The low temperature aluminising kinetics of hot-work tool steels

Abstract

Conventional aluminising procedures are mostly conducted at temperatures well above 900 °C, and can last for hours. When applied to hot-work tool steels, aluminising has to be done at notably lower temperatures in order to prevent grain growth and carbide formation, and to improve creep resistance.The kinetics of aluminium coating formation on hot-work tool steels was studied in the temperature range of 550–610 °C. The pack Al content was varied from 5–15 wt.-% and aluminising time from 1–9 hours. The halide activator AlCl3 was applied. A series of statistically designed experiments were conducted to determine how key process factors influence the aluminide coating formation. A Box-Behnken experimental design was used to evaluate three process factors at three levels. The microstructures of coated samples were analysed by a scanning electron microscope (SEM). Glow Discharge Optical Spectroscopy (GDOS) and energy-dispersive X-ray spectroscopy (EDX) were employed to investigate element distributions in the coating layer