In the current era of rapid industrialization, steel is an important raw material for industrial production. How to reduce material consumption while meeting demand is the main development direction of technological innovation in the steel industry at this stage. For this reason, after continuous exploration and practice by scientific researchers, the high-speed continuous casting process came into being. In view of this, high-speed continuous casting technology emerged. This article is mainly based on the difficulties of high-speed continuous casting of low carbon steel slabs, and systematically analyzes its continuous casting process technology, in order to lay a good foundation for the sustainable development of the industry.
Keywords: conventional low carbon; high speed continuous casting; process difficulties; technical analysis
Analysis of the difficulties in the high-speed continuous casting process of conventional low carbon steel slabs
Simply put, as a comprehensive and systematic technical means, high-speed continuous casting closely cooperates with steelmaking, refining, continuous casting and rolling processes. Although it has reduced equipment construction investment and personnel losses to a certain extent, increased enterprise output, and shortened material operation time, at the same time, there are also the following problems that need to be solved urgently.
Increased risk of bonded steel breakouts
In the high-speed continuous casting process, due to the increase in rotational speed, although the material reaction time can be effectively shortened, at the same time due to the reduction in mold powder consumption, the friction coefficient between the billet shell and the copper plate will increase compared with the traditional process. In addition, the solidification billet shell of the high-speed continuous casting mold becomes thinner and the strength of the billet shell weakens, which significantly increases the risk of bonding and steel breakage.
Increased incidence of central segregation and internal cracks
In the current industrial production process, high-speed continuous casting, as a modern production technology, is of great significance in improving the quality and efficiency of industrial production. But it is undeniable that due to the increase in drawing speed, the solidification time will be extended. When the belly bulge increases, it also leads to central segregation and internal cracks. And compared with traditional construction techniques, the incidence of this problem has increased exponentially.
Increased risk of linear defects in rolled plates
Compared with traditional process technology, the implementation of high-speed continuous casting process causes the crystallizer liquid level fluctuation and surface flow rate to be more severe. At the same time, coupled with the increase in pulling speed, the residence time of inclusions in the crystallizer is shortened. In the long run, the removal quality of certain internal impurities will be affected, which will increase the risk of gate linear defects and at the same time, the overall development of the country will inevitably be affected to a certain extent.
Analysis of high-speed continuous casting technology of conventional low carbon steel slabs
Strong cooling capacity crystallizer technology
During continuous casting operations, the molten steel discharged from the nozzle in the mold undergoes a solidification reaction. A primary green shell with a certain thickness is formed to resist the static pressure of molten steel. However, during the high-speed continuous casting process, the thinning of the billet shell leads to the incidence of steel breakouts, which in turn leads to a series of problems. The “strong cooling capacity crystallizer technology” is mainly used to increase the thickness of the primary green shell. In the process of applying strong cooling capacity crystallizer technology, in order to ensure the maximum application benefits, staff of grassroots industrial organizations and relevant departments need to do the following work : Control the thickness of the copper plate of the crystallizer, reasonably adjust the cooling at the fixing bolts, and increase the flow and speed of the cooling water. Only by ensuring the smooth progress of the above work can we ensure that the application benefits of “strong cooling capacity crystallizer technology” can be maximized.
High-speed continuous casting slag entrainment control technology
Mechanism of crystallizer slag entrainment
By using physical simulation to systematically study the mechanism of mold slag entrainment, it was found that there are five main methods for controlling slag entrainment in high-speed continuous casting: Shear slag entrainment (the stream hits the narrow surface and runs upward along the narrow surface, pushing the molding slag to move near the nozzle), vortex slag entrainment (asymmetric flow field on the left and right sides of the nozzle), unsteady slag entrainment (surface of molten steel Caused by unsteady flow), negative pressure slag entrainment (the high-speed steel flow at the nozzle outlet sucks liquid molding slag along the outer wall of the nozzle) and bubble slag entrainment. After analysis of a large amount of survey data, it is proposed to use the liquid level fluctuation index “F number” to evaluate liquid level fluctuations. Specifically, the relationship between the F number and the defect incidence rate of cold rolled coils is:
Among them, ρ is the density of molten steel, QL is the volume flow rate of molten steel, ve is the velocity of the molten steel stream hitting the narrow surface of the mold, α is the angle of the molten steel stream hitting the narrow side, and D is the distance between the impact point of the stream and the meniscus.
Research on high-speed continuous casting immersed nozzle
In the process of high-speed continuous casting, in order to ensure the maximum benefit of the continuous casting process. Grassroots industrial organizations and relevant departments also need to increase research on high-speed continuous casting immersed nozzles. The main reason is that the immersed nozzle structure is one of the few parameters that is easy to change during the continuous casting process and has a profound impact on the flow field of the mold. After analyzing a large amount of research data, it can be seen that the number of outlet holes, outlet angle, bottom shape, and outlet shape are the main components of the immersed nozzle structure. Through continuous exploration and practice, we can learn that the use of large-angle nozzles is beneficial to reducing liquid level fluctuations and the risk of slag entrainment in high-speed continuous casting molds, and that the use of concave bottom nozzles is beneficial to reducing liquid level fluctuations and the probability of slag entrainment.
High-speed continuous casting mold electromagnetic metallurgy technology
High-speed continuous casting mold electromagnetic metallurgy technology adds an AC magnetic field to the upper magnetic field based on the second generation. At present, the implementation of this continuous casting process can provide 3 modes, namely DC, AC and combined mode. DC mode: Both the upper and lower coils are supplied with DC power, similar to FCMold. AC mode: Only the upper coil is powered by AC power. When used at low pulling speed, a rotating flow field is formed on the meniscus to wash away the inclusions on the solidification front and improve the surface quality. Combined mode: The upper coil is supplied with AC power, and the lower coil is supplied with DC power, which can reduce the flow impact depth and increase the meniscus temperature.
In short, under the new market economic normality with the continuous advancement of industrialization reform at this stage, as the scale and quantity of the steel industry continue to increase, in order to fundamentally increase metal production while reducing energy consumption, high-speed continuous casting technology will be put into practice in the steel industry production, it is currently an important strategic means to promote the sustainable development of the industry.