US2819503A - Method of producing rimmed and capped steel - Google Patents

Description

United States Patent METHOD OF PRODUCING RIMMED AND CAPPED STEEL States Steel Corporation, a corporation of New Jersey No Drawing. Application May 3, 1954 Serial No. 427,346

Claims. (Cl. 22-215) This invention relates generally to the manufacture of steel and, in particular, to the treatment of rimming steel after it has been teemed into ingot molds and before it v has completely solidified therein.

This is a continuation-in-part of my application Serial No. 296,493, filed June 30, 1952, now abandoned.

For well known reasons, rimmed steel is desirable for certain products. Rimmed steel ingots as ordinarily produced, however, exhibit numerous blowholes adjacent the rim and segregation at the center in the upper portionthereof and such portion must accordingly be di verted to the manufacture of common products. Ingots made by the conventional practice including ladle and mold deoxidation, the use of rimming agents and a metal cap on the mold, furthermore, show excessive variation in case thickness and degree of center segregation, not only between ingots of different heats but even between ingots of the same heat. This introduces complications into the subsequent processing and working of the steel.

. Attempts have been made heretofore to improve the quality of rimmed steel ingots. One of these, known as chemical capping, is disclosed in Devaney Patent No. 2,108,254. The procedure there described includes the addition of sufiicient deoxidizer after a predetermined period of rimming, to stop all rimming action in the ingot core or, in other words, to kill it. This practice, how- I ever, frequently produces ingots having dry or wet pipe which increases the amount of metal which must be scrapped;

It is accordingly the object of my invention to provide From the standpoint of its action in the ingot mold,

1 steel may be killed, semi-killed or rimming and the qualities and characteristics of each type are well understood.

My invention concernsjrimming steel only. According to the invention, speaking generally, I permit normal rimming of the ingot to occur for a predetermined time f only. Then I add a dexoidizer to the core, i. e., the metal remaining molten in the upper central portion of the parv tially solidified ingot, to cause a gradual but incomplete deoxidation of the core. The amount of deoxidizer added should be sufficient to substantially arrest the rim- *ming action but not sufficient either to cause crusting over or solidification of the top of the ingot or to prevent a continued rise of the metal in the top of the mold. I then apply a cap to the mold, whereupon the metal conwill continue to rise after placement of the cap and the tinues to rise in the top of the mold until it comes in contact with the cap, as in the case of a conventional capped ingot.

More specifically, in practicing the invention, I make a heat of rimming steel in the known manner, and partially deoxidize it in the ladle by the addition of ferromanganese, ferro-titanium, silico-manganese or aluminum or combinations thereof. The molten metal is then teemed into ingot molds as usual with the addition of known rimming agents and additional deoxidizers to obtain the amount of rimming action desired. The amount of rimming agent or deoxidizer needed for any ingot is adjusted by observing the rimming action of the ingots previously teemed from the same heat. According to conventional practice, the rimming of the ingots is allowed to proceed without check until the ingot has solidified. Alternatively, the rimming of capped steels is terminated after a few minutes, by placing a metal cap on top of the mold.

According to my invention, I permit rimming to proceed unrestrained for a predetermined period only, running from 1 minute to 10 or 12 minutes. This causes the formation of a case of solid metal of controlled thickness surrounding the still molten upper central portion or core. The longer the time, the thicker the case. After the desired rimming has occurred, I add a quantity of a deoxidizer in an amount sufficient to substantially arrest rimming and cause gradual but incomplete deoxidation without causing a crust to form on top of the metal or preventing further rise of the metal in the top of the mold. In other words, the amount of deoxidizer added should not exceed that which permits the ingot to re main open at the top. By such addition, the strong rimming action is reduced to a slow gentle movement on the surface of the metal. The deoxidizer should preferably be in comminuted form, i. e., small lumps or shot, and should be added slowly over an interval of time such as from 15 seconds to 40 or 50 seconds, to prevent excessive deoxidation localized in the core and resulting in a sharp demarcation between the case and core.

The deoxidizer which I prefer to employ is a commercially available calcium-silicon alloy'containing 30 to 33% calcium, 60 to 60% silicon and the balance substantially iron. I may, however, use aluminum, ferrosilicon or the aluminum-silicon-iron alloy sold under the trade-mark Alsifer.

The amount of deoxidizer to be added and the rate of addition can be determined by observation. The surface of the molten metal should exhibit a continuing rise during the addition. In other words, the rate and amount of addition should be controlled so as not to arrest the continuing rise which marks the proper degree of deoxidation. The amount of deoxidizer needed can also be checked by the appearance of macro-sections through billets rolled from the ingot. Such sections will be substantially free of oxides and pipe and if any blowholes are present they will be few and deep within the section if the proper amount of deoxidizer has been :added. Too much deoxidizer gives evidence of pipe. Too little permits oxide segregation to persist in the core.

