Reactive Gas Absorption in Melt Pool
Reactive gas absorption in the weld pool is the unwanted diffusion of oxygen or nitrogen from the process atmosphere into the molten metal, leading to embrittlement and the formation of non-metallic inclusions.
Physical-chemical mechanism of action
Oxygen and nitrogen diffuse from the process atmosphere into the molten metal. This process is controlled by the concentration gradient between the atmosphere and the weld pool. Diffusion is a physical process where atoms or molecules move from a region of higher concentration to a region of lower concentration.
Metallurgical relevance & welding risks
Reactive gas pickup leads to embrittlement of the weld, since oxygen and nitrogen react chemically with the metal. This can cause nonmetallic inclusions like silicate or oxide inclusions, which impair the strength and toughness of the material. In addition, embrittlement can make the weld more prone to cracking and hot cracking.
Shop practice & action items
To minimize reactive gas pickup, run the weld pool in a closed system to reduce contact with the atmosphere. This can be done by using shielding gases like argon or helium. Check and control the process atmosphere regularly to make sure oxygen and nitrogen levels stay below the allowed limits. When picking the shielding gas, make sure it doesn't react with the metal or cause embrittlement.