Investigation of Cooling Rate on Hardness and Microstructure in Casting Fittings Materials

During the set up of piping lines, nodular cast iron fittings which have high hardness values are fractured by the effect of external forces so problems might be occur such as floods. Hardness of the casted product is decreased by austempering heat treatment in order to resolve these problems thus threading operations can be operated easily. However, this treatment significantly increases the production costs.In this study, cooling rates, hardness values and change of microstructures of nodular cast iron fittings were investigated. It was decided to analyze various austempering temperatures and periods for diversified materials in order to reduce cost of production. Cooling rate of casting operation was determined with the help of an infrared heat meter. At the products which have 3-5 mm wall thickness values, 100% cementite formation was observed due to cooling rates. It was determined that the cementite structure of the microstructure has the hardness value of 340 HB. This hardness formation contributes to shorten the tool life of threading equipments.