Alloy steel for machining gear, and gear using the same

Abstract

To provide an alloy steel for machining a gear that can yield high hardness (64 HRC or more by Rockwell hardness C scale) by whole quenching treatment at a low temperature (900°C or less) without applying carburization treatment, and subsequent tempering treatment (150-200°C), and to provide a gear using the same.SOLUTION: An alloy steel for machining a gear comprises, by wt.%, C:0.90% or more and 1.50% or less, Si:0.70-2.50%, Mn:0.10-1.00%, Cr:1.00-4.00%, Mo:0.20-1.50%, W+2Mo:0.40-3.00%, and V:0.10-0.80%, and the balance Fe and inevitable impurities.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an alloy steel for gear machining and a gear using the same. [Background technology]

[0002] Gears used in mechanical parts such as various transmissions are made of mechanical structural alloy steels, such as Ni-Cr-Mo alloy steel and Cr-Mo alloy steel. When mechanical structural alloy steels are used for gears, they are often subjected to carburizing or carbonitriding treatment.

[0003] Traditionally, carburized gears rarely break due to wear or spalling on the tooth surface because of their hard surface, but they often break due to repeated bending stress at the tooth base. In recent years, the tooth base bending strength has been improved by applying shot peening and tooth grinding to gears after heat treatment. As a result, breakage due to tooth base bending has decreased, and the proportion of tooth breakage caused by damage to the tooth surface, such as pitting, has increased. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-120466 Summary of the Invention

[0005] As disclosed in Patent Document 1, alloy steels for machine structures (Ni-Cr-Mo alloy steels and Cr-Mo alloy steels) are often carburized at temperatures of 900°C or higher. Carburized gears have a large amount of retained austenite in the carburized layer and have areas with low surface hardness, which makes wear and spalling of the tooth surfaces problematic.

[0006] However, it is not easy to reduce the amount of retained austenite in the carburized layer. Although it depends on the carbon content of the carburized layer, it is not uncommon for the amount of retained austenite in the carburized layer to exceed 20% by volume. [Problem to be solved by the invention]

[0007] Therefore, the present invention aims to provide an alloy steel for gears that can be subjected to a full quenching treatment at a low temperature (900°C or less) without carburizing, followed by a tempering treatment (150 to 200°C) to obtain high hardness (64 HRC or higher on the Rockwell hardness C scale), and to provide gears made from the alloy steel. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, the alloy steel of the present invention is an alloy steel for gear cutting containing, by weight, C: 0.90% or more and 1.50% or less, Si: 0.70 to 2.50%, Mn: 0.10 to 1.00%, Cr: 1.00 to 4.00%, Mo: 0.20 to 1.50%, W+2Mo: 0.40 to 3.00%, V: 0.10 to 0.80%, with the remainder being Fe and unavoidable impurities.

[0009] Alternatively, the alloy steel for gear cutting contains, by weight, C: 0.90% or more and 1.50% or less, Si: 0.70 to 2.50%, Mn: 0.10 to 1.00%, Cr: 1.00 to 4.00%, Mo: 0.20 to 1.50%, W+2Mo: 0.40 to 3.00%, Nb: 0.05 to 0.40%, with the remainder being Fe and unavoidable impurities.

[0010] Furthermore, in the invention of a gear using the aforementioned alloy steel for composite gear processing, the surface of the gear has a Rockwell hardness of 64 HRC or more on the C scale. [Effects of the Invention]

[0011] The alloy steel for gear cutting of the present invention can be subjected to a full quenching treatment at a low temperature (900°C or less) without carburizing, followed by a tempering treatment (150 to 200°C), thereby achieving sufficient surface and internal hardness (64 HRC or more on the Rockwell hardness C scale) and an appropriate amount of retained austenite.

[0012] Therefore, the gears made from this alloy steel for gear cutting are resistant to wear and flaking. Furthermore, because the gears are fully hardened to the inside, they are less susceptible to breakage at the base and on the tooth surface compared to carburized gears made from alloy steel for machine structures.

[0013] Furthermore, the manufacturing cost of the gear cutting alloy steel can be reduced by limiting the content of rare metals such as Cr, Mo, and V in the gear cutting alloy steel to 5% by weight or less. Furthermore, since the gear cutting alloy steel has excellent resistance to temper softening, the loss of hardness is small even when the temperature rises. DETAILED DESCRIPTION OF THE INVENTION

[0014] As one embodiment of the present invention, the chemical components of an alloy steel for gear cutting and a gear using the alloy steel for gear cutting will be described.

