Study On Arc Welding Process Optimization And Joint Performance Of P91 High Alloy Heat Resistant Steel

P91 heat-resistant steel is widely used in electricity,petroleum,and chemical industries.Good welding and heat treatment processes are the prerequisites for ensuring the application of P91 steel,but there are still some problems in practice.The weld metal in manual arc welding is unstable or even low in temperature impact toughness,which seriously affects the weld performance;At the same time,the different heat treatment timing also affects the impact toughness of the weld.Therefore,how to optimize the welding process and obtain a good comprehensive mechanical performance of welding joints is the focus of this research.In this paper,the control method of reducing heat input and improving toughness is determined through the research of base material and weld structure,and the welding and heat treatment process is further optimized.Finally,the welded joint with high strength and better toughness is obtained.Preheat temperature is an important factor that affects welding heat input.Reducing preheat temperature can effectively reduce heat input,shorten softening area,and improve weld metal toughness.In this thesis,the sensitivity of P91 steel to cold crack under different preheating temperature conditions was analyzed and compared by means of oblique Y type cold crack sensitivity test.The results show that the sensitivity of P91 steel to cold cracks is different when tungsten gas welding and manual welding arc welding respectively.When tungsten gas welding is used,the Preheat temperature reaches 150?or more,the surface and section are free from cracks.When welding by manual welding rod arc,when the preheating temperature reaches 200?,no cracks are generated on the surface and section.On the basis of the above research,the influence of t_8/5/5 time and welding heat input on weld toughness is analyzed to determine the reasonable welding wiring energy.The temperature and time of heat treatment were discussed.The optimized welding process is verified according to the electric power and energy industry standards,and the metallographic structure,normal temperature impact toughness,tensile strength and hardness values of the specimen after heat treatment are analyzed.The results show that the welds and the heat-affected areas are tempering martensite and tempering cable body.The tensile strength of the welded joints reaches 683 MPa or more,and the average impact work of the weld is 82J,which has good room temperature comprehensive mechanical properties.Finally,according to the actual situation of the project,the changes and mechanical properties of welded joint under different heat treatment conditions are studied.The results show that after the welding is completed,if the specimens are kept warm at 80¹00?,heat treatment and 24h are immediately treated.The weld structure and mechanical properties are basically unchanged,but if post-heat treatment is carried out,the impact toughness decreases significantly.The average impact work is only 55J,and the toughness is significantly reduced.It is indicated that in the actual construction process,the construction sequence should be arranged reasonably,and heat treatment should be immediately after welding.If it can not be heat treated in time,it can be slowly cooled to room temperature after being heated at80¹00?and 1² h,and it can not stay in a dry,low-stress environment for more than 24h before heat treatment.