Failure analysis of 90mm low chromium cast grinding balls cracking (3)
2.4 Low-magnification analysis
In order to further analyze the material quality of the dia90 mm low chromium cast grinding ball, the sample was taken at the fracture position parallel to and close to fracturing by electric spark cutting method. The sample was polished by grinding wheel and heated to about 70 °C in 50% hydrochloric acid; 8 minutes later, remove, rinse, and blow-dry. After hot acid erosion, the polished surface has more serious shrinkage porosity. A strip-shaped extension is the final solidification zone where inclusions tend to gather (see figure 5).
3.Conclusions and Measures
According to the above inspection results, 90mm low-chromium cast grinding ball microstructure, unqualified, non-metallic inclusion content (ball-like oxide) exceed the normal, standard requirements, and there are serious casting defects inside the cast ball. All these factors make the toughness of the low-chromium cast grinding ball decrease, which causes the ball to crack early in the casting process. In order to further verify the rationality of the test results, the corresponding improvement measures were taken:
(1) strengthening the control of the raw materials fed into the furnace, paying attention to the purification treatment of hot metal in smelting, so as to ensure the purity of hot metal during pouring.
(2) strictly carry out the melting process and pouring process of low chromium cast ball, avoid the appearance of abnormal cast structure, strictly control pouring, temperature, and ensure adequate feeding.
The low chromium cast ball of 90mm with the improved measures was analyzed by low power analysis, metallographic examination, and ball drop test. The results are shown in figures 6 and 7. The number of ball drop times is 20722.