Mechanical and fractographic characterization of the low activation chrome-steel F82H-mod in the brittle-ductile transition region

The subject of this work is the examination of the basic applicability of the method of the Local Approach on low activation fusion reactor structural steels in the brittle-ductile transition region, by the example of the chrome-steel F82H-mod. Therefore series of differently notched and pre-cracked round specimen were destroyed at temperatures within the range -150 C to ambient temperature. The mechanical break parameters were determined, which are needed as input data for the parameter generation of the model. For the examination of the basic assumptions of the Local Approach, the fracture surfaces of the samples, as well as selected axial cross sections of broken specimens, were qualitatively and if possible also quantitatively evaluated by scanning electro microscopy (SEM). The numeric results show that the failure can be described by this method without problems only for samples with small notch radii (i.e. high stress-multi-axiality), at -150 C. On the basis of the mechanical and fractographic investigations is explainable, that only these samples fulfill all basic assumptions of the model and fail by pure cleavage fracture. For this effect a critical local stress at a characteristic weak point must be exceeded. On all other samples several different critical events leading to failure and accordingly to incompatible numeric results. For the same reason a transferability of the results of non-damaged structures to pre-cracked structures is likewise not possible. In order to apply the model to the examined steel even in the transition region, a modification is inevitable. (orig.)