As the main steelmaking method for smelting high-quality steel in the world, the progress and development of converter steelmaking technology has a huge driving force for energy conservation, emission reduction, cost reduction and efficiency improvement in the steel industry.
The melting behavior of scrap steel was studied from two aspects of theoretical analysis and practical exploration, and the melting mechanism of scrap steel was revealed; the research on the flow characteristics of the converter molten pool by injection mode, bottom blowing process, etc. was analyzed and summarized;
The development status and prospects of converter endpoint control technology were introduced from two aspects of metallurgical mechanism and data model;
Finally, from the perspective of overall optimization of metallurgical process, the progress and existing problems of steelmaking-refining-continuous casting integration technology were introduced from mathematical modeling to platform simulation.
The intelligent development of converters requires more equipment, methods and technologies. Converter intelligent steelmaking is a comprehensive practical application case involving multiple disciplines such as metallurgy, automation, and computer.
Efficient Utilization of Scrap Steel in Converters
Under the background of “dual carbon”, promoting the green and low-carbon transformation of the steel industry is the only way for it to develop in a high-quality way.
The continuous growth of scrap steel resources in recent years has provided the possibility of adjusting the raw material structure of steel production and realizing steel recycling.
According to statistics, using 1 ton of scrap steel to replace 1 ton of molten iron in converter smelting can save 500 kg of standard coal;
For every 1% increase in the scrap steel ratio in converter smelting, the blow-off loss of non-ferrous elements such as manganese and chromium will be reduced by about 0.04%;
For a 10% increase in the scrap steel ratio in converter steelmaking, the total carbon dioxide emissions can be reduced by 6%.
Therefore, efficient use of scrap steel in converters has become one of the important development directions for optimizing converter steelmaking technology.
In industrial practice, steel enterprises improve the converter scrap ratio by developing converter heat efficient utilization technology.
On the one hand, to increase the heat income of converter smelting, measures mainly include increasing the temperature of molten iron, preheating scrap steel, converter slag operation, secondary combustion technology, fuel addition technology, converter bottom powder spraying technology, etc.;
On the other hand, to reduce the heat expenditure of converter smelting, by developing ladle covering and iron ladle covering technology and improving the compactness of production organization and smelting operation level, heat loss during transportation can be reduced.
In theoretical research, the melting rate of scrap steel is the key factor that limits the converter to increase the scrap steel ratio.
Some studies have pointed out that the melting of scrap steel in the iron-carbon molten pool is a continuous phase change process in which the melt carburizes the scrap steel surface to reduce the melting point of the scrap steel, causing the carburized layer to melt, thereby generating a new surface.
The melting of scrap steel occurs due to the generation of temperature and concentration boundary layers on the surface of molten iron and scrap steel, which is affected by the coupling of heat and mass transfer between molten iron and scrap steel.
In order to further clarify the melting mechanism of scrap steel, the carburization phenomenon of the organizational changes of scrap steel melting under different working conditions was analyzed. The figure shows the scrap steel temperature distribution through numerical simulation, the scrap steel melting behavior simulated by water, the scrap steel melting morphology simulated by heat, and the interface carbon concentration distribution during the scrap steel melting process.
Considering the properties of scrap steel, the shape, size and carbon content of scrap steel affect its melting time in the converter: increasing the carbon content and specific surface area of scrap steel can promote the melting of scrap steel; some scholars pointed out that the stacking density of scrap steel also affects the melting state of scrap steel. When the porosity of scrap steel is 0.82, the melting time of multi-grade scrap steel is the same as that of single scrap steel. In addition, some scholars pointed out that the silicon content of scrap steel is inversely proportional to its melting rate in the converter.
From the perspective of the converter molten pool, the composition, temperature and dynamic conditions of the converter molten pool affect the heat and mass transfer between scrap steel and the molten pool.
Some scholars believe that increasing the carbon content, temperature and stirring intensity of the molten pool can accelerate the heat and mass transfer between scrap steel and the molten pool, thereby reducing the melting time of scrap steel:
Increasing the molten pool temperature by 50°C or increasing the carbon mass fraction of the molten pool by 0.6% can increase the melting rate of scrap steel by 1mm/min, as shown in Figure 5a.
In addition, the distribution mode of scrap steel and the gas supply flow rate have a direct impact on the mixing time and flow characteristics of the molten pool. The uniform distribution and tilted distribution of scrap steel shorten the mixing time by 20%~40% compared with the concentrated distribution; the bottom blowing flow rate increases from 15 L/min to 50L/min, and the volume ratio of the low-speed zone decreases by 89.46%.
As shown in Figure 5b and Figure 5c, the distribution mode of scrap steel when numerical simulation and physical simulation are used respectively.
