Study on sensitization characteristics of TP347H stainless steel welded joints
In order to clarify the sensitization characteristics of TP347H stainless steel welded joints,the welded joints were heat treated at different temperatures,and the changes of sensit-ization degrees at different temperatures were studied.The res-ults showed that an obvious sensitization trend was observed in the heat-affected zone(HAZ)of welded joints.During the sens-itization process,because the binding energy of Nb atoms on the grain boundary is higher than that of Cr atoms,coarse primary niobium carbon compounds are formed first,and then fine secondary niobium carbon compounds are formed.When the temperature is kept at 700℃,the sensitization degree of the HAZ of the welded joint shows a trend of first increasing and then decreasing.When the temperature reaches 800℃and above,heat treatment no longer increases the sensitization de-gree of the HAZ of the joint.Comparing with the sensitization characteristics of F347H joints with 21 000 h in the actual pro-duction line,it is confirmed that the sensitization limit can be reached by holding the welded joints of TP347H at 650℃for 100 h.The reason is that the content of Nb is several times that of C,most of C combines with Nb to form NbC,and the diffu-sion of C in the grain has been fully combined with Cr.The resulting sensitization reaches an equilibrium state.
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