Influence of CO2 shielding gas on high power fiber laser welding performance

Abstract

The weldabilities were investigated during 10 kW high-power fiber laser welding of 304 stainless steel with the shielding gases of 100% Ar, 80% Ar + 20% CO2 and 100% CO2, respectively. As the proportion of CO2 in shielding gas increased from 0% to 20% then to 100%, the molten pool became unstable and the optional parameter range for obtaining a good weld appearance became narrow. The defocused distance was more negative during the CO2 shielded welding, where the weld joint without apparent defect, the maximum penetration, and a necking of weld width were formed. Porosity has been suppressed and eliminated in the CO2 shielded weld joint. The highest microhardness was obtained from the Ar + CO2 shielded weld joint, because the denser δ-ferrite appeared in the Ar + CO2 shielded weld joint. The microhardness of CO2 shielded weld joints was relative low because of the oxidation of the elements of C, Si, Mn, and Cr, which reduces the solid solution hardening tendency during the welding process.