Further Studies of Microstructural Development in Low Oxygen Steel Weld Metal: Effects of Al, Ti and V in TIG and Laser Weld Metals

TWI Industrial Member Report Summary 514/1995

N Francis-Scrutton

Background

It is well established that high toughness of C-Mn and microalloyed steel weld metal deposited by submerged arc, metal active gas and manual arc processes is normally associated with a predominantly fine-grained acicular ferrite (AF) microstructure. For these higher oxygen processes it is well established that if the Al/O ratio exceeds unity this can prevent, or at least severely limit, AF formation. Dilution of Al in low oxygen welding processes (e.g. autogenous tungsten inert gas (TIG), laser and electron beam welding) is particularly problematic. This is because, the oxygen level of such weld metals made in normal low oxygen plate may only be a few tens of ppm compared with several hundred ppm in weld metal deposited by manual metal arc and submerged arc processes. Therefore, even very low levels of Al diluted into the low oxygen weld metals can result in an Al/O ratio significantly greater than one. An understanding of how to obtain a fine AF microstructure in low oxygen weld metal without limiting.