The study of GMA welds with different cover gas compositions on HSLA-100 steel

Abstract

The purpose of this study was to investigate the effect of varying cover gas compositions on the microstructure and mechanical properties of single run gas-metal arc welds (GMAW) on HSLA-100 plate and seven different cover gas compositions containing varying amounts of argon, oxygen, and carbon dioxide were evaluated. A statistical and quantitative analysis of the nonmetallic inclusions in the welds metal was performed by scanning electron microscopy (SEM) and energy dispersive analysis of x-rays (EDX). These results showed that increasing the oxygen content of the cover gas reduced the inclusion size but increases the number density compared with pure argon cover gas, and that this was reflected in the weld metal microstructure since increasing amounts of acicular ferrite were detected predominantly to be of the spessartite composition (3MnO, Al2,O3 3SiO2). As a result of increasing cover gas oxygen the strength of the weld metal appeared to be lowered due to the oxidation of aluminum, silicon, manganese, and possibly titanium. In addition, the toughness was improved for weld metal generated from cover gases containing oxygen because the ductile-to -brittle transition temperature was lowered by the increasing amounts of acicular ferrite.