论文部分内容阅读
利用化学分析、金相显微镜、SEM和TEM等手段,从化学成分、组织结构、显微硬度、裂纹形态和断口形貌等方面对失效钎尾进行了分析,对钎尾失效过程中裂纹的萌生与扩展机理以及疲劳失效行为进行了研究。结果表明,钎尾渗碳后外表面碳含量为0.65%,组织为高硬度的孪晶马氏体;心部碳含量为0.23%,组织为韧性较好的下贝氏体。钎尾内外表面均存在应力腐蚀裂纹,裂纹萌生于腐蚀坑底部,扩展方式为穿晶型,腐蚀介质的存在是裂纹萌生与扩展的主要原因,而应力状态、显微组织和夹杂物等对裂纹扩展的影响作用较小。裂纹扩展到一定长度后,在钎尾中心水孔处发生开裂,进而由内向外扩展,最终导致钎尾的断裂失效。
The chemical composition, microstructure, microhardness, crack morphology and fracture morphology were analyzed by means of chemical analysis, metallographic microscope, SEM and TEM. The effect of crack initiation on the failure of shank And expansion mechanism and fatigue failure behavior were studied. The results show that the carbon content of the outer surface of the brazing rod after carburizing is 0.65%, and the microstructure is twinned martensite with high hardness. The content of carbon in the heart is 0.23% and the structure is lower bainite with good toughness. Stress corrosion cracking exists on the inner and outer surfaces of the shank, and the crack initiation occurs at the bottom of the corrosion pits. The extension mode is transcrystallization. The existence of corrosive media is the main reason for crack initiation and propagation. The stress state, microstructure and inclusions, The impact of expansion is small. After the crack is extended to a certain length, cracking occurs in the water hole at the center of the shank, and then expands from the inside to the outside, eventually resulting in failure of the shank.