Effects of high magnetic field on austenite formation and grain size in a hypereutectoid carbon steel
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The effects of magnetic field on the austenite formation and grain size were studied by applying high magnetic field during the different stages. Optical microscopy and scanning electron microscopy were used to characterize the microstructure evolution for the samples treated without and with magnetic field. Magnetic field dramatically retards the austenite formation kinetics including pearlite to austenite transformation and cementite dissolution. The austenite grain size is enlarged by the magnetic field applied during austenite formation and not affected by the magnetic field applied only during austenite grain coarsening. The austenite treated with magnetic field during the whole austenitization process also has a larger grain size. The changes in austenite formation kinetics and grain size are related to lower nucleation rate of austenite caused by magnetic field. I. INTRODUCTION
The effect of high magnetic field processing on microstructure evolution and performance enhancement in steels is a growing research topic. High magnetic field can modify the Gibbs energy of ferromagnetic phase and boundaries (A1 and A3 line) in Fe–C phase diagram.1–4 Influence of high magnetic field on the solid transformation of steels has been shown in many aspects such as martensite transformation,5 bainite transformation,6 proeutectoid ferrite transformation,7–9 pearlite transformation,10–12 recrystallization,13–15 and carbide precipitation in temper.16–18 However, many researchers6,7,11 investigated the influence of magnetic field on the austenitic decomposition by applying high magnetic field during both austenitization and following cooling process. However, this experimental procedure confuses the understanding of effects of magnetic field because it is difficult to separate the coupling effect of magnetic field on the austenitization and following continuous cooling, and even the effect of magnetic field on austenitization is neglected. Therefore, it is helpful to analyze accurately the mechanism of magnetic field effects by investigating the effect of magnetic field on austenitization. Fully pearlitic steel wires exhibit ultrahigh strength and have important applications where high strength and wear resistance are required. The hypereutectoid compositions present a promising potential for increasing the mechanical properties, especially the strength.19,20 The austenitization condition strongly influences the proeutectoid a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2014.149 1448
J. Mater. Res., Vol. 29, No. 13, Jul 14, 2014
http://journals.cambridge.org
Downloaded: 14 Mar 2015
cementite and pearlite transformation.21 Therefore, the magnetic field application to change the austenite state may provide a new way for developing customized microstructure and enhanced performance. Investigation for effects of magnetic field on the austenitization is of importance for scientific research and industrial processing. Austenitization can be divided into two stages: austenite formation and austenite grain
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