Heat treated galvannealed steel material and a method for its manufacture
View Patent ↗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/m 2 and at most 80 g/m 2 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.
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/m 2 and at most 80 g/m 2 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.
2. A heat treated galvannealed steel material as set forth in claim 1 characterized in that the remaining coating contains at most 0.45 mass percent of Al.
3. The heat treated galvannealed material as set forth in claim 1 , characterized in that the heat treated galvannealed steel material is an automobile part.
4. The heat treated galvannealed material as set forth in claim 1 , characterized in that the heat treated galvannealed steel material is a hot-bent pipe.
5. The heat treated galvannealed material as set forth in claim 4 , characterized in that the hot-bent pipe is an automobile part.
6. The heat treated galvannealed material as set forth in claim 1 , characterized in that the heat treated galvannealed steel material is a hot-bent tapered steel member.
7. The heat treated galvannealed material as set forth in claim 6 , characterized in that the hot-bent tapered steel member is an automobile part.
8. The heat treated galvannealed steel material as set forth in claim 1 , wherein the coating-containing steel material has a paint layer on a surface thereof.
9. A hot-formed and heat treated galvannealed steel member having a rapidly-cooled structure, characterized in that a coating remaining on the surface of at least a part of the portion of the steel member has a coating weight of at least 20 g/m 2 and at most 80 g/m 2 per side and an Fe content of at least 15% and at most 35% in mass percent, and eta-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 micrometers.
10. The hot-formed member as set forth in claim 9 characterized in that the remaining coating contains at most 0.45 mass percent of Al.
11. The hot-formed member as set forth in claim 9 , characterized in that the member is an automobile part.
12. The hot-formed member as set forth in claim 9 characterized in that the member is a hot-bent pipe.
13. The hot-formed member as set forth in claim 12 , characterized in that the hot-bent pipe is an automobile part.
14. The hot-formed member as set forth in claim 9 , characterized in that the member is a hot-bent tapered steel member.
15. The hot-formed member as set forth in claim 14 , characterized in that the hot-bent tapered steel member is an automobile part.
16. The hot formed member as set forth in claim 9 , wherein the coating-containing steel member has a paint layer on a surface thereof.