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1 Department of Micro- and Nanotechnology, Technical University of Denmark 2 Magnetic Systems, Department of Micro- and Nanotechnology, Technical University of Denmark 3 Department of Mechanical Engineering, Technical University of Denmark 4 Materials and Surface Engineering, Department of Mechanical Engineering, Technical University of Denmark 5 Department of Management Engineering, Technical University of Denmark 6 SKF Engineering and Research Centre 7 Centre for oil and gas – DTU, Center, Technical University of Denmark
Sub-zero treatment of steels with an Mf below 0°C relies (partly) on a continuation of the martensite formation. The present work reports on the observation of isothermal martensite formation in the sub-zero temperature regime for two steels: AISI 1070 and AISI 52100. Samples were austenitized, quenched in oil, and thereafter investigated with vibrating sample magnetometry, which allows a quantitative assessment of the fraction of retained austenite as a function of the sub-zero temperature and time. Isothermal martensite formation was observed on interrupting the continuous cooling (5 K/min) at temperatures in the range of 80-233 K. The kinetics of isothermal martensite formation depends strongly on the temperature and can be described by Johnson-Mehl-Avrami-Kolmogorov kinetics. Isothermal experiments with dilatometry indicated the occurrence of a volume increase on isothermal holding, consistent with a continuation of the martensitic transformation. On prolonged isothermal holding, a volume reduction was observed for AISI 52100, but not for AISI 1070. Copyright © 2011 by ASTM International.
18th International Federation for Heat Treatment and Surface Engineering Congress: Proceedings, 2012
Dilatometers; Isotherms; Magnetometers; Martensite; Martensitic transformations; Surfaces; Martensitic steel
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Astm Special Technical Publication
18th International Federation for Heat Treatment and Surface Engineering Congress, 2012