In addition to reducing the oxide and sulphide content of liquid steel, calcium treatment improves the workability of free machining grades by transforming hard Al2O3 inclusions into softer calcioaluminosilicates. The kinetics of the inclusion modification process is important in determining hot workability.
The time required to modify solid Al2O3 inclusions into C12A7 was found to increase with the inclusion radius. This is the limiting link in the modification process.
The present invention relates to a steel ladle deoxidizer comprising a core made of solid metal calcium and a protective paper. It has high efficiency and less consumption compared with the conventional method of adding calcium powder or CaSi lumps into the steel melt.
The size, number and morphology of calcium aluminate inclusions in the molten steel after calcium treatment can be controlled by varying the aluminum content in the cored wire. The aluminum enables solute diffusion in the liquid calcium aluminate layer to modify inclusions into 12CaO*7Al2O3 inclusions, thereby reducing their average diameter and enhancing their inclusion number density.
Three heats of laboratory experiments were performed to reveal the evolution of calcium aluminate inclusions after aluminum addition. The results showed that the modification time of inclusions with a 1 mm radius took the longest, followed by those with a 2 mm radius and then those with a 3 mm radius. This result was in agreement with the prediction based on the model.
Various types of cored wire are used in the steel industry. They are capable of providing a number of benefits, including lower oxidation and higher impact strength. They can also reduce silicon deposits in the final weld. However, it is important to ensure that the resulting cored steel has been properly purified. The presence of impurities such as sulphur and oxygen can have negative effects on the final weld.
In the present paper, experimental data obtained from three heats of a steel melting experiment are analysed. The evolution of the inclusions is monitored by the analysis of their composition, size, and morphology using scanning electron microscopy. The kinetics of the modification of the inclusions is studied by modelling the reaction process at the liquid calcium aluminate layer.
The experimental results show that the maximum calcium recovery can be achieved by controlling the injection speed. In addition, a correlation is found between the calcium recovery and physically sound dimensionless numbers such as the Biot number and bath temperature.
The calcium-inclusions have a high capacity to absorve sulfur. During steel solidification, the concentration of sulfur decreases in the inclusions and the remaining sulfur atoms precipitate in the form of calcium sulfide. This reaction is slow and takes place in the presence of CaSi, which acts as an activator.
The kinetic model predicted that the modification time of the Al2O3 inclusions is proportional to the square of their radii. The model also indicated that the smallest radii were modified first. It took about six times longer to modify large radii. The complete modification of the inclusions into the C12A7 liquid phase was a function of the concentrations of Al, Ca, and sulfur in the steel melt.
The kinetic model provides the basis for an improved deoxidizer and desulfurizer for molten steel. Using cored wire, alloy powders can be injected deeper into the steel melt. This reduces the reaction with air and slag and increases the absorptivity of metallurgy additives. It also helps avoid nozzle clogging in cast aluminum killed steel and improves the quality of the resulting casting.
Solid calcium cored wire, which is also called pure calcium cored wire, is used in the refining process outside the furnace of iron and steel enterprises for the purpose of deep reducing oxygen and sulfur in liquid steel. It is also widely used in apricot gold, desulfurization and creeping treatment of cast iron.
During the calcium treatment process, the sulphur and nitrogen present in the liquid steel are converted to sulphide and oxide. The inclusions in the steel become molten calcium aluminates and silicate, and the size of the inclusions decrease due to their surface tension effect.
Our company produces solid calcium cored wire through the whole production line: strip steel wrapping, high-frequency anhydrous welding, fine shaping and intermediate frequency annealing. This equipment can produce metal calcium cored wire with high quality and long storage life. Our product has a lot of advantages compared with other cored wires, such as more sulfur and oxygen removal, lower consumption and the ability to be used for producing different steel grades.
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