Precipitation hardening Precipitation hardening is like tempering martensite at T > Ttr. Precipitation hardening implies quenching a one-phase system to the two-phase region of the equilibrium phase diagram and then slightly reheating the workpiece. Highly pure materials are especially susceptible to precipitation hardening. The higher the precipitation heat is below Ttr, the shorter is the optimal treatment time and the more sensitive are the resulting mechanical properties towards errors in timing