US3199976A

US3199976A - Manufacture of steel

Info

Publication number: US3199976A
Application number: US375746A
Authority: US
Inventors: Dammer August; Breuing Wilhelm
Original assignee: Rheinstahl Huettenwerke AG
Current assignee: Rheinstahl Huettenwerke AG
Priority date: 1960-12-01
Filing date: 1964-06-17
Publication date: 1965-08-10
Anticipated expiration: 1982-08-10
Also published as: DE1177183B; GB999482A

Description

Aug. 10, 1965 A. DAMMER ETAL MANUFACTURE OF STEEL Filed June 17, 1964 Jnvenfars;

fll ausf M0054, W/LHELM skzuhw United States Patent Ofiice ilwfllh Patented Aug. 10, 1065 This application is a continuation-in-part of our co pending application, Serial No. 157,300 filed November 28, 1961, now abandoned, for Manufacture of Steel.

This invention relates to new and useful improvements in the manufacture of steel. The invention more particularly relates to a process for reducing the hydrogen content of steel melts without the necessity of vacuum.

Too high a content of hydrogen in steel may adversely affect the characteristics of steel, as for example the tendency to flake.

Thus, for example, it is generally considered desirable to reduce the hydrogen content of steel which is to be worked by rolling to below 3.0 cu. cm./ 100 grams and to below 2.0 cu. cm./ 100 grams for steel which is to be worked by forging.

In the past, in order to obtain these low hydrogen contents, it was necessary to degas the steelmelt under a high vacuum below 1 torr and as low as .05 to .3 torr. The vacuum degassing could be effected by passing a stream of molten steel into a vacuum chamber by maintaining a bath of the molten steel in a chamber maintained under low vacuum and preferably while passing a scavenging gas into or through the steel or the like. Vacuum degasification requires the use of special, expensive vacuum equipment and pumps and often the steel melt treated must be free of a slag covering layer.

One object of this invention is the reduction of the hydrogen content of steel melts without the requirement of the application of a vacuum.

A further object of this invention is a simplified process for removing hydrogen from steel which may be combined with the blowing of iron melts to steel.

These and still further objects will become apparent from the following description read in conjunction with the drawing which diagrammatically shows an arrangement for effecting the process in accordance with the invention.

In accordance with the invention, we have discovered that the hydrogen content of steel melts may be reduced to a value previously only obtainable with a high vacuum degasification by maintaining a bath of the molten steel with slag covering the surface thereof and blowing a stream of oxygen and .5 to 7% by volume and preferably 1 to by volume, based on said oxygen, of a lower chlorinated or fi'uorochlorinateai alkane against the slag with a velocity suflicient to cause intermixing of the slag and at least the upper portion of the bath.

The term stee as used herein includes any of the known or conventional steels, such as alloyed, unalloyed steels, and includes iron melts from which steel is ultimately produced, as for example, molten pig iron.

The slag which covers the surface of the molten steel bath treated in accordance with the invention may be any known or conventional slag and is generally the conventional slag used in the production of the particular steel in question.

While the content of the slag is not critical and vdoes not affect the treatment in accordance with the invention, the slags generally have the following components:

Percent b.w.

CaO 30-65 MnO 5-25 Si0 10-30 Remainder iron oxides, magnesia and, if any, fluxing means preferably CaF Similarly the thickness of the slag layer is not critical and is generallythat conventionally found in the production of steel, as for example, between 2- and 6 cm.

The chlorine-containing material which is blown against the slag with the oxygen may be a lower hydrocarbon having all of its hydrogen atoms substituted with chlorine or chlorine and fluorine. As lower hydrocarbons, any completely chlorinated or completely fluorochlorinated hydrocarbon having 4 or less carbons atoms may be used but preferably the hydrocarbon should not have more than 2 carbon atoms. Carbon tetrachloride has proven most preferably but very good results are obtained with hexachloroethane or difluorodichloroethane or the like. It is also possible to use mixtures of these lower chlorinated or fiuorochlorinated ethanes.

The steel melt with the slag covering is maintained in any sutiable container used in the steel industry, as for example a furnace crucible or ladle, and the oxygen and chlorine-containing material is blown against the surface through any convenient nozzle or lance or nozzles or lances.

It is not necessary to change the lances and nozzles suitable for the processes in which oxygen is blown on or into a steel bath, as known in open hearth or electric furnaces or LD-crucibles. This is true for the distance between nozzles or lances from the surface of slag surface as known, the distances vary between 300 and 2000 millimeters.

The blowing should be effected with suflicient velocity to cause intermixing of the slag and at least the upper portion of the melt. This velocity will vary in individual cases depending on the conditions, etc. In general, however, a velocity of at least 200 meters/second, preferably 700800 meters/second, have proven siutable.

