Nitrogen Content and Porosity of Mild Steel Weld Metal

Abstract

Effect of the nitrogen partial pressures in the welding atmospheres of several gas mixtures and welding conditions on the nitrogen content and porosity of mild steel weld metals were studied by using an arc atmosphere controlled chamber. The results were summarized as follows ;
1. The nitrogen contents of weld metals decrease with increasing welding current.
2. The anomalous nitrogen absorption into weld metal is observed at low arc atmospheric pressures.
3. The existence of oxidizing gas in arc atmosphere such as oxygen or carbondioxide con-tributes greatly to the nitrogen absorption into weld metals.
4. In reducing gas atmospheres such as nitrogen-hydrogen mixtures, the nitrogen contents in weld metals show a tendency to obey the square root law.
5. Some calculations for the nitrogen absorption into weld metals were made using thermo-dynamic data obtained by an equilibrium study.