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<p>This study investigates the effect of 0.008 wt.% Zr addition on the impact toughness of Mg-treated shipbuilding steel plate at − 20℃ through welding thermal simulation. The microstructure of the Mg-treated steel is predominantly composed of intragranular acicular ferrite (IAF) and polygonal ferrite (PF). The fine ferrite laths and their internal dislocation pile-ups contribute to enhanced plastic deformation capacity. The fracture surface after impact shows a ductile–brittle mixed mode, with evident microstructural deformation and a tortuous propagation path of the main crack. The microstructure of the Mg-Zr complex-treated steel mainly consists of bainite ferrite (BF), ferrite side plate (FSP), and grain boundary ferrite (GBF). The fracture surface displays a cleavage mode characterized by a smooth crack propagation path and limited microvoid formation. The density of secondary cracks beneath the main crack is approximately 3.0 times higher than that in Mg-treated steel. Regularly-shaped (Ti, Zr)(C, N) inclusions measuring about 5&#xa0;<i>μ</i>m observed in the Mg-Zr complex-treated steel serve as effective initiation sites for cleavage fracture. Under a heat input of 400&#xa0;kJ/cm, the low-temperature impact energy values of Mg-treated steel and Mg-Zr complex-treated steel are measured to be 143&#xa0;J and 23&#xa0;J, respectively.</p>

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Effect of Zr Addition on Microstructure, Crack, and Toughness in the Coarse-Grained Heat-Affected Zone of Mg-Treated Steel After High-Heat Input Welding

  • 期刊论文

  • 发表日期：

    2026年5月28日

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  • Yu-qi Zhang,
  • Jian Yang,
  • Yin-hui Zhang,
  • Yan-li Chen,
  • Liang Wang,
  • Zhipeng Dai

摘要

This study investigates the effect of 0.008 wt.% Zr addition on the impact toughness of Mg-treated shipbuilding steel plate at − 20℃ through welding thermal simulation. The microstructure of the Mg-treated steel is predominantly composed of intragranular acicular ferrite (IAF) and polygonal ferrite (PF). The fine ferrite laths and their internal dislocation pile-ups contribute to enhanced plastic deformation capacity. The fracture surface after impact shows a ductile–brittle mixed mode, with evident microstructural deformation and a tortuous propagation path of the main crack. The microstructure of the Mg-Zr complex-treated steel mainly consists of bainite ferrite (BF), ferrite side plate (FSP), and grain boundary ferrite (GBF). The fracture surface displays a cleavage mode characterized by a smooth crack propagation path and limited microvoid formation. The density of secondary cracks beneath the main crack is approximately 3.0 times higher than that in Mg-treated steel. Regularly-shaped (Ti, Zr)(C, N) inclusions measuring about 5 μm observed in the Mg-Zr complex-treated steel serve as effective initiation sites for cleavage fracture. Under a heat input of 400 kJ/cm, the low-temperature impact energy values of Mg-treated steel and Mg-Zr complex-treated steel are measured to be 143 J and 23 J, respectively.