450℃～20℃循环温度幅下车轮铸钢热疲劳破坏行为探讨

Probe into Thermal Fatigue Damage Behavior of Wheel Cast Steel at 450 ℃～20 ℃

研究了一种铸钢车轮材料在450℃～20℃热循环下破坏行为．试样在经受热疲劳实验之后，利用光学显微镜和扫描电镜分别对试样表层、次表层和断口进行观察，综合得到试样的热疲劳破坏机理．研究发现，试样表面未出现明显的破坏，仅有一些腐蚀坑和微裂纹；次表层上主要分布着少量细小的氧化腐蚀坑，次表层和表层的失效非常吻合．试样断口上发现了一些二次裂纹和典型的局部脆性断裂特征，这表明尽管试样表面破坏尚不明显，但试样内部已经出现了开裂现象．实验还发现试样内部的一些夹杂物成为一种重要的热疲劳裂纹源，断口二次裂纹优先沿着试样内部的一些缺陷扩展．

Damage behavior of wheel cast steel was analyzed under thermal fatigue test at 450 ℃ -20 ℃, The thermal fatigue damage mechanisms were obtained by observing the morphology of the surface, the sub-surface and the fracture of specimens with OM and SEM technique after the thermal fatigue tests, Results showed that except some oxidation eroding pits and microcracks, the surfaces of specimens haven＇ t undergone visible damage, The damage of sub-surface was very similar to the dam- age of the surface, mainly with a few oxidation eroding pits. Some secondary cracks and brittle fracture characteristics were found on the fracture section, which showed that although the damage of surface and sub-surface were not so serious, phenomena of cracking have taken place in the inner parts of the matrix. It was also found that some impurities inside the specimens became an important source of initial cracks during the thermal fatigue tests, and the secondary cracks on the fracture would propagate preferentially through some imperfect areas inside the matrix.