Abstract:The high-temperature plasticity of S390 weathering steel for bogie was measured by Gleeble 3500 thermal simulation tester. The fracture tissue, fracture morphology and precipitates were observed and analyzed by optical microscope (OM), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The critical phase transition temperature of S390 weathering steel was measured with a thermal expansion meter. During the solidification process, the precipitation order and temperature of micro-alloy elements were caculated by Thermal-Calc software. The results showed that in the range of 1 250-650 ℃, there were three regions. The brittle zone I of S390 steel was above 1 220 ℃, the fracture mode was intergranular fracture caused by the segregation of S and O. The brittle zone III was 980-650 ℃, the fracture mode was intergranular fracture caused by the pinning effect of precipitates and the precipitation of pro-eutectoid ferrite along the austenite grain boundaries. In the range of 1 220-980 ℃(brittle zone Ⅱ), the occurrence of dynamic recrystallization leads to the intragranular fracture and no brittle zone. In the actual production process, the brittle interval can be avoided to reduce the crack tendency of S390 weathering steel.
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