Effect of inclusions on microstructure and mechanical behavior of multi-pass welded naval grade steel

Abstract

This paper assesses the metallurgical characteristics and mechanical properties of multi-pass gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW) of micro-alloyed steel DMR 249-A. The prime objective was to carry out a comparative study of the microstructure and mechanical properties of the joints produced by the two types of welding. A high volume of larger sized inclusions in GMAW contributed to inferior mechanical properties. The coarse-grained part of the heat-affected zone (CGHAZ) showed a lower microhardness. Fracture always occurred in the heat-affected zone, and it is believed that it is associated with CGHAZ. GTAW joints showed low tensile residual stress, higher hardness, and tensile strength. GTA weldment also showed superior impact toughness at sub-zero temperature (–60 °C). Mn-containing inclusions were seen in GTA weldments; it is believed that they promote the formation of acicular ferrite. This is believed to be responsible for the superior mechanical properties of GTA weldments. The microstructural analysis of the two weldments revealed the presence of a higher volume fraction of acicular ferrite in the GTAW. All in all, GTAW joint was found to perform better than GMAW joint.