US2892699A - Metallurgical process - Google Patents

Description

United States Patent METALLURGICAL PROCESS Chester R. Austin, Martinez, Calif., and Rudolf F. Rinesch, Linz, Austria; said Austin assignor to Henry J. Kaiser Company, Oakland, Calif., a corporation of Nevada, and said Rinesch assignor to Vereinigte Oesterreichesche Eisenund Stahlwerke Aktiengesellschaft, Linz (Donau), Austria, an Austrian joint-stock company No Drawing. Application August 27, 1956 Serial No. 606,225

Claims. (Cl. 75-45) The present invention relates to an improved process for the refining of ferrous metals, such as pig iron or other metallic iron. More particularly, the invention relates to a novel method for the removal of sulfur during refining of ferrous metal, and is more specifically directed to an improved steel-making process in which the molten ferrous metal is surface blown with oxygen or oxygen-enriched air.

Sulfur is a usual impurity in all pig irons, and other metallic irons utilized in the production of steel. The removal of sulfur to the greatest possible extent during the refining of ferrous metals is not only highly desirable, but in the case of many types of steels its removal to a low value is a necessity. The adverse effects of sulfur in steel, usually regarded as present in the form of sulfide inclusions, are well known in the steel making art, and include reduction in ductility and notched-bar impact values, hot shortness (brittleness in hot metal), and reduction in weldability. Accordingly, except where an increase in sulfur content imparts a specific desirable property in the steel, such as machineability, it is the objective in all steel making processes, although not realized to the extent desired, to eliminate sulfur during the refining process.

In the conventional basic steel making processes, such as the open hearth and Thomas converter (basic Bessemer), as well as in the more recently developed processes utilizing oxygen or oxygen-enriched air for at least a part of the refining of the pig iron, the sulfur is partially removed by reaction with the slag, usually by proper control of the free lime content in the slag to form calcium sulfide. Alternatively, or in combination with this procedure for desulfurizing the melt, soda ash (Na C0 may be added in the furnace or converter, or in the iron ladle, to reduce the sulfur content in the finished steel. In any case, the desulfurization by these procedures is dependent upon reaction between the sulfur in the molten metal and a component of the slag whether it be lime, soda ash, or both. The degree of desulfurization during such refining processes varies to a large extent with the skill of the steelmaker, and is limited primarily by the fact that the concentration of the sulfur in the lime slag cannot exceed a relatively low percentage e. g. 0.150%, and the quantity of free lime in the slag cannot be unduly increased without causing the slag to become too viscous for proper working of the heat. Accordingly, by the present methods of desulfurization the percentage removal based on the sulfur content in the ferrous metal charged is generally limited to small percentages, not exceeding about 25 to 30%, and furthermore is subject to large variation between heats. Of course, in the acid processes, the sulfur is not eliminated since basic slag additions cannot be used.

Accordingly, there remains a need for methods of desulfurizing molten ferrous metal in steel making processes in which the degree of desulfurization may be carried farther toward completion and may be rendered ice more uniform in the refining of metals of varying sulfur content. It is to the solution of this problem that the present invention is directed.

The invention is further directed to still another problem which is characteristic of the more recently developed processes for steel making in which the molten ferrous metal is surface blown with oxygen or oxygenenriched air during at least a portion of the refining period, or for the entire duration thereof. In the application of oxygen, whether it be high purity oxygen or oxygen-enriched air, as the effective refining agent for removal in whole or in part of the oxidizable impurities in the molten ferrous metal, such as carbon, manganese and silicon, the oxygen containing gas is made to impinge downwardly upon the molten metal surface with removal of the supernatant slag layer in the area of impingement by the force of the jet, or by submerging the lance through which the gas is supplied. In any case, it is a common characteristic and difficulty encountered in the partial or complete refining of ferrous metal with oxygen or oxygen-enriched air that a relatively dense fume is created and issues from the furnace or converter with the oif gases. It is usually necessary to provide means for collection of this dust or fume in the form of a dust collection system, and in the case of surface blowing with oxygen in the open hearth or other regenerative type furnaces, the plugging of the checkers has been directly attributed to the solids content of the relatively dense smoke or fume produced by the intensity of the reaction of the oxygen with the iron, carbon and other components of the molten ferrous bath. The fume has been subjected to analysis and is found to consist primarily of finely divided particles of ferric oxide (Fe O of micron and sub-micron size. Some manganese oxide is also contained in the fume, particularly in the initial part of the refining period, e.g. the first one-third to one-half of the total refining time. It is known that the temperatures reached in the localized zone of impingement of the oxygen-containing gas in the molten metal exceed the boiling points of iron and manganese and it is postulated that the vaporized iron and manganese are oxidized to produce this objectionable fume or smoke. Accordingly, the present invention in conjunction with the method of desulfurizing is also directed to an elimination of this fume problem characteristic of those steel making processes in which oxygen or oxygen-enriched air is utilized in whole or in part as the refining agent.

