Taking a grinding of coal ball mill (type: BTM 400/800) operating without rocks as an example it is shown that a bombardment of the armour by grinding bodies made of steel 110G13L directly is capable to raise its hardness from 200 to 320HB at the depth of the cold-hardened layer up to 6,7 mm that will approximately 2 times increase its firmness to an abrasion. The time needed for the realization of an effective bombardment is 11 minutes, the period between strengthening cold – work hardenings is 25 days.