As soon as the addition of deoxidizer has. been completed, a conventional metal mold cap is secured in position on top of the mold. The surface of the molten metal resulting elevation of the surface will bring it into contact with the cap -as' in the ordinary -case ofa eapped-ingot,--as solidification proceeds inwardly to the center of the ingot. To insure this result, of course, the mold must be teemed to the proper level which can easily be determined by observing the action of the first few molds, making any necessary correction as the teeming of the remaining molds proceeds. Ordinarily, the desired result will follow, in bottle top molds, if the mold be teemed to the level in the neck such that, after the predetermined period allowed for-rimm-i ng, the molten metal will-stand a'safe-distance,-e. -g.,- one inch, -below the bottom of the cap when placed.

The time-allowed for rimming and the amount of deoxidizer added thereafter just before capping, will depend, amongother t-hings, on the-type ofmold usedy-the size of the ingot and. the particular grade of steel being made. Thefollowing-table gives the significant datafor-typical examples'of the method; using aluminumas the-deoxidizer "applied to ordinary-steelsof varying carbon content. =In all the examples; ingotsweighing approximately 9,000 lbs. were teemed into big-end-dow-n bottle-top molds.

In each-.case,,the deoxidizer was added in the forrnof-shot, about3 oz. at a time, the addition extending over aperiod .;of,frorn-15 to'40 seconds. Themolds were teemed to such ,alevel-and the rimming was so controlled (by adding .-a P mmingagent or-a deoxidizer, as necessary);.that;the rnolten metalrose ,to within three inches of the-top of the mold before the addition of thedeoxidizer-after the desired rimming. After addition of the deoxidize r a metal capwas immediately placed on .top of the mold.

A pr vi ly p ine t e amount of nde xidi gadded in eachcasernust be carefully controlled so that: it rissufiicientm a re t e imm ng ac o o n ar y w bu unotsu fl kntuto preyent a slight,rise-eithetopof the uingotthereafter. ..ith.-the pmp tt mount w i iz add/ed e. steel rises and strikesthecap in about a minute. If an excess ,ofideoxrdizer; be used, it causes the formait n Q Z'P H t flt oc litt e-ox d s e atio -w pe the ente Xces fydeoxidiz mea an nun inth an e-t1 q in t e evane r en c .-as,.'-.75,.-.l ia wuin m pe to .o st e E e a e e .iof .oz ott ,eoxidiz rtpen-touiab ve heop m m amoun will cause some evidence of pipe. Usingaluminumas the .ldeoxidizer, ordinar ly: an. moun ro rom. .23 t 9 p denier ingottuqi -t wi ufiice. -eea; amoun pp o r rnate y. qne-t r rthe mum spec fi i h Devaney ,-patent. Inusingcalcium 'licon asthedeoxidizer, some what larger amounts..\gvill-;be-needed,v i. e., as .much as 8 O Z pel? ton ofisteel, .but some advantage-will be .obtained t.bytus ngranamounttaasmallas.1 z. p 1 eu u .arnount forv an,.ingot,of-4,5, tons is from 3 to ,6oz.per item. If the aluminum;or;other-deoxidizer be added; all ,at once,.instead ofjin steps or .stages a sharp demarcation b ween. rean t ase es t t n .P pe y orm t th otlthe ingot .w xid .se re a o pe is n lower tsufii ieut y. the cap. is d is st "ppecl from the and Willikil' the liquid core of the ingot is fixed as a solid oxide most of which is -fiu-xed ofi. into the -at --the top 'of -the ingot during the final gradual deoxidation. Comparatively ew blowholes remain under the skin of the ingot, and the ingots can therefore be heated faster with the danger of burning the steel greatly reduced. Further, since there is much less gas pressure under the skin, it is not ruptured in rolling even though the skin may be very thin, and the billet gurface obtained is much more nearly free of seams and slivers.

The invention is characterized by several other advantages, some of which have been mentioned briefly. In the first place, the thickness'of case and degree of center segregation may be maintainedsubstantiallyunifiorm not only throughout the same heat but also in separate heats. In addition, fully rimmed as well as thin-skinned capped steels can be; produced by myrnethodwith improved results. The ingots'are relatively free of oxide and sulphur segregation and pipe and. the. case thickness, ,does not ex- PQO ceed a predetermined value. Under normal conditions,

the cases are solid and uniform jndepth from ingot to ingot. There isa'minimum of segregation in the top of the ingots. As a result of these characteristics, it is no longer necessary to divert as large a percentage of the ingot to common products as heretofore. Finally, the

segregation of carbon, phosphorus, -manga-nese and sul- :phur across the section of the ingot is A greatly reduced. This is shown by Table'II givingthepompaiative billet ire-check analysis for-two ingots made-by my invention (numbered 1 and 2) and-a third ingot madeg -by the con- .ventional practice of capping shortly after teeming; for the :purposeof compariso TA L .I

. p'qmparazive billetz recheck analysisof mechanically and ;qlumi,m.l.mmechanically capped ingots, cross sectional sawingsl and section center. drillings Percent Sample 0 -Mn- "P B Total L e t A1 at 7{ at: 3 I Z57 i114 llngotl 17 S 456 .103 "it" t-"til I11 I56 T102 .08 .54 .090. Center...'. .08 .54 .0961' adle. .11 .42 :013 ,7 Saw .10 56 (Jenten... 18

Ingot2 .l zgct-it.

