Microstructure and properties of Nb-bearing high-strength low-alloy surfacing layers

Based on Q345 steel, high-strength low-alloy surfacing layers with Nb content ranging from 0.0041 to 0.26 wt-% were prepared by adding Nb element into electrode coating and manual electric arc welding, the microstructure as well as mechanical properties of surfacing layers were evaluated and analysed. The experimental results show that with the increasing of Nb content, the grain size becomes smaller meanwhile the microstructure distribution is more uniform, the size of hard phase martensite/austenite gradually decreases and the NbC precipitates increases. The yield and tensile strength greatly increase for the fine-grain strengthening of Nb and the precipitation strengthening of NbC, moreover, the impact toughness is significantly improved due to the microstructure variation and obvious grain refinement.