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<p>Repeated confined laser shock peening (LSP) was applied to carburized M50NiL steel to clarify the near-surface microstructural evolution and hardening behavior under repeated LSP. AFM, XRD, EBSD, nanoindentation, and residual-stress measurements were employed for characterization. Within approximately 150&#xa0;<i>μ</i>m from the treated surface, repeated LSP produced a clear gradient-affected layer, in which the effective martensitic block/sub-block size decreased from 1.38&#xa0;<i>μ</i>m (untreated) to 1.19&#xa0;<i>μ</i>m (LSP once) and 1.14&#xa0;<i>μ</i>m (LSP twice), while the corresponding low-angle grain boundary fraction increased from 25.1% to 31.4% and 35.2%. Surface/subsurface XRD showed a progressive decrease in retained austenite and an increase in dislocation density in both phases, with a stronger response in austenite than in martensite. EBSD-based recrystallization-state indicated that austenite evolved from a relatively recrystallized state toward a substructured state, whereas martensite mainly accommodated additional strain through defect rearrangement within the existing lath substructure. Repeated LSP also redistributed texture components and slightly increased the fraction of hard-oriented regions. Consequently, surface nanohardness increased from 8.62&#xa0;GPa (untreated) to 11.62&#xa0;GPa (LSP once) and 12.20&#xa0;GPa (LSP twice), accompanied by a strong increase in compressive residual stress. The second pass provided only a reduced incremental hardening effect, indicating a partially saturated work-hardened state.</p>

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Near-Surface Microstructural Evolution and Hardening of Carburized M50NiL Steel under Repeated Laser Shock Peening

  • 期刊论文

  • 发表日期：

    2026年8月5日

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  • Yang Liu,
  • Xingfu Yu,
  • Gang Wang,
  • Ling Wang,
  • Zhongyuan Fu,
  • Yusheng Wu

摘要

Repeated confined laser shock peening (LSP) was applied to carburized M50NiL steel to clarify the near-surface microstructural evolution and hardening behavior under repeated LSP. AFM, XRD, EBSD, nanoindentation, and residual-stress measurements were employed for characterization. Within approximately 150 μm from the treated surface, repeated LSP produced a clear gradient-affected layer, in which the effective martensitic block/sub-block size decreased from 1.38 μm (untreated) to 1.19 μm (LSP once) and 1.14 μm (LSP twice), while the corresponding low-angle grain boundary fraction increased from 25.1% to 31.4% and 35.2%. Surface/subsurface XRD showed a progressive decrease in retained austenite and an increase in dislocation density in both phases, with a stronger response in austenite than in martensite. EBSD-based recrystallization-state indicated that austenite evolved from a relatively recrystallized state toward a substructured state, whereas martensite mainly accommodated additional strain through defect rearrangement within the existing lath substructure. Repeated LSP also redistributed texture components and slightly increased the fraction of hard-oriented regions. Consequently, surface nanohardness increased from 8.62 GPa (untreated) to 11.62 GPa (LSP once) and 12.20 GPa (LSP twice), accompanied by a strong increase in compressive residual stress. The second pass provided only a reduced incremental hardening effect, indicating a partially saturated work-hardened state.