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The Influence of Chemical Composition and Sulphide Morphology on Impact Toughness of Low-alloyed Cast Steel

The paper is based on the assumption that the dependent variable impact toughness is in a causal relationship with random (unintentional) changes in melting tevhnology parameters. The latter are manifestedas as variations of concentrations of individual chemical components and quantified as changes in impact toughness of the steel casting. Investigations were carried out under industrial conditions and the results obteined present a basis for controlling the melt and optimizing the melting technologyof stel castingin the electric arc furnace. The relationship between the chemical composition and the morphology of the precipitated sulphides was examined for low-alloyed steel casting grade LC2, specified in accordance with ASTM A 352/A in terms of impact toughness measurement in V-noch specimens at - 73 C. The results were statistically analysed and verified by metallographic and fractographic examinations. It was found that impact toughness of steel casting LC2, intended for low-temperature service, was strongly influenced by oxigen, sulphur and manganese contents. Low impact toughness values accompanied by the appearance of brittle fracture , as result of precipitation of type II manganese sulphides, were obtained with precisely defined proportions of the three variables mentioned.

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