Microstructures and selected properties of cast irons used for bridge structures at late XVIII and in XIX century

During recent years, in the area of Germany and Poland numerous repair and renovating works are being carried out of old (of XVIII and XIX centuries) structures of bridges and overbridges. In Germany, such works are preceded by generous research programs resulting in well-grounded diagnoses on f their wear conditions and properties of that time used construction materials. In Poland, such research works result more from own interest of the individual authors of published papers and elaborations. In Wroclaw (Breslau), in use are In this paper, the research subject were cast iron fragments of structure of the Old Mieszczanski Bridge (Wilhelmsbrücke) of 1876 and pillars of the railway overbridge built in 1899. The research was aimed at determining chemical composition of the used materials, their structure properties, as well as selected mechanical properties and referring the results to structures and properties of modern cast irons. It was found using light microscopy and SEM methods that they are grey cast irons with flake graphite, with ferritic and pearlitic matrices. Moreover, they include significant areas of phosphide eutectics and precipitates of titanium-rich phases. These observations are confirmed by results of gravimetric and spectral chemical analyses which indicate maximum phosphorus content of 1.18 % and maximum titanium content of 0.1 % in the examined cast irons. Together with evaluated mechanical properties (based on hardness measurements and previous results), chemical compositions and structures permit classifying the examined materials as cast irons equivalent to grades EN-GJL-100 and EN-GJL-150 acc. to the today's standards.