US2950186A

US2950186A - Method for top blowing pulverulent burnt lime and oxygen into cast iron for refining same

Info

Publication number: US2950186A
Application number: US717932A
Authority: US
Inventors: Allard Marc; Wahl Lucien
Original assignee: Institut de Recherches de la Siderurgie Francaise IRSID
Current assignee: Institut de Recherches de la Siderurgie Francaise IRSID
Priority date: 1957-03-02
Filing date: 1958-02-27
Publication date: 1960-08-23
Anticipated expiration: 1977-08-23

Description

Aug. 23, 1960 fig. 1

fig. 4

ALLARD FI'AL METHOD FOR TOP BLOW OXYGEN INTO CAST IRON FOR REFINING SAME Filed Feb. 27, 1958 ING PULVERULENT BURNT LIME AND 2 Sheets-Sheet 1 -Aug. 23, 1960 M. ALLARD ETAL 2,950,136

METHOD FOR TOP BLOWING PULVERULENT BURNT LIME AND OXYGEN INTO CAST IRON FOR REFINING SAME Filed Feb. 27. 1958 2 Sheets-Sheet 2 nited States Patent IVE/EH01) FOR TOP BLOWING PULVERULENT BURNT LIME AND OXYGEN INTO CAST IRON FDR REFINING SAME Marc Allard, Bernard Trentini, and Lucien Wahl, St.

Germain en Laye, France, assignors to Institut de Recherches de la Siderurgie, Saint Germain en Laye, France, a professional institution of France Filed Feb. 27, 1958, Ser. No. 717,932

Claims priority, application France Mar. 2, 1957 4 Claims. (Cl. 75-52) It is a well known fact that metallurgical methods according to which practically pure oxygen is blown through the agency of nozzles of various shapes over a bath of liquid metal, allow obtaining steel through a refining of the cast iron. The steel thus obtained includes low contents of nitrogen and oxygen dissolved therein. In the case where the phosphorus contents of the original cast iron are not higher than a predetermined value of the magnitude of 0.25%, it is also possible to obtain Very low contents of phosphorus in the final steel which shows thus characteristic properties similar to those of open hearth steel.

However the working of certain large locations of phosphorous iron ore leads to the production of cast iron including much large amounts of phosphorous and the above mentioned limit of about 0.25% may be considerably overstepped. In particular, the iron from the Lorraine mines produces the so-called Thomas or basic cast iron, the phosphorus contents of which are of a magnitude of 2%; other ores lead in practice to the obtention of all the intermediate values between said phosphorus contents ranging consequently between 0.25% and 2%.

It is a well known fact that the application of the above-mentioned method for the production of steel, according to which method practically pure oxygen is blown through nozzles over the bath of liquid metal constituted by cast iron containing more than 0.25% of phosphorus has met with considerable difiiculties. It is not possible in such a case to obtain uniform low contents of phosphorus and of dissolved oxygen as required for obtaining a grade comparable with that of open hearth steel. This is due to the poor contacting conditions for the reaction between the burnt lime and the metal bath, which explains that starting from cast iron the phosphorus contents of which are higher than 0.25%, the elimination of the phosphorus is not yet finished when the desired contents of carbon in the steel have been reached; it is then possible to continue the elimination of the phosphorus only under difiicult conditions and provided a high oxidation of the slag and of the metal is allowed.

As a matter of fact, it is known that, on the one hand, the refining of phosphorous cast iron requires, whatever may be the refinishing method used, large amounts of lime for combining the phosphorus with the slag. More accurately, in the case of the so-called Thomas cast iron containing 1.8% of phosphorus and 0.5% of silicon, there is added as an average 115 kg. of burnt lime per metric ton of cast iron and consequently the amount of lime required for the refining of a bath containing 40 metric tons of castiron for instance rises to a figure of 4,600 kg. which is a very large volume indeed.

It is known on the other hand that the refining of cast iron through the agency of a nozzle blowing practically pure oxygen above the bath clearly distinguishes from a metallurgical standpoint when compared with the refining of cast iron inside a basic converter into the bottom of which the blast is blown.