The chlorine-containing material and oxygen pass through the same nozzles with the chlorine material being fed into the oxygen stream, as for example by use of a conventional dosing pump.

It is preferred to blow all oxygen together with the chlorine containing material but it is also possible to blow only a portion of the oxygen together with said additional material and to blow the remaining portion of oxygen through an additional lance or nozzle or additional lances or nozzles.

The amounts of oxygen may vary over wide limits, as for example between 33 and normal cu. meters per metric ton of steel.

The total amount of the chlorine containing material used is also dependent upon the conditions and the degree of reduction of the hydrogen, content. In general however, amounts of .3 to 1.5 normal cu. meters may be required per metric ton of steel treated.

The treatment in accordance with the invention may be effected at any stage in the production of the steel after the melt has been formed and may be used in cona hot blast cupola furnace and which had the following approximate analysis:

. C 4.0 junction with any of the known or conventlonal meth Si 0.1 of producing steel in any of the known 1 COHVeHtlOIlal 5 Mn 0.45 furnaces. P 0.050

Most preferably, however, the treatment 1s combln 5 0,020 with the production of SL1 involving an oxygen blow ng To each'of the charges gooykg lime and 300 g fluorof the melt as for example in the LD process utmzing p spar were added before blowmg. Each of the charges for example an LD crucible. In accordance with the was blown with oxygen passed through the. lance 2, invention, the blowing of the oxygen onto thesurface of d t t f 800 f th 7 bath to convert itto steel may be combined W was mamtame a a ance O mm e h p 1g Hon I surface of the slag. The, gas'pressure 1n the lance was with the treatment 1n accordance with ihedl'lVfillllOl'l by maintained. at between 4 and 6V atmosphgres and the mcludlfdg fi gi g g mammal mtopthe Oxynozzle. velocity of the gas emitted from the lance was gen or e 9 between 700 and 800 meters per second.

In other steelmakmg processes or open hearth and elec- AS a Lava1 N0ZZ1e was used the velocity of the g tricfurnace process the treatment is effected 1n a similar Striking slagrwas Substantially the same The Image %;3; t m in accordance with the invehtion may be outlet diameter of the lance was millimeters, and 1650 e reame t started at a point in the steel production where the slag 20 2:3 5;'5333$3 5 3g g fisgigg ggig g i :2 layer is replaced by difierent slag layer. If'the treata by meansrof the dosingpumps at a constant rate ment has been Started before i' l replaced by Table '1 below shows the total carbon tetrachloride a new Slag, it has been foundpref'ambl3 f subject blown into each of the charges,the blowing time for each steel after replacement of the slag layer with a blowing 25 f e charges the analysis f Steel melt produced and with oxygen and the chlorine-containing material in aC- the hydrogen content as analyze ,b two i di i ll cordance with the invention. takensamples from each charge: a

Table 1 Total abrlnountof Blowing Final analyses of the steel Hz content, ppm. I Charge N0. Cvhmgrtgn, 1n miirrlxlilctbs V V p 7 V p C Si Mn P '8 Cr Cu A1 Samplel SampleZ 78(18 N1n 27 .09 .22 .36 .014 .020 .30 .21. .007 i 1.44 1.4-t .80 (18.5 Nin 25 .08 .25 .37 .007 .024 .12 .13 .002 .ss .88 s2 (10 NIIl 25 .10 .19 .35 .012 .024; .18 .005 .96 1. 04

Furthermore, if after the treatment the melt is to be The hydrogen content analysis was determined by maintained so that it would normally be in contact with means of a hot aging determinauon at 600 C. (see: the ambient air as would occur, for example, by a delay Mitteilungen des Kaiser Wilhelm Institut fiir Eisenforin tapping or pouring, it has been found preferable to schungl-Vol. XIX (1937). Lfg.8, page 105-112 and maintain the steel free from contact withrthis ambient Iron and Coal, '15. 8. 1960, page 301-304). air b flowin with an inert gas with or without chlorine- In comparison thereto identical melts were blown under y g I n I V a containing material. This is done to prevent a rise 1n the substantially identical conditions without the C 31 the hydrogen content of the melt which could occur, however, the hydrogen content was above 4.0 ppm. and through the absorption of hydrogen from the moisture the steel melt produced had the following analysis:

in the ambient air. Theexpression inert gas does not mean only argon, helium etc., but means all gases which do not affect the bath. 7

7 Thus, for example, waste gas, as for example, blast furnace or hot cupola gas may be used, being blown on the surface of the melt at a suflicient rate to. prevent contact with the air. It has been found that even a small hydrogen content of, for example about 12% hydrogen in such gas is not detrimental.

