Grinding Balls for the First Stage of Iron Raw Grinding in Tumbling Mills

The study results of the effect exerted by steel grade and heat treatment of grinding balls with a diameter of 100 mm on the hardness, wear and impact resistance, as well as on the tendency to quenching crack embrittlement, are presented. The following effects have been studied: alloying carbon steel (0.6–1.5% of C) with 0.9–5.0% of Cr; 0.6–3.0% of Mn and 0.4–1.7% of Si, and for additional alloying (≤12.0% of Cr) exerted on the structure, surface and bulk hardness; as well as relative wear resistance on the impact resistance of balls in the initial and heat-strengthened condition. By dilatometry means, critical temperatures A_c1 and A_c3 of the onset and completion of the polymorphic transformation α → γ in the studied hypoeutectoid and hypereutectoid steels have been determined in the course of heating. It is recommended to perform the quenching of balls with a diameter ≥100 mm made of hypoeutectoid (0.6–0.75% of C) steels alloyed with 0.9–1.1% of Cr, 0.6–0.8% of Mn and 0.2–0.4% of Si in water or oil. In this case, the quenching temperature should amount to 830–850°C or 860–880°C, respectively, whereas the tempering after quenching should be performed at a temperature of 280–320°C.