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<p>In this study, computer simulation was used to plot a&#xa0;pseudo-binary diagram for Fe-9Cr-1Mo steel microalloyed with niobium and containing up to 0.06 wt. % carbon, and the phase-structural mechanisms of its crystallization were clarified. The steel maintains a&#xa0;single-phase structure of high-temperature δ‑ferrite in the entire solidification interval due to one-step crystallization (Liquid → δ) without a&#xa0;peritectic reaction or peritectic transformation. No micron-sized niobium-rich carbide phases were detected by metallographic analysis of the experimental steel ingot microalloyed with Nb up to 0.09 wt. % obtained by remelting in a&#xa0;laboratory vacuum induction furnace. It has been shown that at the crystallization stage, the interdendritic space becomes enriched with Cr, Mo, Si, Mn, Ni, and Nb, which segregate directly and form a&#xa0;solid solution with increased contents of carbide-forming elements. However, insignificant differences in the compositions of the microsegregation zones ensure the maximum possible macroscopic homogenization of the structure, thus allowing for the achievement of various strength classes (e.g., P110, C90, and L80) for the studied steel by properly selecting the final heat treatment conditions.</p><p>Metallographic studies of cast and deformed samples revealed thermally stable anomalous “white” zones with an increased content of all alloying elements relative to the standard crystallization zone. At the same time, the internal volumes of the “white” zones, in the form of inclusions with a&#xa0;high-angle boundary, contain a&#xa0;solid solution with molybdenum and niobium contents of up to 2.9–3.1 and up to 0.12 wt. %, respectively. This specifically leads to intensive pitting formation in these zones as early as during the metallographic etching of the samples, thus indicating their low resistance to aggressive environments. Therefore, like any other inhomogeneities in the bulk of a&#xa0;solid solution, the anomalous “white” zones with high-angle matrix boundaries exhibit reduced resistance to aggressive environments. Consequently, an increase in corrosion resistance can be expected by preventing the formation of “white” zones with an increased content of all alloying elements.</p>

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Specifics of the structure formation of Fe-9Cr-1Mo martensitic steel microalloyed with niobium

  • 期刊论文

  • 发表日期：

    2026年3月1日

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  • V. V. Yushchuk,
  • A. A. Komissarov,
  • E. D. Dolgach,
  • A. Yu. Davydenko,
  • L. V. Palatkina,
  • L. I. Romanov,
  • A. M. Mikhailov,
  • A. V. Muntin,
  • A. V. Chervonny

摘要

In this study, computer simulation was used to plot a pseudo-binary diagram for Fe-9Cr-1Mo steel microalloyed with niobium and containing up to 0.06 wt. % carbon, and the phase-structural mechanisms of its crystallization were clarified. The steel maintains a single-phase structure of high-temperature δ‑ferrite in the entire solidification interval due to one-step crystallization (Liquid → δ) without a peritectic reaction or peritectic transformation. No micron-sized niobium-rich carbide phases were detected by metallographic analysis of the experimental steel ingot microalloyed with Nb up to 0.09 wt. % obtained by remelting in a laboratory vacuum induction furnace. It has been shown that at the crystallization stage, the interdendritic space becomes enriched with Cr, Mo, Si, Mn, Ni, and Nb, which segregate directly and form a solid solution with increased contents of carbide-forming elements. However, insignificant differences in the compositions of the microsegregation zones ensure the maximum possible macroscopic homogenization of the structure, thus allowing for the achievement of various strength classes (e.g., P110, C90, and L80) for the studied steel by properly selecting the final heat treatment conditions.

Metallographic studies of cast and deformed samples revealed thermally stable anomalous “white” zones with an increased content of all alloying elements relative to the standard crystallization zone. At the same time, the internal volumes of the “white” zones, in the form of inclusions with a high-angle boundary, contain a solid solution with molybdenum and niobium contents of up to 2.9–3.1 and up to 0.12 wt. %, respectively. This specifically leads to intensive pitting formation in these zones as early as during the metallographic etching of the samples, thus indicating their low resistance to aggressive environments. Therefore, like any other inhomogeneities in the bulk of a solid solution, the anomalous “white” zones with high-angle matrix boundaries exhibit reduced resistance to aggressive environments. Consequently, an increase in corrosion resistance can be expected by preventing the formation of “white” zones with an increased content of all alloying elements.