Local Strain‐Hardening in Sheet Metal and Forging Components

Abstract

Metastable austenitic stainless steel has a good adaptability for different challenges in forming processes due to its good ductility and high corrosion resistance. Metastable austenitic steels are applied in the automotive industry as well as in the chemical and oil industries. The spectrum could be enlarged by optimised properties due to locally adapted material characteristics in components and assemblies. Load adapted components can be produced by selective generation of transformation‐induced martensite. The formation of martensite is realised in special forming processes of sheet metal and bulk metal components. By an upsetting process the martensitic microstructure is generated in cylindrical raw parts. One example of martensite generation in sheet metal forming is the structuring of certain areas with small buckles of pins, or the defined stretching of a local area. By this local attributes the components could be strengthened in critical areas. Alternatively, the local martensitic high‐strength areas and austenitic ductile regions lead to a defined buckling of components in case of a crash. In this paper the mechanism of martensite evolution is described and investigations and their results on sheet metal and bulk metal components are presented. A testing routine has been developed to get fast and precise information about the martensite content. In experimental studies promising results have been achieved in first crash tests with a sample geometry and in the generation of ‘structure fields'. Additionally, a suitable mathematical description of martensite evolution during deep drawing processes has been developed. The model has been successfully implemented in a finite element analysis and is used to study various arrangements of structure fields in sheet metal.