After the austenitic stainless steel pressure vessel is formed by the plate rolling machine, it will be welded. What should we pay attention to?
In general, austenitic stainless steels have excellent weldability. Almost all fusion welding methods can be used to weld austenitic stainless steel. The thermophysical properties and microstructure characteristics of austenitic stainless steel determine the key points of its welding process.
5 welding points of austenitic stainless steel
Due to the small thermal conductivity and large thermal expansion coefficient of austenitic stainless steel, it is easy to generate large deformation and welding stress during welding, so the welding method with concentrated welding energy should be selected as much as possible.
Due to the small thermal conductivity of austenitic stainless steel, it can obtain a larger penetration depth than low alloy steel under the same current. At the same time, due to its high resistivity, in order to avoid redness of the electrode during arc welding, the welding current is smaller than that of carbon steel or low alloy steel electrodes of the same diameter.
Generally, high energy is not used for welding. In electrode arc welding, it is advisable to use small-diameter electrodes and fast multi-pass welding. For high-demand welds, even pour cold water to accelerate cooling. For pure austenitic stainless steel and super austenitic stainless steel, due to the sensitivity of hot cracks The welding line energy should be strictly controlled to prevent the serious growth of the weld grains and the occurrence of welding hot cracks.
Welding area cleaning
In order to improve the thermal crack resistance and corrosion resistance of the weld, special attention should be paid to the cleanliness of the weld area during welding to prevent harmful elements from penetrating the weld.
Preheating is generally not required when welding austenitic stainless steel. In order to prevent the grain growth and the precipitation of carbides in the weld and the heat-affected zone, and to ensure the plasticity, toughness, and corrosion resistance of the welded joint, the lower interlayer temperature should be controlled, generally not exceeding 150 °C.
How to choose austenitic stainless steel welding consumables
- The selection principle of austenitic stainless steel welding consumables is to ensure that the corrosion resistance and mechanical properties of the weld metal are basically equal to or higher than the base metal under the condition of no cracks. Generally, the alloy composition is generally required to be roughly the same as that of the base metal. match.
- Corrosion-resistant austenitic stainless steel generally contains a certain amount of ferrite, which can not only ensure good crack resistance but also have good corrosion resistance. However, in some special media, such as the weld metal of urea equipment, ferrite should not exist, otherwise, its corrosion resistance will be reduced.
- For heat-resistant austenitic steels, the control of the ferrite content in the weld metal should be considered.
- For austenitic steel weldments operating at high temperatures for a long time, the ferrite content in the weld metal should not exceed 5%.