Study On Creep Deformation And Fracture Behavior Of 316H Steel Welded Joints

Creep damage and failure of welded joints is the main failure form of nuclear power pipelines at high temperature.In the fourth-generation nuclear energy system,materials with better performance are required to be used as nuclear power pipeline materials owing to the harsh service environment.Due to its excellent high temperature properties,316H stainless steel may be used as the main structural material for the important pipelines of the fourth-generation nuclear power system.Therefore,studying the high temperature creep deformation and fracture behavior of different areas of 316H stainless steel welded joints can contribute to the construction of nuclear power system,which is of great significance.High temperature creep tests of 316H stainless steel base metal,welded joints,heat-affected zone and deposited metal were carried out at 525?,with stress 190?430MPa.The effects of stress on the creep process of different areas of welded joints were investigated,the relationship between creep rupture time and stress was analyzed,the extrapolation method and Larson-Miller parameter method were used to predicted long-term strength of different areas.Scanning and transmission electron microscopy were used to investigate the microstructure evolution and fracture mechanism.The results show that,the weld metal is the weakest area in the welded joint at the same creep condition.The long-term strength of different areas calculated by extrapolation and Larson-Miller parameter method is higher than the specified value in ASME standard.After creep deformation,the chain-like Cr₂₃C₆ at the austenite grain boundary in the base metal and the heat-affected zone has a high growth rate,which promotes the nucleation and expansion of the intergranular crack and finally causes the mixed fracture.Laves phase,Cr₂₃C₆ and?phase were observed in weld metal and the deposited metal after creep.The creep cavities formed near Cr₂₃C₆ and?phase is the creep damage form of weld metal region and deposited metal.The fracture morpholgy indicates that ductile fracturing is the dominant fracture mechanism of weld metal region and deposited metal.