2,950,186 Patented An 23, 1960 ice In the case of the refining of cast iron in a basic converter into the bottom of which a blast is blown, an enormous volume of nitrogen, about four times the volume of oxygen, is distributed through numerous openings in said bottom and passes through the bath inside which it expands as a consequence of its heating and produces a considerable stirring. Consequently, the burnt lime loaded at the beginning or" operation is energetically stirred, in spite of its large volume, inside the metal bath throughout the duration of the refining, which leads to extremely favorable conditions of contact and reaction with the bath.

In contradistinction, in the case of the refining obtained through a nozzle projecting practically pure oxygen over the surface of the cast iron bath, the stirring conditions and consequently the conditions of reaction with the lime are much less favorable. The gas does not have to pass throughout the mass of metal and there is no nitrogen for ensuring an energetic stirring. Consequently, the sole stirring produced practically is that produced by the evolution of carbon dioxide through the combustion of the carbon, which evolution occurs chiefly in the upper layers. This stirring is less intense and produces contacting conditions and therefore reaction conditions between the lime required for refining and the metal bath which are not sufiicient for obtaining the desired result. Furthermore, no stirring at all is produced as soon as the combustion of the carbon is at end, so that the elimination of the phosphorus from the metal can be obtained only if an exaggerated oxydation of the slag and of the steel through an action of oxygen in localized sections of the bath is allowed.

It is also known that the conditions of contact may be improved by reducing the granular size of the lime eg by resorting to crushed lime. Thus, it is known that in the case of a basic converter into the bottom of which the blast is blown, it is possible to feed the pulverulent lime together with the blast through the openings in the converter bottom.

This general idea of acting on the granulometric size of the lime and of blowing crushed burnt lime together with the refining gas is to be considered when said gas is constituted by pure oxygen and more particularly when said oxygen is blown over the surface of the bath through the agency of a nozzle positioned at one end of a water cooled lance or nozzle. However, for the refining of cast iron or pig iron, whatever may be its contents of phosphorus, the same drawbacks will arise by reason of an insutficient penetration of the jet through the layer of slag and into the bath of metal and also of the presence of an amount of agglomerated lime which is digested only with diificulty as a consequence of an insuificient stirring. Furthermore, the localized formation of iron oxide leads to a violent frothing leading to losses of time, losses of heat and losses of metal, so that it is not possible to provide for the systematic and economical production of steel with low phosphorus contents, the grade of which is at least equivalent to that of open hearth steel. Intricate or expensive methods have also been resorted to, such as for instance the rotation at a more or less high speed of a furnace of a special design which allows obtaining the changing of the contact surfaces and the stirring of the slag and metal and thus reaching phosphorus contents which are sufiiciently low when the carbon contents have been lowered to the desired value.

Our invention has chiefly for its object to remove this drawback of insutficient contact and of poor reaction conditions between the burnt lime and the metal in the method of blowing practically pure oxygen through a nozzle over the surface of a bath of molten pig iron, this being obtained by improvements leading to the obtention of a steel the grade of which is equal to that of open hearth steel, starting from pig iron of any phosphorus content, and particularly from pig iron containing an amount of phosphorus of a magnitude of 2%.

To this end, our invention has for its object a method for'refining. cast iron or pig iron 7througlia lance blowing substantially'pure oxygen over the surface of the bath, our invention being characterized by the fact that the pulverulent burnt lime is fed totally or'partly in a pro gressive manner, that a jet of oxygen and lime of a high penetrating capacity is formed which has a momentum per unit of time which is very large and is concentrated in the vicinity of the axis of the jet blown over the bath, a decarbonization and a dephosphoriza-tion being obtained simultaneously so as to 'ensure"p'ho'sphorus contents which are sufficiently low when the metal has'reached the desired carbon contents.

According to a further feature of our invention, the momentum per unit of time through the surface of contact between the jet. and the theoretical plane of the bath when'at rest, for a distance between said plane and the output end of the nozzle, which is equal to at least 8 times the diameter of the latter, is such that at least 30% of its total value is concentrated round the axis of the jet within a cross-sectional area equal to the output opening of the lance or nozzle.

According to a further feature of our invention, the average momentum per unit of Surface and per unit of time within the above defined area is above 1 kg. per square centimeter (980,000 dy'nes per sq. cm.).

