Study On Microstructure And Mechanical Properties Of Welded Dissimilar Joint Between CLAM And 15-15Ti Steel

The cladding tube and the end plug are important part of nuclear fuel components,welding quality of the cladding tube and the end plug is an key factor for the reactor running safely.15-15 Ti stainless steel was selected as candidate material for China's lead-based fuel cladding components of the reactor owing to its good high temperature mechanical properties,irradiation resistance and corrosion resistance of liquid lead alloy.The CLAM steel are considered as one of the most promising structural materials for the lower end plug because of their good structural stability and high strength in the irradiation environment to prevent premature failure of cladding tube due to vibration and fatigue.This will involve in the welding of CLAM/15-15 Ti dissimilar steel.In this paper,the CLAM/15-15 Ti dissimilar joint was performed by TIG welding without wire filing.The microstructure and mechanical properties before and after heat treatment were analyzed.The high temperature aging experiments was carried out at 500?up to 1500 h.The main results are as follows.Continuous?ferrite was found in CLAM fusion zone and the hardness of which was low.The complete quenching zone of CLAM was martensite.The incomplete quenching zone was composed of fine martensite and ferrite mixed with a small amount of precipitates.The welding seam with highest hardness was mixed structure between martensite and a small amount of ferrite without precipitates;The tensile specimens of the joints fractured at the HAZ of 15-15 Ti steel.With the increase of heat treatment temperature,the hardness of the CLAM steel decreased gradually,however,the M₂₃C₆ increased along the ferrite boundary in the fusion zone of CLAM.The M₂₃C₆ grew up at grain boundaries in the complete quenching zone and the incomplete quenching zone of CLAM,and the amount number of MX phase inside grains decreased in this zone.The martensite strip refined with the hardness decreased first and then increased.The weld seam had M₂₃C₆,Ni₃Mo,Mo₂C three kinds of precipitates;number of precipitates in fusion zone grain boundary increased first and then decreased.The heat affected zone of 15-15 Ti stainless steel hardness have not obvious changes.After heat treatment at680?.The tensile specimens of the joints ruptured at the heat affected zone of 15-15 Ti steel.After heat treatment above 720?,the joint ruptured on the side of CLAM steel.The yield strength of the joint first increased and then decreased.After aging for 500 h,9.7%reversed austenite had appeared in the welding seam.As the increase of the aging time,number of reversed austenite gradually decreased.After aging for 1,500 h the reversed austenite had 0.43%.The hardness of the weld gradually decreased;The hardness of the complete quenching zone gradually decreased,however,the hardness of the incomplete quenching zone tend to increase.The carbides of 15-15 Ti stainless steel increased gradually,resulting in the increase of hardness.And the joints ruptured in heat-affected zone of 15-15 Ti stainless steel.