Design and preliminary characterization of a novel carbide-free 9Cr-ODS martensitic steel

Abstract

A novel 9Cr-ODS martensitic steel was designed for application in the advanced fusion reactors by reducing carbon content to an extremely low level to avoid the precipitation of M23C6 carbides and increasing manganese content to promote the martensite formation. The preliminary investigation was carried out by means of thermodynamics calculation, phase transformation measurement, microstructural observation and mechanical property testing. The results showed that the desired tempered martensitic structure and elimination of unstable M23C6 around grain/subgrain boundaries were achieved successfully in the fabricated steel with a final composition of Fe-9.25Cr-1.02W-1.05Mn-0.27Y2O3-0.012C (in wt%). Characterized by a homogeneous distribution of nano-size yttrium oxides with an ultrahigh density, absence of coarse M23C6, fine grains with high density dislocations, the designed 9Cr-ODS steel exhibited a relative good tensile properties after normalization and tempering treatments. Due to the slight decline of austenite temperatures (Ac1 and Ac3), a tempering temperature higher than 800 ℃ should be avoided.