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<p>Austempered ductile iron (ADI) is characterized by the presence of reacted metastable austenite, which can transform into martensite under applied stress. In this study, shot peening was applied to ADI samples isothermally quenched at 230&#xa0;°C, 300&#xa0;°C and 380&#xa0;°C to evaluate the effect of surface treatment on microstructural stability. This transformation mechanism provides the basis for exploring how shot peening influences the material’s properties. The resulting microstructural evolution and microhardness change were investigated using optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and micro-Vickers hardness testing. This study focused on elucidating the mechanism by which shot peening induces martensitic transformation and enhances surface microhardness in ADI. Experimental results showed that after isothermal quenching, the matrix of ADI mainly consisted of acicular ferrite and retained austenite, with the latter occupying relative volume fractions of 28.1&#xa0;vol%, 27.9&#xa0;vol% and 34.0&#xa0;vol% at 230&#xa0;°C, 300&#xa0;°C and 380&#xa0;°C, respectively. Following shot peening, a portion of the reacted metastable austenite transformed into martensite, with conversion rates of 45.8%, 30.9% and 39.7% corresponding to the three quenching temperatures. Moreover, the surface microhardness of ADI increased significantly after peening, with measured increments of 175.5&#xa0;HV0.05, 167.5&#xa0;HV0.05 and 186.4&#xa0;HV0.05 for the 230&#xa0;°C, 300&#xa0;°C and 380&#xa0;°C samples, respectively.</p>

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Influence of Surface Stress-Induced Martensite Phase Transformation on Hardness in Austempered Ductile Iron

  • 期刊论文

  • 发表日期：

    2025年11月8日

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  • Yongbo Qi,
  • Chao Yang,
  • Ke Wang,
  • Bailing Jiang,
  • Zhijie Gao

摘要

Austempered ductile iron (ADI) is characterized by the presence of reacted metastable austenite, which can transform into martensite under applied stress. In this study, shot peening was applied to ADI samples isothermally quenched at 230 °C, 300 °C and 380 °C to evaluate the effect of surface treatment on microstructural stability. This transformation mechanism provides the basis for exploring how shot peening influences the material’s properties. The resulting microstructural evolution and microhardness change were investigated using optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and micro-Vickers hardness testing. This study focused on elucidating the mechanism by which shot peening induces martensitic transformation and enhances surface microhardness in ADI. Experimental results showed that after isothermal quenching, the matrix of ADI mainly consisted of acicular ferrite and retained austenite, with the latter occupying relative volume fractions of 28.1 vol%, 27.9 vol% and 34.0 vol% at 230 °C, 300 °C and 380 °C, respectively. Following shot peening, a portion of the reacted metastable austenite transformed into martensite, with conversion rates of 45.8%, 30.9% and 39.7% corresponding to the three quenching temperatures. Moreover, the surface microhardness of ADI increased significantly after peening, with measured increments of 175.5 HV0.05, 167.5 HV0.05 and 186.4 HV0.05 for the 230 °C, 300 °C and 380 °C samples, respectively.