Heat treated galvannealed steel material and a method for its manufacture

摘要

A heat treated galvannealed steel material having excellent post-painting corrosion resistance and a high strength which is suitable for use as an automotive part and a method for its manufacture are provided. A galvannealed steel material having a galvannealed coating on at least one side thereof is heat treated by heating at least a portion thereof to a temperature range in which hardening is possible. The coating remaining on the surface of at least a part of the portion which underwent heat treatment has a coating weight of at least 20 g/m2 and at most 80 g/m2 per side and an Fe content of at least 15% and at most 35%, an η phase is present in the coating, and the centerline average roughness Ra of the surface of the coating is at most 1.5 μm.

主权项

1. A heat treated galvannealed steel material formed from a galvannealed steel material, characterized in that the steel material has a rapidly cooled structure, a coating remaining on the surface of at least a part of the portion of the steel material has a coating weight of at least 20 g/m2 and at most 80 g/m2 per side and an Fe content of at least 15% and at most 35% in mass percent, an η phase is present in the coating, and the centerline average roughness Ra prescribed by JIS B 0610 of the surface of the coating is at most 1.5 μm.