US1564139A - Manufacture of alloy steels and irons - Google Patents

Description

Dec. 1 1925- B. D. SAKLATWALLA MANUFACTURE OF ALLOY STEELS AND IRONS 2 Sheets-Sheet 1 Filed April 8. 1924 INVENTOR 2 Sheets$heet 2 INVENTOR W g-aim A4 MW WIN Dec. 1, 1925- B. D. SAKLATWALLA MANUFACTURE OF ALLOY STEELS AND IRONS Filed April 8.

Passed Deal, 19.25.

UNITED STATES 156%??? PATENT OFHE.

BYRAHJI D. SAKLATWALLA, OF GRAFTON, PENNSYLVANIA.

MANUFACTURE OF ALLOY STEELE ANI) IBdNS.

Application filed. April 8, 1924. Serial No. 704,952.

tion.

facture of alloy steels and irons, and more particularly to the reduction of the alloying elements directly from their unreduced compounds or ores and the production of the respective alloy steels or irons without the introduction of excess carbon in the polished steel or iron.

The invention also relates to furnaces for carrying out the process.

In the manufacture of alloy steels or irons under the practice heretofore pnevalent, the alloying elements in the already reduced metallic state, mostly in the form of fer'ro-alloys, are added to a molten bath of steel or iron, for example, to obtain the respective alloy steels thereof, ferro-manganese, ferro-chromium, ferro-titanium, ferrotungsten, ferro-vanadium; ferro-uranium, ferro-molybdenum, ferro-nickel or metallic nickel, and ferro-cobalt or cobalt metal are added to steel in the molten state in the furnace or after it is tapped in the ladle. As the regular commercial grades of such ferroalloys contain an appreclable amount of carbon, this practice introduced an undue amount of carbon in the steel. If special low carbon ferro-alloys are used, the cost is so hi h as to prohibitively increase the cost of t e alloy steel produced. These disadvantages in the use of the ferro-alloys are especially apparent in the case of steels where the content of the alloying element must be high and the carbon content low,

as in the case of the so-called stainless or rustless steels or irons which have a chromium content usually between 9 and 15%, and a low carbon content.

It is not commercially practicable to use the regular high carbon ferro-alloys and then decarbonize the steel after their addition, because the process of oxidation of the carbon is accompanied by oxidation and consequent waste of the valuable alloying elements, this being especially high in the case of readily oxidizable alloying elements, such as chromium.

The present invention relates to the manu-.

Another difiiculty met in the usual meth-- ods of manufacturing alloy steels by the addition of metallic ferro-alloys to molten steel is the phenomenon of segregation. Theferroalloy is added in the solid state in the form of lumps thrown over the surface of the molten steel. This icauses points :of concentration of the alloying element at the location of the lumps. As the ferro-alloy 1s either added to the steel immediately before tapping or in the ladle in order to avoid an undue oxidation of the alloying elements, these points of higher concentration do not ordinarily have sutlicientopportunity to become e ualized over the entire mass of metal by diffusion. Moreover, the ferro-alloys have various constituents of different melting points and degrees of solubility, as, for example, the carbides in the ordinary grades of ferro-allo s. Such carbides have a melting point higher than the remainder of the alloy. When such carbidecontaining alloys are added, the carbide content may still remain in the solid state floating in the melting steel after therest of the ferro-alloy has been completely assimilated. Such undissolved solid particles of the carbide will therefore persist in the steelon solidification and revent segregation. They will also withhold from the steel a certain amount of the alloying metal.

I have discovered that the above mentioned difficulties in making alloysteel or 5 iron may be overcome by adding the alloying element to the molten bath of steel or iron in the form of an unreduced compound, such as the oxide or ore, and reducing the alloying metal out of. such unreduced com- Dound bv means of the electric current. For

.the purpose of such an electrolysis, a supernatant electrolytic bath in which the unreduced compound can be dissolved, is formed on top of the bath of molten steel or iron. As the electrolyte, the calcium salt or salts of the alloying element or elements may be used, or a fluoride bath consisting of the double fluorides of aluminum and sodium or of aluminum and calcium, in'

which the unreduced compound such as the oxide or ore dissolves, may be used. In fact any suitable molten electrolyte is adaptable to the process.

