Effect of weld microstructure on the tensile properties and impact toughness of the naval, marine-grade steel weld joints

Abstract

Pulsed direct current (PDC) gas tungsten arc welding (GTAW) of 12 mm thick plates of naval, marine-grade high strength low alloy steel (HSLA) using ER80S–Ni3 filler metal was investigated. The microstructural characteristics were examined by both optical microscopy and field-emission scanning electron microscopy (FE-SEM) techniques. The fusion zone is comprised of mixed microstructures of acicular ferrite (AF), polygonal ferrite (PF), grain boundary ferrite (GBF), and bainite ferrite (BF) laths in the various welding passes. The yield and tensile strengths of the PDCGTA weld joints were found to be superior to that of the base metal. A joint efficiency of 122% was observed for the weld seams while conducting the notch tensile studies (NTS). The impact toughness of the weld joints was higher than that of the base metal. The tensile and impact properties in the room temperature (RT) conditions were superior due to the formation of acicular ferrite (AF) and bainite ferrite (BF) laths in the weld seam microstructure. A higher toughness value of 173 J and ductile fracture mode was observed when the joints were impact loaded at −40 °C. On the other hand, the brittle cleavage fracture was observed for the joints subjected to impact loading at −196 °C. The impact toughness data indicated that the joints experienced a transition from a ductile to a brittle mode of fracture on lowering the temperature.