Large Diameter CADI Research Of Grinding Ball Organization Performance

In order to satify with the tendency of increasing with the market demand for the largediameter grinding ball, the CADI material alloying by Mn、Si and Cr for ф120mmgrinding ball was designed and prepared. The microstructure, mechanical properties,wear-resistance and hardening behaviour of CADI after austempering processed werecarried out. On this basis, the comparison was made with other two kinds of steel forgrinding ball.The test result of isothermal quenching show that the hardness of CADI descendedand the toughness enhanced when the temperature of isothermal transformation rised. TheMn content in CADI is a dominated influence factor of the transformation dynamics ofbainite. The CADI with Mn content below2.0%was austempered at290℃holding2.5h,led to form bainite largely. Si content in CADI affect obviously the morphology of bainite,and the typical lower bainite was changed to more finer pesudo-lower bainite morphologywhen Si contend increased.According to the end-quenching and surface temperature of the ball measureexperimental result, the heat-treatment process of ф120mm CADI grinding ball wasdetermined as:500℃holding1h, and840℃holding2.5h, then water-cooled57s, followedby290℃salt bath isothermal2.5h. After heat treatmented, the hardness distribution fromthe surface to the center of the ф120mm ball was uniform, and all above55HRC.Results of the abrasion resistance test show that, the abrasion wear resistancedecreased with the hardness decreased; When the hardness of material is not much different,the enhancement of toughness is helpful to improve the anti-wear grain abrasion resistance.In the process of wear and tear, CADI grinding ball appear the work hardeningphenomenon, because large amounts of residual austenite exits in the matrix of CADIgrinding ball, and the phenomenon improved the property of wear resistance.Work hardening experiments show that, the mechanism of work hardening of theCADI grinding balls is maily phase transformation strengthening. Under the action of stress,the residual austenite translated into martensite, which generated the phase transformationstrengthening. Isothermal time effect of work hardening phenomenon is not obvious.In included, After isothermal quenching heat treatment process:840℃isothermal 30min, then isothermal quenching for2.5h in the290℃salt bath, CADI grinding ballfinally can obtain high hardness (57HRC), and also has a higher impact toughness (13J),showing the best work hardening properties, wear resistant of the highest.