US1913833A - Method of producing and refining tungsten steel - Google Patents

Description

Patented June 13, 1933 UNITED STA ANTHONY G. DE GOLYER, OF NEW YORK, N. Y.

METHOD OF PRODUCING AND REFINING TUNGSTEN STEEL No Drawing.

This invention relates to a method for producing and refining tungsten alloy steels and relates particularly to a method for producing and refining tungsten steels by the direct smelting of ores.

The general practice for manufacturing tungsten steels, especially the grades known as high speed steels, heretofore has required the intermediate manufacture of metallic tungsten either-in the form of tun sten metal powder or as a ferro alloy containing 60 to 80% tungsten. In addition to the cost of making tungsten metal or ferro tungsten,

there are unavoidable losses of tungsten in the the manufacturing processes. Consequently many efforts havebeen made to develop a method for smelting ores directly in the steel bath to form a final tungsten steel. However, the great majority of tungsten ores available contain appreciable'percentages of one or more harmful impurities. By the terms harmful impurity and harmful impurities used herein and in the appended claims I intend any one or more of the elements phosphorous, arsenic, tin, sulphur or copper when present in tungsten ore in a percentage or percentages equal to or greater than the maximum percentage or percentages of such element or elements allowable in the specifications for the particular steel being produced.

ft is generally known that if ore containing an appreciable percentage of any one or more of these harmful impurities is introduced into a\steel bath for the purpose of adding material quantities of tungsten to the steel, the removal of sufficient of the impurities to bring the composition of the steel within the specifications, by methods previously proposed, has either been impossible or so costly as to prohibit the use of such ores. Therefore, it has not been possible heretofore to make general use of tungsten ores for directv smelting in the final steel.

Application filed December 18, 1930. Serial No. 503,240.

ores and relatively inexpensive calcium tung state. Furthermore, this process obviates the necessity of producing ferro tungsten or tungsten metal powder.

I have found that by introducing into a steel bath both tungsten ores containing appreciable amounts of harmful impurities, such as Wolframite, and also calcium tungstate, either substantially free from, or containing relatively small percentages of harmful impurities; and effecting reduction of the tungsten in both the impure ore and the calcium tungstate in the manner herein- 4 after described, that virtually all of the tungsten in the impure ore and in the calcmm tungstate is reduced to the metallic form and alloys or otherwise combines with the components of the bath, and the resultant: steel contains the desired percentage of tungsten and less than the allowable maximum percentages of harmful impurities. Furthermore, tungsten produced directly in the bath according to the present process is more readily soluble in the steel than tungsten in ferro tungsten or tungsten metal, consequently the resultant steel is more uniform in composition.

In the production and refining of tungsten steel by this process it is essential that a major portion of the tungsten in ores containing harmful impurities should be reduced simultaneously with, or prior to the reduction of the tungsten in the calcium tungstate. The reason for this, I have discovered, is that when calcium tungstate is reduced in a metal bath the reduction reaction apparently produces metallic tungsten, which enters the bath, and metallic calcium in aphysical condition which renders it particularly active and efficient in reacting with and removing 90 from the bath such harmful impurities as may be present' It should be understood that it is not the objectof the present process to remove all of theharmful impurities, but to reduce theamount of such impurities to 95 percentages required by therspecifications of commercial tungsten steels.

The calcium tungstate employed in carrying out the present processmay be either artificially prepared material, or a natural calcium tungstate, such as Scheelite ore. The use of natural calcium tungstate ore will be governed by the amount of harmful impurities therein and also by the relative ease with which such ore reacts with the reducing agent employed. Experiments I have made indicate that somewhat better results are generally. obtained by employing artificial calcium tungstate rather than Schcelite ores. I have further found that it is not desirable nor economically possible to substitute calcium oxide or other calcium compounds for calcium tungstate, and I wish it to be understood that the operation of this, process requires the use of calcium tungstate as herein described, first, as a source of a portion of the tungsten added to the bath; second, as a source of the calcium or calcium compound which is necessary for, and particularly effective in the removal of harmful impurities.

I am aware that Scheelite ores have previousl been used for the direct addition of tungsten to a steel bath. However, the use of such ores for direct smelting. has been confined to limited quantities of unusually pure ores. The present process provides a means for the general use of all classes of tungsten ores, virtually regardless of the content of harmful impurities, for the direct production of tungsten steel. It is especially adapted to the use of VVolframite and Ferberite ores containingharmful impurities, which classes provide the major source of tungsten.

5 As an illustration of the operation of my present invention I give the following exam-" ple in the production of a steel containing approximately 18% tungsten. The desired quantity of scrap carbon steel and scrap tungsten steel is melted in an electric arc furnace. Approximately one half of the tungsten content of the final steel can be obtained by melting high speed steel scrap. The bath is protected by a slag, the composition of which is suitable for the given operation. When all of the scrap is molten a mechanical mixture comprising tungsten ore, in the form of Wolframite containing harmful impurities, calcium tungstate and a carbonaceous reducing agent, such as coke, is introduced into the bath. It will be understood that the original slag may be removed in whole or in part before the'tungsten ore and calcium tungstate are introduced. Also that the charge mixture of tungsten ore, calcium tungstate and carbon may contain, in addition, material such as silica,flu0rspar,

etc. in order to producea slag. having any particular characteristics. The charge mixture containing tungsten ore and calcium tungstate is introduced in such a manner that it will be heated by the arc, and the carbon or other reducing agent will react with the oxides of tungsten. The volume of slag .which will be formed during the course of -from time to time.

the reduction operation will depend more or less upon the quantity of calcium tungstate used, that is, if the charge contains a lar e percentage of calcium tungstate it may e necessary to remove a portion of the slag The metallic calcium or other calcium material resulting from the reduction reaction will react with a large proportions of the harmful impurities con tained in the Wolframite ore and in general will react with a considerable proportion of harmful impurities which may be contained in the bath resulting from the melting of scrap. Such calcium reaction products readily separate fromthe steel to form a slag. In some cases, in addition to tungsten it is also necessary to add chromium and vanadium to the bath in order to bring the composition of the steel within the specifications for some purposes. Furthermore, it may be necessary to-carburize or decarburize the bath in accordance with the final carbon percentage required. After the various additions have been made and the bath has been raised to proper temperature, the steel is ready for casting in the usual manner.

