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In order to compare the hot deformation behavior and microstructure evolution of the rack steels with and without segregation, hot compression tests are carried out in the temperature range of 1173–1423 K and the strain rate range of 0.01–10 s−1 on a DIL805A/D quenching and deformation dilatometer. The flow stress, constitutive relation, processing map, and microstructure characterization are investigated. The results show that the flow stress increases with the increase of strain rate and the decrease of deformation temperature. The calculated activation energy (Q) and stress exponent (n) for the segregated samples are 395.245 kJ mol−1 and 6.046, which are higher than segregated samples, showing 376.815 kJ mol−1 and 5.930. The processing maps show that the workability of the nonsegregated steel is significantly more excellent than segregated steel. The segregated steel shows a higher kernel average misorientation angle and local strain. Complete dynamic recrystallization occurs at a high strain rate, and high deformation temperature can refine the grains. [ABSTRACT FROM AUTHOR]

A multistep quench−lamellarization−tempering treatment (QLT) is designed for a low‐carbon high‐Ni martensitic steel to obtain extra high strength, low yield‐to‐tensile ratio, and extra high cryogenic toughness. A mixed microstructure composed of intercritical ferrite, tempered martensite, and Ni‐rich retained austenite (RA) is obtained under the QLT treatment process. The volume fraction of Ni‐rich RA is 13.6% in the QL655T sample. The QL655T sample has a yield strength of 915 MPa and tensile strength of 1080 MPa, leading to a lower yield‐to‐tensile ratio of 0.85. In addition, a total elongation to failure of 19.9% and Charpy impact toughness of 190 J at −196 °C are encouraging in comparison with the conventional counterparts. During tensile deforming, the blocky RA grains can transform easily with increasing strain, while the strain leads to rotations of the film‐like RA grains before the transformation. The RA grains with high thermal stability are attributed to the enrichment of Ni and the effect of size, which makes the ≈11.6% RA grains remain at −196 °C in the QL655T sample. During impact, the transformation‐induced plasticity (TRIP) effect of RA leads to the excellent cryogenic toughness of the QL655T sample. [ABSTRACT FROM AUTHOR]

A suite of xenoliths of eclogite, garnet clinopyroxenite, and felsic gneiss is found in Early Cretaceous high-Mg [[Mg.sup.#] >45, where [Mg.sup.#] = molar 100 x Mg/(Mg + [Fe.sub.total])] adakitic intrusions from the Xuzhou-Huaibei (Xu-Huai) region along the southeastern margin of the North China craton. The primary mineral assemblage of garnet + omphacite/augite + quartz + rutile [+ or -] pargasite of the eclogite and garnet clinopyroxenite xenoliths defines a minimum pressure of >1.5 GPa, while the estimated peak metamorphic temperatures range from 800 to 1060 [degrees]C. An Sm-Nd whole-rock--garnet isochron and zircon U-Pb dates show that timing of the eclogite facies metamorphism took place ca. 220 Ma. This Triassic age agrees with the age of eclogites from the Dabie-Sulu ultrahigh-pressure metamorphic (UHPM) belt. The ages of abundant Late Archean to early Paleoproterozoic (2.3-2.6Ga) inherited zircons correspond to the most prominent crustal growth event in the North China craton. In addition, these xenoliths and their host high-Mg adakitic intrusions have complementary major and trace element compositions, suggesting that the adakites formed by partial melting of Archean metabasalts that were the protoliths of the Xu-Huai eclogite and garnet clinopyroxenite xenoliths. Trace element and Sr-Nd isotopic modeling shows that the high-Mg adakitic intrusions can be modeled as melts from ~40% partial melting of the metabasalts in the eclogite facies, followed by interaction with the convecting mantle and variable degrees of crustal assimilation. Together with the similar zircon age populations between the xenoliths and the host rocks, these lines of evidence strongly suggest their genetic link via thickening, foundering, and partial melting of the Archean North China craton mafic lower crust, followed by adakitic melt-mantle interaction. The crustal thickening resulted from Triassic collision between the Yangtze craton and the North China craton, which produced the Dabie-Sulu UHPM belt in the subducting Yangtze plate and eclogitization of the basaltic crustal root of the overriding North China craton plate. Such processes may have played an important role in generating the high-Mg character of the continental crust. Keywords: eclogite, adakite, tonalite-trondhjemite-granodiorite, continental crust, partial melting, North China craton.