High speed steel (HSS or HS) is a subset of tool steels, commonly used in tool bits and cutting tools. It can withstand higher temperatures without losing its temper (hardness). This property allows HSS to cut faster than high carbon steel. T-grade and M-grade tool steels are used for cutting tools where strength and hardness must be retained at temperatures up to or exceeding 760 °C. High speed steel (HSS or HS) is a subset of tool steels, commonly used in tool bits and cutting tools. It can withstand higher temperatures without losing its temper (hardness). This property allows HSS to cut faster than high carbon steel. T-grade and M-grade tool steels are used for cutting tools where strength and hardness must be retained at temperatures up to or exceeding 760 °C.