Effect of Nb and V on Microstructure and Mechanical Properties in Hot-stamping Steel

The influence of micro alloy niobium(Nb) and vanadium(V) on microstructure and mechanical properties in hot-forming steel was investigated by optical microscope(OM),scanning electron microscope(SEM) and transmission electron microscope(TEM).The results show that the volume fraction of martensite or bainite in continuous annealing strip increased with the microalloying addition,which would promote the recrystallization nucleation ratio during the reaustenitizing process.therefore,the microstructure would be refined effectively duringthe subsequent heat treatment process.The sizes of martensitic packets and lath lamellar spacing reduce simultaneously with micro-alloying addition for the tested steel.Though both Nb and V addition improve the mechanical properties,the Nb-bearing steel shows poor tempering stability compared with the V-bearing steel.