Effects Of Weldingparameters And Post Weld Heat Treatment Temperature On The Mechanical Properties Of Weld Seam Between T92/Super304H Dissimilar Steels

The global energy crisis and environmental pollution have been believed to accelerate the rapid development of clean and efficient thermal power generation techniques.In recent years,thermal power generation in China is reported to be a large proportion of electricity supply.Moreover,the policy of Chinese government on the strategy of electricity supply in China is pursuing higher capacity of electric generator units other than small ones.Among them,ultrasupercritical thermal power unit is the most efficient and green power generation technique.To meet the requirements along with harsh operating conditions,the novel martensitic,austenitic heat-resistant steels arewidely used in ultrasupercritical unit timber,such asT92,Super304 H.Due to excellent high-temperature performance and the cost efficiency,T92 steel has been recognized to replace some Super304 H steels,and it has been one of the main materials to fabricate the unit parts.Hence,dissimilar steel welding between T92 and Super304 H has been attracted increasingly attention in critical applications,and it is of significant importance to evaluate systematically the mechanical properties the weld seam between T92 and Super304 H steels.As for the welding processing and post-weld heat treatments on the welding of dissimilar materials between T92 and Super304 H pipes,nickel welding wire and argon arc welding were employed,in which the input welding energy should be carefully optimized.Then,several post-weld heat treatment processing were used to investigate the microstructure evolution and the mechanical properties of the seams.The results showed that the welding seam after the control on welding current and high-tempering(765℃)presents the best mechanical properties during the six samples.The tensile strength of joint was 8.6% higher than that of welded joints.The variation range of micro-hardness in the HAZ of T92 was greatly reduced,and the maximum reduction was 44.4%.The hardness of the joints was more stable and the impact toughness was raising when thetemperature oftempering increasing,and the impact absorbing energy of heat-effected zone near T92 bond line increased by 4.1 timesafter 765℃ heat-treatment.There were a lot of dispersed carbide particles on the welding joints after the post weld heat treatment(PWHT).On one hand,these dispersed carbide particles improved the dispersion strengthening and tensile strength,meanwhile,reduced the plasticity,on the other hand,the matrix of T92 side transformed from the martensite to the equiaxed sub-grains and thesolid solution elements released,which reduced the hardness and improved the impact toughness.Therefore,it improved thecomprehensive performance of the welding joints when theSuper304 H dissimilar steel joint waspost weld heat treatment.