JPS5811489B2 - Manufacturing method of austenitic stainless steel strip with small in-plane anisotropy of plastic strain ratio - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention reduces the plastic anisotropy of an austenitic stainless steel strip to produce deep drawn products such as earrings.
The present invention relates to a method for manufacturing an austenitic stainless steel strip with small in-plane anisotropy of plastic strain ratio, in order to suppress the occurrence of ing) and improve material yield and multi-stage deep drawability.

Austenitic stainless steel sheets have excellent formability and corrosion resistance, so they are used in a wide range of applications, but the thin steel sheets are very often manufactured into products by press working, and moreover, they are manufactured in multiple stages. There are often cases where pressing is performed to increase the drawing ratio.

When forming by deep drawing, if the in-plane anisotropy of the plastic strain ratio (r value) of the material is large, the earrings produced during press forming will be thick (this will reduce the material yield and reduce the multi-stage drawing performance). This will result in a decrease in

For example, the reference diagram shows the component composition C0.06%, Si0.68
%, Mn1.48%, Cr18.23%, Ni8.90
% (steel type 5US304) and a steel plate with the same composition but smaller earrings are deep-drawn in three stages so that the final drawing ratio is 2.7. This is a photograph showing the appearance. The processed product on the left in the photo was manufactured from a steel plate manufactured by a conventional method, and the processed product in the cloth in the photo was manufactured from a steel plate manufactured by the method of the present invention. However, when squeezing a large material for earrings, the lower part becomes a square tube during the drawing process in the third stage, so the squeezing resistance becomes so great that it breaks just above the first part of the punch (α break). While there are
It can be seen that the material of the small earrings has a slight prismatic shape and is narrowed down.

In this way, for austenitic stainless steel sheets, the deep drawing performance, especially during multistage drawing, is determined not only by the strain hardening index (n value) and plastic strain ratio (r value) of the steel sheet, but also by the index of the degree of earring. It can be seen that the r value also depends on the magnitude of the in-plane anisotropy (Δr).

Nowadays, in order to reduce manufacturing costs, conventionally, the two-time cold rolling method (hereinafter referred to as the two-time rolling method) is used, in which the hot-rolled material is first cold-rolled, then softened and annealed, and then cold-rolled again. (
A steel plate with a thickness that was manufactured by a method (secondary rolling) to obtain a product thickness is rolled to a product thickness by one-time cold rolling method (hereinafter referred to as one-time rolling method), i.e., only by first cold rolling. There is a strong tendency for manufacturing to be carried out using this method.

In the case of the single-rolling method, the rolling ratio in rolling before final annealing is inevitably larger than in the case of the double-rolling method.
In a single-rolling steel plate made under conventional manufacturing conditions, the directionality of mechanical properties is significantly greater than in a double-rolling steel plate, and Δr is also significantly larger in the single-rolling process.

This situation is shown in Figure 1. Therefore, as mentioned above, the steel plate produced by the single rolling process is inferior to the steel plate produced by the double rolling process in terms of material yield during press working and multi-stage deep drawing performance.

The purpose of the present invention is to improve the in-plane anisotropy (Δr
) to a degree comparable to that of double-rolled products, and to establish a single-rolling method that eliminates the practical drawbacks of steel sheets caused by large Δr.

In order to achieve the above object, the present invention heat-treats a hot-rolled steel sheet at a heating temperature of 1150-100°C, which is approximately 100°C higher than the heating temperature conventionally adopted for austenitic stainless steel.
The rolling process after annealing at 1250°C is performed by a conventional method, but more preferably,
In order to prevent strain-induced transformation during rolling of hot-rolled materials annealed at such high temperatures, the temperature is reduced to 35 to 25 depending on the composition of the steel.
This relates to rolling at 0°C.

Next, the present invention will be explained in detail.

By rolling a hot-rolled iron-based alloy material with face-centered cubic crystals at a temperature higher than the temperature at which martensitic transformation (strain-induced transformation) begins, the material after annealing has isotropic mechanical properties. It has been reported that

However, according to the research of the present inventor, even if hot-rolled austenitic stainless steel material having face-centered cubic crystals is rolled at a temperature higher than the temperature at which martensitic transformation begins, the material after annealing does not always have isotropic properties. Depending on the heat treatment conditions applied to the hot-rolled material, it may exhibit anisotropic mechanical properties compared to when rolling is performed at or below the temperature at which martensitic transformation begins. It turned out that.

