Abstract: Disclosed is a high frequency heat treatment method of hot-stamping-treated ultra-high strength parts, which comprises: a first step of heating the parts until the temperature of a heat treatment zone thereof becomes the AC3 transformation point or higher; a second step of maintaining the temperature until phase transformation of the heat treatment zone to austenite is completed; and a third step of cooling the heat treatment zone to transform the structure thereof to ferrite-pearlite. The present method improves the energy absorbing efficiency by increasing the parts' elongation ratio by locally forming a softening structure which absorbs energy.

Abstract: A spot welding method for a high strength steel sheet is provided. The method includes a first pulse step for applying electric current of about 8 to 9 kA about 1 to 3 cy and a first cooling step for cooling for about 1 to 3 cy. In addition, the method includes a second pulse step for applying electric current less than the electric current applied in the first pulse step and a second cooling step for cooling for about 1 to 3 cy. A third pulse step includes applying electric current greater than the electric current applied in the second pulse step.

Abstract: Disclosed herein is a method of welding aluminum sheets, including: supplying aluminum sheets overlapping each other between an upper electrode and a lower electrode; supplying thin metal sheets plated on both sides thereof with nickel (Ni) between the upper electrode and an upper aluminum sheet and between the lower electrode and a lower aluminum sheet, respectively; and supplying power to the upper and lower electrodes and then welding the aluminum sheets.

Abstract: Disclosed is a material of a kick-down drum comprising fine ferrite and microdispersion spheroidized cementite for an automobile also disclosed is a method for manufacturing the kick-down drum material. The kick-down drum of this invention can greatly improve hardenability and durability of the spline member and also has advantages of reducing production costs due to a simplified process of adding only a heating process.