S390级转向架用耐候钢的高温塑性

利用Gleeble 3500热模拟试验机对S390转向架用耐候钢的高温塑性进行测定。通过金相显微镜、扫描电镜及能谱仪对断口组织、断口形貌和析出物进行观察和分析。利用热膨胀仪测定S390耐候钢的临界相变温度,通过Thermal-Calc软件计算微合金元素的热力学析出温度。结果表明,在1 250~650 ℃范围内,存在3个区间,第Ⅰ脆性区在1 220 ℃以上,断裂形式是由S、O等元素偏析引起的沿晶断裂;第Ⅲ脆性区为980~650 ℃,断裂形式是由析出物钉扎晶界及先共析铁素体析出引起的沿晶断裂;在1 220~980 ℃第Ⅱ脆性区内,由于动态再结晶的发生,不出现脆性区,断裂形式为穿晶塑性断裂。实际生产过程中可避开脆性区间,以减轻S390耐候钢的裂纹倾向。

High temperature plasticity of S390 weathering steel for bogie

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.