Nowadays, pearlite ductile cast irons are widely used for producing shafts, wheels and gears due to its good mechanical properties and excellent castability. Compared with carbon steels, ductile irons have relatively low melting temperatures, good fluidity and castability, and moderate shrinkage during solidification and cooling.
There are several heat treatment methods to improve the mechanical properties of ductile cast iron such as annealing, normalizing, quenching and tempering. These heat treatments could be partially replaced by adequate balances of alloying elements. It is an easy and economical way of obtaining different microstructures and good mechanical properties in ductile cast irons.
As the demand for pearlite ductile irons increases day by day, nickel, copper, and molybdenum are common alloying elements in as-cast pearlite ductile irons. In view of the international trend in the rising cost of nickel and molybdenum, there is a renewed interest in exploiting the strengthening effect of manganese and copper in ductile irons. Both manganese and copper are FCC metals and they are highly soluble in austenite. The use of alloying elements stabilizing the pearlite such as Cu and Mn can be considered as the most appropriate method to control the amount of pearlite in the matrix and enhance the mechanical properties.
Kim Yu Chol, a researcher at the Faculty of Materials Science and Technology, studied the effect of cheaper alloying elements like copper and manganese on the mechanical properties and microstructure of ductile cast iron, thus obtaining as-cast pearlite ductile cast iron with high tensile strength, good elongation and high hardness.
There was, practically, no free ferrite in the ductile cast iron alloyed with Mn and Cu. When the content of Mn was 0.53% and the additive amount of Cu was 0.6%, the pearlite content was 86%. At that time, the as-cast pearlite ductile cast iron had tensile strength of 720 MPa, elongation of 4.6% and hardness of HB 268.
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