METHOD FOR STRENGTHENING STEEL PLATE MEMBER

摘要

Provided is a method for strengthening a steel plate member in which: a first heating step is for heating the entirety of a steel plate to a non-quenching temperature (NQT) set to be less than a transformation start temperature (AC1) and then temporarily stopping the heating; a partial cooling step is for cooling a non-strengthened portion of the steel plate so that a temperature difference arises between a strengthened portion and the non-strengthened portion, as guided by a temperature difference (DeltaT) established by subtracting the non-quenching temperature (NQT) from a quenching temperature (QT) set to be not less than a transformation end temperature (AC3); a second heating step is for once again heating the steel plate until the non-strengthened portion halts at less than the transformation start temperature (AC1) and the strengthened portion of the steel plate reaches the quenching temperature (QT), stopping the heating, and transitioning to a total cooling step; and the total cooling step involves quenching only the strengthened portion but not quenching the non-strengthened portion, by rapidly cooling the steel plate in a state where heating has been stopped.