Crack resistance of tool steels corresponding with the chemical composition of their matrices

Purpose: of the presented investigations was showing that the crack resistance of tool steels depends on their hardenability and phase transformations occurring in the quenched matrix at tempering. The chemical composition of austenite decides on the steel hardenability while phase transformations after tempering can be influenced (apart from the chemical composition) by the heating method. Design/methodology/approach: of investigations was based on the analysis of dilatograms and the achieved aim was to obtain the hard tool steel (app. 500 HV30) for hot works. Samples of a diameter of 10 mm (without a notch) made of this steel were not broken by the Charpy impact test of energy of 30 kGm. Findings: of these investigations are practical. Grain boundaries of prior austenite should be protected against secondary precipitates, which constitute natural nuclei of diffusive structures. It is also possible to control phase transformations at tempering. Research limitations/implications: constitute the availability of the adequate equipment for investigating the kinetics of phase transformations of undercooled austenite and the kinetics of phase transformations after tempering. Practical implications: for the industry are such that the proposed tool steels of a high crack resistance contain molybdenum and nickel. Thus, these steels are very expensive. Originality/value: of these investigations was confirmed in the industrial practice.