[0015] 《C (Carbon)》 The gear cutting alloy steel of the present invention contains 0.90% to 1.50% C by weight. Carbon ensures the hardness of the gear cutting alloy steel after quenching and tempering, and plays a role in ensuring a high fatigue life when used as a material for machine parts. If the C content in the gear cutting alloy steel is less than 0.90%, the required surface and internal hardness cannot be obtained, while if it exceeds 1.50%, the amount of retained austenite (γ amount) becomes too large, deteriorating the fatigue life of the machine parts.

[0016] Silicon The Si (silicon) content is set to a range of 0.70% to 2.50% by weight. Silicon plays a role in increasing the temper softening resistance of the gear cutting alloy steel. If the Si content in the gear cutting alloy steel is less than 0.70%, the required temper softening resistance cannot be obtained, and if it exceeds 2.50%, the hot forgeability deteriorates significantly. Preferably, the Si content is 1.50% to 2.50%.

[0017] Manganese (Mn) The Mn (manganese) content is 0.10% or more and 1.00% or less by weight. Manganese improves the hardenability of alloy steel for gear cutting, and is effective in improving fatigue life when used as a machine part material. If the Mn content in the alloy steel for gear cutting is less than 0.10%, the hardenability of the alloy steel for gear cutting is deteriorated, and if it exceeds 1.00%, the hot forgeability is significantly deteriorated.

[0018] 《Cr (Chromium)》 The Cr (chromium) content is set to 1.00% or more and 4.00% or less by weight. Chromium improves the hardenability of the gear cutting alloy steel and also thermally stabilizes cementite, preventing the cementite from dissolving in the matrix at high temperatures. If the Cr content in the gear cutting alloy steel is less than 1.00%, the hardenability of the gear cutting alloy steel will deteriorate, and if it exceeds 4.00%, coarse carbides will form in the gear cutting alloy steel.

[0019] Mo (Molybdenum) The content of Mo (molybdenum) is 0.20% or more and 1.50% or less by weight. Molybdenum forms carbides in the gear cutting alloy steel, contributing to ensuring hardness. If the Mo content in the gear cutting alloy steel is less than 0.20%, the required temper hardness and softening resistance cannot be obtained. On the other hand, if the Mo content exceeds 1.50%, coarse carbides are formed.

[0020] "V (Vanadium)" The V (vanadium) content is 0.10% or more and 0.80% or less by weight. V, when added in combination with silicon in the gear cutting alloy steel, serves to increase temper softening resistance. Furthermore, if the V content in the gear cutting alloy steel is less than 0.10%, the required temper softening resistance cannot be obtained, and if it exceeds 0.80%, coarse carbides are generated. Note that a similar effect can be achieved by adding Nb (niobium) as a substitute element for V. In this case, the Nb content is preferably in the range of 0.05% or more and 0.40% or less by weight.

[0021] W (Tungsten) W (tungsten) can be included in the range of 0.40% to 3.00% by weight as the W equivalent (W + 2Mo). In this case, tungsten, like molybdenum, forms carbides in the gear cutting alloy steel, contributing to ensuring hardness. If the W equivalent in the gear cutting alloy steel is below 0.40%, the required temper hardness and softening resistance cannot be obtained. On the other hand, if the W equivalent exceeds 3.00%, coarse carbides will form.

[0022] Gears made from the aforementioned alloy steel for gear cutting have a surface hardness of 64 HRC or higher on the Rockwell C scale. They can be used for a variety of gear types, including spur gears, internal gears, helical gears, double helical gears, bevel gears, screw gears, hypoid gears, and worm gears.

Claims

1. An alloy steel for gear cutting, characterized in that it contains, by weight%, C: 0.90% or more and 1.50% or less, Si: 0.70 to 2.50%, Mn: 0.10 to 1.00%, Cr: 1.00 to 4.00%, Mo: 0.20 to 1.50%, W+2Mo: 0.40 to 3.00%, V: 0.10 to 0.80%, with the remainder being Fe and unavoidable impurities.

2. An alloy steel for gear cutting comprising, by weight%, C: 0.90% or more and 1.50% or less, Si: 0.70 to 2.50%, Mn: 0.10 to 1.00%, Cr: 1.00 to 4.00%, Mo: 0.20 to 1.50%, W+2Mo: 0.40 to 3.00%, Nb: 0.05 to 0.40%, with the remainder being Fe and unavoidable impurities.

3. 3. A gear made from the alloy steel for gear cutting according to claim 1 or 2, wherein the surface of said gear has a Rockwell hardness C scale of 64 HRC or more.