Effect of post-weld heat treatment and cooling techniques on mechanical performance of AH36 steel for marine structures

Abstract

The mechanical properties of structural steels used in marine environments are significantly affected by welding procedures. This research examines the impact of various cooling techniques, coupled with post-weld heat treatment (PWHT), on the strength and ductility of AH36 steel welded via shielded metal arc welding (SMAW). Heat treatments were conducted at temperatures of 450 °C, 600 °C, and 750 °C. Oil quenching and normalizing were employed as the two cooling processes. Tensile strength, elastic modulus, elongation, and impact toughness were measured through mechanical testing. The findings demonstrate that oil quenching after treatment at 450 °C yields the most favorable tensile strength and elongation properties, surpassing established safety standards. Conversely, increasing the treatment temperature to 600 °C and 750 °C reduces strength and ductility, presumably due to grain coarsening and microstructural weakening. Impact toughness is substantially improved by normalizing, especially at 600 °C, which offers the best balance of strength and toughness. These findings show that PWHT at 600 °C followed by normalizing markedly improves the mechanical properties of AH36 steel, ensuring dependable performance in harsh marine environments. This research helps improve weld quality and the safety of marine structures by carefully selecting heat treatment and cooling procedures.