Wear and corrosion resistance of Nb-V carbide layers produced in vermicular cast iron using TRD treatments

Nb, V and Nb-V carbide layers were produced by means of the diffusion thermo-reactive treatment (TRD) in a vermicular cast iron, in baths composed of sodium borate, aluminum, ferro-niobium and/or ferro-vanadium, at 1000 degrees C with 2 h treatment time. Austempering was carried out after the TRD treatment in a molten salt bath at 300 degrees C. The samples were characterized by optical microscopy, XRD, Vickers microhardness, Daimler-Benz Rockwell-C, microadhesive wear tests and corrosion tests using potentiodynamic polarization tests. The TRD treatments were highly efficient in the production of uniform carbide layers, with thicknesses above 25 mu m and with good adhesions to the substrates. The layers showed hardness above 2300, 2500 and 3050 HV for the cases of Nb, V and Nb-V carbides, respectively. The wear resistance of the samples was increased from 10 to 30x in relation to the austempered substrate. The layers also showed corrosion resistance much higher than that of the substrate. The results obtained indicated the great effectiveness of the TRD treatment for the production of high performance carbide layers in vermicular cast iron.