Weathering steels have been used since a long time in bridges, large structural applications, transmission towers, containers and marine transportation. Such engineering structures have to often withstand cyclic loading for a long time and steadily fulfill safety standards. Weathering steels of the trademark COR-TEN® were established and patented in the thirties of the last century in the USA.
Similar steels marked Atmofix have been developed in former Czechoslovakia in the sixties of the last century and subsequently broadly applied to engineering constructions in traffic and power distribution network. They were developed to obviate the need for surface treatment like painting. A stable rust-like protecting layer develops and regenerates continuously on their surface when subjected to the influence of weather. Due to their chemical composition these steels exhibit good resistance to atmospheric corrosion when compared to unalloyed steels.
Formation, duration, cohesion and protective effect of the covering layer depends also upon the character of the atmosphere.
Though weathering steels exhibit good corrosion resistivity, the continuous regeneration of the protective
layer results in mass losses and reduction of component dimensions. Moreover, there is an effect of development of surface morphology and a danger of formation of corrosion cracks in the surface layer. All these effects are closely related to the fatigue performance of engineering structures. Long time application of weathering steels raises presently the questions of the safety factors, particularly concerning the remaining fatigue life. The safety of structures like bridges, which are operated since many years in atmospheric conditions and often also in salt solution during the winter months, is of increasing
significance . The chemical composition and kinetics of development of protective corrosion rust layer (often called patina) on Atmofix steels have been a matter of research in the past, however the fatigue damage mechanism was not studied in sufficient detail. The investigation of corrosion kinetics and development of a rust layer brought evidence of an increase of surface roughening, which can be related
with substantial decrease of fatigue strength. The fatigue strength decrease can be related to the surface
roughness expressed in terms of maximum height of the profile or arithmetic mean deviation Ra . On the other hand, in some papers, the influence of corrosion cracks, which can develop in exposed material, is being considered the most decisive factor deteriorating the fatigue performance.
The evaluation of the remaining lifetime of components fabricated from weathering steels and applied
for long time needs both the experimental determination of the drop of fatigue performance due to exposure and simultaneously to identify the damage mechanism in the particular case. There is a basic difference when the damage is caused by the development and growth of corrosion cracks in base material below the corroded layer and in the case of development of surface roughness due to
The aim of this study was to experimentally determine the reduction of fatigue strength of Atmofix 52A steel, which is in use for transmission towers in the rural atmosphere in Bohemia for more than 20 years and to investigate the mechanism of fatigue damage.