Cyclic behaviour of carburized steel
Sammanfattning: The fatigue properties of carburized low alloyed steel have been investigated. The tests in axial fatigue showed that surface carbon below 0.8% and low amounts of retained austenite are advantageous. In bending fatigue the effects of tempering and of surface condition were studied. It was found that internal oxidation in the as-quenched surface deteriorates the fatigue properties considerably. Tempering has slightly adverse effect on the fatigue limit. Large grain size proved to have more serious consequences on the core properties than the presence offerrite. At surfaces, fatigue cracks initiate at stress concentrating defects or at grain boundaries of prior austenite. Sub-surface cracks initiate at slag inclusions or at concentrated slip in large grains. Low cycle fatigue properties of homogenous high carbon steel containing retained austenite showed a significant dependence on initial strain direction. The stress-strain properties found were used in computer calculations of the residual stress state in a carburized cylinder. The residual stresses, which are of great importance for the properties of case-hardened components, are redistributed due to plastic deformation. This was predicted by calculations and experimentally verified.
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