Abstract An EA4T steel billet was forged at the different initial forging temperatures (1050, 1150, and 1250 °C). The microstructure and fatigue fracture of forged samples were observed by laser scanning confocal microscopy and scanning electron microscopy, respectively. The fatigue performance of samples forged at an initial forging temperature of 1250 °C was better owing to the presence of fine polygonal ferrite (PF). The difference in yield strength and ultimate tensile strength can be attributed to the average grain size of PF and acicular ferrite (AF) content, respectively. A relationship between the tensile strength and fatigue limit of EA4T steel is proposed. The mechanism of grain size and dislocation slip affecting the fatigue property was elucidated. Because the fine PF grains delayed the dislocations moving to the surface and inhibited the formation of intrusion and extrusion, premature cracks were not easily produced. This contributed to excellent fatigue behavior. Additionally, the pearlite colonies and fine PF delayed the crack growth rate and changed the crack propagation path. Studies on fatigue behavior provided a foundation for quality control and engineering application of EA4T steel.

中文翻译：

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初锻温度对EA4T钢力学性能和疲劳行为的影响

摘要 EA4T钢坯在不同的初始锻造温度（1050、1150和1250℃）下进行锻造。分别采用激光扫描共聚焦显微镜和扫描电子显微镜观察锻造试样的显微组织和疲劳断口。由于细小多边形铁素体 (PF) 的存在，在 1250 ℃ 初始锻造温度下锻造的样品的疲劳性能更好。屈服强度和极限抗拉强度的差异可分别归因于 PF 的平均晶粒尺寸和针状铁素体 (AF) 含量。提出了EA4T钢的抗拉强度和疲劳极限之间的关系。阐明了晶粒尺寸和位错滑移影响疲劳性能的机制。由于细小的PF晶粒延迟了位错移动到表面并抑制了侵入和挤压的形成，因此不易产生过早裂纹。这有助于产生出色的疲劳性能。此外，珠光体群和细小 PF 延迟了裂纹扩展速度并改变了裂纹扩展路径。疲劳行为的研究为EA4T钢的质量控制和工程应用提供了基础。