Abstract: A current density changing portion is formed in a heating process on an upper base side with respect to a center portion of a flat metal plate in a direction of current flow, by passing current from a lower base side to the upper base side of the flat metal plate which is rectangular when viewed from above. As a result, a quenchable portion is formed on the upper base side with respect to the center portion of the flat metal plate in the direction of current flow, and a non-quenchable portion is formed on the lower base side with respect to the center portion of the flat metal plate in the direction of current flow. The flat metal plate is press-formed after the heating process, so a complex die cooling structure is not necessary during press-forming, which enables the die cost to be reduced.

Abstract: In a hot press molding method for press-molding a heated material and cooling the material while holding the material in a mold, during press molding of the material, shape changes including a portion that curves with respect to a longitudinal direction of the material are molded at longitudinal opposite end portions of the material and resistance to thermal contraction force of the material in the longitudinal direction during cooling is imparted. In one embodiment of the present invention, the shape changes molded on the material during the press molding are minute protrusions provided on surfaces of the longitudinal opposite end portions of the material. The invention makes it possible to suppress thermal contraction of the material during cooling in hot press molding to thereby prevent defects associated therewith.

Abstract: A current density changing portion is formed in a heating process on an upper base side with respect to a center portion of a flat metal plate in a direction of current flow, by passing current from a lower base side to the upper base side of the flat metal plate which is rectangular when viewed from above. As a result, a quenchable portion is formed on the upper base side with respect to the center portion of the flat metal plate in the direction of current flow, and a non-quenchable portion is formed on the lower base side with respect to the center portion of the flat metal plate in the direction of current flow. The flat metal plate is press-formed after the heating process, so a complex die cooling structure is not necessary during press-forming, which enables the die cost to be reduced.