The relationship between the mechanical properties and microstructure of an extrafine high-speed steel wire has been studied. The microstructure of the extrafine wire mainly consists of a ferrite parent phase, MC and M6C carbides. From the results of tensile tests, some of the wires indicate a discontinuous yielding behavior. These wires with a discontinuous yielding behavior indicate superior elongation compared with typical yielding wires. The occurrence of discontinuous yielding is strongly affected by the volume fraction of the carbides as well as size distribution. The discontinuous yielding appears in the case of a small volume fraction (<30%) of the carbides, or a small volume fraction of the finer carbides (<2μm). This implies that the carbon content in the matrix phase is higher in the material that shows the discontinuous yielding behavior. That is, the dissolution of the carbides leads to a higher carbon content in the ferrite matrix; thus, carbon solute atoms pin the dislocations, which contribute to the typical yielding behavior. Therefore, the productivity and the drawing process of the extrafine high-speed steel wire can be expected to have an improvement by controlling carbide size as well as volume fraction.
