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<p>Low heat input welding is widely used in the industry. The microstructure and toughness of the welded joints under low heat input conditions have received less attention than those under high heat input. The impact toughness, microstructure and failure mechanisms of the coarse-grain heat-affected zone (CGHAZ) in a micro-alloyed steel were investigated by welding thermal simulation with the heat input ranging from 15 to 65&#xa0;kJ/cm. The impact toughness of CGHAZ is highly sensitive to variations in low heat input. The failure mechanisms were discussed from the viewpoints of micro-voids formation and micro-cracks propagation. The micro-voids are preferred to be formed and grow at soft phase of grain boundary ferrite (GBF). At the heat inputs no more than 22&#xa0;kJ/cm, martensite was dominantly formed, and the micro-cracks initiated from the GBF were propagated into the grain interiors, leading to the brittle fracture and low toughness. When the heat input was increased to 31.2&#xa0;kJ/cm, granular bainite became the dominant constitute, causing cracks to deflect away from GBF and propagate into prior austenite grains. The high density high-angle and low-angle grain boundaries and the presence of retained austenite, effectively restricted the crack propagation, resulting in ductile fracture behavior and enhanced toughness. High heat input (62.3&#xa0;kJ/cm) promoted coarse GBF formation, providing continuous paths for microcrack propagation. This direct intergranular crack progression caused brittle fracture and low toughness. Industrial cold cracking in the CGHAZ can thus be controlled by heat input optimization to maximize toughness.</p>

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Toughening response of simulated CGHAZ under low welding heat input for a micro-alloyed steel and failure mechanisms

  • 期刊论文

  • 发表日期：

    2026年2月13日

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  • Xian-Guang Zhang,
  • Shou-Li Feng,
  • Jiang-Hua Qi,
  • Peng Shi,
  • Chun-Yang Shu,
  • Huang-Xun Guo

摘要

Low heat input welding is widely used in the industry. The microstructure and toughness of the welded joints under low heat input conditions have received less attention than those under high heat input. The impact toughness, microstructure and failure mechanisms of the coarse-grain heat-affected zone (CGHAZ) in a micro-alloyed steel were investigated by welding thermal simulation with the heat input ranging from 15 to 65 kJ/cm. The impact toughness of CGHAZ is highly sensitive to variations in low heat input. The failure mechanisms were discussed from the viewpoints of micro-voids formation and micro-cracks propagation. The micro-voids are preferred to be formed and grow at soft phase of grain boundary ferrite (GBF). At the heat inputs no more than 22 kJ/cm, martensite was dominantly formed, and the micro-cracks initiated from the GBF were propagated into the grain interiors, leading to the brittle fracture and low toughness. When the heat input was increased to 31.2 kJ/cm, granular bainite became the dominant constitute, causing cracks to deflect away from GBF and propagate into prior austenite grains. The high density high-angle and low-angle grain boundaries and the presence of retained austenite, effectively restricted the crack propagation, resulting in ductile fracture behavior and enhanced toughness. High heat input (62.3 kJ/cm) promoted coarse GBF formation, providing continuous paths for microcrack propagation. This direct intergranular crack progression caused brittle fracture and low toughness. Industrial cold cracking in the CGHAZ can thus be controlled by heat input optimization to maximize toughness.