Method for heat-treating structural material and heat-treated structural material

A method for heat-treating a structural material provided with a bent section that extends in one direction of said structural material and is bent in a direction perpendicular to said direction. Said method: determines the effective width ( e ) for the bent section; defines an effective-width region as the region, including the bent section, in which the distance from the bent section, in the abovementioned perpendicular direction, is no greater than the aforementioned effective width ( e ); determines a range for a hardening percentage ( f M ), said hardening percentage ( f M ) being defined as the percentage of the effective-width region hardened by heat treatment, on the basis of the rate at which a yield stress ( σ Y ) changes as a function of the hardening percentage ( f M ); and heat-treats the effective-width region of the structural material such that the hardening percentage ( f M ) falls within the aforementioned range.