Characterization of Niobium Carbide Layers Produced in Ductile Cast Iron Using Thermo-Reactive Treatments

Abstract

Ductile cast irons are materials with good ductility and toughness, but they are susceptible to high wear rates since they have low hardness. One way to increase their wear resistance is through thermo-reactive diffusion treatments (TRD), in which carbide layers are produced on the surface of the material. In this study, two ductile cast irons (with and without the addition of copper) were treated in a salt bath composed of borax, ferroniobium (16 wt.%) and aluminum (3 wt.%) at 1000°C for 4 h. The XRD and micro-hardness analysis indicated that NbC layers were produced with hardness values higher than 2000 HV. Two methods were used to examine the adherence of the layer to the substrate. In the first method, indentations were performed using Rockwell C scale (VDI 3198). The second method used Vickers micro-hardness indentations (loads 100, 200, and 300 gf) at the interface layer/substrate. In both tests, the layers showed good adhesion to substrates. The 3198 VDI test also showed that the NbC layer produced good toughness. The results of micro-adhesive and micro-abrasive wear tests showed that the layer was very effective in increasing wear resistance.

Improvement of the Tribological Characteristics of AISI 8620, 8640 and 52100 Steels through Thermo-Reactive Treatments

“…In recent studies, researchers achieved promising results with this technique on different metallic substrates, increasing wear resistance comparing with corresponding substrate. Soares et al [15] studied the formation of niobium carbide layer on ductile cast iron with salt bath TRD technique. A regular coating with 31 µm thickness was obtained.…”