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<p>This study investigates the tempering brittle fracture mechanism of a novel martensitic low-density steel (45Mn5Al4) under different tempering temperatures and cooling conditions. The analysis focuses on mechanical properties, microstructural evolution, and tensile fracture behavior. Experimental results show that, within the tempering brittleness range, the matrix is primarily martensite, with a small amount of ferrite precipitated along the prior austenite grain boundaries. The brittle fracture observed between 375&#xa0;°C and 600&#xa0;°C is attributed to this ferrite precipitation. In conjunction with the high dislocation density of the tempered martensite (BCT), this leads to microstructural discontinuities that promote stress concentration. Auger electron spectroscopy (AES) further reveals significant boron segregation at the grain boundaries, which reduces interfacial bonding strength. The combined effects accelerate crack initiation and propagation, ultimately resulting in tempering brittleness. This study reveals the intrinsic mechanism from the perspectives of microstructure, interfacial characteristics, and element distribution. These findings provide a theoretical foundation for optimizing heat treatment processes and enhancing the application potential of this novel steel in lightweight structural components.</p>

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Investigation of Tempering-Induced Brittle Fracture Mechanism in a Novel Low-Density Martensitic Steel

  • 期刊论文

  • 发表日期：

    2025年7月8日

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  • Chuanxing Fu,
  • Ce Sun,
  • Jie Zhou,
  • Fanghui Guo,
  • Junru Li

摘要

This study investigates the tempering brittle fracture mechanism of a novel martensitic low-density steel (45Mn5Al4) under different tempering temperatures and cooling conditions. The analysis focuses on mechanical properties, microstructural evolution, and tensile fracture behavior. Experimental results show that, within the tempering brittleness range, the matrix is primarily martensite, with a small amount of ferrite precipitated along the prior austenite grain boundaries. The brittle fracture observed between 375 °C and 600 °C is attributed to this ferrite precipitation. In conjunction with the high dislocation density of the tempered martensite (BCT), this leads to microstructural discontinuities that promote stress concentration. Auger electron spectroscopy (AES) further reveals significant boron segregation at the grain boundaries, which reduces interfacial bonding strength. The combined effects accelerate crack initiation and propagation, ultimately resulting in tempering brittleness. This study reveals the intrinsic mechanism from the perspectives of microstructure, interfacial characteristics, and element distribution. These findings provide a theoretical foundation for optimizing heat treatment processes and enhancing the application potential of this novel steel in lightweight structural components.