Optimization of heat treatment parameters of Mo-free high-Cr cast iron mill balls

A Mo-free high-Cr cast iron with superior impact-wear resistance was tried to develop for mill balls by alloy design and subsequent heat treatment. The Cr/C ratio was varied up to 7.7 in order to minimize and eventually eliminate Mo addition, still ensuring hardenability. For the proper balance between abrasion resistance and toughness, the combined effects of each heat treatment parameters on the mechanical properties were systematically investigated using Taguchi method and response surface method (RSM), well recognized as powerful tools of the designs of experiments (DOE). It was found that hardness and impact energy were mainly affected by tempering and destabilization conditions, respectively. It is noted that high impact energy of 5.2 J/cm(2) was obtained without deteriorating hardness (54 HRc) during the verification experiments under the heat treatment condition optimized by the DOE analyses.