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实验分析了灰口铸铁经周期性的高温氧化处理后,其抗拉强度、基体组织、断口形貌与化学成分的变化规律,并探讨了热疲劳载荷下灰口铸铁失效的微观-宏观机制。结果表明:灰口铸铁的抗拉强度和抗热疲劳性能在微观上与石墨形貌、基体组织和晶粒尺寸有关,宏观上受温度、氧化条件、载荷周期和化学成分的影响。随着高温氧化处理次数增加,试样脱碳越来越明显,珠光体逐步减少直至消失;同时,短小而零碎的新石墨不断形成,断口处石墨暴露率逐步增大,基体连续性显著恶化;此外,试样基体铁素体化后,尽管脱碳速率降低,但基体晶粒逐步粗化、二次渗碳体析出使晶界弱化,各温度下抗拉强度随碳含量减小而显著下降。
The changes of tensile strength, matrix structure, fracture morphology and chemical composition of gray cast iron after cyclic high temperature oxidation were analyzed experimentally. The microscopic-macroscopic mechanism of gray cast iron failure under thermal fatigue loading was also discussed. The results show that the tensile strength and thermal fatigue resistance of gray cast iron are microscopically related to graphite morphology, matrix structure and grain size, and macroscopically affected by temperature, oxidation conditions, loading cycle and chemical composition. With the increase of the number of high temperature oxidation treatment, the sample decarburization becomes more and more obvious, the pearlite gradually decreases until it disappears. At the same time, the short and fragmented new graphite continuously forms, the graphite exposure rate increases gradually and the matrix continuity deteriorates significantly. In addition, after the sample matrix ferrite, although the decarburization rate decreased, the matrix grains gradually roughened, secondary cementite precipitation grain boundary weakening, the tensile strength at each temperature decreased significantly with the decrease of carbon content .