铁路货车用高强耐蚀钢的高温热塑性及断裂机理研究

Study on hot ductility and fracture mechanism of high strength corrosion-resistant steel for railway wagons

通过高温拉伸试验研究了拉应力条件下铁路货车用高强耐蚀钢在650~1200℃范围内的高温热塑性,使用扫描电子显微镜、金相显微镜和场发射电子探针观察其不同温度下的高温拉伸试样断口形貌和断口附近显微组织,并分析了其断裂机理及影响因素。结果表明:实验钢在650~1200℃的高温热塑性曲线呈“W”形,存在一个温度范围为735~955℃的塑性低谷区,其中在铁素体与奥氏体两相区内热塑性降低的主要原因是网状的先共析铁素体薄膜沿奥氏体晶界析出,产生了应力集中,导致沿晶脆性断裂;在奥氏体单相区内发生脆化主要是因为大尺寸的(Nb,Ti)(C,N)、Al_(2)O_(3)、MnS等第二相粒子在晶界析出,降低了实验钢的热塑性,为微裂纹的产生和扩展提供了条件。此外,钢中较高的Sb含量还易产生非平衡晶界偏聚,使晶界强度弱化,恶化了实验钢的高温热塑性。因此,为保证高强耐蚀钢的铸坯质量,在制定矫直温度区间时应避开此塑性低谷区温度范围。

The hot ductility of high strength corrosion-resistant steel for railway wagons under tensile stress was studied by high temperature tensile test in the temperature range of 650-1200℃.The fracture morphology and microstructure near the fracture surface of high temperature tensile specimens were observed by scanning electron microscope,optical microscopy and field emission electron probe micro-analyzer at different temperatures,and the fracture mechanism and influencing factors were analyzed.The results revealed that the hot ductility curve of the experimental steel within the range of 650-1200℃was W-shape,and there was a ductility trough zone in the temperature range of 735-955℃.In the ferrite and austenite two-phase region,the reduction of the hot ductility was mainly due to the precipitation of the net-like pre-eutectoid ferrite film along the austenite grain boundaries,resulting in stress concentration and leading to intergranular brittle fracture.The embrittlement in the austenite single-phase region was mainly due to the precipitation of large-sized second-phase particles such as(Nb,Ti)(C,N),Al_(2)O_(3),and MnS at the grain boundaries,which reduced the hot ductility of experimental steel and provided conditions for the generation and propagation of microcracks.In addition,the high content of Sb in steel tended to produce non-equilibrium grain boundary segregation,which weakened the strength of grain boundaries and deteriorated the hot ductility of experimental steel.Therefore,in order to ensure the quality of the high strength corrosion-resistant steel billet,the temperature range of the ductility trough zone should be avoided when setting the straightening temperature range.