Investigation and Prediction of the Influence of Shielding Gas Composition on Residual Stress

Abstract

Residual stresses are internal stress distribution locked up within a material or weldment area. They usually exist inside the material (or weld) irrespective of external loading. These stresses are generated upon equilibrium of materials after plastic deformation caused either by applied mechanical loads, thermal loads or phase change and they play key role in the failure of these joints. Therefore, accurate prediction and reduction of residual stress are critical in improving the quality of a weldment. Welding process generates residual stresses of various magnitudes, and the combination of shielding gases at various percentages might affect the amount of residual stresses in weldment. The resultant residual stress from shielding gas on welded joint is unknown and has been based on trial and error assumption. This study therefore, focused on the investigation and prediction of shielding gas mixtures to minimize residual stress formation in mild steel welded joint, employing scientific design of experiment using Box-Beckhen's design (BBD) matrix, statistical and mathematical models to measure the residual stresses from various gas mixtures. The argon (Ar) and carbon-dioxide (CO₂) shielding gas variations considered for the experiment were: 100%wt. Ar and 0%wt. CO₂; 75%wt. Ar and 25%wt. CO₂; 50%wt. Ar and 50%wt. CO₂; 25%wt. Ar and 75%wt. CO₂, 0%wt Ar and 100%wt. CO₂. The weldment produced by shielding gas of 100%wt. Ar and 0%wt. Co₂ had the highest residual stress while the weldment of 50%wt. Ar and 50%wt. CO₂, 25%wt. Ar and 75%wt. CO₂, 0%wt. Ar and 100%wt. CO₂ produced weld with lesser residual stress values.