V The following examples are given by Way of illustration and not limitation:

EXAMPLE 1 An arrangement consisting of an LD-crucible and a lance as shown in FIG. 1 is utilized for treatment. In the drawing the LD-crucible is designated with 1,. the, lance capable of being raised and lowered is designated with 2. The closing pump 3 has to pump the fluid CC], from a container d by means of a pressure conduit 5 at 6 into the lance 2 and thereby into a stream of oxygen. 7 is the tapping hole. r

The LD-crucible 1 which had a capacity of 35 metric tons was charged with 3 separate charges of pig iron which had been produced from scr'apiron and coke in EXAMPLE 2 Example 1 was repeated except that the (PS1,; was replaced by the following chlorine containmg materials:

(a) Hexachloroethane (b) Dichlorodifluoroethane '(c) Decachlorobutane Q i (d) Mixtures of the above.

, In each case the hydrogen content of the'melt is re-- duced to below 1.6 p.p.m.

EXAMPLE3 Example 1 was further repeated exceptthat the 50% of the slag was withdrawnafter a blowing period of 14 minutes together with 44 liters (10.3 normal cubic meters) CC-l After adding of lZO k-g. lime and .120-lzg. fluo.r-' spar blowing was continued for 17 minutes with the result that hydrogencontent was 1.8 -p.p.m.

In a steel containing: .12 C, .24 Si, .38 Mn, .014 P, .024 S, .19 Cr, .20 Cu, .008 Al, all percents by weight, in the final analysis.

While the invention has been described in detail with reference to certain specific embodiments, various changes and modifications which fall Within the spirit of the invention and scope of the appended claims will become apparent to the skilled artisan. The invention is therefore only intended to be limited by the appended claims or their equivalents wherein We have endeavored to claim all inherent novelty.

We claim:

1. Process for reducing the hydrogen content of steel melts, which comprises maintaining a bath of molten steel with slag covering the surface thereof and blowing a stream of oxygen and .5 to 7% by volume, based on said oxygen, of a member selected from the group consisting of lower completely chlorinated alkanes, lower completely fiuorochlorinated alkanes, and mixtures thereof, against the slag with a velocity sufiicient to cause intermixing of the slag and the upper portion of the bath for a period of time sufiicient to substantially reduce the hydrogen content of the melt.

2. Process according to claim 1 in which said group member is blown in said stream of oxygen.

3. Process according to claim 1 in which said group member is utilized in amount of about 1 to 5% by volume, based on said oxygen. 7

4. Process according to claim 1 in which said group member is C01 5. Process according to claim 1 in which said group member is utilized in amount of .3 to 1.5 normal cu. meters per metric ton of steel treated.

6. Process according to claim 1 in which the bath of molten steel is maintained at normal pressure.

7. Process according to claim 1 which includes protecting the melt with an inert gas from prolonged contact with moisture-containing ambient atmosphere after said treatment.

8. In a process for blowing iron to steel in which a stream of oxygen is blown against a bath of slag covered molten iron, the improvement for producing steel with a lowered hydrogen content which comprises eifecting the blowing with a stream of oxygen additionally containing .5 to 7% by volume of a member selected from the group consisting of lower completely chlorinated alkanes, lower completely fluorochlorinated alkanes, and mixtures thereof.

9. Improvement according to claim 8 in which said group member is present in amount of about 1 to 5% by volume.

10. Improvement according to claim 8 in which said group member is CCl 11. Process according to claim 1 which includes removing said slag from said bath of molten steel, covering the surface of said bath of molten steel with a different slag and continuing said blowing against the new slag.

12. Process according to claim 1, in which said oxygen is blown in at least two separate streams, at least one of said streams containing said group member.

References Cited by the Examiner UNITED STATES PATENTS 2,068,785 1/37 Bain 12 2,770,860 11/56 Webbere 22-2l4 3,046,107 7/62 Nelson et al 7560 3,060,015 10/62 Spolders et al 75-60 BENJAMIN HENKIN, Primary Examiner.

Claims

1. PROCESS FOR REDUCING THE HYDROGEN CONTENT OF STEEL MELTS, WHICH COMPRISES MAINTAINING A BATH OF MOLTEN STEEL WITH SLAG COVERING THE SURFACE THEROF AND BLOWING A STREAM OF OXYGEN AND .5 TO 7% BY VOLUME, BASED ON SAID OXYGEN, OF A MEMBER SELECTED FROM THE GROUP CONSISTING OF LOWER COMPLETELY CHLORINATED ALKANES, LOWER COMPLETELY FLUOROCHLORINATE ALKANES, AND MIXTURES THEREOF, AGAINST THE SLAG WITH A VELOCITY SUFFICIENT TO CAUSE INTERMIXING OF THE SLAG AND THE UPPER PORTION OF THE BATH FOR A PERIOD OF TIME SUFFICIENT TO SUBSTANTIALLY REDUCE THE HYDROGEN CONTENT OF THE MELT.