According to a still further feature of our invention, the average speed of the particles along the axis of the jet is equal to at least 0.4 times the speed of the gas which latter is of the magnitude of at least 150 meters per second.

According to another feature of our invention, the concentration of the lime in the oxygen ranges between 0.3 and 30 kg. per cubic meter under normal conditions corresponding to a column of mercury of 76.0 mm. at a temperature of C., said concentration assuming predetermined values between said two limits as required by the operator in accordance with the nature of the pig iron to be treated and to the stage of the operation.

According to yet another feature of our invention, the contents of iron oxide in'sidethe liquid slag is kept under 10% for carbon contents higher than or approximating 1.5% by adjusting the concentrationof the lime in accordance with the chemical composition of the bath, in particular its contents of phosphorus and silicon.

The pulverulent lime blown with the jet may also incorporate substances furthering the formation of the reacting slag, such in particular as fluorspar.

According to a modification, the pulverulent lime blown through the nozzle may incorporate iron oxide, chiefly iron ore. The pulverulent lime may also incorporate a variable amount of lime-stone flux. It is known as a matter of fact that lime-stone flux decomposes and produces CaO which is particularly pure and devoid of sulfur since it is not soiled by the residual material produced by the baking in lime burning kilns.

It will be readily ascertained that the novel feature of the invention resides in the fact that the conditions of contact and reaction between the lime, the oxygen and the bath are extremely favorable. The jet of oxygen and finely subdivided burnt lime assumes, according to our invention, a total moment-um which is far higher than the momentum of the oxygen considered alone, which isobtained -in the same jet. On the other hand, the distribution of said momentum inside the jet is transformed through the introduction of the lime, according to our improved method. These two phenomena allow producing and adjusting through a modification of the concentration of the burnt lime the desired grade of elimination of the carbon, which ensures an eificient stlrring and also an active elimination of the phosphorus.

As a matter of fact, it should be remarked that the elimination of the carbon produced through a particularly penetrating jet of oxygen and finely subdivided suspended burnt lime furthers the local elimination of the phosphorus which is obtained simultaneously and makes it highly efficient, said elimination of the carbon completing said removal of the phosphorus through the resultant stirring of the bath.

Hitherto the methods referred to did not ensure a uniform or suificient penetration of the fluid so that they did not allow refining, inside a converter or the like container, a mass of cast iron including high contents of phosphorus and reducing systematically, simply and economically the contents of phosphorus in steel down to a sufiiciently low figure corresponding to high grade steel. As a matter of fact, as soon as the phosphorus contents in the cast iron were higher than a predetermined limit which was comparatively low, say of a magnitude of 0.2%, the contentsof phosphorus in the metal were still too high when the desired contents of carbon in the steel were reached, even in the most favorable case of the production of steel having low contents of carbon, as in the case of extra mild steel. The continuation of the blowing for such low contents of carbon did not allow' lowering substantially the phosphorus contents in the metal in spite of a substantial enrichment of the slag with iron oxide, which was due to an insuflicient stirring by-the jet, even if its kinetic energy was high. It was impossible to obtain thus lowcontents of phosphorus in the final steel in spite of this enrichment of the slag with iron oxide which enrichment was detrimental to the grade of the steel and also to the economic execution of the method. 7 7

Our improved method allows also solving the difiicult problem of refining simply and economically cast iron having silicon contents above 0.5% together with high contents of phosphorus.

In certain'cases, and as a consequence of the dangerous formation of large amounts of iron oxide due to the lack of penetration of the oxygen jet, it waseven necessary to resort to a supplementary operation consisting chiefly in removing as a preliminary step the silicon from the cast iron. Thus, in the case of basic or Thomas cast'iron, the method of refining through pure oxygen in a rotary kiln required this preliminary treatment as soon as the silicon contents of the cast iron rose above 0.5 V

In contradistinction, the method according to our invention cuts out the tendency of producing projections ascribable to the silicon of the cast iron, and this tendency is opposed in fact by an increase at'the required moment of the concentration of finely subdivided burnt lime in the oxygen, saidincrease being defined and adjusted in accordance with the silicon contents of the cast iron to be treated, the energetic penetration of the blast ensuring the neutralization of the silica in situ at the moment of its formation, said blast cutting out the local formation of iron oxide.

