Oxides in steel weld metals can initiate fracture or can improve toughness by influencing the development of beneficial microstructures. In this work, experiments have been conducted in which the oxygen concentration was varied from 20 to 560 ppmw (parts per million by weight) in weld metals with tensile strength in the range 580-780 MPa. It is demonstrated that low and medium strength weld metals benefit from oxides up to a concentration of about 200 ppmw as consistent with previous research, because acicular ferrite is stimulated in the microstructure. By contrast, oxides are detrimental to the toughness of high strength weld deposits at low oxygen concentrations under 140 ppmw, because the microstructure remains predominantly martensitic and the oxides simply serve to nucleate fracture. In high strength weld metal, therefore, good toughness is achieved even at low oxygen concentration of 20 ppmw O.
Science and Technology of Welding and Joining 11 (2006) 509-516.
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