Aluminium-assisted alloying of carbon steel in submerged arc welding with Al-Cr-Ni unconstrained metal powders : thermodynamic interpretation of gas reactions

Abstract

Unconstrained metal powders of chromium and nickel, in combination with aluminium, were used in the submerged arc welding (SAW) process to simplify weld metal alloying. Unconstrained metal powders refer to non-alloyed metal powders that are not constrained in tubular wire, such as fluxed-cored and metal-cored wire. Aluminium powder is used to control the oxygen potential at the molten flux–weld pool interface. The results presented here show that the addition of aluminium powder to the weld metal enhances Cr and Ni yields to 89% for Cr and 91% for Ni, compared to lower values reported in pre-alloyed powder application. Alloying of the carbon steel in the base plate and weld wire combination was achieved at 6.0% Cr, 6.2% Ni, and 4.5% Al, with the weld metal oxygen controlled to 162 ppm O. Thermodynamic analysis was applied to investigate the likely gas reactions in the arc cavity emanating from the chemical interaction between Cr, Ni, and Al. The effects of gas-based chemical reactions on the yield of Cr and Ni to the weld pool are discussed and incorporated into our SAW reaction flow diagram. Overall SAW process productivity gains can be accomplished by using unconstrained metal powders to alloy the weld metal because expensive and time consuming steps, such as the manufacturing of alloyed wire and alloyed powder, can now be eliminated.