US1616393A - Manufacture of alloy steels - Google Patents

Description

' making furnace.

"dium, ferro-uranium,

Patented at. 1, i927.

UNITED STATES 1,616,393 FICE.'

mew or I MANUFACTURE 'or'aLLoY srnELs.

Ro Drawing. Application filed April 15,

This application is a continuation in part of my copending application, Serial No. 543,082,-filed March 11, 1922. I

The present invention relates to manufacture of alloy steels, and more particular- 1 to the reduction of the alloying elements directly from their ores, and the production of the respective allow steels, without the introduction of excess carbon in the finished steel.

The process of the present invention is "particularly ap licable to the making of chrome steel, w ereby the major portion, if not all, of the chromium is introduced into thesteel by its direct reduction from an unreduced chromium compound, such as chrome ore, added. to the bath in the steel- In the manufacture of allo steels, under the practice heretofore preva exit, the alloying elements, in the already reduced metallic state, mostly in the form of a ferro-alloy, are added. to a molten bath of steel. For. example, to. obtain the respective steels thereof, form-manganese, ferro-chromium,

ferro-titanil'im, ferre-tungsten, ferro-vanaform-molybdenum,

" ferro-nickel ormetallic nickel and ferrocobalt or cobalt metal, are added to steel, in'the molten state in the furnace, or after it is tapped in the ladle. As theregular practice introduces an undue amount of caron in the steel. 61f special adesof lowcarbon ferro-alloys are used, t e cost of such alloys. is comparatively so high as to-prohibitively increase the cost of steel produced; These] defects are especially apparent in the case of steels where the content of the alloying element has to be high and the carbon content'low, as in the case of the so-called stainless steels, which have a chromium content of 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, as the process of oxidizingthe carbon is accompanied by an oxidation, and consequent waste, of the valuable alloying ele ments.

Anotherdefieiency of the existing methods of manufacturin alloy steels, by the addition of metallic ferro-alloys to molten steel. is the phenomenon of segregation. The al- 1922. Serial No. 553,019.

alloying element, these points of higher coneentration have 'no opportunity to equalize themselves over the entire mass of metal by diffusion. Moreover, the ferro-alloy-s' have various constituents of different melting points and de rees of solubilit as for example the car ides in the ordlnary grades of alloy. Such carbides have a higher melting point than the remainder of the alloy. Sucha carbide-containing ferro-alloy, when added to molten'steel, will have the result that when the rest of the allo will be com: pletely assimilated, the carbi e .contentwill still be in the solid state,- floating in the molten steel, without giving up its alloying element content to the bath. Such solid particles with a high alloying element content will persist in thesteel on solidification and present segregations.

I overcome the above mentioned difliculties by adding the alloying element to the.

bath in the formof the oxide or ore and reducing-it with a reducing agent contained in the molten steel. The reducing agent and the alloying material are added separately. This permits the reducing agent, as for example, silicon, to be incorporated-into the metal bath unmixed with the alloying material, and permits the alloying mate-' rial, as for example, chrome ore, to be in-' corporated into the slag unmixed with the reducing agent. The reducing agent and alloying material can therefore each become disseminated through its own layer of the bath, and the reaction between'them will then take place at the contact surface between the metal and slag'layers. Moreover,-

the separate addition of the reducing agent andthe alloying material permits one to be added prior to the other. It is preferred to add either the reducing agent or the alloying material long enough rior to the additionof the other, so that t 1e one'first added may have an o portunity to be disseminated before the ad ition of the other. For ex.-

ample, if the alloying-ore such as chromite is added first, it will becomedisseminated oxide tormthe chromlum canno be burned throughout the slag la er, and as it is in the during the dissemination time. Or if the reducing agent, such for example as silicon, is added first, it can become disseminated through the steel layer before the alloying ore is thrown onto the slag. When the alloying ore is thrown onto the slag layer it becomes diffused in it and meets the reducing agent at the surface of contact between the slag and steel, the reaction taking, place over the entire contact surface. The reduced alloying metal in its nascent state is in contact with steel bath, and therefore the best conditions are obtained for the alloying and uniform disseminating of the alloying metal throughout the steel. The alloying element is obtained from a cheap source. The introduction of carbon and segregation are avoided inthe finished steel. The action of the alloying oxide or ore in oxidizing the reducing agent in the steel and action of the added fiuxing material, generally lime, in absorbing and neutralizing the oxidized reducing agent together with undesirable metalloids, such asphosphorous and sulphur, causes a refining of the steel to take place simultaneously with the production of the alloy.