.Tab I h 1 .s i htl fiifiemm rm anieuluhu segre a onm ge smadei fie e ith the-invention, using 492. of calcium vsil the, cor, st,! -.=a.h at;lie in the, 1.Q-.. %..c r 2 2 i.94.6% man anese; Q-Q' .Q%

and '0;028% sulphur.

. 1e! mor h...

I TABLE III Calcium silicon pr'ecapped ingots Ingot Number.. 16 20 1 24 Type Sample Sawings Center Center Center Drill Drill Drill Per- Per- Per- Per- Per- Per- Per- Per- Percent Line cent cent cent cent cent cent cent cent 8 O S O S O S 92 Rimming Time.-- 3 Minutes 3 Minutes 3 Minutes For the purpose of comparison, Table IV gives a similar showing taken from ingots made from the same heat practice (ingots 2, 4, 8 and 15) segregation increases progressively to the top of the ingot. With the calcium silicon precap practice (ingots 16, and 24) the segregation increases but at a much slower rate to the 17% line. Above the 17% line to the top of ingot segregation decreases.

Of special significance is the fact that the maximum segregation on calcium-silicon precapped steel with no top diversion is less (.044% S--center drill #16 ingot 10 17% line) than on mechanically capped steel with a 20% top diversion (050% S-#8 ingot 27% line).

The highest segregation on the calcium-silicon precapped steel analyzed only .23% C and 044% S (ingot #16, 17% line center drill).

Chemical capping with 23 ounces of calcium silicon (#25 ingot) does not retard segregation as well as the combination of precapping with 18 ounces of calcium silicon and then mechanically capping. Further. a bad slag pipe was evident on the etch test of ingot #25 at the 7% line.

The improved quality of the ingots produced by my invention is shown by Table VI comparing the results obtained therefrom with those of the conventional capping practice.

by the conventional mechanical capping procedure. 25

TABLE IV Mechanically capped ingots Ingot Number 2 4 8 15 '1 e Sam le Center 5 Center V" Center Sawln s Center W p Drill Drill 111111 E Drill Per- Per- Per- Per- Per- Per- Per- Per- Per- Percent Line cent cent cent cent cent cent cent cent cent cent 0 S O S O S C S S .28 .050 .40 .125 .28 .073 .17 .34 .103 .17 .35 .110 .22 .049 .22 .048 .28 .070 .17 .24 .053 .15 .21 .040 .18 .032 .10 .043 .19 .050 .17 .20 .041 .15 .17 .029 .14 .14 .026 .15 .13 .025 .14 .14 .026 .13 .12 .025 .12 .12 .025 02 .13 24 .13 .023 Rimming Time 1M.nute 13 Mnutcs 2Minntes SMlnu For further comparison, Table V gives the results ob- TABLE VI tamed 1n one ingot made from the sameheat by adding lngot practice an excess of 1 oz. per ton of calcium-silicon to the core after a rimming time of 3 minutes. Although segregation therein is less than in the ingots listed in Table IV, Comm 33,123? it was not as low as in the ingots listed in Table III. In tional tion and addition, the small excess of deoxidizer caused a pipe to cappmg 32 335 3 appear and the top portion of the ingot therefore had to herein be scrapped.

TABLE V Number of heats involved 101 99 Ingot yield of cold-heading quality. .-.percent.. 53.1 73 C l i ili cappedfiqw h i l cap Billet diversion to common pr0ducts...perccnt.. 32. 2 11.4 Bingflliecclglnsz s B T t 52 as ca 5 pa earns urns ears.percen Ingot Number 25 Mechanical iietects rind bent billets.--do. 11 09 {Type Sample Center Drill Total 45 Percent Line Percent Percent 5 A further advantage of the invention is that. it reduces C S the necessary amount of hot-process deseaming of billets to be rolled in rod mills, thus materially decreasing cost k f as compared to prior practice. 17. .19 .052 Although I have disclosed herein the preferred em- T555 bodiment and practice of my invention, I intend to cover Rimming Time 8 Minutes as well any change or modification therein which may be A comparison of the center drillings shows that there is no significant difference in segregation with either practice below the 32% line. With the mechanical capping made without departing from the spirit and scope of the invention.

