Mechanism of the Fe₃(B,C) and Fe₂₃(C,B)₆ solid-state transformation in the hypoeutectic region of the Fe-C-B system

详细信息    查看全文

• 作者：Jonathan Lentz ; ^{Jonathan.Lentz@Ruhr-Uni-Bochum.de" class="auth_mail" title="E-mail the corresponding author} ; Arne Rö ; ttger ; Werner Theisen
• 关键词：Fe-C-B ; Ternary alloys ; Boron ; Steel ; Solid state phase transformation
• 刊名：Acta Materialia
• 出版年：2016
• 出版时间：15 October 2016
• 年：2016
• 卷：119
• 期：Complete
• 页码：80-91
• 全文大小：6200 K

文摘

This study investigates the microstructural mechanisms involved in the solid-state transformation of the Fe₃(B,C) → Fe₂₃(C,B)₆ phases in the hypoeutectic region of the iron-carbon-boron (Fe-C-B) system. We analyzed the influence of different initial microstructural characteristics on the Fe₃(B,C) → Fe₂₃(C,B)₆ transformation with regards to the matrix phase, matrix C content, B/(C + B) ratio, and agglomeration of the parental Fe₃(B,C) phase. We performed thermodynamic calculations using the CALPHAD method, validated by laboratory melts with varying B/(B + C) ratios. These laboratory melts were then microstructurally characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and wavelength-dispersive X-ray spectroscopy (WDS). We particularly focused on solid-state transformation of borides and carboborides of type M₃(C,B) and M₂₃(C,B)₆ in the hypoeutectic region of the ternary system Fe-C-B, investigated via both in situ and ex situ XRD measurements. It was found that the solid-state transformations are influenced by enriched B inside the eutectic structure, a result of solidification. This increased B content is not reduced in solid state due to the kinetic limitations of B and C inside the hard-phase structure. Thus phase stability is subject to local equilibria depending on the local C and B concentration of the hard-phase structure. In this process the Fe₂₃(C,B)₆ phase also forms a shell-like structure surrounding the Fe₃(B,C) and Fe₂B phases.