In other words, when hot-rolled steel strips are processed into product thickness by one cold rolling, these hot-rolled copper strips are cold-rolled without being heat-treated, and strain-induced transformation occurs during the rolling. Rolled so that it doesn't.

The in-plane anisotropy of the plastic strain ratio after annealing is rather large in steel strips compared to steel strips rolled in such a way that strain-induced transformation occurs; After that, when cold rolling is performed, the heat treatment temperature is 1150~1150℃.
A temperature of 1250°C is effective, and in a hot-rolled copper strip heat-treated in such a temperature range, even if strain-induced transformation occurs during cold rolling, the Δr of the cold-rolled annealed plate will be significantly small. Also, such a high temperature (1150-1250
A hot-rolled copper strip annealed at .degree. C. is characterized in that when it is cold-rolled so as not to cause strain-induced transformation, the Δr of the cold-rolled annealed sheet becomes even smaller.

Table 1 and Figure 2 show the above situation,
From the same table and figure, in order to obtain in-plane isotropy of the plastic anisotropy of the material after finish annealing, it is necessary to appropriately combine the heat treatment conditions and rolling processing conditions of the hot rolled steel strip. It is clear that this is essential.

The heat treatment temperature for the hot-rolled steel strip in order to obtain isotropy of the plastic strain ratio in the plate plane is 1150-1250, which is higher than the temperature normally applied to austenitic stainless steel hot-rolled materials. It must be thrown at ℃.

Whether or not the hot-rolled steel strip is heat-treated before cold rolling, and if it is heat-treated, the heat treatment temperature is Without regulating these conditions, 'cold rolling of the hot-rolled material above the Md point' will immediately affect the mechanical properties and the in-plane anisotropy of the plastic strain ratio of the cold-rolled annealed material. In the three present inventions that clearly do not impart isotropy to
The reason why the heat treatment temperature of hot rolled steel sheets is limited to within the range of 1150 to 1250°C is that when heat treated at a conventional heat treatment temperature lower than 1150°C, the Δr of the finish annealed material after rolling is 2.
Steel plates manufactured by the round rolling method do not become smaller;
On the other hand, heat treatment at temperatures higher than 1250°C causes significant oxidation of the surface of the steel sheet during heating, making it difficult to finish the cold-rolled annealed steel sheet with a beautiful surface. Furthermore, the crystal grains of the hot-rolled steel sheet become coarser, causing strain-induced In materials rolled at temperatures above the temperature at which transformation begins, the crystal grains of cold-rolled annealed sheets also become larger.
In order to cause surface roughness in the press-formed product, it is necessary to limit the heat treatment temperature of the hot rolled steel sheet within the range of 1150 to 1250°C.

In the present invention, the reason why the temperature during cold rolling is set within the range of 35 to 250°C is that according to the heat treatment temperature of the hot rolled steel sheet of the present invention, the Δr is significantly lower than that of the material obtained by the conventional single rolling method. Although it is possible to obtain a small material by one-time rolling, it was newly discovered that Δr can be further reduced by cold rolling within the range of 35 to 250°C due to the combined effect with the heat treatment temperature. Therefore, when rolling at a temperature lower than 35°C, the improvement in Δr is small, while when rolling at a temperature higher than 250°C, the surface of the steel sheet becomes thinly colored, and the current rolling oil has a high risk of ignition. To avoid this, special equipment is required, which is impractical, and the economic advantage of adopting the single-rolling method is lost, so the temperature during cold rolling must be within the range of 35 to 250°C. .

Next, the present invention will be explained in detail with reference to Examples.

Example 1 SUS304 (C; 0.06, Si; 0.65, Mn;
1.52, Cr: 18.30, Ni: 9.90, wt,
%) 4.0 mm thick hot rolled plate was heat treated at 1100°C for 7 minutes and at 1200°C for 5 minutes, then immersed in silicone oil kept at 100°C for 5 minutes for each pass. 0.8mm by immediately cold rolling
Then, it was rolled once to 0.5 mm using a rolling method.

In this case, no martensite was generated in the rolled plate.

Furthermore, the above hot rolled annealed plate was heated to 0.3 and 0.5 mm at 20°C.
It was rolled once by the rolling method.

The amount of martensite in each rolled plate was 12.18%.

Δr was measured for the steel plates obtained by annealing these rolled plates at 1100° C. for 2 minutes.

The results are shown in Table 1.

Comparing the effect of the hot-rolled sheet heat treatment method of the present invention and the effect of the rolling method on the reduction of Δr, the former is thicker (the steel sheet heat-treated by the method of the present invention and rolled by the method of the present invention is thicker). Δr is the smallest.