It is a primary purpose and object of the invention to provide an improved method for desulphurizing molten ferrous metal during the refining thereof for the production of steel, which is applicable to any steel making process whether basic or acid, and particularly to those steel making processes in which at least a portion of the refining is accomplished by surface blowing with oxygen.

It is another object of the invention to provide a process, which by the action of a single addition agent, accomplishes the desulfurization of ferrous metal and the elimination of objectionable fume or smoke in the refining of such metal in whole or in part by the surface blowing of the metal with oxygen or oxygen-enriched air.

A further object of the invention is to provide an improved method of desulfurizing impure molten ferrous metal, such as pig iron, in which the elimination of sulfur is not dependent upon the reaction thereof with components of the slag, such as lime or soda ash (Na CO and consequently is not limited by the resulting sulfur concentration in the slag with respect to such slag component. The method of the present invention provides a means for eliminating sulfur primarily in gaseous form, which consistently results in a high degree of desulfurization. The invention further permits actual increase of the initial sulfur content in the charge in certain instances where it is desirable to effectively overcomethe. swelling of a heat during teeming, or blistering during rolling caused by hydrogen gas.

It is a further distinct object and advantage of the invention to provide a method of working steelmaking ferrousjmetal heats which are surface blown with oxygen or, oxygen enriched air during at least a part of the refiningso that the effective desulfurizing addition agent may also operate to cool the melt in the high temperature zone of impingement of the oxygen-containing gas and thereby eliminate the objectionable smoke or fume characteristic of such oxygen blowing processes.

These, and other objects and advantages of the inventionwill become apparent with the following detailed description thereof.

It-has been found according to the present invention that the introduction of water, preferably either vapor or liquid, in the refining of impure molten ferrous metals containing sulfur is effective to satisfactorily eliminate this element, and that degrees of desulfurization attained may greatly exceed those obtainable with the conventional slag additions, such as lime and sodium carbonate. It is to be understood, of course, that this novel addition agent may be employed alone for the purpose of desulfurizing, or may be used in conjunction withta lime-containing basic slag necessary to the basic steel making processes, or even with soda ash additions at, an appropriate point in the processing of the ferrous metal, such as in the iron ladle, in the slag during, refining, or as otherwise normally added. However, it is readily understood that with the uniform and high degree of desulfurization obtainable by the invention, it is an advantage to dispense with soda ash additions or excess lime charge in the slag.

For the purpose of the desulfurizing function, either water vapor (steam) or liquid water is preferred, but water in the solid phase, that is, ice, and even water isotopes may be employed where such use is desirable. It is believed on the basis of tests and experimental evidence that the water, when introduced so as to contact themolten metal surface, is largely dissociated into hydrogen and oxygen, and the hydrogen effectively reacts-with the sulfur content in the metal to form gaseous hydrogen sulfide which escapes from the melt with the off gases. Where the intended function of the addition agent is only desulfurizing, hydrogen, or any suitable hydrogen-yielding material dissociating at the temperatures of the melt may be employed in place of water, and various mixtures of water, hydrogen, and/or other hydrogen-yielding compounds also are regarded as suitable. Among such hydrogen-yielding compounds, there may be mentioned as particularly suitable those organic compounds containing only carbon and hydrogen, or carbon, hydrogen and oxygen, such as hydrocarbons, carbohydrates, alcohols, and other combustibleorganic compounds which either decompose to provide hydrogen or burn at the temperatures of the molten ferrous metal bath with formation of water, and consequent dissociation of the water in contact with the melt to provide the hydrogen for the desulfurizing action. It is advantageous to employ waste materials containing such hydrogen-yielding substances such as waste oil, or other industrial waste liquors containing hydrocarbons or compounds of carbon, hydrogen and oxygen.

