| In recent years,large scale semiautogenous grinding process has been adopted in large mining enterprises,and the diameter of semi-autogenous mill has increased year by year,and the diameter of semi-autogenous mill has reached more than 10 m,and the size of forged steel grinding balls are more than 125 mm.More and more grinding balls of 140 mm and 150 mm in diameter are used by foreign countries,the domestic market space is huge.Firstly,the Φ150 mm grinding ball is manufactured based on the material GN-6A forging steel,the paper starts with two different quenching processes: afterheat quenching and secondary heating quenching,to explore the best process parameters and performance under different quenching methods.The new type of grinding ball steel was designed on the basis of GN-6A material.A new type of high carbon,low alloy steel for forging grinding balls with large size(Φ150 mm)(core hardness ≥ 58 HRC,surface hardness ≥ 60 HRC,original austenite grain size number ≥ 7)has been developed.Two kinds of quenching process of GN-6A Φ150 mm grinding ball were studied: Under the condition of afterheat quenching of GN-6A Φ150 mm forged ball,the hardness in the center of grinding ball was ≥ 58 HRC,and the surface hardness was ≥ 60 HRC.Due to the high temperature of forging heating,the grain size of the ball was coarse and the grain size number is 4 to 5 grade,the impact power of the grinding ball is 8~14 J,and the anti-crushing performance is poor.In order to ensure the hardenability of GN-6A Φ150 mm grinding ball,the secondary heating quenching temperature is still high.Under the condition of secondary heating,the center part is ≥58 HRC,the surface hardness is about 60 HRC or so,the impact power of the grinding ball is about 16 J,the grinding ball grain size number is 5.7 grade,and the test number of falling ball damage is about 3000 times.In view of the defects of GN-6A Φ150 mm grinding ball,two new types of steels D1 and D2 for grinding ball are proposed: D1 is put forward by adding to 0.03%-0.05% Nb on the basis of GN-6A material;D2 is put forward by mainly decreasing C,increasing Si,adding to Mo and Nb on the basis of GN-6A,D2 has higher surface hardness and higher property of impact toughness and resistance to surface decarbonization,especially the grain size number is over 8 grade.Finally it is determined that D2 is the ideal material for Φ150 mm forging grinding ball,and the optimum heat treatment technology is explored.The best performances of D2 grinding balls are as follows: core hardness ≥59 HRC,surface hardness ≥61 HRC,impact energy over 30 J,grain size number more than 8 grade,the surface decarbonization resistance is good,the number of single ball drops is more than 4000 times,and the crushing resistance is superior. |
