Effect of tempering temperature on carbide precipitation behaviours in high strength low alloy steel under high magnetic field

Abstract

The influence of high magnetic field on carbide precipitation behaviours during the tempering of a high strength low alloy steel was investigated by means of transmission electron microscopy. TEM analysis results indicated that the applied high field effectively promoted the precipitation of Fe₅C₂ type carbide at low temperature (200°C) and the precipitation of M₆C type carbide at intermediate temperature (530°C). The promotion of specific carbides at low and intermediate temperature was caused by the reduction in magnetic Gibbs free energy. Regarding the magnetic Gibbs free energy of carbides, not only the magnetization but also the internal field induction related to the morphology of carbide was taken into consideration. It was observed that there was no pronounced effect of high magnetic field on the precipitation sequence of alloy carbides when specimens were tempered at 700°C, because they were changed into paramagnetic phases at this temperature.

Keywords:

• Alloy
• Phase transformation
• High magnetic field
• Precipitation
• Transmission electron microscopy

Acknowledgements

The authors are grateful to Professor M. Enomoto, Ibaraki University, Japan, for providing alloy specimens. The authors acknowledge gratefully the Center for Electron Microscopy Wuhan University. The authors are also grateful to the financial support for this work from State Ministry of Education (grant no. NCET-05-0680), International Science and Technology Cooperation Program of China (grant no. S2012ZR0211), Hubei Province Key Laboratory for Systems Science on Metallurgical Processing (grant no. Y201104) and Student Innovation Fund (grant no. 11ZRA113).