JP2003266105A - Super-plastic stainless steel manufacturing method, and super-plastic working method of stainless steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an efficient super-plastic austenitic stainless steel manufacturing method, and a super-plastic working method of stainless steel. <P>SOLUTION: Stainless steel is cold-worked at or below the temperature (Md) at which stainless steel is martensitic-transformed if it is subjected to plastic working at the temperature to generate martensite (Step 1). Then, the stainless steel is heated and subjected to intensive working in a hot condition (Step 2). Intensive working can be performed under a small load. The stainless steel is then annealed or worked at or above the temperature (As) at which martensite is inverse-transformed at or above the temperature (Step 3). The austenitic stainless steel is subjected to the plastic working at or above Md point and at or below the recrystallization temperature, and martensitic- transformed in the super-plastic stainless steel manufacturing method. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a stainless steel material for superplastic working, and more particularly to a superplastic working method for a stainless steel material which can be worked with a small load and is less likely to crack, and a superplastic working method for a stainless steel material Regarding processing method.

[0002]

2. Description of the Related Art As shown in FIG. 3 for example, the inventors of the present invention have a martensitic transformation temperature of 85% below a temperature (hereinafter referred to as Md point) at which martensitic transformation occurs when plastic working is applied to austenitic stainless steel at a temperature below that temperature. Adding the above plastic working,
Proposal of a method to make almost all of Martensite (hereinafter referred to as α ') and directly deform it above the temperature (hereinafter referred to as As point) at which α'reverse-transforms to austenite (hereinafter referred to as γ) (Patent No. 29166
No. 19).

It has also been clarified that superplastic behavior is exhibited when an alloy is annealed at a temperature above the As point and then deformed above the As point (Iron and Steel, Vol.
94), No. 3, pp. 67-71).

[0004]

In the prior art, it is necessary to carry out cold strong working in the manufacturing process of superplastic stainless steel, and in order to manufacture it, it is necessary to apply a large load to the material, so that a large member is manufactured. Is difficult (Issue 1).

Further, there is a problem that cracking occurs due to strong working of martensite, which is relatively brittle, and the material yield is low (problem 2).

Therefore, an object of the present invention is to solve these problems and provide an efficient method for producing a superplastic austenitic stainless steel material and a method for superplastic working a stainless steel material.

[0007]

[Means for Solving the Problems] In order for austenitic stainless steels to exhibit superplastic behavior, it has conventionally been necessary to subject austenitic stainless steels to a strong working of about 90% or more at a temperature below the Md point. It was This is because by processing below the Md point, α'is generated, and by giving a large strain, when this is held above the As point, recrystallization accompanied by reverse transformation behavior from α'to γ, Particle size about 1
This is because it was considered indispensable that processing and α'generation proceed simultaneously in order to generate a very fine grain structure of μm or less.

However, the inventors of the present invention predict that even if α ′ production and processing are performed separately, if the content of α ′ and the total amount of processing added are equal, the recrystallization behavior accompanied by reverse transformation will be the same. Then, it was confirmed by an experiment.

This fact, and in general, the higher the temperature is, the lower the load of deformation of a metallic material is, the martensite is generated by the minimum necessary cold working, and then it is heated to a temperature below the As point to distort the strain. Invented the method of addition.
As a result, the above-mentioned problem 1 can be solved.

Further, paying attention to the fact that γ is higher in ductility than α ′, most of the working is added to the austenitic stainless steel above the Md point and below the recrystallization temperature, and then the minimum necessary cold working is performed. Alternatively, the inventors invented a method of producing martensite by deep-cooling treatment and substituting it for about 90% cold working which is a conventional manufacturing method of stainless steel for superplastic working. As a result, the problem 2 can be solved.

More specifically, the present invention relates to claim 1.
The invention according to (1) is a method for producing a superplastic stainless steel material, which is characterized in that austenitic stainless steel is transformed into martensite and then heated to a temperature of Ms point or more and As point or less to perform plastic working.

[0012] The invention according to claim 2 is a martensitic transformation of austenitic stainless steel,
This is a method for producing a superplastic stainless steel material, which is characterized by heating to a temperature from the Md point to the As point and below, performing plastic working, and then annealing at the As point and above.

According to the invention of claim 3, the austenitic stainless steel is martensitic transformed,
This is a superplastic working method for a stainless steel material, which is characterized in that heating is performed at a temperature from the Md point to the As point to perform plastic working, and the superplastic working is performed at a temperature above the As point.

Further, the invention according to claim 4 is a method for producing a superplastic stainless steel material, which comprises subjecting austenitic stainless steel to plastic working at a temperature not lower than the Md point and not higher than the recrystallization temperature, and then performing martensitic transformation. It is what

The invention according to claim 5 is characterized in that austenitic stainless steel is subjected to plastic working at a temperature not lower than the Md point and not higher than the recrystallization temperature, then subjected to martensitic transformation, and then annealed at the As point or higher. And a method for producing a superplastic stainless steel material.

Further, the invention according to claim 6 is to subject austenitic stainless steel to plastic working at a temperature not lower than the Md point and not higher than the recrystallization temperature, and then subjecting it to martensite transformation, which is superplastic worked at a temperature not lower than the As point. This is a superplastic working method for a stainless steel material.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an outline of a manufacturing process to which the superplastic working method for a stainless steel material according to the present invention is applied. The temperature at which martensitic transformation occurs when plastic working is performed below that temperature ( Cold work below Md) to produce martensite (step 1). Then, this is heated and subjected to strong working in a warm state (step 2). In that case, strong processing can be performed with a small load. After that, annealing or working is performed at a temperature (As) or higher at which the martensite reversely transforms to austenite at the temperature or higher (step 3).