When utilizing water as the preferred desulfurizing' agent, either liquid water, or steam, which may be superheated, is introduced into the melt in such a mannerthat it'is carried into contact With the molten metal, for example, the slaglayer may be penetrated by a jet-'orjets of water or steam. Such jets may be suppliedindependently or with jets of other refining gas such as oxygen or oxygen-enriched air blown ,onto. the

melt surface. Alternatively, it has been found effective to introduce the water by drenching a slag-forming addition agent, such as iron ore, mill scale, fluorspar, bauxite, limestone or lime. This water or steam addition or injection into the melt may be carried out from the beginning of the refining process, but in most instances should be discontinued while the melt is still vigorously agitated by the carbon boil, that is, while the carbon content of the ferrous metal being refined is still sufiiciently high to insure vigorous evolution of carbon monoxide (CO). In this manner, it has been found that the presence of occluded hydrogen in the melt at the time the carbon end point or final carbon content is reached is avoided, since the hydrogen gas formed by the dissociation of the water reacts with the sulfur and is eliminated as gaseous H 8, and where larger quantities of Water are used, uncombined hydrogen is also effectively eliminated due to the vigorous boiling action of the melt. Thus, the ferrous metal may be effectively desulfurized without adverse effects characteristic of hydrogen content in the finished steel, such as swelling duringv teeming, gas porosity in the ingot, and blistering on rolling.

In the practice of the process for desulfurizing the molten ferrous metal, the Water, hydrogen, or other hydrogen-yielding substance may be added in an amount exceeding stoichiometric, calculated on the basis of the total sulfur content in the metal charge. This is recommended, since the degree of dissociation of the water, or other hydrogen-yielding compounds, may vary with variation in conditions of a heat, particularly temperature, and at least in the case of Water as a hydrogensupplying substance, such dissociation is usually not complete. Of course, lesser quantities of the desulfurizing agent may be utilized, but a somewhat corresponding lower degree of desulfurization may be expected.

The utilization of water in either liquid or vapor state for desulfurizing of molten ferrous metals is particularly advantageous in those steel making processes in which oxygen or oxygen-enriched air is surface blown onto the melt for completely refining the ferrous metal, or merely during a portion of the refining period, such as in the intermediate and final stages of the open hearth or electric furnace processes for accelerating decarburization. The extensive development in the field of oxygen utilization insteelmaking has resulted in the commercial adoption of high tonnage oxygen for the surface blowing of open hearth and electric furnace melts for accelerating decarburization, particularly after the melt down period, and up to the final carbon content for tapping. In addition, converter processes for the refining of ferrous metals by surface blowing with oxygen have been commercially developed, such as disclosed in US. Patents 2,741,554 and 2,741,555. In

all of these processes, the oxygen is impinged onto the melt surface from above in the form of a high velocity jet or jets and forms a zone or zones of oxygen-metal reaction at which extremely high temperatures are developed. These temperatures exceed the boiling point of iron, and consequently iron is evaporated, along with some manganese, giving rise to the formation of a dense reddish brown fume or smoke which is emitted from the furnace along with the other off gases. This fume represents a loss of iron in such processes, which may amount to as much as 0.8 to 1.0% by weight based on the total iron in the charge, a loss which desirably should be avoided. However, the dust problem created by the fume is the most serious consequence as indicated by size analyses showing about of the particles in the dust to be below one micron in size. This gives rise to a difficulty in separation or precipitation of the dust from the effluent gases, and many dust collection systems, including cyclones and washers have beensuggestedto overcome this problem.

0.5 to as high as 1% or slightly above.

In addition in regenerative furnaces, such as the open hearth, this dust has caused clogging of the checkers.

It has been found according to the present invention that water employed as a desulfurizing agent in the re fining of ferrous metals by surface blowing with oxygen, when directed into the high temperature oxygen-metal reaction zone results in substantially complete elimination of the iron oxide fume characteristic of these processes. Due to the highly endothermic nature of the dissociation of water into hydrogen and oxygen, it is postulated that the heat evolved due to the oxygen-metal reactions in such localized zones is absorbed to a substantial extent by the dissociation of the water, and accordingly the temperatures in such reaction zones are effectively controlled to a point where they are below the boiling point of iron. This cooling eifect also contributes to a longer refractory life in these oxygen surface blown processes. Thus, the evaporation of iron, and its oxidation to form the finely divided particulate iron oxide fume or smoke, is substantially completely eliminated by the impingement of water or water vapor in the zone of oxygen impingement on the melt surface.

