Experimental Method for Characterization of Fatigue Behaviour of Carburized Layers.

Experimental Method for Characterization of Fatigue Behaviour of Carburized Layers. Fatigue data of material states with different carbon contents are necessary for calculation of carburized parts. Experimental results on the correlation of local material structure and local endurance are not available. Up to now only carburized notched specimens and components have been investigated. In this investigation a new tube specimen with homogenous carbon content in the wall resulting from carburization process was developed. Carbon contents of 0.18 %, 0.40%, 0.55 % und 0.70% in the thin wall tube specimen have been tested. Specimens were loaded with cyclic internal and monotonic external pressures. Special test rig with two pressure intensifier is introduced. With the aid of the cyclic internal and constant external pressure the whole Haigh-diagram with ratios of pressure or stress of R = infinity until R = 0.5 could be covered. Main load direction in the tube specimen is perpendicular to the steel rods axis. Results obtained for the used 20MnCrB5 steel grade show the same endurance limit for different carbon contents or hardness, respectively, and are significantly affected by big non-metallic inclusions.