US3507642A - Process for producing corrosion resistant steel - Google Patents

Description

A ril 21, 1970 R. B. sHAw I PROCESS FOR PRODUCING CORROSION RESISTANT STEEL Filed June 2, 1969 4 3 3 2 2 2 4 0 ash 5 221E925 a Slag Bus/city %Ca0+Mg0 /NVEIVTOR. R/CHARD B. SHAW wmnifiw Attorney United States Patent 3,507,642 PROCESS FOR PRODUCING CORROSION RESISTANT STEEL Richard B. Shaw, Natrona Heights, Pa., assignor to Allegheny Ludlum Steel Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Continuation-impart of application Ser. No. 603,717, Dec. 22, 1966. This application June 2, 1969, Ser. No. 829,630

Int. Cl. C21c 7/00 US. Cl. 75--52 26 Claims ABSTRACT OF THE DISCLOSURE An oxygen refining process for producing corrosion resistant stainless steels. A charge of liquid hot metal and scrap is combined in a vessel with slag forming ingredients. Oxygen is injected into the vessels contents, thereby refining the charge and forming a slag containing chromium, iron and manganese metallic values. A reducing agent is added to the slag and turbulently mixed with the slag and metal, effecting a return of the metallic values to the metal. The metal is transferred to a container wherein adjustments are made to the steels chemistry to bring it up to specifications.

This application is a continuation-in-part of application Ser. No. 603,717 filed Dec. 22, 1966 now abandoned, which in turn is a continuation-impart of now abandoned application Ser. No. 517,435 filed Dec. 29, 1965, which in turn is a continuation-in-part of now abandoned application Ser. No. 290,299 filed June 25, 1963.

The invention relates to an oxygen refining method for producing corrosion resistant steels and more particularly to an oxygen refining method for producing corrosion resistant steels utilizing either the Electric Furnace or the Basic Oxygen Furnace.

Prior to this invention, the production of corrosion,

resistant steels required a costly and time consuming subsequent operation to recover chromium from the slag. When oxygen is injected into a molten metal bath, chromium, iron and manganese are oxidized into the slag along with silicon, while carbon is given off as a gas; e.g., carbon monoxide. Thermodynamically, this could be avoided by injecting oxygen at a temperature in the order of 3800 F. since carbon preferentially oxidizes with respect to chromium at these temperatures. Use of these temperatures is today, however, out of the question as refractories which could withstand them and which would be compatible with the production of corrosion resistant steels are not commercially available.

The present invention describes an oxygen refining method for producing corrosion resistant stainless steels which economically recovers chromium values from the slag without need for a subsequent operation, while maintaining temperatures low enough to protect the refractory material of the vessel. It further provides a process for making final chemistry adjustments within the container; e.g., dummy ladle, which receives the molten metal from the vessel. This is a considerable time saving over prior processes which returned the metal to the vessel for final adjustments. Prior to this invention, long furnace refining times were thought necessary for good quality corrosion resistant steel.

It is accordingly an object of this invention to provide an oxygen refining process for producing corrosion resistant steels.

It is a further object of this invention to provide an oxygen refining process for producing corrosion resistant steels which obviates the need for a subsequent operation to recover chromium values from the slag.

It is an additional object of this invention to provide an oxygen refining process for producing corrosion resistant steels which permits final chemistry adjustments without a return of molten metal to the furnace; i.e., the vessel.

The foregoing and other objects of the invention will be best understood from the following description, reference being had to the accompanying drawing, wherein the figure is a plot showing how the percentage of chromium in the reduced slag of this invention varies with slag basicity.

The following paragraphs describe the oxygen refining process of this invention. They are directed to Basic Oxygen Furnace (BOF) type processes since they constitute a large portion of oxygen refining processes. Reference, however, will be made to Electric Furnaces where pertinent.

