US3737302A - Method of treatment of liquid steel under vacuum - Google Patents

Method of treatment of liquid steel under vacuum Download PDF

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Publication number
US3737302A
US3737302A US00744744A US3737302DA US3737302A US 3737302 A US3737302 A US 3737302A US 00744744 A US00744744 A US 00744744A US 3737302D A US3737302D A US 3737302DA US 3737302 A US3737302 A US 3737302A
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Prior art keywords
steel
chamber
ladle
vacuum
pipes
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US00744744A
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English (en)
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J Pomey
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Est Aciers Fins
SOC ACIERS FINS de l EST FR
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Est Aciers Fins
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/10—Handling in a vacuum

Definitions

  • the present invention concerns this latter process. It is known that one of the disadvantages of theknown methods of treatment of steel in a steel-works ladle is that neither the temperature nor the time of treatment sists of enclosing the ladle of steel in a chamber in which a vacuum is created. This method has the particular disadvantage of necessitating a large volume which correspondingly increases the time necessary to obtain the vacuum, due to the necessarily limited capacity of the pumping equipment. In addition, it is desirable to ensure stirring of the steel. l
  • the invention also enables all these complications to be avoided.
  • IIn another also known method of treatment of steel in which the ladle is placed in a vacuum chamber use is made of electro-magnetic stirring induced by an inductor winding placed in the vacuum chamber, at its lower portion round the ladle.
  • This method makes it necessary, on the one hand to employ a frequency of the order of 0.5 to 2 Hz. which does not permit any heating by the Joule er'ect and on the other hand, it necessitates that the ladle should have a casing of nonmagnetic steel (stainless austenitic, 18 Cr-8 Ni) sozas-to avoid it becoming the seat of large induced currents.
  • nonmagnetic steel stainless austenitic, 18 Cr-8 Ni
  • the vacuum is created in a horr-tight refractory chamber having at its lower portion one or two pipes immersed in the liquid steel contained in a conventional steel-works ladle.
  • the vacuum the steel rises from the ladle into this chamber to a level defined by the hydrostatic pressure.
  • the chamber is preheated by a cylindrical graphite rod which passes right through the chamber and which is heated by the Joule effect of a low-tension electric current.
  • this method of pre-heating does not permit the chamber to be maintained at a temperature equal to or higher than that of the steel; it cannot wholly compensate for the heat losses and a fortiori, it cannot heat the steel.
  • the method according to the invention enables all these advantages to be overcome.
  • This method has two disadvantages: on the one hand it is necessary to subject very heavy equipment to these vertical oscillations: either the vacuum chamber or the ladle full of steel, and on the other hand, the free level of the steel, alloy or other metal is also subjected to vertical oscillations, which results in a cooling and a continual re-oxidation by atmospheric air, even if the steel bath is covered with slag. In the method according to the invention, these two disadvantages are avoided.
  • the vacuum chamber is connected to the ladle by two plunging pipes and a circu latory flow of the steel is established, rising inside one pipe and falling inside the other. It is from this principle that the method according to the invention is derived.
  • this flow is established by bubbling argon through one of the two pipes, which reduces the mean density in this column, so that the steel in the column circulates from the bottom towards the top.
  • This method makes it necessary to utilize argon, and further has the disadvantage of reducing the degree of vacuum and of being an additional cause of cooling. These disadvantages are avoided by means of the method according to the invention.
  • the gas contained in the chamber is sucked out so as to maintain a constant vacuum, ensuring the rise of the steel bath and its stabilization at a pre-determined hydrostatic height, a circulation of liquid steel 'being effected through the intermediary of the pipes between the ladle and the chamber, while the steel is heated by induction.
  • the method according to the invention is characterized by the fact that the said circulation is induced by means of an inductor winding surrounding the refractory charnber insidel an outer fluid-tight metal casing and traversed by an alternating current, the voltage and the frequency of which, are so chosen that the current induced in the liquid steel produces a centripetal radial electro-magnetic force, which tends to move the steel from the peripheral part of the chamber towards its centre.
