Metallurgical Examination of Failed T-158 Cast Austempered Ductile Iron (CADI)Track Shoes

摘要

The U.S. Army Research Laboratory (ARL), Materials Directorate (MD) conducted ametallurgical examination of prototype cast austempered ductile iron (CADI) tank track shoe bodies at the request of the U.S. Army Tank-Automotive Command (TACOM). The T-158 track bodies had failed during field testing on an Ml/Al battle tank. Each of the failed parts had been previously fitted with an ice cleat in service which most likely caused an undue stress concentration. The test results indicated that the failure was the result of poor part design and process control. The CADI track shoes had been fabricated according to the dimensional requirements of a forged component, instead of a separate cast design. The CADI material exhibited a variation in mechanical properties. Retained austenite measurements by X-ray diffraction correlated with the differences observed in mechanical properties. Chemical analysis revealed a high level of silicon which adversely affected the fracture toughness of the material. The CADI contained a low (but acceptable) nodule count and some of the nodules were flaked which decreased fatigue and impact resistance. Recommendations were made by ARL to redesign the track shoe utilizing casting technology criteria and to control the chemistry and microstructure. Metallurgical examination, Cast austempered ductile iron, Retained austenite.