A novel precipitation mechanism of Laves phase in Fe-30Cr-2Mo super ferritic stainless steel: In-situ phase transformation

Laves phase is generally prejudicial to the performance of ferritic stainless steels, so understanding the under-lying formation mechanism should be technologically useful. Here we demonstrate a new precipitation behavior of Laves phase in Fe-30Cr-2Mo super ferritic stainless steel by using transmission electron microscopy. It is revealed that the MC carbides firstly precipitate adhere to the M2SC carbosulphides with an orientation rela-tionship (OR) of (0001)M2SC//(111)MC and [1120]M2SC//[011]MC. Subsequently, the interfaces between MC carbides and ferrite matrix provide preferential nucleation sites for Laves phases, which hold OR with MC as follows: (111)MC//(0003)Laves and [011]MC//[1120]Laves. Notably, the transformation from MC to Laves phases is an in-situ process based on the dissolution of MC carbide, which supplies the niobium element for nucleation and growth of Laves phase. This work enriches the recognition of the precipitation mechanism of Laves phase, and should therefore facilitate the design of high-performance ferritic stainless steels.