Comparison of fatigue behaviour of Co-Cr laser cladded steel plates for railway applications

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Comparison of fatigue behaviour of Co-Cr laser cladded steel plates for railway applications

Niederhauser, S. / Karlsson, B.

The fatigue behaviour of steel plates cladded with Co-Cr alloys is studied. The laser cladding in two successive layers with parallel runs to cover a whole plate results in a heat affected zone of tempered martensite below the clad. The mechanical behaviour of such cladded plates is investigated in two cases, as minor changes in the process parameters in depositing the Co-Cr powder materials result in difference hardness levels of the clad as well as its thickness. Following conclusions can be drawn: 1) Tempering of the primarily created martensite in the heat affected zone takes place in the following passes of the laser beam. The resulting hardness of this zone is fairly constant and seems independent of the process parameters used. 2) The two cases studied show fairly similar fatigue lifetimes as expressed in a Coffin-Manson diagram with plastic strain amplitudes. The higher clad hardness in one of the plates, though, results in larger fatigue lifetimes at predetermined stress amplitudes. 3. The residual stress fields set up during initial formation of martensite in the heat affected zones survives both tempering and cyclic loading during the fatigue test. It also leads to an asymmetry in the tensile and compressive peak stresses. This asymmetry ceases at higher imposed strain amplitudes during fatigue testing and is independent of the hardness of the clad. 4. Tempering of created martensite in the heat affected zone seems to be determining for the fatigue behaviour of the layered structure as seen by lifetimes and mean stresses for different imposed strain amplitudes.