Feasibility study on developing high-nitrogen steels by refining in suspended state under high pressure

High-nitrogen steels are finding increasing use in the industrially developed nations. However, they are still not being used to their full potential. Among the reasons are the time and money needed to develop new grades of high-nitrogen steels. This article reports on the progress made in this area by the Institute of Metallurgy of the Bulgarian Academy of Sciences. As an example, it describes the quick and efficient process followed in developing a new nickel-free low-manganese austenitic stainless steel obtained by refining in the suspended state under pressure. __________ Translated from Metallurg, No. 2, pp. 37–41, February, 2007.     

Metallurgy under pressure

The development of iron and steel production is briefly reviewed. Metallurgy under gas pressure appeared at the end of the twentieth century. Even at this early stage, some significant benefits of metallurgy under pressure over traditional metallurgy and vacuum metallurgy have been established, such as fourfold increase in yield point with reduced consumption or elimination of some expensive alloying elements (Ni, Mo, Co, W, etc.); the possibility of alloying with nontraditional elements (Ca, Zn, Pb, etc.); low environmental impact; and stable development. Metallurgy under pressure may be expected to give rise to breakthroughs in the production of high-quality and special metal. Of the currently existing methods, the most promising is the use of a large steel-smelting bath.     

Processes of precipitation and intercrystalline corrosion in high-nitrogen Cr-Mn steels after isothermal annealing

Conclusions Susceptibility to ICC is the determining factor in selecting nitrogen-containing steels after technological operations that involve heating.The best combination of resistance to ICC and high mechanical properties of nickel-free Cr–Mn steels is obtained with 0.5–0.6% N.Institute of Metal Science and Technology of Metals, Bulgarian Academy of Sciences. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 5, pp. 13–15, May, 1981.     

Three-dimensional object-oriented modeling of the stomach for the purpose of microprocessor-controlled functional stimulation

Three-dimensional (3-D) object-oriented models are needed for optimizing gastric electrical stimulation by performing virtual computer experiments. The aim of the study was to create a 3-D object-oriented electromechanical model of the stomach in vivo for the purpose of microprocessor controlled functional stimulation. The stomach was modeled using coaxial truncated conoids as objects. The strength of an external stimulating electric field generated by circumferentially implanted wire electrodes is related to artificial neurogenic and myogenic control of smooth muscle depolarization and contraction. Variation of the field strength modulates the frequency and concentration of acetylcholine release, as well as the transmembrane voltage of the muscle cells. Mechanical response of the stimulated tissue was quantified by two parametric functions of the electric field strength representing the relative contractile force and geometrical displacement of the gastric surface. Data from previously conducted canine experiments were used to test the validity of the model. The model was applied to simulate contractions with different positions, orientation and number of the circumferentially implanted stimulating electrodes. The model combined most of the existing theoretical and experimental findings concerning functional gastric stimulation and can be utilized as a flexible tool for virtual medical tests involving external high-frequency (50 Hz) neural stimulation.     

Application of an object-oriented programming paradigm inthree-dimensional computer modeling of mechanically activegastrointestinal tissues

The aim of this study was to develop a novel three-dimensional (3-D) object oriented modeling approach incorporating knowledge of the anatomy, electrophysiology, and mechanics of externally stimulated excitable gastrointestinal (GI) tissues and emphasizing the “stimulus-response” principle of extracting the modeling parameters. The modeling method used clusters of class hierarchies representing GI tissues from three perspectives: 1) anatomical; 2) electrophysiological; and 3) mechanical. We elaborated on the first four phases of the object-oriented system development life-cycle: 1) analysis; 2) design; 3) implementation; and 4) testing. Generalized cylinders were used for the implementation of 3-D tissue objects modeling the cecum, the descending colon, and the colonic circular smooth muscle tissue. The model was tested using external neural electrical tissue excitation of the descending colon with virtual implanted electrodes and the stimulating current density distributions over the modeled surfaces were calculated. Finally, the tissue deformations invoked by electrical stimulation were estimated and represented by a mesh-surface visualization technique