Ti-Mg氧化物型热轧变厚度钢板的组织演变和力学性能研究

Study on microstructure evolution and mechanical properties of hot rolled longitudinal profiled plate containing Ti-Mg oxide

纵向变厚度钢板具有轻量化、节约、环保的优点,应用于船舶、桥梁等领域。由于不同厚度部位的变形和冷却参数不同,容易产生组织性能不均的问题,其生产难度明显大于等截面钢板。针对变厚度钢板的组织调控,提出氧化物析出控制与控轧控冷相结合的技术思路,开展了实验研究,探索了不同变形冷却条件下Ti-Mg氧化物型热轧变厚度钢板组织演变规律,考察了不同板厚热轧组织性能调控效果。结果表明:Ti-Mg实验钢中的典型夹杂物为MgO-TiO-MnS-TiN型复相析出物,可有效促进晶内针状铁素体形核。实验钢过冷奥氏体连续冷却转变过程中,随着冷速的增加,发生多边形铁素体、针状铁素体、粒状贝氏体和板条贝氏体的转变;随着变形量的增大,其CCT曲线中各相变区间向上方移动。实验钢在未变形条件下宏观维氏硬度高于变形条件下的硬度,并且各变形条件下的硬度基本一致。在高温轧制和控制冷却条件下,12、20 mm两种厚度实验钢板的组织均为针状铁素体;12 mm厚钢板的屈服强度为426 MPa,冲击功为186 J;20 mm厚钢板的屈服强度为407 MPa,冲击功为190 J。

Longitudinal profiled(LP) plate has the advantages of lightweight, resource-saving and environmental protection, which is used in ships, bridges and other fields. The deformation and cooling parameters of different thickness parts are different, which is easy to produce the problem of uneven microstructure and properties, and its production difficulty is significantly greater than that of equal section plate. Aiming at the microstructure control of LP plate, the technical idea of combining oxide precipitation with controlled rolling and controlled cooling was put forward, and the experimental research was carried out. The microstructure evolution law under different deformation and cooling conditions of LP plate containing Ti-Mg oxide was explored, and the control effect of microstructure and properties of hot rolled plates with different thickness was investigated. The results showed that the typical inclusion in Ti-Mg experimental steel was MgO-TiO-MnS-TiN multiphase precipitation, which could effectively promote the nucleation of intragranular acicular ferrite(AF). During the continuous cooling transformation of undercooled austenite in the experimental steel, the transformation of polygonal ferrite, acicular ferrite, granular bainite and lath bainite occurred with the increase of cooling rate. With the increase of deformation, each phase transition region in CCT curve moved upward. The macro Vickers hardness of the experimental steel under undeformed condition was higher than that under deformed condition, and the hardness under each deformed condition was basically the same. Under the conditions of high temperature rolling and controlled cooling, the microstructure of 12 mm and 20 mm thick experimental plates was acicular ferrite. The yield strength of 12 mm thick plate is 426 MPa and the impact energy is 186 J;the yield strength of 20 mm thick plate is 407 MPa and the impact energy is 190 J.