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

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.