Abstract
The structure–property relationship in heat-affected zone (HAZ) of a low-carbon steel bearing V–N subjected to gas-shielded arc welding was explored. The microstructural characteristics of base metal (BM), coarse-grained HAZ (CGHAZ), fine-grained HAZ, and intercritical HAZ were significantly different. The effect of grain-refinement strengthening and transformation hardening on HAZ contributed to equivalent hardness of 260.8–278.5 HV in comparison with BM hardness of 272.0 HV. Moreover, excellent impact toughness at − 20 °C was obtained because of high resistance to crack propagation by high-misorientation boundaries, leading to impact fracture consisting of dimples. In CGHAZ, free N was partly fixed by V(C, N) precipitates, such that the deterioration effect of N on toughness was considered to be nearly eliminated. In comparison with CGHAZ, weld metal contained higher fraction of acicular ferrite with fine plates, while the impact toughness was inferior because of the detrimental influence of coarse inclusions from the welding wire. The nanoscale V(C, N) precipitates in CGHAZ had weak effect on toughness because of small size.
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