LOCAL SURFACE STRENGTHENED MEMBER AND METHOD OF STRENGTHENING LOCAL SURFACE

摘要

PROBLEM TO BE SOLVED: To provide a manufacturing method for a local surface strengthened member in which a vicinity of a surface of a specific site (local portion) of a steel member is strengthened compared to a neighboring area.;SOLUTION: A method of strengthening a local surface according to the invention includes: a plastic processing step in which a vicinity of a surface of at least one or more local positions of a work consisting of steel material is subjected to plastic processing by which an equivalent strain at a specific position of 0.5 mm inside from an outermost surface of the local position is 0.8-20; and a nitriding step in which at least the plastic-processed local position is subjected to nitriding treatment at a treatment temperature of less than a transformation temperature of the steel material. This results in a local surface strengthened member in which an inside hardness at the local position, which represents a Vickers hardness (HV) at the specific position, is greater by 50 HV or more than that of a base material hardness of the steel material around the local position, a maximum hardness of the local position, which represents a maximum Vickers hardness within a specific area which is from an uppermost surface of the local position to the specific position, is greater by 100 HV or more than the base material hardness, and a nitriding depth is 0.15 mm or more, which is about 1.2 to 3 times deeper than a case where no strain is introduced.;COPYRIGHT: (C)2015,JPO&INPIT