焼鈍した鉄鋼およびシリコン鉄の室温内部摩擦

抄録

The strain-amplitude dependence of internal friction was measured at room-temperature in an electrolytic iron, a magnetic soft iron, commercial low-carbon steels, a eutectoid steel and a 3%Si-Fe alloy, which were all annealed at 950°C for 2 hours in vacuo. The factors that had perceptible effects on the room-temperature internal friction were given and biscussed, and the origin of the room-temperature internal friction was also discussed. The measurements of in internal friction were carried out by a transverse vibration method excited and detected electro-magnetically at about 1.5 kc/sec. The strain-amplitudes were varied within the range of abut 1×10⁻⁸∼1×10⁻⁴. The amplitude-dependent internal friction was observed for strain-amplitudes higher than 1×10⁻⁶ (electrolytic iron and eutectoid steel) and 1×10⁻⁷(all other specimens). The magnitude of the amplitude-dependent internal friction was considerablly decreased when internal streses due to plastic deformation or quenching existed. It was also decreased when the specimens had either a higher concentration of carbon or nitrogen in solution satisfied the Granato-Lücke plot in a limited range of strain-amplitudes. The principal cause of this amplitude-dependent internal friction, however, is considered to be the magneto-mechanical hysteresis loss, because dislocations in annealed iron and steel with relatively low purity, as in this experiment, are supposed to be bound by carbon or nitrogen atoms so tightly that the dislocations cannot easily break away from the pinning points. The amplitude-independent part was very low (Q⁻¹=5×10⁻⁵∼8×10⁻⁵) and it may be caused by the background damping due to the tail of the Snoek peak, the thermo-elastic effect and many other sources.