355 MPa级转向架构架用钢连续冷却转变行为

高速动车组转向架构架对高速动车组的运行品质、行车安全起到至关重要的作用。为向355 MPa级转向架构架用钢的工业试制提供指导，在Gleeble-3800热模拟试验机上进行了热模拟试验，结合热膨胀法和金相-硬度法，绘制了355 MPa级转向架构架用钢动态连续冷却转变曲线，研究了试验钢在连续冷却条件下的显微组织演变规律。结果表明，冷速小于1 ℃/s时，其组织主要为多边形铁素体和珠光体；冷速大于5 ℃/s时，贝氏体类组织快速增加；冷速达到50 ℃/s时，为板条贝氏体组织。因此，对于355 MPa级转向架构架用钢，冷速控制在1~5 ℃/s较为适宜，其组织主要由比例适中软硬性相结合的铁素体、珠光体和贝氏体构成，可以获得优良的强韧性匹配。

Continuous cooling transformation behavior of 355 MPa grade steel for bogie frame

The bogie frame plays a vital role in running quality and driving safety of high-speed EMU train.To provide guidance for the industrial trial manufacture of 355 MPa grade bogie frame steel,the thermal simulation test was carried on Gleeble-3800 thermal simulator and the dynamic continuous cooling transformation curve was drew in combination with thermal expansion and metallographic hardness methods,and the microstructural evolution law of tested steel under continuous cooling condition was studied.The results show that polygonal ferrite and pearlite are the main microstructures when cooling rate is less than 1 ℃/s;the bainite type microstructres increases rapidly when cooling rate is more than 5 ℃/s；the microstructre is lath bainite when the cooling rate reaches 50 ℃/s.Therefore,the cooling rate of the 355 MPa grade bogie frame steel should be controlled at 1~5 ℃/s,and the microstructure is mainly composed of ferrite,pearlite and bainite,which are combined with soft and hard phase in a moderate proportion,and excellent strength and toughness matching can be obtained.