Pack Siliconizing Optimization of AISI D2 Tool Steel

The paper describes the pack siliconizing optimization procedure for AISI D2 tool steel. Pack siliconizing was performed by employing diferent treating temperatures (falling in the range 650–950 °C) and times (falling in the range 2–4 h). The siliconizing atmosphere was obtained through silicon (at 12 wt.%) with the addition of diferent percentages of NH4Cl (falling in the range 0.5–1 wt.%), Al2O3 was used as halide activator. The coatings’ phases evolution was analyzed through X-ray difraction; the coatings’ thickness was measured through scanning electron microscopy observations of the cross section of the samples; the mechanical properties were evaluated through micro hardness measurements. The results showed that the coatings’ thickness and hardness increase as the treating time and temperature as well as the halide activator percentage increase. The coating procedure optimization was performed by employing the response surface methodology based on BoxBehnken method. The results of the optimization procedure led to the of the optimal combination of processing parameters: 1 wt.% of halide activator, 3.575 holding time, 950 °C in temperature.