JPS5925933A - Production of thin ferritic stainless steel sheet having excellent workability - Google Patents

Abstract

PURPOSE:To obtain a thin ferritic stainless steel sheet having excellent processability in a simplified stage, by subjecting a ferritic stainless steel slab contg. limited amts. of Al and C to a specific heat treatment after rough rolling then subjecting the same to post finish rolling. CONSTITUTION:A ferritic stainless steel slab contg. 0.08-0.5% Al and 0.03- 0.1% C is heated to >=950 deg.C and is roughly rolled. The resultant rough-rolled slab is heated and held within 10min in a 900-1,100 deg.C temp. range; thereafter the slab is subjected to finish rolling with a continuous finishing mill then to hot rolling followed by cold rolling, whereby the thin ferritic stainless steel sheet having excellent processability is produced in the simplified production stage contg. no box annealing.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a ferritic stainless thin steel sheet, and particularly to a method for manufacturing a ferritic stainless thin steel sheet that can simplify the manufacturing process and has excellent workability.

Unless otherwise specified in the following description, ferritic stainless steels usually include 11-20% Cr, up to 0.1% C, up to 1% Mn, and up to 1% SIsO.
, containing up to 0.05% N, is melted in a converter or electric furnace, and when made by the ingot method, it is made into a cis-slab by blooming, and when it is made by a continuous casting method, it is made directly into a slab. This is made into a hot-rolled steel strip by the hot rolling method, and after hot-rolled plate annealing, cold rolling is performed once or two or more times with intermediate annealing in between, and then final annealing is performed. refers to products that have been subjected to

In the manufacturing process of stainless thin steel sheets, a method of box annealing at 800 to 850° C. for 2 hours or more is usually used for annealing the hot rolled sheets. Box annealing of hot-rolled sheets has technical significance in (1) reducing writhing that occurs during forming, (2) improving deep drawability, and (3) improving cold rollability. In the conventional process, box annealing of the hot rolled sheet was an essential condition.

Generally, in order to reduce ridging of ferritic stainless thin steel sheets, it is known that it is good to perform large reduction hot rolling in the α and γ two phase regions to promote recrystallization. It is believed that ridging can be reduced by increasing the amount of air containing N, Mn, etc. However, if hot rolling is completed with such a large amount of γ phase present, the γ phase changes into a hard martensitic phase in the as-hot rolled state. Therefore, when the steel is cold rolled by -1, it is hard and brittle, resulting in extremely poor cold rollability and a significantly low r value. Therefore 1
The martensitic phase was transformed into a ferrite phase and carbide by box annealing described for 1J, but the present inventors found that by adding 0.08% or more At, the γ→α transformation occurred in a short time. Focusing on this, in the rough rolling process, high reduction hot rolling is performed in the α and γ two-phase region as in the conventional technology to promote recrystallization and refine the structure, thereby improving the ridging properties. By carrying out heat retention or heating for a short time to (i) promote the r→α transformation and (ii) fix N by promoting the precipitation of ALH, the cold rollability of the hot-rolled sheet annealed material is not affected. We have found that the r value can be improved without any problems.

That is, the inventors) Azo, 08-0.5%, C0,0
For ferritic stainless steel containing 3 to 0.1%, the rough rolled piece is heated to 900 to 1100°C before finishing rolling.
By holding or heating within a temperature range of 10 minutes,
The present invention has been completed by discovering that even if the hot-rolled sheet is cold-rolled without box annealing, which was considered an essential condition in the past, the same effect or effect as box annealing can be obtained. It is.

The present invention will be explained in detail below.

Figure 1 shows Cr 17%, C 0.05%, N 100
Thickness 2 containing ppm+At0.15% and 0.06%
00m17) Ferritic stainless steel slab 100m
After heating for 2 hours at a temperature of 0℃, 4 arms (120m → 80m)
+ mn → 4 degree tone → 20 degree) to make 20 tone, and finish rolling as it is, and before starting finish rolling at 900 ° C. for 5 minutes to 15 minutes.
Minutes.

Starting from a hot-rolled sheet that has been finish-rolled after heating at 1000℃ for 5 to 15 minutes and held at 1100℃ for 0 seconds to 10 minutes, the final thickness is determined by one cold rolling without hot-rolled sheet annealing. 7 shows the relationship between the product's 7 value (Rankfredo value) and the rolling height (μm) and hot rolling conditions. From the same figure, in the case of the material containing 0.6% AtO, no improvement in r value is observed even when heat-retained or heated before the start of finish hot rolling, but in the case of the material containing 0.15% AtO. , it can be seen that by performing such heat treatment, the r value is improved.

