The Development Of New Forging Steel Grinding Ball Based On Abnormal Failure Analysis Of Grinding Balls Inner Mill

The abnormal failure of grinding balls in mills results in the decrease of grinding efficiency and the increase of grinding cost.It is of great significance to solve the abnormal failure of grinding balls in engineering field.Aiming at the abnormal failure of 2B?110mm grinding ball during the pratical application,the analysis and discussion of abnormal failure was carried out.The results showed that the abnormal failure of 2B grinding ball was the results of the coarse austenite grains size of high carbon grinding ball steel before quenching,which was converted to coarse acicular martensite and small amounts of other microstructures,leading to the decrease of impact fatigue life of grinding ball.The higher content of retained austenite in 2B grinding ball was the indirect reason for the cracking of grinding ball.On this basis,the production process of grinding balls was improved and the performance of grinding ball was also enhanced.The overall hardness of grinding ball was gently decreased,the volume hardness was decreased to 56.3HRC,and the impact energy was higher than 12J.Moreover,the microstructure was refined,the length of martensite plate was about 30?m,pearlite was observed at 1/2R,and the non-martensite was increased at the core.After the practical application,the cracking of grinding balls was significantly reduced.However,there were many irregular shaped grinding balls and it still cannot meet the requirements.In order to improve the problem of abnormal failure grinding balls obviously,a new type of 3B forging grinding ball steel was developed.Its main chemical composition is(wt%):0.60?0.72%C,0.70?0.90%Si,0.80?1.0%Mn,and 0.60?0.80%Cr.The temperatures of Ac₁ and Ac₃ of 3B steel are 719?and 739?respectively,the starting temperature of martensite phase transformation is 254?,and the critical cooling rate is 4.5?/s.Residual heat quenching temperature field of 3B?110mm grinding ball was simulated and the experiments under different heat quenching processes was done,the optimum heat treatment process of 3B steel?110mm grinding ball is:pre-cooling to 790±10??water quenching(water temperature 34?36?,water cooling time 140?160s)?Outlet air cooling(maximum return temperature 130?150?)?tempering(280?×5h).It can be find that the microstructure of the prepared grinding balls were mainly tempered martensite with fine size and uniform distribution.The grain size number was above 7 grades.The content of retained austenite was less than 10%.The hardness of core and surface was greater than 55HRC and57HRC.The volume hardness was 57.1HRC.The impact energy was more than 28J.And there were no spalling and cracking after 6000 times of single ball spalling test.The effect of grinding process on grinding performance was investigated.The optimized grinding process was:steel balls were added in a certain proportion every day,the concentration of mineral was between 70%and 80%,filling rate of grinding balls was between 35%and 45%.After six months of mine grinding experiments,results showed that the overall performance of 3B?110mm grinding balls was excellent.The problem of abnormal failure grinding balls was solved.The wear rate was reduced from 1.5kg/t to 1.1kg/t,various indicators and the grinding effect were improved.Consequently,the grinding cost was also reduced.