Abstract
Martensitic steels used for ball mill liners were prepared. The effect of tempering on the microstructures, Rockwell hardness, and impact toughness of the tested steels was evaluated at room temperature. The fracture morphologies were observed by using metallurgical microscopy, scanning electron microscopy and energy-dispersive spectroscopy. The results showed that tempering decreased the Rockwell hardness and significantly improved the impact toughness of the tested steel. However, the impact toughness of the tempered steels was unstable. Fracture of the tested steel before tempering was quasi-cleavage fracture; however, it changed to ductile and quasi-cleavage fracture after tempering. Carbide segregations formed at the local grain boundaries became the crack source and were the preferred ways for crack propagation during the impact test. The existence of segregations was inferred to be the main reason for the fluctuation of impact toughness.

Key words
martensitic steel, tempering, mechanical properties, fracture

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