Reactor materials play a vital role in ensuring the longevity and safety of reactors. As the reactor core operates under extreme environmental conditions—including high temperatures, radiation, and corrosive media—continuous research is essential to develop advanced materials that can maintain structural integrity over extended service lifetimes. This study investigates the effect of partially replacing Ni with Mn and N and Cr with Al on the mechanical properties and corrosion resistance of austenitic stainless steel alloys. AISI 316 stainless steel was used as the baseline material, and its composition was modified by incorporating 2.46, 0.33, and 0.8 wt% of Mn, N, and Al (SSAlMnN1), and 4.24, 0.81, and 1.44 wt% of Mn, N, and Al (SSAlMnN2). The structural examination, conducted using optical microscopy, X-ray diffraction, and a Schaeffer diagram, indicated the formation of a pure austenite structure along with carbides (MC), nitrides (CrN and AlN), and Al2O3 and MnAl2O4 phases. The presence of these secondary phases confirmed that the alloying additions not only preserved the desirable austenitic matrix but also contributed to strengthening mechanisms through the dispersion of fine precipitates and the formation of a passive film. These additions and the resulting structural changes significantly influenced the mechanical properties and corrosion resistance of AISI 316 stainless steel. A balanced improvement in strength properties—yield strength, ultimate tensile strength, and hardness—and ductility was observed with increasing Mn, N, and Al content. Compared to AISI 316, the SSAlMnN1 alloy exhibited improvements of 1.92%, 14.4%, 5.0%, and 14.1% in yield strength, ultimate tensile strength, hardness, and elongation, respectively. In contrast, the SSAlMnN2 alloy showed more significant enhancements, with increases of 10.2%, 31.5%, 10.2%, and 21.6% in these properties. These enhancements were primarily attributed to three synergistic strengthening mechanisms: solid solution hardening (induced by Mn, N, and Al), precipitation hardening (via MC, CrN, and AlN phases), and grain-boundary strengthening through refined microstructures. The corrosion behavior was strongly dependent on the alloying concentration. The SSAlMnN1 alloy exhibited improved corrosion resistance compared to AISI 316 in both 3.5% and 5 wt% NaCl solutions, attributed to the formation of a stable, adherent passive film enriched with Al2O3 and Mn-based oxides. In contrast, SSAlMnN2 showed reduced corrosion resistance in both 3.5% and 5% NaCl solutions, despite its mechanical advantages. This was attributed to excessive Cr and Ni substitution, leading to destabilized passive films, grain boundary precipitation, and higher corrosion currents. Electrochemical measurements, including potentiodynamic polarization and electrochemical impedance spectroscopy (EIS), supported these findings, indicating that while SSAlMnN1 maintained a dense and uniform passive film, SSAlMnN2 exhibited reduced film integrity and lower polarization resistance.

Developed high-strength and corrosion-resistant stainless steel alloys for in-core of nuclear reactors

期刊论文
发表日期：

2025年8月7日

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Dalal Abdullah Aloraini,
Aly Saeed

摘要

Reactor materials play a vital role in ensuring the longevity and safety of reactors. As the reactor core operates under extreme environmental conditions—including high temperatures, radiation, and corrosive media—continuous research is essential to develop advanced materials that can maintain structural integrity over extended service lifetimes. This study investigates the effect of partially replacing Ni with Mn and N and Cr with Al on the mechanical properties and corrosion resistance of austenitic stainless steel alloys. AISI 316 stainless steel was used as the baseline material, and its composition was modified by incorporating 2.46, 0.33, and 0.8 wt% of Mn, N, and Al (SSAlMnN1), and 4.24, 0.81, and 1.44 wt% of Mn, N, and Al (SSAlMnN2). The structural examination, conducted using optical microscopy, X-ray diffraction, and a Schaeffer diagram, indicated the formation of a pure austenite structure along with carbides (MC), nitrides (CrN and AlN), and Al₂O₃ and MnAl₂O₄ phases. The presence of these secondary phases confirmed that the alloying additions not only preserved the desirable austenitic matrix but also contributed to strengthening mechanisms through the dispersion of fine precipitates and the formation of a passive film. These additions and the resulting structural changes significantly influenced the mechanical properties and corrosion resistance of AISI 316 stainless steel. A balanced improvement in strength properties—yield strength, ultimate tensile strength, and hardness—and ductility was observed with increasing Mn, N, and Al content. Compared to AISI 316, the SSAlMnN1 alloy exhibited improvements of 1.92%, 14.4%, 5.0%, and 14.1% in yield strength, ultimate tensile strength, hardness, and elongation, respectively. In contrast, the SSAlMnN2 alloy showed more significant enhancements, with increases of 10.2%, 31.5%, 10.2%, and 21.6% in these properties. These enhancements were primarily attributed to three synergistic strengthening mechanisms: solid solution hardening (induced by Mn, N, and Al), precipitation hardening (via MC, CrN, and AlN phases), and grain-boundary strengthening through refined microstructures. The corrosion behavior was strongly dependent on the alloying concentration. The SSAlMnN1 alloy exhibited improved corrosion resistance compared to AISI 316 in both 3.5% and 5 wt% NaCl solutions, attributed to the formation of a stable, adherent passive film enriched with Al₂O₃ and Mn-based oxides. In contrast, SSAlMnN2 showed reduced corrosion resistance in both 3.5% and 5% NaCl solutions, despite its mechanical advantages. This was attributed to excessive Cr and Ni substitution, leading to destabilized passive films, grain boundary precipitation, and higher corrosion currents. Electrochemical measurements, including potentiodynamic polarization and electrochemical impedance spectroscopy (EIS), supported these findings, indicating that while SSAlMnN1 maintained a dense and uniform passive film, SSAlMnN2 exhibited reduced film integrity and lower polarization resistance.