US2111893A - Method of making steel - Google Patents

Description

Patented Mar. 22, 1938 UNITED as ,lll,89t

METHUD t No Drawing. Application May 29, 193

Serial No. $2,652

This invention relates to an improved steelmaking process and. more particularly to a method of producing low phosphorus steel from high phosphorussteel. This application is a continuation-in-part of my prior application Serial No.

10,715, filed March 12, 1935.

When. pig iron is blown" or oxidized, as in the Bessemer process, the initial phosphorus in the pig iron of between .07-.10% is raised to between approximately .075-.110% due to the elimination of various metalloids such as carbon, manganese, and silicon. No phosphorus is eliminated from the metal in the process. Steels containing phosphorus contents of this order, .08-.11%, are much stiffer than basic open hearth steels with the same carbon and manganese contents. Bessemer steels by reason of the lack of ductility are, therefore, limited in their useful applications.

It is well known that in the presence of oxidizmolten steel baths can be lowered. In the presence of calcium oxide,'the phosphorus pentoxide obtained by the action of phosphorus with iron oxide forms a relatively stable calcium phosphate compound in accordance'with the following re- The usual basic materials employed are limestone or lime, and the usual oxidizing materials employed are ore, roll scale, cinder, etc. These melt down together to form slags. These materials must be converted into liquid form before the phosphorus reaction may be obtained. In basic open hearth and basic electric furnace processes the above materials are incorporated as part of the charge. Special methods of dephosphorizing Bessemer steel have been proposed whereby the aforesaid basic and oxidizing materials mixed in various proportions are added to the ladle and the steel to be dephosphorized is poured thereon or therethrough. These materials, when once used and converted into a molten form (slag), cannot be again used for dephosphorizing subsequent heats.

45 The use of special mixtures of basic and oxidizing materials for dephosphorizing purposes and the restriction of themixture to a single use is highly undesirable from an economic standpoint, wherein the initial cost of the materials is a rela- 50 tively small item. The heating to fusion in separate vessels, the apportionina of definite amounts of the fused material for given masses of molten metal, the practice of the dephosphorizing process on a relatively small scale, are

factors which largely increase the costs of such processes.

One of the objects of the present invention is to provide a relatively simple, cheap and effective process for the dephosphorizing of Bessemer or ing and basic slags the phosphorus content of other high phosphorus steels. Another object is to provide a relatively inexpensive and efficient slag composition effective for the dephosphorizingof steels containing relatively high phosphorus. Another object is to provide a process effective for dephosphorizing high phosphorus steels on a large scale basis. Other objects and advantages will be apparent as the invention is more fully disclosed;

In accordance with these objects I have found that the end slag product of. theusual open hearth furnace wherein a low carbon basic steel has been produced is admirably suitable for the dephosphorizing of high phosphorus steels particularly those steels which are in the highly oxidized condition which Bessemer steels are in at the conclusion of the oxidizing blow. I have further found that these slags have a relatively high power of absorbing phosphorus and that consequently they may be repeatedly employed as dephosphorizing agents.

1 therefore propose a new method for manufacturing low phosphorus steels which essentially comprises a duplex process wherein I first produce a melt in a regenerative furnace of basic low. carbon steel in accordance with standard practice, withdraw the melt, retaining the slag on the hearth, and then charge repeatedly into the furnace a number of melts of oxidized high phose phorus steel, retaining each charge in contact with the slag to permit the dephosphorizing reaction to proceed to completion, and withdrawing each charge at the conclusion of this time interval into a ladleor other suitable vessel for the addition thereto of such other constituents as may be desired in the steel, such as manganese, aluminum, silicon, etc.

The phosphorus absorbing properties of the slag in the furnace gradually become lowered and when the slag is unable to remove the phosphorus from the molten metal down to the point desired. the slag is withdrawn from the furnace and a second melt of low carbon basic steel ismade therein. The slag resulting is then utilized to dephosphorize further successive melts or increments of oxidized Bessemer steel in the same manner as heretofore described. Thus the proces of the present invention may be practiced as a continuous p'rocessof manufacturing low phosphorus steels. v

By my process I have been able to lower the phosphorus content of Bessemer blown metal (steel) containing between .075 to 1l ll;% phosphorus down to as low as .010% phosphorus, the steel so produced possessing required physical properties'for useful employment in products not now satisfactorily served by present types of Bessemer steels.