FIG. 2 shows an outline of another manufacturing process to which the superplastic forming method for a stainless steel material according to the present invention is applied. The temperature (Md) at which the martensite transformation occurs when plastic working is performed at a temperature below that temperature. The warm working is performed below (step 1). No cracking occurs in the processing at this time.
This is subjected to a minimum cold working at a temperature below the Md point (step 2). In this process, the occurrence of cracks is minimized. After that, annealing or working is performed at a temperature (As) or higher at which martensite reversely transforms to austenite at the temperature or higher (step 3). (Example)

In the following, an example in which the austenitic stainless steel SUS304 is adjusted to a stainless steel material for superplastic working according to the present invention and it is confirmed that the same superplastic behavior as the conventional method is confirmed is shown.

[0020] The material used is commercially available solution-treated SUS3
This is a 04 plate material (plate pressure 12 mm). From this, a small piece for rolling with a thickness of 10 mm was cut out and a comparative experiment was conducted.

In the production of superplastic stainless steel by the conventional method, the small pieces for rolling were rolled to a thickness of 1 mm (reduction ratio = 90%) while cooling with ice water (hereinafter referred to as conventional material).

In the present invention, according to FIG. 1, a rolling piece is rolled with ice water to a thickness of 2.5 mm (reduction ratio = 75%), and then the material is heated to 300 ° C. Thickness 1
Rolled up to mm (integral reduction ratio = 90%) (hereinafter, referred to as Example 1
That).

According to the present invention shown in FIG. 2, a rolling strip is heated to 300 ° C. and rolled to a thickness of 4 mm, and then,
While cooling the material with ice water, the material was rolled to a thickness of 1 mm (cold rolling reduction = 75%, cumulative reduction = 90%) (hereinafter referred to as Example 2).

Further, as a comparative material, a small piece for rolling having a thickness of 4 mm was cut out and rolled to a thickness of 1 mm (cooling ratio = 75%) while cooling with ice water (hereinafter referred to as comparative material).

Observation of the appearance of the material after rolling revealed that a comparatively large amount of edge cracks occurred in the conventional material, but it was small in the present invention.

Annealing at 700 ° C. × 3600 seconds was added to these four materials, and a tensile test piece was cut out from these materials and a JIS No. 7 test piece was used to perform a tensile test at 700 ° C. at a strain rate of 1/10000 per second. went.

As a result, it is considered that the conventional material exhibits an elongation of 312% and exhibits superplastic behavior.

And Example 1 shows an elongation of 383%,
Example 2 showed an elongation of 364%. From this, Example 1
It can be confirmed that Example 2 is also a superplastic stainless steel material.

Furthermore, since the comparative material shows only 228% elongation, it can be proved that the warm working carried out in Examples 1 and 2 was effective in producing superplastic stainless steel.

From this, it can be confirmed that the manufacturing load of the superplastic stainless steel material can be provided in which the load of processing required for manufacturing is reduced, the number of cracks during manufacturing is small, and the material yield is high.

In Examples 1 and 2, warm plastic working is applied only before or after the martensitic transformation, but the one obtained by applying warm working to both of them is also used. Of course, it is included in the scope of the invention.

Further, this method is applied directly to the superplastic working method of the patent No. 2916619 proposed by the present inventors as described above without applying annealing before superplastic working, and directly at the As point or higher. It goes without saying that it can be processed.

[0033]

EFFECTS OF THE INVENTION Since the present invention is configured as described above, a superplastic austenitic stainless steel material manufacturing method and a stainless steel material superplastic working method that can be processed with a small load and are resistant to cracking are provided. You can

[Brief description of drawings]

FIG. 1 is a diagram showing an aspect of a first manufacturing process in a method for manufacturing a superplastic stainless steel material according to the present invention.

FIG. 2 is a diagram showing an aspect of a second manufacturing step in the method for manufacturing a superplastic stainless steel material according to the present invention.

FIG. 3 is a diagram showing an aspect of a manufacturing process of a conventional method.

Claims (6)

[Claims] 1. A method for producing a superplastic stainless steel material, which comprises subjecting an austenitic stainless steel to a martensitic transformation, and then heating the material to a temperature not lower than the Ms point and not higher than the As point to perform plastic working. 2. A superplastic stainless steel material characterized by performing martensitic transformation of austenitic stainless steel, heating it to a temperature of Md or higher and As or lower to perform plastic working, and then annealing it at the As or higher. Manufacturing method. 3. A martensitic transformation of austenitic stainless steel, heating to a temperature above the Md point and below the As point for plastic working, and superplastic working at a temperature above the As point. Superplastic forming method for stainless steel. 4. A method for producing a superplastic stainless steel material, which comprises subjecting austenitic stainless steel to plastic working at a temperature not lower than the Md point and not higher than the recrystallization temperature, and then performing martensitic transformation. 5. Production of a superplastic stainless steel material, which comprises subjecting austenitic stainless steel to plastic working at a temperature not lower than the Md point and not higher than the recrystallization temperature, then performing martensite transformation, and then annealing at the As point or higher. Method. 6. A stainless steel material characterized by subjecting austenitic stainless steel to plastic working at a temperature not lower than the Md point and not higher than the recrystallization temperature, then undergoing martensite transformation, and superplastic working this at a temperature not lower than the As point. Superplastic forming method.