ABSTRACT

In order to improve the collision safety of automobiles, the application of hot stamping has been expanding, and body-in-white parts have been manufactured. In hot stamping, manganese–boron steel, 22MnB5, in which the quenchability is improved by adding elements such as manganese and boron, is generally used. In hot stamping, the steel sheet is heated to about 900°C in the furnace and is formed under austenite. For hot-stamped parts from the non-coated sheet, the oxide scale on the surface is removed by shot blasting treatment. The bending load is reduced to about 1/3 to 1/4 of that for cold stamping, and thus high-strength parts can be produced for a small stamping load. In cold stamping, the forming load increases with increasing strength of the steel sheet, and the springback induced by the elastic recovery in unloading becomes large. In cold stamping, the draw-type tools are generally employed, and the tension is applied with the sheet holders to reduce the springback.