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<p>This study investigates the corrosion behavior of modified 9Cr-1Mo steel with dual-phase bainitic and martensitic microstructures developed through tailored heat treatments. The test samples were divided into two groups based on processing conditions. Group-I includes Set-I and Set-II samples, which were austenitized at 1000 °C for 1 h, then austempered at 460 °C for different durations, followed by either water quenching (Set-I) or air-cooling (Set-II). Group-II includes Set-III and Set-IV samples, which were austenitized at 1000 °C, austempered at 460 °C (Set-III) or 480 °C (Set-IV) for a fixed 6 h, and then tempered at 760 °C for different durations. Corrosion resistance was evaluated using potentiodynamic polarization and electrochemical impedance spectroscopy in 3.5% NaCl solution at ambient conditions. Surface morphology and phase compositions were analyzed using scanning electron microscopy (SEM) and Raman spectroscopy. The results showed that all heat-treated samples exhibited significantly enhanced corrosion resistance compared to the as-received material, with Group-I samples (bainitic-dominant) outperforming Group-II (tempered) samples. Within Group-II, Set-III samples exhibited lower corrosion rates than Set-IV, indicating the detrimental effect of higher austempering temperatures. It was also observed that longer tempering durations led to increased carbide precipitation and reduced corrosion resistance. Detailed surface analysis confirmed the formation of protective oxides, and Raman spectroscopy provided phase-specific insights, introducing a phase ratio to quantify oxide layer protectiveness, an approach not previously applied in this context. This study provides the first comprehensive electrochemical assessment of dual-phase modified 9Cr-1Mo steel and establishes clear correlations between microstructural evolution and corrosion behavior. The findings offer valuable guidance for designing thermally treated steels with improved corrosion resistance for critical nuclear and high-temperature applications.</p>

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Corrosion Properties of Dual-Phase Bainitic and Martensitic Microstructures in Modified 9Cr-1M Steel

  • 期刊论文

  • 发表日期：

    2025年9月24日

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  • Satish Kumar,
  • S. Sangal

摘要

This study investigates the corrosion behavior of modified 9Cr-1Mo steel with dual-phase bainitic and martensitic microstructures developed through tailored heat treatments. The test samples were divided into two groups based on processing conditions. Group-I includes Set-I and Set-II samples, which were austenitized at 1000 °C for 1 h, then austempered at 460 °C for different durations, followed by either water quenching (Set-I) or air-cooling (Set-II). Group-II includes Set-III and Set-IV samples, which were austenitized at 1000 °C, austempered at 460 °C (Set-III) or 480 °C (Set-IV) for a fixed 6 h, and then tempered at 760 °C for different durations. Corrosion resistance was evaluated using potentiodynamic polarization and electrochemical impedance spectroscopy in 3.5% NaCl solution at ambient conditions. Surface morphology and phase compositions were analyzed using scanning electron microscopy (SEM) and Raman spectroscopy. The results showed that all heat-treated samples exhibited significantly enhanced corrosion resistance compared to the as-received material, with Group-I samples (bainitic-dominant) outperforming Group-II (tempered) samples. Within Group-II, Set-III samples exhibited lower corrosion rates than Set-IV, indicating the detrimental effect of higher austempering temperatures. It was also observed that longer tempering durations led to increased carbide precipitation and reduced corrosion resistance. Detailed surface analysis confirmed the formation of protective oxides, and Raman spectroscopy provided phase-specific insights, introducing a phase ratio to quantify oxide layer protectiveness, an approach not previously applied in this context. This study provides the first comprehensive electrochemical assessment of dual-phase modified 9Cr-1Mo steel and establishes clear correlations between microstructural evolution and corrosion behavior. The findings offer valuable guidance for designing thermally treated steels with improved corrosion resistance for critical nuclear and high-temperature applications.