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将Mn-B系高强度贝氏体钢板轧成25 mm规格采用超快冷系统进行加速冷却。冷却后钢板可以获得710~850 MPa的高抗拉强度,但断后伸长率仅12.0%~13.0%。通过光学显微镜、扫描电镜、透射电镜等对钢板及单向拉伸断口的显微组织、析出物等进行分析。结果表明,在超快冷条件下钢板表层可以获得广泛的板条贝氏体组织,板条贝氏体中的渗碳体分布于板条及板条束间的界面上,形成类似珠光体的片层结构,明显提高钢板强度。在变形过程中,渗碳体内易生成微裂纹,降低基体组织的加工硬化能力,导致断后伸长率偏低、钢板塑性下降。
The Mn-B series of high-strength bainitic steel rolled into 25 mm specifications using ultra-fast cooling system for accelerated cooling. After cooling, the plate can obtain high tensile strength of 710 ~ 850 MPa, but the elongation after break is only 12.0% ~ 13.0%. The microstructure, precipitates and the like of the steel sheet and unidirectional tensile fracture were analyzed by optical microscope, scanning electron microscope and transmission electron microscope. The results show that extensive lath bainite can be obtained on the surface of the steel under ultra-fast cooling conditions. The cementite in the lath bainite distributes at the interface between the lath and the lath so as to form a pearlite-like Lamellar structure, significantly improve the strength of steel. In the deformation process, easy to generate micro-cracks in the cementite, reducing the work hardening ability of the matrix, resulting in low elongation after fracture, steel plasticity decreased.