Austenitic stainless steel material and method for manufacturing the same

Abstract

To provide an austenitic stainless steel that has hardness equivalent to that of martensitic stainless steel while maintaining non-magnetic properties, and also holds high strength and a method for producing the same.SOLUTION: An austenitic stainless steel comprises, in percentages by weight, C: 0.18-0.33%, Si: 0.30% or less, Mn: 1.8-4.0%, (P: 0.030% or less) S: 0.30% or less, Cr: 21.0-25.0%, Ni: 7.0-11.0%, Cu: 1.0% or less, Nb: 0.20% or less, B: 0.005% or less, N: 0.20-0.35%, the balance being Fe and unavoidable impurities, with its hardness exceeding 50 HRC in Rockwell C scale.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a steel material made of austenitic stainless steel and a method for manufacturing the same.

Background Art

[0002] Austenitic stainless steel typified by the steel grade SUS304 is superior in corrosion resistance to martensitic stainless steel typified by steel grades such as SUS440C and SUS420J2, and has also been developed for applications that utilize its non-magnetic properties.

[0003] However, since austenitic stainless steel has a lower hardness than martensitic stainless steel, its applications have been limited. In addition, since martensitic stainless steel has magnetism, it has not been applied to applications such as electromagnetic components that require non-magnetism.

[0004] Therefore, in Patent Documents 1 to 3, techniques have been disclosed in which austenitic stainless steel is subjected to predetermined processing to have a hardness equivalent to that of martensitic stainless steel while having non-magnetic properties.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, these austenitic stainless steels had a problem: cold working, performed to increase hardness, caused some of the structure to undergo martensitic transformation, resulting in the loss of their original non-magnetic properties and the development of magnetism.

[0007] Therefore, the objective of this invention is to provide an austenitic stainless steel material that maintains non-magnetic properties while exhibiting high hardness and high tensile strength. [Means for solving the problem]

[0008] To solve the aforementioned problems, the austenitic stainless steel material of the present invention has the following composition by weight percent: C: 0.18~0.33%, Si: 0.30% or less, Mn: 1.8~4.0%, P: 0.030% or less, S: 0.30% or less, Cr: 21.0~25.0%, Ni: 7.0~11.0%, Cu: 1.0% or less, Nb: 0.20% or less, B: 0.005% or less, N: 0.20~0.35%, with the remainder being Fe and unavoidable impurities.

[0009] Furthermore, the hardness shall exceed 50 HRC on the Rockwell C scale. In particular, the total amount of carbon and nitrogen contained can be limited to 0.38% or more by weight. [Effects of the Invention]

[0010] The austenitic stainless steel material of the present invention can maintain non-magnetic properties while possessing hardness comparable to martensitic stainless steel and high strength, by optimizing the carbon and nitrogen content. [Modes for carrying out the invention]

[0011] An embodiment of the austenitic stainless steel material of the present invention will be described. First, the content of the main elements (C, Mn, Cr, N) contained in the austenitic stainless steel will be described.

[0012] First, the amount of carbon (C) is set to 0.18-0.33% by weight, while the amount of nitrogen (N) is set to 0.20-0.35% by weight. Carbon (C) is an element that increases the hardness of the austenitic stainless steel material of the present invention, but if it is included in excess, the workability will deteriorate, so it is set to 0.18-0.33% by weight. Also, nitrogen (N) is an element that stabilizes the austenite structure and also increases hardness, but if it is included in excess, the workability will deteriorate, so it is set to 0.20-0.35% by weight.

[0013] The amount of manganese (Mn) should be 1.8 to 4.0% by weight, and chromium (Cr) should be 21.0 to 25.0% by weight. Both manganese and chromium are austenite structure stabilizing elements and also increase the solubility of nitrogen in the structure.

[0014] Next, the method for manufacturing the austenitic stainless steel material of the present invention will be described. The austenitic stainless steel material of the present invention is manufactured by melting, forging, and rolling an austenitic stainless steel base material. In order to dissolve any undesirable structures or precipitates that appear during hot working processes such as forging and rolling (or originate from the ingot) into the base material, the base material is subjected to a solution treatment at a temperature range of 1150 to 1200°C after the forging or rolling process.

