Effects of structural inhomogeneities on the steel balls resistance to loading

When conducting impact tests of protective glasses, nonunique cases of destruction of balls made of bearing steel ShKh15 were recorded. The causes of their destruction were determined. The state of the material was studied by fractographic and metallographic analysis, hardness and microhardness measurement. In the structure of the metal of all the balls, no critical defects were found such as flockens, shells and microcracks, but adverse factors were detected in the microstructure of the material, namely, the presence of fineneedle martensite with excessive carbides. It is established that the detected structural factors lead to liability to brittle fracture, an increase in the hardness of the material, a decrease in plasticity. To prevent brittle fracture of the balls and provide a reserve of plasticity of steel ShKh15 at high shock loads assessment calculations of ductility coefficient were made; and it was recommended to limit the maximum hardness of the material critical value HV=5.70 HPa (54 HRC), with the corresponding plasticity coefficient equal to 0.8.

balls, impact tests, fracture, crack, microstructure, carbide inhomogeneity, hardness, microhardness, plasticity coefficient

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