1) Austenitic Stainless Steel
Intergranular corrosion is the most severe type of damage to austenitic stainless steel. To avoid intergranular corrosion, the following steps can be taken:
A) Use stainless steel welding rods with ultra-low carbon content (C≤0.03%) or with stabilizing elements like titanium or niobium.
B) Use welding parameters that reduce time spent in harmful temperature zones, such as using low current, welding quickly, and preventing lateral oscillation.
C) Use forced cooling on the weld to hasten the cooling process and decrease the heat-affected zone.
Hot Cracking: To prevent hot cracking, the weld metal structure should be managed to generate a dual-phase structure with a ferrite concentration of 3% to 5%.
Effective measures include carefully designing forming and assembly processes and using appropriate welding procedures, such as post-weld solution treatment.
Poor Weld Formation: When welding austenitic stainless steel, poor surface formation of the weld can negatively impact low-temperature performance. To address this, narrow groove welding techniques should be used, welding speed should be controlled, and good fusion should be maintained.
Stress Corrosion Cracking: Stress corrosion cracking is a delayed cracking phenomenon that occurs when tensile stress acts on a welded joint in a specific corrosive environment.
2) Ferritic Stainless Steel
Choose the Right Filler Metal: To avoid cracking and improve corrosion resistance, use a filler metal with a little greater nickel content than the base metal.
Control Heat Input: Excessive heat input during welding might cause deformation and cracking. To avoid this, reduce heat input and keep the interlayer temperature below 100°C during multilayer welding.
Protect the Molten Pool: When welding ferritic stainless steel, special care must be taken to avoid contamination of the molten pool surface, which can affect weld quality. To improve protection, consider employing double-layer gas shielding, expanding the nozzle diameter, modifying the argon gas flow rate, or installing a protective gas hood below the welding torch.
Welded Joint Treatment: Intergranular corrosion and embrittlement are potential difficulties with ferritic stainless steel welded joints. Proper heat treatment can ease these issues.
3) Martensitic Stainless Steel
Pre-welding Preparation:
Clean the groove and surrounding regions well to eliminate any oil, water, or other pollutants that may introduce hydrogen.
Dry the welding rods at high temperatures to remove moisture and reduce cold crack sensitivity.
Preheating below the martensite transition temperature (150-400°C) can reduce cracking risk.
