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<p>A central driving force for the development of advanced high-strength steels (AHSS) is the need to reduce vehicle emissions without sacrificing crashworthiness. Dual-phase (DP) steels offer an excellent combination of strength and energy absorption, making them ideal for lightweight automotive structural components. This study addresses the challenge of achieving superior crashworthiness in DP1190 steel resistance spot welds through an innovative in situ local post-weld heat treatment approach. The proposed method employs a secondary current pulse with gradual current ramp-down to control weld cooling rates and microstructural evolution. Finite element analysis demonstrated that this technique significantly reduces cooling rates within the fusion zone without remelting. Experimental results showed that the fusion zone hardness decreased from 484 HV to as low as 410 HV (comparable to base metal), accompanied by increased peak failure load (13.2 kN to 14.9 kN) and 35% higher energy absorption. Microstructural analysis revealed the transformation of fully brittle martensite to a favorable mixed martensite–bainite structure, which underpinned the enhanced mechanical performance.</p>

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A Novel in Situ Local Post-weld Heat Treatment of the DP1190 Steel Resistance Spot Welds

  • 期刊论文

  • 发表日期：

    2026年4月10日

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  • Vignesh Raja Sukumar,
  • Mahesh Kumar Talari,
  • Gopi Krishna C,
  • N. Kishore Babu,
  • G. V. Sarath Kumar,
  • Bharath Bandi

摘要

A central driving force for the development of advanced high-strength steels (AHSS) is the need to reduce vehicle emissions without sacrificing crashworthiness. Dual-phase (DP) steels offer an excellent combination of strength and energy absorption, making them ideal for lightweight automotive structural components. This study addresses the challenge of achieving superior crashworthiness in DP1190 steel resistance spot welds through an innovative in situ local post-weld heat treatment approach. The proposed method employs a secondary current pulse with gradual current ramp-down to control weld cooling rates and microstructural evolution. Finite element analysis demonstrated that this technique significantly reduces cooling rates within the fusion zone without remelting. Experimental results showed that the fusion zone hardness decreased from 484 HV to as low as 410 HV (comparable to base metal), accompanied by increased peak failure load (13.2 kN to 14.9 kN) and 35% higher energy absorption. Microstructural analysis revealed the transformation of fully brittle martensite to a favorable mixed martensite–bainite structure, which underpinned the enhanced mechanical performance.