Specialized metallurgical processes – compositions for use therei – Compositions – Solid treating composition for liquid metal or charge
Reexamination Certificate
2000-04-10
2002-04-16
Andrews, Melvyn (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Compositions
Solid treating composition for liquid metal or charge
C075S316000, C420S022000, C420S023000
Reexamination Certificate
active
06372014
ABSTRACT:
The present invention relates to a composition of an agent and a method for the treatment of molten ferrous metal, and more particularly to a magnesium-containing agent and method for the treatment of molten ferrous metal.
BACKGROUND OF THE INVENTION
Cast iron is primarily an iron alloy that contains carbon and silicon. Wide variations of the properties of cast iron material can be achieved by varying the amount of carbon and silicon, and by adding various metallic alloys to the cast iron. Commercial cast irons include gray, ductile, malleable, compacted graphite and white cast iron, among others. With the exception of white cast iron, the cast iron steels have a common micro-structure that consists of a graphite phase and a matrix that may be ferritic, pearlitic, bainitic, tempered martensitic, or combinations thereof. Gray iron has flake shaped graphite, ductile iron has nodular or spherically shaped graphite, compacted graphite iron (also called vermicular graphite iron) is intermediate between these two, and malleable iron has irregularly shaped globular graphite that is formed during tempering of white cast iron. White cast irons do not have any graphite in the microstructures, but instead the carbon is present in the form of cementite (iron carbide). Cast irons are also classified as either unalloyed cast irons or alloyed cast irons. Unalloyed cast irons are essentially iron-carbon-silicon alloys with only trace amounts of other elements. Alloyed cast irons are considered to be those casting alloys based upon iron-carbon-silicon systems that contain one or more alloying elements that are intentionally added to enhance one or more useful properties of the cast iron.
In the production of ductile and compacted graphite cast iron, pure magnesium or alloys having varying amounts of magnesium are added to molten cast iron. The addition of the magnesium to the cast iron improves the strength properties of the cast iron by modifying the graphite matrix in the cast iron. Various techniques can be used to introduce the magnesium into the cast iron. Small particles of pure magnesium can be directly added to the molten cast iron. The magnesium particles can be plunged into a ladle of the molten cast iron. Injection of the magnesium particles through a lance can be used, but this method requires large volumes of transport gas, otherwise the magnesium particles melt prior to being injected into the molten cast iron thus resulting in the plugging of the lance. The large volumes of transport gas can cause severe splashing, rendering the process impractical. The addition of magnesium particles on the surface of the molten cast iron is generally not used since much of the magnesium vaporizes before it can modify the cast iron. Magnesium has a boiling point of about 2025° F. The cast iron in the ladle or melting pot is generally maintained at about 2300-2850° F. As a result, the magnesium rapidly vaporizes on contact with the molten cast iron and vaporizes into a gas without modifying the cast iron. Several methods have been developed to increase the recovery of the magnesium on the cast iron. For example, one method involves magnesium deposited on the bottom of the melting pot or ladle and then being covered with reaction retarding steel plates, whereupon the iron is poured over the magnesium. Other methods require similar cumbersome preparation.
The most common method for producing ductile and compacted graphite cast iron alloys is to add ferrous metal alloys that include magnesium into the molten cast iron. The ferrous metal alloys typically are made of iron, silicon and magnesium so as to not introduce any undesired substances into the cast iron. The ferrous metal alloy is introduced in solid form into the molten cast iron. The ferrous metal alloy slowly melts in the molten cast iron and the magnesium in the ferrous metal alloy is recovered in much higher percentages than compared with adding pure magnesium to the cast iron.
The ferrous metal alloy is commonly made by smelting liquid ferro-silicon alloys in dedicated furnaces and then tapping the liquid ferro-silicon alloys in transport ladles and adding metallic magnesium in the form of large ingots in the liquid bath in an amount sufficient to obtain the desired magnesium content in the ferro-silicon alloy. Another common method used to add magnesium to the ferro-silicon alloy is to add the metallic magnesium in the form of cored wire with the metallic magnesium contained in a rod formed by a steel sheath. In each of these production methods, the liquid bath and the transport ladle must be stirred, by mechanically stirring the bath with the addition, and/or by stirring with inert gas injected through a porous plug within the ladle and/or through a lance submerged into liquid bath. After the desired amount of magnesium is obtained in the ferro-silicon alloy, the liquid ferro-silicon is poured out of the ladle for solidification for further use by the gray iron foundries. Another method used to add magnesium to molten ferro-silicon alloy is the injection of magnesium granules through a refractory lance. Besides delivering the magnesium directly to the bottom of the bath, at the end of the injection lance, the injection method enables the user to add other alloy fines as a blend with the magnesium granules. However, experience with injection of magnesium into molten pig iron in the steel industry has shown that unless large quantities of transport gas are used, magnesium particles injected alone, without any carrier material, will tend to melt inside the lance, thus plugging the transport pipe, resulting in much lost time and expense in the unplugging of the lance. Unfortunately, the carrier materials used for the injection of magnesium into molten pig iron, for example lime and/or calcium carbide, can also introduce unwanted contaminants into certain grades of ferro-silicon alloys.
In view of the present methods for the formation of magnesium-ferro-silicon alloys for the subsequent use in the alloying of cast iron, there is a need for an improved method and additive for the formation of magnesium-ferro-silicon alloys which results in increased amounts of magnesium alloying and which simplifies the alloying process and reduces the costs and wastes associated with the formation of the magnesium-ferro-silicon alloys. Moreover, these treatment agents and methods used for introducing magnesium into the molten ferrous metal, ferro-silicon, can also be applied for the treatment with magnesium of the molten ferrous metal, cast iron, for the production of ductile cast iron.
SUMMARY OF THE PRESENT INVENTION
The present invention overcomes the problem with adding magnesium particles by the injection of magnesium particles alone into the ferro-silicon alloys by using an improved mixture of treatment particles. The present invention also simplifies the alloying process, eliminates the need for adding possible contaminates to the magnesium-ferro-silicon alloy, improves the amount of alloying of the magnesium in the ferro-silicon alloy, and/or reduces the amount of waste associated with the production of the magnesium-ferro-silicon alloy. However, the invention has broader applications in that the treatment particles can be directly added to molten iron to alloy and/or desulfurize the molten iron without the use, or in combination with the use, of a magnesium-ferro-silicon alloy.
In accordance with the principal aspect of the present invention, magnesium particles are injected into a ferro-silicon alloy by a lance to alloy a desired amount of magnesium in the ferro-silicon alloy. The melting of the metallic magnesium in the transport pipe of the lance is inhibited or overcome by mixing the magnesium particles with high melting temperature particles. The high melting temperature particles are designed to absorb heat as the high melting temperature particles and the magnesium particles are transported through the lance and into the ferro-silicon alloy. The absorption of heat by the high melting temperature particles inhibits or prevents the magnesium
Bieniosek Thomas H.
Fahey Jerome P.
Andrews Melvyn
Rossborough Manufacturing Co. L.P.
Vickers Daniels & Young
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