The reason why the r value increases when At is high is that this heat treatment promotes the γ-deca transformation and that ktN precipitates.

The ridging properties are almost determined by the recrystallization behavior of the two-phase region hot rolling in the rough rolling process, so even if such heat treatment is performed after rough rolling, it is hardly affected as shown in the figure, but the γ amount In the case of heating at 1100°C, which increases r
Although the value deteriorates, the effect of reducing ridging can be seen. The reason why the r value deteriorates is that the amount of AtN precipitated decreases and the martensite phase increases during hot rolling and rolling, and the reason why the ridging decreases is that the finishing hot rolling process also It is difficult to recrystallize in the cold rolling annealing process because the hard phase increases in the as-hot-rolled state (10
This is thought to be due to progress in recrystallization refinement in the 03<110> orientation.

In the present invention, At 0.08% or more is defined as 0.08% or more.
This is because if the kl is less than 1, there is no effect of the heat treatment after the completion of rough rolling.The reason why At is set to 0.5% or less is that even if the amount of At added exceeds 0.5%, the effect of improving the r value can be seen as the amount added increases. However, since it is not economical to increase the amount of At added, the upper limit is set to 0.5%. The reason why C is set to 0.03% or more is because if the C value is less than this, the r value improves, but the ridging deteriorates rapidly.The reason why C is set to 0.1% or less is that %, the r value decreases and the spreadability deteriorates. The reason why the slab heating temperature is set to 950° C. or higher is that at a temperature lower than 950° C., the recrystallization refinement in the rough rolling region is insufficient and the effect of improving ridging properties is small.

The reason why the heat treatment conditions for the rough rolled material in the present invention are set within the temperature range of 900 to 1100° C. for 10 minutes or less is as follows. The reason why the heat treatment temperature was set at 900°C or higher is because at a temperature lower than 900°C, the temperature drop during the finish hot rolling process is significant, especially when the process is performed without annealing the hot rolled sheet, there is no effect of improving the r value! 7. The reason for setting the heat treatment temperature to 1100°C or lower is that at a temperature exceeding 1100°C, AtN precipitation is small and there is no effect of reducing the amount of γ, so the r value does not improve.
The reason why the heating time is within minutes is that although heating for a longer time is effective, heating for more than 10 minutes lowers the hot rolling efficiency and is not economical.

The above description has been made of a process in which finish annealing is performed after cold rolling to the product thickness without hot-rolled sheet annealing, but in the present invention, hot-rolled sheet annealing is performed continuously at 900 to 1100°C for several minutes. It goes without saying that even if a process of box annealing at 800 to 850°C for several hours is applied, there is an effect of improving the r value.

Next, the present invention will be specifically explained according to examples.

Example I Co, oso%, NO, 010%, At 0.20%,
Cr17%.

A continuously cast slab with a thickness of 200 m consisting of the balance Fe and impurities was made into a rough rolled piece with a thickness of 20 m at 5/4 s.

The temperature after rough rolling was 1000°C. This rough-rolled piece was immediately finish hot-rolled into a 3.8mm hot-rolled plate (
Two types of hot-rolled sheets were prepared: a comparative method) and a hot-rolled sheet having 3.8 fins by holding at a temperature of 1000° C. for 5 minutes and finishing hot-rolling (invention method). These hot-rolled sheets were cold-rolled to a thickness of 0.7 mm by one cold rolling without hot-rolled sheet annealing, and then heated to 840°C.
Annealing was performed for 2 minutes. For comparison, AtO, 05%
Slabs with the same chemical composition except that they contained were also treated in the same process. Table 1 shows the r value and ridging properties of the products thus manufactured. As shown in the table, the present invention was heated to 1000°C during rough to finish hot rolling.
When held for 5 minutes, both r value and ridging showed good characteristics.

