Analysis of Acoustic Emission Signal Generation During Martensitic Transformation

Abstract

The formation of cold cracks during welding of high strength steels is almost always preceded by martensite formation. Real time detection of both the martensite and cracks formed is a basic necessity of automated welding systems. Acoustic emission has been found to be highly suited for this purpose. Unfortunately, most of the work done to date on AE generation during martensitic phase transformation has been qualitative in nature. This paper presents a quantitative analysis of AE signal generation during martensite formation, using an energy method. This formulation relates the chemical free energy change which is the driving force for the transformation to the RMS value which is a measure of the energy content of AE signals. The analysis shows that the RMS signal is dependent on carbon concentration, volume transformed, cooling rate, and temperature. This is consistent with previous experimental work.