Phase Characterization and Formation Behavior in 6 wt% Si High-silicon Austenitic Stainless Steel during Isothermal Agin
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Phase Characterization and Formation Behavior in 6 wt% Si High‑silicon Austenitic Stainless Steel during Isothermal Aging Sihan Chen1,2 · Tian Liang1,3 · Yangtao Zhou1 · Weiwei Xing1 · Chengwu Zheng1 · Yingche Ma1 · JinMing Wu3 · Guobin Li4 · Kui Liu1 Received: 23 June 2020 / Revised: 10 August 2020 / Accepted: 27 August 2020 © The Chinese Society for Metals (CSM) and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The precipitation behavior of different phases in a high-silicon stainless steel (6 wt% Si) during aging at 600–1050 °C for 24 h was investigated. The morphology, crystal structure and composition of various precipitates were detailly characterized using optical microscopy, scanning electron microscopy and transmission electron microscopy. Four phases were mainly identified: χ-phase, M6C carbides, σ phase and a new type of fcc-phase. During aging at 600–900 °C, the main precipitate was (Cr, Mo and Si)-rich χ-phase which was directly precipitated from γ matrix. The χ-phase was calibrated as bcc structure with a lattice parameter of 8.90 Å. The peak temperature for the precipitation of χ-phase was 800 °C, and it was dissolved when aging at temperatures above 1000 °C. The σ-phase was observed only at 700 °C and grew next to χ-phase. Above 700 °C, a new fcc-phase was found to be precipitated along with χ-phase, with a space group of Fd3c and a lattice parameter of 12.56 Å. The M6C carbides started to be precipitated at 700 °C in the vicinity of χ-phase. And its amount basically increased with the increasing of temperature. An orientation relationship between M6C/γ was found: [100]c//[100]γ, (001)c//(001)γ, i.e., the cube-on-cube relationship. Keywords High-silicon austenitic stainless steel · Precipitates · χ-Phase · Precipitation behavior
1 Introduction High silicon-containing stainless steels (Si > 4 wt% in general) possess excellent corrosion resistance in hot concentrated sulfuric acid or concentrated nitric acid [1, 2]. They Available online at http://link.springer.com/journal/40195. * Tian Liang [email protected] * Kui Liu [email protected] 1
Key Laboratory of Nuclear Materials and Safety Assessment, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
2
School of Materials Science and Engineering, University of Science and Technology of China, Hefei 230026, China
3
State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China
4
Zhejiang Xindeda Special Pipe Industry Co., Ltd, Wenzhou 325024, China
thus have wide applications in the apparatus for sulfuric acid, nitric acid, chemical fertilizer and irradiation fuel reprocessing. Because of the high Si content, the steels are prone to forming a layer of double-deck passivation coating when exposed to highly oxidative concentrated sulfuric or nitric acid at high temperatures [3, 4]. The passivation coating can inhibit cathodic reactions and prevent the homogeneous intergranular corrosion [5–7]. The corrosion resistanc
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