An investigation on the fracture of 70Cr2 steel balls during a grinding process and water quenching

The balls of a mill have the highest application in different industries like cement, steel (as forged steel), and copper (as casting ductile iron), and their role is to grind and produce suitable grinded materials. These balls are required as a production agent of mineral substance in the processing industries of metallic and non-metallic minerals consisting of cement factories, iron ore mines, and copper mines. But then again, they are limitedly employed in some defense industries and heavy metal mines. In this research, the factors affecting the fracture of steel balls produced from a continuous-casted 70Cr2 ingot were investigated during a grinding process and water quenching. The studied samples consisted of two destructed balls and one sound ball. The destructed balls fractured during the production process and before locating in the exploitation state of affairs meaning after the quenching process and/or the tempering process. To investigate the reasons of destruction, eye inspection, emission spectroscopy tests (quantummetry), metallography, hardness test, and scanning electron microscopy (SEM) equipped with EDS analysis were conducted. By analyzing the results, the fracture reasons of balls were related to the presence of inappropriate structure at the center and on the surface of the ball, the high hardness of the sample initiated from unsuitable heat treatment, and the creation of a crack in the middle of the cooling process and at the moment of applying an impact to the balls from the location of forging defects, as well as underneath the surface in the location of grain boundaries, defects, and impurities.