Patent ID: 11898217
Assignee: TOYOTA JIDOSHA KABUSHIKI KAISHA
Field: Materials, metallurgy (Chemistry)
Classification: CPC C  B  Y | IPC B  C

Claim 0:
1. A method for producing a steel plate member, comprising:
a hot press forming step comprising heating the steel plate member to a temperature higher than an austenite transformation finish temperature A3 and subsequently cooling the steel plate member at a cooling rate faster than an upper critical cooling rate while press forming the steel plate member; and
a tempering step comprising reheating a second region of the steel plate member to a temperature higher than an austenite transformation start temperature A1 without reheating a first region of the steel plate member after the hot press forming step using an induction heating apparatus including a coil that is a horizontally-positioned plate member having a U-shaped cross section to cover the entire upper and lower surfaces of the steel plate member in an x-axis direction, and subsequently cooling the steel plate member at a cooling rate slower than a lower critical cooling rate, wherein
a hard region containing martensite is formed in the first region and a soft region containing ferrite and pearlite is formed in the second region, and
the cooling process of the tempering step includes correcting the shape of the second region in a temperature range from a temperature that is equal to or lower than the austenite transformation start temperature A1 to a temperature that is equal to or higher than a temperature at which transformation into ferrite and pearlite is finished while maintaining the cooling rate slower than the lower critical cooling rate.