THE EFFECT OF POST-WELD HEAT TREATMENT ON THE PROPERTIES OF STAINLESS STEEL OVERLAID JOINT FOR PRESSURE VESSELS

This paper was aimed at investigatiing the influence of post-weld heat treatment on the mechanical properties of stainless steel overlaid joint and discussing the relaiion between the change in impact toughness and micro structure in the overlaid cladding.The base metal was Q-T treated Ni Cr-Mo-V high strength steel.In the inner surface of vessel two layers of clad metal were deposited by submerged arc welding with chromium-nickel stainless steel strip as the consumable electrode.The first layer was 0Cr20Ni10 and the second layer was 00Cr20Ni10 stainless steel.A series of test specimens were taken from the overlaid cladding,bonding line and heat affected zone of welded pieces,which had been heat treated at 600,625,650 and 680℃ for 15,30,50 and 100 hours.The results obtained are as follows:(1)The post-weld heat treatment temperature shouldnt be over 650℃ for Q-T treated Ni-Cr-Mo-V high strength steel.(2)All side bending specimens are free of cracks after bending,but the ductility in the bonding area decreases with increased time of post-weld heat treatment and its temperature.Ductility loss is associated with the width of diffusion of carbon from base metal to the overlaid cladding.(3)The toughness of the overlaid cladding decreases with increased time of post-weld heat treatment and its temperature.The decrease of toughness also depends on ferrite content and carbon content.(4)0Cr20Ni10 low carbon stainless steel cladding is less susceptible to embrittlement than 0Cr20Ni10Nb cladding.(5)The embrittlement of 00Cr20Ni10 extra low carbon overlaid cladding after post-weld heat treatment is due to the Cr23C6 precipited along the ferrite boundries as well as the formation of a very small amount of σ phase.