Ball-mill grinding kinetics of master alloys for steel powder metallurgy applications

The grinding kinetics of three newly developed master alloys for steel powder metallurgy applications were investigated using a laboratory ball-mill. Non-first order grinding kinetic is observed for the three master alloys as the breakage rate increases with grinding time due to the work hardening of the ductile phase in the microstructure. Agglomeration of fine particles is observed after a critical time at which d90 reaches its lowest value (~ 30 μm). Critical times are related to the hardness and the microstructure of the different master alloys. Agglomeration of fine particles can be overcome with the use of a process control agent. In this study, the addition of stearic acid to master alloy powders prior to grinding successfully eliminates agglomeration for long grinding times (d90 ~ 16 μm after grinding for 270 min).