Microstructural Transformation and Precipitation of an Ultra-high Strength Steel under Continuous Cooling

We investigated phase transition and precipitation of ultra-high strength steel（UHSS）in a new ＂short process＂ with controlled rolling and controlled cooling.Thermalexpansion test combined with metallographic observation was used to research the continuous cooling transformation（CCT）curve.Moreover,the microstructuraltransformation and precipitation law was revealed by morphologicalobservation and alloying elements by electron probe micro-analyzer（EPMA）.Transmission electron microscopy（TEM）was utilized to analyze the composition and grain orientation of microstructure.The study showed that the measured criticaltransformation temperatures of Ac1 and Ac3 were 746 and 868 ℃,respectively.The CCT curve indicated that the undercooled austenite was transformed into proeutectoid ferrite and bainite with HV 520 in a broad range of cooling rate 0.1^（-1） ℃·s^（-1）.When subjected to a cooling rate of 1 ℃·s^（-1）,the undercooled austenite was divided into small-sized blocks by formed martensite.With further increase of cooling rate,micro-hardness increased dramatically,the microstructure of specimen was mainly lathe bainite（LB）,granular bainite（GB）,lath martensite（LM）and residualaustenite.By diffraction test analysis,it was identified that there was K-S orientation relationship between martensite and austenite for {110}_α//{111}_γ,{111}_α//{101}_γ.EPMA clearly showed that carbon diffused adequately due to staying for a long time at high temperature with a lower cooling rate of 2 ℃·s-1.Phase transition drive force was lower and the residualaustenite existed in the block form of Martensite austenite island（M-A）.With the increase of cooling rate to 10 ℃·s^（-1）,the block residualaustenite reduced,the carbon content of residualaustenite increased and α phase around the residualaustenite formed into a low carbon bainite form.

Some studies on mechanics of continuous mediums viewed as differential manifolds

The continuous mediums are divided into two kinds according to their geometrical configurations,the first one is related to Euclidian manifolds and the other one to Riemannian manifolds/surfaces in the point of view of the modern geometry.Two kinds of finite deformation theories with respect to Euclidian and Riemannian manifolds have been developed in the present paper.Both kinds of theories include the definitions of initial and current physical and parametric configurations,deformation gradient tensors with properties,deformation descriptions,transport theories and governing equations of nature conservation laws.The essential property of the theory with respect to Euclidian manifolds is that the curvilinear coordinates corresponding to the current physical configurations include time explicitly through which the geometrically irregular and time varying physical configurations can be mapped in the diffeomorphism manner to the regular and fixed domains in the parametric space.It is quite essential to the study of the relationships between geometries and mechanics.The theory with respect to Riemannian manifolds provides the systemic ideas and methods to study the deformations of continuous mediums whose geometrical configurations can be considered as general surfaces.The essential property of the theory with respect to Riemannian manifolds is that the thickness variation of a patch of continuous medium is represented by the surface density and its governing equation is rigorously deduced.As some applications,wakes of cylinders with deformable boundaries on the plane,incompressible wakes of a circular cylinder on fixed surfaces and axisymmetric finite deformations of an elastic membrane are numerically studied.

α decay energies and half-lives from a macroscopic-microscopic model

α decay energies of 323 heavy nuclei with Z ≥82 are evaluated with a macroscopic-microscopic model. In this model, the macroscopic part is treated by the continuous medium model and the microscopic part consists of shell and pairing corrections based on the Nilsson potential. α decay half-lives are calculated bY Viola-Seaborg formula. The results of α decay energies and half-lives are compared with experimental values and satisfactory agreement is found. The recoiling effect of the daughter nucleus on α decay half-life is also discussed.