Ductile cast iron can be heat-treated to obtain a significant property improvement austempering, resulting in Austempered Ductile Iron (ADI). Performance can be further improved by using boronized surface layers which are capable of reaching high hardnesses (2100 HV). In this work, samples of nodular cast iron alloyed with copper, copper-nickel and copper-nickel molybdenum were borided in a salt bath (borax + aluminum) at temperatures 850, 900 and 950 °C for 2 and 4 hours. After these treatments, the samples were directly austempered from the boriding temperature in salt baths at temperatures of 240, 300 and 360°C (boroaustempering) which avoided the need for a subsequent reheating for such processing. The boriding treatment produced uniform layers with thicknesses in the range 35-130 micrometers and hardness in the range from 1300 to 1700 HV.

Boriding thermochemical treatment produces layers with high hardness which improves the tribological performance of ductile cast iron while the austempering treatment improves the mechanical performance of the substrate. In this work, samples of the ductile cast iron alloyed with copper, copper-nickel and copper-nickel-molybdenum were borided in a salt bath (borax + aluminum) at temperatures of 850, 900 and 950°C during 2 and 4 hours. The data for the layers obtained were used to determine the diffusion coefficients and activation energies of this process. The results of the calculated diffusion coefficients were similar to those obtained by the direct measurements of the layer thicknesses. For the sample alloyed with Cu or Cu-Ni the activation energy obtained was 141.27 kJ/mol, and for the sample alloyed with Cu-Ni-Mo the value was 212.98 kJ/mol. The statistical parameters and the correlation coefficients (R) showed satisfactory agreement.

AHTF (Aerodynamic Heat Treating Furnaces) furnaces, in which air or gas is heated to 600-700°C without electrical or other special heaters, have been developed and placed in operation in a number of plants for heat treating aluminum, magnesium, and titanium alloys, and also steels. The AHTF chamber furnace is thermally insulated without the use of firebricks. It has a centrifugal fan with vanes having a special contour. The fan, operating in a closed system, converts, into heat, almost all the energy used to turn it; the heat is transferred to the parts by convection. In most machine-building plants aluminum alloys are heat treated in ERF furnaces (electric resistance furnaces with forced air circulation) or in salt baths. This research deals with an investigation of the heating conditions for various semi-finished products of aluminum alloys in the AHTF-3 in comparison with the ERF-2 (Electrical Recirculation Furnace) furnace and a potassium nitrate bath of approximately the same working volume.