Study On Microstructure And Properties Of HAZ Of Modified Medium Manganese Steels

Modified Medium manganese steels(MMMS)have diminished carbon and manganese contents and additional alloying elements compared with Hadfield steel.The variation of the chemical composition leads to an elevated wear resistance and work-hardening ability because of the formation of strain-induced martensite and twins.Consequently,MMMS could serve under low and medium loading conditions,while the high manganese steels may fail under the same conditions.Optical microscope(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM),microhardness tester and micro-force testing machine were used to investigate the change of microstructure and mechanical properties.The results indicate that,the microstructure of the simulated HAZ was composed of equiaxed austenite with some twins.Cementite precipitated at the grain boundary at 650°C~850°C,and cementite precipitation behavior was changed slightly as the HI increased.Dispersed vanadium carbide(VC)precipitates formed at a T_p of 650°C,then coarsened with the increasing T_p.Moreover,the coarsening of the VC particles was severe as the HI increased.The precipitation of VC was primarily limited by the volume diffusion of V in the austenite matrix.The variation in the lattice parameter of the austenite at different temperatures was attributed to carbide precipitation.The tensile strength in the simulated HAZs first increased and then decreased with the increasing T_p,but it decreased monotonically with the increasing HI.However,the toughness of the simulated HAZs shows an opposite trend with tensile strength.The ductility loss was mainly ascribed to the precipitation of the grain boundary cementite.