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Induction heat treatment facilities have a wide application range for heat treatment of cylindrically shaped materials in the steel processing industry due to their reduced process-time and high throughput. The adjustment of the heat treatment process usually aims at reaching a desired hardness. However, the question arises whether the full potential of the applied material is actually exploited. Therefore, this work systematically investigates the influence of the primary microstructure, austenitisation and tempering conditions to the resulting notch impact energy and flow behaviour of a 50CrMo4 quenched and tempered steel, with normalised and soft-annealed prior microstructures. The heat treatments, performed with a laboratory induction heat treatment facility, show that low austenitising temperatures lead to a distinct yield point with reduced strain hardening, while increasing the tempering heating rate results in the precipitation of smaller carbides and a significant increase in tensile strength. Austenitising needs to be adjusted to the primary microstructure to reach an optimum solution state to exploit the hardness and notch impact energy potential.

Goal of this work is to study the effect of initial microstructure and different fast austenitization treatments with high heating rates and short dwell times on the transformation behavior of austenite to martensite and the resulting microstructural martensite features. A deeper understanding is gained regarding influences of the time temperature program during austenitization on strain within the martensite. Therefore, specimens with two microstructures, a ferritic/pearlitic and a soft annealed state, are heat treated with heating rates of 1–100 K s–1 to different austenitization temperatures and held for 3 s. Distinct differences in initial microstructures is their cementite size and morphology. For the investigations of the martensitic transformation, its microstructure and its distortions dilatometry experiments are conducted and Electron Back Scattered Diffraction (EBSD) is used. The investigations show that strain and inhomogeneities within the austenite are passed to the martensitic microstructure and lead to higher distortions within the ferritic martensite crystals. Strain within the martensitic microstructure decreases with increasing austenitization temperature and decreasing heating rates. Especially, the carbon content in solution, which is increasing with increasing austenitizing temperature and smaller initial cementite size, is influencing martensitic features, such as martensite start temperature and block sizes.