Nitrogen Absorption
Nitrogen pickup is the absorption of nitrogen from the air into the molten weld pool, leading to porosity and embrittlement.
Physicochemical mechanism of action
Nitrogen pickup occurs when nitrogen molecules from the surrounding air diffuse into the molten pool. This happens especially at high temperatures and low pressure differential between air and weld pool.
Metallurgical relevance & risks in welding
Nitrogen pickup leads to porosity, as the gas remains in the molten pool and becomes pores upon solidification. This can impair the mechanical properties of the weld and lead to embrittlement, especially if the nitrogen content exceeds 0.2 %.
Workshop practice & instructions
To minimize nitrogen pickup, the weld pool should be well shielded. If nitrogen levels in the air are high, the pool can be kept under pressure or a shielding gas atmosphere such as argon can be used. Minimize the time the pool stays molten.