QT500-7球墨铸铁汽车制动钳与支架反白口产生原因

Causes of inverse chill of QT500-7 nodular cast-iron automobile brake caliper and bracket

某QT500-7球墨铸铁汽车制动钳与支架日常检验中出现两种不同特征的反白口缺陷,采用宏观观察、化学成分分析、金相检验、显微硬度测试、扫描电镜与能谱分析等方法对反白口缺陷的产生原因进行分析。结果表明:成分偏析是制动钳试样反白口缺陷形成的主要原因,而成分偏析和孕育衰退是支架试样反白口缺陷形成的主要原因;制动钳试样存在反石墨化元素的偏析,增大了铁水的过冷倾向,从而形成反白口缺陷;支架试样中心区域存在孕育衰退,加上反石墨化元素的偏析,使试样形成反白口缺陷。

Two kinds of inverse chill defects with different characteristics appeared in the daily inspection of a QT500-7 nodular cast-iron automobile brake caliper and bracket.The causes of inverse chill defects were analyzed by means of macroscopic observation,chemical composition analysis,metallographic examination,microhardness test,scanning electron microscopy and energy spectrum analysis.The results show that the composition segregation was the main reason for the formation of the inverse chill defect of the brake caliper sample,and the composition segregation and inoculation recession were the main reasons for the formation of the inverse chill defect of the bracket sample.There was segregation of anti-graphitization elements in the brake caliper sample,which increased the supercooling tendency of molten iron and formed the inverse chill defect.There was inoculation recession in the central area of the bracket sample,and the segregation of anti-graphitization elements made the sample form the inverse chill defect.