热疲劳上限温度对球墨铸铁抗热疲劳性能的影响

摘要

研究了热疲劳不同上限温度Tmax(600℃、700℃、800℃)对球墨铸铁的抗热疲劳性能以及组织的影响.随着上限温度升高,珠光体分解加快,石墨与基体剥离,且基体表面出现凹陷,球铁的抗热疲劳性能下降.上限温度增加对裂纹扩展方式影响不大,主裂纹的扩展总是从人工缺口出发,穿过低强度的铁素体基体,联接沿线石墨或凹陷基体,向试样的另一端扩展.随着热循环次数增加,球铁硬度呈现先上升后下降的趋势,Tmax为800℃时,硬度的上升和下降速率显著增大.%Influence of thermal fatigue maximum temperatureTmax(600 ℃, 700 ℃, 800 ℃)on thermal fatigue resistance and microstructure evolution of ductile iron was studied. Decomposition rate of pearlite was accelerated, graphite separated from matrix, and pits emerged in the matrix surface, and the thermal fatigue resistance declined with the maximum temperature increasing. The increasing ofTmax had a little effect on major crack propagating way, which tended to beginning from the artificial gap, passing low strength ferrite region, and attaching graphite or matrix pits along the line, to the other end of specimen. The hardness of the ductile iron increased at first and declined later with the increasing of thermal cycles,and the ascending and declining rate increased remarkably whenTmax was 800 ℃.