Abstract
In submerged arc welding (SAW) of chromium containing steels, the chromium in the weld metal is usually sourced from weld wire. Manufacturing of precise weld wire compositions for alloying of the weld metal is expensive. In addition, alloying of weld metal with high levels of copper via weld wire is hindered by work hardening of the weld wire. In the SAW process, a large quantity of oxygen is added to the weld pool. Because chromium has a high affinity for oxygen, the oxygen partial pressure at the weld pool-molten flux interface must be controlled to ensure high recovery of chromium to the weld metal. This study illustrates the application of copper as stabilizer, in conjunction with aluminum, to enhance chromium transfer to the weld pool. The stabilizer effect occurs because the Cr-Al-Cu alloy liquidus temperatures are much lower than the pure Cr liquidus temperature. The result is an increase in the total quantity of Cr, Al, and Cu powder melted into the weld pool. The application of Al powder additions to control the partial oxygen pressure at the molten flux-weld pool interface is confirmed in the presence of Cr and Cu metal powders to ensure the weld metal ppm O content is maintained at the acceptable level of 300 ppm.
Highlights
Submerged arc welding (SAW) is applied in heavy engineering industries to weld thick steel plate sections [1]
Three welding test scenarios are reported: the base case (BC) in which no metal powders were added to the weld metal, MP2 weld metal formed with Al and Cr metal powder addition, and MP4 weld metal formed with Al, Cr, and Cu metal powder addition
The results presented here confirm the feasibility of using unconstrained Al powder additions in SAW to reduce the oxygen potential at the molten flux-weld pool interface to achieve increased metal transfer from metal powders to the weld pool
Summary
Submerged arc welding (SAW) is applied in heavy engineering industries to weld thick steel plate sections [1]. Electrical current is passed between the continuously fed weld wire tip and the steel base plate to generate an arc which drives the complex chemical and electrical processes in SAW. Welding flux is continuously fed with the weld wire. As the weld wire is fed into the arc cavity, it melts into droplets which are transferred to the weld pool. The SAW process in the arc cavity and in the trailing weld pool consists of complex interactions of physical and chemical phenomena of heat and mass transfer [1,2]. The overall SAW chemical reaction time is set by the steel solidus temperature because chemical reactions between the molten weld pool and its covering slag may continue as long as the weld metal remains partially molten [3,4]. It has been empirically determined that the weld metal total oxygen content, and hydrogen content, are maintained at low levels if the flux composition is specified to ensure that the basicity index (BI) is held higher than 1.5, see Equation (1)
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