In the embodiment of the invention directed to obtaining both desulfurizing and fume elimination, it is preferred to start introduction of water at such time that the fume or smoke is first observed, which usually occurs immediately after oxygen flow is initiated if the charge is melted, or when melt down is near completion if oxygen is used in melting. However, water flow may be initiated at the same time oxygen flow begins. The water may be introduced as a jet or jets from lances or blast nozzles, preferably water cooled, such as are utilized for the introduction of gaseous refining agents, for example, oxygen or oxygen-enriched air. The water, either in the form of steam or liquid water may by this means be introduced separately from the oxygen gas, or it may be delivered to the melt through the same lance or water cooled nozzle used for supplying the oxygen refining gas by any appropriate means for introducing or metering the water into the oxygen line. When the steam or water is premixed with the oxygen, it is preferable to insert it into the oxygen line by an atomizing nozzle, and sulficiently removed from the oxygen nozzle to insure thorough mixing.

In accordance with the recommended practice of the invention, as above indicated, the water supply to the melt during the refining period is preferably discontinued while the carbon boil (evolution of CO) is still sufficiently active to sweep out the hydrogen sulfide and hydrogen gas generated by dissociation of the water. The particular carbon contents at which water injection is discontinued depends on the particular steelmaking process to which the invention is applied. In those pneumatic processes for the oxygen refining of the metal which are completed in a period comparable to the ordinary Bessemer air blown process, for example, 12 minutes up to 30 minutes, or less than 1 hour, and which therefore involve rapid decarburization, the water supply may be discontinued from 3 to 6 minutes before the carbon end point is reached, or at carbon contents of, for example, However, in the particular process of Patents Nos. 2,741,554 and 2,741,555, above referred to, it is an advantage that the water supply may be continued to the end of the blow,

since the carbon boil is vigorous in such process up to the carbon end point, that is, the flame drop. In the conventional open hearth and the electric furnace steelmaking processes modified by oxygen accelerated decarburization, the oxygen blowing may not be initiated until after the melt down period, that is when carbon does not greatly exceed 0.5%, and accordingly the water supply may be discontinued at carbon contents of as low. as 0.10, since the rate of decarburization in the final phases is substantially lower than in the pneumatic processes.

to 20 minutes before the time for tap. In all cases, such procedure insures that the finished steel is substantially free of hydrogen, and at the same time the fume is substantially eliminated, since the solids content or dust in the waste gases is greatly reduced in the final decarburizing stage. However, where severity of the fume is greatly diminished prior to final decarburizing, such as in the intermediate or even initial decarburizing periods as in certain instances, the water supply may be regulated or discontinued relatively earlier. Accordingly, the invention as a novel method for desulfurizing and for elimination of fume in oxygen surface blowing refining processes is eminently suitable for the production of all types of steels, such as plain carbon fully killed, and semi-killed steels, as well as rimmed steels, since the gas content of the melt, particularly hydrogen, is maintained at a low level.

It may be mentioned in connection with the production of rimming steels according to the present invention, that the water supply may be continued up to the carbon end point in the oxygen blown pneumatic processes, or to the time for tap (final carbon content) in the oxygen blown open hearth and electric furnace processes, since the hydrogen content retained in the melt is not objection able in the production of such effervescent steels. I In the utilization of water for desulfurizing and fume elimination in oxygen blown melts, the amount of water introduced into the molten ferrous metal may be widely varied. Thus, where the objective is simply to desulfurize the metal, limited amounts of water may be supplied, which preferably are in excess of the stoichiometric amount based on calculated sulfur content of the charge, although less than stoichiometric quantities may be employed, particularly where used in conjunction with lime addition for desulfurizing. The water, or other hydrogenyielding material may be introduced, as above stated, in the form of a jet, or as jets impinging at several points on the melt surface. In basic processes it may be supplied by drenching a slag forming constituent with water, for example, to impart a water content of from 5 to 6% based on the weight of the constituent charged. It is recommended in using this latter method of water addition when lime is the drenched constituent to finish liming of the heat with dried lime so as to avoid retention of hydrogen in the melt. This is also true of water added with any slag-forming constituent, additions of which are made in the final stages of the heat.

