Influence of nitriding on the fatigue behavior and fracture micromechanisms of nodular cast iron |
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Authors: | R Kone?ná G Nicoletto V Majerová P Baicchi |
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Affiliation: | (1) Department of Materials Engineering, University of Žilina, Žilina, Slovakia;(2) Department of Industrial Engineering, University of Parma, Parma, Italy |
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Abstract: | Surface modification processes are increasingly used to fully exploit material potential in fatigue critical applications
because fatigue strength is sensitive to surface conditions. Nitriding is extensively adopted with ferrous materials because
it forms a hard and strong surface layer and a system of superficial compressive residual stresses. Fatigue, however, is strongly
dependent also on defects and inhomogeneity. When nitriding is applied to nodular cast iron, the relatively thin hardened
layer (about 300 μm) contains graphite nodules (diameter of the order of 30 μm), casting defects and a heterogeneous matrix structure. The paper presents and discusses the influence of nitriding on the
fatigue response and fracture mechanisms of nodular cast iron. A ferritic nodular cast iron and a synthetic melt with different
content of effective ferrite were initially gas-nitrided. Then, (i) structural analysis of nitrided layers, (ii) fatigue testing
with rotating bending specimens, and (iii) fatigue fracture surface inspection were performed. Performance and scatter in
fatigue performance is discussed by selective inspection of fracture surfaces and identification fracture micromechanisms.
A semiempirical model explains observed trends in test results and is used for the process optimization.
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Translated from Problemy Prochnosti, No. 1, pp. 85–88, January–February, 2008. |
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Keywords: | nodular cast iron nitriding fatigue fracture mechanisms |
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