Steel of highest fracture energy

The strength of common steels is considerably raised by thermomechanical treatment, heat treatment or cold working, however at the expense of toughness, which is usually defined as the work to fracture, i.e. the fracture energy. In part it depends on the loading conditions, e. g. the ratio of the hydrostatic stress and the equivalent shear stress as well as on the thermal activation contained in the temperature and velocity of loading. A drastic change of loading conditions (e.g. a sharp notch or a subzero temperature) may displace a ductile steel from the upper shelf of toughness to the brittle lower shelf. The present study is therefore based on uniaxial tensile tests to reveal the toughening of new steels at the upper shelf. In addition ISO-V notch impact tests are performed to indicate an embrittling transition range. It is the aim of this investigation to overcome the brittleness of some high-strength steels and develop a steel of high strength and high toughness.