Effect of microalloying with Nb and/or V on the microstructure and mechanical properties of GPa grade deposited metals

The deposited metals are prepared by flux cored arc welding used metal cored wire with Nb-V microalloying. The effects of Nb-V microalloying on microstructure, precipitate evolution, and mechanical properties of deposited metal as-welded and post-weld heat treatment (PWHT) are studied. The microstructure of deposited metals without Nb/V is bainite and massive martensite. The microstructure of deposited metals with 0.08%Nb is granular bainite and M-A constituents. The 0.06%V microalloying promotes the formation of lath bainite, and deposited metal with 0.08% Nb&0.06%V is lath bainite. The Nb and V microalloying shifts the continuous cooling transformation curve of deposited metal to left, which is conducive to the formation of bainite. After PWHT, the precipitated phases of deposited metals containing Nb and V are mainly Cu-rich particles and MC-type carbide. The yield strength of deposited metals with Nb and V as-welded are 764 similar to 795 MPa, owing to fine grain strengthening and dislocations strengthening. The grain refinement effect of V is better than Nb. Meanwhile, the yield strengths of deposited metals with Nb and V are 868 similar to 884 MPa after PWHT, which is obviously improved by precipitation of MC and nano-Cu particles and little reduction of dislocation density. The anti-softening effect of V is remarkable. The MC precipitation strengthening of deposited metal with 0.08%Nb is similar to 94 MPa, which is better than that of 0.06%V. The MC precipitation strengthening reached similar to 111 MPa of deposited metal with 0.08%Nb and 0.06%V.