Quantification of early stages of age hardening in Fe-12Ni-6Mn maraging type alloy

The effect of heat treatment and composition on the toughness and hardness of mar aging alloys based on Fe-Ni-Mn is first summarised. Age hardening data for an Fe-12Ni-6Mn alloy have been subjected to quantification. In the early stages of aging, the increase in hardness (∆H) has been found, both practically and theoretically, to follow the relationship ∆H = (Kt)n, where t is the isothermal aging time and K a temperature dependent rate constant, giving an activation energy of 79 ± 1.3 kJ mol−1 for the process. This is reasonablefor pipe diffusion of Ni and Mn, as is the value of for the effective diffusion coefficient Do for the temperature range 350–425°C.