Austenitic stainless steel refers to stainless steel with austenitic structure at room temperature. When the steel contains about 18% Cr, 8%~10% Ni, and about 0.1% C, it has a stable austenite structure. Austenitic chromium-nickel stainless steel includes the famous 18Cr-8Ni steel and high Cr-Ni series steel developed on this basis by increasing the content of Cr and Ni and adding Mo, Cu, Si, Nb, Ti and other elements. Austenitic stainless steel is non-magnetic and has high toughness and plasticity,However, the strength is low, and it is impossible to strengthen it through phase transformation. It can only be strengthened through cold working. If elements such as S, Ca, Se, Te are added, it has good machinability.
Austenitic stainless steel pipes have good weldability, low temperature toughness and non-magnetic properties.Its characteristics are that the carbon content is less than 0.1%, and the single-phase austenite structure is obtained by combining Cr and Ni, and it has good cold deformation ability, high corrosion resistance and plasticity.It can be cold drawn into very thin steel wire, cold drawn into very thin steel strip or steel pipe. At the same time, after a large amount of deformation, the strength of the steel is greatly improved, because in addition to the cold work hardening effect, the deformation-induced martensitic transformation is superimposed. Austenitic stainless steel pipes have good resistance to uniform corrosion, but there are still some problems in resistance to localized corrosion. The main problems of austenitic stainless steel pipe welding are: intergranular corrosion of welded joints, stress corrosion cracking of welded joints, hot cracking of welded joints, etc.
Welding method of austenitic stainless steel pipe
There are many welding methods for austenitic stainless steel pipes, such as manual welding, gas shielded welding, submerged arc welding, plasma welding and so on. The most commonly used welding method is manual welding (MMA), followed by metal gas arc welding (MIG/MAG) and junction inert gas welding (TIG).
1. Manual electrode arc welding. The heat of electrode arc welding is relatively concentrated, the heat affected zone is small, and the welding deformation is small; it can adapt to various welding positions and process requirements of different plate thicknesses, and the equipment used is simple.In the construction process, in order to control the welding line energy and prevent intergranular corrosion, the welding speed must be controlled, and the welding can be carried out quickly on the premise of ensuring the penetration.At the same time, in order to reduce the heat of the welding pool and improve the corrosion resistance of the weld metal, the welding rod is not allowed to swing laterally during welding, and the narrow weld bead technology is used to speed up the cooling rate.The width of the weld is generally not more than 2 times the diameter of the electrode, and the thickness of each layer of the multi-layer welding is not more than 3mm to reduce heat input and facilitate gas evolution, and the interlayer temperature is not higher than 150 ° C.
2. Jun pole ammonia gas shielded welding is an ideal welding method for welding austenitic stainless steel pipes. Due to the good effect of ammonia protection, the excessive coefficient of alloying elements is high, and the weld composition is easy to control;Due to the concentrated heat source, the line energy during welding is very small, and the ammonia gas cooling effect, the welding heat affected zone is narrow, the weld strength and plastic toughness are excellent, no slag cleaning is required after welding, and all-position welding and mechanized welding are possible. .
In the actual welding process, the arc length should be minimized under the condition that the arc is not short-circuited, and the arc voltage is generally controlled within the range of 9~20V. In order not to damage the protection of the molten pool by the airflow, the welding speed should not be too fast. At the same time, in order to improve the production efficiency, the residence time of the welded joint at the dangerous temperature of 450~850℃ should be reduced as much as possible.It is beneficial to improve the corrosion resistance of welded joints of stainless steel pipes.
Austenitic stainless steel pipes have good weldability, low temperature toughness and non-magnetic properties.Its characteristics are that the carbon content is less than 0.1%, and the single-phase austenite structure is obtained by combining Cr and Ni, and it has good cold deformation ability, high corrosion resistance and plasticity.It can be cold drawn into very thin steel wire, cold drawn into very thin steel strip or steel pipe. At the same time, after a large amount of deformation, the strength of the steel is greatly improved, because in addition to the cold work hardening effect, the deformation-induced martensitic transformation is superimposed. Austenitic stainless steel pipes have good resistance to uniform corrosion, but there are still some problems in resistance to localized corrosion. The main problems of austenitic stainless steel pipe welding are: intergranular corrosion of welded joints, stress corrosion cracking of welded joints, hot cracking of welded joints, etc.
Welding method of austenitic stainless steel pipe
There are many welding methods for austenitic stainless steel pipes, such as manual welding, gas shielded welding, submerged arc welding, plasma welding and so on. The most commonly used welding method is manual welding (MMA), followed by metal gas arc welding (MIG/MAG) and junction inert gas welding (TIG).
1. Manual electrode arc welding. The heat of electrode arc welding is relatively concentrated, the heat affected zone is small, and the welding deformation is small; it can adapt to various welding positions and process requirements of different plate thicknesses, and the equipment used is simple.In the construction process, in order to control the welding line energy and prevent intergranular corrosion, the welding speed must be controlled, and the welding can be carried out quickly on the premise of ensuring the penetration.At the same time, in order to reduce the heat of the welding pool and improve the corrosion resistance of the weld metal, the welding rod is not allowed to swing laterally during welding, and the narrow weld bead technology is used to speed up the cooling rate.The width of the weld is generally not more than 2 times the diameter of the electrode, and the thickness of each layer of the multi-layer welding is not more than 3mm to reduce heat input and facilitate gas evolution, and the interlayer temperature is not higher than 150 ° C.
2. Jun pole ammonia gas shielded welding is an ideal welding method for welding austenitic stainless steel pipes. Due to the good effect of ammonia protection, the excessive coefficient of alloying elements is high, and the weld composition is easy to control;Due to the concentrated heat source, the line energy during welding is very small, and the ammonia gas cooling effect, the welding heat affected zone is narrow, the weld strength and plastic toughness are excellent, no slag cleaning is required after welding, and all-position welding and mechanized welding are possible. .
In the actual welding process, the arc length should be minimized under the condition that the arc is not short-circuited, and the arc voltage is generally controlled within the range of 9~20V. In order not to damage the protection of the molten pool by the airflow, the welding speed should not be too fast. At the same time, in order to improve the production efficiency, the residence time of the welded joint at the dangerous temperature of 450~850℃ should be reduced as much as possible.It is beneficial to improve the corrosion resistance of welded joints of stainless steel pipes.
