| P92 heat-resistant steel because of the high thermal resistance excellent has been widely used in ultra supercritical turbine main steam pipeline,market prospects.Laser arc hybrid welding,combined with the advantages of laser heat source and arc heat source,has many advantages,such as small heat input and high welding efficiency.It has great potential.And obtaining excellent welded joints will be very conducive to further application of P92 heat-resistant steel.Considering the absorption mechanism of metal matrix of Nd:YAG laser,including Fresnel absorption and laser scattering and absorption,heat source is generated by ray tracing method,establishes a mathematical model of gas liquid solid three-phase unified fiber laser arc hybrid welding process of the weld pool and keyhole dynamic process simulation of laser hybrid welding process.The simulation results show that the volatility of keyhole internal under force,when the keyhole depth formed at about 3 mm,the dynamic process of weld pool and keyhole can form a stable keyhole,not closed,when the formation of the keyhole depth was about 6mm,weld pool and keyhole.Can not form a stable weld pool dynamic process,partial collapse,the bottom of the keyhole is closed,the bubble can't escape,causing blowhole formation.The U groove is designed for P92 heat-resistant steel plate with thickness of 8mm by laser arc composite welding,and the test of plate welding with different preheating temperatures is carried out.With the increase of preheating temperature,the martensitic plate in the weld zone widened and a small amount of ferrite appeared,while some grains were coarse-grained in the heat affected zone,the martensitic slab widened and the microhardness of the welded joint decreased.When the preheating temperature is 200?,the welding crack can be avoided,the weld hardness and the inhomogeneity of the base metal can be reduced,and the microstructure and properties of the weld can be improved.At room temperature tensile test and high temperature tensile test,the fracture position is the base metal,the high temperature tensile near the fracture structure changes,but the weld has no obvious change,which indicates that the weld strength is high and meets the mechanical properties of welding.The welded joint was treated at 750?high temperature for aging.The microstructure of the joint was observed.The size and shape of the precipitates in the joint were analyzed by TEM and SEM.The precipitates were quantitatively analyzed by EDS spectrum.The results show that with the increase of aging time,the microstructure of the weld zone and the heat affected zone is a martensitic slab with different orientations,and the martensitic partial slab fusion becomes wider and the number of precipitates increases.It can be determined that during the aging process,M23C6 phase,Laves phase and a small amount of MX phase are precipitated on the welded joint of P92 heat-resistant steel.The precipitates grow at the initial stage of aging treatment and begin to aggregate at the later stage.With the increase of aging time,the M23C6 phase and MX phase change relatively stable,and the Laves phase precipitates more.The microhardness test shows that the overall hardness of the joint decreases with the base material gradually,and the softening range of the heat affected zone is small.The tensile and tensile properties at room temperature were tested.The tensile fracture locations of different aging specimens were all the base metal,indicating that the strength of weld is still higher than that of base metal. |
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