  • One of the two pipes opens in proximity to the axis of the chamber; the other opens into the said peripheral portion.'
  • the winding is cooled by water circulation as in the case of all induction furnaces working at high or medium frequencies.
  • the circulation, without modification of the level of the steel in the chamber, is maintained for a sufficient period to obtain the degree of purification desired throughout the whole mass of the steel, following which the vacuum is removed in the chamber by the introduction of a neutral or reducing gas after each degasifying operation.
  • the voltage and the frequency are advantageously chosen such that the current induced in the liquid steel produces, in addition to the said radial force, a Joule effect which ensures the heating iof the liquid steel in the chamber.
  • the refractory chamber may be heated internally before each degasifying operation and during this operation 'by means of a horizontal and coaxial graphite ring housed in the upper internal portion of the refractory chamber and heated by induction by means of another inductor winding surrounding the chamber and inside the external metal casing.
  • FIG. l is a very simplified view in vertical section of a device for carrying the method into elect
  • FIG. 2 is a more detailed view in cross-section of the same device taken along line II-II of FIG. 3;
  • FIG. 3 is a view in horizontal section taken along the line III-III of FIG. 2.
  • the refractory vacuum chamber .1 shown in diagrammatic form in FIG. l, is a vertical cylinder of revolution closed at its base along a straight horizontal section 2 and at its upper portion by a spherical cap or dome 3.
  • the vacuum connection 4 is a pipe placed for example in the dome 3.
  • the base comprises two vertical pipes plunging into the steel bath contained in the ladle 9.
  • One of these pipes 5 is located at X-X' approximately in the axis Z-Z of the vacuum chamber while the other pipe 6 is located laterally at the periphery against the cylindrical wall of the vacuum chamber, along the axis Y-Y.
  • p1 is the atmospheric pressure
  • p0 is the pressure inside the vacuum chamber
  • the steel rises in the chamber 1 to a level h above the base 2.
  • An inductor winding 7 with water circulation surrounds the whole of the refractory body and the heat insulation of the cylindrical chamber, as in the case of coreless induction furnaces. This winding is traversed .by a single phase alternating inductor current of appropriate frequency. This frequency may be that of the commercial electric power or a lower frequency, and a capacitor in parallel can keep the voltage and current in phase.
  • e is the conventional thickness of the skin-effect currents and p is the resistivity of the steel.
  • d is given a high value, for example 2 m. for an installation treating a ladle of 40 tons of steel so as to permit -a good action of the vacuum.
  • the inductor winding l is given, this being of the same order as the height h of the bath of steel in the vacuum chamber; there is therefore an advantage in giving l a fairly low value so as to give a high ratio of P/ Werf.
  • the value of l being thus fixed by construction, the ratio P/ Weff can be regulated at that moment by the level h of the steel in the vacuum chamber, which, for a given degree of vacuum, is obtained by the adjustment ofthe position of a jack lwhich actuates a lifting device on whichv the ladle rests.
  • the structure of the apparatus is rather more complicated.
  • the circulation I ⁇ between the steel and the ladle may be a maximum, it is necessary (see FIG. 2) that the-lateral delivery pipe of the steel coming from the ladle 9 delivers into the base 2 of the vacuum chamber through a peripheral channel 10 covering a sufficient-circular arc, but the Width of which counted radially is less than the thickness e of the skinl currents.
  • d 2 m.
  • the radial width e of this channel is preferably comprised between 8 and 12 cm., while its depth is determined at will and is preferably decreasing aS it moves away 0n each side from' the axis Y-Y of the lateral pipe.
  • This circular varc may be as large as desired and may even cover the complete'circumference in order thus to ensure the best centripetal distribution of the steel in the vacuum chamber and thereby to ensure the best efliciency of the vacuum.
  • the radial width e of the channel is constant, but its depth decreases up to the point P, diametrically opposite to the axis -Y-Y of the lateral pipe.
  • the down-pipe 5 is slightly displaced towards the side opposite to the rising pipe, for the purpose of improving the uniformity of the centripetal circulation of the steel in all directions.
  • the vacuum-tightness is ensured by a metal casing 11 external to the refractory chamber 22, to its heat lagging 23 and to the inductor winding 7.
  • the lines of magnetic flux are channelled to the exterior of the refractory chamber and lagging, to the exterior of the inductor winding and to the interior of the uid-tight casing by packets of iron sheets 12 or of silicon iron suitably cut-out and oriented in meridian planes.
