JPH0694572B2 - Method for producing austenitic stainless steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION “Object of the Invention” The present invention relates to a method for producing an austenitic stainless steel sheet, and a product having preferable workability or corrosion resistance by omitting the solution treatment after hot rolling the austenitic stainless steel sheet. Is what you are trying to get.

(Industrial field of application) Manufacture of austenitic stainless steel sheet (Prior art) Austenitic stainless cold-rolled steel sheet represented by 18% Cr-8% Ni is hot-melted steel in a converter or electric furnace. After rolling and annealing the obtained hot rolled sheet at 1000 to 1150 ° C,
It is manufactured by pickling, cold rolling, annealing and pickling.

In the manufacturing process as described above, for hot-rolled sheet annealing, it is necessary to reheat the hot-rolled sheet to a high temperature of 1000 to 1150 ° C, and if such annealing can be omitted, annealing equipment becomes unnecessary and energy saving is achieved. In addition to cost reduction from any aspect, it can be expected that productivity will be significantly improved by saving steps. Therefore, although various studies have been made on the omission of such hot-rolled sheet annealing,
In omitting this annealing, it is necessary to consider the following relationships.

Since the recrystallization temperature of austenitic stainless steel is significantly higher than that of ordinary steel, unlike ordinary steel, recrystallization cannot be completed as hot rolled. Therefore, the hot-rolled sheet is annealed to recrystallize and soften the hot-rolled sheet to reduce the mill load during the subsequent cold working or cold rolling of the hot-rolled sheet.

Since the carbides generated in the cooling process after hot rolling are solid-soluted again by the hot-rolled sheet annealing, the intergranular corrosion in the subsequent pickling is prevented and the deterioration of the surface quality is prevented. That is, when the hot-rolled sheet annealing is omitted and the hot-rolled sheet in which the carbides are precipitated is pickled, dropout of crystal grains and intergranular cracks occur due to intergranular corrosion, and these are cold-worked or This may cause surface roughness, surface cracks, and bald spots in cold rolling, leading to poor gloss.

Particularly in the case of cold-rolled sheet, recrystallization of the hot-rolled sheet is indispensable for homogenizing the mechanical properties of the cold-rolled sheet, and the annealing of the hot-rolled sheet is omitted and the cold-rolled sheet is cooled without recrystallization. When hot-rolled or annealed, the in-plane anisotropy of the steel sheet increases, which causes an increase in earrings, especially in deep drawing.

When hot-rolled sheet annealing is omitted, there are the above-mentioned problems, and even if they are solved to some extent by the development of cold rolling equipment and cold working technology in recent years, each of them will be improved individually. There are some examples. That is, JP-A-51-77523 and JP-A-60-255921 disclose that precipitation of carbides is suppressed by rapid cooling after hot rolling in order to prevent deterioration of surface properties. Further, in JP-A-58-221232 and JP-A-60-203307, the cold rolling conditions are optimized, and in JP-A-59-13028 and JP-A-58-22328, the components and hot rolling are Optimize the rolling conditions or cold rolling conditions, or
58-224113 and JP-A-60-262921 disclose that the combination of hot rolling conditions and cold rolling conditions is optimized to reduce the internal anisotropy. Japanese Patent Laid-Open No. 59
No. 129731 and Japanese Patent Laid-Open No. 60-59022 disclose a technique for preventing the deterioration of the surface properties by considering the pickling method in addition to reducing the in-plane anisotropy.
Japanese Patent Laid-Open No.-70404 discloses that the hot rolling sheet as it is, the cumulative rolling reduction and the finishing temperature are regulated, and the finished rolling is air-cooled for 3 to 10 seconds, then rapidly cooled and wound.

(Problems to be solved by the invention) However, the conventional ones as described above are basically to individually improve the above-mentioned problems when the hot-rolled sheet annealing is omitted, in particular. is there. That is, it does not bring about any improvement in in-plane anisotropy, and does not solve the deterioration of surface properties. Or, even if the purpose is to improve one, because there is no consideration to prevent the precipitation of carbides which is the root cause of the deterioration of the surface properties,
The surface quality is considerably worse than that of the hot-rolled sheet annealed. However, even if the Cr carbide is rapidly cooled in this way, it is difficult to completely prevent its precipitation. Therefore, the above-mentioned (1) to (3) are both improved without performing hot-rolled sheet annealing, and a workability equivalent to that of hot-rolled sheet annealing, particularly a steel sheet having both a slight in-plane anisotropy and good surface properties. Cannot be manufactured economically.

