TWI Industrial Member Report Summary 197/1982
By M J Vines and N Bailey
Background
Exploratory tests have been carried out to examine the influence of core wire deoxidation practice on the welding behaviour, composition and toughness of mild steel weld metal, particularly when welding positionally. Core wires of rimming steel and killed continuously cast steels of medium and high deoxidant levels were used with cellulosic, rutile and basic coatings, generally without changing the coating formulation.
Changes in welding behaviour with the different core wires, although apparent to the welders, were slight and not sufficient to impair weld quality. Differences in burnoff rate were seen only with one thin cellulosic coating.
The change from rimming steel core wires led to increases in deposit silicon content but these could be minimised in practice by restricting core wire silicon levels and possibly modification to the coating.
Killed core wires tended to give higher deposit nitrogen and lower oxygen contents with cellulosic and rutile coatings but not with the basic coatings. These changes were not simply a result of the different contents of these elements in the core wires.
Slight increases in weld strength and hardness were found when changing to the killed core wires. Changes in toughness were relatively small and did not appear to be related to core wire type, except that increasing the silicon content of basic weld metal above about 0.45% tended to affect the microstructure adversely and reduce toughness.