Electrical resistivity and phase transformation in steels

Changes in electrical resistance accompanying transformations in steels with magnetic change (e.g. gamma --> martensite/bainite) and without magnetic change (e.g. gamma --> alpha, above Curie temperature) have been examined; the former class affects the resistivity the latter does not. Next, while the efficacy of electrical resistivity measurement in capturing the well-known features of austenite stabilization (e.g. over - ageing, reversibility, and influence of prior martensite amount and so on) in high carbon steels has been reported in an earlier publication, new features (e.g. increase in resistance-increase at very low temperatures, change in temperature co-efficient of resistivity in the stabilized material etc.) are highlighted here. Finally, the work shows that a quantitative estimate of precipitation in the copper bearing, age-hardenable HSLA-100 steel during tempering can be done by continuous electrical resistivity measurement. These data also allow an in-depth kinetic analysis using the Johnson-Mehl-Avrami equation.