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Steel Modification in Ingots

#G-1161


Study and Development of the Process of Steel Modification in Ingots

Tech Area / Field

  • MAT-ALL/High Performance Metals and Alloys/Materials

Status
3 Approved without Funding

Registration date
16.06.2004

Leading Institute
Georgian Technical University, Georgia, Tbilisi

Supporting institutes

  • Institute of Metallurgy, Georgia, Tbilisi

Collaborators

  • University of Toronto / Department of Materials Science and Engineering, Canada, ON, Toronto\nColorado School of Mines, USA, CO, Golden\nConsulting and Educational Services, Inc., USA, MA, Boston

Project summary

Improvement of steel quality, of machine design, decrease of specific metal content and simultaneous increase of operating reliability is an especially important and expedient trend in science and technology today. Substantial reserves and possibilities of steel quality improvement were foreseen in the possibilities of active and target-oriented development of the ingot structure by introduction of rationally selected and scientifically grounded modifiers and micro-regulating additives (dopes) into the melt during the stage of crystallization.

Steel modification is the most economic and highly efficient method of effect on the formation of the cast structure of the ingots, and provision of increased technological and working features. Modifiers, added into the melt have substantial effect on crystallization and liquation processes. They provide for the elimination of non-metal impurities and gases, metal densification, homogenization of the ingot chemical composition, etc. Metal hardening rate and mechanism are based on physical and chemical phenomena, proceeding in the melts, and resulting in various phase and structural conversions during further metal refining processes, and in the end resulting in substantial product defects. This circumstance, together with non-completed development of the theory and practice of modification have negative effect on the rates and volume of introduction of progressive design and development results into high-quality metallurgy. Thus a necessity exists of both detailed study of theoretical grounds and conduction of experiments on the selection of optimal composition and quantity of the additives and processes of their doping into liquid metal. Scientists of USA, Japan, Russia and other countries are working in this direction.

The Project authors have developed and tested a unique method of steel modification in the ingot moulds. The developed method comprises introduction of a container with the modifier into liquid steel immediately after filling the ingot mould with the metal. The method of container introduction into the metal consists of four operations, as follows: Preparation of the modifier mixture with passivity agent for the heating inhibition and gradual evaporation of the modifier; Preparation of the container for the mixture; mixture compaction in the container; submersion of the container into the liquid metal when the ingot mould is filled with the metal. The mixture is prepared by thorough mixing the modifier with the iron powder (passivity agent). Mixture compaction in the container is made under increased pressure. The compacted mixture in the container preserves its physical state when stored in the atmospheric air; it is portable and safe. When the container is placed in the metal melt the mixture is heated gradually from the container surface to the center, and under preset pressure the modifier evaporated gradually, and simultaneously control over the process of metal modification in the ingot is performed.

The results of preliminary experiments show that the process of modifier evaporation starts in a minute after its introduction into the liquid steel and lasts for approximately 10 minutes. Out coming modifier vapors set liquid metal in motion, comminute large crystals, homogenize metal chemical composition in the ingot, refine the metal of the impurities, density the ingot, eliminate the axis porosity, decrease gas content in the metal, change the morphology of the remaining impurities, improve the mechanic parameters of the metal. Modification processes result in substantial improvement of the steel ingot qualitative parameters, and increase the metal yield by 5 % after the initial refining process. Conducted experiments allow concluding that the offered modification technology can be successfully used for making high-quality steels and large ingots for nuclear power engineering and reactors, and for making special purpose high-alloy steels, working in corrosive media. Practical application of such method of steel modification in ingots will allow improving the quality of special purpose steel ingots with minimal modifier demand.

Additional theoretical and experimental studies, foreseen within the frames of the present Project Proposal are necessary to develop the technology and to define optimal parameters of the process of steel modification by the proposed method. The Project Proposal also foresees theoretical studies of the laws of thermodynamic and thermo-physical processes, observed during steel crystallization in conditions of metal modification. A series of theoretical and experimental studies are planned to determine optimal parameters of steel ingot modification processes. Experimental melting of pipe steel, carbon steel, high-quality and alloy steels in cast iron moulds in induction furnaces will be conducted, followed by the ingot modification. Study of the qualitative parameters in experimental samples of the metal are planned to investigate the effect of the process of steel modification in the moulds. For this purpose longitudinal templates will be prepared from every experimental ingot. To study the macrostructure the templates will be etched with 20 % water solution of nitric acid. To disclose the initial dendrite structure the templates will be etched with 50 % water solution of hydrochloric acid at 700C. To study chemical heterogeneity of elements distribution in the ingots template sample chips will be cut in five horizons from specific points.

The Project also plans making metallographic specimens and samples for electrolytic extraction of non-metal impurities, and for mechanical tests for rupture, impact, etc. Metallographic specimens will be used to study the metal microstructures, morphology, distribution of non-metal impurities. Chemical composition and mechanical parameters of steel will be studied for each experimental specimen, and quality certificate will be made.

Theoretical and experimental studies will define dependence of efficiency of steel modification in ingots on specific consumption of the modifier, percent composition of the mixture of the modifier and passivator in the container, repeated modifier introduction into liquid steel (especially for large weight ingots), the depth of container submersion into the metal etc. The investigations will make it possible to develop the process of steel modification in ingots. Optimal parameters of the modification process of steel ingots of various weights will be defined.

Georgian Technical University and F.N.Tavadze Research Institute of Metallurgy and Material Science possess all the necessary equipment for the investigations, planned in the Project, and in particular: microscopes for metallurgic study of micrographic specimens, microscopes to study electrolytically extracted non-metal impurities in transmitted and reflected light, a microprobe for micro-x-ray-spectrographic analyses of the specimen structure; plants for mechanic tests, chemical laboratory for general micro-chemical analyses of metal and non-metal impurities. 40, 50 and 100 kg capacity induction furnaces will be used for making steels of various qualities. Georgian Technical University will design and make iron containers, provided with special facilities for modifier introduction into liquid metal. Besides, the University is also planned to prepare mixtures of modifier and passivity agent, and to conduct the mixture compaction in containers.

Within the frames of the proposed Project foreign Collaborators will promote integration of Georgian scientists into international scientific community. Constant scientific and technical collaboration, discussion of the Work Plan of research and technology works will be conducted with Foreign Collaborators. Quarterly obtained research results will be discussed, conferences, consultations and exchange with information will be arranged during the Project implementation. Problems, related to commercialization of the developed technologies will also be solved in cooperation with Foreign Collaborators.

High skilled specialists are attracted to the Project implementation: 3 Doctors of Technical Sciences, a Candidate of Phys. &Math. Sciences (Ph.D), 6 Candidates of Technical Sciences (Ph.D), Research workers and skilled engineers with substantial working experience. Basic participants in the Project and research and engineering personnel, former involved in the development and improvement of the processes, combined under nomination “weapon of mass destruction”. The Project implementation will provide opportunity to reorient and integrate former weapon specialists into the field of peaceful creative works.


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