Microstructure and Mechanical Properties of High-Strength Steel 22SiMn2TiB by Pulsed Melt Inert-Gas Welding with Activated Nitrogen Arc

Strength weakening exists in high-strength steel welds. Most of the researches focus on the composition of welding wire to regulate the weld strength. This article aims to study the role of nitrogen in steel welding by changing the proportion of nitrogen in the protective gas. By adding oxygen, explore the effect of activated nitrogen arc on the weld microstructure and mechanical properties of high-strength steel. Pulsed melt inert-gas welding (PMIG) technology is used to weld high-strength steel, and explore the impact on mechanical properties under activated nitrogen arc conditions. The PMIG welding process is adopted on high-strength steel, and an activated nitrogen arc is formed by Ar + N + O. The results show that under the condition of low heat input, using ER307Mo welding wire, the microstructure of the weld zone is uniform, and the grain is small. With the increase in nitrogen ratio, the actual welding current value decreases, the actual voltage value increases, the nitrogen decomposition reduces the arc energy and the solid nitrogen content of the weld increases. When the nitrogen ratio reaches 30% (vol.%) and O2 is 2.5% (vol.%), the nitrogen content reaches the maximum value, which is 0.5% (wt.%). The tensile strength reaches 970 MPa. The use of activated nitrogen arc welding can effectively increase the nitrogen content of the weld, promote the solid solution of nitrogen elements, refine the grain, and effectively improve the mechanical properties of the weld of high-strength steel.