- The process may be carried out in the following manner The steel, to which the-alloying element is to be added, is firstbrought to a molten condition, in an ordinary steel making furnace, such as an open-hearth furnace, electric furnace, or other suitable furnace.

Next, the reducing agent, which may be a carbonaceous materiahfor instance in the form of metal carbide, such as pig iron, or wash metal, or which may be a so called metallic reducing agent, such as silicon or its alloys, such as ferro-silicon, manganese,- calcium, magnesium, or the like or their alloys, is added to the bath of molten steel and sufficient time allowed for iti complete assimilation through the body of the molten metal. These so called metallic reducing agents have an exothermic reaction with the oxides of the alloying metals and may therefore be -referred to as exothermic rehowever, smaller specific gravities than their ferro-alloys, and consequently, may not become incorporated into the metal layer until after they have become molten. Iii 01"- der to facilitate the sinking of the redueerably in the presence of lime, or lime,

fluor-spar and borax as a flux. The urpose and function of the flux is to pro uce a slag with the gangue of the raw material contalning the alloying element, and is of such a nature as to effectively remove by chemical combination the product formed by oxidation of the reducing agent, for example, in the case of chromite which is in its natural state highly refractory and chemically inert, the flux combines with the gangue, (which consists principally of silica, alumina and magnesia) to form a molten slag leaving the chromium and iron oxides in a condition amenable to reduction. The

slag containing the fluxing material is capable of absorbing the silica produced by the oxidation of the silicon content of the metal bath when silicon is employed as the reducing agent. Thepractical result achieved by the flux, therefore, is the removal ofthe presence of the reducing agent in the finished steel. aFor example, a lime flux combines with and neutralizes the silicon oxide formed when silicon is the reduc-- ing agent. The specific gravity of the raw alloying material is such that it remains in the slag layer. This raw material and flux combining at the temperature of the furnace form a supernatent, non-metallic, liquid layer over the molten body of metallic steel and in contact with it. The reducing reaction then proceeds at the surface of contact of the non-metallic and metallic liquid bodies. At the end of this reaction period the temperature in the furnace may be raised, in the case of an electric furnace,

for instance, by increasing the current density and voltage, in order to eliminate the last traces of the reducing agent in the finished steel, accelerating the effect produced by the fluxing agents added for this purpose.

At the ordinary refining temperatures, the silicon and chromium are more readily oxidized. than carbon, and the carbon is therefore diflicultto eliminate. However, when the tel'nperature is increased, as above described. the spcedof reaction between oxygen and carbon is increased relatively more than the speeds of reaction between oxygen and silicon and oxygen and chromium, so that the effect of vincreasing the furnace temperature before tapping'is to cause an elimination ofthe carbon relatively greatcrpthan that of silicon and chrom1um.- Thls 1s of particular importance in the production of very low carbon chrome steelsor irons. The ordinary refining temperatures are about from 1500 to 1600 degrees-C. for an electric furnace or 1400 to 1500 degrees C. for a fuel heated open hearth furnace. The tempera-- ture increase above described is usually from about 50 to 250 degrees above the usual refining temperatures. .In the case of carbon which, of course, is always a reducing agent, the increase in temperature will eliminate it down to .1 to 06% or even lower. Where there are two reducing agents present, such as carbon and silicon, the increased 1 ducing the reducing temperature will eliminate both of them, the carbon to .1 to .06%, and the silicon to about the same degree. I

In general it is preferred to add the reducing agent to the molten steel first, then adding the raw material containing the allo ing element. The tolerance limits in t e ,finished steel of elements such as carbon or silicon, forming the reducing agent, are usually much narrower than the tolerance limits of the alloying element, and by introagent first, limits ma be accurately controlled by successive additions of raw alloying material until the presence of the reducin agent is eliminated to the desired extent. n the other hand, if the tolerance limits for the alloying element are narrow,- the order of procedure may be reversed, and the raw allo ing elementcontain- I first togetherwith the fl 'ugg and the reducmg agent charged ing material may beic ar then in successive portions, until the desired limit of alloying is cfi'ected. Y

