Analysis of transformation kinetics by nonisothermal dilatometry

Abstract

Nonisothermal dilatometry was shown to provide a powerful method for the analysis of solid-state transformation kinetics by measuring the shifts of the temperatures of inflection points on dilatometric curves as a function of heating rate. The method was applied to iron-nitrogen martensite specimens. To that end iron was nitrided in a NH3/H2 gas mixture and subsequently quenched. The experiments allowed the assessment of residual terms in the theoretical development. To demonstrate the high sensitivity of the method, the activation energy was determined for the initial stage of tempering iron-nitrogen martensite, involving a minute decrease of specific volume. The method developed is equally applicable to methods where other physical properties of the material under investigation(e.g., electrical resistivity, magnetization) are measured on isochronal annealing.