The results of experimental research on forecasting post-fire resistance to brittle failure of selected steel grades used in construction are presented and discussed in this paper. The conclusions are based on detailed analysis of fracture surfaces obtained in instrumented Charpy tests. It has been shown that the relationships formulated based on these tests agree well with conclusions drawn based on precise analysis of appropriate F-s curves. Furthermore, other relationships between lateral expansion LE and energy Wt required to break the sample constitute an additional verification in both qualitative and quantitative terms. These relationships are accompanied here by values of the SFA(n) parameter, which are different, depending on the character of the fracture. Steel grades differing in microstructure have been selected for the detailed analysis, including: S355J2+N-representative for materials of ferritic-pearlitic structure, and also stainless steels such as X20Cr13-of martensitic structure, X6CrNiTi18-10-of austenitic structure and X2CrNiMoN22-5-3 duplex steel-of austenitic-ferritic structure.
Keywords: brittle cracking; fracture surface; impact test; post-fire properties; shear fracture appearance; steel microstructure; toughness.