\Vhile it is usually preferred to first form the molten bath by melting down. the charge so as to form the steel layer and slag layer and then to add the reducing agent and unreduced ore to the respective layers, it will be obvious that the reducing agent and ore may be otherwise incorporated into their respective layersof the bath. For example, the reducing agent, such as a slhcon reducing agent, may be'int-roduced into the furnace along with the unmelted charge, so that the becomes incorporated into' as a silicon alloy containing one of the alloying metals may also be advantageously used. For instance, in the case f the manufacture of so-called stain:

less steel a silico-chromium alloy may be incorporated in the molten steel and its sili con content utilized to reduce a further quantity of chromium from chrome ore added tothebath. This procedure is especially mg a high percentage of the alloying element.

In the case of alloy steels containing a plurality of. alloying elements, this procedure may be carried out in the same manner, the raw materials in the right proportions, containingthe plural alloying elements, being charged together on top of the molten bath of steel containing the reducing agent. In such cases a flux may be separately added or the. raw alloying materials may be selected of such composition asto have in' their gangue the necessarytaxing com onents.

Also a plurality of re ucing a ents may be used suchas a mixture of car onaceous and metallic reducing agents or several different metallic reducing agents. stance a -ferro-silicon alloy containing car-. bon maybe used, both its silicon and carbon contents being utilized for the reduction. purpose. Also any reducing agents originally nal. steel will take place. Also t e fluxes add;-

ed with the alloying-element-containing raw i 7 advantageous in the case of a steel contain-'- For in- .present in the steel bath may be effectively used, in which case during the reduction operation. a'simultaneous refinin of theorigi-J material will have the secondary efiect of refining the steel of the metalloid contents such as sul bar and phosphorus simultaneously with t 1e reducing operation. I

If desired, after reduction of the alloying element or elements in the steel, 8. small quantity of additional ferro-silicon or ferromanganese may be added as a deoxidizing cleanser, before tapping, as is the common practice in making alloy steels.

The advantages of this process of alloying are especially marked" in the case of using silicon as-a reducing agent, and producing chrome steels with a' high alloy content and very low carbon content. As such an instance may be cited the manufacture of socalled stainless iron containing 9 to 15% chromium and less than 0.1% carbon.. Also the advantages of this process'are apparent inthe case of alloying a highly oxidizable and diflicultly soluble element as uranium in steel. The alloying element being produced in the nascent state and directly in contact with the steel, the chances of its oxidizing or not dissolving are reduced to a minimum. v

Also, as the carbon content of the finished steel can be eliminated to any desired extent, simultaneously during the process of reducing, the exact percentage of carbon in the finished alloysteel can he arrived at more accurately by recarburizing before tap ing. In the case of metallic reducing agents eing se t a pre ence in the finished steel 15 practically eliminated by the action of fluxes' Thus by the recess of this invention a steel of predetermined given composition can be more accurately Xroduced than by the use of ferro-alloys. lso by this process, as the .valuable alloying elements do not exist at any time in the metallic state, unless dissolved and alloyed in the steel itself, and as after their solution in the steel there is no occasion to. subject, such steel to an oxidizing process for removal of carbon, for instance, as in the older processes, there is no loss suffered through oxidation, rendering the process extremely economical.

While certain features of the present process, and particularly the substantial elimination of the reducing agents by increasing the final furnace temperature,are novel and useful in the; manufacture of various alloy steels, the present invention is particularly applicable to the production of chrome steel in which. a substantial quantity of chromium is introduced 'into' the steel. The chromium content is furnished principally, if not entirely, by the chrome ore which is charged into the slag layer and which reacts with the silicon reducing agent in the metal layer to thereby directly reduce the chromium from the ore to the metallic state inthe bath of the steel-making furnace. \Vhile the chromium ore charged into the slag is contemplatedas being the principal, if not the entire, source of the chromium, minor proportions of chromium may be lntroduced y some of the other constituents added to.

the bath. I

Asv above pointed out, the chromium is supplied from a-very cheap source, and the necessity of employing a relatively expensive chromium alloy as the source of chro mium' is obviated. Moreover, the treatment permits the production of a low carbon chrome steel and when desired, also a low SlllCOIl chrome steel.

