Abstract
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.
Highlights
Submerged arc welding (SAW) is applied in the welding of thick steel plates in heavy engineering industries such as shipbuilding and pressure vessel construction [1]
CaF2 is added to control the slag solidification temperature which should be approximately 50°C below the solidification temperature of the welded steel plate to ensure increased time for element transfer reactions between the flux and weld pool [4,7]. This is an important flux design parameter used to ensure that the slag layer remains molten for a longer period of time than the weld metal to ensure oxide inclusions incorporate into the slag layer at the slag-weld pool interface, ensuring weld metal cleanliness in terms of oxide inclusion content [8]
Increased Si and Mn contents in the metal powder addition (MP) weld metal, compared to the Base case (BC) weld metal, confirm that sufficient contact time was established between Al powder and molten flux to enable reactions (2) and (3) to proceed forward
Summary
Submerged arc welding (SAW) is applied in the welding of thick steel plates in heavy engineering industries such as shipbuilding and pressure vessel construction [1]. CaF2 is added to control the slag solidification temperature which should be approximately 50°C below the solidification temperature of the welded steel plate to ensure increased time for element transfer reactions between the flux and weld pool [4,7]. This is an important flux design parameter used to ensure that the slag layer remains molten for a longer period of time than the weld metal to ensure oxide inclusions incorporate into the slag layer at the slag-weld pool interface, ensuring weld metal cleanliness in terms of oxide inclusion content [8]. Chemical reactions between oxides and fluorides form volatilised fluorides which lower the partial pressure of
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