Towards improved ODS steels: A comparative high‐temperature low‐cycle fatigue study

Abstract

Within the frame of this work, the mechanical behaviour of a bimodal ferritic 12Cr‐ODS steel as well as of a ferritic‐martensitic 9Cr‐ODS steel under alternating load conditions was investigated. In general, strain‐controlled low‐cycle fatigue tests at 550°C and 650°C revealed similar cyclic stress response. At elevated temperatures, the two steels manifest transitional stages, ie, cyclic softening and/or hardening corresponding to the small fraction of the cyclic life, which is followed by a linear cyclic softening stage that occupies the major fraction of the cyclic life until failure. However, it is clearly seen that the presence of the nano‐sized oxide particles is certainly beneficial, as the degree of cyclic softening is significantly reduced compared with non‐ODS steels. Besides, it is found that both applied strain amplitude and testing temperature show a strong influence on the cyclic stress response. It is observed that the degree of linear cyclic softening in both steels increases with increasing strain amplitude and decreasing test temperature. The effect of temperature on inelastic strain and hence lifetime becomes more pronounced with decreasing applied strain amplitude. When analysing the lifetime behaviour of both ODS steels in terms of inelastic strain energy calculations, it is found that comparable inelastic strain energies lead to similar lifetimes at 550°C. At 650°C, however, the higher inelastic strain energies of 12Cr‐ODS steel result in significant lower lifetimes compared with those of the 9Cr‐ODS steel. The strong degradation of the cyclic properties of the 12Cr‐ODS steel is obviously linked to the fact that the initial hardening response appears significantly more pronounced at 650°C than at 550°C. Finally, the obtained results depict that the 9Cr‐ODS steel offers higher number of cycles to failure at 650°C, compared with other novel ODS steels described in literature.

The Precipitated Particle Refinement in High-Cr ODS Steels by Microalloying Element Addition

“…The rapidly growing demand for energy has pressed scientists to develop new hightemperature, high-performance structural materials for nuclear fission and fusion reactors [1][2][3]. Advanced materials can enable an improved reactor performance with increased safety margins and higher design flexibility [4,5] by providing an increased fatigue resistance, an enhanced thermal creep resistance, a superior corrosion resistance and an excellent neutron radiation damage resistance [6][7][8][9][10]. In recent years, oxide-dispersion-strengthened (ODS) steels have been considered as a promising candidate for nuclear materials, owing to their special microstructures in which nano-sized and highly stable precipitated oxide particles disperse uniformly in the matrix [11].…”

Effect of Thermo-Mechanical Treatment on the Microstructure and Tensile Properties of the Fe-22Cr-5Al-0.1Y Alloy

“…The excellent abilities to withstand high temperatures and resistance to oxidation were obtained by the addition of rare earth elements and thermal stable oxides [5][6][7][8], such as Y 2 O 3 [9] and Al 2 O 3 [10]. The thermodynamically stable oxide particles dispersed in the matrix can improve the strength, creep, and fatigue resistance via hindering the movement of dislocations and grain boundaries [2,9,[11][12][13][14].…”