Processing in accordance with this invention; i.e., for BOF embodiments, is begun by forming an initial charge of liquid hot metal and cold or preheated scrap. For the purpose of this invention scrap is considered to be all additions with the exceptions of the liquid hot metal, slag forming ingredients, slag conditioners and reducing agents. The relative amounts of liquid hot metal and scrap and their makeup are thermally balanced so that the final temperature of the oxygen blown metal (discussed below) is in excess of 3250 F. and preferably between 3400 and 3600 F. The initial charge preferably contains at least 50% liquid hot metal. Higher percentages of scrap can be used if it is preheated. The liquid hot metal can be chromium free or chromium containing. A typical analysis for a chromium free hot metal is 4.25% C, 0.5% Si, 0.5% Mn, less than 0.25% S, less than 0.03% P, balance Fe and a typical analysis for a chromium containing hot metal is 4.0% C, 0.2% Mn, 1.00% Si, 11.65% Cr, 8.9% Ni, less than 0.03% P, less than 0.03% S, balance Fe. Chromium free hot metal is preferred as it permits greater flexibility in the melt shop. The scrap is preferably stainless steel and/or high C ferrochromium. Other sources of scrap are chromium bearing materials such as ferrochromiurn-silicon and chrome ore. The initial charge could use low C ferrochromium and/or metallic chromium but their use would not be economical. Chromium free scrap is usable when a chromium containing hot metal is employed. Nickel could be present in the liquid hot metal and/ or the scrap; e.g., nickel-bearing materials or nickel sinter, if a chromium-nickel steel is to be produced. The average nickel content in the charge is preferably the analysis desired in the final product but could be 1 to 2% higher than the final analysis because of non-nickel bearing materials added later in the process; e.g., low C ferrochromium. The relative order of charging; i.e., scrap or hot metal first, is of little importance.

Slag forming ingredients and possibly slag conditioners are added to the charge. They can be added before and/ or during oxygen blowing (discussed below). Typical slag forming ingredients are burnt lime and dolomitic burnt lime. They are added to form a calculated CaO-l-MgO/SiO slag ratio of at least 0.5, preferably 1.0-2.0, after reduction (discussed below). The minimum ratio of 0.5 and the minimum preferred ratio of 1.0 are set as they place a maximum limit on the amount of chromium within the reduced slag. The figure shows how the chromium content of the reduced slag varies with slag basicity. Minimum basicity ratio settings are additionally beneficial since refractory lining attack is minimized with high bascity ratios. The upper preferred ratio is set at 2 as slags with higher basicity ratios return only slightly larger amounts of chromium to the molten metal and require considerably larger amounts of slag forming ingredients; e.g., lime. Furthermore, these larger quantities of slag forming ingredients produce larger quantities of slag which could result in slag slopping over the vessel or container. Slopping is hazardous to operating personnel and can result in the loss of an appreciable quantity of slag, together with its contained chromium content. Slag conditioners can be added to prevent the slag containing layer from becoming too thick and impervious to good oxygen penetration during oxygen blowing. Typical slag conditioners are fluorspar, sodium carbonate, aluminum dross, cryolite and sodium nitrate.

Oxygen is injected into the charge of liquid hot metal and scrap by top blowing; i.e., blowing from a position some fixed distance over the calculated height of the slag containing layer, by submerged blowing; i.e., blowing from a level below the calculated height of the slag containing layer or by combinations of both top and submerged blowing. Heat size and lance configuration; e.g., number of orifices and angles of orifices, determine the height of top blowing. The injected oxygen reacts with the chromium, iron, manganese, silicon and carbon of the liquid hot metal, thereby generating heat which raises the temperature of the liquid hot metal and melts the scrap. It supply is shut off when the carbon content of the charge is believed to be below 0.15%, preferably below 0.10%, and when the final temperature of the molten metal is at least 3250 F., preferably 3400 to 3600 F. The heat can be reblown if the temperature is too low or if the carbon content is too high. Silicon can be added to the charge to help it attain the desired temperature. Molten metal at temperatures less than 3250" F. is not conducive to further treatment. It is not hot enough to accept the quantities of reduction mix necessary to adjust the alloy composition. Furthermore, Cr, Mn and Fe would preferentially oxidize at lower temperatures. Low temperatures favore the oxidation of chromium, manganese and iron while higher temperatures favor the oxidation of carbon.

