gold mill manufacturer ding steel balls2 inch Ball mill grinding media forged and rolling steel balls for gold mining TSF50 Taishan Products Made In China China Manufacturer 2 inch Ball mill grinding media forged and rolling steel balls for gold mining Description process forged or rolling 45# steel 60Mn steel 65Mn steel B2 steel B3 steel B6 steel hardness 5068HRC 50mm/ inch