Nitrogen solubility in the austenitic stainless steel melts was measured in the laboratory by bubbling nitrogen gas under different partial pressures of nitrogen and temperatures. A new thermodynamic model for the calculation of nitrogen solubility in molten stainless steel in a wide range of alloy concentrations, temperatures, and pressures has been successfully established by introducing a new term for the effect of pressure on the nitrogen activity coefficient. The calculation results were in good agreement with the measured values. The influences of temperature, nitrogen partial pressure and chemical composition on the nitrogen solubility in molten stainless steel are discussed based on the calculated results. It is possible to produce high nitrogen steels at normal pressure by optimizing the design of the alloy composition and controlling the lowest melting temperature from a thermodynamic point of view.
The secondary refining of molten steel in gas-stirred ladle has played a more and more important role in the production of high quality steel. In the present work, a mathematical model of the fluid flow and inclusions behaviour in a 150t gas-stirred ladle was presented, and the variations in concentration, size and density for non-metallic inclusions in the ladle during the refining process were predicted. The results show that during the refining process, the variations in the number density of the inclusions differed depending on size. The inclusions with a diameter less than 25 urn decrease during the whole period, while inclusions with diameter larger than 25 urn increase in the first stage of the treatment and gradually decrease during the later stage. After 15 minutes, all inclusions show a tendency to decrease, but the removal rate for inclusions of smaller size becomes slower. After treatment in the ladle, inclusions with a diameter larger than 50 urn were removed, the number of inclusions with a size between 30-40 urn was not high, while inclusions that were smaller than 25 urn still remained in the molten steel. Two-jet bubbling demonstrated an advantage over one-jet for inclusion removal. The practice of bubbling argon with a higher gas flowrate initially, followed by a lower flowrate in the ladle was found to be beneficial for inclusions removal.
To elucidate the morphology evolution of the inclusions in 16MnCrS5 steel with various masses of Mg addition, the experiments and thermodynamics were carried out with a high-temperature tube electric resistance furnace and FactSage software, respectively. The evolutions of the inclusions after the smelting and hot-processing were described. The experimental results show that with Mg addition of 35-42 ppm, many spindle and spherical inclusions with the size below 20 μm appeared, whereas the long-strip inclusions above 20 μm disappeared; after hot-processing, particularly, the h value was above 50%, beneficial to obtaining more spindle inclusions, and most spherical inclusions at 35 ppm were also obtained. The thermodynamics show that with Mg mass between 0.349 and 6.076 ppm, Al 2 O 3 was easily converted to MgO•Al 2 O 3 , whereas above 6.076 ppm, Mg was directly converted to form MgO; above more, MgS coexisted with MgO.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.