The term steel as herein employed is intended as a term of general description and not of limitation, and is intended to include the so-called stainless irons which .are, in reality, steels having-very low carbon and metalloid contents. The term chrome steel is also intended as a term of general descri tion, and not of limitation, and is mten ed to include steels having chromium as the principal alloying metal, although conlltl tain-ing other alloyin metals.

The expression silicon reducing agent is intended as a term nfgeneral description and not of limitation, and is intended to include not only substantially pure silicon, but also alloys of silicon with other metals or metalloids.

The silicon and chrome ore may be in whole or in part incorporated into their respective layers ofthe bath, either before or luring-the maintenance of the reaction temperature in thefurnace, and I therefore do not intend to limit my claims, except when specifically stated therein, to any particular sequence of steps of incorporating the reducing agents, and unreduced compounds and the maintenance of the reacting temperature.

While my process is particularly applicable to the production of chrome steel, it

may be employed in the production of'alloy steels in general and especially to steels contamlng an alloying metallic element of the ,sixth group of the periodic system, such metallic elements being chromium, molybdenum, tungsten and uranium.

While the preferred method of carrying out my process has been specifically described, it is to be understood that theinvention is not limited to all of the described details, but may be otherwise embodied in processes of making alloy steels, within the scope of the following claims.

-I claim:

1. The process of making chrome'steel, comprlsing forming a molten bath of steel having a metal layer in which is inco orated a silicon reducing agent and a s ag layer in which. is incorporated an unreduced chromium compound in an amount suflicient to furnish the major portion,- if not all, of the chromium content of the steel, and maintaining the bath at a 'rated an unreduced chromium compoun in an amount sufiicient to furnish the major portion, if not all, of the chromium content of the steel, and maintaining the bath at a temperature suflicient to cause a reaction between the retlucing agents in the metal layer and the unreduced chromium compound in the slag layer to thereby reduce in the bath chromium directly fromits unreduced com pound, substantially as described.

3. The process of making chrome steel, comprising forming a molten bath of steel having a metal layer in' which is incor rated a silicon reducing agent and a s ag layer in which is incorporated an unreduced chromium compound in an amount sufiicient 'to furnish the major portion, if not all, of

the chromium content of the steel and a fluxing material which removes 'by chemical combination the silica produced by the oxidation of the silicon together with'ob'ection able. metalloids such as sulphur an ,phosphorous, and maintaining the bath at a temperature sufiicient to cause a reaction between the reducing agent in the metal layer and unreduced chromium compound inthe slag layer, the chromium compound being in.

an amount suflicient to furnish the major portion, if not all, of the chromium content of the steel, and maintaining the bath at atemperature sufficient to cause a reaction be-' tween the reducing agent and the unreduced chromium compound to thereby reduce in the bath chromium directly from its unreduced compound, substantially as described.

5. The process of making chrome steel,

comprising forming a bath of steel havinga metal layer and a supernatant slag layer,

' an unreduced adding separately to the metal layer a silicon reducing agent and to the slag layer an unreduced chromium content in an amount sufiicientto furnish the major portion, if not all, of the chromium content of the steel, and allowing suflicient time between to permit the one first added to become disseminated whereby segregation of.' the chromium is avoided, and maintainingthe bath at a temperature sufficient to cause a reaction between the reducing .agent in the metal layer and unreduced chromium com ound in the slag layer to thereby reduce in the bath chromlum directly from its unreduced com- 7 pound, substantially as described.

6. The process of making chrome steel, comprising forming a molten bath of steel having a metal layer and a supernatant slag layer, and adding separately to the metal layer a reducing agent and to the slag layer amount sufficient to -furnish the major por-. tion, if not all, of the chromlum content of the steel, the one containing the element whose percentage is to be most accurately controlled in the finished steel being added first, and maintaining the bath. at a temperature suflicient to cause a reaction between the reducing agent in the metal layer and unreduced chromium compound in the slag layerv to thereby reduce in the bath ChIOIIllllm directly from its unreduced compound, substantially as described. a

-7. The process of. making chrome steel,

comprising forming a molten bath of steelhaving a metal layer in which is incorporated a silicon reducing agent and a supernatant slag layer, thereafter adding to the slag chromium compound in an .tially as described.

layer an unreduced chromium compound in' an amount sufiicient to furnish the major portion, if'not all, of the chromium content of the steel, and maintaining the bath at a temperature sufficient to' cause a reaction between the r'educing agent in the metal layer and the unreduced chromium compound in" the slag layer to thereby reduce in thebath chromium directly from its unreduced compound, substantially as described.