I claim:

1. The method of producing rimmed steel ingots which 2,-s-19,-sos

minutes;progressivelyadding to-zthe :core' of the ingotthen remainingrmoltens a deoxidizer inthe amount -of from 1?..toe81ouncesper tonsof-..ingot*weigl 1t, over aperiod'of from 15 to 50 seconds and then applying a metalcapto thez mold 2.-,The;method defined by claim- 1' characterized by said;- deox-idizer being calciumsilicon alloy.

3': Thevmethod definedby claim lvcharacterized by said deoxidizer being aluminum.

4. The method of producing rimmedsteel ingots which consists inteeming rimmingv steel into an ingot mold, allowing the steel in the mold to rim for atew minutes, then-,while the. steel isstill effervescing,progressively adding to thecore-then remaining molten, over a period of from .15' to50 seconds, sufiicient deoxidizer to substantially arrest the rimmingv action but less than .the amount ,neededto preventacontinued rise of metal in themold,

and then applying a metal cap to the mold.

S;=,The;method-, of making rimmed steel which consists in: teeming a heat of moltenrimming steel into ingot molds, allowing the steel to stand in the .molds for undisturbed rimming to produce the desired thickness of case, then, while the steel is still effervescing at the top of the mold, progressively arresting the rimming action by progressively adding to the central core of the steel mass remaining molten, a deoxidizer in an amount of from 1 to 8 ounces pentonrofingot weight, thereby substantially arresting the rimming action of said core yet preventing e'xee'ssive' localized 'deoxidation in the core bycausing the-top of the-core to remainopen-wit-h continued rise to the metal, and thereby eliminating. the shar=p demarcation-between-case andv corethen placing a metal cap on=' top of ithe mold-and, in conductingsaid' teeming, filling" the molds to a level such that said continued rise of 'theto'pj ofth'e' core brings the'teeme'd metal into contact with said cap;

ReferencesCited.inthefile of this patent, UNITED STATES PATENTS 587-,105 MeConnell July'27, 1897 1,727,088 Williams et al Sept. 3, 1929 2,108,254 Devaney- "Feb. 15, 1938 2,204,585 Gagnebin:- June 18, 1940 2,652,324- Hignett Sept. 15, 1953 OTHER REFERENCES The' Deoxidation ef-Steel, C'. H: Herty, Bulleti'n'No. 69, 1934; pages "41-42 relied' on.

OpenzvHearth Proceedings, vol. 32, 1949, A I; M; 15., page 226:

OpenrHearth:Proceedings vole 34, 1951, Ail. M, E., pages 234-237.

The Making, Shaping," and Treating of Steel, U. S. Steel (6thted.)-.1951;- pagesc444, 571-573 relied on.

U. S. DEPARTMENT OF COMMERCE I5ATENT OFFICE CERTIFICATE OF CORRECTION Patent Noa 2,819,503 January 14, 1958 Vincent 0 r. Bouce-k It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Let oers Patent should read as corrected below.

Column 2, line 44, for "60 to 60%" read 60 to 65% g column 8, line 5, for "rise to read rise of Signed and sealed this 11th day of March 1958,,

(SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSON Attesting Officer Conmissioner of Patents

Claims (1)

1. 5. THE METHOD OF MAKING RIMMED STEEL WHICH CONSISTS IN TEEMING A HEAT OF MOLTEN RIMMING STEEL INTO INGOT MOLDS, ALLOWING THE STEEL TO STAND IN THE MOLDS FOR UNDISTURBED RIMMING TO PRODUCE THE DESIRED THICKNESS OF CASE, THEN, WHILE THE STEEL IS STILL EFFERVESCING AT THE TOP OF THE MOLD, PROGRESSIVELY ARRESTING THE RIMMING ACTION BY PROGRESSIVELY ADDING TO THE CENTRAL CORE OF THE STEEL MASS REMAINING MOLTEN, A DEOXIDIZER IN AN AMOUNT OF FROM 1 TO 8 OUNCES PER TON OF INGOT WEIGHT, THEREBY SUBSTANTIALLY ARRESTING THE RIMMING ACTION OF SAID CORE YET PREVENTING EXCESSIVE LOCALIZED DEOXIDATION IN THE CORE BY CAUSING THE TOP OF THE CORE TO REMAIN OPEN WITH CONTINUED RISE TO THE METAL, AND THEREBY ELIMINATING THE SHARP DEMARCATION BETWEEN CASE AND CORE THEN PLACING A METAL CAP ON TOP OF THE MOLD AND, IN CONDUCTING SAID TEEMING, FILLING THE MOLDS TO A LEVEL SUCH THAT SAID CONTINUED RISE OF THE TOP OF THE CORE BRINGS THE TEEMED METAL INTO CONTACT WITH SAID CAP.