NON-DESTRUCTIVE IN SITU MONITORING OF THE MICROSTRUCTURAL DEVELOPMENT IN HIGH PERFORMANCE STEEL COMPONENTS DURING HEAT TREATMENT

摘要

A new monitoring system was developed, that enables a contact-free and in situ, non-destructive monitoring of the material's transformation and microstructure's development during the cooling phase from the austenitic region. For this purpose characteristic changes in the electrical and magnetic properties that occur during the formation of ferromagnetic phases and microstructures are measured using eddy-current technology and the analysis of harmonic signal components. The monitoring system provides information about the onset of the transformation, the current transformation level and the end of the transformation in steel components as well as information about the evolution of the microstructural components, i.e. ferrite-pearlite, bainite and martensite. By evaluating the measured signal online in real time it is possible to classify and differentiate the evolution of microstructures, to regulate the cooling parameters, and therefore to specifically set the component's properties. The monitoring system and the robust eddy-current sensors can be employed in industrial environments at component temperatures of up to 1250°C in different environments, such as salt-baths, furnaces, spraying fields or in air.