Secondary hardening behavior in ausformed martensitic alloys with different Co content

The influence of Co addition on the secondary hardening behavior in ausformed high Co-Ni secondary hardening alloy steels was analyzed using small-angle neutron scattering and differential scanning calorimetry coupled with a modified Johnson-Mehl-Avrami kinetic model. In severely ausformed alloy steels, an increase in Co content increased the degree of secondary hardening but did not accelerate their aging kinetics. This was determined by Co-independent cementite precipitation, thus leading to the precipitation of M2C carbide nucleated around and/or on cementite during the same aging time of 5 h.