The role of microstructure in fatigue crack initiation and propagation in 9-12Cr ferritic-martensitic steels

M.N. BATISTA; S. HEREÑÚ; I. ALVAREZ

Lago di Como

Simposio; XVII International Colloquium on Mechanical Fatigue of Metals (ICMFM17); 2014

Politecnico di Milano, Department of Mechanical Engineering

Previous low-cycle fatigue studies on 9-12Cr ferritic-martensitic steels showed that cyclic softening occurs due tomicrostructural instability over a wide range of temperatures [1-5]. This effect could become a serious engineering problem affecting creep, swelling and segregation phenomena during irradiation. Cyclic softening of 9-12Cr steels is associated with instability of the dislocation structure over the entire range of temperatures and, with the coarsening of carbides at high temperatures.Nowadays, the softening stage in 9-12Cr steels is clearly associated with the increase of the subgrain size regardless of the temperature. Moreover, the softening has been at least partially explained by lath and sub-grain boundary elimination [6].The aim of this paper is to correlate the microstructural evolution with microcracks nucleation and propagation