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<p>This research focused on the development of DP600 and DP800 steels with a high strength-elongation balance (product of ultimate tensile strength in uniform elongation). Initially, a dual-phase (DP) structure was produced through step-quenching heat treatment, resulting in coarse martensite islands embedded within a coarse-grained ferrite matrix. The steel was subsequently annealed at intercritical temperatures of 740&#xa0;°C and 770&#xa0;°C for 12&#xa0;min followed by water quenching to produce DP600 and DP800 grades. Microstructural studies using scanning electron microscopy revealed that martensite islands were notably refined after intercritical annealing, leading to two distinct morphologies in the final DP steels: equiaxed and fibrous martensite. Additionally, some martensite in the DP600 steel appeared as sub-micron particles. Both DP steels exhibited a bimodal distribution of ferrite grains, comprising both coarse and ultrafine sizes. This refined microstructure significantly enhanced the strength-elongation balance compared to the original coarse-grained DP steel. The resulting high strength-elongation balance exceeding 15000&#xa0;MPa% for these DP steels surpassed that of commercial counterparts and those documented in the literature with similar tensile strengths. The DP800 steel demonstrated a three-stage work hardening behavior according to the modified Crussard–Jaoul method, while the DP600 steel showed a two-stage work hardening response. The dominant fracture mode for the developed DP steels was ductile, with ferrite-martensite interface decohesion being the main mechanism for void nucleation in both DP600 and DP800 grades.</p>

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Development of DP600 and DP800 Steels with High Strength-Elongation Balance via a Simple Heat Treatment Schedule

  • 期刊论文

  • 发表日期：

    2025年3月25日

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  • H. Ashrafi,
  • M. Karimi,
  • Z. Soleimani Bistegani

摘要

This research focused on the development of DP600 and DP800 steels with a high strength-elongation balance (product of ultimate tensile strength in uniform elongation). Initially, a dual-phase (DP) structure was produced through step-quenching heat treatment, resulting in coarse martensite islands embedded within a coarse-grained ferrite matrix. The steel was subsequently annealed at intercritical temperatures of 740 °C and 770 °C for 12 min followed by water quenching to produce DP600 and DP800 grades. Microstructural studies using scanning electron microscopy revealed that martensite islands were notably refined after intercritical annealing, leading to two distinct morphologies in the final DP steels: equiaxed and fibrous martensite. Additionally, some martensite in the DP600 steel appeared as sub-micron particles. Both DP steels exhibited a bimodal distribution of ferrite grains, comprising both coarse and ultrafine sizes. This refined microstructure significantly enhanced the strength-elongation balance compared to the original coarse-grained DP steel. The resulting high strength-elongation balance exceeding 15000 MPa% for these DP steels surpassed that of commercial counterparts and those documented in the literature with similar tensile strengths. The DP800 steel demonstrated a three-stage work hardening behavior according to the modified Crussard–Jaoul method, while the DP600 steel showed a two-stage work hardening response. The dominant fracture mode for the developed DP steels was ductile, with ferrite-martensite interface decohesion being the main mechanism for void nucleation in both DP600 and DP800 grades.