There are some technological difficulties in the actual welding of duplex stainless steel 2205, but in fact, if we grasp 2205 of the related material characteristics, many problems will be solved when welding is processed. Here are the following aspects.
First, compared with the first generation duplex stainless steel, 2205 has further increased the nitrogen content, and enhanced the stress corrosion resistance and pitting corrosion resistance of the material in acid medium with high chloride concentration. Nitrogen is a strong austenite generating element. Adding into duplex stainless steel can not only enhance the strength of the material, but also damage the plasticity and toughness of stainless steel, and also inhibit and delay the precipitation of carbide.
Secondly, we need to understand the organizational characteristics of 2205. Under room temperature, the austenite and ferrite structure are about half of the solid solution, so 2205 has two phase organization characteristics. It not only preserves the low thermal conductivity, corrosion resistance, crevice corrosion and chloride stress corrosion resistance of ferritic stainless steel, but also possesses excellent toughness of austenitic stainless steel, low brittle transition temperature, intergranular corrosion resistance, excellent welding and excellent mechanical properties.
The weldability of the duplex stainless steel 2205 is good, which is reflected in the low sensitivity of both cold and hot cracks. No heat is needed before welding, and no heat treatment is needed after welding. Because the nitrogen content is high, the single phase ferrite tendency of heat affected zone is also low. If we choose the right welding material, we can control the welding energy effectively, and the welding head has excellent comprehensive performance.
The thermal crack sensitivity of 2205 duplex stainless steel is much less than that of austenitic stainless steel. This is because the nickel content is small, it is easy to produce low melting point eutectic impurities very little, and it is not easy to form a low melting point liquid film. In addition, the grain has no risk of rapid growth at high temperature.
During the welding process of the duplex stainless steel, a series of changes in the metallographic structure of the weld metal and the heat affected zone are produced by the influence of the heat cycle. At high temperature, the microstructure of all duplex stainless steel is completely formed by ferrite structure. Austenite microstructure is precipitated during cooling process, and there are many factors that affect the austenite microstructure.
Thermal cycling is the most important feature in the process of duplex stainless steel welding. It is manifested that the welding thermal cycle will have great influence on the microstructure of welded joints, regardless of whether the weld or heat affected zone will undergo phase transformation, which will greatly affect the performance of welded joints.
So, it is necessary to 2205 welding process of multi pass welding, with subsequent heat treatment on the weld bead before the role of weld metal in ferrite austenite transformation into further, become the dominant two-phase structure of austenite; thermal shadow adjacent welds in the austenite ring is in effect and increased. You can also refine ferrite grain, reduce carbides and nitrides from grains and grain boundaries, so as to improve the performance of welding joint microstructure.
Source: China Duplex Stainless Steel Pipe Fittings Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)