature on the earring ratio of 8US304 cold rolled annealed sheet in which finish hot rolling was performed at low temperature and hot rolled plate annealing was omitted. Figure 3 shows the biting temperature in hot rolling finish rolling. It is a figure which shows the relationship between and the rolling reduction rate per pass. (loo) (ioO) Pole 2
Figure n extension temperature (°c)

Claims (1)

[Claims] After hot rough rolling of austenitic stainless steel, hot finish rolling is performed at a rolling reduction ratio of OA, B, C, D, E, AO range +7) and a biting temperature of -1 without annealing.
A method for producing an austenitic stainless steel sheet that does not easily form earrings, the method comprising rolling it in a cold rolling mill at a temperature range of 5° C. or higher and 70° C. or lower.