The process may be carried out in any suitable furnace. For example, the process may be carried out in any of the known steel making furnaces, such as an open out the process, although it is to be understood that the process can be carried out in other types of furnaces. In the drawings a Figure 1 is a vertical section throughan electric furnace and also showing the wiring connections diagrammatically, and

Figure 2 is a similar view showing a modlfication.

In the illustrated embodiments of furnaces for carrying out the process, the reference numeral '1' indicates the hearth of an ordinary steel making electric furnace. Projecting through the roof of the furnace are the usual carbon electrodes 2 for melting the charge. current for melting the charge from threephase alternating current busses 3.

While the drawings illustrate furnaces in which electric current is used for melting the charge, it"is to be understood that other sources of heat may be employed for this purpose, the present invention, in so far as it relates to the furnaces, being concerned more particularly with the arrangements for passing the electrolyzing current through the electrolyte bath.

In operating the furnace, the ironor steel and the electrolyte are melted so as to form a molten metallic layer or bath 4 and a supernatant electrolyte molten layer or bath 5. After the charge has been brought to this condition, the electrolyzing current may be passed through the electrolyte bath to reduce the alloying metal therefrom. In the form of furnace shown in Figure 1, the heating current electrodes 2 are employed as anodes and an electrode 6 in the bottom of the hearth is employed as the cathode for passing the electrolyzing current through the bath. In order to protect the metal These electrodes are supplied with\ out the body of the molten steel or iron, thus preventing segregation.

In the form of furnace shown in Figure 2,

direct current busses 9. In this case the electrolyzing current flows through the electrolyte bath but without flowing through the bath 4 of the steel or iron. In this case the reduced alloying metal is formed on the electrode 10 or 11 which happens to be the cathode and descends through the electrolyte layer by gravity into the molten bath. In carrying out the process it is preferred to melt down the steel or iron in the usual manner, and then to charge the electrolyte forming ingredients, such as the calcium salts of the alloying metal or the fluorides, on top of the molten steel or iron. The electrolyte forming ingredients are then melted down to prepare the electrolyte bath for electrolysis. In the case of an electric furnace this melting down may be accomplished by the current from the usual steel melting electrodes. After the bath has thus been prepared, the melting current is switched off and the electrolyzing current is switched on through the auxiliary electrodes. The electrolyzing current causes a reduction of the alloying metal to take place at the cathode, which may be either an auxiliary electrode or the upper surface of the steel or iron, from which it descends by gravity into the body of the molten steel or iron to be diffused therein. As the electrolysis proceeds, more of the unreduced compound of the alloying metal, such as the oxide of ore, is added to the electrolyte bath to keep up its concentration to the requisite degree. If the heat produced by the electrolysis current is from the carbon of the electrode 6, a layer 7 'w not suflicient to keep the electrolyte and the of some material which is a conductor when hot, such, for example, as magnesite, is placed over the electrode 6. A switch 8, shown diagrammatically, is provided for disconnecting the electrodes 2 from the alternating current busses 3 and to connect them and the electrode 6 to the direct current busses 9 which supply the electrolyzing current. In this arrangement the molten metal forms the cathode and the reduced alloying metal formed by the electrolysis of the ore in the electrolyte bath is delivered directly to the steel or iron and is quickly absorbed therein. The electrolyzing current flowing through the molten steel or iron has a tendency to produce convection currents therein, mlxmg the reduced alloying metal throughsteel baths in fluid condition, the melting current can be switched on intermittently as required to bring up the temperature to the necessary degree. When the requisite per centage of the alloying metal has been'introduced into the steel or iron bath, the electrolyte is tapped off and any necessary additions of ferro-alloys, such as ferro-silicon, ferro-manganese, etc., for deoxidizing purposes are made, and the steel or iron is tapped in the usual manner.

In this process the reduced alloying metal in its nascent state is in contact with the steel bath, and erefore the best conditions are obtained for the alloying and uniform dissemination of the alloying metal throughout the steel. The alloying element is obtained from a cheap source. The introduction of carbon and segregation are avoided in the finished steel.

The action of the, alloying oxide or ore in oxidizing the undesirable elements, such as carbon and silicon, in the steel, and action of the electrolytic bath containing fluxes, such as lime, fluorides, etc., in absorbing and neutralizing the oxidized elements, together with undersirable metalloids, such as sulphur and phosphorus, causes a refining of the steel to take place simultaneously fvith the electrolytic production of the al- In the case of alloy steels containing a plurality of alloying elements, this procedure may be carried out in the same manner, the oxides or ores of the different alloymg elements being charged into the elec-' trolytic bath in the right proportions.

