Aluminium assisted nickel alloying in submerged arc welding of carbon steel : application of unconstrained metal powders

Abstract

Nickel alloying of carbon steel is used to enhance steel strength and toughness. Nickel alloying of the weld metal via solid weld wire presents several difficulties as highlighted previously, such as work hardening of the solid weld wire in manufacturing and feeding through the SAW wire feeding mechanism, and expensive and time consuming manufacturing of multiple weld wire formulations. The application of nickel and aluminium powders in unconstrained format, meaning not as fluxed cored wire or as metal cored wire, is used to simplify weld metal alloying. Al powder is used to control the oxygen potential at the weld pool-molten flux interface. The results presented here show that the addition of Al powder to the weld metal enhances Ni yield to the weld metal, at 85%, compared to pre-alloyed powder Ni yields of 57–78% as applied in previous work. Carbon steel was alloyed to 6.9% Ni and 3.7% Al. Thermodynamic analysis is applied to elucidate the chemical interaction between Ni and Al, and its effects on Ni yield in the weld pool. Overall process productivity gains stem from weld metal alloying from unconstrained metal powders because the expensive and time consuming step of manufacturing alloyed wire and alloyed powder is eliminated