RuT400蠕墨铸铁热疲劳性能研究

Study on Thermal Fatigue Properties of RuT400 Vermicular Graphite Cast Iron

采用光学显微镜(OM)、扫描电镜(SEM)、能谱分析(EDS)及热疲劳试验等对比分析了RuT400蠕墨铸铁在不同循环温度区间的热疲劳性能,研究了裂纹萌生及扩展的规律,并分析了不同开裂现象的成因。结果表明:在450~25℃及650~25℃热疲劳循环温度下,疲劳裂纹长度随着循环周次的增加呈线性增长,且温度越高,增长越快。在420~25℃循环温度下,仅形成了表面裂纹,裂纹没有贯穿材料基体,其原因是该温度尚不足以引起晶界滑动。当循环上限温度超过450℃时,晶界滑动促进了裂纹的形成。热疲劳条件下石墨和铁素体相界首先开裂,随后向铁素体区扩展,多个脱粘微裂纹形成主裂纹。

Thermal fatigue properties of RuT400 vermicular graphite cast iron at different cycle temperatures were compared and analyzed by optical microscopy(OM),scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS)and thermal fatigue test.The law of initiation and propagation of crack was studied,and the causes of different cracking phenomena were analyzed.The results showed that fatigue crack length increased linearly with the increase of cycle number during the thermal fatigue test at 450℃to 25℃and 650℃to 25℃,and the higher the temperature,the faster the growth was.At the cycling temperature of 420℃to 25℃,surface cracks only were formed,and the cracks did not penetrate the material matrix,the reason was that the temperature was not high enough to cause grain boundary sliding;when the upper limit of the cycling temperature was above 450℃,the grain boundary sliding promoted the formation of cracks.Under the thermal fatigue conditions,the phase boundaries of graphite and ferrite first crack,then expand to ferrite region,and multiple debonding microcracks connect and grow to form main cracks.