Aisin Aw Co., Ltd.

Yoshimi Watanabe

Takao Taniguchi

Kouji Ohbayashi

Michio Maruki

Naohisa Momiyama

Fumitomo Yokoyama

Hideji Kato

Masayoshi Imakire

Masataka Shimazaki

In a steel member surface treatment method, only a surface layer portion of the steel member is heated to its melting point or higher to form a melt, by high density energy-beam irradiation. Subsequently, the melted portion is rapidly cooled to a martensitic transformation region, to form a martensitic structure. The temperature increasing rate in irradiation of the surface layer of the steel member is preferably 7500&deg; C./second or greater. Thereby, thermal strain and quenching failure are reduced even if the steel member is a thin plate component and a high production efficiency can be achieved.

Steel member surface treatment method

A surface hardening method, in which a surface layer on a thin steel plate member is stably melted and solidified to provide a high surface resistance against wear includes irradiation with a high density energy beam to melt a process surface portion of the steel member followed by rapid cooling. The melted surface portion includes a fully melted layer and an adjacent imperfectly or partially melted layer. At least the cooling to solidify the molten steel is performed in a short time period less than an austenitic transformation completion time at temperatures below melting, e.g., one-twentieth of the normal austenitic transformation time, and preferably both heating to melt the surface layer and cooling to solidify and harden the surface layer are performed in a time period less than the normal austenitic transformation completion time period. The high density energy beam can be divided to irradiate plural regions to melt the surfaces of the plural regions at the same time. The thermal capacity (or thickness) of the entire steel member can be designed to be as small as four times the thermal capacity of the process portion (or depth of melted portion) and still allow self cooling of the steel member to produce surface hardening. Additionally the melted-hardened surface has improved smoothness such as exhibited by a roughness which is only sixty percent or less of the roughness of non-processed surfaces.

Surface processing method for a steel member and surface processed steel

A lockup clutch for torque converter which prevents engaging and disengaging shock when a transmission torque suddenly changes, includes a lockup clutch assembly, a lockup clutch piston operating the lockup clutch assembly, and a damper device disposed between the lockup clutch piston and an output member for absorbing changes of transmission torque occurring in association with the operation of the lockup clutch assembly. The lockup clutch piston is made of steel and has a thermally treated portion placed at a surface in contact with springs of the damper device wherein the thermally treated portion is hardened by rapid local melting with high density energy radiation such as electron beam followed by rapid cooling.

Lockup clutch for a torque converter and method of thermally treating a

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Okazaki, Japan

Yoshimi Watanabe