Quench-temper and precipitation hardening processes of 4330M and 17-7PH steels are analyzed as a function of mechanical Q; internal friction, Q⁻¹, is the reciprocal of this parameter. The free decay of the resonant, unrestrained, fundamental torsional mode of vibration is used in the Q measurements of the test specimens. A tuned Q technique is employed which provides a measurement of mechanical Q under conditions of minimum external background loss, selected pure mode of vibration, and precise mechanical-electrical phase matching. The tuned Q measurements have proved very sensitive in following both tempering and precipitation hardening processes. It is believed that the observed changes in Q are dependent on the degree of lattice distortion or internal strain of the materials as brought about by these heat treatment processes. Also, the tuned Q measurements are shown to be a means of analysis of the relative stability of materials as a function of stress and time.