Toughness and toughness behaviour of two high-speed steels

Abstract

The fracture toughness and fatigue crack growth characteristics of a conventionally produced M2 high-speed steel and of a hot isostatically pressed M2/3 high-speed steel have been measured as afunction of heat treatment. The behaviour of these materials in these heat-treated conditions during a fairly severe milling operation has also been analysed. The mode of tool tip fracture was found to depend on the hardness, and at levels greater than 820HV, failure occurred in both high-speed steels by cracking leading to catastrophic chipping of the cutting edge. The tool life up to this distinct point of failure was also estimated from a simple fracture mechanics approach based on the approximate tool tip stress and on microstructural characteristics. A limited degree of correlation was found between this estimate and the measured tool life.

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