Mechanical Properties And Microstructural Evolution By Defromaiton And Thermal Cycle For A Novel High-Mn Cryogenic Steel

The mechanical properties from room temperature to cryogenic temperature were investigated for a novel high-Mn cryogenic steel with 0.5C,25Mn and 4Cr(in wt.%)based on understanding the relationship between stacking fault energy(SFE),microstructural evolution and deformation mechanism.The superior cryogenic toughness around~201 J was achieved and no ductile-brittle transformation temperature was found due to the highly thermal stable austenite.Only~2.5%?-martensite was detected in impact sample fractured at-196°C and consequently the ductile-dimpled fracture is dominant from room temperature to cryogenic temperature.The yield strength of 350 MPa,tensile strength of810 MPa at room temperature increased to 820 MPa and 1380 MPa at-196°C.It is controlled by the dominant twin deformation hardening mechanism with the SFE of 24.1mJ/m~2 at room temperature and combination of twin deformation hardening mechanism and martensitic transformation hardening mechanism at-196°C.Due to the lower SEF at cryogenic temperature,and encountered by strain and stress,martensite transformation should be enhanced.The welded joint of 25Mn investigated steel showed that the crack tip opening displacement(CTOD)were very high in all the matrix,coarse grained heat affected zone and the weld metal,indicating that the joint had excellent crack propagation resistance.Thermal simulation sample peak temperature is from 600°C to 1300°C,The impact toughness values are all higher than 160 J.It shows that the heat affected zone has excellent low temperature toughness.Peak temperature 600°C,1100°C and 1300°C samples exist obvious plastic deformation and mechanical twin in the instantaneous of tension and compression of impact process.This is a major cause of increasing its impact toughness values.