The high-speed steel (shorten as HSS) consist of Fe and several kinds of transition metal carbides. The cutting tools or wear-resistant materials made from HSS experience relatively high thermal shock brcause a coolant such as water or oil is flowed over the surface of heated HSS. The purpose of this research is to incorporate a hard ceramic material with high strength in HSS matrix. This paper describes the processing, microstructure and mechanical properties of the oriented unidirectional mullite fiber/HSS composite. The unidirectional mullire fibers of 10 um diameter were dispersed by the ultrasonic irradiation of 38 kHz in an ethylenglycol suspension containing HSS powder of 11 um median size. The dried green composites with 4~68 vol% fibers were hot-pressed for 2h at 1000℃ in Ar atmosphere under a pressure of 39 MPa. The higher density was achieved in the composite with a lower content of fibers. The oriented unidirestional fibers were well dispersed in the HSS matrix. The average sidtance between the center of fibers in the cross section was close to the calculated from the fiber fracrion. No reaction occurred at the unterfaces between HSS and mullite fibers in the composites. The composite with 13.6 vol% fibers showed 1000 MPa of four point flexural strength at room temperature. The thermal expansion of composite with heating was influenced by the orientation of mullite fibers.

Keywords: High speed steel, Mullite fiber, Composite, Hot-pressing, Microstructure, Strength, Thermal expansion