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<p>The resistance spot welding (RSW) joint of an ultra-high-strength hot-stamped (HS) steel (1.8 GPa grade) was investigated, focusing on the relationship between elemental segregation within the halo ring and the resulting mechanical behavior. Nano-secondary ion mass spectrometry (Nano-SIMS) analysis revealed localized segregation of grain boundary embrittling elements (S, Mn, and P, with P exhibiting a significantly higher enrichment factor), as well as grain boundary cohesion-enhancing elements (C and B) along prior austenite grain boundaries (PAGBs) within the halo ring. The distribution of these segregants was non-uniform, with certain boundary segments exhibiting significantly elevated concentrations. Regions with local elemental segregation are believed to reduce grain boundary cohesion, promoting intergranular crack initiation and compromising fracture toughness. Under cross-tension loading, the welds exhibited brittle failure localized within the halo ring, resulting in low cross-tension strength. Electron backscatter diffraction (EBSD) and fractographic analyses revealed a mixed fracture mode consisting of intergranular fracture along PAGBs and transgranular fracture, accompanied by isolated intergranular secondary cracks. These observations suggest that the fracture mechanism within the halo ring is governed by a competition between segregation-induced grain boundary embrittlement and transgranular fracture, the latter driven by the brittleness of the martensitic microstructure in this region.</p>

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Role of Local Elemental Segregation in Brittle Fracture of the Halo Ring in Resistance Spot Welds of Ultra-High Strength Hot-Stamped Steel

  • 期刊论文

  • 发表日期：

    2025年8月21日

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  • Sunusi Marwana Manladan,
  • Yeojin Jang,
  • Savyasachi Nellikode,
  • Soomin Lee,
  • Yun-il Choi,
  • Dongok Kim,
  • Young-Kook Lee,
  • Yeong-Do Park

摘要

The resistance spot welding (RSW) joint of an ultra-high-strength hot-stamped (HS) steel (1.8 GPa grade) was investigated, focusing on the relationship between elemental segregation within the halo ring and the resulting mechanical behavior. Nano-secondary ion mass spectrometry (Nano-SIMS) analysis revealed localized segregation of grain boundary embrittling elements (S, Mn, and P, with P exhibiting a significantly higher enrichment factor), as well as grain boundary cohesion-enhancing elements (C and B) along prior austenite grain boundaries (PAGBs) within the halo ring. The distribution of these segregants was non-uniform, with certain boundary segments exhibiting significantly elevated concentrations. Regions with local elemental segregation are believed to reduce grain boundary cohesion, promoting intergranular crack initiation and compromising fracture toughness. Under cross-tension loading, the welds exhibited brittle failure localized within the halo ring, resulting in low cross-tension strength. Electron backscatter diffraction (EBSD) and fractographic analyses revealed a mixed fracture mode consisting of intergranular fracture along PAGBs and transgranular fracture, accompanied by isolated intergranular secondary cracks. These observations suggest that the fracture mechanism within the halo ring is governed by a competition between segregation-induced grain boundary embrittlement and transgranular fracture, the latter driven by the brittleness of the martensitic microstructure in this region.