Effect of Al Content on the Thermal Conductivity and Corrosion Resistance of Die Steel

Effect of Al content on the microstructure, hardness, corrosion resistance, and thermal conductivity of the die steel was examined. It was shown that after adding 0.37 wt.% Al, the microstructure is still composed of lath-shaped tempered martensite, and the hardness is increased slightly. However, when the Al content rises to 1.34 wt.%, ferrite occurs in the microstructure besides tempered martensite, and the hardness is decreased significantly. The thermal conductivity of the die steel is decreased gradually with increasing Al content from 0.37 to 1.34 wt.% at all the tested temperatures. Thermal conductivity is decreased with the increase of temperature without Al addition. However, the maximum thermal conductivity occurs at 450 °C whenever 0.37 or 1.34 wt.% Al is added. Potentiodynamic polarization tests indicate that the corrosion current density in 0.5 mol·L⁻¹ HCl solution is decreased from 3.08 to 2.62 mA·cm^-2 when 0.37 wt.% Al is added. However, the corrosion current density is slightly increased from 2.62 to 2.74 mA·cm⁻² when Al content is increased to 1.34 wt.%. The corrosion resistance of the die steels with Al addition by potentiodynamic polarization is in agreement with the electrochemical impedance spectroscopy (EIS) results.