Precipitation correlation between MC carbide and Nb-rich M2P phosphide in a TP347H austenitic stainless steel

Abstract

The precipitation correlation between Nb-rich MC carbides and Nb-rich M2P phosphides has been investigated in a TP347H austenitic stainless steel during rupture test at 750 degrees C. Needle-like Nb-rich M2P phosphides as well as round-shaped Nb-rich MC is observed during rupture test. The Nb-rich M2P phosphides form an orthorhombic NbNiP-type structure and show the orientation relationship of [0 (1) over bar0]M2P//[100]gamma and (20 (1) over bar )M2P//(0 (11) over bar)gamma. The fraction of the Nb-rich MC carbides decreases abruptly after a critical rupture time, while that of M2P phosphides is roughly little changed. This means that the dissolution of the pre-formed Nb-rich MC carbides into the matrix for meeting the equilibrium phase fraction of each phase activates the active precipitation and growth of the Nb-rich M2P phosphides. Such a precipitation correlation may delay intergranular cracking occurring in the austenitic stainless steel. (C) 2016 Elsevier Inc All rights reserved.