Role of applied stress on the changes of precipitation and phosphorus segregation behavior in a TP347H austenitic stainless steel

The effect of applied stress on the precipitation (Nb-rich MC and Nb-rich M2P) behavior in the matrix and its role in the phosphorus segregation at the grain boundary (GB) are investigated in a TP347H austenitic stainless steel. The two parts (gage and grip) in the rupture test specimens under the applied stress of 80 MPa at 750 degrees C are investigated using TEM, SEM, and EPMA. Continuous precipitation and saturation behaviors of MC and M2P were observed in the grip part. Excess precipitation behavior of MC in the early stage of rupture test and the retarded precipitation of M2P were confirmed in the gage part. The retarded precipitation and the low volume fraction of M2P promoted phosphorus segregation at the GB. The correlation between the matrix precipitation and GB phosphorus segregation under the applied stress is further discussed.