A reduction mix is added to the vessel to adust the alloy composition when the carbon content of the charge is below 0.15% and when the temperature of the metal is at least 3250 F. It should contain a suflicient quantity of reducing agent to substantially reduce the oxidized chromium, manganese and iron. The preferred reducing agents are silicon-bearing materials. Typical silicon-bearing materials are ferrosilicon and ferrochromium silicon. The reduction mix can also contain scrap; e.g., low C ferrochromium and low C stainless steel, and slag conditioners. The scrap is added to reduce the temperature to a suitable vessel tapping temperature; e.g., less than 3200 F. and to adjust the chemistry. Nickel could be present in the scrap; e.g., nickel bearing material or nickel sinter, if a chromium-nickel steel is being produced. Slag conditioners such as fluorspar, sodium carbonate, aluminum dross, cryolite and sodium nitrate assist in the reduction.

To achieve proper reduction it is necessary to create a turbulent mixing of slag and metal. This can be accomplished in a number of ways. A fluid under pressure could be injected into the molten metal and slag by top blowing; i.e., blowing from a position some fixed distance over the calculated height of the slag containing layer, by submerged blowing; i.e., blowing from a level below the calculated height of the slag containing layer or by combinations of both top and submerged blowing. Typical mixing fluids are dry air; e.g., air with a dew point of less than about -20 F., non-reactive gases; e.g., argon and nitrogen, and mixtures thereof, An alternative or additive method involves tapping over a lip of the vessel rather than through a tap hole. This mixes slag and molten metal as it passes from the vessel to the container. A third method comprises the injection of a fluid under pressure into the container receiving the molten metal and 4 slag while the molten metal and slag is being tapped into it. This method can be coupled with either or both of the first two methods to effect still greater mixing. Addi tional methods include paddling and induction coil stirring. Mixing results from electric furnace power is not sufiicient to achieve proper reduction.

Molten metal and slag are poured; e.g., tapped, from the vessel into a container; e.g., dummy ladle. The slag can be partially or substantially fully reduced at this time. If it is not substantially fully reduced, reduction is completed during pouring or shortly thereafter; e.g., before the temperature drops below 3050 F. The container could have additions; e.g., electrolytic manganese, electrolytic nickel and low C ferrochromium, added to it prior to pouring. These additions are determined by analyzing the results of turndown tests performed immediately after oxygen blowing. After pouring, preliminary chemical and temperature tests of the molten metal are taken and the slag is removed; e.g., decanted or siphoned. Typical chemical tests check for C, Mn, P, S, Cr, Ni, Mo, Pb, Cu and Sn. A thin layer of slag can be left upon the molten metal while awaiting results from the preliminary chemical tests. Insulating material; e.g., vermiculite, is placed on top of the container to minimize heat loss and maintain molten metal at a temperature high enough to accept final additions. This temperature is dependent upon the quantity and makeup of the final additions as well as the heat size and is generally between 2800 F. and 3200 F., preferably 2900" F. to 3100 F. If the temperature of the molten metal is too cold to satisfactorily accept final additions, it can be effectively increased by controlled additions of a silicon-bearing material; e.g., ferrosilicon, followed by a short oxygen blow. This blowing, however, generates the formation of a siliceous slag which should be decanted off before the final additions and final slag ingredients are added. Final additions; e.g., low C ferrochromium, electrolytic Mn, electrolytic Ni, ferrosilicon and ferrotitanium, are added to the molten metal upon receipt of the preliminary chemical test results to adjust the steels chemistry to specifications. Slag forming ingredients; e.g., burnt lime, and slag conditioners; e.g., fluorspar, could be added along with the final additions, thereby forming a final slag. The molten metal is preferably agitated to aid in the melting and alloying of the final additions and to aid in forming a slag by liquefying the slag forming ingredients. A preferred form of agitation comprising injection of a fluid under pressure. Typical agitating fluids are dry air; e.g., air with a dew point of less than about 20 F., inert gases; e.g., argon and nitrogen, and mixtures thereof. Illustrative methods of in ection are:

(1) Passing fluid through a porous plug with which the container is equipped; and

(2) Passing fluid through a refractory tube within the container. Other means for agitating include induction coils.

The molten metal in the container and the final slag are poured into a second container; e.g., teeming ladle, When the final chemistry adjustments are completed and when the temperature of the molten metal is in the desired range. This desired temperature range varies with the chemistry of the steel and is generally between 2700 and 2950 F. Final additions could be made within the second container if the molten metal is at a sufliciently high enough temperature to satisfactorily accept them. Titanium additions are preferably made in the second container since they are dissolvable at low temperatures and readily oxidize. The second container can be supplied with desulphurizing ingredients prior to pouring so as desulphurize the metal during pouring. Metal in the second container may be held for a predetermined time before being cast into ingots.

