ESSC & DUPLEX 2019

Impact toughness is a key parameter for many applications of duplex stainless steels. Conventional parameters that are known to have a strong influance on macro properties include phase fraction and austenite spacing. In this paper, we illustrate how image analysis can be used to extract new parameters and demonstrate that these parameters have an even stronger correlation to macro properties such as the impact toughness. Two novel parameters with a particularly high correlation to impact toughness were: (1) a serrated boundary index, which measures the ruggedness of the phase boundary (2) an austenite distance algorithm, which measures directionally independent inter-austenite spacings. This is particularly useful for non-directional structures, as can be found in cast material or in transverse cross sections of rolled material. The relevance of these indices is proven in a correlation exercise where automated evaluation is used to extract features from more than 2000 light optical micrographs. These new indices, together with conventional entities such as austenite spacing, phase fractions, heat compositions etc., were matched with impact toughness data. The new indices came out with strong correlations.