Similarly, and whereas the known methods of refining through a jet of oxygen allow only with ,difiiculty the incorporation of additions such as that of ores having substantial contents of silica, by reason of the danger. of projections, our improved method allows resorting to such additions without any difficulty.

According to our improved method and as a consequence of the large penetrating power of the 'jet, the

' surface of the bath does not act as a reflector for the oxygen or the particles of burnt lime, which'cuts out any carrying along of droplets of liquid cast iron towards the outside of the container and improves the efliciency of the oxygen jet even for high outputs and for lances opening at a distance from the surface.

Our improved method is in fact applicable even more easily to cast iron the phosphorus contents of which are assua e lower than 0.25% and for which the addition of lime is less considerable than in the case of cast iron with higher phosphorus contents, while remaining still large. We obtain thus phosphorus contents in the final steel which are systematically very low and lower in particular than in the cases where our improved method is not applied.

In order to allow our invention to be more clearly understood, we will now describe an embodiment given by way of a mere exemplification, reference being made to the accompanying drawings, wherein:

Fig. l is a perspective view of a jet of homogeneous fluid.

Fig. 2 illustrates in the case of a gasiform jet the distribution of the momenta per unit of time in a plane passing through the axis of the jet of fluid.

Fig. 3 illustrates the distribution of the momenta per unit of time in the case of a jet containing pulverulent material assuming a low speed.

Fig. 4 illustrates the distribution according to our invention of the momenta per unit of time for a jet of pulverulent material forming a suspension in a gas, in a plane passing through the axis of the fluid jet.

Fig. 5 is a diagrammatic view of an arrangement for executing the method according to the invention.

Fig. 6 is a graph showing the modifications in the contents of carbon and phosphorus in the bath during a refining executed in accordance with our method.

In the erspective view according to Fig. 1, the straight line It registers with the axis of the jet, the plane 2 corresponds to the theoretical surface of the liquid bath at rest, the surface 3 to the section of the jet .at the starting point thereof. 4 designates a frusto-cone illustrating the actual jet, and 5 the curve of intersection of said cone with the surface of the metal bath. The curve 6 defines the intersection between the theoretical surface of the bath and the cylinder having as a base the area 3 at the starting point of the jet and the generating lines of which are parallel with the axis of the jet, the surface 7 being the area inside said curve 6.

In Fig. 2, the distances of the different points of the free bath level to he considered are given in abscissae. The ordinates corresponding to each abscissa define the momentum per unit of surface and per unit of time. This magnitude has the dimensions of a pressure and may be expressed in kilogrammes per sq. cm. We obtain thus a curve 8 illustrating the distribution of the momenta per unit of time for difierent points located in the theoretical plane of the bath level with a conventional jet.

Fig. 3 is similar to Fig. 2 but it relates to a jet containing pulverulent material assuming a low speed. The curve 9 illustrates the distribution of the momenta per unit of time in the plane of the figure for points located in the theoretical plane defining the surface of the bath. The gradient of the momenta per unit of time in the vicinity of the axis of the jet difiers but slightly from that illustrated in Fig. 2.

Fig. 4 is obtained in a similar manner, the curve giving the distribution of the momenta per unit of time being shown at 10. In this case, the gradient of the momenta per unit of time is very high in proximity with the axis of the jet: the momenta passing per unit of time through the surface 7 illustrated in Fig. l is equal to at least 30% of the total momenta passing per unit of time through the surface 5 of the said Fig. 1.

Said Fig. 4 illustrates graphically the advantageous properties of our improved jet, which allows a penetration of the oxygen and of the burnt lime throughout the depth of the bath, providing thus the optimum conditions of contact and of reaction between the cast iron and the refining reagents. This surprising efiect is obtained through the concentration of the momenta in the vicinity of the axis of the jet, which is allowed by the increased impulse given to the particles of lime.

The arrangement illustrated in Fig. 5 includes chiefly a converter or the like container 10 provided with a refractory basic lining 12 of tar-coated dolomite the composition of which is similar to that generally used in steelworks producing basic steel. The bottom of said converter, also made of tar-coated dolomite is solid and is not provided with any perforation.

