Weldability and brief introduction of T91 / P91 steel

With the rapid development of electric power industry, high parameter and large capacity units are emerging, which can put forward higher requirements for the high temperature creep performance and stress corrosion resistance of steel pipe materials. For this reason, a large number of researches have been carried out in the world’s major industrial developed countries, and a series of new type of heat-resistant iron cable steel has been developed successively, which has been successfully used in large capacity thermal power generating units, among which the high CT type 9cr1 movnbn heat-resistant steel is T91 / P91 steel. T91 / P91 steel is widely used in high parameter thermal power generation units because of its following advantages in service performance: Compared with stainless steel, the steel has low coefficient of thermal expansion and good thermal conductivity. ② the guillotine has high tensile strength at room temperature, with δ b up to 770mpa and good plasticity. ③ the impact toughness and material brittle transition temperature of the steel are obviously better than those of the same kind of X20 and eml2 steel ④ the steel has higher high temperature endurance strength and allowable stress. The high temperature endurance strength after 105h operation at 550 ℃ is twice that of T22 steel, and the allowable stress in 540-610 ℃ is significantly higher than that of T22, TP304H and X20 steel. ⑤ the steel has good bending performance. ⑥ the high temperature fatigue property of the steel is better than that of T22 and TP304H steel, and the high temperature oxidation resistance is also much higher than that of T22 steel. Key points of welding process for T91 / P91 steel T91 steel pipes for superheater and reheater of utility boiler are of common specifications of ψ 54mm and ψ 57mm, with wall thickness of 4mm, 8mm and 9mm. Large diameter main steam P91 steel pipe has many specifications, such as ψ 457mm × 45mm, ψ 347mm × 46mm, etc. In the field construction of small diameter pipe, horizontal butt joint is usually used for fixing and positioning, which requires one side welding and two sides forming, and the back side weld is not oxidized. In order to make the joints have satisfactory performance, the early welding process mainly adopts two methods: one is all argon arc welding (TIG backing TIG filling); the other is argon arc welding (TIG backing electrode arc welding filling). The key points of welding process are as follows: (1) adopt correct groove shape and size. (2) select reasonable welding materials (TIG welding wire and filler electrode). (3) select correct welding specifications (including welding wire and electrode brand and diameter, tungsten electrode diameter, welding current, argon flow, power polarity, number of weld layers and passes, etc.). (4) select correct preheating temperature of workpiece and interpass temperature of weld. (5) select reasonable post weld heat treatment specifications (including temperature rise and fall speed, tempering temperature and holding time, etc.). (6) adhere to the correct joint assembly positioning welding and skilled, superb manual operation skills, etc. After welding methods and welding materials are determined, the key technological measures to obtain high-quality joints are preheating before welding, controlling layer temperature, and “timely and effective” post welding heat treatment. The essence of preheating before welding is to control the hydrogen behavior in the welding area, reduce the hardness and stress peak value of the welding area and improve the toughness. On the one hand, the control of interpass temperature is to prevent weld overheating; on the other hand, it is to maintain slow cooling. Timely and effective post weld heat treatment has two meanings: first, the process can improve the weld and its HAZ structure, improve the toughness and high temperature endurance strength of the joint, and eliminate the welding internal stress; second, when implementing the process, it is necessary to strictly control the minimum post weld cooling temperature of the weldment and the time interval to the post weld heat treatment. The latter is very important to obtain excellent joint performance.铜焊丝,Copper Welding Rods,铝焊丝,aluminium welding wire,镍焊条,Nickel electrode,药皮焊条,Flux Coated Brazing Welding Rods