8. The process of making chrome steel containing other alloying metals, comprising formlng a molten bath of steel having a metal layer in which is incorporateda silicon reducingagent'and' a slag layerin which are incorporated unreduced compounds of chromium and the other alloyin metal, or metals in amounts sufiicient J-to, urnish the major portion, if not all, of the alloying metal contents of the steel, and maintaining the bath ata temperature sufiicient to cause a reaction between the reducing agent in the metal layer and unreduced alloying metal' compounds in the slag layer to thereby re duce in the bath the alloying metals directly from their unreduced compounds, substantially as described.

9. The process of making alloy steel, com-' prising forming a molten bath of steel ha-ving a metal layer in which is incorporated a reducing agent and a slag layer in which is incorporated an unreduced compound of the alloying metal, maintaining the bath at a temperature sufiicient to cause a reaction between the reducing agent in the metal layer and the unreduced compound of the alloying metal .in the slag layer to thereby directreducethe alloying metal in the bath, and

ally increasin the temperaturesufiiciently to substantia ly eliminate any reducing agents from the finished steel, substantially as described. a v

.10. The process of making an alloy steel containing as an alloying metal a metallic element of the sixth group of the periodic system, comprising forming a molten bath of steel having a metal layer'in which isincorporated a sili'con reducing agent and a slag layer in which is incorporated an. unreduced compound of the alloying metalin an amount sufiicient to furnish the major too portion, if not all, of the said alloying metal content ofv the steel, and maintainingthe bath at a temperature suflicient to cause a reaction between the reducing agent inthe metal *layer and the unreduced alloying metal compound in the slag layer ,to'thereby reduce in the bath the alloying/metal" direct ly from its unreduced compound, substan- 11. The process of ma'king an .alloy steel containing as an alloying metal a metallic element of the sixth group of the periodic system, comprising forming a molten bath of steel having a metal lay'erin' which is in- 1 corporated a reducing agent and a sla layer inwhich 1s mco orate an unreduce l compound of the a oying metal an amount suflicient to furnish the major portion, if not the unreduced alloyin all, of the said alloying metal content of the steel, and maintaining the bath at a temperature suflicient to cause a reaction between the reducing agent in the metal layer and metal compound in the slagtlayer, to there y reduce in the bath the alloying metal directly from its unreduced compound, substantially as described;

12. The process of making an alloy steel containing as analloying metal a metallic elementof the sixth group of the periodic system, comprising forming a'molten bath of steel havmg a metal layer containing a reducing agent and a supernatant slag layer,

thereafter adding to the slag layer an un-- comprising'forming a molten bath of steel having a metal layer and a slag layer in which slag layer is incorporated an unreduced chromium com ound in an amount suflicient to furnish t e major portion, if

not all, of the chromium content of the steel, thereafter adding a silicon reducing agent to the metal layer, and maintaining the bath at a temperature suflicient to cause a reaction between the reducing agent in the -metal layer and theiunreduced chromium compound in the slag layer, to thereb reducein the bath chromium direct-1y fro n its unreduced scribed.

14, The process of making an alloy steel containing as an alloying metal a metallic element of the sixthgroup of theperiodic system, comprising forming a molten bath of steel having a metal layer and a slag layer in which slag layer is incorporated an unreducedcompound of the alloying metal-in.

compound, substantially as de an amount 'suflicient to furnish,the major portion, if not all, of thesaid alloying metal content of the steel, thereaftera'dding a reducing agent to the metal layer, and maintaining the bath at a temperature suflicient to cause a reaction between the reducing" agent in the metal layer and the unreduced compound in the slag layer,-to thereby reduce in the bath the alloying metal directl v from its unreduced compound, substantially as described.

In testimony whereof I have hereunto set my hand. BYRAMJI D. SAKLATWALLA.