Mechanical Properties of Urea Nitrocarburised Nodular Graphite Cast Iron with Hard Eye Structure

The mechanical properties of urea nitrocarburised nodular cast iron with a hard eye structure have been studied and compared with the same urea nitrocarburised cast iron with a bull eye structure. If the hard eye structure was introduced before urea nitrocarburising, the impact strength and the elongation were higher while its wear resistance, fatigue strength, and tensile strength were lower than for material with the bull eye structure. In the case where the cast iron was heat treated to produce a hard eye structure after it had been urea nitrocarburised in the ferritic state, its impact strength was only slightly increased; but its toughness was improved significantly if it was subsequently subjected to this hard eye heat treatment. A hf hardened urea nitrocarburised nodular cast iron with a bull eye structure exhibited the best fatigue strength and wear resistance. It is then concluded that the toughness and elongation of the investigated cast iron could be improved by introducing a hard eye structure of tempered martensite, while the fatigue strength, tensile strength, and wear resistance were strongly dependent on the structures of the compound layer and of the matrix.