Acoustic emission monitoring of bainite formation during continuous coating

This paper concerns acoustic emission (AE) measurements during continuous cooling of steel C45 using a Gleeble 1500 thermo-mechanical simulator. After austenizing at a certain temperature, the studied specimen was cooled down and the root mean square (rms) voltage (V rms ) of the AE signals was measured. During cooling two distinct peaks in the V rms data were observed at temperatures of 500-600 °C and 200-300 °C, which are attributed to bainite and martensite formation respectively. The observed bainite peak unambiguously implies that the mechanism of growth of bainite is displacive, i.e. is martensitic in nature. From the ratio of the martensite peak to the bainite peak information can be obtained about the amounts of martensite and bainite formed. The AE monitoring of bainite and martensite formation is supported by dilatation measurements, which were performed simultaneously. The effect of the austenite grain size on the evolution of the bainite and martensite formation was studied by varying the austenizing temperature.