JP3128273B2 - Method for improving workability of SUS430 stainless cold rolled steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for improving the workability, particularly bending workability, of a cold rolled SUS430 stainless steel sheet.

[0002]

2. Description of the Related Art SUS430 ferritic stainless steel is widely used mainly as a thin plate because it is less expensive than austenitic stainless steel. However, since the workability of this type of steel is considerably inferior to that of austenitic stainless steel, various studies have been conducted to improve its workability.
A method of adding l or Ti at the time of melting so as to contain 0.10 to 1.00% has been performed.

[0003]

When Al or Ti is added to SUS430 stainless steel in the above amounts, the immersion nozzle may be closed in the continuous casting process. Also, Al
In order to stabilize the yield of Ti and Ti in steel, Al and Ti
Since it is necessary to sufficiently remove slag containing chromium oxide and the like before adding the alloy, there is also a problem that valuable metals such as chromium in the slag are wasted. Further, T
If the content of i is high, surface defects such as titanium streaks are generated on the hot-rolled sheet, resulting in a decrease in yield and an increase in cost due to the high cost of the Ti alloy.

[0004] In particular, the above-mentioned specific
To avoid the problem, add Al instead of Ti
To improve the bending workability of SUS430 series steel.To
However, it takes a long time to adjust the appropriate amount of Al component,
Productivity problems such as the occurrence of clogging and clogging of immersion nozzles
Attached.

[0005] The present invention is directed to solving such a problem.

According to the present invention, Al is set to 0.010%.
The following is intended to improve the workability of SUS430 stainless steel cold-rolled steel sheets in which N is regulated to 0.040% or less .
During the smelting of the steel, degassing and refining are performed so that S: 0.005% or less and O: 50 ppm or less, and a Ti source is added so that the Ti content in the steel is 0.010 to 0.05% in the final refining stage of the molten steel. Morphology of inclusions in the cold-rolled steel sheet by JI
It is characterized in that it is changed to a C-based inclusion specified in SG 0555 .

[0006]

[Function] The present inventors have investigated and analyzed the factors governing the workability, particularly the bending workability, of a SUS430 stainless cold-rolled steel sheet and obtained the following findings.

[Effect of components on bending workability] SUS430
A series of stainless steels were tested and manufactured with Al and Ti varied in the range of 0 to 1.00%, and the effects of components on bending workability were investigated. That is, a cold-rolled coil with a final plate thickness of 2.0 mm and a BA (bright annealing) finish is manufactured from steel with these components changed, and samples are collected from these coils.
A 0 ^° contact bending test was performed, and the test was classified into a group (A) in which no crack occurred even when bent and adhered 180 ^° , and a group (B) in which a crack occurred. As a result, the steels containing Al and Ti belonged to 95% in Group A and 5% in Group B. On the other hand, steels that do not contain Al or Ti
%, Belonged to group B 90%.

[0008] The composition difference between the group A and the group B for the latter steel containing no Al or Ti was examined. As a result, all the steels belonging to the group A had S of 0.005% or less and O of 50 ppm or less. , Group B steel has 0.002 to 0.008 S
% And O varied greatly from 30 to 70 ppm, and many of them had higher S and O than those of Group A.

[Effect of Inclusions on Bendability ] Inclusions in the steel of the cold-rolled coil were investigated according to a test method specified in JIS G 0555 . According to the regulations, the types of inclusions are as follows.
Divided into types. (1) A-based inclusions: Viscous deformations caused by processing (sulfides, silicates, etc.). If there should further divided into sulfides and silicates, former A _1-based inclusions, that the latter A ₂ inclusions. (2) B-based inclusions: those in which granular inclusions are arranged discontinuously in a group in the processing direction (such as alumina). Divided into the oxide and carbonitride-based Ti, such as more alumina if required there in steels containing Ti, former B ₁ type inclusions, that the latter B ₂ type inclusions. (3) C-based inclusions: C-based inclusions that disperse irregularly without viscous deformation (eg, particulate oxides). Divided into necessary and further oxide and carbonitride-based Ti If there in steel containing Ti, former C ₁ type inclusions, the latter is called C ₂ inclusions.

