发动机排气歧管用高硅钼球墨铸铁抗热疲劳性研究

Study on Thermal Fatigue Resistance of High Si-Mo Nodular Cast Iron for Engine Exhaust Manifold

参照德国标准GGG-Si Mo51,制备了汽车发动机排气歧管用高硅钼球墨铸铁,利用砂型铸造制备Y形试样。通过不同上限温度的热疲劳测试以及显微组织观察,研究了高硅钼球墨铸铁的抗热疲劳性能。结果表明：高硅钼球墨铸铁在热循环过程中会产生变形,积累到一定程度,将在表面形成疲劳裂纹。热循环上限温度越高,形成裂纹的倾向就越大。热疲劳裂纹主要在晶界处产生,在热裂纹扩展过程中,球状石墨能改变裂纹的扩展方向。高硅钼球墨铸铁合理的工作温度为840℃以下。

With reference to the German standard GGG-SiMo51, high silicon molybdenum nodular cast iron used for car engine exhaust manifold was prepared, and Y type samples were prepared by using sand mold casting. By thermal fatigue test at different upper temperature and microstructure observation, the thermal fatigue resistance of high silicon molybdenum nodular cast iron was studied. The results show that the high silicon molybdenum nodular cast iron produces deformation in the process of thermal cycle. When the deformation accumulates to a certain degree, the surface can form thermal fatigue cracks. The higher the temperature of heat cycle limit, the greater the tendency to form crack. The thermal fatigue crack s produce mainly in the grain boundary. In the hot crack propagation process, the spherical graphite can change the direction of crack extension. The reasonable working temperature for high silicon molybdenum nodular cast iron is below 840 ℃.