电脉冲对铸态高韧性球墨铸铁凝固组织及性能的影响

对铸态高韧性球墨铸铁QT400-18的凝固过程进行电脉冲处理,电脉冲参数为电压2 600 V,频率0.88 Hz,电容200μF,处理时间15min。通过对比试验可知:电脉冲处理可使铸铁的过冷度相比未处理的升高12K,改善了石墨形核和生长的动力学条件,从而使球状石墨的粒径减小,石墨球数量增加。铸铁经过电脉冲处理,球化率由未处理的平均80%提高到平均91%,石墨球数由平均172/mm~2提高到209/mm~2,石墨不易变态生长,圆整度得到改善。同时,球墨铸铁的凝固组织得到了改善,铁素体数量增加,达到83%,相比未电脉冲处理的试样提高了26.6%,铁素体晶粒小于未处理试样,基体中分布的珠光体数量和片层间距减少,在抗拉强度符合要求的条件下,伸长率提高了4.89%,-233K的冲击功Akv提高了3.56J。

Effects of Electric Pulse on the Solidification Structure and Properties of Cast High Toughness Ductile Iron

Cast high toughness ductile iron QT400-18 was treated by the electrical pulse.The electric pulse parameters were voltage 2 600 V,frequency 0.88 Hz,capacitance 200 μF and the processing time 15 min.The results showed that the undercooling degrees of cast iron specimen treated by the electrical pulse increased 12 K comparing with the untreated one,for improving the graphite nucleation and the dynamic conditions of growth.Then the size of spherical graphite decreased and the number of nodular graphite increased.After the electric pulse treatment,the nodularity was increased from an average of 80 ％ to 91 ％ and the spherical graphite number was increased from 172/mm2 to 209/mm2.The graphite was not easy to abnormal growth and the roundness was improved.At the same time,the solidification structure of nodular cast iron has been changed,with the ferrite number increased,83 ％,compared to untreated specimen increasing 26.6 ％.The grain size of ferrite was less than that of untreated and the number and interlayer spacing of pearlite in the matrix decreased.The tensile strain increased by 4.89％ and the impact work Akv at-233 K increased by 3.56 J.