Effect of ageing on the microstructural evolution in a new design of maraging steels with carbon

A new maraging steel, based on carbide precipitation, is described. Two alloys were designed namely Fe-10Mn-0.25C-2Cr-1Mo wt% (2CrMo) and Fe-10Mn-0.25C-1Cr-2Mo wt% (Cr2Mo). These compositions were chosen to achieve ultra-high strength and high tensile elongation; the former and latter are promoted through the simulatenous precipitation of Cr- and Mo-rich carbides and Mn-rich reverted austenite. The alloys were manufactured through the standard melting, casting and hot working route. Following a solution treatment at 870 °C and quench, which gave a fully martensitic structure, the alloys were aged for various times at 510 °C. The microstructure and tensile properties were investigated in detail as a function of ageing time. The microstructure observed was dominated by micron scale and nanometre scale Mn segregation which determined the local Ac3 temperature. Austenite reversion occurred in both alloys, peaking at 16 h in both cases. In the 2CrMo alloy, the reverted austenite was mainly globular in morphology due the Ac3 temperature being lower than the ageing temperature, but was acicular in the Cr2Mo with Ac3 similar to the ageing temperature of 510 °C. Moreover, acicular austenite was promoted by Mn segregation at martensite lath boundaries in Cr2Mo. In the 2CrMo steel, carbide precipitation (M3C and M7C3) occurred during heating to the ageing temperature, but the carbides gradually dissolved with further ageing. In contrast, in the Cr2Mo alloy, precipitation of carbides (M7C3 and M2C) occurred during ageing, the volume fraction of which increased with ageing time. In both alloys a TRIP effect was observed, but the extent of this was greater for the Cr2Mo alloy. The complex microstructure obtained after 16 h led to an excellent combination of strength of 1.3 GPa and elongation of 18%. Physics-based models for the microstructure in martensite, precipitation kinetics, as well as for TRIP in austenite were employed to explain and predict the individual strengthtening contributions of the microstructure to the total strength, confirming that the maximum strength-elongation relationship found after 16 h is due to an optimal combination of a slightly overaged - but still strong- martensite and 30% of reverted austenite, for increased work hardening and ductility

Mitochondrial physiology

As the knowledge base and importance of mitochondrial physiology to evolution, health and disease expands, the necessity for harmonizing the terminology concerning mitochondrial respiratory states and rates has become increasingly apparent. The chemiosmotic theory establishes the mechanism of energy transformation and coupling in oxidative phosphorylation. The unifying concept of the protonmotive force provides the framework for developing a consistent theoretical foundation of mitochondrial physiology and bioenergetics. We follow the latest SI guidelines and those of the International Union of Pure and Applied Chemistry (IUPAC) on terminology in physical chemistry, extended by considerations of open systems and thermodynamics of irreversible processes. The concept-driven constructive terminology incorporates the meaning of each quantity and aligns concepts and symbols with the nomenclature of classical bioenergetics. We endeavour to provide a balanced view of mitochondrial respiratory control and a critical discussion on reporting data of mitochondrial respiration in terms of metabolic flows and fluxes. Uniform standards for evaluation of respiratory states and rates will ultimately contribute to reproducibility between laboratories and thus support the development of data repositories of mitochondrial respiratory function in species, tissues, and cells. Clarity of concept and consistency of nomenclature facilitate effective transdisciplinary communication, education, and ultimately further discovery

Mitochondrial physiology

As the knowledge base and importance of mitochondrial physiology to evolution, health and disease expands, the necessity for harmonizing the terminology concerning mitochondrial respiratory states and rates has become increasingly apparent. The chemiosmotic theory establishes the mechanism of energy transformation and coupling in oxidative phosphorylation. The unifying concept of the protonmotive force provides the framework for developing a consistent theoretical foundation of mitochondrial physiology and bioenergetics. We follow the latest SI guidelines and those of the International Union of Pure and Applied Chemistry (IUPAC) on terminology in physical chemistry, extended by considerations of open systems and thermodynamics of irreversible processes. The concept-driven constructive terminology incorporates the meaning of each quantity and aligns concepts and symbols with the nomenclature of classical bioenergetics. We endeavour to provide a balanced view of mitochondrial respiratory control and a critical discussion on reporting data of mitochondrial respiration in terms of metabolic flows and fluxes. Uniform standards for evaluation of respiratory states and rates will ultimately contribute to reproducibility between laboratories and thus support the development of data repositories of mitochondrial respiratory function in species, tissues, and cells. Clarity of concept and consistency of nomenclature facilitate effective transdisciplinary communication, education, and ultimately further discovery