Effects of Inclusions and Grain Size on Impact Toughness of a Cleaning Wheel Steel at Room Temperature

The cleaning wheel steel was heat-treated at different temperature to get microstructure with different grain size. Charpy V impact toughness of the wheel steel with different grain size was tested at room temperature. And the fracture surfaces were examined by scanning electron microscope with energy-dispersive X-ray spectroscopy. The results show that part of the impact specimens initiated from Ti(C, N) inclusions, and no inclusion was found on the other impact specimens’ fracture surfaces. Ti(C,N) inclusions with diameter less than 10 μm in the specimens didn’t decrease the impact toughness. The impact toughness of the wheel steel increased with the decreasing of grain size. The results relayed on the critical event of the impact cleavage fracture at room temperature was the micro-cracks propagating through grain boundaries.