Papers by Keyword: Nitrogen

Abstract: A manufacturing process was developed using an electric through-type furnace for capillary tubes used for single-use injection syringes. The process flow diagram consisting of a number of sequential steps and tube heat treatment conditions in protective atmosphere of pure hydrogen providing also for the tube purging with inert gas were considered. The electric furnace installed capacity and heating element dimensions were found as a result of the thermotechnical calculations. Industry research was carried out with a view to optimize the annealing process of capillary tubes in the electric furnace. A choice of material for the muffle fabrication was justified. Temperature fields inside the muffles were evaluated. The optimal flow of protective gas and the maximum allowable flow of purging gas in the form of nitrogen and argon were determined. Mechanical properties were studied for tubes (stocks), welded at the medical goods fabrication plant in Tumen and fabricated at the Pervouralsky Novotrubny Plant. Test data were obtained for optimal rates of tube movement in the furnace, allowing production of capillary tubes, acceptable for medical needle fabrication after annealing. It was demonstrated that capillary tube heat treatment, ensuring the required condition of both outside and inside surfaces, as well as required mechanical properties, is possible with the use of nitrogen as protective (instead of hydrogen) and purging gases. At that probability of better tube surface condition significantly grows.

Abstract: In this article the time and heat dependence of the nitrogen distribution upon steel alloying of 04Cr20Ni6Mn11Mo2NVNb steel grade by the nitrided manganese of Mn85N10 grade at the holding in the air atmosphere from 2 to 30 minutes in the temperature range 1450-1550 °С was experimentally determined. It was determined that the highest degree of nitrogen transition into steel is 99% and is observed with a short holding time of 2 min (after the introduction of nitrided manganese into the steel melt) in the low-temperature region ~ 1450 °С. Further holding and / or temperature growth results in the release of nitrogen in the gaseous form, due to the thermal dissociation of the nitrogen-containing compounds contained in the melt and removal of nitrogen from the melt into the gas phase, which leads to a decrease in the degree of nitrogen transition to the steel. The key possibility for obtaining a steel of the indicated grades group with a nitrogen content of 0.45-0.6% is shown when alloying in an air atmosphere in a low-temperature region (1450-1500°C), while optimizing the holding time.

Abstract: The influence of aluminium content on the hot ductility behaviour in V-N steels was investigated. Cylindrical specimens were subjected to thermal cycles and strain rates approximating those experienced by a conventional slab surface during continuous casting. The resulting microstructures were examined using light optical and electron microscopy and correlated with measured reduction-in-area (RA) values, calculated precipitate chemistries and volume fractions, as well as the flow stress behaviour. It was found that removal of aluminium significantly improved the hot ductility. However, increasing the total [V][N] product in Al-free steels reduces RA. Poor hot ductility is caused by low austenite grain boundary mobility characterized by high work hardening rates. The fracture mode in brittle specimens is intergranular along thin ferrite films. AlN appears to inhibit austenite grain boundary mobility in V-high N steels when the cooling rate and strain rate are both very slow as experienced during unbending. SEM analysis of fracture surfaces revealed the presence of MnS-AlN particles in microvoids. TEM-EDAX spectra showed that the larger particles observed in the Al-containing steels are mostly a constitution of duplex/triplex grain boundary precipitates, i.e., MnS-AlN and V(C,N). Conversely, good ductility in austenite is associated with high grain boundary mobility that produces fine, recrystallised grains and subsequent dimple fracture after plastic tensile stress.

Abstract: Microalloying has received increased attention in recent years. The aims of the study were to identify and to examine the influence of nitrogen concentration in steel and small additions of nitride-forming elements on the hardenability of a boron-treated manganese-vanadium steel 40GF-VI. The study has shown that the increase in nitrogen concentration from 0.004% to 0.015% increases the hardenability of steel. It was found that a small amount of titanium (about 0.02%) in steel with low concentration of nitrogen (0.004%) is sufficient to bind it to nitrides, which makes it possible to save the most of boron in an active state (in a solid solution). A residual amount of titanium and aluminum in the range of 0.015-0.020% of each in steel with nitrogen concentration in the range of 0.010-0.015%, which is typical of an electric arc melting steel, is insufficient to bind all nitrogen. As a result, a part of nitrogen is spent on the formation of boron nitrides, which reduces the effect of boron on the hardenability of manganese-vanadium steel microalloyed with boron. Some methods of protecting boron in steel are briefly described. The study has established that grain refinement is observed with increasing nitrogen content in steel. Introduction of boron, in absence of titanium, does not change the size of the austenite grain in the entire range of the investigated temperatures. The optimum combination of strength, plastic and ductility characteristics in steel microalloyed with boron and additives of aluminum and titanium was obtained.