The slag or end product of a low carbon basic open hearth steel, due to the fact that the carhon is oxidized by means of the slag, must necessarily be highly oxidizing. It is also true that such slags are also very basic. Characteristic open hearth slags from low carbon steel are as follows:

In order to satisfy the S102 and P205 contents of the slag itself, a certain amount of the lime (CaO) is required. For each part (by weight) of S102 in the slag approximately 1.86 parts CaO is required. A. low carbon slag usually contains Sim-12%; Ciao-43%; FeO total-30%; Pam-2%. In such a slag there is available an excess CaO content of 24.70% beyond that required for satisfying the silica (S102) and the phosphorus (PzOs) content of the slag. The slag, therefore, is extremely basic. Slags of this character are also highly oxidizing as indicated by the iron oxide content of the slag and, therefore, useful in dephosphorizing Bessemer or other steels.

In accordance with the present invention the method is practiced preferably as follows:

A tilting basic open hearth furnace is preferably used in the practice of the present invention. A standard basic low carbon steel is made therein by standard practices. Such standard practice may be varied widely as one skilled in the art will recognize. The furnace is charged -with pig iron (hot metal), blown metal together with lime, limestone and ore each in proportions suitable for the purpose and the charge is melted down. As an example, three typical charges are listed below:

airless retained in the furnace, only enough of this slag being voided from the furnace to cover the steel ladle in the customary manner. The furnace is again charged with more blown metal and the process repeated again and again until the slag becomes ineffective to reduce the phosphorus content of the blown metal to the extent desired. The slag then is removed and a second melt of basic open hearth steel is made in the furnace and the end slag thereof is retained therein when the melt is tapped out.

Each successive charge of dephosphorized metal after tapping from the furnace may be treated in the ladle with various addition materials and alloying constituents, such as manganese, silicon, carbon, aluminum, etc. to form the steel composition desired.

If any siliceous Bessemer slag is accidently charged into the tilting furnace along with the "blown metal, only sufficient lime is introduced into the bath to compensate for this extra silica (SiOz). By this process it is possible to use an extremely small amount of slag. to effect the required dephosphorization of a relatively large volume of oxidized high phosphorus steel through repeated use of the initial end slag of the basic open hearth furnace.

The following example illustrates the repetitive character of the process. After a low carbon heat was made on a ISO-ton basic open hearth tilting furnace, the final slag of that heat which was retained in the furnace, weighed 24,000 pounds and analyzed as follows:

To this slag I added four successive batches or melts of blown" Bessemer steel as follows:

r r and heaten? Heat #1 Analysis of blown metal M1 chmn 011mm Time charged Weight of blown furnace metal Feinoro, scale, m 1.5 4.5 O P s t 25 sac a1 a gi 3,31 m 12:19 p.m 111.100 .05 .03 .080 .028 .003 s m so as r ses as a a a a Addmqm M 1E 9 11mm-.. 0,060 Hot metal in I01 I080 1028 1179 Total metallic charge-.. 100. 0 100. 0 100. 0 (P18 Limestone 5.00 eoo 5.65 Dolomite 250 as"! 1.58 Fluorspar 2o 2s Final steel analysis The resultant slags are highly oxidizing and PM we pm, mi m, basic and have the composition above indicated. "1181mm The molten low carbon steel thus formed is tapped out of the tlltingfurnace in customary Heat manner but the molten or end slag is retained in the furnace. To the furnace is then added a Analysis of blown metal charge of blown or oxidized high phosphorus Tl g c l w e woizht im l wn steel such as blown Bessemer steel. A reaction 0 Mn 5 81 immediately takes place between the blown metal and the slag and dephosphorization of the steel m 04 076 (m m is eflected thereby. If required, a small amount 2 m 3: 800 Ice Ice 1010 I020 1002 of "hot metal or pig iron is added to accele Z533 311 :1111: co m metal a' 1% It; 11% and increase the reaction. The rapidity of the (pi ir n) process depends largely upon the rapidity of getting the blown metal into the furnace, since rmnsmimnm the process itself is to all intents and purposes 1 instantaneous To pod 3:10 p. m. and indie addi- The charge having now been dephosphorized, is on! mm m4 .02

tapped out of the furnace, but the slag is still Heat #3 Analysis of blown metal Time charged Weight oi blown furnace metal Mn P s1 3:44p.m 124.900 .05 .04 .070 .004 .002 3:57pm 5,000 bot metal 3.94 .61 .081 .003 1.50

(p m- 4:07p.m 21,800 .04 .05 .073 .000 1.50

Final steel analysis Tapped 4:24 p. m. and ladle addi I tionsmade 0.05 0.29 0.025 0.030