Example 2 SUS304 steel (C; 0.06, Si; 0.70, Mn
:1.50, Cr:18.30, Ni:8.30, wt
%) was heat-treated at 1050°C for 10 minutes and at 1160°C for 5 minutes, and then immersed in a tank maintained at 20°C for 5 minutes for each pass. 0.8mm and 0.5mm by immediate rolling
It was rolled once by the rolling method.

The amount of martensite in the rolled material is 23.0°28.
It was 0%.

Δr was measured for the steel plates obtained by annealing these rolled plates at 1100° C. for 2 minutes.

The results are shown in Table 2.

Compared to the steel sheet heat-treated by the conventional method, the Δr of the steel sheet heat-treated by the method of the present invention is smaller, indicating that the heat treatment of the hot-rolled sheet has an influence on Δr.

Example 3 SUS301 steel (C; 0.10, Si: 0.62, Mn
:102, Cr;17.37, Ni7.02, wt, %
) was heat-treated at 1100°C for 10 minutes and at 1200°C for 5 minutes.

After each pass in silicone oil kept at 300℃,
0.8m by soaking for 5 minutes and rolling immediately.
It was rolled by a rolling method once every m.

During rolling, the rolling rolls were preheated to 150°C.

Further, when the temperature of the rolled plate was measured with a surface contact thermometer, the temperature immediately after rolling was 210°C.

No strain-induced martensite was observed in the rolled sheet.

The Δr was measured for the steel plate obtained by annealing this rolled plate at 1100° C. for 2 minutes, and the results are shown in Table 3.

Even for 301 steel, the Δr of the steel sheet made by the method of the present invention is smaller than that of the conventional method, and it can be seen that the heat treatment of the hot-rolled sheet has an influence on the Δr.

Example 4 SUS304 (C; 0.05, Si; 0.75, Mn;
1.45, Cr: 18.23, Ni: 9.01, wt.
%) on a 4.0 mm thick hot-rolled plate at every 50°C.
Heat treatment was performed at a temperature range of 0 to 1250°C for a heating time of 5 minutes.

The steel plate is immersed in silicone oil kept at 150°C for 5 minutes for each pass and immediately rolled. ℃ rolling method) is 0.
It was set to 8mm.

The amount of martensite produced in the rolled plate was 0% when rolled at 150°C, and about 17% when rolled without temperature control.

The Δr of the steel plates obtained by annealing these rolled plates at 1100° C. for 2 minutes was measured.

The results are shown in FIG.

Δr becomes smaller as the annealing temperature of the hot rolled sheet increases, especially at 1150°C or higher (in the temperature range of the present invention).
becomes noticeably smaller.

When rolling is performed in the γ single phase region, Δr becomes smaller.

Among them, the hot-rolled plate is annealed at 1150°C to 1250°C,
The Δr of the steel plate rolled in the γ single-phase region is as small as the Δr of the steel plate made by the two-roll method shown in Figure 1, and if the steel plate is manufactured using the method of the present invention, It can be seen that even if it is made by the rolling method, the Δr is comparable to that of the steel plate made by the two-time rolling method.

As described above, according to the present invention, an austenitic stainless steel strip having small in-plane anisotropy of plastic strain ratio can be manufactured.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the relationship between 5US304 steel plate produced by conventional hot rolling plate heat treatment and the normal rolling method and rolling reduction;
FIG. 2 is a diagram showing the relationship between Δr of 5US304 steel sheet and hot-rolled sheet heat treatment temperature.

Claims (1)

[Claims] 1. After annealing a hot-rolled austenitic stainless steel strip, it is rolled to the product thickness in one cold rolling process, which is then conventionally employed in the production of austenitic stainless steel strips. In a method of manufacturing an austenitic stainless steel strip by performing finish annealing under conditions of
A method for producing an austenitic stainless steel strip with small in-plane anisotropy of plastic strain ratio, characterized in that the annealing temperature of the hot-rolled copper strip is within a range of 1150 to 1250°C. 2 After annealing a hot-rolled austenitic stainless steel strip, it is rolled to the product thickness in one cold rolling process, and then finished under the conditions conventionally used for manufacturing austenitic stainless steel strips. In a method of manufacturing an austenitic stainless steel strip by annealing,
In-plane anisotropy of plastic strain ratio, characterized in that the annealing temperature of the hot rolled copper strip is within the range of 1150 to 1250°C, and the temperature during cold rolling is within the range of 35 to 250°C. A method for manufacturing small austenitic stainless steel strips.