【摘要】 通过合理地控制孕育条件和冷却速度，获得了化学成分基本相同，而石墨大小、数量互异的铸态铁素体球铁试样，测定了它们的疲劳门槛值△Ｋ＿（ｔｈ）．结合裂纹附近的金相组织分析发现：在球化良好的情况下，△Ｋ＿（ｔｈ）值有随单位面积石墨球数量Ｎ的减少而增大，或随平均石墨间距和平均石墨球径的增加而增大的趋势，通过简化的力学模型对这种有悖于一般强度变化规律的反常特性进行了分析讨论，并作出了相应的解释。更多还原

【Abstract】 The As-cast ferrite ductile iron specimens with the same chemical composition but the differ-ent graphite nodule sizes and numbers are obtained,through controlling reasonably inoculation condi-tion and cooling rate,The fatigue threshold △K_th and the metallographic structure near the crack are de-tected.Under the better nudularization conditions,it is discovered that △K_th increases with the decreaseof graphite nodule numbers per unit area or with the increase of average interval and or with the in-crease of average intervdl and of average graphite nodule diameter.The abnormal characteristic whichis against the general principle of variatiin in strengh,is analysed accoding to the simplified mechanicalmodel,and the reasonable explanation is expressed.更多还原