In utilizing water for combined desulfurizing and elimination of iron oxide fume in surface blowing with oxygen, the quantty of water introduced is largely dependent upon the amount necessary to abstract sufficient heat in the localized high temperature zone of oxygen-metal reaction to maintain the temperature below the boiling point of iron. In general, it has been found that the proportion of water vapor to total gas volume in the steam-oxygen mixture may vary from small percentages to as high as 50% with satisfactory or substantially complete elimination of the ferric oxide fume. The volume proportions indicated are taken from steam and oxygen both at p.s.i.g., steam at 325 F. and oxygen at 60 F. It is observed that any dilution of the oxygen with water will reduce the solids or dust content of the gases to an appreciable extent. In those processes where maximum additions of scrap are desired, it is advantageous to limit the quantity of water introduced to the minimum consistent with satisfactory fume elimination. However, it has been found that adequate quantities of water to accomplish this objective may be employed along with acceptably high scrap additions without unduly cooling the melt in those processes in which the ferrous metal is more or less completely refined by surface blowing with oxygen. This is particularly true, where the water supply is discontinued in the final stages of the blow, which permits the melt temperature to be increased to a point satisfactory for teeming. In the open hearth and electric furnaces,

the scrap charges are normally added and melted down prior to initiating surface blowing with oxygen, and accordingly little or no limitation is imposed on the quantity of water employed during the oxygen blowing phase of the refining process. In addition, any excessive cooling may be offset by fuel regulation since oxygen blowing permits large reduction in fuel consumption.

The proportions of water vapor, or the equivalent in liquid water, may be varied during a given heat in conjunction with variation of the rate of oxygen introduction or independently thereof. Also, this variation in water vapor to oxygen proportion may be advantageous, since in the initial period of refining in the fully pneumatic processes the rate of heat evolved is greater in view of the higher rate of decarburization, and larger quantities of water may be utilized in such period without undue cooling of the melt. Furthermore, evidence indicates the fume may be heavier in the initial refining period, during desiliconizing and while manganese is being oxidized.

The combined oxygen-water surface blowing particularly at relatively high percentages of water also provides a supplemental source of oxygen due to dissociation of the water. This permits a reduction in the amount of high purity or commercially pure oxygen required. Thus, the oxygen supply per ton of metal charge may be calculated considering the total volume of water added and a conservatively estimated degree of dissociation.

The invention is described in further detail with reference to the specific examples set forth below, which are not to be construed as a limitation of the invention, but rather as illustrative of complete specific embodiments thereof.

EXAMPLE 1 The invention as applied to the converter process utilizing surface blowing of the melt with high purity oxygen is illustrated below. A two ton basic converter of conventional design except for the closed bottom was employed. High purity oxygen (99.8%) was supplied through a water-cooled nozzle overhanging the central portion of the melt in the converter and spaced from the melt surface about 100 to 300 mm. The nozzle had an internal diameter of 10 mm. and the oxygen pressure at the nozzle was 8 atmospheres. 2000 kilograms of liquid pig iron were charged to the converter after addition of 300 kilograms of scrap, followed by a charge of 100 kilograms of burnt lime. Blowing was then initiated with the rate of flow of oxygen under the conditions above set forth being suflicient to reach the carbon end point of about 0.05% C. in about 20 minutes total blowing time.

In these heats the water supply for the desulfurizing action was provided from the condensation water present in the oxygen pipe line, since the oxygen gas for the two ton converter was not dried. The comparative results based on heats of this character compared with heats in which dried oxygen was introduced clearly indicate the effectiveness of relatively small quantities of water in desul-furizing of the molten pig iron charge.

Two ton converteroxygen not dried10 mm. nozzle pressure 8 atmospheres:

Average of 12 heats- Sulfur in the charge-0.038% S Sulfur in the blown metal-023% S Degree of desulfurization40.0%

Two ton converter-oxygen driedl0 mm. nozzle-O pressure 8 atmospheres:

Average of 3 heats- Sulfur in the charge.l05% S Sulfur in the blown metal-108% S Increase in sulfurization2.0%

As may be seen from the foregoing results, the lime charge in these heats was not calculated to accomplish desulfurizing,but only for basic slag formation to retain phosphorus. For comparative purposes, reliance was placed solely on the water content in the oxygen gas to accomplish desulfurizing.