A particular embodiment of this invention utilizes a charge of liquid hot metal containing at least 10% by weight of chromium and in excess of 1% carbon and scrap metal comprising about 10 to 40% by weight of the liquid hot metal. It comprises the following steps:

(1) Forming the charge of liquid hot metal and scrap in a vessel;

(2) Adding slag forming ingredients and directing a stream of oxygen to impinge upon the charge within the vessel to reduce the carbon content of the charge below about 1%;

(3) Continuing the flow of oxygen through a submersible lance to said charge until the carbon content of the liquid hot metal is less than 0.10%;

(4) Interrupting the flow of oxygen through said submersible lance;

(5) Adding a reduction mix containing a reducing agent and a chromium-containing compound;

(6) Introducing a submersible lance into the slag containing layer and flowing a non-reactive gas under pressure through said lance to said slag to effect a turbulence, to thereby aid in the reduction of the chromium contained in the slag;

l (7) Transferring the contents of the vessel to a dummy adle;

(8) Passing a non-reactive gas through the contents of the ladle to aid in the completion of the reduction of the metallic values contained within the slag and to homogenize the steel bath with respect to chemistry, the gas passing through a refractory tube inserted within the contents of the ladle or through a porous plug with which the ladle is equipped;

(9) Decanting the slag;

(10) Adding the final additions for proper chemistry and the final slag forming ingredients;

blown onto the charge at 6500 cubic feet per minute at a pressure of 160 pounds per square inch. Six thousand pounds of burnt lime, 2500 pounds of dolomitic lime and 1500 pounds of iron ore pellets were added to the vessel. Oxygen supply was shut off when the temperature of the molten metal was 3480 F. A reduction mix was added to the vessel. It comprised 17,500 pounds of type 430 stainless steel (slab form), 8,470 pounds of chromiumsilicon and 1100 pounds of spar. The slag and metal were mixed with argon to promote reduction. After mixing, the temperature was 3250 F. The slag and metal were then tapped over the lip of the vessel into a dummy ladle. Five hundred pounds of electrolytic manganese were placed in the dummy ladle prior to tapping. Argon was passed through the dummy ladle during tapping. The slag was decanted and the metal was tested for temperature and chemistry. Chemical tests revealed that the metal was comprised of 0.045% C, 0.39% Mn, 0.29% Si, 11.68% Cr, 0.13 Ni, balance Fe. One hundred sixty pounds of aluminum were plunged into the molten metal and the ladle was covered with vermiculite (zonolite). A temperature reading of 3055" F. was taken. One hundred pounds of electrolytic manganese were added to the dummy ladle and argon was passed through the molten metal. The argon was shut off and the remaining slag was decanted. A temperature reading of 2890 F. was taken. The metal was poured into teeming ladles which contained 1600 pounds of 90% titanium scrap, 80 pounds of aluminum and 100 pounds of cryolite. Casting of the metal into ingots followed.

Found below in Table I are the results of Example I.

TABLE I C Mn P S Si Cr Ni Al Ti Aim 1 0. 060 0. 40/0. 50 1 0. 025 1 0. 025 0.30/0. 40 11. 00/11. 50 1 0. l 0. 10 60 FinalA 0.050 0.45 0.028 0.44 11. 46 46 Final B 0. 048 0. 44 0. 028 0. 018 0. 43 11. 46 0. 11 0. 032 46 Final 0 0. 047 0. 44 0. 44 11. 4 45 1 Maximum.

(11) Passing a non-reactive gas through a refractory tube or a porous plug with which the ladle is equipped to aid in alloying the steel bath and fluxing the final slag;

(12) Pouring the contents of the dummy ladle into a teeming ladle; and

(13) Teeming the contents into ingots.

