CeramTec AG is a well-known manufacturer of cutting tool materials, especially for inserts based on silicon nitride. Some years ago it started the production of alpha/beta-SiAlONs because of their superior properties. Due to strong competition in the cutting tool business there is a constant need for further development of the cutting tool materials. One possibility to increase wear resistanceand life time of cutting tools is to increase the hardness and maintaining the good toughness at the same time. This can be done by adding hard particles like e.g. SiC to an alpha/beta- SiAlON. In 2003 an improved grade had been presented: a SiC-reinforced alpha/beta-SiAlON. This composite material shows a significantly reduced wear during machining of cast iron. The effect of SiC-addition on mechanical properties is discussed.