Change rule the microstructure evolution and mechanical properties of 55NiCrMoV7 die steel under different quenching temperature (790~910°C)

and tempering temperature (100 ~650°C ) are studied by means of scanning electron microscopy (SEM)

hardness test

V-impact test

uniaxial tensile test combined with finite element modeling and simulation. The results show that

with the increase of quenching temperature

spherical caibide gradually dissolves into martensite matrix

martensite structure grows and coarsens

and residual austenite increases gradually； after quenching

the HRC hardness value is basically stable at 42 ~ 46

and the yield and tensile strength first increase and then decrease

reaching a maximum of 1380 MPa and 1485 MPa after quenching at 870 °C

and the maximum value of impact toughness is 26 J after quenching at 850 °C. In different temperature tempering process

the content of martensite structure basically stable

with the increase o£ tempering temperature

the retained austenite gradually disappears

fine and dispersed carbides begin to precipitate at the boundary of martensite. Quenching at 870°C 4 h and tempering at 560°C 6 h can make 55NiCrMoV7 steel to have good comprehensive mechanical properties.