Other embodiments of this invention utilize medium phosphorus containing liquid hot metals; e.g., ODS-0.5% P, and high phosphorus containing liquid hot metals; e.g., 1.5-2.5 These liquid hot metals generally require at least one additional oxygen blow to lower the phosphorus content to below 0.05%, before processing as described herein can begin. Temperatures in the order of 25003000 F. are preferred for dephosphorizing. Slag forming ingredients; e.g., burnt lime, dolomitic burnt lime and iron oxide bearing materials, and slag conditioners; e.g., fluorspar, are added to the hot metal. High slag basicities, high FeO slags and low temperatures contribute to phosphorus removal. However, if the temperature is too low, difficulty may be encountered ,in deslagging the bath. Furthermore, high iron oxide contents contribute to lower metallic yield.

The following examples are illustrative of several embodiments of the invention.

EXAMPLE I A 144,300 pound charge was placed in a vessel along with 1500 pounds of spar. The charge comprised 105,200 pounds of hot metal and 39,100 pounds of scrap. The composition of the hot metal was 4.44% C, 0 .45% Mn, 0.027% P, 0.018% S, 0.36% Si, 0.067% Cr, 0.056% Ni, 0.092% Cu, 0.005% Sn, balance Fe. The scrap comprised 22,500 pounds of type 430 stainless steel and 16,600 pounds of high C ferrochromium. Oxygen was It shows the chemistry aimed for by the operator and that achieved. Final A is the chemistry of the first ingot poured, final C is the chemistry of the last ingot poured and final B is the chemistry of one of the middle ingots. The process as set forth in Example I resulted in an 87.9% chromium yield and a 90.6% metallic yield.

EXAMPLE II A 33,600 pound charge was placed in a vessel along with 500 pounds of burnt lime, 500 pounds of dolomitic lime and 300 pounds of fiuorspar. The charge comprised 24,800 pounds of hot metal and 8800 pounds of scrap. The composition of the hot metal was 4.28% C, 0.61% Mn, 0.03% P, 1.34% Si, 11.55% Cr, 9.43% Ni, balance substantially Fe. It was at a temperature of 2510 F. The scrap was 18-8 stainless steel. Oxygen was blown onto the charge at 1200 cubic feet per minute. Seventeen hundred pounds of burnt lime, 400 pounds of iron ore pellets and 600 pounds of chrome ore were added to the vessel. Oxygen supply wasshut off when the temperature of the molten metal was 3430 F. Chemical tests revealed that the metal was comprised of 0.043% C, 0.28% Mn, 0.04% P, 7.53% Cr, 10.32% Ni, balance substantially Fe. A reduction mix was added to the vessel. It comprised 2000 pounds of ferrochromium-silicon, 2600 pounds of low C ferrochromium, 800 pounds of stainless steel, pounds of manganese-silicon and 300 pounds of fluorspar. The slag and metal were mixed with dry nitrogen to promote reduction. After mixing, the temperature was 3230 F. The slag and metal were then tapped over the lip of the vessel into a dummy ladle. Two hundred twenty pounds of electrolytic manganese, 180 pounds of electrolytic nickel and 50 pounds of low C ferrochromium were placed in the dummy ladle prior to tapping. The

7 metal was tested for temperature and chemistry. Chemical tests revealed that the metal was comprised of 0.051% C, 0.90% Mn, 0.026% P, 0.43% Si, 18.32% Cr, 9.45% Ni, balance substantially Fe. A temperature reading of 3070 F. was taken. The ladle was covered with vermiclance to said slag to effect a turbulence to thereby aid in the reduction of the chromium contained in said slag, and thereafter refining the liquid metal to the desired composition.

3. The process set forth in claim 2 in which the conulite. Final alloying additions were made. The final alloy- 5 tents of the vessel are transferred to a container equipped ing additions comprised 25 pounds of low C ferrochrome, with a porous plug, a nonreactive gas is admitted through pounds of electrolytic manganese, pounds of electhe porous plug to the contents of the container to aid trolyt1c nickel, 55 pounds of 75% ferrosilicon and 70 m the completlon of the reduction of the metallic values pounds of 70% ferrotitanium. Also added were 400 10 contained Within the slag and to homogenize the steel pounds of burnt lime, pounds of fluorspar, 50 pounds bath with respect to chemlstry prior to refining the liquid of slag thinner and 20 pounds of aluminum grain. Argon metal to the desired chemistry.

was passed through the molten metal to agitate the addi- 4. The process set forth in claim 2 in which the contions. The argon was shut off and the remaining slag was tents of the vessel are transferred to a container, a decanted. A temperature reading of 2890 F. was taken. 15 refractory tube is inserted within the contents of the con- The metal was poured mto teeming ladles and then cast tamer, and a non-reactive gas is admitted through the into ingots. refractory tube to the contents of the container to aid in Found below in Table II are the results of Example II. the completion of the reduction of the metallic values TABLE II 0 Mn Si P S Ct Ni Aim 0.07 1.00 0. 45 0. 03 0. 025 18.35 9. 50 Final 0.053 1.06 0. 51 0.029 0.007 18.65 9.25

Max.

