Determination of the relationship between hardness and toughness for short heat treatment cycles

Short-cycle heat treatments are typical manufacturing conditions for surface hardening processes and welding. These conditions are characterized by rapid changes of the temperature over the time, and by significant local variations of the heat treatment cycles. To measure the relationship between hardness and toughness for such conditions, a new testing method, based on a quenching dilatometer and the use of micro impact samples has been developed. The samples not only provide an impact toughness value and related micro hardness results, but also possibilities for investigations of the microstructure and fracture surface. The relationship between hardness and toughness shows a similar trend, independent from the heat treatment cycles, except from secondary hardening effects which do not occur at very short tempering cycles. The method also provides the possibility to compare the behaviour of different steels or filler materials.