DEVELOPMENT OF HYPOEUTECTOID GRAPHITIC STEEL WITH ENHANCED DRAWABILITY FOR WIRES

摘要

Graphitic steels are mainly used for machine structural parts. However, in the present study, it has been shown that graphitic steels can be used for wire drawing application with extensive drawability. It is generally seen that the elongation in high carbon steels used for wire drawing applications is less than 10% and the YS is close to UTS. However, by transforming the ferrite- cementite structure to a ferrite, graphite and spheroidised cementite structure, drawability of the wires can be increased substantially and at the same time, after first softening by graphitization, the strength can be regained by dissolving graphite in austenite and quenching. The graphitization process during the annealing of carbon steel consists of two steps: 1) dissolution of cementite and 2) nucleation of graphite. The approaches adopted to accelerate graphitization are 1) by destabilization of the cementite phase by alloying with Si and reducing Mn and Cr and 2) by provision of heterogeneous nucleation sites, for example, non-metallic inclusions, such as