The detail structure of heavy rust layers with large swelling and laminated layers formed on weathering steel bridges have been investigated by optical microscope and laboratory powder X Ray diffraction (XRD) and synchrotron XRD in SPring 8. Some large gaps (inter layer) and many linearly arrayed voids (LAV) were found along layers. The mass ratio of spinel type iron oxide [mainly Magnetite (Fe 3 O 4 )] in average composition of the whole layer was 30 40 mass. In contrast the mass ratio of spinel in its local parts, i.e. outer layer, inter layer and inner layer position was not higher in common but mass ratio of b FeOOH was higher. Thus we propose a multilayer model structure for these unique rust layers which are made of Spinel Poor, Rich and Poor unit cell structure (SPRaP cell) compartmentalized by LAV.

We have examined fatigue crack propagation behavior in the [ferrite/bainite] Hybrid materials with different hardness under a constant stress intensity factor range. It was found that crack propagation in the ferrite phase decelerated with reaching to the [ferrite/bainite] interface, probably due to supression of plastic deformation at the crack tip. This suppression tendency of the crack propagation became higher when hardness difference between ferrite and bainite was larger. In the case with the highest hardness difference, fatigue crack did not pass through the [ferrite/bainite] interface. Lower crack propagation rate was also found in the bainite which showed higher work softening due to crack propagation.

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Al bearing steels showed high corrosion resistance into coastal environments. The layer of the rusts containing Al was formed on the surface of those alloys after long periods of exposure to the coastal environments, and it was suggested that the Al plays an important role in the corrosion resistivity. In this work, we applied X ray diffraction, electron microscopy, Raman scattering and X ray absorption near edge structure measurements for investigating the state of Al in the rust layer. It was found that the increase in the Al content of those alloys increased amorphous and goethite type iron oxide in the rust. The Al K XANES spectra indicated that the Al substituted goethite, a Fe 1-x Al x OOH, formed on those alloys. This action of Al has an effect on the properties of rust and serves to increase the protective ability of rust layer.

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