Improvement in steel smelting by studying melt behavior

Abstract

106Today, we may characterize metallic melts in terms of quasi crystalline structure and microheterogeneity and also in terms of disequilibrium. In a solid-liquid phase transition, the disequilibrium of the melt is asso ciated with its inheritance of heterogeneity and struc tural defects from the crystals and the activational character of change in melt structure. Solidification from nonequilibium melts results in unstable structure and properties of the final steel, according to many researchers. (For example, see [1].)In modern steel smelting, consisting of the smelt ing of a low carbon intermediate product and the sub sequent adjustment of its composition in ladle refin ing, the disequilibrium of the melt is due to intense melting processes, the addition of large masses of material for carburization and alloying, and the exten sive use of gas, liquid, and solid reagents.From research on pipe steel production by means of a superpowerful DSP 135 arc furnace, a ladle-fur nace unit, a vacuum treatment system, and a contin uous casting machine, we conclude that disequilib rium of the melt is primarily associated with decrease in plasticity of the final steel, as indicated by experi mental data (Fig. 1). The disequilibrium of the melt is estimated from the damping time of fluctuations in the kinematic viscosity (the relaxation time) in isothermal laboratory experiments. The steel samples character ized by a long relaxation time-that is, by greater dis equilibrium-are characterized by reduced relative elongation in fracture tests. In general, disequilibrium of the melt's structure is associated with defects of the cast billet.We now consider in more detail the sources of melt disequilibrium and its relationship with the properties of the final steel [2]. That provides the basis for the development and optimization of parameters for dif ferent stages of the process. SMELTINGThe oxidation of the intermediate product has the determining influence on the disequilibrium of the melt and the plasticity of the steel (Fig. 2). For stabili zation and enhancement of steel quality, the oxidation of the intermediate product should not exceed 800 ppm. Parameters characterizing the smelting of the intermediate product have been developed so as to ensure regulated oxidation by optimizing the oxygen injection and the slag conditions. To obtain oxidation in the range 500-800 ppm, the total oxygen consump tion in the melt should be no more than 3000 m 3 (Fig. 3a). Correspondingly, the FeO content in the slag should be no higher than 20-30% (Fig. 3b). ALLOYING IN THE LADLE-FURNACE UNITThe alloying of the steel has a significant influence on the disequilibrium of the melt and the performance of the solid metal. Increase in the mass of ferroalloy Abstract-Analysis shows that the disequilibrium of melts may be used to characterize metal quality and to optimize smelting technology. For the production of pipe steel by means of a superpowerful DSP 135 arc fur nace, a ladle-furnace unit, a vacuum treatment system, and a continuous casting mac...

Physicochemical characteristics of melts of corrosion resistant nitrogen-alloyed steels

“…- ние реологических свойств расплавов (характера их временных и температурных зависимостей) выступает в настоящее время в качестве основного физико-химического метода исследований структурных состояний металлических расплавов [15 - 18]. Исходя из установленного научного факта взаимосвязи свойств жидкого и твердого металла, результаты этих исследований используют для выявления резервов повышения и стабилизации эксплуатационных свойств сталей и сплавов [19,20]. В результате проведенных исследований установлено (табл.…”

“…В качестве оптимальной степени легирования азотом может рассматриваться концентрация, которая не превышает предельного значения для рассматриваемого химического состава, выше которого резко возрастает неравновесность структурного состояния расплава. Как свидетельствуют данные для промышленных сталей это может существенно стабилизировать и повысить уровень эксплуатационных свойств [19,20].…”

Technologies Development for Thermo-Temporal Melt Processing in Order to Improve the Quality of Metal Products

“…The quality of steel products, their service properties, ensuring high durability of machines and structures, is mainly determined by steelmaking [1][2][3][4][5][6]. However, the effective use of metal production processes, ensuring their quality can be achieved only if there is a significant improvement in the control of metallurgical processes occurring in steelmaking aggregates, steelteeming ladles during after-smelting metal processing and during casting [1,5,[7][8][9].…”