FORMED BODY OF STEEL PLATE MEMBER, AND MANUFACTURING METHOD THEREFOR

摘要

PROBLEM TO BE SOLVED: To reliably obtain a formed body having the sufficiently high strength characteristic after the nitriding while ensuring the plastic workability of a steel plate in obtaining the formed body of a steel member of high strength by implementing the nitriding after a stock steel plate is plastically worked. SOLUTION: The stock steel plate having the tensile strength of <=500 MPa and containing nitriding elements is prepared, the stock steel plate is plastically worked to manufacture the formed body of a predetermined shape, and the formed body is nitrided so that the mean hardness of the obtained steel plate in the thickness direction is >=Hv 300 of Vickers hardness. In addition, the differential hardness between a surface portion of the steel plate and an internal center in the thickness direction is <=Hv 200 of Vickers hardness.