Abstract: 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° 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.

Abstract: 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.

Abstract: An internally toothed member is shown suitable for use as a clutch drum in an automatic transmission. The internally toothed member has the shape of a cup with an open end and a central axis. The cup-shaped member has first internal teeth extending in the axial direction and second internal teeth extending further toward the open end of the member than the first internal teeth. The internal teeth are each formed on an inner circumferential surface of the cup-shaped member in each of a plurality of locations spaced in the circumferential direction. Also, a groove for receiving a snap ring is formed in the second internal teeth closer to the open end than end faces of the first internal teeth facing the open end. Because the first and second internal teeth are formed projecting radially inward, they do not lower the rigidity of the internally toothed member.

Abstract: A bainite forming process for treating a steel material reduces the time required for a complete thermal treatment as well as the cycle time for the thermal treatment device without necessitating any special means for handling the steel material. The steel material is heated to a temperature higher than the austenitic transformation point, and temporarily quenched to an intermediate point temperature higher than the martensitic transformation point. Then, the temperature of the steel material is again raised towards the range corresponding to bainitic transformation to form a bainitic structure. The reheating is discontinued before the temperature corresponding to the austenitic transformation point is reached, and the steel material is then quenched. In the heating steps, only the portion to be treated by the bainite forming process is locally irradiated with a high-density energy beam.

Abstract: 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.