| In the present study, for the metallurgical process in Chengde iron & steel making company(later referred to as ChengGang) in which vanadium-titanium bearing magnetite ore is used as the main resource, the author firstly solved the important technical problems such as molten-iron-adhibiting-pot, low capacity of desulphurization, recovery of coal gas brought during smelting semi-steel by converter and waste heat utilization and so on from acclimating the special rule which must be followed during smelting vanadium-titanium bearing magnetite ore. Based on those, the choke point in technological pocesses consist of iron-making?desulphurization?vanadium extraction?steel making?continous casting was solved through optimizing the operation. And a process by which ChengGang can smelt clean steels with lower cost was elementarily striked up through investigating the quality of the steel-making system, and a series of famous products with resource and technical characteristics such as series of vanadium-bearing reinforced bar and hot rolled steel plate used for the cross-beam of motorcar and so on, which makes the vanadium bearing steels into the characteristics and symbol of ChengGang. Through developing a series of new techniques by which vanadium-titanium bearing magnetite ore are smelted, tremendous economical benefit was achieved and a systemic theory based on which vanadium-titanium bearing magnetite ore smelting was established.The main work and innovative results are as follows:1. Through the development and optimization of equipment for continuous desulfurization of iron melt, the difficult problems on vanadium-titanium molten iron desulfurization was solved and a solid foundation for smelting clean steel was laid. Not only the desulfurization rate was improved but also the automatic separation of liquid iron and slags was also implemented. There are so many telling advantages in the developed system, such as simple equipment, easy operation, works steadily, small size, environment friendly, stable efficiency and low costs.(1) Through optimizing the position of parapet and lance, the reaction time of desulfurization medium and hot metal is increased, which decreases the temperature lowering of mo;ten iron and improves the desulfurization efficiency. Most importantly, the automatic division between hot metal and slag was obtained.(2) While the parapet was removed in the desulphurization tank, a positive fluency of hot metal around lance was observed. This improved the availability of desulfurization tank.(3) With a stable desulfurization rate and remarkable effectiveness, this facility characterizes simpleness, reliability, easy control, low occupation of land, and environmental friendly, as well as lower cost than the desulphurization by pulverization of powder. It is worthy of spreading.2. In accordance with the characteristics of vanadium-titanium molten iron with high slag rate, low temperature and high viscosity, the performance and the state of slag is improved by adding modifiers into the desulphurization tank. As a result, the the increasing rate in tank weight by tank adhering of vanadium-titanium molten iron and the affecting range was well controlled. Application of the technology significantly increases the lining life of mixer and torpedo, reduces the consumption of refractory material, improves the economic performance and makes the production more smoothly.(1) The newly emerged technology enhanced significantly the longevity of the lining of torpedo and puddling furnace, which means a lower refractory consumption and a smooth production flow.(2) After the technology was improved, the volume of slag was much more less as compared with traditional production process. Consequently, after melting in the vanadium-extraction BOF, vanadium slag quality was notably strengthened.3. From starting with quality survey from the steel-making process, through investigating the technologies by which the clean steels are produced by using semi-steel making process, the technological processes and controlling objectives for producing clean steels were initially established. Based on the result of quality survey, the flow field in the continuous casting tundish and crystallizer were studied.(1) The oxygen content in slab is controlled from 60ppm before the optimization of the technology to 15ppm below after the optimization. This indicates that the controlling of the cleanliness of steel after optimization of the technology is better that by the conventional production process.(2) When transferred from ladle to tundish, the increases in oxygen and nitrogen contents occur. This phenomenon is strikingly serious at the beginning of casting. Steel melt in mold would be reoxidized as well. Admittedly. The inclusions in slab mainly include the calcium aluminate around 3 to 10 micrometers, CaS and the complex inclusion of Al2O3+CaO+CaS; the inner crack in a few slabs were found; which implies that a further upgrade of the flow field in mould and the structure of tundish should be conducted.4. Based on the results for analysis of slab quality, the flow fields in tundish and crystallizer for continous casting were investigated. In accordance with the results in laboratory, the technological optimization of continous casting was carried out. The results of analysis before and after the improvement of technological processes indicate:(1) The total oxygen content in steel was decreased by 12 percent;(2) The number of micro-inclusions was reduced from 4.76 per square millimeter to 3.94 per square millimeter.(3) The main contents in the larger inclusions consist of calcium aluminate, silicon aluminate and refractory. The amount of inclusions mentioned above was decreased from 5.33 milligram per 10 kilogram slab to 1.15 milligram per 10 kilogram.(4) The difference in flow velocity of surface in crystallizer was decreased by the technological process parameters after the improvement, which is favourable to the stabilization of flow field in the mould.As those key problems during the production of clean steel by vanadium-titanium bearing magnetite ore are solved, Chengde Steel has been liberated from obstacles of low desulfurization efficiency and the purity of semi-steel melting such as uncompetitive metal yield. This also enables ChengGang invest heavily in clean steel development and establish the target specification of different procedures. Until now, a series of characteristic products have been developed and produced, such as the reinforcing rods containing vanadium and the hot rolled automobile plate. |
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