Strain Gauge Factor and Electrical Properties of Fe–Co–Mn Alloys

Abstract

The strain gauge factor K at room temperature, the electrical resistivity ρ at 20°C, the mean temperature coefficient of electrical resistivity C_f at 0∼40°C and the mean thermoelectromotive force relative to copper E_mf at 0∼40°C have been measured for wire specimens which had been prepared from Fe–Co–Mn alloys of high workability containing 20∼50%Mn and less than 80%Fe by a cold work of about 94% reduction. The value of K attains the highest value of 5.4 in an Fe–Mn binary alloy containing 30%Mn and decreases gradually with the addition of Co, but the value becomes higher than 4 in the nonmagnetic γ phase region. The value of ρ for Co–Fe alloys increases with increasing Mn content, while the E_mf shifts from a negative to a positive value. The value of C_f is high in Fe–Mn and Fe–Co alloys but decreases with the respective addition of Co and Mn. In an Fe-30%Co-45%Mn alloy which shows the lowest C_f value of 2.4×10⁻⁴, the values of K, ρ and E_mf are 4.6, 98 μΩ-cm and +0.2 μV/°C, respectively. The variations of these values by heat treatment below 500°C for 150 hr have also been measured.