Fatigue Life Improvement of Holed Plates Made of an Innovative Medium C Micro-Alloyed Steel by Local Plastic Deformation

This paper deals with the influence of local plastic deformation on the fatigue strength of holed plates manufactured with an innovative medium-carbon micro-alloyed steel with high silicon content (hi-Si MCM). Local deformation around the hole is achieved by means of an interference fitted pin. The effect was investigated both experimentally and numerically. Microstructural characterization, hardness, and tensile tests were carried out first. Tension–tension fatigue tests were performed under two different conditions: open-hole (OH) specimens and specimens with a press fitted pin with 0.6% nominal specific interference. A 2D elastic–plastic finite element analyses (FEAs) investigation was done as well, in order to analyze the stress field in the vicinity of the hole. The stress history and distribution in the neighborhood of the hole indicate a significant reduction of the stress amplitude produced by the external loading (remote stress) when a residual stress field is generated by the pin insertion. In fact, experimental stress-life (SN) curves pointed out increased fatigue strength of the interference fit specimens, compared with the OH ones. Finally, scanning electron microscope (SEM) analyses of the fractured fatigue specimens were carried out, in order to investigate the mechanisms of failure and to relate them to the peculiar microstructural features that characterize this innovative steel

The evolution and characterisation of the corrosion scales formed on 3Cr steel in CO2-containing conditions relevant to geothermal energy production

The corrosion behaviour of 3Cr steel at CO2 partial pressures (pCO2) of 2.7/28.5 bar and 200 °C was investigated. The evolution of double-layered corrosion scales was analysed by surface analysis to identify physical and chemical nature and results are combined with an analysis of thermodynamic calculations. Both experimental and thermodynamic results show that the corrosion scales comprise a crystalline FeCO3 outer layer and an inner Fe3O4, FeCr2O4, and Cr(OH)3 at 2.7 bar pCO2. At 28.5 bar pCO2, the inner layer evolves to be a mixture of FeCr2O4 and Cr(OH)3 containing concentrated Cl- ions, and this induces an enhancement of localised corrosion