Precipitation Kinetics of M₂C Carbide in Severely Ausformed 13Co-8Ni Secondary Hardening Steels

With continuous heating calorimetric data as a basis, the kinetics of M₂C formation during isothermal aging was modeled in severely ausformed 13Co-8Ni steels using the Johnson–Mehl–Avrami theory coupled with a variation of effective activation energy with respect to the degree of transformation. These results were compared with small-angle neutron scattering measurements and discussed in terms of variations in the thermodynamic and kinetic behavior of M₂C precipitation. In particular, the M₂C carbides in the deformed samples contained more Fe content compared with the non-deformed samples. As this can be ascribed to the ausforming effect increasing the driving force for M₂C nucleation, it consequently leads to the decrease of the growth/coarsening rate for M₂C carbides at over-aged conditions.