Martensitic transformation occurs in a diffusionless manner at high velocity, with acoustic emission (AE) being generated during the process. The AE signal contains information about the dynamic process of martensitic transformation. In this analysis, a model is developed for the AE signal, or dynamic displacement, from the transformation strains and the growth process of martensitic transformation in an elastic half-space using Green’s functions. The AE signal amplitude is found to be inversely proportional to the distance between the martensite source and the sensor, and to the duration of transformation. It also depends on the orientation of the martensite plate. The spectral bandwidth increases as the duration of plate formation decreases. In addition, raising the carbon content increases the fraction of plate martensite, and consequently the signal amplitude.

A relationship developed earlier between acoustic emission signals and the process of athermal martensitic transformation based on the free energy associated with the process is extended and verified experimentally. The relationship is found to model the process characteristics very well. The intensity of AE signal generated during transformation was found to be proportional to the temperature derivative of the fraction of martensite, the cooling rate, and volume of specimen. The AE signal was also found to be related to the carbon content of the steel. During transformation, the signal intensity was found to increase to a peak, and then tail off near the end of the transformation. Values of the martensite start temperature obtained from plots of the total RMS squared AE signals were also found to correlate well with values from the literature.