Deoxidation of Weld Metal When Welding with Self-Shielding Cored Wires

With self-shielding cored wires, high-quality and high-productivity welding can be carried out without an external shielding. In this case, porosity of welds is usually prevented by the major weakening of the oxygen activity in the weld metal by means of a strong deoxidation by titanium and aluminum. The weakening of the oxygen activity in the weld metal prevents the generation of carbon monoxide in the weld pool in the course of welding.

Alloying of the weld metal with titanium and aluminum, however, has an unfavorable influence on the quality of welded joints. An increased titanium content, i.e., above 0.3 wt%, produces a primarily martensitic microstructure with a toughness level below 20 J at 20°C. Also, the deoxidation by aluminum provides a little lower toughness at the expense of a less favorable microstructure. Welds with around 0.75% of Al and 0.1% of Ti show a ferritic/pearlitic microstructure with toughness of around 100 J at 20°C.

With some types of cored wires for surfacing, surfacing without an external shielding can produce high-quality surfacing welds. These are cored wires for surfacing of casting metals containing strong deoxidants (Ti, Al, etc.) and also cored wires for surfacing of wear-resistant materials with a high carbon content, i.e., above 2 wt%. The occurrence of porosity in wear-resistant surfacing welds is prevented by a strong deoxidation of the weld metal by carbon and by an increased partial pressure of carbon monoxide generated above the weld pool due to carbon combustion at elevated arc temperatures.