Welding characteristics of austenitic stainless steel: 1, which is easy to produce hot cracks. Preventive measures: (1) Try to make the weld metal in a biphasic structure, and control the ferrite content below 3-5%. Because ferrite can dissolve many harmful S and P impurities. (2) Try to choose high-quality alkaline coated covered electrode to limit the content of S, P and C in weld metal. 2. Intergranular corrosion: According to the theory of chromium deficiency, when the weld and heat affected zone are heated to the sensitization temperature of 450-850℃, chromium carbide precipitates on the grain boundaries, resulting in chromium-deficient grain boundaries, which is not enough for corrosion resistance. Matters needing attention: (1) Use low-carbon or ultra-low-carbon welding materials, such as A002 using covered electrode containing stable elements such as titanium and niobium, such as A 137 and A 132. (2) A certain amount of ferrite forming elements are melted into the weld with welding wire or covered electrode, so that the weld metal becomes austenite+ferrite dual-phase structure (ferrite is generally controlled at 4- 12%). (3) Reduce overheating of welding pool, choose smaller welding current and faster welding speed, and speed up cooling. (4) carrying out post-weld stabilization annealing treatment on weldments with high requirements for intergranular corrosion resistance; 3. Stress corrosion cracking: Stress corrosion cracking is a delayed cracking phenomenon when the welded joint is subjected to tensile stress in a specific corrosive environment. Stress corrosion cracking of austenitic stainless steel welded joints is a serious failure form of welded joints, which shows brittle failure without plastic deformation.

Measures to prevent stress corrosion cracking: (1) Formulate reasonable molding and assembly technology, minimize cold deformation, avoid forced assembly, and prevent all kinds of scars during assembly (all kinds of assembly scars and arc burn marks will become the crack source of SCC and easily cause corrosion pits). (2) Reasonable selection of welding materials: the welding seam should be well matched with the parent metal, and there will be no bad structures such as grain coarsening and hard-brittle martensite; (3) Adopt proper welding technology: ensure the weld is well formed and free from defects such as stress concentration or undercut; Adopt reasonable welding sequence to reduce welding residual stress level; (4) Stress relieving treatment: post-weld heat treatment, such as complete annealing or post-weld annealing; When heat treatment is difficult, post-weld hammering or shot peening is adopted. (5) Production management measures: control impurities in the medium, such as O2, N2 and H2O； in liquid ammonia medium; H2S； in liquefied petroleum gas; O2, Fe3+ and Cr6+ in chloride solution; Anticorrosion treatment: such as coating, lining or cathodic protection; Add corrosion inhibitor. 4. Low temperature embrittlement of weld metal: For austenitic stainless steel welded joints, the plasticity and toughness of weld metal are the key issues when used at low temperature. At this time, the existence of ferrite in the weld structure will always reduce the low temperature toughness. Preventive measures: A single austenitic weld can be obtained by selecting pure austenitic welding materials and adjusting welding process. 5. σ phase embrittlement of welded joint: After heating at high temperature for a certain period of time, brittle σ phase will precipitate in the weld, which will lead to embrittlement of the whole joint and obvious decrease of plasticity and toughness. The precipitation temperature range of σ phase is 650-850℃. In the process of high temperature heating, σ phase is mainly transformed from ferrite. The longer the heating time, the more σ phase precipitates. Preventive measures: (1) limit the ferrite content in weld metal (less than15%); Super alloy welding material, that is, high nickel welding material, is adopted. (2) adopting small specifications to reduce the residence time of weld metal at high temperature; (3) When conditions permit, solid solution treatment is carried out on the precipitated σ phase to dissolve the σ phase into austenite.