EXAMPLE 2 In a fiftteen ton converter of similar design and operated in a manner similar to the two ton converter of Example 1, 3500 kilograms of scrap were charged to the converter followed by 13,000 kilograms of liquid pig iron and 750 kilograms of burnt lime. The oxygen nozzle of 24 mm. inside diameter was lowered to 400 mm. above the bath surface and oxygen blowing was initiated at 8 atmospheres pressure at the nozzle. The rate of flow of oxygen under these conditions was sufficient to reach the carbon end point, that is, the flame drop in about 22 minutes.

In these tests, the water supply was also provided by the condensed Water in the oxygen supply line and the following results were obtained:

Average of 9 heats:

Sulfur in the charge.030% S Sulfur in the blown metal-.0l6% S Degree of desulfurization-47.0%

Average of 19 heats:

Sulfur in the charge.038% S Sulfur in the blown metal.016% S Degree of desulfurization-58.0%

It may be seen from the foregoing results, that desulfurization accomplished solely by the water contained in the oxygen gas at least equals or exceeds the maximum degrees of desulfurization which are normally obtainable utilizing lime or soda ash for desulfurizing.

EXAMPLE 3 Sulfur Contents Water Degree of Eeat No. Added, Desulfur- Liters Charge, Finished ization, percent Steel, percent percent BV 218 28 O46 027 41 BV 221 0 3O 078 037 52 The effectiveness of water in desulfurizing is markedly shown in this example, since the water supply was discontinued after the first half of the total refining period.

The following tests and results illustrate the effectiveness of water, either as steam or liquid water, in eliminating or substantially reducing the iron oxide-containing fume generated in refining of pig iron by surface blowing with oxygen.

The tests were conducted in a small laboratory converter of 25 pound capacity, the oxygen gas (above 99% 0 being supplied through a pressure regulator in the oxygen line to an uncooled copper tube inserted through the mouth of the converter to an appropriate position above the melt surface. In the steam-oxygen mixture tests, steam was supplied at regulated pressures from a small flash boiler, so that both the oxygen and steam were at p.s.i.g., the quantities being measured by Fisher Porter rotometers, the two gases being intermixed and supplied together to the above-mentioned copper lance. In the tests utilizing water instead of steam, water was introduced into a oxygen line by means of a Mi" water line, the water being taken from a 120 p.s.i. source, and regulated by a calibrated needle valve to permit the introduction of varying quantities of water into the oxygen stream.

The converter was heated to operating temperature using coke and oxygen. Solid red hot pig iron was added on the top of the burning coke and oxygen blowing was continued to melt the pig iron with silicon oxidation occurring more or less simultaneously with melting.

Asset forth in the tabulated data below, visual observations were made of the gases emitted from the converter at several intervals during a given blow, and test conditions in regard to quantities of steam or liquid water were alternated with control conditions, that is, no steam or water addition. This procedure permitted a more accurate observation of the actual changes effected between test conditions and control conditions. As also indicated in the tables below, photographic evidence was taken with each observation during the test runs. The blowing time .to reach the carbon flame drop (carbon end point) for the small charges at the indicated oxygen flow rates was about 7 to 9 minutes measured from about three minutes after adding the solid pig iron, which was approximately the end of the melt down period.

Table l.--Oxygen-steam mixtures 2 By volume steam at 80 p.s.i.g. 325 F.; oxygen at 80 p.s.i.g. 60 F.

Table II.-Oxygen-water mixtures 7 Flow Water, Approximate Time, Minutes Photo Rate Lbs/Cu.

, 1 Number Oxygen, Ft. e f.m.

66 6 None 68 5 None 71 5 None 73 4. 6 None 75 4. 5 None 1 After adding pig iron.

In addition to the foregoing test runs, other tests were performed alternating the conditions with oxygen only and approximately equal volumes of oxygen and steam both at 80 p.s.i.g. with the steam at a temperature of 325 F., this proportion of oxygen and steam being maintained during those intervals when the mixture was used. In such tests the oxygen flow rate was about 7 s.c.f. per minute. In still another test, oxygen was supplied at about 6 c.f.m. with steam at approximately 5 c.f.m. (80 p.s.i. and 325 F.) throughout the test during those alternate intervals when steam was added.

Throughout all of the foregoing tests during those intervals in which oxygen alone was blown onto the metal, a relatively heavy dust laden fume or smoke was visibly evident in the ofi gases from the converter, with the sole exception of a noticeable reduction in the amount of fume or smoke in run 0 at seven minutes, which was near the end of the blowing period as determined by the carbon flame drop. A visible and substantial reduction in the fume or smoke, that is, the dust content of the off gases was evident, even at the smallest quantities of steam or water utilized. With increase in amounts of either steam or water, the reduction in smoke or fume increased so that it was completely eliminated, or substantially so, throughout substantially all of the ranges of steamoxygen and water-oxygen test mixtures.

