Kinetics of precipitation of χ-phase and M 23 C 6 carbide in a cast of Type 316 stainless steel

A selective etching technique was used to reveal the χ-phase in a cast of Type 316 steel (18Cr-12Ni-2.5Mo). The volume fraction of the χ particles revealed by this technique was measured by using the Quantimet 720 image-analysing computer. The data obtained suggest that the precipitation of χ at 750°C and 815°C follows a law of the form V = f(t/τ), where V is the volume fraction of χ formed in a time t and τ is a ‘characteristic time’ dependent upon temperature. The kinetics of M₂₃C₆ precipitation in Type 316 steel at 625°C was also studied by a bulk extraction method. The data obtained obey the Johnson-Mehl equation with n ≃ 1