"Structure of the Invention" (Means for Solving Problems) The present invention solves the problems when the hot-rolled sheet annealing as described above is omitted, that is, the increase of the in-plane anisotropy and the deterioration of the surface properties. Therefore, as a result of intensive studies on the metallurgical significance of hot-rolled sheet annealing for 18% Cr-8% Ni equivalent steel, the following conclusions were reached.

That is, the in-plane anisotropy of the cold-rolled sheet increases when the hot-rolled sheet annealing is omitted because it is caused by cold rolling the hot-rolled sheet before the recrystallization is completed, and therefore the hot-rolled sheet is not rolled. In order to reduce the in-plane anisotropy, it is not necessary to anneal the hot rolled sheet as long as the recrystallization is completed.

In addition, of course, the optimization of the finishing temperature is a requirement for the completion of recrystallization in the as-rolled state, and the optimization of the components is also important, so that C + N is controlled within an appropriate range, and Si + 9.5Mn + 6. 0Cr
Reducing the amount of -2.0Ni leads to a significant promotion of recrystallization. Further, the deterioration of the surface quality when the hot-rolled sheet annealing is omitted is due to the fact that the carbide induces intergranular corrosion during pickling, and the amount of C is sufficiently reduced to precipitate the carbide in the cooling process after hot rolling. Avoid by preventing.

That is, according to the present invention based on such a concept, 1.C: 0.002 to 0.02 wt%, Si: 1.0 wt% or less, Mn: 0.1 to 2.5 wt%, P: 0.03 wt% or less, Cr: 16.0 to 20.0 wt%, Ni: 6.0-13.0wt%, N: 0.001-0.03wt%, S: 0.015wt% or less, and C + N = 0.005-0.03wt%, Si + 9.5Mn + 6.0Cr-2.0Nh98%. , A balance of Fe and hot rolled steel consisting of unavoidable impurities at a finishing temperature of 880 ~ 1050 ℃, and a method for producing an austenitic stainless steel sheet, characterized by not hot-rolled sheet annealing, 2.C: 0.002-0.02 wt%, Si: 1.0 wt% or less, Mn: 0.1 to 2.5 wt%, P: 0.03 wt% or less, Cr: 16.0 to 20.0 wt%, Ni: 6.0 to 13.0 wt%, N: 0.001 to 0.03 wt%, S : 0.015wt% or less, C + N = 0.005-0.03wt%, Si + 9.5Mn + 6.0Cr-2.0Ni98%, the balance of which is Fe and unavoidable impurities. Hot rolled sheet without annealing Perform ring, a subsequent method for manufacturing the austenitic stainless steel sheet characterized by cold rolling.

(Operation) FIG. 1 (c) shows the difference in tensile test values for hot-rolled sheet annealing for steels with various changes of C and N by the amount of C + N. That is, except for C and N, wt% (hereinafter simply referred to as%) is Si 0.5%, Mn 1.0%, Cr 17.2%,
Under constant conditions of Ni9.6%, (Si + 9.5Mn + 6.0Cr-2.0Ni94%), steels with various changes in C and N contents were hot-rolled at finishing temperatures of 900 ° C and 840 ° C. The change in tensile test values after hot-rolled sheet annealing and after hot-rolled sheet annealing at 1020 ° C are arranged by the amount of C + N, where C + N is 0.00
Both ΔEl and ΔTS are low in the range of 5 to 0.03%.

Further, FIG. 2 (a) shows that the same steel as described above is used, and these are hot-rolled at a finishing temperature of 900 ° C. and 840 ° C. and then provided as a hot-rolled sheet or immediately without annealing the hot-rolled sheet. The earring rate of cold rolled and annealed and hot rolled sheet annealed at 1020 ° C, then cold rolled and annealed was C +.
The earring ratio was calculated by the following formula from the unevenness of the cup edge at that time when a blank of 110 mmφ was deep-drawn by a punch of 50 mmφ.

However, Ht: height from the bottom of the cup to the top of the convex portion at the edge of the cup measured.

Hb: Height from the cup bottom to the bottom of the recess at the edge of the cup measured.