  • the upper part of the chamber contains the heating device.
  • This device (see FIG. 2) consists of a coaxial graphite ring 13 located inside the heat-insulated chamber and heated by induction by means of a winding 14, cooled by water and placed outside the refractory heat-insulated chamber.
  • the ring 13 may be constituted by a sludge of graphite agglomerated while hot with molten pitch, or better still it may be an assembly of graphite bricks put together dry or with a hot illing constituted by graphite powder and molten pitch.
  • the binder is a conductor of electricity and its pyrogenatiou converts it to monolytic graphite which is a very good conductor of electricity.
  • the frequency of the single-phase alternatingl inductor current is chosen between 150 and 1500 Hz., taking into account the thickness of the ring and its resistivity.
  • this current may advantageously be a current having a frequency three times or better still nine times that of the commercial supply, by means of static frequency multipliers known per se.
  • the advantageous frequency is 450 or 540 Hz., depending on whether the commercial supplyfrequency is 50 or 60 Hz.
  • the magnetic eld is channelled between the metal vacuumtight casing 11 and the winding 14 by packets of iron sheets 15, appropriately cut-out and placed in meridian planes.
  • the empty spaces between the packets may advantageously be packed with a suitable ferrite, a substance with the formula FezOaMO in which M is a suitable bivalent metal; these are well known insulating and ferro-magnetic substances.
  • Diaphragms of very thin steel sheet are stuck by means of a suitable glue, such as Araldite, to the lower extremities of the pipes 5 and 6, thus closing the two pipes.
  • a suitable glue such as Araldite
  • the vacuum is created in the chamber; the current at 450 Hz. in the upper inductor heats the graphite ring 13 which, by conductivity and especially 4by radiation, progressively heats the whole chamber 1 to a temperature of 1600 C.
  • the vacuum is destroyed by the introduction of nitrogen coming from a cylinder of compressed gas, or of a reducing gas such as blast-furnace gas.
  • the steel was prepared without superheat, so that its oxidation condition was a minimum. It was poured into a standard steel-works ladle 9 which is for example a ladle lined with silico-aluminous refractory materials in a packed sludge or with assembled bricks, with a conventional metal frame of ordinary steel, thus ferro-magnetic and economical. This may be, according to the usual practice, a ladle with a gas-nozzle, a plug and a stopper-rod. The central metal rod of the stopper may be tubular and may be traversed by a ow of cooling air (not shown on the drawings).
  • the slag can be poured into the ladle with the steel alternatively the steel alone may be poured and can be covered with a thin layer of highly meltable synthetic eutectic slag and with a thicker layer 16 of the same slag CTI remaining in powdered form and heat insulating, and made reducing by powdered carbon, which ensures between the grains an atmosphere containing carbon monoxide and free from oxygen.
  • the ladle full of steel 9 is brought under the vacuum chamber 1 and a jack 17 lifts it vertically, so that the two pipes of the chamber plunge into the steel.
  • the thin sheets melt and the steel passes into the two pipes.
  • the vacuum is gradually restored, the steel passes into the chamber 1 and the current is connected to the lower inductor, which effects at vthe same time the heating of the steel and the centripetal circulation of the steel in the chamber.
  • the steel rises up the lateral pipe 6 and falls down the axial pipe 5.
  • the convection currents continually renew the metal which passes into the lateral pipe 6.
  • the level in the steel-works ladle also remains constant.
  • the surface of the steel bath in the ladle is quiet.
  • the steel is only subjected to horizontal movements resulting from convection.
  • the powdered layer 16 which covers the slag is calm and carries out its heat insulating and de-oxidizing action.
  • the stopper rod is immersed in steel, in which slow convection currents take place, practically without turbulence so that if its axial down-pipe is cooled by a circulation of air, its operation is reliable and without risk of trouble as long as may be desired.
  • the materials of the gas-nozzle and the plug may be chosen sufficiently refractory so that there is no risk of sticking.
  • the apparatus comprises one or more hoppers 18 comgrised between two gates 19 and 20 forming a lock cham-
  • the gate or the vacuum-tight cover 20 By opening the gate or the vacuum-tight cover 20, there is introduced into the hopper the dosed quantity of any additional constituent to be introduced into the steel.
  • the valve 21 After closing the gate 20, the valve 21 is opened and puts the hopper 18 into communication with the vacuum chamber 1.
  • the gate 19 is opened s0 as to allow the additive to fall into the bath of steel contained in the ladle.