The blast nozzle 13 blowing oxygen above the bath is subjected to a water cooling, as provided by a water jacket having input ports 14 and output ports 15, surrounding the nozzle and carried by the pivoting bracket 16. An apparatus 17 distributing finely subdivided burnt lime is connected with the converter through a pipe 18; said distributor is executed in a conventional manner so as to produce uniform outputs of predeetrmined volumes of very fine powders in suspension in oxygen. This distributor feeds compressed oxygen and finely subdivided lime into the blast nozzle 13. A control board 19 carries the pressure gauges, flow meters and different valves controlling the fluid throughput, and forms part of the arrangement.

According to an experiment made, the apparatus 17 distributing finely subdivided products contains about 800 kg. of lime, the granulometric analysis of which is as follows:

% lower than 1.5 mm. 50% lower than 0.5 mm. 50% lower than 0.1 mm.

of said nozzle is ensured by an intense flow of Water supplied by a pump feeding 10 cubic meters per hour under a pressure of 4 kg. per sq. cm.

At the moment of the charging of the cast iron, the lining heated by the preceding load was at a temperature of 1,200" C. as measured by examining through the nozzle by means of an optic pyrometer of the vanishing filament type.

A charge of 3 metric tons of cast iron was introduced into the converter, said cast iron containing:

Percent 355 2.05 0.50 0.60 S 0.073

The temperature of the cast iron after pouring into the converter was equal to 1180 C.; as measured by means of a thermo-couple of the immersion type. No addition of lime was made over the bath before the raising of the converter. The conveter being raised and set in its vertical position, the bracket carrying the nozzle was caused to pivot, so as to allow sinking said nozzle vertically and bringing it at a distance of about 60 cm. from the static level of the cast iron bath.

The blowing had begun with a throughput of oxygen of 12 cubic meters and of 42 kilogrammes of burnt lime per minute, which corresponds to a concentration of 3.5 kg. of burnt lime per cubic meter of oxygen. Said adjustment had been retained uniformly during the three first minutes. The dangerous period corresponding to the possible projection at the end of the silicon-removing stage being ended, it has been possible to reduce the addition of lime, and during the four following minutes, oxygen has been blown in at the same rate of 12 cubic meters per minute, while the throughput of lime was reduced to 24 kg. per minute, i.e. to a concentration of 2 kg. per cub. met. The throughput of oxygen was then *7 lowered down to 10 cub. met. per minute and the throughput of lime down to 18 kg. per minute, i.e, to a concentration of 1.8 kg. of lime per cub. meat. of oxygen and this adjustment has been retained during minutes. These three periods considered as a Whole lasted 12 minutes and formed the first stage of operation during which stage and for reasons of thermal adjustment, there were introduced gradually through a removable water-cooled spout which has not been illustrated a charge of Swedish ore weighing 75 kg. and having iron contents of 55%, lime contents of 2% and silicon contents of After this first stage, the nozzle was raised, the lime and oxygen admission was switched olf and the converter was returned into its horizontal position.

It has been found, during this first stage, that apart from the very beginning of the refining, corresponding chiefly to the elimination of the silicon from the cast iron, the flame was very hot, which proved an intense decarbonization. .The analysis of a sample of metal removed after this first stage has shown 1.44% of carbon and only 0.210% of phosphorus, the temperature measured with the pyrometer of the immersion type being equal to 1,620 C. Said analysis showed that there was simultaneously obtained a considerable elimination of 'the phosphor-us. Thus, the adjusted and controlled blast of finely subdivided lime suspended in oxygen allowed obtaining simultaneously, under the action of the high penetration of the jet, a highly satisfactory decarbonization and elimination of the phosphorus. This simul-' taneous removal of carbon and phosphorus has led-furthermore to the lowering of the contacts of iron oxide in the slag down to a figure of only 5.2%, which allows a smooth progression of operation at the end of this stage.

The liquid slag showed high contents of sulfur equal to 0.31% which explained the low contents of sulfur in the corresponding metal sample, which was equal to 0.018%. This corresponds thus to a high gradeof desulfuration equal to 75% in relative value. The liquid slag was then skimmed off to a large extent and it was possible to estaimate the weight of slag thus removed in the converter. The converter was then raised again and the nozzle was returned into its operative position and lowered down to a point at about 50 cm. above the bath, i.e., 10 cm. less than during the preceding stage, for which the adjustment was at 60 cm. above the bath.

