Boroaustempering Treatment on Alloyed Ductile Cast Irons

Nodular cast iron can be heat-treated to a significant improvement of its properties by austempering, resulting in Austempered Ductile Iron (ADI). Their performance can be further improved using boronized surface layers, which is capable of reaching high level of hardness (2100 HV). In this work, samples of the nodular cast iron alloyed with copper, copper-nickel and copper-nickel-molybdenum were borided in a salt bath (borax + aluminum + alumina) at temperatures 850, 900 and 950 ° C during 2 and 4 hours. After these treatments, the samples were directly austempered from the boriding temperature in salt baths at temperatures of 240 ⁰C and 360 ⁰C 300 ⁰C (boroaustempering) which avoided the need of a subsequent reheating for such processing. The boronizing treatment produced uniform layers with thicknesses in the range 35-130 microns and hardness in the range from 1400 to 1670 HV.