That is, from the results shown in FIGS. 1 (a) and 2 (a), when steel having a C + N content of 0.005 to 0.03% was hot-rolled at a finishing temperature of 900 ° C. There is no difference in the tensile test value after annealing, that the recrystallization is completed even if hot-rolled sheet is annealed even as hot-rolled, and immediately cold-rolled without hot-rolled sheet annealing, It can be seen that even when annealed, a low earring rate equivalent to that obtained by performing hot-rolled sheet annealing can be obtained. On the other hand, the amount of C + N is less than 0.005% and 0.0
If it exceeds 30%, or if the C + N content is 0.005 to 0.030% and the finishing temperature is as low as 840 ° C, the difference between the tensile test values after hot-rolling and after hot-rolling sheet annealing is large, and as-hot rolling remains. However, it is clear that recrystallization is not completed, and that the earring ratio increases when cold-rolled and annealed without annealing the hot-rolled sheet. From the above results, in order to obtain the same earring ratio as that of hot-rolled sheet annealing without hot-rolled sheet annealing, the C + N amount was regulated to 0.005 to 0.03%, and hot rolling was performed at an appropriate finishing temperature. Will be required. The proper range of the finishing temperature will be described later.

Next, for C and N, C0.007%, N0.005%
(C + N 0.012%), the steel with various changes in Si, Mn, Cr, and Ni was used.
As in Figure (a), after hot rolling them at finishing temperatures of 900 ℃ and 840 ℃, without hot-rolled sheet annealing or 1020
After hot-rolled sheet annealing was performed at ℃, cold rolling and annealing were performed, and the recrystallization state as hot-rolled and the earring rate after cold rolling and annealing were investigated. Fig. 1 (b) shows the difference between the as-hot-rolled state at that time and the tensile test value after hot-rolled sheet annealing, Si + 9.5Mn +
It is arranged by the amount of 6.0Cr-2.0Ni, and Fig. 2 (b) shows that the earring rate after cold rolling and annealing is Si +
It is arranged by the amount of 9.5Mn + 6.0Cr-2.0Ni. From these figures 1 (b) and 2 (b), Si + 9.5Mn + 6.0
When steel with a Cr-2.0Ni content of 98% or less was hot-rolled at a finishing temperature of 900 ° C, there was no difference in the tensile test values between as-rolled and after-annealed hot-rolled sheet, and recrystallization was performed as-rolled. Is completed, and it is understood that even if they are cold-rolled or annealed without hot-rolled sheet annealing, a low earring rate equivalent to that obtained by hot-rolled sheet annealing can be obtained. On the other hand, the amount of C + N is 0.012% and the first
Even in the proper range shown in Fig. 2 (a) and Fig. 2 (a), the Si + 9.5Mn + 6.0Cr-2.0Ni content exceeds 98%, and even if it is 98% or less, the finishing temperature is 840 ° C. If the value is low, the difference in tensile test value between as-rolled hot-rolled sheet and that after hot-rolled sheet annealing is large, and recrystallization cannot be completed if hot-rolled as it is. It can be seen that the earring rate increases when annealed. From these results, in order to obtain an earring ratio as low as that obtained by hot-rolled sheet annealing without hot-rolled sheet annealing, C +
In addition to optimizing N content and finishing temperature, Si + 9.5Mn + 6.0Cr-
It is essential that the amount of 2.0Ni be 98% or less.

Next, the proper range of the finishing temperature during hot rolling will be described. In Fig. 3, C0.007% and N0.005% (C + N0.
012%), Si0.5%, Mn1.0%, Cr17.2%, Ni9.6
% (Si + 9.5Mn + 6.0Cr-2.0Ni94%) and a steel with the composition adjusted to an appropriate range, hot-roll this at various finishing temperatures from 800 ℃ or less to 1000 ℃ or more, and then hot-roll the sheet. The difference between the tensile test values after hot-rolled sheet annealing and after hot-rolled sheet annealing, and the earring rate after cold-rolled / annealed. It is organized according to temperature. As is clear from FIG. 3, the amount of C + N is 0.012%, Si + 9.5Mn + 6.0C
Even if the r-2.0Ni content is within the proper range of 94%, the finishing temperature is 88%.
If the temperature is lower than 0 ° C, there is a large difference in tensile test values between the as-rolled hot-rolled sheet and the annealed hot-rolled sheet, and recrystallization cannot be completed if hot-rolled as it is. -The earring rate after annealing is significantly increased as compared with the case where hot-rolled sheet annealing is performed. Therefore, it is understood that the finishing temperature during hot rolling needs to be 880 ° C or higher, while the upper limit of the finishing temperature is about 1300 ° C because the upper limit of the heating temperature during hot rolling is Usually, the upper limit is about 1050 ° C, and if the finishing temperature is higher than this, the deterioration of the surface texture due to increase in scale and the coarsening of the structure will occur, so the upper limit is
Must be 1050 ° C.

