Abstract The effects of the cooling rate after hot deformation on phase transformation, the microstructure of the designed nonquenched and tempered medium-carbon carbide-free bainitic steel have been investigated during the dynamic continuous cooling process. The results show that with the increase of the cooling rate, the morphology of the carbide-free bainite of the experimental steel evolves from granular bainite to lath bainite. Meanwhile, the hardness increases, and the amount of the retained austenite decreases with the increase of the cooling rate. Besides, the morphology evolution of the retained austenite from block to film is revealed by EBSD. Moreover, 0.5°C/s is considered to be the favorable cooling rate to obtain the best strength–toughness matching. Furthermore, the semi-industrial experimental results proved that the tensile strength, yield strength and Charpy impact energy were 1,298 MPa, 847 MPa and 38 J, respectively.

中文翻译：

---

中碳无碳化物贝氏体钢的动态连续冷却转变、组织和力学性能

摘要 研究了热变形后冷却速度对相变的影响，在动态连续冷却过程中研究了所设计的非调质中碳无碳化物贝氏体钢的显微组织。结果表明，随着冷却速度的增加，试验钢的无碳化物贝氏体形貌由粒状贝氏体向板条贝氏体演变。同时，随着冷却速度的增加，硬度增加，残余奥氏体量减少。此外，EBSD 揭示了残余奥氏体从块状到薄膜的形态演变。此外，0.5°C/s 被认为是获得最佳强度-韧性匹配的有利冷却速度。此外，