Stainless steel is a kind of delayed crack steel. Compared with ordinary carbon steel, this kind of steel has a lower thermal conductivity, a higher expansion coefficient, and slower thermal conductivity. It is easy to expand when heated and has a large expansion range. Based on this property, many problems may occur in the welding process of stainless steel plates, such as undercut, pores, lack of fusion, cracks and so on. Do you know why there are cracks in stainless steel plates during welding? Wuxi Zhongruijian Steel Trading Co., Ltd. will take you to understand. The cracks of stainless steel plates can be divided into cold cracks, hot cracks and reheat cracks according to the temperature and time of their generation.

       Hot crack， refers to the hot crack generated when the weld seam and the metal in the heat-affected zone are cooled to a high temperature range near the solidus line during the welding process.

       Preventive measures: Strictly control harmful impurities such as sulfur content and phosphorus content of stainless steel plates and welding materials, reduce the sensitivity of hot cracks; adjust the chemical composition of the weld metal, improve the weld structure, refine the grain, improve plasticity, reduce Or disperse the degree of segregation; use alkaline welding materials to reduce the impurity content in the weld and improve the degree of segregation.

       Cold cracking，refers to the generation of cold cracks when the welded joint is cooled to a lower temperature (that is, below the temperature at which austenite begins to transform into martensite).

       Preventive measures: choose low-hydrogen welding materials and weld in strict accordance with the regulations; eliminate oil stains and moisture on the weldments before welding to reduce the hydrogen content in the weld; choose reasonable welding process parameters and heat input to reduce the hardening of the weld Hydrogen removal treatment is carried out immediately after welding to make hydrogen overflow from the welded joint.

       Reheat crack， refers to the crack that occurs when the stainless steel plate is reheated within a certain temperature range (stress relief heat treatment or other heating process) after welding, which is called reheat crack.

       Preventive measures: On the premise of meeting the design requirements, choose low-strength welding materials, so that the weld strength is lower than that of stainless steel plates, and the stress is relaxed in the weld to avoid cracks in the heat-affected zone; minimize welding residual stress and stress concentration; Control the welding heat input of the welded pipe, reasonably select the preheating and heat treatment temperature, and avoid the sensitive area as much as possible.

       Stainless steel plates are generally welded after preheating. During the welding process, attention should be paid to the surrounding environment and adjustments should be made in time. If non-destructive testing is required, it is generally necessary to wait 24 hours after welding for flaw detection