灰口铸铁低频热疲劳载荷下的微观组织与拉伸性能

Microstructure and tensile properties of grey cast iron under low frequency thermal fatigue loads

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。

Tensile strength,microstructure,fracture morphology and chemical composition of grey cast iron after different cycles of high temperature oxidation pretreatment were experimentally analyzed.The results show that the tensile strength and thermal fatigue resistance of grey cast iron depend on graphite shape,matrix microstructure,grains size,which are affected by temperature,oxidation conditions and thermal loads periods.As the cycles of low frequency high temperature pretreatment increases,the carbon content becomes lower,resulting in less pearlite in the matrix.In the meantime,new graphite with short and small sizes appears,leading to larger exposure rate of graphite at the fracture.In addition,although the decarburization rate in the specimens with ferrite matrix is smaller than that with pearlite matrix obviously,the carbon content is of more influence on tensile strength,due to the grain coarsening of the ferrite matrix specimens.