It shows the chemistry aimed for by the operation and contained within the slag and to homogenize the steel that achieved. The prgcess32s4 set fort? in Example II bath lwltlzthretsipect :10 fihemistry prior to refining the liquid resulted inametal weig tof O0 poun s. meta to e esire c emistry.

It is noted that the hot metal of Example I was 5. The process set forth in claim 2 in which the conchromium and niclitel free anc thalt lthe hot rneta}t of tents ofd the t1Yessel are transferred to a first container Example II was c romium an nic e contammg. 1s equlppe wi a porous ug, a non-reactive gas is adalso noted that the sequencecf operations beginning with mitted through the porous plug to the contents of the oxygen blowing, as set out In Examples I and II, could first container to aid 1n the completion of the reduction have been performed in an electric furnace mstead of a 35 of the metallic values contained Within the slag and to basic oxygen furnace. homogenize the steel bath with respect to chemistry, de-

I claim: h cantmg the slag, adding the final additions for chemistry 1. In -the prod1t1 ct1on of ctflrrosion reslstarlltf steells, t; and slag-formimg m gredients to the contents of the first steps comprising, ormmg a c arge lnavesse rom 1qu1 contamer an passing a non-reactive gas through the hot metal and scrap, the liquid hot metal containing at porous plug to aid in alloying the steel bath and flux the least 10% by W ig of mlum and a carbon content final slag, pouring the contents of the first container into inwexgess of hl%f, lthedscgap cirnlprfillgftirfll gnsggil :3 a second container and thereafter pouring the same into 0 y werg o 1qu1 0 me a 1r m'go s. yg to impinge P the Charge Within the Vessel to 6. The process set forth in claim 2 in which the conreduce the carb n C n of the Charge, Such Yg tents of the vessel are transferred to a first container, a l'eactlhg Wlth some of h Fompohehts 0f the Charge to refractory tube is inserted within the contents of the first forumb :tn slragbtllei'ggg tigntslalllillti 21:; fivzlgfv zgf s ar i a ge go cofntaitner, i112 atnorllireactive gas ifs gldmfiitted through the a s e s re rac ory u e o e contents 0 e rst container to the liguiddcttmtinis who; tli l yr nd tut fh fl aid in the completion of the reduction of the metallic 1 re nce o e ow a ou a an C0 g e 0W va ues contained within the slag and to homogenize the of Oxygen t oug d subrflersed lance Untll h Carbon steel bath with respect to chemistry, decanting the slag, eOIlteIlt 0f the hquld metal 15 less thanb0.10%g ,1 lrit p adding the final additions for chemistry and slag-forming g h h of y h through salfi S11 mel'sl e ance to ingredients to the contents of the first contamer and F 0 :1 fg gui r g ibi igggg i ilgto t lfe slgg 31 3 53:5 passing 1? non-reactive 1glajts tlhrough thehreffi-actory tube to n r u 1 g sa1 rn ai in a oyingt e stee at and flux t e nal slag, pour- 1 l f if t i sgull gii tg gl g e fi i i ir l t fiz 55 ing the contents of the first container into a second con- 0 sa1 s ag o e ec a 11 tainer, and thereafter pouring the same into ingots. redhctloh of e chromlhrh {Ohtamed 531d slag f 7. In the production of corrosion resistant steels the et l'efihlhg the hquld metal to the desn'ed steps comprising: injecting oxygen into a vessel holding a Pos1 10H. chromium containin metallic char e with a rbon co 111 the Production of corrosiqn resistant steels: h tent in excess of 0.1.5 and slag fofming ingr ients, sai d Steps compnsmg, formmg aqchflrge a Vessel m ,hquld oxygen reacting with chromium and other metallic and i i f? i li i hot netal ccgntammii non-metallic components of the charge to form reactant F 0 Y Welg t o c romlum '9, a E on is; en products -wh1ch form a sla g together with the slag formexcess f h t compnsldng 1 1 0 to ing ingredients; discontinuing the injection of oxygen 2 by h 9 hquld g f g fi striam into said vessel when the temperature of the metal is in g gi g g g g gfi gggi g g g iyg i gg excess of about 3250 F. and when the carbon content is some of the components of the charge to form additional gi fl i .:f g i z g i fslag thereon, continuing the flow of oxygen through a m g ahgen S S ag 0 re an 5 antla y submersible lance to said charge until the carbon content return t e components to 1 of the liquid metal is less than 010% interrupting the bulently mixing said slag to promote said reduction and flow of oxygen through said lance to the liquid metal, Sald return of metalhc Y adding to the vessel contents a reduction mix containing according to clamfl 7 Wherem Said a reducing agent and a chromium-containing compound, eontlIllllIlg of said ygen injection occurs when the and flowing a nonreactive gas under pressure through said carbon content is less than about 0.10%.

