Effect of heat and thermomechanical treatments on the structure and physical and mechanical properties of the N30K10T3 invar

Invar alloy N30K10T3, whose austenite is metastable with respect to the martensitic γ → α transformation that occurs upon cooling below the martensitic point (M _s = ?80°C), has been studied. The following six ways of the alloy strengthening have been tested: (1) aging (a) in a temperature range of ΔT _a = 20–700°C; (2) liquid-nitrogen cooling (lnc) of the material preliminarily hardened by aging under the aforementioned conditions (route 1) (a + lnc); (3) preliminary phase-transformation-induced hardening (ph) (γ → α → γ_ph) and aging in the temperature range of ΔT _a (ph + a); (4) liquid-nitrogen cooling of the material preliminary hardened via route 3 (ph + a + lnc); (5) preliminary cold deformation (to 30%) at room temperature and aging in a temperature range of ΔT _a (cd + a); and (6) liquid-nitrogen cooling of the material preliminary hardened via route 5 (cd + a + lnc). The six ways of hardening were found to affect the hardness, electrical conductivity, magnetic permeability, and temperature dependence of the thermal expansion coefficient.