铁素体球墨铸铁低温冲击断裂行为的影响因素

Influence Factors of Ferrite Cast Iron of Low-temperature Impact Fracture Behavior

对QT400-18L牌号球墨铸铁件进行系列温度Charpy缺口冲击试验,采用扫描电镜对冲击断口形貌进行分析,基于X射线衍射方法测试在冲击过程中各个温度下冲击断口附近铁素体基体内位错密度的变化,分析表明QT400-18L铁素体球墨铸铁断口附近石墨球的损伤模式主要有以下几种:层状开裂或层状剥离、石墨核芯开裂以及石墨球基体界面解体;低温下位错在晶界处的塞积产生很高的内应力,微裂纹更容易在晶界处萌生,晶界处夹杂物的存在导致韧窝断口中往往存在一些细小的显微孔洞,这种由夹杂物引起的显微孔洞的连接导致了材料的最终断裂;随着温度的降低铁素体内位错密度有所下降,室温下QT400-18L铁素体内部位错密度约为1.32×10^(15)m^(-2),而-60℃下其位错密度约为0.39×10^(15)m^(-2)。

Impact toughness of QT400-18 L ductile iron is measured by V-notch Charpy impact test at room and low temperatures. scanning electron microscope（SEM） is used to analyze the impact fracture morphology. The dislocation density near impact fracture surfaces at different temperatures is calculated by X-ray diffraction（XRD） diffraction method. Experimental results show that the energy absorbed by impact test decreases significantly with the decrease of graphite grade. Three damage models of graphite nodules are found during impact fracture. Cracks mainly form at grain boundaries under low temperatures due to dislocation pile-up. Inclusions on grain boundaries lead to the formation of microcavities on dimple fracture. As the temperature decreases, both the density of dislocation and the number of mobile dislocation are decreased. The density of dislocation is about 1.32×10^15m^-2 at room temperature, and the density of dislocation is about 0.39×10^15m^-2at-60 ℃.