The present invention relates to a cored wire comprising a solid calcium inner core wire encased in an aluminum sheath. The sheath is closed by a lock seam as shown in FIGS. 3a, 3b and 3.
Powder addition creates splashing and reactivity in the steel ladle which causes problems for the steelmaker. The cored wire alloy addition method eliminates these problems and improves the deoxidation, desulphurisation and inclusion modification.
Used as a composite deoxidizer and desulfurizer, calcium silicon manganese steel can reduce the amount of iron-based slags produced during smelting of iron or ferrous metals. Its reactivity with oxygen and sulfur greatly improves the quality of molten steel, reduces smelting costs, shortens the smelting time and helps to control the content of easily oxidized elements and non-metallic inclusions.
In the cored wire of this invention, a calcium alloy is contained within a steel liner that is covered with paper. The application of the paper delays the temperature increase due to the melting of the calcium core and prevents it from reoxidizing in the liquid steel bath and increasing its reactivity.
The cored wire of this invention is capable of being immersed in a liquid steel ladle at a much greater depth than conventional cored rods. This allows the steel powders to be introduced into the molten steel more efficiently and completely, avoids reaction with air and slag and increases absorptivity of metallurgical additives. It also eliminates abrasion of the aluminum strip, thereby reducing surface damage and surface oxidation.
The composite core wire of the invention consists of a solid calcium metal core encased in an aluminum strip and steel liner to form a composite deoxidizer or desulfurizer. This invention eliminates many of the problems encountered in introducing calcium into a ladle of molten iron. These include reactivity which is often unacceptable due to limitations in ladle free board, powder blends that result in inconsistent results and nonmetallic inclusions which are undesirable for the final steel product.
The outer jacket or sheath may be present in an amount, by weight per unit length of the cored wire, between 15 and 85% of the total wire weight. Wires with a steel jacket of greater than 15% are difficult to handle and do not permit the desired alloying of the calcium and aluminum in the core. On the other hand, a jacket too low in steel content provides inadequate protection to the cored wire. Numerical simulations show that the outer layers of paper encasing the cored wire serve as thermal insulators and delay the increase in temperature by about 0.7 seconds compared with the reference wire which is not protected by any paper (curve 21 a). This delay allows a larger amount of cored material to be introduced into the molten iron than would be possible with a reference wire alone.
Deoxidation and control of inclusionary state are very important operations for steel fabricators, which require a high level of know-how. However, they also represent complex operations that are susceptible to a variety of pitfalls, particularly splashing and reactivity of calcium metal.
The present invention provides cored wire with the advantage of reducing such problems. This is achieved by using a composite calcium wire covered with a jacket of aluminum. The ratio of the two components can be controlled, allowing for precise control of the reactivity of calcium metal.
In addition, this type of cored wire allows for much faster deoxidation. This is due to the fact that the reactivity of calcium metal can be reduced by incorporating a significant quantity of manganese. This can lead to the formation of less noxious oxides, which are more likely to adhere to the internal walls of flow regulation nozzles in continuous casting machines and thus prevent them from being blocked. This is also true for reoxidation, which can occur in the presence of alumina inclusions or manganese sulfides (MnS). This is due to the chemical affinity of these elements for oxygen.
In the steel industry calcium silicon alloys are used as deoxidizers and desulfurizers. They can remove oxides, sulfides and impurities in the electric arc furnace steelmaking process, decrease oxygen content, change the form of steel impurities and improve the quality of finished products.
It has good corrosion resistance in most reagents except those which attack aluminum, e.g., copper and iron which reduce corrosion resistance significantly. Corrosion resistance is improved by adding manganese and chromium. It has good corrosion resistance in diluted acid, alkaline solutions and steam.
It is difficult to inject solid calcium metal into a ladle of molten steel due to its high reactivity, especially at the temperature at which the liquid steel bath melts. Cored wire is a new technology that enables calcium to be injected into the molten steel bath. The present invention provides a core composite comprising a solid calcium metal core encased in a sheath of another reactive metal such as aluminum. A mechanical lock seam is employed to close the sheath. The sheath is inserted smoothly into the molten steel and melted therein to produce a chemical reaction. It avoids reaction with air and slag, increases element yield and improves the quality of steel.
In addition to the good tensile and toughness properties of this alloy it has excellent wear resistance. Its low machinability is due to its high silicon content and relatively soft matrix; phosphorus additions decrease the machinability but iron, nickel, boron, silver and zirconium additions improve it.
The present invention reduces the splashing and reactivity of calcium metal introduced into a bath of molten steel by providing a cored wire consisting essentially of a solid calcium core surrounded by an outer sheath or jacket of aluminum. The core composite is continuously roll formed into a tube with a mechanical lock seam so that the reactive calcium metal is encapsulated or locked inside.
The insertion of the cored wire into the molten steel ladle causes it to melt in a proper position for a physicochemical reaction with the metallurgy additives. This avoids reaction with air and slag and increases element yield. Furthermore, the treatment of the steel with calcium changes the shape of inclusions, so that they do not clog continuous caster nozzles. This leads to better fatigue resistance.
English
Write a Message