The advantages of this process of alloying are especially marked in the "case 'of producing a steel or iron with a high alloy content and a very low carbon or silicon content. Such an instance may be cited in the manufacture of the so-called stainless or .rustless iron or steel containing upwards of 8% chromium and less than 0.1% carbon. Also the advantages of thisprocess are apparent in the case of alloying a highly oxidizable and diflicultly soluble element such as uranium in steel. The alloying element being reduced in the nascent state and directly in contact with the molten steel, the chances of its oxidizing or not dissolving are reduced to a minimum. Also as the carbon content of the finished steel can be eliminated to any desired extent, the exact percentage of carbon in the alloy steel can be arrived at more accurately by recarburizing before tapping.

In cases where it is desired to keep traces of reducing agents out of the finished steel or iron as far as possible, the reduction of the alloying metal is carried out entirely by electrolysis. However, under some circumstances, it may be desirable to accelerate the electrolytic action by the use of reducing agents. In such cases, a reducing agent, such as silicon, aluminum, carbon or the like may be introduced into the electrolyte bath so that the reduction of the alloying metal may be effected jointly by the electrolytic action of the electric current and the chemical action of the reducing agent or agents added.

The present invention is not limited to the details of the process described above or to the use of the illustrated forms of furnaces, but may be otherwise carried out within the scope of the invention as defined in the following claims.

Iclaim:

1. The process of introducing an alloying metal into steel or iron, comprising forming a'molten bath of steel or iron and a molten supernatant electrolyte bath containing an unreduced compound of the alloying metal, and reducing the alloying metal from such compound vby electrolysis, substantially as described. Ii 2. The process of introducing an alloying metal into steel or iron, comprising forming a molten .bath of steel or iron and a molten supernatant electrolyte bath contain ing an unreduced compound of the alloying metal, reducing the alloying metal from such compound by electrolysis, and allowmg the reduced alloying metal to descend into the molten steel or iron to become diffused therein, substantially as described.

3. The process of making alloy steel or iron, comprising forming a molten bath of steel or iron and a molten supernatant electrolyte bath containing an unreduced compound of the alloying metal together with a metalloid absorbing flux, and reducing the alloying metal from its said compound by electrolysis and simultaneously refining the steel or iron, substantially as described.

4. The process of making alloy steel or iron, comprising reducing an alloying metal by electrolyzing a molten bath containing an unreduced compound of the alloying metal, and introducing the alloying metal immediately and in its molten state into mol ten steel or iron, substantiallv as described.

5. The process of making alloy steel or iron, comprising reducing an alloying metal by electrolyzing a molten bath containing an unreduced compound of the alloying metal, introducing the alloying metal immediately and in its molten state into molten steel or iron, and simultaneously refining the molten steel or iron, substantially as described.

6. The process of introducing chromium into steel or iron, comprising forming a molton bath of steel or iron and a molten supernatant electrolyte bathcontaining an unreduced chromium compound, and reduc-' ing the chromium from its said compound by electrolysis, substantially as described.

7. The process of introducing chromium into steel or iron, comprising forming a molten bath of steel or iron and a molten supernatant electrolyte bath containing an unreduced chromium compound, reducing the chromium from its said compound by electrolysis, and allowing the reduced metallic chromium to descend into the molten steel or iron and become disseminated therein, substantially as described.

8. The process of making chrome steel or iron, comprising forming a molten bath of steel or ir and a molten supernatant electrolyte bagli containing an unreduced compound of "ie alloying metal and a metalloid absorbing flux, and reducing the chromium from its said compound by electrolysis, and simultaneously refining the lyzing current through the electrolyte bath, steel or iron, substantially as described; and current controlhn means for prevent- 10 9. An electric furnace having a hearth ing the heating and e-ectrolyzing currents for holding a bath of molten metal and a from being introduced. at the same time, b supernatant electrolyte bath, electrode consubstantially as described.

nections for passing heating current into the In testimony whereof I have hereunto set furnace for bring ng the baths 'to roper my hand. fluid condition and for passing an e ectro- BYRAMJ I D. SAKLATWALLA.

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