Although the invention has been specifically exemplified as applied to the process of blowing with high purity oxygen in a basic converter, it should be pointed out as a definite advantage of the invention that desulfurization by this method may be accomplished in the acid converter processes in which, of course, desulfurizing by lime or soda ash cannot be accomplished, since the basic slag components would attack the acid silica lining. In addition, the process of the invention is equally applicable to any steelmaking process, including the more widely used open hearth and electric furnace processes, where effective desulfurizing is desired.

The invention is further fully applicable for the combined result of desulfurizing and fume elimination in all of those processes employing oxygen or oxygen-enriched air, that is, a refining gas containing oxygen in amount exceeding the normal 21% by volume in ordinary air, in which such refining gas is surface blown onto the melt during the entire refining period or for any portion thereof. All such processes, including submerged oxygen lancing, as well as high velocity oxygen jets blown from above the melt surface have a charatceristic iron fume problem which the present invention substantially eliminates.

The term water as employed in the appended claims is intended to embrace the compound H O in either the liquid or vapor state. It should also be noted that the invention is not limited to steam or liquid water impingement upon the molten metal surface, it being only neces sary that the water or other hydrogen-yielding substance be brought into contact with the melt surface. Such condition would include the addition of water with a slag forming component by drenching thereof, e.g. lime; and

- also the introduction of water as vapor or liquid slightly below the melt surface, although this latter procedure is regarded as more feasible when employing steam. Specifically, such alternative would recommend itself in the application of the invention to submerged oxygen lancing, and should greatly contribute to an increased life on the tip of the submerged lance, whether metallic or refractory.

It is to be noted that the present invention distinguishes from previously proposed processes of bottom blowing in conventional Bessemer or Thomas converters with steam and oxygen in that the absorption of hydrogen in the finished steel is unavoidable in such processes due to the extreme mixing effect caused by blowing the refining gas through the entire depth of the melt. This is clearly recognized in such processes, where it is indicated that adsorbed hydrogen difficulties are avoided only with respect to effervescent steels, i.e., rimming steels. This bottom blown process is not amenable to discontinuing the steam supply due to excessive refractory wear or tuyere destruction when only oxygen is blown through bottom tuyeres.

Various modifications may be made to the process without departing from the essential principles of the invention, which is intended to be limited only by the scope of the appended claims.

What we claim is:

1. In the method of refining impure molten ferrous metal in the presence of a slag in a refractory-lined converter vessel by surface blowing with an oxygen-containing gas, the improvement in desulfurizing the molten metal under oxidizing conditions by removal of sulfur as a gaseous product, which comprises introducing a hydrogen providing substance from above the molten metal surface through the slag layer onto the surface of the molten metal in the area of the high temperature oxygen-metal reaction zone for reaction with the sulfur in substantially the entire melt.

2. In the production of steel by the refining of a molten ferrous metal bath comprising carbon and sulfur impurities by surface blowing with an oxygen-containing gas, the improved method of desnlfurizing said molten metal by removal of sulfur as a gaseous product, which comprises under oxidizing conditions during the refining of the molten metal introducing water from above the molten metal surface into the localized high temperature oxygen-metal reaction zone so as to contact the molten metal surface, the hydrogen liberated by dissociation of the water at the temperature of the molten metal reacting with the sulfur in substantially the entire melt to produce gaseous hydrogen sulfide.

3. A process according to claim 2 in which the introduction of water into the refining zone is discontinued prior to the end of the refining period to remove contained hydrogen from the molten metal by agitation due to carbon monoxide evolution.

4. A process according to claim 2 in which the water is introduced into contact with the molten metal surface in the form of a water-wetted slag-forming constituent.

5. A process according to claim 4 in which the water wetted slag-forming constituent is limestone.

6. In the refining of impure molten ferrous metal in which a refining gas containing oxygen in excess of 21% by volume is surface contacted with the molten metal during at least a portion of the refining period, and an iron oxide-containing fume is produced by the high temperature oxygen-molten metal reactions, the improved method of desnlfurizing said impure molten ferrous metal and substantially eliminating said fume, which comprises introducing from above the molten metal surface a substance containing a hydrogen-yielding compound so as to contact the surface of the molten metal in the zone of high temperature oxygen-metal reaction, said hydrogen-yielding compound dissociating at the temperature of the molten metal by endothermic reaction thereby cooling the oxygen-metal reaction zone and preventing fume formation, and desnlfurizing said metal by reaction of the hydrogen liberated from said hydrogen-yielding compound with the sulphur content of said metal.

