Tomota Yo
Research Center for Structural Materials, National Institute for Materials Science (NIMS), Tsukuba, Japan.
Research Institute for Measurements and Analytical Instrumentation, National Institute of advanced Industrial Science and Technology (AIST), Tsukuba, Japan.
Sci Technol Adv Mater. 2019 Dec 2;20(1):1189-1206. doi: 10.1080/14686996.2019.1699389. eCollection 2019.
Applications of neutron diffraction to microstructure evaluation of steel investigated by a project commissioned by the Innovative Structural Materials Association are summarized. The volume fraction of austenite (γ) for a 1.5Mn-1.5Si-0.2C steel was measured by various techniques including backscatter electron diffraction (EBSD) and X-ray diffraction. It is recommended to measure volume fraction and texture simultaneously using neutron diffraction. The γ reverse transformation was monitored using dilatometry, EBSD, X-ray diffraction and neutron diffraction. The γ reversion kinetics showed excellent agreements between dilatometry and neutron diffraction, whereas the γ formation started at higher temperatures in EBSD and X-ray diffraction measurements. Such discrepancy is attributed to the change in chemical compositions at the specimen surface by heating; Mn and C concentrations were decreased with heating. Phase transformations from γ upon cooling were monitored, which enabled us to elucidate the changes in lattice parameters of ferrite (α) and γ affected by not only thermal contraction but also transformation strains, thermal misfit strains and carbon enrichment in γ in the above hypoeutectoid steel. Pearlitic transformation started after the carbon enrichment reached approximately 0.76 mass% and contributed to diffraction line broadening. Martensitic transformation with or without ausforming at 700°C was monitored for a medium carbon low alloyed steel. Dislocation density after ausforming was determined using the convolutional multiple whole profile fitting method for 10 s time-sliced data. The changes in γ and martensite lattice parameters upon quenching were tracked and new insights on internal stresses and the axial ratio of martensite were obtained.
总结了由创新结构材料协会委托的一个项目所研究的中子衍射在钢的微观结构评估中的应用。通过包括背散射电子衍射（EBSD）和X射线衍射在内的各种技术测量了1.5Mn-1.5Si-0.2C钢中奥氏体（γ）的体积分数。建议使用中子衍射同时测量体积分数和织构。使用膨胀仪、EBSD、X射线衍射和中子衍射监测γ逆转变。γ再转变动力学在膨胀仪和中子衍射之间显示出极好的一致性，而在EBSD和X射线衍射测量中，γ形成在较高温度下开始。这种差异归因于加热导致试样表面化学成分的变化；加热时Mn和C浓度降低。监测了冷却时从γ发生的相变，这使我们能够阐明在上述亚共析钢中，铁素体（α）和γ的晶格参数变化不仅受热收缩影响，还受热应变、热失配应变以及γ中碳富集影响。珠光体转变在碳富集达到约0.76质量%后开始，并导致衍射线宽化。对一种中碳低合金钢监测了在700°C下有或无奥氏体形变的马氏体转变。使用卷积多重全谱拟合方法对10 s时间切片数据确定奥氏体形变后的位错密度。跟踪了淬火时γ和马氏体晶格参数的变化，并获得了关于内应力和马氏体轴比的新见解。
