This paper presents a comprehensive study on the strain-induced martensitic transformation and reversion transformation of the strain-induced martensite in AISI 304 stainless steel using a number of complementary techniques such as dilatometry, calorimetry, magnetometry, and in-situ X-ray diffraction, coupled with high-resolution microstructural transmission Kikuchi diffraction analysis. Tensile deformation was applied at temperatures between room temperature and 213 K (−60 °C) in order to obtain a different volume fraction of strain-induced martensite (up to ~70 pct). The volume fraction of the strain-induced martensite, measured by the magnetometric method, was correlated with the total elongation, hardness, and linear thermal expansion coefficient. The thermal expansion coefficient, as well as the hardness of the strain-induced martensitic phase was evaluated. The in-situ thermal treatment experiments showed unusual changes in the kinetics of the reverse transformation (α′ → γ). The X-ray diffraction analysis revealed that the reverse transformation may be stress assisted—strains inherited from the martensitic transformation may increase its kinetics at the lower annealing temperature range. More importantly, the transmission Kikuchi diffraction measurements showed that the reverse transformation of the strain-induced martensite proceeds through a displacive, diffusionless mechanism, maintaining the Kurdjumov–Sachs crystallographic relationship between the martensite and the reverted austenite. This finding is in contradiction to the results reported by other researchers for a similar alloy composition.

This paper reports the successful synthesis of spinel‐type CuFe ₂ O ₄ ferrite nanoparticles with an average particle size of 24 nm, produced using the citrate sol–gel autocombustion method. The structure of the synthesized material was analyzed through x‐ray diffraction (XRD) and further supported by Raman and FT‐IR spectroscopy. The analysis confirmed that the material formed a spinel ferrite structure with the Fd3m space group. Valence states and energy levels of the elements were examined using x‐ray photoelectron spectroscopy (XPS). Surface morphology was studied using scanning electron microscopy (SEM), coupled with elemental analysis. The magnetic properties of the synthesized CuFe ₂ O ₄ ferrite nanoparticles were investigated using a vibrating sample magnetometer (VSM). Magnetization measurements revealed that the sample exhibited characteristic magnetic parameters of copper ferrite, with a saturation magnetization (Ms) of 23.10 emu/g, a coercivity Hc of 415 Oe, and a remnant magnetization (Mr) of 12.80 emu/g. These magnetic properties enable efficient magnetic separation of the nanoparticles from aqueous solutions, thereby enhancing process efficiency and minimizing catalyst loss during photocatalytic applications. Optical and photocatalytic properties were investigated using spectrophotometry, revealing an optical band gap of 1.85 eV, which demonstrates potential for photocatalytic activity under visible light. The CuFe ₂ O ₄ ferrite effectively degraded dyes such as methylene blue (MB), malachite green (MG), Safranine (S), Congo Red (CR), and Rhodamine B (RhB) within 180 min, highlighting its practical application potential. The study identified that hydroxyl radicals (·OH), generated from H ₂ O ₂ decomposition under visible light irradiation, played a critical role in enhancing the efficiency of the photo‐Fenton reaction. A proposed mechanism involves the excitation of CuFe ₂ O ₄ under visible light, facilitating electron transfer that leads to the generation of ·OH radicals, which degrade the dye molecules. Among the tested dyes, CR exhibited the highest degradation percentage with a rate constant of 0.033 min⁻ ¹ and followed a pseudo‐first‐order kinetic model. The effect of hydrogen peroxide concentration on dye degradation efficiency was also evaluated.