| In order to cope with the shortage of energy and environmental crisis,China’s power industry is facing the severe challenge of improving the economy and environmental protection about coal power,the efficiency of thermal power plant can be effectively improved by increasing the steam parameters(temperature and pressure),so this makes a higher requirement for the performance of the steel for the ultra supercritical boiler.P92 steel is a new type of 9% Cr ferrite heat-resistant steel,which is based on the P91 steel by improving the composition of the alloy and adopting the method of multiple strengthening.P92 steel has been used in the superheater and reheater of the ultra(ultra)critical thermal power unit with its excellent comprehensive performance,which can effectively improve the efficiency of power plant and the stability of long-term safe operation of thermal power units,and it has been gradually applied to China’s ultra-supercritical units.At present,the domestic research on the application of P92 steel welding is still relatively small,so through the study of suitable welding process and post-weld heat treatment process,analysis of the relationship between the microstructure and performance of joints to provide theoretical and data support for the application of P92 steel welding.In this paper,P92 ferritic heat-resistant steel with 6 mm thickness produced by Baosteel was selected as the object of study.TIG welding technique was used to select the surface welding process of P92 steel with appropriate welding parameters,and then make different post-weld heat treatment process.The microstructures,mechanical properties and electrochemical corrosion tests were carried out on the joints of different post-weld heat treatment processes,the mechanical properties of the test including microhardness distribution,impact performance and friction properties,the metallographic analysis focused on the size and morphology of δ-ferrite in the joint,the microstructure and morphology of the impact fracture were observed and analyzed.To study the relationship between the microstructure and properties of P92 steel joints.The results show that δ-ferrite appears in P92 steel joints after TIG self-welding,and the δ-ferrite is mostly distributed in the heat affected zone,and the probability of small strip in the weld center,the hardness of the δ-ferrite is significantly lower than the adjacent lath martensite.The average hardness of weld in P92 steel joints is higher than that of the base metal,the hardness of the weld is the highest and the impact toughness is the lowest,which is mainly due to the high hardness and brittleness of the quenched martensite.After post-weld heat treatment at 760 ℃,the microhardness of the weld zone was significantly reduced,the impact toughness was improved and the content of delta ferrite was significantly reduced.With the extension of the tempering time,the hardness of the welded joint is not significant,but the impact toughness of the weld is improved,the impact fracture morphology transformed from ductile / brittle mixed fracture to ductile fracture.At the same time,after the post-weld heat treatment process,the electrochemical corrosion resistance of the welded joint gradually weakened and the wear resistance decreased gradually,the wear morphology changed from abrasive wear to adhesive wear and surface fatigue wear.In this paper,the exploratory experiment of active argon arc welding(A-TIG)for P92 steel was also carried out.The results show that the hardness and impact toughness of the weld are less than that of the traditional TIG weld,but the weld penetration is obviously increased.It is necessary to further study on the choice of active flux in the welding of P92 steel. |
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