To summarize the above, in order to obtain a low earring rate equivalent to that of hot-rolled sheet annealing without hot-rolled sheet annealing, the amount of C + N should be 0.005 to 0.030% from the aspect of composition, Si + 9 Set the amount of .5Mn + 6.0Cr-2.0Ni to 98% or less, and regarding the finishing temperature during hot rolling, 880 ℃ or more and 1050 ℃ or more
The following are respectively essential conditions. Regarding the coiling temperature, if the components and the finishing temperature are regulated in this way, the recrystallization is completed in the hot rolling, and if the C content is regulated to 0.020% or less as described later, Since the precipitation of carbides, which is the cause of the deterioration of the surface properties, is prevented even at the coiling temperature of, the present invention does not further prescribe it.

C + N amount and Si
The amount of + 9.5Mn + 6.0Cr-2.0Ni may be specified as above, but there are other requirements to be considered, and therefore the amount of each component is further limited as follows.

In order to obtain good surface properties equivalent to those obtained by performing hot-rolled sheet annealing while suppressing grain boundary corrosion at the time of pickling, without annealing the hot-rolled sheet, C is used in the cooling process after hot rolling. It is necessary to suppress the precipitation of carbides, and for that purpose, the C content must be 0.020% or less. Moreover, the corrosion resistance of the steel sheet is further improved by setting the C content to 0.020% or less. On the other hand, reducing the C content extremely increases the steelmaking cost, so the lower limit is made 0.002%.

If Si is contained in a large amount, it impairs the hot workability, so it is necessary to control it to 1.0% or less.

Mn is required to be 0.1% or more in order to secure hot workability, but when it is contained in a large amount, the formability is impaired, so the upper limit is 2.
5%

Cr needs to be 16.0% or more in order to obtain sufficient corrosion resistance. On the other hand, the content of Cr exceeding 20.0% impairs hot workability through an increase in ferrite phase, so the upper limit is made 20.0%.

Ni does not have sufficient corrosion resistance if it is too small,
In addition, since austenite becomes unstable, a large amount of martensite is generated during press forming, which deteriorates formability. In order to prevent this, the steel of the present invention must contain 6.0% or more of Ni, but on the other hand, since this Ni is expensive, its upper limit is 13.0%.
And

The upper limit of N is 0.030% according to the regulation of the amount of C + N. However, the extreme lowering of N increases the cost of steelmaking, so the lower limit was made 0.001%.

It is necessary to regulate P to 0.030% or less because it impairs moldability.

S impairs corrosion resistance and formability, so it is necessary to regulate S to 0.015% or less.

According to the present invention, even if hot-rolled sheet annealing is omitted, a hot-rolled sheet equivalent to the case where hot-rolled sheet annealing is performed as hot-rolled can be obtained. Descaling after the hot-rolled sheet, cold rolling, and subsequent annealing may be performed by known methods, and no particular regulation is provided. Therefore, it goes without saying that the present invention is applicable not only to ordinary cold rolling and annealing once but also to cold rolling and annealing twice or more.

(Example) A specific example of the present invention will be described below.

Example 1 Steels according to the present invention and comparative steels specifically adopted by the present inventors are as shown in Table 1 below. A to G steels are steels according to the present invention and HM steels are It is a comparative steel.

That is, the steels shown in Table 1 were melted in a converter, hot-rolled under the conditions of a heating temperature of 1250 ° C, a finishing temperature of 800 to 940 ° C, and a winding temperature of 550 ° C, and a hot rolled sheet having a thickness of 3.2 mm. I got a plate.

The surface properties and tensile test values of the obtained steel sheet are summarized in Table 2 below.

That is, A1 to G2 according to the present invention are equal to or more than those of the conventional hot rolled sheet annealing (hot rolled sheet annealing in a-1 to g-2). On the other hand, when the finishing temperature is lower than that of the present invention and the hot-rolled sheet is not annealed, the properties of G-3 and G-4, and the steel composition which is out of the specified range of the present invention, are the same as those of the present invention. Has not been obtained.

Example 2. Each of the steels shown in Table 1 above was made into a hot-rolled sheet having a plate thickness of 3.2 mm under the same conditions as in Example 1, and then these hot-rolled sheets were not annealed or hot-rolled. According to law 1050
After hot-rolled sheet annealing at ℃ × 2 min, pickling, cold rolling, annealing at 1050 ° C × 30 sec, and pickling again
A 0.8 mm cold rolled sheet was obtained. Then, the surface properties and tensile test values of these cold-rolled sheets were examined, and deep drawing was performed by the method described above to evaluate the in-plane anisotropy, and the earring rate at that time was measured.

