Bi-modal microstructure in a powder metallurgical ferritic steel
(State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, China)
Abstract: Ferritic steel with a nominal composition of Fe−14Cr−3W−0.42Ti−0.32Y was prepared by mixing gas-atomized prealloyed powder and mechanically alloyed powder. The microstructure is much different from other ferritic steels with the same composition and prepared via only mechanically alloyed powder. A bi-modal structure, which consists of pure ferritic grains and martensitic grains, was obtained after hot forging and air cooling. A phase transformation of αbcc→γfcc→α´bcc was also discovered in microstructural observation. The bi-modal microstructure shows a good combination of high strength and high ductility.
Key words: ferritic steel; powder metallurgy; phase transformation; bi-modal microstructure; mechanical property