US3372022A - Process for alloying metallic melts - Google Patents

Description

3,37Z,fiZZ Patented Mar. 5, 1968 8 Claims. (51. 7s z7 This invention relates'to a process for preparing alloyed metallic melts, particularly iron and steel melts, using alloying materials which preferably have a melting point above the casting temperature.

In the production of iron and steel materials, it is known to prepare alloys by the addition of high purity metals, such as for example, molybdenum, vanadium, tungsten, chromium, nickel, and the like, which alloys are distinguished from unalloyed materials as a result of the special properties they possess. The action of the alloying elements may consist, for example, in influencing critical cooling velocity, in the capability of forming special carbides, in the separation-hardening behavior, or also in an inoculation effect. By the addition of alloying materials, it is possible to obtain definite economic improvements of specific properties, for example, wear and tear resistance, volume stability, heat resistance, scaling resistance, corrosion resistance, and the like. The amount of the alloying material employed is influenced by considerations of manufacting, further processing, and treatment of the steels in order to obtain the full exploitation of the advantages of the alloy. Particularly in highly alloyed melts, the particular properties of the alloy must be considered at the time of the preparation or manufacture thereof, and treatment thereof.

The choice as to the method of manufacture depends generally upon the intended application and the requirements resulting therefrom. For example, steels used for mass produced goods, such as rails, are produced in a Thomas converter or in a Siemens-Martin furnace having a high capacity. In accordance with the various methods of manufacture and the quantity of the alloying constituents, various alloying techniques have been found to be particularly suitable. The selection of the alloying technique is generally determined by the melting temperature and the solubility of the alloying elements.

In a technique presently known, alloying of the melt is effected in a known manner either by adding the elements in the pure form thereof or in the form of readily meltable ferro-al-loys.

When alloying cast iron with molybdenum, for example, small amounts of ferromolybdenum up to approximately 0.5 percent by weight molybdenum may be dissolved in the pan despite the high melting point thereof. Using sufficiently comminuted ferromolybdenum it is possible to dissolve from 1 to 1.5 percent by weight molybdenum in very hot iron. In a cupola blast furnace, the waste of molybdenum may be maintained below about 10 percent by weight. If molybdenum is added in a flame furnace or in an electric furnace about 10 to minutes prior to tapping, the waste may be maintained at from 4 to 8 percent by weight, if the charge is properly handled. For chilled roll iron, it is known to premelt ferromolyb denum with some crude iron or specular cast iron and add it to the pan in the liquid form thereof, whereby the waste may be considerably reduced. Molybdenum also may be added in the flame or electric furnace directly as the oxide thereof or also in the form of calcium molybdate, for example. Furthermore, it is known to add pulverized ferromolybdenum to the pan since it dissolves easily.

For the manufacture of steel, the addition of molybdenum may be made, in a Siemens-Martin furnace, in the form of an ore such as calcium molybdate with a waste of about 10 percent by weight, or in the form of ferroalloys. It is also known to add molybdenum sulfides to the iron so that elemental molybdenum is formed therein by reduction and a sulfur concentration is effected, for example during the preparation of rust-free chromiummolybdenum alloys containing from 13 to 15 percent by weight of chromium which are intended for processing on automatic equipment.

An alloy of vanadium and cast iron may be made, for example, by the addition of high purity ferrovanadium in the cupola furnace and the waste may be reduced by employing readily soluble ferrovanadium alloys. When manufacturing austenitic cast iron, it is also known to employ two cupola furnaces, a smaller furnace serving for melting down the alloying metals and both metals are tapped in the liquid form thereof in the same pan. For steel, vanadium is generally alloyed in the pan.

For alloying iron with tungsten, a low-carbon ferrotungsten alloy preferably is used which dissolves relatively easily in iron despite the high melting point thereof. When making tungsten steels which are produced in acid as well as basic Siemens-Martin furnaces, and particularly also in electric furnaces, tungsten is added in the form of ferrotungsten. T ungsten-containing scrap preferably is melted only in electric furnaces which reduces the slag produced during the melting-down process, thereby avoiding unnecessary losses. For reasons pertaining to alloying techniques, induction furnaces have, in such case, advan tages compared to electric arc furnaces.

The manufacture of chromium and chromium-nickel steels is generally effected both in the Siemens-Martin furnace and in the electric furnace. Since chromium is more readily oxidizable than iron, the addition'of chromium is made after a preliminary deoxidation by other deoxidizing agents. In order to prevent an unnecessary loss, the electric furnace is best suited for the preparation of steel of high chromium content and for the use of high chromium or chromium-nickel-containing scraps. The alloying process with chromium generally is effected with the latter in metallic form. It is possible, however, also to employ chromium ore which is mixed with reducing agents such as aluminum or silicon. In such case, it is difficult, however, to produce alloys containing more than 12 to 13 percent by weight of chromium.

In low-chromium cast iron grades, the chromium addition conventionally is effected in a cupola furnace since ferrochromium is only difiicultly soluble in liquid cast iron. In such case, chromium waste of from 10 to 25 percent by weight must be expected, depending upon the amount of the addition and the manner of operation of the furnace. A ferrochromium as low in carbon as possible is employed as a pan addition.

It is also known to add alloying elements, preferably in the for-m of ferroalloys or prealloys, to the deoxidized melt prior to tapping, to liquefy the alloying metals in separate furnaces and add the same to the melt in the liquid form thereof, to concomitantly melt them down directly in the furnace, or also in the spout, or to add them to the casting jet emerging from the furnace or forehearth.