[0015] Furthermore, in order to increase the hardness of the base material after solution treatment, the austenitic stainless steel base material is subjected to cold working such as wire drawing or drawing, and then aged at a temperature range of 450 to 550°C. As a result, the hardness of the austenitic stainless steel material of the present invention can be made to exceed 50 HRC. In this application, "base material of austenitic stainless steel material" refers to the names of each manufacturing process, such as melting, forging, and rolling, until the austenitic stainless steel material of the present invention is produced. [Examples]

[0016] (Example 1) Using the austenitic stainless steel (the inventive material) according to the present invention and two commercially available austenitic stainless steels (comparative materials 1 and 2), the relative permeability of each austenitic stainless steel was measured. The relative permeability of the austenitic stainless steel used in this example was read for each applied magnetic field strength with a dedicated measuring device in a state where the applied magnetic field strengths were set at four levels of 100 (A / m), 200 (A / m), 5000 (A / m), and 15000 (A / m) for each austenitic stainless steel to be measured. Table 1 shows the chemical compositions of the inventive material and comparative materials 1 and 2 used in this example.

[0017]

Table 1

[0018] As a result, the relative permeability (average value) of the inventive material was 1.003. In contrast, the relative permeability (average value) of comparative material 1 was 1.003, and the relative permeability (average value) of comparative material 2 was 1.004. From the above test results, it was found that the relative permeability of the inventive material was equal to or higher than that of commercially available comparative materials 1 and 2.

[0019] (Example 2) Next, using the inventive material used in Example 1 and two commercially available martensitic stainless steels (SUS440C: comparative material 3) and austenitic stainless steel (SUS304: comparative material 4), the corrosion resistance of these stainless steels was evaluated.

[0020] The test pieces used in this test were the inventive material and comparative materials 3 and 4 as cylindrical samples with a diameter of 8 mm and a height of 10 mm, and those obtained by grinding the surfaces of these samples with 800 - grit paper were used. After grinding, for each sample of the inventive material and comparative materials 3 and 4, the Vickers hardness was measured at a position of D / 4 (2 mm outside from the center: D represents the diameter) with a diameter of 8 mm with a test force of 20 kgf.

[0021] Furthermore, the corrosion conditions for this test consisted of two conditions: immersion in a 10% sulfuric acid aqueous solution (liquid temperature: 25°C) for 2 hours (corrosion condition 1) and immersion in a 47% sodium hydroxide aqueous solution (liquid temperature: 90°C) for 120 hours (corrosion condition 2). After the predetermined time had elapsed under each condition, the sample was removed and its weight was measured before and after the test. The corrosion rate (unit: g / m³) was then calculated from the weight difference of the sample. 2 The hardness (unit: HV) and corrosion rate of the inventive material and comparative materials 3 and 4, which are the results of the corrosion resistance test, are shown in Table 2.

[0022] [Table 2]

[0023] Based on the results of this test, the corrosion rate of the invented material under corrosion condition 1 was 3.3 g / m³. 2 ( / h), under corrosion condition 2, 0.41 (g / m 2 The corrosion rate of comparative material 3 was 98.5 g / m³ under corrosion condition 1. In contrast, the corrosion rate of comparative material 3 was 98.5 g / m³. 2 ( / h), under corrosion condition 2, 7.77 (g / m 2 The corrosion rate of comparative material 4 was 3.6 g / m³ under corrosion condition 1. 2 ( / h), under corrosion condition 2, 0.25 (g / m 2 The result was / h). In other words, it was found that the inventive material has hardness equivalent to martensitic stainless steel (SUS440C) while having corrosion resistance equivalent to commercially available austenitic stainless steel (SUS304).

Claims

1. An austenitic stainless steel material characterized by having, by weight percent, C: 0.18-0.33%, Si: 0.30% or less, Mn: 1.8-4.0%, P: 0.030% or less, S: 0.30% or less, Cr: 21.0-25.0%, Ni: 7.0-11.0%, Cu: 1.0% or less, Nb: 0.20% or less, B: 0.005% or less, N: 0.20-0.35%, with the remainder being Fe and unavoidable impurities, and having a hardness exceeding 50 HRC on the Rockwell C scale.

2. The austenitic stainless steel material according to claim 1, characterized in that the sum of the C content and the N content is 0.38% or more by weight.

3. The austenitic stainless steel material according to claim 2, characterized in that its relative permeability is 1.010 or less.

4. A method for producing an austenitic stainless steel material according to any one of claims 1 to 3, characterized in that the base material of the austenitic stainless steel material is subjected to solution treatment at a temperature range of 1150 to 1200°C.

5. The method for producing an austenitic stainless steel material according to claim 4, characterized in that the base material of the austenitic stainless steel material is further cold-worked and then subjected to aging treatment in a temperature range of 450 to 550°C.

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