Reactions at the molten flux-weld pool interface in submerged arc welding

Abstract

In submerged arc welding (SAW) of chromium (Cr) containing steels, Cr is usually added to the weld metal from the weld wire, and not from the welding flux. Manufacturing of weld wires of specific compositions is expensive and time consuming and cannot closely match all the desired alloy compositions. Therefore, the weld wire chemistry is usually over matched to the base plate composition. Better matching between the weld metal and base plate is possible if the weld metal incorporates Cr from Cr containing metal powder, instead of sourcing Cr from weld wire of limited Cr content. Because Cr is easily oxidised, the oxygen partial pressure in SAW must be controlled. This work illustrates the control of the oxygen potential at the molten flux-weld pool interface by using aluminium (Al) powder addition. The controlled oxygen potential at the molten flux-weld pool interface ensures increased Cr powder transfer into the weld pool, without interfering with oxygen transfer from the plasma arc to the weld pool. The objective of this work is to use targeted powder additions to better control Cr reactions in SAW to improve Cr metal transfer to the weld metal and maintain an acceptable level of oxygen in the weld metal.