Duplex Stainless Steel Pipe Welding performance
Duplex stainless steel tube has good welding performance, compared with the ferritic stainless steel and austenitic stainless steel, it is neither like ferritic stainless steel weld heat affected zone, as grain coarsening and make the plastic toughness sharply lower, also don't like austenitic stainless steel, the welding thermal crack is more sensitive.
Duplex stainless steel because of its special advantages, is widely used in petroleum chemical industry equipment, water and waste water treatment equipment, oil gas transmission pipeline, paper making machinery and other industrial areas, has also been used for bridge bearing structure field in recent years, has the very good development prospect.
The two-phase stainless steel is half of the ferritic and austenitic elements in its solid quenched tissue, and the normal minimum phase of the phase may be up to 30%.
Double phase stainless steel pipe safety use restriction and requirement
1. The need to control the phase ratio, the most appropriate proportion is ferrite and austenite meet each half, including a number of not more than 65%, so as to ensure the best comprehensive performance. If the two phases are misaligned, such as the excess of ferrite, it is easy to make a single phase iron in welding HAZ, which is sensitive to stress corrosion cracking in some medium.
2. Need to master organization change law of duplex stainless steel tube, and familiar with each steel grade TTT CCT curve, this is the correct guidance for duplex stainless steel heat treatment, hot forming technology is the key, such as precipitation of duplex stainless steel brittle phase are much more sensitive than austenitic stainless steel.
3. Continuous use of duplex stainless steel tube - 50 ~ 250 ℃ temperature range, the lower limit depends on the brittle transition temperature, steel cap is limited by 475 ℃ brittleness, the maximum temperature should not exceed 300 ℃.
4. The duplex stainless steel tube after solid solution treatment need to be fast, slow cooling leads to the precipitation of brittle phase, which can lead to the toughness of the steel, especially the local corrosion resistance.
5. High chrome molybdenum hot working of duplex stainless steel tube and the lower limit of thermoforming temperature not lower than 950 ℃, super duplex stainless steel is not less than 980 ℃ low chromium molybdenum duplex stainless steel is not less than 900 ℃, avoid caused by brittle phase separation in the process of surface crack