Abstract: The paper presents theoretical and practical study of formation of non-metallic inclusions in a medium-carbon free-cutting structural steel. FactSage software package was used for thermodynamic modelling of inclusion behaviour. Formation temperature and the amount of aluminium oxides, boron nitrides, manganese sulphides and aluminium nitrides were calculated. Inclusions in the steel form in the sequence Al₂O₃ > BN > MnS > AlN. The object of practical research was a cast billet of A38KhGMAR grade steel. It was melted in a laboratory induction furnace; boron and nitrogen were introduced after deoxidation of the melt with primary aluminium. Quality analysis included determination of chemical composition, macro-and microstructure, type and shape of non-metallic inclusions. Fine and uniformly distributed boron nitride inclusions were obtained throughout the metal matrix; their distribution was studied both qualitatively and quantitatively. Beside isolated particles, boron nitrides are also presented as a component of complex inclusions with manganese sulphides. Inclusion morphology is mostly spherical. The size of BN inclusions varies from 0.41 to 7.23 μm.

Abstract: The paper presents the results of studies on increasing the efficiency of wastewater treatment from nitrogen compounds during the re-engineering of sludge bioreactors with the use of contact carriers for biomass immobilization. To assess the contribution of the indicative species of microorganisms involved in the processes of nitrification and denitrification, an analysis of the indices of species diversity by functional zones was carried out. The results of the operation of the bioreactor are given when using reticulate contact carriers in the form of partitions to separate the functional zones. It was noted that the oxidation-reduction potential of the bioreactor in nitrogen increased 1.7 times after re-engineering.

Abstract: This study describes the thermal diffusivity of thin duplex steel plates in the thickness direction measured using the laser-flash method after welding. The work reports the experimental efforts in recording temperature profiles of the grade UNS S32304 duplex steel during autogenous welding. The butt weld autogenous joints were carried out by the GTAW (gas tungsten arc welding) process with either argon or argon - 2% nitrogen atmospheres. The amount of nitrogen in the heat affected regions, after welding, was measured and correlated with the variation of the thermal diffusivity of the studied material. The temperature profiles were obtained using k-type thermocouples connected to a digital data acquisition system. Different thermal cycles and thermal diffusivity values were observed in the heat-affected zone (HAZ) for both samples. In the solidified zone (SZ) was observed similar increase of the thermal diffusivity values for the plates welded with pure argon and argon plus nitrogen atmosphere.

Abstract: Oxygen (O₂) enriched air combustion via adaption of polymeric membranes has been proposed to be a feasible alternative to increase combustion proficiency while minimizing the emission of greenhouse gases into the atmosphere. Nonetheless, majority of techno-economic assessment on the O₂ enriched combustion evolving membrane separation process are confined to assumption of constant membrane permeance. In reality, it is well known that membrane permeance is highly dependent upon the temperature and pressure to which it is operated. Therefore, in this work, an empirical model, which includes the effect of temperature and pressure to permeance, has been evaluated based on own experimental work using polysulfone membrane. The empirical model has been further validated with published experimental results. It is found that the model is able to provide an excellent characterization of the membrane permeance across a wide range of operating conditions for both pure and binary gas with determination coefficient of minimally 0.99.

Abstract: In this work, we study the effects of NO anneals on the interface of 4H-SiC MOSFETs via spin dependent charge pumping, an electrically detected magnetic resonance technique. We make measurements at high and ultra-low resonance frequencies. Our results indicate that the NO anneals both change the silicon vacancy energy levels as well as induces disorder at the interface. In addition, our results indicate that the changes in energy levels involve N atoms very close to V_Si sites.

Abstract: A common and straightforward method for the standardisation in electron-probe microanalysis (EPMA) is the use of homogeneous reference materials prepared by various techniques such as by melting, sintering, high-temperature annealing and hot-pressing. The reference materials have to be analysed by independent methods accurately in order to define their “true” composition. For some compounds the preparation techniques are difficult because of their specific thermo-chemical properties (e.g. low diffusivities, high equilibrium nitrogen pressure, incongruent melting). In addition, many compounds show large homogeneity ranges with an a priori existing uncertainty in composition, contrary to what is generally preferred: to use compounds with a narrow homogeneity range (“line compounds”). For the latter, diffusional preparation techniques can be applied to yield diffusion layers instead of massive samples for standardisation. However, also single-phase samples with narrow homogeneity ranges can be prepared by diffusion, depending on the phase equilibria in the corresponding system. The presentation summarises efforts that have been made in order to prepare various reference materials for carbon and nitrogen standardisation of EPMA by various techniques. The boundary conditions such as phase stabilities, phase compositions and diffusion kinetics, which are important for their preparation to obtain well-defined reference samples are discussed. These samples were applied to various WDS/EPMA-based studies of phase diagrams and diffusion kinetics by means of Cameca SX 50 and SX 100 microprobes.