As a result of _an examination in accordance with the microscopic test method under the above-mentioned rules, among the steels containing Al and Ti, those belonging to group A are all C-based inclusions, and those belonging to group B are C-based inclusions. And A-type inclusions were mixed, and A-type inclusions were present in 0.010% or more. On the other hand _, among the steels that do not contain Al and Ti, those belonging to Group A contained 0.010% or less of A-based inclusions, and some C-based inclusions also existed. Further, among the steels that do not contain Al and Ti and belong to Group B, only A-type inclusions are contained, and
It was more than 1% _and averaged 0.030%.

From the above results, the following has been found for the SUS430 stainless cold rolled steel sheet. (i) If there are many A-based inclusions, processing cracks will occur during bending. In order to prevent bending cracks, add 0.01A
It must be 0% or less, preferably 0%. (ii) It is important to reduce S and O in order to reduce A-based inclusions in steels that do not contain Al or Ti.
However, a decrease in S and O alone does not eliminate A-type inclusions. (iii) Steels containing Al and Ti are mainly composed of C-based inclusions, and the content of A-based inclusions is reduced. Therefore, the bending workability is better than steels containing no Al or Ti.

However, although the bending workability is improved by adding Al or Ti, it is usual to contain 0.10 to 1.00% of Al or Ti as described above in order to obtain this improvement effect. In this case, as described above, there are problems such as an increase in cost, a decrease in productivity, and occurrence of surface flaws. Then, the present inventors investigated in detail the relationship between the Al and Ti contents and the A-based inclusions. At that time, the test steel had a component range specified in SUS430, but S in the steel was less than 0.005% and O was less than 50 ppm.

[Relationship between Al content and A-based inclusions] The morphology of inclusions was investigated by changing the Al content, and the results shown in FIG. 1 were obtained. The figure shows the component ranges and manufacturing conditions of the test cold-rolled steel sheet. As can be seen from the results in FIG.
%, The A-based inclusions and the C-based inclusions coexisted.
When Al is 0.04% or more, there is no A-based inclusion, and Al
It was a C-based inclusion of ₂ O ₃ .

[Relationship between Ti content and A-type inclusions] The results of FIG. 2 were obtained after the morphology of inclusions was investigated by changing the Ti content. The figure shows the component ranges and manufacturing conditions of the test cold-rolled steel sheet. As can be seen from the results in FIG.
%, The A-based inclusions and the C-based inclusions coexisted.
When Ti is 0.010% or more, there is no A-based inclusion, and T
It was a C-based inclusion of SiO ₂ or TiN.

[0015] From these results, under the conditions of S: 0.005% or less and O: 50 ppm or less, when Al is added, even if the Al content is at least 0.04%, the A-type inclusions can be completely eliminated, and the remaining inclusions can be eliminated. It can be changed to C-based inclusions, and in the case of Ti addition, even if the Ti content is at least 0.010%, A
It was clarified that the system inclusions could be completely eliminated and the remaining inclusions could be changed to C system inclusions.

As described above, the conditions for the lower limits of the Al content and the Ti content for eliminating the A-based inclusions have been clarified. Problem is not solved at all. Therefore, in order to find out the relationship between problems in the actual operation and the contents of Al and Ti, we investigated these contents while changing them. When Al was less than 0.04%, the cost of Al could be reduced. In the continuous casting process, clogging of the immersion nozzle frequently occurred, and the productivity was greatly reduced. Since slag must be removed, valuable metals such as chromium are wasted. In particular, when Al was about 0.02%, a linear surface flaw occurred in the cold-rolled product. Al is 0.04
%, The cost increases due to the cost of Al, the productivity decreases due to clogging of the immersion nozzle, and the loss of valuable metals such as chromium occurs. For this reason, if the Al content is set to 0.04% or more, it is possible to improve the bending workability by changing all the inclusions to C-based inclusions, but it is necessary to improve the bending workability by adding Al. A number of problems with gender have been identified.

Next, when a test production was carried out by changing the Ti content, when the Ti content was 0.05% or less, no clogging of the immersion nozzle occurred, and the slag was removed before adding Ti because the Ti content was small. There was no need, and valuable metals such as chromium could be used effectively. Further, surface defects such as titanium streaks did not occur on the hot-rolled sheet. If Ti exceeds 0.05%, there is a problem that valuable metals such as chromium are lost because the cost increases and slag must be removed due to the cost of Ti. In particular, when Ti is 0.20% or more, N
If the content exceeds 100 ppm, problems such as clogging of the immersion nozzle and surface defects such as titanium streaks have occurred.

