Research On Plasma Welding Process Of P92 Steel

P92 steel is a new type of heat-resistant steel among boiler steels.It has the advantages of high strength,high temperature corrosion resistance and good high temperature oxidation resistance.The commonly used welding method for P92 steel is argon tungsten arc welding base+manual arc welding cover,in order to further improve production efficiency and obtain good performance P92 welded joints,this article uses plasma welding technology to weld 6 mm thick P92 steel.in order to analyze the influence of welding process parameters on the mechanical properties of welded joints,in-situ tensile test of P92 steel plasma welded joints to study the fracture mechanism of different areas of the welded joints,the mechanical properties and precipitated phases of welded joints under post-weld heat treatment are studied.In order to further study the effects of the three main parameters of welding current,plasma gas flow and welding speed on the surface forming and mechanical properties of welded joints,research indicates:For the 6 mm thick P92 steel plate,its welding current is the best when the welding current is 126 A;The plasma gas flow mainly affects the penetration depth of the P92 plasma welding joint,finally,when the plasma gas flow rate is 4.5 L/min,the surface forming of the welded joint and the mechanical properties of the welded joint are the best;The influence of welding speed on welded joints is mainly reflected in the amount of heat input to its welded joints per unit time,finally,when the welding speed is 170 mm/min,the heat input distribution per unit time is the most uniform,the surface shape is the best,and the mechanical properties of the welded joint are the best.Based on infrared thermal imaging technology,study the influence of welding current,plasma gas flow rate and welding speed on the temperature field distribution of the molten pool,the study found that the welding current and welding speed affect the amount of heat input to the welded joint during the welding process,excessive welding current and low welding speed will cause excessive heat input to the welded joint per unit time during the welding process,which will cause the coarsening of the welded joint structure.If the welding current is too small and the welding speed is too high,the heat input of the welding joint during the welding process will be too small,which is not enough to penetrate the 6 mm thick P92 steel plate.Plasma gas flow affects the longitudinal distribution of heat in the welding joint during the welding process,the main function of the plasma gas flow is to make the heat generated per unit time to be longitudinally distributed and increase its penetration.Since the working environment of P92 steel is under high temperature conditions,the high temperature tensile mechanical properties of P92 plasma welded joints are studied,the study found that with the increase of tensile temperature,the mechanical properties of P92 steel welded joints began to gradually decrease,and the grain size at the fracture surface gradually increased.The hardness value of the welded joint gradually decreases with the increase of the tensile temperature.In-situ tensile tests were performed on different areas of the welded joint,and the fracture mechanism of the different areas of the P92 plasma welded joint was obtained.After the in-situ tensile specimens in the weld zone have undergone the passivation zone SZW during the stretching process,the cracks started at the mesophase M23C6,the entire fracture is a trans-layer fracture;The heat-affected zone is the weakest link of the entire P92 plasma welding joint,the final section shows a cleavage fracture,after the in-situ tensile specimen in the base metal zone undergoes SZW in the passivation zone,the cracks propagate in a plastic fracture mode,the yield strength 8s of different areas of the welded joint satisfies the relationship:?s base material area>?s weld zone>?s heat affected zone,the passivation zone SZW early plastic crack propagation length Xf satisfies the relationship:Xf base material area>Xf weld zone>Xf heat affected zone.In order to study the effect of tempering temperature on the mechanical properties of welded joints,and at the same time conduct a qualitative analysis of the second phase after tempering,the results show that as the tempering temperature increases,the tensile strength of the welded joints gradually decreases,but at the same time the toughness of the welded joints is also improved.Finally,the welded joints are tempered for 2 h at a tempering temperature of 650?.In the future,the comprehensive mechanical properties of its welded joints will be the best,during the tempering process,the intermediate phases M23C6,Laves phase and MX phase will be generated at the welded joints.A certain amount of precipitated phase M23C6 will have a precipitation strengthening effect on the mechanical properties of welded joints.Excessive carbide M23C6 will cause the martensite structure to soften and decrease the hardness,which will reduce the mechanical properties of the welded joints.The formation of Laves phase will affect the mechanical properties of welded joints.The creep performance of the P92 plasma welded joint has an enhanced effect.The nano-level mesophase MX is formed at the grain boundary.Because of its fine distribution at the grain boundary,the precipitation strengthening effect of the MX phase is better than that of the M23C6 phase,which is P92 steel Ideal precipitated phase for plasma welded joints.