  • the quantity of additives is not limited; by virtue of the previous de-oxidation of the steel and due to the vacuum, even highly oxidizable additives such as silicon, titanium, aluminum amongst others can be employed without direct oxidation by air and with very good eiciency.
  • the vacuum is removed, preferably by filling the chamber 1 with an inert gas such as nitrogen, or a reducing gas such as blast-furnace gas.
  • an inert gas such as nitrogen, or a reducing gas such as blast-furnace gas.
  • the ladle 9 is lowered and thus liberated is transferred to the area for pouring into ingot moulds.
  • the operation of treatment under vacuum can therefore be carried out for the time required for the total purification of the steel and in order that, at the end of this operation, the temperature is absolutely correct for subsequent pouing into ingot moulds, either by conventional pouring or by continuous pouring methods.
  • the winding surrounding the lower part of the chamber is no longer required to create h'eating by the Joule effect, it is only required to ensure intense stirring by the electro-magnetic effect of the currents induced in the liquid steel contained in the chamber this steel becoming the seat of a centripetal electro-magnetic force which ensures the circulation of the steel between the ladle and the vacuum chamber.
  • the steel rises from the ladle into the vacuum chamber through the lateral pipe 6 and moves down from this chamber into the ladle through the axial pipe 5.
  • the frequency is very low, and is comprised between 1 Hz. and 20 Hz.
  • a ferromagnetic circuit of packets of iron sheets 12V is arranged between the winding 7 and the casing 11.
  • Thge vacuum chamber 1 can advantageously be equipped with the heating device comprising the graphite ring 13 heated by means of the winding 14, as has already been shown in FIG. 2.
  • the method according to the invention permits the production of steel, alloys, and other metal which are better de-oxidized than with the methods previously known, due to the fact that the operation can be prolonged for the time required and because of the methodical and intense circulation of the steel in the vacuum chamber.
  • This method makes it possible to avoid excess heating and overoxidation of the steel at the time of pouring from the preparation furnace into the steel-works ladle; finally this method makes it possible to obtain the steel at the correct fairly-low temperature for de-oxidation under vacuum and also at the correct and higher temperature for pouring into ingot moulds, advantages which the previously known methods do not possess.
  • the ladle is of the standard type with an external casing of ordinary ferro-magnetic steel.
  • the method further provides:
  • a method of degasifying molten steel comprising pouring molten steel into a casting ladle, covering the molten steel with a layer of slag, im-ersing in said molten steel the lower extremities of two substantially vertical refractory pipes, the upper parts of which open into the bottom of a vacuum-tight heat-insulated refractory charnber which is in the form of a body of revolution with a vertical axis, maintaining a substantially constant vacuum in said chamber by which occluded gases are entrained by suction and by which molten steel is caused to rise into the chamber ⁇ and is lstabilized at a predetermined hydrostatic height, induction heating the molten steel, and circul-ating the molten steel between the ladle and the chamber through the two refractory pipes by passing an alternating current through an inductor winding which surrounds the refractory chamber inside an external metal casing, said alternating current inducing in the molten steel a radially centripetal electromagnetic force tending
  • a method in accordance with claim 2 further comprising the step of, during the de-gasifying operation, passing the steel into the chamber through the peripheral pipe which opens into the bottom of a peripheral channel formed in the base of the said chamber and covering a circular arc of at leas-t 180, the radial width of the said channel being less than the thickness of the induced ⁇ skin effect currents.
  • a method in accordance with claim 1 further comprising the step of covering the surface of the liquid steel poured into the ladle, which is covered with a layer of reducing molten slag, with a layer of reducing powdered material containing carbon.
  • a method in accordance with claim 1 further comprising the step of regulating the level of the steel in the chamber during ythe course of the de-gasifying operation by varying the height of the ladle with respect to the chamber.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Treatment Of Steel In Its Molten State (AREA)
  • Furnace Details (AREA)
US00744744A 1967-07-27 1968-07-15 Method of treatment of liquid steel under vacuum Expired - Lifetime US3737302A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
FR115946A FR1545666A (fr) 1967-07-27 1967-07-27 Nouveau procédé de traitement de l'acier liquide par le vide

