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Grade 91 (9Cr-1Mo) steel was subjected to various heat treatments and then to high-pressure torsion (HPT) at different temperatures. Its microstructure was studied using transmission electron microscopy (TEM) and X-ray diffraction (XRD). Effects of the tempering temperature and the HPT temperature on the microstructural features and microhardness in the ultrafine-grained (UFG) Grade 91 steel were researched. The study of the UFG structure formation takes into account two different microstructures observed: before HPT in both samples containing martensite and in fully ferritic samples.

The impact of equal‐channel angular pressing in combination with additional heat treatment on microstructure and fatigue of ferritic/martensitic steel is investigated. It is shown that the formation of both the ultrafine‐grained (UFG) structure with an average grain size of about 0.8 μm and the enhanced share of boundaries with the coincidence site lattice (CSL) relationships (the CSL boundaries) leads to an increase in the fatigue endurance limit of more than 50% compared with samples after tempering. Dynamic strain aging is found in the fracture zone of the UFG of samples after fatigue tests. The influence of structural parameters on the fatigue endurance limit of the UFG samples is discussed.

The paper reports on microstructure, strength and fatigue of ultrafine-grained (UFG) samples of the Al-Cu-Mg-Si aluminum alloy processed by high pressure torsion (HPT) at various temperatures. Application of the HPT treatment led to strong grain refinement, as well as to a raise of the mean-root square strains and dynamic precipitation. In case of optimal HPT treatment the UFG samples have demonstrated the enhanced thermal stability, an increase in ultimate tensile strength in 2.5 times and enhancement in fatigue endurance limit by 20 % in comparison with coarse-grained alloy subjected to standard treatment. It is shown that the regime of the HPT treatment governs the volume fraction of precipitates and segregations, thereby affecting a grain size and thermal stability of ultrafine-grained structure.

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