Martensitic stainless steel sintered body

Abstract

To provide a martensitic stainless steel sintered body applicable to tools having a blade part for cutting or processing foods and the like, exhibiting high hardness while combining blade-sharpening characteristics, grinding characteristics, and chipping resistance.SOLUTION: A martensitic stainless steel sintered body according to the present invention comprises, in terms of weight%, C: more than 1.2% and 1.5% or less, Si: 0.3% or less, Mn: 0.3% or less, P: 0.02% or less, S: 0.02% or less, Ni: 0.2% or less, Cu: 0.2% or less, Cr: 13.0-20.0%, V: 1.0-4.0%, Mo: 2.0-5.0%, and N: 0.10-0.20%, the balance being Fe and inevitable impurities.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a martensitic stainless steel sintered body produced by powder metallurgy. [Background technology]

[0002] Traditionally, martensitic stainless steels, such as SUS440C, have been the mainstream stainless steel used for cutting tools such as knives and kitchen knives (see Patent Documents 1 and 2). To improve the sharpness and life of cutting tools, and to increase hardness (hardness of 62 to 63 HRC) and corrosion resistance, elements such as Mo, V, and Cr are sometimes added to the alloy components of SUS440C. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 10-1703 [Patent Document 2] Patent No. 2764659 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when the content of Mo, V, Cr, etc. in martensitic stainless steel exceeds a certain value (so-called high alloying), coarse carbides precipitate in the matrix structure, which has a significant impact on the sharpening characteristics and grinding properties with other alloys.

[0005] Therefore, an object of the present invention is to provide a martensitic stainless steel sintered body that has high hardness and also has good sharpening properties, grinding properties, and chipping resistance, for use in tools with cutting edges used in cutting or milling food products and the like. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, the present invention provides a martensitic stainless steel sintered body containing, by weight, C: more than 1.2% and not more than 1.5%, Si: not more than 0.3%, Mn: not more than 0.3%, P: not more than 0.02%, S: not more than 0.02%, Ni: not more than 0.2%, Cu: not more than 0.2%, Cr: 13.0 to 20.0%, V: 1.0 to 4.0%, Mo: 2.0 to 5.0%, N: 0.10 to 0.20%, with the remainder being Fe and unavoidable impurities.

[0007] Alternatively, the martensitic stainless steel sintered body may contain, by weight, C: more than 1.2% and not more than 1.5%, Si: not more than 0.3%, Mn: not more than 0.3%, P: not more than 0.02%, S: not more than 0.02%, Ni: not more than 0.2%, Cu: not more than 0.2%, Cr: 13.0 to 20.0%, V: 1.0 to 4.0%, W+2Mo: 4.0 to 10.0%, N: 0.10 to 0.20%, with the remainder being Fe and unavoidable impurities.

[0008] Furthermore, the martensitic stainless steel sintered body may contain, by weight, C: more than 1.2% and not more than 1.5%, Si: not more than 0.3%, Mn: not more than 0.3%, P: not more than 0.02%, S: not more than 0.02%, Ni: not more than 0.2%, Cu: not more than 0.2%, Cr: 13.0 to 20.0%, Nb: 0.5 to 2.0%, Mo: 2.0 to 5.0%, N: 0.10 to 0.20%, with the remainder being Fe and unavoidable impurities.

[0009] Furthermore, the martensitic stainless steel sintered body may contain, by weight, C: more than 1.2% and not more than 1.5%, Si: not more than 0.3%, Mn: not more than 0.3%, P: not more than 0.02%, S: not more than 0.02%, Ni: not more than 0.2%, Cu: not more than 0.2%, Cr: 13.0 to 20.0%, Nb: 0.5 to 2.0%, W+2Mo: 4.0 to 10.0%, N: 0.10 to 0.20%, with the remainder being Fe and unavoidable impurities.

[0010] The surface hardness of these martensitic stainless steel sintered bodies is preferably 61 HRC or more on the Rockwell C scale. In the present invention, the term "sintered body" is synonymous with the "sintered body" specified in JIS Z2500, that is, it means "a sintered body of (metallic) powder or green compact." [Effects of the Invention]

[0011] The martensitic stainless steel sintered body of the present invention has the effect of providing high hardness and excellent sharpening properties, grinding properties, and chipping resistance for tools with cutting edges used in cutting or milling food and other materials. DETAILED DESCRIPTION OF THE INVENTION

[0012] The contents of the main elements contained in the martensitic stainless steel sintered body, which is one embodiment of the present invention, are described below. The C (carbon) content in the martensitic stainless steel sintered body of the present invention is in the range of more than 1.2% to 1.5% by weight. In the martensitic stainless steel sintered body of the present invention, C is dissolved in the matrix (base structure) by quenching treatment, and is an element that contributes to hardness and strength.

[0013] At the same time, it combines with Cr, V, Mo, etc. to form carbides, which contribute to wear resistance. If the C content exceeds this range, it may impair the toughness of the martensitic stainless steel sintered body. On the other hand, if it is less than this range, the required hardness (61 HRC or higher on the Rockwell C scale) cannot be obtained.

[0014] The content of Si (silicon) should be 0.3% or less by weight. Si acts as a deoxidizer and also contributes greatly to the hardenability of the sintered body. If the Si content exceeds 0.3% by weight, there is a possibility that the plastic workability will decrease.

[0015] The Mn (manganese) content is set to 0.3% or less by weight. Mn, like Si, acts as a deoxidizer and also contributes greatly to the hardenability of the sintered body. If the Mn content exceeds 0.3% by weight, it may embrittle the matrix structure and ultimately reduce plastic workability.