The present process may be utilized for adding the entireiamount or any portion of the total tungsten required in any given heat of steel.

It will be understood from the foregoing that all or any portion of the tungsten con tained in ore, such as Wolframite, may be introduced into the bath prior to the introduction and reduction of the calcium tungstate. I have found, however, that when using VVolframite ores containing appreciable amounts of harmful impurities that it is usually of advantage to introduce at least a large portion of the ore in such a manner that it is reduced more or less simultaneously with the calcium tungstate. It will be-evident, that some of the tungsten required in the steel may be introduced in ,the form of ferroo tungsten or tungsten metal without departing from the scope of this invention.

I have found that when tungsten ores are introduced into the furnace, in accordance with methods I have outlined, that the-only reducing agent necessary to obtain a virtually complete recovery of the tungsten in the final steel is carbon in such form as coke, charcoal, etc. However, I have found that if I employ a reducing agent which has a higher heat of combination with oxygen than carbon that the effectiveness of the calcium as a purifying agent is appreciably increased. This may be. due to the fact that the temperature of the bath is raised, or to the fact that the calcium or calcium material formed is in a physical condition in which it reacts more readily with the harmful impurities, or to a combination of these or other factors. Consequently I'have found that when the percentages of one or i a reducing agent whichhas relatively high ample, I have found that IVolframite can b be mixed with calcium tungstate and sufii exothermic reaction with W0 As an excient carbon to reduce approximately of the total tungsten in these materials, and a reducing agent such as calcium carbide, silicon or aluminum can be employed to reduce the balance of the tungsten. The proportions of tungsten reduced by means of carbon and other reagents can, however, be varied in accordance with different conditions.

Although my present invention is particularly adapted to the direct smelting of Volframite and other ores containing relatively high percentages of harmful impurities, in some instances it is of advantage to subject \Volframite or other tungsten ores to a preliminary treatment on a magnetic separator with the object of removing a portion of such impurities. Likewise tungsten ores may be subjected to chemical treatment or to roasting before be ng utilized in this process. In general none-0f these operations contemplate nor accomplish the complete removal of harmful impurities, consequently when ores which have been so treated are used for the direct introduction of tungsten into steel it is-necessary or desirable tocarry out the operation in accordance with this process. For example, in the case of an ore containing 1.50% tin or more I have found it to be of advantage in many instances to treat such ore on a magnetic separator in such a manner as to form a product in the nature of a concentrate containing more than half of the original tungsten and less than half of the harmful impurity or harmful impurities, and a second product in the nature of a reject or tailings containing the balance of the tungsten, the

' balance of the harmful impurities and a considerable amount of ganguc or other undesirable material. The concentrate so produced may be used in the operation of the process of the invention. The reject may be further treated on a magnetic separator for the recovery of additional tungsten, or it may be subjected to a suitable chemical treatment for the recovery of tungsten in the form of calcium tungstate which is substantially free from the original harmful impurities in the ore. The

calcium tungstate so produced can be used in accordance with the herein described process. By thus employing magnetic separator treatment or chemical treatment or both I have found that I can utilize \Volframite and other tungsten ores which contain excessively large percentages of harmful impurities. By employing these combined operations, i.e., treatment of the original ore or concentrate on a magnetic separator and the use of the reject therefrom for the production of high grade calcium tungstate. I can recover from 97 to 99% of the original tungsten content of ore in the form of metallic tungsten in tungsten steel and the cost for so obtaining tungsten in the final steel is very much less than the cost by anyother method heretofore proposed.

I wish it to be distinctly understood that the method of operating the present process, as cited above for an example. may be varied and modified within a considerable range without departing from the scope of my invention.

I claim:

1. The method of producing tungsten steel which comprises adding to a steel bath tungsten ore containing harmful impurities, calcium tungstate and reducing agent selected from the group carbon, silicon, aluminum and calcium.

2. The method of producing and refining tungsten steelwhich comprises adding to a steel bath tungsten ore containing harmful impurities and calcium tungstate and reducing agent selected from the group carbon, silicon, aluminum and calcium; and holding while the reducing agent reacts with' the tungsten ore and calcium tungstat-e to produce'metallic tungsten and the calcium resulting from the reduction of the calcium tungstate combines with harmful impurities of the bath.

'3. In the method'of producing and refining tungsten steel by means of adding to a bath of steel containing appreciable amounts of harmful impurities, tungsten ore containing harmful impurities andcalcium tungstate;

the step which comprises reducing the calcium tungstate with a reagent selected from the group carbon, aluminum, silicon and cal cium, whereby the tungsten produced by the reaction enters the steel and the calcium produced by the reaction combines with harmful impurities of the steel and ore.

I Signed at New York in the county of New York and State of New York this 15th day of Dec., 1930.

ANTHONY G. DE GOLYER.