Ferrite formation and decomposition in 316H austenitic stainless steel electro slag remelting ingot for nuclear power applications

IF 4.8 2区材料科学 Q1 MATERIALS SCIENCE, CHARACTERIZATION & TESTING

Materials Characterization Pub Date : 2024-11-23 DOI:10.1016/j.matchar.2024.114581

Yang Wang , Chao Chen , Ruijie Ren , Zhixuan Xue , Haozheng Wang , Yunzhe Zhang , Junxian Wang , Jian Wang , Lei Chen , Wangzhong Mu

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引用次数: 0

Abstract

316H austenitic stainless steel used in nuclear power has higher requirements for material magnetism, and the main magnetic phase is ferrite. Thus, the ferrite content in 316H steel castings needs to be strictly controlled. This study investigated the ferrite phases in 316H austenitic stainless steel electro-slag remelting (ESR) ingot used in nuclear power applications. The morphology, content and decomposition of ferrite as well as microsegregation in 316H ESR ingot are studied by optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and electron probe microanalysis (EPMA). The solidification process is calculated by thermodynamic calculation using Thermo-Calc. Besides, the empirical chromium and nickel equivalent formulas and phase stability diagram are used for prediction of the solidification mode and ferrite content. The experiment results show that the ferrite morphology changes greatly in the direction of the thickness of ESR ingot. From surface to center of the ESR ingot, the ferrite morphology varies as granular → short rod-shaped → blocky → skeletal → parallel short rod-like + network-like. The ferrite content in the thickness direction of the electroslag ingot varied from 1.92 to 3.57 %, showing an “A” shape distribution. There are three kinds of decomposition behavior of ferrite: decomposition into Sigma phase and austenite phase by the eutectoid reaction, transformation into Chi phase in regions enriched with high Mo element along grain boundaries, and direct transformation into secondary austenite phase. In addition, the thermodynamic calculation and most of empirical formulas predicts the solidification mode is FA mode. From the microstructure analysis, the solidification mode of ESR ingots change from AF mode to FA mode from surface to center. Furthermore, the formulas proposed by Hull provides most accurate predictions results in ferrite content.

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核电用 316H 奥氏体不锈钢电渣重熔锭中铁素体的形成与分解

核电用 316H 奥氏体不锈钢对材料磁性要求较高，主要磁性相为铁素体。因此，需要严格控制 316H 钢铸件中的铁素体含量。本研究调查了核电应用中使用的 316H 奥氏体不锈钢电渣重熔（ESR）铸锭中的铁素体相。通过光学显微镜（OM）、扫描电子显微镜（SEM）、电子反向散射衍射（EBSD）和电子探针显微分析（EPMA）研究了 316H ESR 钢锭中铁素体的形态、含量和分解以及微偏析。凝固过程通过 Thermo-Calc 进行热力学计算。此外，还利用经验铬镍当量公式和相稳定图来预测凝固模式和铁素体含量。实验结果表明，铁素体形态在 ESR 铸锭的厚度方向上变化很大。从 ESR 铸锭的表面到中心，铁素体的形态变化为颗粒状 → 短杆状 → 块状 → 骨架状 → 平行短杆状 + 网络状。电渣铸锭厚度方向的铁素体含量从 1.92% 到 3.57% 不等，呈 "A "型分布。铁素体的分解行为有三种：通过共晶反应分解成西格玛相和奥氏体相；在晶界富含高钼元素的区域转变成驰放相；直接转变成二次奥氏体相。此外，热力学计算和大多数经验公式都预测凝固模式为 FA 模式。从微观结构分析来看，ESR 钢锭的凝固模式从表面到中心由 AF 模式转变为 FA 模式。此外，Hull 提出的公式对铁素体含量的预测结果最为准确。

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来源期刊

Materials Characterization 工程技术-材料科学：表征与测试

CiteScore

7.60

自引率

8.50%

发文量

746

审稿时长

36 days

期刊介绍： Materials Characterization features original articles and state-of-the-art reviews on theoretical and practical aspects of the structure and behaviour of materials. The Journal focuses on all characterization techniques, including all forms of microscopy (light, electron, acoustic, etc.,) and analysis (especially microanalysis and surface analytical techniques). Developments in both this wide range of techniques and their application to the quantification of the microstructure of materials are essential facets of the Journal. The Journal provides the Materials Scientist/Engineer with up-to-date information on many types of materials with an underlying theme of explaining the behavior of materials using novel approaches. Materials covered by the journal include: Metals & Alloys Ceramics Nanomaterials Biomedical materials Optical materials Composites Natural Materials.