Table 3 below summarizes the results by the finishing temperature during hot rolling and the presence or absence of hot-rolled sheet annealing.

That is, as is clear from Table 3, according to the method of the present invention, when hot-rolled sheet annealing is omitted (A-1 to F-1 and G
-1, 2), the earring rate is the same as when hot-rolled sheet annealing (a-1 to f-1 and g-1, 2),
It remains below 5%, which is practically no problem. On the other hand, when the hot-rolled sheet annealing is omitted (G-3 and G-4) even if the finishing temperature is lower than the regulation of the present invention, or when the composition is out of the regulation of the present invention, the hot-rolled sheet is hot rolled. When the annealing is omitted (H-1 to M-1), the earring rate is remarkably larger than that when the hot rolled sheet annealing is performed (g-3, 4 and h-1 to m-1). And the in-plane anisotropy is extremely poor. Regarding the surface texture, even if the hot rolled sheet annealing is omitted in the method of the present invention, a good surface condition equivalent to that of the hot rolled sheet annealed can be obtained, whereas the C content is the upper limit defined by the present invention. When hot-rolled sheet annealing is omitted for steels exceeding M (M-
In 1), rough skin and poor gloss occur, and the surface properties are poor.

[Advantages of the Invention] In the case of the present invention as described above, in the production of this type of austenitic stainless steel sheet, in-plane anisotropy that could not be avoided in the past when the hot-rolled sheet annealing was omitted. Of austenite with the same in-plane anisotropy and good surface quality as those without hot-annealing can be accurately prevented. It is possible to obtain a stainless steel sheet (hot rolled or cold rolled). As mentioned above, since the in-plane anisotropy is small, the earrings generated during deep drawing are small, and the amount of cut-off after pressing is reduced. It has a great effect on yield improvement such as reduction, reduction of required blank size before deep drawing, and deterioration of surface quality is unavoidable in the prior art, so surface care such as flaw removal was required. of On the other hand, according to the present invention, a steel sheet having a good surface property can be obtained without requiring such maintenance, so that the yield and the productivity can be expected to be significantly improved. Further, the steel sheet according to the present invention has a reduced C content. The invention has many excellent effects such as excellent corrosion resistance due to the above, and is an invention having a large effect industrially.

[Brief description of drawings]

The drawings show the technical contents of the present invention. FIG. 1 shows tensile test values (ΔTS and ΔTS) after hot-rolling and as-hot-rolled sheet annealing.
El) is C + N (%) and Si + 9.5Mn + 6.0Cr-2.0Ni (%)
Figure 2 summarizes the chart, Figure 2 shows the relationship between C + N (%) and Si + 9.5Mn + 6.0Cr-2.0Ni (%) in the earring rate of cold rolled and annealed sheets, and Figure 3 shows hot rolled as it is. It is the chart which summarized and showed the difference of the tensile test value after hot-rolled sheet annealing, and the relationship between the earring rate of the cold-rolled annealed sheet and the finishing temperature.

Claims (2)

[Claims] 1. C: 0.002 to 0.02 wt%, Si: 1.0 wt% or less, Mn: 0.1 to 2.5 wt%, P: 0.03 wt% or less, Cr: 16.0 to 20.0 wt%, Ni: 6.0 to 13.0 wt% , N: 0.001-0.03wt%, S: 0.015wt% or less, C + N = 0.005-0.03wt%, Si + 9.5Mn + 6.0Cr-2.0Ni98% with the balance Fe and unavoidable impurities A method for producing an austenitic stainless steel sheet, characterized in that the steel is hot-rolled at a finishing temperature of 880 to 1050 ° C and is not annealed. 2. C: 0.002 to 0.02 wt%, Si: 1.0 wt% or less, Mn: 0.1 to 2.5 wt%, P: 0.03 wt% or less, Cr: 16.0 to 20.0 wt%, Ni: 6.0 to 13.0 wt% , N: 0.001-0.03wt%, S: 0.015wt% or less, C + N = 0.005-0.03wt%, Si + 9.5Mn + 6.0Cr-2.0Ni98% with the balance Fe and unavoidable impurities A method for producing an austenitic stainless steel sheet, comprising hot rolling steel at a finishing temperature of 880 to 1050 ° C, performing descaling without annealing the hot rolled sheet, and then cold rolling.