Effect of plasma heat source characteristics on nitrogen absorption in gas tungsten arc weld metal

Abstract

Effects of plasma heat source characteristics on nitrogen absorption in gas tungsten arc (GTA) weld metal was investigated using two-dimensional spectroscopic measurements and numerical analyses. In the condition of 1 % nitrogen-mixed shielding gas, nitrogen content of weld metal in a helium arc or an argon-hydrogen arc decreased compared to that of an argon arc. These changes in nitrogen content had a strong correlation with arc voltages for the respective shielding gases, so it was considered that nitrogen absorption in weld metal was affected by arc plasma heat source characteristics. The spectroscopic measurements of these arcs showed that the plasma temperature near the molten pool surface in the helium arc or the argon-hydrogen arc indicated around 6,500 K, while the plasma temperature in the argon arc achieved more than 10,000 K. Additionally, from numerical analyses of GTA dealing with metal vapor, it was found that the plasma temperature in the helium arc was reduced by the metal vapor generated from the molten pool. As a result, the reduction of nitrogen disassociation caused by decreasing plasma temperature was considered as the significant factor in lowering nitrogen absorption in the helium arc.

Numerical Analysis of Heat Transfer from Plasma to Base Metal Surface in Gas Tungsten Arc Welding with Metal Vapor

“…Additionally, when an Ar arc and a He arc on a steel plate were compared, it was demonstrated that the plasma temperature in the He arc dropped to less than the plasma temperature of the Ar arc, where almost no metal vapor was generated 3) .…”

Simulação De Tensões Residuais De Soldagem E Seu Alívio Por Teste Hidrostático

“…Figura 3.4: Arco elétrico com eletrodo de tungstênio e gás de proteção de hélio em chapa de cobre resfriada por água, [27].…”