Komatsu Corporation

Kabushiki Kaisha Komatsu Seisakusho

Naoji Hamasaka

Takemori Takayama

Takashi Kuse

Chikara Nakao

Chigo Okayama

Junji Mizoguchi

Hayao Takahashi

Hideo Hisada

High surface pressure resistant steel parts and their producing methods are disclosed. These steel parts are useful as gears, cams, bearings and similar high-strength compact steel articles which are required to have wear resistance and strength to withstand fatigue in rolling or rolling-slipping applications. In a steel part formed according to the invention, a fine nitride and/or carbonitride having at least an average grain size of 0.3 &mgr;m or less is dispersed in the contact surface structure; a multi phase structure composed of martensite, which is divided into extremely fine pieces, forming a disordered shape, by the nitride and/or carbonitride, is formed; and a carbide having a grain size of 3 &mgr;m or less is dispersed to increase the hardness of the surface. Such a steel part is produced by carrying out carbonitriding or carburization/carbonitriding so as to precipitate extremely fine AlN, using nitrogen permeating from the surface and by carrying out quenching or quenching/tempering, starting from a temperature region where the parent phase is austenite.

High surface pressure resistant steel parts and methods of producing same

High surface pressure resistant steel parts and their producing methods are disclosed. These steel parts are useful as gears, cams, bearings and similar high-strength compact steel articles which are required to have wear resistance and strength to withstand fatigue in rolling or rolling-slipping applications. In a steel part formed according to the invention, a fine nitride and/or carbonitride having at least an average grain size of 0.3 &mgr;m or less is dispersed in the contact surface structure; a multi phase structure composed of martensite, which is divided into extremely fine pieces, forming a disordered shape, by the nitride and/or carbonitride, is formed; and a carbide having a grain size of 3 &mgr;m or less is dispersed to increase the hardness of the surface. Such a steel part is produced by carrying out carbonitriding or carburization/carbonitriding so as to precipitate extremely fine AIN, using nitrogen permeating from the surface and by carrying out quenching or quenching/tempering, starting from a temperature region where the parent phase is austenite

Crawler belt bushings and heir producing methods, with which productivity and cost performance can be improved over the carburization treatment and the induction hardening treatment. After a workpiece made from steel is heated from its outer circumferential surface such that at least the surface temperature of the inner circumferential surface of the workpiece is raised to a quenching temperature, a series of quenching operation is performed to form quench hardened layers which extend toward the core from the inner and outer circumferential surfaces respectively and a soft, imperfectly hardened layer between these quench hardened layers. The quenching operation comprises: cooling the workpiece from the inner circumferential surface; cooling the workpiece from the inner circumferential surface while heating from the outer circumferential surface; and cooling the workpiece from the outer circumferential surface.

Bushing for crawler belt and method of manufacture

A carburizing method is described which is capable of dispersing cementite grains in the surface of steel uniformly and finely as not to affect fatigue strength and capable of fining the crystal grains of austenite. To prevent cementite precipitation during high temperature carburization at 980&deg; C. or more, steel contains Al in an amount in the range of 0.05&lE;&lsqb;Al wt %&rsqb;&lE;2.0 and Cr in an amount in the range of 0.3&lE;&lsqb;Cr wt %&rsqb;&lE;4.0, and the composition of the steel satisfies the requirement represented by 1.9&gE;&minus;5.6&lsqb;Si wt %&rsqb;&minus;7.2&lsqb;Al wt %&rsqb;&plus;1.1&lsqb;Mn wt %&rsqb;&plus;2.1&lsqb;Cr wt %&rsqb;&minus;0.9&lsqb;Ni wt %&rsqb;&plus;1.1&lsqb;Mo wt %&rsqb;&plus;0.6&lsqb;W wt %&rsqb;&plus;4.3&lsqb;V wt %&rsqb;.

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Hirakata, Japan

Naoji Hamasaka