ISSN: 1546-962X
CODEN: JAIOAD
Published Online: 4 April 2011
Page Count: 9

Isothermal Martensite Formation at Sub-Zero Temperatures

Stojko, Allan
Formerly at Technical Univ. of Denmark, Dept. of Manufacturing Engineering and ManagementGrundfos A/S, Kgs. LyngbyBjerringbro,

Hansen, Mikkel F.
Technical Univ. of Denmark, Dept. of Micro- and Nanotechnology, Kgs. Lyngby,

Slycke, Jan
Formerly at SKF Engineering and Research Centre, Nieuwegein,

Somers, Marcel A. J.
Technical Univ. of Denmark, Dept. of Mechanical Engineering, Kgs. Lyngby,

(Received 5 October 2010; accepted 9 March 2011)

Abstract

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.

Keywords:
sub-zero treatment, isothermal martensite, magnetometry, dilatometry

Paper ID: JAI103459
DOI: 10.1520/JAI103459
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