The blowing'was then resumed during this last stage during 6 minutes with a throughput of oxygen of 10 cub. met. per minute and a throughput of lime of 20 kg. per minute, i.e. a concentration of 2 kg. of limeper cub. met. of oxygen. During this second stage and-for reasons of thermal adjustment, 75 kg. of the same ore as precedingly were fed gradually through the same means as precedingly. At this moment'440 kg. of lime have been injected, which was sufiicient for the refining of the charge of cast iron; the oxygen and lime injection was stopped, the nozzle was raised and the converter returned to horizontality. At this moment, it was found that the bottom of the converter lying, when raised, in alignment with the axis of the jet, had been subjected to a slight erosion due to the action of the lime particles which had passed through the bath. The distance of 60 cm. separating the nozzle from the bath is therefore small and it is possible to increase it.

The final temperature measured with the immersion pyrometer was equal to 1610 C.; the sample obtained showed the following analysis:

C P, S, N, Percent Percent Percent Percent .tentsof carbon and phosphorus being shownat 111.

We will now describe as a second example the chemical and thermal changes arising during the refining of a bath of 20 tons of cast iron through our improved method.

The pig iron had the following composition at the start:

C, Si, Mn, P, Percent Percent Percent Percent Percent and its temperature was1185 C. after pouring into the vessel.

At the end of the first phase (43 cub. met. of oxygen per ton of pig iron), the jet of oxygen and powdered lime had brought the phosphorus contents of the metal to 0.208% while .the carbon contents were still 1.13%. The temperature of 1645 C. permitted the elimination of part of the phosphorus and sulfur initially contained in the pig iron, into the liquid slag containing only 3.8% of iron in' the form of oxide.

At the end of the second phase (9 cub. met. of oxygen per ton of iron, the phosphorus contents of the metal were only 0.035% while there was still 0.520% carbon, and the temperature was 1625 C. The slag containing 10.6% iron was again poured out in part, for the elimination of phosphorus and sulfur.

After the final phase (6 cub. met. of oxygen per ton), the liquid metal in the vessel had the following composition:

0, Mn, P, S, Percent Percent Percent Percent 0, Mn, P, S, N, Percent Percent Percent Percent Percent These very low contents of nitrogen form one of the characteristic properties of the metal obtained according to our invention and it will be remarked that these surprisingly low contents are clearly lower than those obtained in hearth furnaces.

Furthermore, in spite of the use of cast iron with comparatively high contents of sulfur, we have obtained a steel with very low contents of sulfur, which low contents form also a characteristic feature of the met-a1 obtained. 7

Associated with the very low phosphorus contents, these very low contents of nitrogen and sulfur allow considering the metal obtained as a high grade steel.

The examples given show that it is possible to obtain easily, through the method disclosed, an extra-mild high grade steel.

The method according to our invention allows also obtaining directly without any subsequent reintroduction of carbon, high grade steel with higher contents of carbon.

Generally speaking, the method according to our invention shows further and important advantages:

Thus, it leads to a low consumption of basic refractory material per metric ton of steel, said consumption being clearly lower than that obtained with the methods applied hitherto for blowing pure oxygen over the bath. As a matter of fact, on the one hand, the lining is no longer subjected to the projection of droplets of oxidized metal, as generally appear at the point of impact of the jet and, on the other hand, the energetic penetration of the jet concentrates the reaction area inside the bath at a substantial distance from the lining. Furthermore and for the same reasons, it has been found that our improved method allows reducing substantially the evolution of reddish fumes which are highly objectionable in the methods applied hitherto for the refining by means of pure oxygen.

This also cuts out the formation over the surface of the bath of substantial amounts of iron oxide which are detrimental to the life of the lining as occurs when the jet does not penetrate.

Furthermore, the method disclosed allows a napid start ing of the reaction without any special arrangement such as a solid part to be secured to the lance or else to be projected into the bath, as required according to other methods, for perforating the layer of slag protecting the metal bath.

