EFFECT OF LONG-TERM THERMAL AGING AT 475 °C ON EMBRITTLEMENT OF Fe-32Cr-4Ni-4Cu MODEL ALLOY

Xiaoming  Du; Zhendong Sun; Xue Ma; Ming Ma; Zhijun Wang; Tianfu Li

doi:10.17222/mit.2023.1044

Xiaoming Du School of Materials Science and Engineering, Shenyang Ligong University, Shenyang 110159, China1School of Materials Science and Engineering, Shenyang Ligong University, Shenyang 110159, China
Zhendong Sun School of Materials Science and Engineering, Shenyang Ligong University, Shenyang 110159, China
Xue Ma School of Materials Science and Engineering, Shenyang Ligong University, Shenyang 110159, China
Ming Ma School of Materials Science and Engineering, Shenyang Ligong University, Shenyang 110159, China
Zhijun Wang China Institute of Atomic Energy, Beijing 102413, China
Tianfu Li China Institute of Atomic Energy, Beijing 102413, China

DOI: https://doi.org/10.17222/mit.2023.1044

Keywords: model alloy, thermal aging, spinodal decomposition, Cu-rich precipitate, fracture mechanism

Abstract

The microstructure evolution and mechanical properties of a Fe-32Cr-4Ni-4Cu model alloy after long-term thermal aging at 475 °C was investigated in this study. The spinodal decomposition of the model alloy during thermal aging and the crystal structure evolution of Cu-rich precipitates were observed and analyzed using high-resolution transmission electron microscopy (TEM). It was revealed that after long-term thermal aging, the crystal structure of the precipitated Cu-rich phases in the Fe-32Cr-4Ni-4Cu model alloy transformed from a BCC structure to a multi-twin 9R or 2H structure, ultimately transforming into a stable FCC structure. During long-term thermal aging at 475 °C, the precipitated Cu-rich phase and the Cr-rich ’-phase produced by spinodal decomposition cause an increase in the hardness of the model alloy. The hardness of the model alloy in the early stage of thermal aging greatly depends on the Cu-rich precipitates. After continuous thermal aging for 1000 h, the hardness of the alloy depends on the Cr-rich ’-phase. The results of an oscillographic impact test indicate that the fracture mechanism of the model alloy after thermal aging at 475 °C is brittle fracture, which is mainly influenced by the precipitation of Cu-rich phases during the thermal aging process.

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