Table 1 Product characteristics Example 2 C0,045%, NO,010q6. AtO, 15
%, 17% Cr, the balance F@ and impurities, a continuous casting slab with a thickness of 200 mm was heated at 1150°C for 2 hours and then 5 mm (170++ on - + 120 mm → 70 wI →
40 gourd → 20 gourd) and a rough rolled piece with a thickness of 20 mm. Next, the rough rolled piece was held at a temperature of 1000°C for 10 minutes, and the piece without intermediate heat retention was finished hot rolled for 3 days.
．． It was made into a hot-rolled sheet for 8 hours. Next, this hot-rolled sheet was heated to 1000°C.
After heating to 840℃ and air cooling, cold rolling to a thickness of 0.7m.
Annealing was performed for 2 minutes. Table 2 shows the r value and ridging characteristics of the products manufactured in this way. When held at 1000°C for 10 minutes between rough and finishing as in the present invention,
It can be seen that the r value has improved.

Table 2 Product characteristics example 3 C0,065%, No, 015%, AtO, 15%, C
r 17%.

A continuous casting slab with a thickness of 250 mm consisting of the remainder Fe and impurities was heated for 2 hours at a temperature of 1050 °C and then heated for 6 passes (20 mm).
0m-+160tam → 115 pus → 70 minutes → 40 parrot → 2
A rough rolled piece with a thickness of 20 cm was obtained. Then, this rough rolled piece was immediately finish rolled (comparative method) and 975°C
Two types of hot-rolled sheets were made, one of which was heat-retained for 5 minutes and then finished hot-rolled (method of the present invention). Then, without performing hot-rolled plate annealing, cold rolling was performed once to a thickness of 0.7 ttm, and
Annealing was performed at 0°C for 2 minutes. The third light shows the r value and ridging characteristics of the product thus manufactured. As in the present invention, when held at 975°C for 5 minutes between rough and finishing, r
It can be seen that the value has improved.

Table 3 Product characteristics Example 4 C0,055%, NO,010%, kl 0.15%
Thickness 2 consisting of y Cr 17% balance Fe and impurities
00 tone continuous casting 97" f 5 z4 [200 mm →
120 tone → 80 tone → 40 degree → 10 g] to obtain a rough rolled piece with a thickness of 10. Then, the rough-rolled piece was immediately made into a hot-rolled plate with a thickness of 3.7 mm by 3 passes. In addition, according to the method of the present invention, a rough rolled piece was held at a temperature of 1000° C. for 1 minute and then finished rolled to produce a hot rolled sheet. The hot-rolled sheet manufactured under these two conditions was cold rolled without hot-rolled sheet annealing to a thickness of 0.
After forming a cold-rolled sheet with a diameter of 7 mm, it was annealed at 840° C. for 2 minutes. Table 4 shows the r value and ridging of the material thus produced. As in the present invention, 1 at 1000℃ between rough and finishing
It can be seen that both the r value and ridging are improved when the sample is held for a minute.

Fourth display product characteristic example 5 C0,050%, NO,012%, At0.12%,
Thickness: 200 m consisting of 17% Cr, balance Fe and impurities
Continuously cast slag of 57 mm (200 mm → 120 mm → 80 mm)
+n+a→40wm→10wm) to obtain a rough rolled piece with a thickness of 10−. Next, the rough rolled piece was kept at a temperature of 1000° C. for 1 minute and then heated for 3 times to form a hot rolled sheet with a thickness of 3.7 m.

For comparison, a hot-rolled sheet was also experimentally produced by immediately rolling a rough-rolled piece of lOW+ by 3 passes.

After cold-rolling the hot-rolled sheet manufactured under these two conditions without annealing the hot-rolled sheet to obtain a cold-rolled sheet with a thickness of 0.7+mm,
Annealing was performed at 840°C for 2 minutes. Table 5 shows the r value and ridging of the material thus produced. It can be seen that the r value of the thin steel sheet manufactured by the method of the present invention is improved.

Fifth mounting material characteristics

[Brief explanation of drawings]

Figure 1 shows the r value of the material processed in the process without hot-rolled plate annealing,
FIG. 3 is a diagram showing the effect of heat treatment during hot rolling on ridging. Kudzu / diagram

Claims (1)

[Claims] AtO, 08~0.5%, CO, 03~0.1%
In manufacturing a ferritic stainless steel sheet by hot rolling a ferritic stainless steel slab containing a rough rolling mill and a continuous finishing rolling mill in a hot rolling mill, and then cold rolling the slab. 950
The rough rolled piece obtained by heating to above ℃ and rough rolling was heated to 900℃
A method for manufacturing a ferritic stainless thin steel sheet with excellent workability, which comprises holding and heating in a temperature range of ~1100°C for less than 10 minutes, followed by finish rolling.