Defects as a root cause of fatigue failure of metallic components. III: Cavities, dents, corrosion pits, scratches

Experimental analysis and constitutive modelling of cyclic behaviour of 316L steels including hardening/softening and strain range memory effect in LCF regime

Cyclic hardening/softening behavior of 316L stainless steel at elevated temperature including strain-rate and strain-range dependence: Experimental and damage-coupled constitutive modeling

Microstructure characterization and strengthening mechanisms of oxide dispersion strengthened (ODS) Fe-9%Cr and Fe-14%Cr extruded bars

The role of extrusions and intrusions in fatigue crack initiation

Heat resistant austenitic Sanicro 25 steel was subjected to in-phase and out-of-phase thermomechanical fatigue (TMF) loading conditions with different amplitudes of mechanical strain in a wide interval of temperatures (250–700 °C). Cyclic hardening/softening curves, cyclic stress-strain curves and fatigue life curves were evaluated for both type of loadings. Scanning electron microscopy combined with FIB cutting and EBSD imaging in longitudinal sections containing cracks revealed the mechanisms responsible for fatigue crack initiation and growth. Fatigue cracks developed rapidly in oxidized grain boundaries during in-phase loading and intergranular crack growth resulted in short fatigue life. Multiple cracks in out-of-phase loading perpendicular to the stress axis have arisen only afterwards oxide layer was formed. The delayed initiation and transgranular growth led to longer fatigue life. The effect of grain boundary oxidation and surface oxide cracking on fatigue life was discussed.

Thermomechanical fatigue and damage mechanisms in Sanicro 25 steel

Cyclic response and early damage evolution in multiaxial cyclic loading of 316L austenitic steel

Austenitic stainless 316L steel in cold worked condition was subjected to torsional cyclic loading with equivalent strain amplitudes of 0.3% and 0.4% and multiaxial (in-phase and out-of-phase) cyclic loading with equivalent strain amplitude of 0.35% at room temperature. Cyclic plastic response has been measured and analyzed. Internal structure in the as-received state was compared with the deformation microstructures that developed during cyclic straining with various strain histories. In all three investigated cases the volumes with dislocation structures corresponding to cyclic strain localization (persistent slip bands, irregular wall and channel structures) were found. In addition, also islands of deformation induced α′-martensite were observed. Transmission electron microscopy, selected area electron diffraction and ferritscope measurements allowed to estimate the fraction and distribution of α′-martensite islands. The shape of fatigue hardening/softening curves has been discussed in relation with the localization of cyclic plastic strain in the low energy dislocation structures and its blockade by the islands of α′-martensite.

Microstructure and martensitic transformation in 316L austenitic steel during multiaxial low cycle fatigue at room temperature

The remarkable microstructural stability of high chromium steels prepared by powder metallurgy and strengthened by dispersion of nanometric yttrium oxides in cyclic loading at high temperatures is reported. Contrary to the continuous cyclic softening and profound changes in the microstructure during fatigue of common high chromium steels, the addition of 0.3wt% Y2O3 stabilizes the microstructure and significantly reduces cyclic softening of investigated steels. The evolution of microstructure as a result of fatigue loading at room temperature, 650 and 750 degrees C, was examined by means of transmission electron microscopy. Only minor changes in the microstructure were detected. The stability of oxide particles after high-temperature exposure was confirmed by energy dispersion spectroscopy chemical analysis. The microstructural features are discussed in relation to the cyclic behaviour of the oxide dispersion strengthened steels. The analysis of the hysteresis loop indicates that oxide nanoclusters are intersected and dissolved in slip bands of ODS Eurofer steel. This process contributes to cyclic softening.

Viktor Škorík

Papers

Thermomechanical fatigue and damage mechanisms in Sanicro 25 steel

Cyclic response and early damage evolution in multiaxial cyclic loading of 316L austenitic steel

Microstructure and martensitic transformation in 316L austenitic steel during multiaxial low cycle fatigue at room temperature

Microstructural stability of ODS steels in cyclic loading

Influence of dwell times on the thermomechanical fatigue behavior of a directionally solidified Ni-base superalloy