The incorporation of self-propagating,high-temperature synthesis-formed Fe-TiB2 into ferrous melts

Steel-matrix particulate composites were processed by direct addition of an Fe-TiB₂ master alloy powder to a BS970:080M30 medium-carbon steel. This powder was produced using a self-propagating, high-temperature synthesis (SHS) reaction and consisted of a dispersion of fine TiB₂ particles (2 to 5 μm), respectively, in an iron binder. The addition of the Fe-TiB₂ powder resulted in the formation a parasitic Fe₂B phase and TiC within the steel microstructure. In response to this, an SHS master alloy composed of Fe-(50 pct TiB₂+50 pct Ti) was manufactured, which, when added to the steel, prevented the formation of Fe₂B and resulted in a composite containing a mixture of TiB₂ and TiC particles. The effect of master alloy composition and addition level on the microstructural phases generated is discussed in detail. The response to heat treatment of composite materials manufactured in this way was also investigated. It was found that an isothermal hold at 840 °C leads to a substantial softening of the material processed using the Fe-TiB₂ additive, while at 1000 °C, a hardness level equivalent to that of the as-cast material was maintained. The same heat treatment of samples in which the formation of Fe₂B was suppressed resulted in no appreciable difference in hardness level or microstructure.