Table 1 summarizes the above results. As can be seen from the results in Table 1, the most advantageous method for controlling the inclusions by adding Al or Ti to improve the bending workability of cold rolled SUS430 stainless steel sheet contains 0.010 to 0.05% Ti. It is a way to make it. in this case,
It is necessary to limit S to 0.005% or less and O to 50 ppm or less. Although Al has various problems in production, when Ti is added in the above range, it may be present in steel at 0.010% or less.

[0019]

[Table 1]

In addition, when adding the Ti source to molten steel, the S content is reduced to 0.005% or less and the O content is reduced to 50 ppm or less.
After melting (degassing and refining) S430 stainless steel, a Ti source is added in the final component adjustment stage so that the Ti content in the steel is 0.010 to 0.05%. Then, it is continuously cast, and hot-rolled and cold-rolled according to a usual process to produce a cold-rolled steel sheet. The chemical composition of the cold rolled SUS430 stainless steel sheet excellent in bending workability obtained by the method of the present invention is, specifically, the specified range of SUS430, C: 0.12% or less, and Si: 1.
00% or less, Mn: 1.00% or less, P: 0.040% or less, Ni:
0.60% or less, Cr: 16.00 to 20.00% or less, and based on the above findings, N: 0.040% or less,
Al: 0.010% or less, S: 0.005% or less, O: 50ppm or less,
Ti: contains 0.010 to 0.05%, and substantially all of the inclusions remaining in the steel sheet are C as specified in JISG 0555.
It is a system inclusion. The N content is 0.040%
The reason is as follows. If the amount exceeds this amount, TiN increases, and even when the Ti amount is 0.05% or less, surface defects such as titanium streaks may occur.

[0021]

EXAMPLE The ferrite stainless steel of the five components shown in Table 2 was melted by the converter-degassing method, and Ti was added in the final component adjustment stage to continuously cast the slab. Annealed by cold rolling and cold rolling to a final thickness of 2.0 mm
Manufactured cold rolled coils having a BA finish.

[0022]

[Table 2]

In any of these steels, clogging of the immersion nozzle did not occur in the continuous casting process. Further, even if slag was not cut during the tapping of the converter, the Ti content was small, so it was easy to properly apply Ti, and valuable metals such as chromium were not wasted. Since the amount of Ti added was as small as 1.5 kg / T, a significant increase in cost was avoided. There were no surface flaws on the hot and cold rolled sheets. Measurement of the inclusions of the final product, the bending harmful A type inclusions in the processing or no, the C type inclusions 0.010
0.025% was present. Bending tests were performed on the final product coil by bending it 180 °, and no cracks occurred in any of the coils.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between Al% and inclusion morphology.

FIG. 2 is a diagram showing the relationship between Ti% and the form of inclusions.

──────────────────────────────────────────────────続 き Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C21C 7/00 C22C 38/00 C22C 38/50 JICST file (JOIS)

Claims (2)

(57) [Claims] 1. To improve the workability of a SUS430 stainless steel cold-rolled steel sheet in which Al is controlled to 0.010% or less and N to 0.040% or less, S: 0.005% or less when the steel is melted.
O: Degas refining to 50 ppm or less, and adding Ti source in the final refining stage of the molten steel so that the Ti content in the steel is 0.010-0.05%, to reduce inclusions in the cold-rolled steel sheet. A method for improving the workability of a SUS430 stainless cold-rolled steel sheet, characterized by changing the form to a C-based inclusion specified in JIS G 0555 . 2. The cold-rolled steel sheet has C: 0.12% or less, Si: 1.0% or less.
0% or less, Mn: 1.00% or less, P: 0.040% or less, Ni: 0.
60% or less, Cr: 16.00 to 20.00% or less, N: 0.040% or less, Al: 0.010% or less, S: 0.005% or less, O: 50ppm or less, Ti: 0.010 to 0.05%, the rest from inevitable impurities and Fe The method according to claim 1, wherein substantially all of the inclusions remaining in the steel sheet are C-based inclusions specified in JIS G 0555 .