Laves Phase in 22Cr-27Ni-2Ti-Al Austenitic Valve Steel

The Thermo-Calc software was employed to calculate the equilibrium phase of 22Cr-27Ni-2Ti-Al austenitic valve steel, and the Laves phase in this steel was investigated after solid solution and aging by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Results show that the microstructure of the experimental steel consists of γ, γ′, Laves and NbC. Laves phases mainly precipitate on grain boundaries, with granular and fibrous morphologies. The size of the granular Laves phase is about 50-600 nm, and the fibrous Laves phase is composed of short strip Laves phases which are 300-600 nm in length and 50-150 nm in width. These two morphologies of Laves phase coarsen with increasing aging temperature, and this steel possesses the highest strength and hardness at aging temperature of 760 °C.