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<p>This study investigates the influence of niobium (Nb) on the heat-treatment behavior of multi-alloyed white cast iron containing 5&#xa0;wt% each of Cr, Mo, W, and V, together with 2&#xa0;wt%Co and 2.00–2.40&#xa0;wt%C. Alloys with Nb contents ranging from 0.00 and 2.58&#xa0;wt% were produced and subjected to annealing, austenitizing at 1050 and 1100&#xa0;°C, quenching in a liquid nitrogen spray and tempering at 400–600&#xa0;°C. The as-cast microstructure consisted of primary austenite dendrites (γ<sub>p</sub>), eutectic carbides. At Nb levels above 1.05&#xa0;wt%, primary MC carbides (MC<sub>p</sub>) were also observed. The eutectic (γ + MC) fraction reached a maximum at 0.70&#xa0;wt%Nb and then decreased, while the eutectic (γ + M<sub>2</sub>C) fraction decreased continuously with Nb addition. In the as-hardened state, hardness decreased to a minimum at 1.05&#xa0;wt%Nb due to matrix C depletion. However, it increased again at higher Nb levels as additional C (from 2.00 to 2.40&#xa0;wt%) compensated for carbide formation. The volume fraction of retained austenite (Vγ) increased slightly with Nb content, particularly at elevated austenitizing temperatures. Upon tempering, all alloys exhibited secondary hardening associated with secondary carbide precipitation and the martensitic transformation of retained austenite. The maximum tempered hardness (H<sub>Tmax</sub>) was consistently achieved at 525&#xa0;°C, reaching 927 HV30 in the alloy containing 2.58&#xa0;wt%Nb austenitized at 1100&#xa0;°C. Overall, Nb strongly affects carbide precipitation and retained austenite stability, exerting a dominant influence on hardness evolution. Notably, hardness values approaching 930 HV30 confirm that Nb addition is critical to sustaining the high hardness of multi-alloyed white cast iron through heat treatment.</p>

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Influence of Niobium on Hardness and Microstructural Evolution in Heat-Treated Multi-alloyed White Cast Iron

  • 期刊论文

  • 发表日期：

    2026年5月15日

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  • Krittapart Sriboonrueang,
  • Sarum Boonmee,
  • Sudsakorn Inthidech,
  • Jatupon Opapaiboon,
  • Kaoru Yamamoto,
  • Yasuhiro Matsubara

摘要

This study investigates the influence of niobium (Nb) on the heat-treatment behavior of multi-alloyed white cast iron containing 5 wt% each of Cr, Mo, W, and V, together with 2 wt%Co and 2.00–2.40 wt%C. Alloys with Nb contents ranging from 0.00 and 2.58 wt% were produced and subjected to annealing, austenitizing at 1050 and 1100 °C, quenching in a liquid nitrogen spray and tempering at 400–600 °C. The as-cast microstructure consisted of primary austenite dendrites (γp), eutectic carbides. At Nb levels above 1.05 wt%, primary MC carbides (MCp) were also observed. The eutectic (γ + MC) fraction reached a maximum at 0.70 wt%Nb and then decreased, while the eutectic (γ + M2C) fraction decreased continuously with Nb addition. In the as-hardened state, hardness decreased to a minimum at 1.05 wt%Nb due to matrix C depletion. However, it increased again at higher Nb levels as additional C (from 2.00 to 2.40 wt%) compensated for carbide formation. The volume fraction of retained austenite (Vγ) increased slightly with Nb content, particularly at elevated austenitizing temperatures. Upon tempering, all alloys exhibited secondary hardening associated with secondary carbide precipitation and the martensitic transformation of retained austenite. The maximum tempered hardness (HTmax) was consistently achieved at 525 °C, reaching 927 HV30 in the alloy containing 2.58 wt%Nb austenitized at 1100 °C. Overall, Nb strongly affects carbide precipitation and retained austenite stability, exerting a dominant influence on hardness evolution. Notably, hardness values approaching 930 HV30 confirm that Nb addition is critical to sustaining the high hardness of multi-alloyed white cast iron through heat treatment.