Precipitation and evolution of nodular graphite during solidification process of ductile iron

The quantity and morphology of spheroidal graphite have an important effect on the properties of ductile iron, and the characteristics of spheroidal graphite are determined by the solidification process. The aim of this work is to explore the precipitation and evolution of graphite nodules in hypoeutectic, eutectic, and hypereutectic ductile irons by thermal analysis, liquid quenching and metallographic technique. Results show that hypoeutectic ductile iron has the longest solidification time and the lowest eutectic temperature;eutectic ductile iron has the shortest solidification time;hypereutectic ductile iron has the highest eutectic temperature. After solidification is completed, hypoeutectic ductile iron has the lowest nodule count, nodularity and graphite fraction;eutectic ductile iron has the highest nodule count, nodularity and the smallest nodule diameter;hypereutectic has the highest nodule diameter and graphite fraction. The nucleation and growth of graphite nodules in hypereutectic ductile iron starts before bulk eutectic crystallization stage, however, the precipitation and evolution of graphite nodules of hypoeutectic and eutectic ductile irons mainly occur in the eutectic crystallization stage. The graphite precipitated in eutectic crystallization of hypoeutectic, eutectic, and hypereutectic ductile irons, are 61%, 68% and 43% of total graphite volume fraction, respectively. Simultaneously, there are plenty of austenite dendrites in hypoeutectic and hypereutectic ductile irons, which are prone to shrinkage defects. Therefore, the eutectic ductile iron has the smallest shrinkage tendency.

Simulation on stress of large diameter CADI grinding ball based on ANSYS

The falling ball tests were carried out on theΦ125 mm diameter Carbidic Austempered Ductile Iron(CADI)grinding balls with Mn content of 2.0wt.%,2.3wt.%,2.6wt.%and 3.0wt.%,respectively,and the kind of grinding ball with the most serious spalling was selected for stress simulation.The stress distribution between four grinding balls in the elbow of the falling ball test device when they collided with each other was simulated based on ANSYS.Results of the falling ball tests show that the spalling and mass loss of a CADI grinding ball increases with the increase of Mn content,and the CADI grinding ball with 3.0wt.%Mn shows the most obvious spalling and mass loss.The simulation results of stress distribution of a CADI grinding ball show that the maximum impact stress does not appear in the center of the contact area,but in the annular area(inner diameter of^20 mm and outer diameter of^50 mm)in the section with a depth of 5-15 mm below the grinding ball surface.The actual spalling of the ball is consistent with the simulation results,and the oxide-based impurities in CADI grinding ball accelerate the spalling of the grinding ball in service.