Magnetic and mechanical properties of Cu-strengthened aged HSLA-100 steel

Abstract

Magnetic and mechanical properties were evaluated for various heat-treated Cu-strengthened HSLA-100 steels. After austenitizing at 1183 K for one hour and then water quenching, the material was aged at different temperatures ranging between 623 K and 973 K for one hour. Scanning and transmission electron microscopes with an energy dispersive X-ray attachment were used for microstructural analysis. Nanosize coherent copper precipitates caused an increase in hardness with increase in ageing temperature. The steel exhibited maximum hardness at 773 K followed by decrease in hardness with over-ageing. Copper precipitates coarsened and lost coherency during over-ageing. Ageing behaviour again exhibited an increase in hardness at 973 K due to the formation of new martensite islands. Magnetic hysteresis loop and magnetic Barkhausen emissions techniques were used to characterize the aged materials. No correlation was observed between the magnetic parameters and hardness. The results were explained by the fact that nanosize Cu precipitates, the size of which is much smaller than the domain wall width, did not influence the magnetic domain dynamics.

Acknowledgements

The authors are grateful to Prof. S.P. Mehrotra, Director, NML, for giving necessary permission to publish this work. Valuable suggestions from Prof. D.C. Jiles of Iowa State University and presently with Wolfson Centre for Magnetics, UK, for interpretation of magnetic properties of the present materials are gratefully acknowledged. The authors also wish to thank Dr. R.N.Ghosh and Dr. S. Das of NML for their valuable suggestions and keen interest in the work.