Evaluation of Notch Tensile Strength for High Strength Steel with Inclusions:(for Casting High Speed Steel)

In order to establish a strength evaluation method of a high strength material with a notch which has an inclusion, tensile tests of materials, which have various notch radii, and fracture toughness tests for casting high speed steel were performed. The validity of considering that an inclusion is equivalent to a crack and considering the influence of the interference between an inclusion and a notch on the tensile strength using the fracture mechanics was examined. The tensile fracture conditions were evaluated by defining one formula which calculates the stress intensity factor that used the √<I>area</I> parameter model as the tensile fracture conditions <I>K</I><SUB>IB</SUB> (ρ). As a result of the testing, as for the high strength notch material containing many inclusions, the notch root maximum elastic stress at the time of the fracture varied, and it was shown clearly that the cause was the size scatter of an inclusion. Moreover, a strength evaluation with little scatter was possible by factoring <I>K</I><SUB>IB</SUB> (ρ) into the fracture conditions. That is, it was clearly shown by considering that an inclusion is equivalent to a crack which is effective when considering the influence that the interference between an inclusion and a notch has on the tensile strength using a stress intensity factor.