Komatsu Corporation

Kazuya Hashimoto

Koji Yamamoto

Kensuke Sato

Yusuke Hiratsuka

A machine component includes a core made up of a steel for machine structural use, and a medium carbon-containing layer and a high carbon-containing layer formed of the steel for machine structural use, the medium carbon-containing layer covering the core, the high carbon-containing layer covering the medium carbon-containing layer and having a carbon concentration of 0.8-1.5%. The high carbon-containing layer is made up of a martensitic structure having carbides dispersed therein and a residual austenitic structure, wherein spheroidized carbides with an aspect ratio of 1.5 or less constitute 90% or more of a total number of the carbides, and the number of spheroidized carbides on prior austenite grain boundaries is 40% or less of the total number of the carbides.

Machine component

A method for producing a machine component excellent in pitting resistance characteristics and toughness includes a carburizing step, performed on a steel material containing 0.13-0.30% C and 0.90-2.00% Cr in mass % and at least one of Si, Mn, Ni, Mo, Nb, V, Ti, B, Al, and N, balance Fe and unavoidable impurities; heating the material to 850-1030&#xb0; C. to attain carbon concentration in a surface of 0.8-1.5%; cooling the material at an average rate of 5&#xb0; C./sec or lower from a temperature higher than the Apoint of a surface layer to a cooling end temperature that is at least 50&#xb0; C. lower than the Apoint to cause the surface layer to have a pearlite or bainite structure with dispersion; spheroidizing annealing at a temperature not higher than the Apoint at the surface layer; heating the material to not higher than the Apoint at the surface layer; and performing tempering.

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Himeji, Japan

Kazuya Hashimoto