Microstructure Formation and Carbon Partitioning with Austenite Decomposition during Isothermal Heating Process in Fe-Si-Mn-C Steel Monitored by In Situ Time-of-Flight Neutron Diffraction
Microstructure Formation and Carbon Partitioning with Austenite Decomposition during Isothermal Heating Process in Fe-Si-Mn-C Steel Monitored by In Situ Time-of-Flight Neutron Diffraction
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DOI：
10.3390/met12060957
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发表时间：
2022-06
期刊：
影响因子：
2.9
通讯作者：
Y. Onuki;K. Umemura;K. Fujiwara;Yasuaki Tanaka;T. Tomida;K. Kawano;S. Sato
中科院分区：
文献类型：
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作者：
Y. Onuki;K. Umemura;K. Fujiwara;Yasuaki Tanaka;T. Tomida;K. Kawano;S. Sato
残余奥氏体是贝氏体高强度钢实现相变诱发塑性的关键特征。在这项研究中，作者利用原位中子衍射技术重点研究了等温加热过程中 Fe-0.61C-1.9Si-0.98Mn (mass%) 中亚稳态奥氏体的形成。除了基于奥氏体晶格参数的碳浓度估计之外，还可以通过应用考虑晶体织构的原位相分数分析来定量讨论碳分配过程。碳分配行为不均匀，导致奥氏体中碳浓度分布呈双峰。富碳的高碳奥氏体在 673 K 等温加热过程中保持稳定，甚至在冷却至室温后也能保持不变。其余为低碳奥氏体，逐渐被贝氏体转变所消耗。在723 K以上，由于Si的快速扩散，高碳奥氏体也分解为铁素体和渗碳体。相反，低于 623 K，即使没有 Si 扩散，渗碳体也会稳定。这些渗碳体形成机制阻止了高碳奥氏体的形成和保留。必须仔细考虑不均匀的碳分布和渗碳体形成，以精确预测加硅贝氏体钢的微观结构形成。
Retained austenite is a key feature used to realize the transformation-induced plasticity in bainitic high strength steels. In this study, the authors focused on the formation of metastable austenite in Fe-0.61C-1.9Si-0.98Mn (mass%) during isothermal heating processes using in situ neutron diffraction techniques. Quantitative discussion of carbon partitioning processes is enabled by applying an in situ phase fraction analysis considering crystallographic textures, in addition to the carbon concentration estimation based on the lattice parameter of austenite. The carbon partitioning behavior is inhomogeneous, resulting in a bimodal carbon concentration distribution in austenite. The carbon enriched, high carbon austenite is stable during isothermal heating at 673 K and is retained even after cooling to room temperature. The remainder is low carbon austenite, which is gradually consumed by bainite transformation. Above 723 K, the high carbon austenite also decomposes to ferrite and cementite due to the fast diffusion of Si. Conversely, below 623 K, cementite is stabilized even without the diffusion of Si. These cementite formation mechanisms prevent the formation and retention of high carbon austenite. The inhomogeneous carbon distribution and cementite formation must be carefully considered to precisely predict the microstructure formation in Si-added bainitic steels.