All of these prior art alloying techniques have, however, specific disadvantages which include, for example, the fact that the elements must generally be converted, for alloying purposes, into low-melting ferroor prealloys or they must be premelted in separate furnaces to be added in liquid form, which results in undesired waste losses. When the high-melting alloying constituents are added in solid form, overheating of the melt generally is required to compensate for the heat losses resulting from the heat required to melt the solid material and the necessary standing time.

The present invention provides a process for preparing alloyed iron and steel melts using alloying materials which preferably have a melting point above the required casting temperature. In the present process, the alloying materials are melted down by exothermically-reacting masses, such as aluminothermic masses, and are added to the melt in liquid form.

The process of the present invention may be performed in difierent ways. It is possible to admix with an exothermically-reacting aluminothermic mass, such as a mixture of aluminum powder with a heavy metal oxide, for example iron oxide, the alloying elements being either pure or in the form of a compound, for example as ferroor prealloys, and ignite the mixture in a reaction crucible whereby the alloying elements are melted down by the reaction products and then, after completion of the re action, are tapped into a pan simultaneously with the deoxidized and refined melt. It also is possible to perform the reaction of the aluminothermic masses, intermixed with the alloying agents, directly in the pan or the alloying elements may be melted down by pouring the aluminothermically-produced superheated metal thereover and the resulting melt is added to the melt to be alloyed as concentrated alloy, in any desired manner.

It is known in the foundry technique to employ exothermic masses, for example for purposes of heating risers or ingots, or heating inserts in molds or for exothermically-reacting additional packs or melts. It is also known to use aluminothermically-produced steel for welding purposes, in which case the amount of alloying elements added depends upon the heat content of the melt which is still present after the elements have been melted down and which must be sufiicient for safely melting the Workpieces to be welded and for uniformly connecting the same.

The known uses of exothermic, particularly aluminothermic masses, in foundries, accordingly involve agents which are employed either in solid or loose form and act directly upon the melt and, thus, influence the process of solidification or else involve masses the characterizing properties of which are utilized for welding purposes.

In the process of the present invention, no direct influence or action on the melt by the exothermically-reacting mass, particularly aluminothermic masses, is effected but, instead, the heat which is liberated during the reaction is entirely utilized for liquefying the alloying elements, whereby a highly concentrated alloy melt consisting of the aluminothermically-produced metal, preferably of iron and the alloying elements, is produced which is added in liquid form to iron or steel melts prepared according to any desired processes.

Using the process of the present invention, high-melting alloying elements can be melted, particularly those having a melting point above the casting temperature, in both th pure form thereof as well as in the form of ferroalloys or prealloys, without using melting furnaces for liquefying the alloying elements, while eliminating unnecessary overheating of the melt and unnecessary standing times, while reducing Weight losses, and while increasing the accuracy of the alloy content of the iron or steel to be alloyed.

The invention will be further illustrated by reference to the following specific examples:

Example 1 20 kilograms of molybdenum are mixed with 40 kilograms of a mixture of 76 percent by weight of iron oxide and 24 percent by weight of aluminum. The mixture is charged into a reaction crucible, lined with magnesite, and the mixture is then ignited whereupon the aluminothermic reaction begins. As a result of the heat liberated, the mixture is melted and a homogeneous iron-molybdenum melt is produced which is covered by a slag primarily consisting of aluminum oxide. After the completion of the reaction, which lasts approximately 60 seconds, the melt is added to an iron or steel melt to be alloyed.

Example 2 Following the procedure of Example 1 above, a melt consisting of molybdenum and iron is produced directly in a casting ladle. The iron or steel melt to be alloyed is then added to the liquid molybdenum-iron alloy. The slag which is produced during the aluminothermic reaction and which primarily consists of aluminum oxide, 001- lects on the melt of the alloyed iron or steel and is drawn off from the surface of the resulting alloy melt.

Example 3 22.22 kilograms of a commercial iron-molybdenum alloy containing percent by weight molybdenum is mixed with 44.44 kilograms of an aluminothermic mass consisting of 76 percent by Weight of iron oxide and 24 percent by weight of aluminum. This mixture is charged into a reaction crucible and ignited. The molten alloy produced by the aluminothermic reaction is added to an iron or steel melt to be alloyed.

It will be obvious to those skilled in the art that many modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.

What is claimed is:

1. A process for preparing an alloyed metallic melt which comprises melting at least one alloying material with an exothermically-reacting mass and adding the molten material to the melt.

2. A process according to claim 1 in which the alloying material has a melting point higher than the casting temperature of the melt.

3. A process according to claim 1 in which the exothermically-reacting mass is an aluminothermic mass.

4. A process according to claim 1 in which the alloying material is employed in elemental form.

5. A process according to claim 1 in which the alloying material is employed in the form of a compound.

6. A process according to claim 1 in which a mixture of the alloying material and an aluminothermic mass is ignited in a reaction crucible and the resulting melt is tapped into a pan simultaneously with the metallic melt to be alloyed.

7. A process according to claim 1 in which a mixture of the alloying material and an aluminothermic mass is ignited in a pan to form an alloying melt and the metallic melt to be alloyed is then tapped into the pan.

8. A process according to claim 1 in which the alloying material is melted by pouring aluminothermicallyproduced metal thereover to form a concentrated alloy which latter is added to the metallic melt to be alloyed.

No references cited.

BENJAMIN HENKIN, Primary Examiner.

Claims (1)

1. A PROCESS FOR PREPARING AN ALLOYED METALLIC MELT WHICH COMPRISES MELTING AT LEAST ONE ALLOYING MATERIAL WITH AN EXOTHERMICALLY-REACTING MASS AND ADDING THE MOLTEN MATERIAL TO THE MELT.