Issue34

G. Lesiuk et alii, Frattura ed Integrità Strutturale, 34 (2015) 290-299; DOI: 10.3221/IGF-ESIS.34.31 291 for the modern technical objects. In case of objects erected at the turn of the 19th and 20th centuries, the diversification of operating conditions, as well as the peculiar characteristics of materials used for their building require individualized approach in the assessment of their condition. This fact is associated with insufficient knowledge of the material properties – the puddled and mild (rimmed) steel. Also, the presence of degradation processes makes impossible adaptation of material data from the literature. Typical macro- and microstructure vies have been shown in Fig. 1. Specimen after tension test (puddled iron produced in 1890). Sulphurous print (puddled iron produced in Germany in 1882) Microscan with large slags (some mm) in layered structure. Figure 1 : Characteristics of puddled iron [5]. Specimen after tension test (rimmed steel, produced in 1900). Sulphurous print (rimmed steel, produced in 1900). Micro-scan with large diameter of grain (  50  m). Figure 2 : Characteristics of early mild iron (rimmed steel), [5] The difference in the structure of these steels is significant. Their macroscopic structure and the manufacturing process are essential for the strength properties - what emphasizes the obtained results. From the historical point of view, it can be assumed that by the end of the 19th century the puddled steel was commonly operating. At the beginning of the 20th century it was completely displaced by the mild rimmed steel. These low-carbon steels (typically less than 0.1% C) tend to degradation processes and brittleness. From the application point of view, it is necessary to determine the safe life of the construction or the structural components from puddled/mild rimmed steel. In order to evaluate the sub-critical period of fatigue crack growth - it is necessary to know the material constants responsible for kinetic of fatigue crack growth rate (i.e. Paris law constants C and m). In this case, despite the similar chemical compositions, for such a type of steel – mainly puddled – the range and variability of mentioned constants is relatively large. The problem of cracks in the puddled steels is particularly important due to their common location in the joints - steel pieces were joined using riveting as a dominant technique. After 100-hundred operating time, the cracks caused by fatigue and corrosion existed. In conjunction with the microstructural degradation processes (precipitation of carbides and nitrides inside ferrite grains, precipitation of carbides at ferrite grain boundaries and degeneration of pearlite areas) such combination can be especially dangerous. M ATERIAL EXAMINATION or the material examination the structural components were gained from old historic building and viaducts. Three types of beams were examined; B (steel beam I220, 1855-1857) and S (steel beam, 1899-1904) – coming from the 19 th century Main Railway Station in Wrocław, and W – steel (flat bar from balustrade, 1885 year) – is gained from F