9. A method according to claim 7 wherein said discontinuing of said oxygen injection occurs when the temperature of the metal is from about 3400 F. to about 3600 F.

10. A method according to claim 7 wherein said metallic charge is a chromium and nickel containing metallic charge.

11. A method according to claim 7 wherein said slag forming ingredients are selected from the group consisting of burnt lime and dolomitic burnt lime and wherein said reducing agent is a silicon-bearing material.

12. A method according to claim 11 wherein said reduced slag has a CaO-j-MgO/SiO ratio of at least about 0.5

13. A method according to claim 12 wherein said reduced slag has a CaO-i-MgO/SiO ratio of from about 1.0 to about 2.0.

14. A method according to claim 7 wherein said turbulent mixing comprises injecting a fluid under pressure into said vessel.

15. A method according to claim 14 wherein said fluid is selected from the group consisting of dry air and nonreactive gases.

16. In the production of corrosion resistant steels the steps comprising: injecting oxygen into a vessel holding a chromium containing metallic charge with a carbon content in excess of 0.15% and slag forming ingredients, said oxygen reacting with chromium and other metallic and non-metallic components of the charge to form reactant products 'which form a slag together with the slag forming ingredients; discontinuing the injection of oxygen into said vessel when the temperature of the metal is in excess of about 3250" F. and when the carbon content is less than about 0.15%; adding sufficient quantities of reducing agents to said slag to reduce it and substantially return the metallic components to the metal; turbulently mixing said slag to promote said reduction and said return of metallic values; pouring said metal into a container; and making final alloy additions in said container to effect the production of a corrosion resistant steel of a desired composition.

17. A method according to claim 16 wherein said discontinuing of said oxygen injection occurs when the carbon content is less than about 0.10%.

18. A method according to claim 16 wherein said discontinuing of said oxygen injection occurs when the temperature of the metal is from about 3400 F. to about 3600 F.

19. A method according to claim 16 wherein said metallic charge is a chromium and nickel containing metallic charge.

20. A method according to claim 16 'wherein said slag forming ingredients are selected from the group consisting of burnt lime and dolomitic burnt lime and wherein said reducing agent is a silicon-bearing material.

21. A method according to claim 20 wherein said reduced slag has a CaO+MgO/Si0 ratio of at least about 0.5.

22. A method according to claim 21 wherein said reduced slag has a CaO-i-MgtO/SiO ratio of from about 1.0 to about 2.0.

23. A method according to claim 16 wherein said turbulent mixing comprises injecting a fluid under pressure into said vessel.

24. A method according to claim 23 wherein said fluid is selected from the group consisting of dry air and nonreactive gases.

25. A method according to claim 16 wherein said turbulent mixing and said pouring comprises injecting a fluid under pressure into said vessel and pouring said slag and said metal over a lip of said vessel into said container.

26. A method according to claim 16 including the step of agitating said metal and said final alloy additions in said container to aid in the melting and alloying of said final alloy additions.

References Cited UNITED STATES PATENTS 3,003,865 10/1961 Bridges 6O 3,158,464 11/1964 Chynoweth 7560 3,218,157 11/1965 Dobrowsky et a1. 75-60 RICHARD O. DEAN, Primary Examiner US. Cl. X.R.

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