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<p>This research investigates the mechanical properties and microstructural evolution of JIS SK85 high-carbon steel subjected to various heat treatments. The study encompassed oil quenching, low-temperature austempering (320°C), and high-temperature austempering (420°C), followed by tempering at 320°C, 420°C, and 460°C. Microstructural characterization was performed using Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) for retained austenite quantification. Tensile deformation analysis utilized the Kocks-Mecking (K-M) method. Distinct microstructures were identified: martensite (quenched), lower bainite (320°C austempered), and upper bainite (420°C austempered). Tempering minimally affected upper bainite properties but significantly reduced the yield strength and stability of martensitic and lower bainitic structures. Quenched steel tempered at 420°C and 460°C exhibited a singular K-M slope (β≈0.031), indicating a uniform deformation mechanism. While low-temperature austempered steel tempered at 320°C showed minor changes (β between 0.033 and 0.038), higher tempering temperatures (420°C and 460°C) diminished its properties, revealing distinct K-M slopes due to altered deformation mechanisms. Interestingly, high-temperature austempered steel, despite minimal microstructural change, displayed two K-M slopes pre- and post-tempering, alongside a notable increase in strain hardening rate after tempering. The specimen austempered at 320°C and subsequently tempered at 320°C demonstrated an optimal balance of properties: 1,850 MPa ultimate tensile strength, 1,450 MPa yield strength, 17.5% elongation, and 130 mJ/mm<sup>3</sup> toughness.</p>

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Correlation of microstructure, mechanical properties, and strain hardening response via kocks-mecking analysis in heat-treated JIS SK85 high-carbon steel

  • 期刊论文

  • 发表日期：

    2025年7月29日

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  • Narongsak Thammachot,
  • Nipon Taweejun,
  • Tanabodee Praditja,
  • Patiphan Juijerm,
  • Wanna Homjabok

摘要

This research investigates the mechanical properties and microstructural evolution of JIS SK85 high-carbon steel subjected to various heat treatments. The study encompassed oil quenching, low-temperature austempering (320°C), and high-temperature austempering (420°C), followed by tempering at 320°C, 420°C, and 460°C. Microstructural characterization was performed using Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) for retained austenite quantification. Tensile deformation analysis utilized the Kocks-Mecking (K-M) method. Distinct microstructures were identified: martensite (quenched), lower bainite (320°C austempered), and upper bainite (420°C austempered). Tempering minimally affected upper bainite properties but significantly reduced the yield strength and stability of martensitic and lower bainitic structures. Quenched steel tempered at 420°C and 460°C exhibited a singular K-M slope (β≈0.031), indicating a uniform deformation mechanism. While low-temperature austempered steel tempered at 320°C showed minor changes (β between 0.033 and 0.038), higher tempering temperatures (420°C and 460°C) diminished its properties, revealing distinct K-M slopes due to altered deformation mechanisms. Interestingly, high-temperature austempered steel, despite minimal microstructural change, displayed two K-M slopes pre- and post-tempering, alongside a notable increase in strain hardening rate after tempering. The specimen austempered at 320°C and subsequently tempered at 320°C demonstrated an optimal balance of properties: 1,850 MPa ultimate tensile strength, 1,450 MPa yield strength, 17.5% elongation, and 130 mJ/mm3 toughness.