The role of nitrogen in stainless steel welded pipe is mainly reflected in the structure, mechanical properties, and corrosion resistance of stainless steel.

Firstly, the structure of stainless steel:  nitrogen is a strong element that can form and stabilize austenite and expand the austenite phase.It can also replace part of nickel in stainless steel, reduce ferrite content, and make austenite more stable. Even under cold working conditions, the precipitation of harmful intermetallic phases and martensitic transformation can also be prevented.

Secondly, the effect of nitrogen on the mechanical properties of stainless steel: Nitrogen can significantly increase the strength of stainless steel without reducing the plasticity and toughness of stainless steel. Nitrogen can also improve the creep resistance, fatigue resistance, wear resistance, and yield strength of stainless steel.

Last, as an element that improves corrosion resistance, nitrogen can also form nitrogen gas in NH4+ in the pores, eliminate the generation of H+, suppress the pH value, thereby inhibiting the occurrence and dissolution rate of pitting corrosion in metal pores, and effectively improve localized corrosion.

Therefore, 304 stainless steel pipes have always insisted on using nitrogen as internal protection in production, which greatly reduces the chance of pipes being rusted from the weld in the later stage, and some pipes produced without nitrogen internal protection are easy to crack and rust at the weld.