[0016] The content of W (tungsten) is in the range of 4.0 to 10.0% by weight as the W equivalent (W + 2Mo). W forms carbides with C and plays a role in contributing to the strength of the sintered body of the present invention. If the content as the W equivalent (W + 2Mo) is less than 4.0% by weight, the required strength may not be obtained. On the other hand, if the content exceeds 10.0% by weight, the amount of carbides becomes excessive, which may impair toughness.

[0017] The Cr (chromium) content is set to the range of 13.0 to 20.0% by weight. Cr forms carbides with C, which contributes greatly to wear resistance. At the same time, by dissolving in the matrix structure, it also contributes greatly to improving corrosion resistance and hardenability. If the Cr content is less than 13.0%, the required corrosion resistance cannot be obtained. On the other hand, if the Cr content exceeds 20.0%, the amount of carbides becomes excessive, which may impair toughness.

[0018] Mo (molybdenum) should be in the range of 2.0 to 5.0% by weight. Like W, Mo forms carbides with C and contributes to strength. If the Mo content is less than 4.0% by weight, the required strength may not be obtained. On the other hand, if it exceeds 10.0% by weight, the amount of carbides becomes excessive, which may impair toughness.

[0019] V (vanadium) can be contained in the range of 1.0 to 4.0% by weight. V is an element that combines with C (carbon) to form carbides and significantly contributes to strength and wear resistance. If the content is less than 1.0% by weight, the necessary strength and wear resistance cannot be obtained. On the other hand, if the content is more than 4.0% by weight, the excessive amount of carbides may impair toughness.

[0020] Nb (niobium) can be contained in the range of 0.5 to 2.0% by weight. Like V, Nb is an element that forms carbides by bonding with C (carbon), and contributes greatly to strength and wear resistance. If the content is less than 0.5% by weight, the necessary strength and wear resistance cannot be obtained. On the other hand, if the content is more than 2.0% by weight, the presence of an excessive amount of carbides may impair toughness.

[0021] The content of N (nitrogen) should be in the range of 0.1 to 0.2% by weight. Like C, N dissolves in the matrix structure during quenching and is an element that contributes to the hardness and strength of the martensitic stainless steel sintered body. If the content is less than 1.0% by weight, the martensitic stainless steel sintered body will not achieve the required hardness and strength, and corrosion resistance may be impaired. On the other hand, if the content is more than 0.2% by weight, internal defects may occur in the martensitic stainless steel sintered body.

[0022] Next, a method for producing a martensitic stainless steel sintered body according to one embodiment of the present invention will be described. A molten metal having the above-mentioned chemical components is gas atomized to obtain powder. This powder is filled into a cylindrical steel can, which is then vacuum degassed and sealed.

[0023] Thereafter, hot isostatic pressing (HIP) is performed in an argon gas atmosphere under conditions of a pressure of 50 to 200 MPa and a temperature of 1050 to 1250°C to obtain a compact, which is then hot forged and hot rolled to a forging ratio of 4 or more, and further annealed to obtain a round bar with a diameter of 30 mm.

[0024] Test pieces of predetermined dimensions are cut out from the round bar. These test pieces are quenched at 1050 to 1120°C and then tempered at least twice to obtain the powder martensitic stainless steel. The tempering temperature is adjusted so that the hardness of the tempered test pieces is in the range of 62 to 63 HRC.

Claims

1. A martensitic stainless steel sintered body characterized by containing, by weight, C: more than 1.2% and not more than 1.5%, Si: not more than 0.3%, Mn: not more than 0.3%, P: not more than 0.02%, S: not more than 0.02%, Ni: not more than 0.2%, Cu: not more than 0.2%, Cr: 13.0 to 20.0%, V: 1.0 to 4.0%, Mo: 2.0 to 5.0%, N: 0.10 to 0.20%, and the balance being Fe and unavoidable impurities.

2. A martensitic stainless steel sintered body characterized by containing, by weight, C: more than 1.2% and not more than 1.5%, Si: not more than 0.3%, Mn: not more than 0.3%, P: not more than 0.02%, S: not more than 0.02%, Ni: not more than 0.2%, Cu: not more than 0.2%, Cr: 13.0 to 20.0%, V: 1.0 to 4.0%, W+2Mo: 4.0 to 10.0%, N: 0.10 to 0.20%, and the balance being Fe and unavoidable impurities.

3. A martensitic stainless steel sintered body characterized by containing, by weight percent, C: more than 1.2% and not more than 1.5%, Si: 0.3% or less, Mn: 0.3% or less, P: 0.02% or less, S: 0.02% or less, Ni: 0.2% or less, Cu: 0.2% or less, Cr: 13.0 to 20.0%, Nb: 0.5 to 2.0%, Mo: 2.0 to 5.0%, N: 0.10 to 0.20%, and the balance being Fe and unavoidable impurities.

4. A martensitic stainless steel sintered body characterized by containing, by weight, C: more than 1.2% and not more than 1.5%, Si: not more than 0.3%, Mn: not more than 0.3%, P: not more than 0.02%, S: not more than 0.02%, Ni: not more than 0.2%, Cu: not more than 0.2%, Cr: 13.0 to 20.0%, Nb: 0.5 to 2.0%, W+2Mo: 4.0 to 10.0%, N: 0.10 to 0.20%, and the balance being Fe and unavoidable impurities.

5. 5. The martensitic stainless steel sintered body according to claim 1, wherein the surface hardness is 61 HRC or more on the Rockwell C scale.