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US (1) US3737302A (nl)
AT (1) AT288458B (nl)
BE (1) BE718095A (nl)
CS (1) CS152301B2 (nl)
DE (1) DE1758696B1 (nl)
ES (1) ES356521A1 (nl)
FR (1) FR1545666A (nl)
GB (1) GB1240876A (nl)
LU (1) LU56511A1 (nl)
NL (1) NL156444B (nl)
SE (1) SE357003B (nl)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4104057A (en) * 1972-06-10 1978-08-01 Hermann Maas Method for making low carbon high chromium alloyed steels
US4212665A (en) * 1978-07-27 1980-07-15 Special Metals Corporation Decarburization of metallic alloys
US4298376A (en) * 1980-04-14 1981-11-03 Kobe Steel, Ltd. Method for treating molten steel and apparatus therefor
US5091000A (en) * 1987-12-25 1992-02-25 Nkk Corporation Method for cleaning molten metal and apparatus therefor
US20030172773A1 (en) * 2000-06-05 2003-09-18 Ichiro Sato High-cleanliness steel and process for producing the same
US20120263207A1 (en) * 2011-04-12 2012-10-18 Panasonic Corporation Method and apparatus for manufacturing thermoelectric conversion element

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2480785A1 (fr) * 1980-04-18 1981-10-23 Kobe Steel Ltd Procede et appareil pour traiter de l'acier en fusion
LU84093A1 (de) * 1982-04-16 1983-12-16 Arbed Einrichtung zum metallurgischen behandeln von fluessigen metallen
DE4114607C2 (de) * 1991-05-04 1998-12-17 Vacmetal Gmbh Verfahren und Vorrichtung zum Umlaufentgasen von Stahl

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2994602A (en) * 1958-10-03 1961-08-01 Yawata Iron & Steel Co Method of vacuum degasifying molten steel by circulation

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4104057A (en) * 1972-06-10 1978-08-01 Hermann Maas Method for making low carbon high chromium alloyed steels
US4212665A (en) * 1978-07-27 1980-07-15 Special Metals Corporation Decarburization of metallic alloys
US4298376A (en) * 1980-04-14 1981-11-03 Kobe Steel, Ltd. Method for treating molten steel and apparatus therefor
US5091000A (en) * 1987-12-25 1992-02-25 Nkk Corporation Method for cleaning molten metal and apparatus therefor
US20030172773A1 (en) * 2000-06-05 2003-09-18 Ichiro Sato High-cleanliness steel and process for producing the same
US20080025865A1 (en) * 2000-06-05 2008-01-31 Sanyo Special Steel Co., Ltd. Process for producing a high-cleanliness steel
US7396378B2 (en) * 2000-06-05 2008-07-08 Sanyo Special Steel Co., Ltd. Process for producing a high cleanliness steel
US20080257106A1 (en) * 2000-06-05 2008-10-23 Sanyo Special Steel Co., Ltd. Process for Producing a High-Cleanliness Steel
US20120263207A1 (en) * 2011-04-12 2012-10-18 Panasonic Corporation Method and apparatus for manufacturing thermoelectric conversion element
US9087963B2 (en) * 2011-04-12 2015-07-21 Panasonic Intellectual Property Management Co., Ltd. Apparatus for manufacturing thermoelectric conversion element

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Publication number Publication date
CS152301B2 (nl) 1973-12-19
BE718095A (nl) 1968-12-16
GB1240876A (en) 1971-07-28
FR1545666A (fr) 1968-11-15
ES356521A1 (es) 1970-04-01
LU56511A1 (nl) 1968-10-28
NL156444B (nl) 1978-04-17
NL6810697A (nl) 1969-01-29
DE1758696B1 (de) 1971-12-23
SE357003B (nl) 1973-06-12
AT288458B (de) 1971-03-10

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