Evaluation of Tool Steels by Standing Contact Fatigue Testing

Abstract: Tool steels are required to show high hardness and fracture toughness, as well as good wear resistance. Furthermore, other properties such as chipping and contact fatigue resistance are also essential in order to improve the life-time of the tool. The goal of this thesis is to analyze the chipping and contact fatigue resistance of several steels and try to evaluate the correlation between these two properties. On the one hand, the performance of different ausferritic or carbide-free bainitic steels as tool steels have been studied, by taking a high-silicon steel and subjecting it to two austempering treatments, to evaluate their properties next. On the other hand, several quenched & tempered commercial tool steel have been evaluated, produced either by conventional metallurgy, powder metallurgy or electro slag remelting. The microstructure and microhardness of all the steels have been studied first, and standing contact fatigue tests have been performed next. Finally, with the obtained results, the relation between the chipping resistance and contact fatigue resistance has been evaluated. Among the commercial tool steels Calmax, Vanadis 4 Extra and Caldie show much better standing contact fatigue resistance than AISI D2. Ausferritic steels have also shown good resistance, comparable to the Calmax or, in some cases, even better. Regarding the microhardness, ausferritc steels are not as hard as the commercial tool steels, but the values are not much lower than Calmax or AISI D2 for example. Finally, Caldie, the steel with the highest standing contact fatigue resistance shows, according to the provider, the best chipping resistance. The presented work has brought some insight to the evaluation of tool steels. Standing contact fatigue tests can be used to obtain useful information and the results indicate that there might be a relation between the SCF resistance and the chipping-resistance. Moreover, it has been determined that ausferritic steels show properties similar to some commercial tool steels, and therefore, it would be possible to use them in some tool applications in the near future.