Effect Of Nb And V On Microstructure And High Temperature Microdeformation Behavior Of 20Cr10Co10W6MoV Steel

The hot work die steel is easy to crack and fail due to the combined action of temperature and pressure.The development of high alloy die steels with better properties has become the rigidneed of the industrial field.Here,we use 20Cr10Co10W6 MoV steel to observe the high-temperature micro-deformation behaviors at different temperatures in situ by employing OM,SEM,EDS,XRD and high-temperature laser confocal microscope,as well.Furthermore,the effects of different contents of Nb and V on the high temperature mechanical properties were investigated.The deformation behavior of the tested steel at room temperature,300? and 600?shows that the tensile strength of the steel decreases gradually,the elongation after fracture increases gradually,and the crack propagation rate decreases gradually with the increase of the tensile temperature.No obvious crack propagation was observed in the test steel at room temperature.When the tested steel is stretched at 300? and 600?,the small island area surrounded by M6 C type carbides accelerates the crack propagation,and M6 C is a harmful phase.With the addition of 0.04%,0.1% and 0.3% Nb in 20Cr10Co10W6 MoV steel,the size of columnar and equiaxed grains in the as-cast microstructure decreases gradually with the increase of Nb content.When 0.1%Nb is added,the refinement effect is the most obvious.After quenching and twice tempering treatment,the size and number of blocks surrounding M6 C carbide in the microstructure are the largest,and the crack propagation is the fastest at300?.When 0.04%Nb is added,the tensile strength,elongation after fracture and strong plastic volume of the steel are 925 MPa,9.18% and 8.491GPa?%,respectively.When 0.6%,0.7% and 0.8% V are added to 20Cr10Co10W6 MoV steel,the dendrite is refined in the as-cast structure.When the content of V is 0.7%,the effect of refining austenite grain is the most obvious.After quenching and twice tempering,the island chain surrounded by M6 C in the microstructure is the most aggregated,with a larger size and the fastest crack growth.When 0.8%V is added,the tensile strength,elongation after fracture and strong plastic volume of the test steel are 943 MPa,9.73% and 9.175GPa?%,respectively.The tensile strength,elongation after fracture and strong plastic volume of20Cr10Co10W6 MoV steel are 941 MPa,9.85% and 9.268GPa?%,respectively,when both0.04%Nb and 0.7%V are added at the same time,and the mechanical properties of the steel are better than those of 0.04%Nb or 0.7%V.The above findings might provide important theoretical basis for the improvement of industrial properties of high alloy die steels.