Development of rapid heating and cooling (flash processing) process to produce advanced high strength steel microstructures

Flash processing of an AISI8620 steel sheet, which involves rapid heating and cooling with an overall process duration of <10 s, produced a steel microstructure with a high tensile strength and good ductility similar to that of advanced high strength steels. Flash processed steel [ultimate tensile strength (UTS): 1694 MPa, elongation: 7·1], showed at least 7 higher UTS and 30 greater elongation than published results on martensitic advanced high strength steel (UTS: 1585 MPa, elongation: 5·1). The underlying microstructure was characterised with optical, scanning electron, transmission electron microscopy as well as hardness mapping. A complex distribution of bainitic and martensite microstructures with carbides was observed. A mechanism for the above microstructure evolution is proposed.