What we claim is:

1. In a method for making low phosphorus, low nitrogen steel from pig irons of widely varying phosphorus content, the step of blowing through a lance having an outelt opening of predetermined cross-sectional area, a jet stream of substantially pure oxygen having suspended therein pulverulent burnt lime against the top surface of a molten bath of said pig iron in downward direction with such a force and in such a manner that said jet stream of oxygen with said pulverulent lime suspended therein penetrates downwardly throughout the depth of the bath into a region near the bottom thereof with the cross-sectional area of said penetrating jet stream remaining substantially equal to the cross-sectional area of the outlet opening of the lance, whereby, due to the substantially complete penetration of the bath depth by the oxygen having the pulverulent lime suspended therein, the reaction thereof with the pig iron bath will occur in that region of said bath where it is most efllcient while, simultaneously, due to the substantially constant diameter of the jet during penetration of the bath, there will be avoided within the bath any substantial turbulence thereof which might adversely affect the reaction between the pig iron and the oxygen having pulverulent lime suspended therein.

2. The method of claim 1 wherein the size of the burnt lime particles is inferior to 2 mm. and their speed along the axis of the jet is equal to at least 0.4 times the speed of oxygen, the latter being equal to at least meters per second.

3. The method of claim 1 wherein the concentration of the burnt lime in the oxygen ranges between 0.3 and 30 kg. per cubic meter under normal conditions corresponding to a column of mercury of 760 mm. at a temperature of 0 C.

4. The method of claim 1 wherein a fluxing agent is incorporated in the suspended pulverulent burnt lime.

References Cited in the file of this patent UNITED STATES PATENTS 723,501 Thofehrn Mar 24, 1903 1,145,506 Pasquier July 6, 1915 2,668,759 Tenenbaum Feb. 9, 1954 2,741,555 Cuscoleca et al Apr. 10, 1956 FOREIGN PATENTS 642,084 Great Britain Aug. 30, 1950 685,326 Great Britain Dec. 31, 1952 756,429 Great Britain Sept. 5, 1956 1,131,035 France Oct. 8, 1956

Claims

1. IN A METHOD FOR MAKING LOW PHOSPHORUS, LOW NITROGEN STEEL FROM PIG IRONS OF WIDELY VARYING PHOSPHORUS CONTENT, THE STEP OF BLOWING THROUGH A LANCE HAVING AN OUTLET OPENING OF PREDETERMINED CROSS-SECTIONAL AREA, A JET STREAM OF SUBSTANTIALLY PURE OXYGEN HAVING SUSPENDED THEREIN PULVERULENT BURNT LIME AGAINST THE TOP SURFACE OF A MOLTEN BATH OF SAID PIG IRON IN DOWNWARD DIRECTION WITH SUCH A FORCE AND IN SUCH A MANNER THAT SAID JET STREAM OF OXYGEN WITH SAID PULVERULENT LIME SUSPENDED THEREIN PENETRATES DOWNWARDLY THROUGHOUT THE DEPTH OF THE BATH INTO A REGION NEAR THE BOTTOM THEREOF WITH THE CROSS-SECTIONAL AREA OF SAID PENETRATING JET STREAM REMAINING SUBSTANTIALLY EQUAL TO THE CROSS-SECTIONAL AREA OF THE OUTLET OPENING OF THE LANCE, WHEREBY, DUE TO THE SUBSTANTIALLY COMPLETE PENETRATION OF THE BATH DEPTH BY THE OXYGEN HAVING A PULVERULENT LIME SUSPENDED THEREIN, THE REACTION THEREOF WITH THE PIG IRON BATH WILL OCCUR IN THAT REGION OF SAID BATH WHERE IT IS MOST EFFICIENT WHILE, SIMULTANEOUSLY, DUE TO THE SUBSTANTIALLY CONSTANT DIAMETER OF THE JET DURING PENETRATION OF THE BATH, THERE WILL BE AVOIDED WITHIN THE BATH ANY SUBSTANTIAL TURBULENCE THEREOF WHICH MIGHT ADVERSELY AFFECT THE REACTION BETWEEN THE PIG IRON AND THE OXYGEN HAVING PULVERULENT LIME SUSPENDED THEREIN.