Heat #4 Analysis of blown metal Time charged Weight 01 blown in furnace metal 0 Mn 1? e si 5:57p.m 1 00o--; .00 .06 .ms .034 .001 6:13p.m 200 hot metal 3.93 .62 .073 .030 L50 (pigiron). 0:23p m 121,100 04 04 .014 .007 .005

Final steel analysis Tapped6237p.m .00 .32 .025 .027

. Pounds Total metal charged in furnace 1,220,800 Total ferro-alloysadded to steel ladles 11,500

Gross total metal used 1,232,300 Weight of ingots produced 1,190,000 Weight of scrap produced. (skulls, pit

scrap, etc.) 17,100

I Per cent Yield from charge to ingots 07.05 Scrap produce 1.39 Loss 1.56

Total weight Tons ingots of ingots Time 01' heat per hour (gross tons) melting time Heat No.1 14s 111:.17111111--- 115.4 Heat No.2 150 1hr.15min... 124.8 114 0111-. 10m 170.9 Heat No.4 110 0111:4051 173.9

Total production 534 tons Total over-all time required including delays between heats 6 hrs. 18 mins. Grand total production per operating hour 84.8 tons The temperature of the blown" or oxidized high phosphorus metal as it comes from the converter is relatively high and when charged directly into the open hearth furnace no addition-al heat energy other than that required to keep the slag molten and the furnace up to operating temperature need be added. As a result, the fuel consumption in my process is extremely low. The process can be operated with 500,000 B. t. u. or less per ton of ingots produced. A comparison of the fuel consumption with the process described in this application as against standard methods shows a striking economy in fuel consumption:

Standard basic Standard Practice as open hearth duplex herein practice practice described Normal gross B. t. 11. per 4,000,000 to 2,000,000 400,000 to ton of ingots. 5,000,000 to 3,000,000 700,000

A further decided advantage of the process is the greatly increased production possible from basic open hearth furnaces. Since the process is extremely rapid, as much as 100 tons or more of dephosphorized steel can be obtained per hour. The following indicates the normal productive capacity of 150-ton furnaces with various processes:

Comparison of ingot production per hour on 150-ton furnaces with various processes Standard basic 0 Practice as described hearth pen Standard duplex herein 14 to 11 tons 20 m 40 tons 85 to 125 tons.

. apparent that there may be modifications and adaptations made therein without departing from the nature and scope thereof and all such modiflcations and adaptations are contemplated as may fall within the scope of the following claims.

What I claim is:

1. The method of manufacturing low phosphorus steel which comprises producing in a basic open hearth furnace a melt of basic low carbon steel in accordance with standard practice utilizing the usual basic and oxidizing slag therein, removing this melt, leaving the molten slag in the furnace, adding to the furnace blown Bessemer metal, holding the same in contact with the molten slag for a sumcient time interval to obtain the removal of phosphorus from the metal, tapping the metal from the furnace, adding a second batch of blown Bessemer metal to the furnace and treating it similarly to the first batch, tapping the same, and .1: 1 further additions of metal to the furnace until the slag in the furnace becomes saturated with phosphorus to the extent that the treated Bessemer metal retains an undesirable amount of phosphorus, tapping then the said slag and producing a second melt of basic low carbon steel as before and treating further batches of blown Bessemer steel with the second slag to dephosphorize the'same until the second slag is similarly saturated with phosphorus, continuing the said process ad inflnitum, the treated dephosphorized Bessemer steel resulting being adjusted by suitable ferro-alloy additions to a' desired composition prior to casting.

2. A dephosphorlzing slag composition for use in the removal of phosphorus from blown Bessemer steel comprising a basic and oxidizing slag characteristic of and resulting as an end product in the'manufacture of low carbon steel by standand practices in a basic open hearth furnace, said slag containing between 8% and 12% silica, 35% and 50% lime,25% and 40% iron oxide, 5% and 10% nganese omde, 1.5% and 2.0% phosphorus pentomde, 1.5% and 2.5% of aluminum and titanium oxides combined, and .10% and 20% sulphur.

3. The method of manufacturing low phosphorus steel from blown Bessemer metal which comprises forming a melt of basic low carbon steel in a regenerative furnace, removing the melt retaining the end slag product in the furnace, charging the blown Bessemer metal into the said furnace onto said retained slag and withdrawing the charge from the furnace after a time interval adapted to permit the said slag to remove phosphorus and other oxidized impurities from the said blown metal.

CLARENCE D. KING.