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In order to improve the rolling contact fatigue (RCF) behavior of gear steels, a concept to increase their damage tolerance is developed alternatively to the conventional approach of improving the degree of steel cleanliness. For that purpose, Cu is used as a main alloying element in order to trigger the precipitation of nano-sized Cu precipitates which shall improve the strain-hardening rate of the martensitic matrix of Cu-alloyed 18CrNiMo7-6 steel surrounding a non-metallic inclusion during plastic deformation. In this way, early component failure may be avoided and the maintenance costs of, e.g., wind energy converters may be kept low. The experimental analysis shows that nano-sized Cu precipitates influence the material's strength, ductility, and strain-hardening behavior under tension, depending on their coherence. Among others, the latter is related to strain-induced martensitic transformation of coherent Cu. The structure of the Cu precipitates is studied by TEM and SANS analysis. The Cu-alloyed steel also shows an increased hardening-exponentCHT studied by cyclic hardness test (CHT) PHYBALCHT. Fatigue tests of specimens with coherent precipitates show cyclic hardening until a critical stress amplitude. Above that, stress amplitude cyclic softening is detected. An increased damage tolerance could be obtained for a 1 mass-% Cu-alloyed 18CrNiMo7-6 steel. [ABSTRACT FROM AUTHOR]

The article discusses a study which examined fatigue crack propagation in the friction stir welded Al-Mg-Si alloy, 6082, and the parent alloy AA6082. At low road and a low stress intensity, the propagation rate in the weld was higher than in the parent material, by a factor of 3 to 5. However, the propagation rates were approaching each other close to fracture.