7. A process according to claim 6 in which oxygen is the refining gas and water is the hydrogen-yielding compound and they are introduced as a mixture.

8. A process according to claim 7 in which oxygen is the refining gas and the water is steam supplied in an amount up to about 50% by volume of the oxygenwater mixture.

9. In the method of refining impure molten ferrous metal in the presence of a slag-in a refractory-lined converter vessel by blowing an oxygen-containing gas downwardly into contact with the surface of the metal, the improvement in desnlfurizing the molten metal under oxidizing conditions by removal of sulfur as a gaseous product, which comprises discharging from above the molten metal surface at least one stream of water downwardly through the slag layer onto the surface of the molten metal in the area of the high temperature oxygen-metal reaction zone, the hydrogen liberated by dissociation of water at the temperature of the molten metal reacting with the sulfur in substantially the entire melt to produce gaseous hydrogen sulfide.

10. In the production of steel by the refining of molten ferrous metal containing carbon and sulfur impurities, wherein said metal is substantially completely refined by blowing oxygen gas downwardly onto the surface of the molten metal during a portion only of the refining period to accelerate decarburization and the resulting high temperature oxygen-metal reaction zone produces a dense iron oxide-containing fume in the ofi gases, the improved method of desnlfurizing said ferrous metal and substantially completely eliminating said fume, which comprises initially introducing water from above the molten metal surface with the start up of the flow of oxygen at a carbon content in the molten metal of not substantially in excess of 0.5% C. into contact with the molten metal in the high temperature oxygen-metal reaction zone to cool the metal in said zone by endothermic dissociation of the water, desnlfurizing said molten metal by reaction of the hydrogen produced by said water dissociation with the sulfur in the melt, and discontinuing the supply of water about 5 to 20 minutes prior to the end of the oxygen blowing period.

References Cited in the file of this patent UNITED STATES PATENTS 65,830 Reese June 18, 1867 152,617 Dillon June 30, 1874 283,241 Henderson Aug. 14, 1883 627,855 Key June 27, 1899 723,501 Thofehrn Mar. 24, 1903 1,019,965 Kelly Mar. 12, 1912 2,598,393 Kalling et al May 27, 1952 2,672,413 Daubersy Mar. 16, 1954 2,741,555 Cuscoleca et al. Apr. 10, 1956 FOREIGN PATENTS 1,001 Great Britain 1854 2,314 Great Britain 1879 3,624 Great Britain 1879 533,911 Great Britain Feb. 24, 1941 752,555 Great Britain July 11, 1956 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,892,699 June 30, 1959 Chester R, Austin et a1.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should readas corrected below.

Column 9, line 35,. Table I, opposite "Run P:-- 5"" under the sub-heading ""1335. Per C11 Ft. 0. for-"0.2 read .02 c'olumn 10 line 30. for "charatceristic" read characteristic Signed and sealed this 13th day of September 1960.

(SEAL) Attest:

KARL H. AXLI'NE? ROBERT C. WATSON Attesting Officer Commissioner of Patents

Claims (1)

1. IN THE METHOD OF REFINING IMPURE MOLTEN FERROUS METAL IN THE PRESENCE OF A SLAG IN A REFRACTORY-LINED CONVERTER VESSEL BY SURFACE BLOWING WIHT AN OXYGEN-CONTAINING GAS, THE IMPROVEMENT IN DESULFIRIZING THE MOLTEN METAL UNDER OXIDIZING CONDITIONS BY REMOVAL OF SULFUR AS A GASEOUS PRODUCT, WHICH COMPRISES INTRODUCING A HYDROGEN PROVIDING SUBSTANCE FROM ABOVE THE MOLTEN METAL SURFACE THROUGH THE SLAG LAYER ONTO THE SURFACE OF THE MOLTEN METAL IN THE AREA OF THE HIGH TEMPERATURE OXYGEN-METAL REACTION ZONE FOR REACTION WITH THE SULFUR IN SUBSTANTIALLY THE ENTIRE MELT.