Method for continuous casting of metals
United States Patent Balevski et a1.  
  1*Apr. 29, 1975 METHOD FOR CONTINUOUS CASTING OF METALS Inventors: Anguel Tonchev Balevski; Ivan Dimov Nikolov. both of Sofia. Bulgaria Institut Po Melalognanie I Technologia N0. Metalite, Sofia. Bulgaria Assignee:  
 Notice: The portion of the term of this patent subsequent to Mar. 21. 1989. has been disclaimed.  
 Filed: Apr. 5, 1972 Appl. No; 241.251  
 Foreign Application Priority Data Apr. 7. 1971 Bulgaria 17295 LS. C1. 164/55; 164/66; 164/82 Int. Cl B22d 27/20 Field of Search [56] References Cited UNITED STATES PATENTS 3.650.313 3/1972 Balcvski ct a1 164/55 3.689.048 9/1972 Foulard ct a1. 164/66 X 3.718.175 2/1973 Rincsch 164/259 X PI&#39;IHIUI&#39;) E.\&#39;aminer-Andrew R. Juhasz Assistant E.\&#39;uminc/&#39;John E. Roethel Attorney. Agent, or FirmKarl F. Ross; Herbert Dubno [57] ABSTRACT A system for the continuous casting of a molten metal containing gas in solution wherein the molten metal is treated with gas under pressure in a first chamber con taining the soluble gas together with an inert gas which may or may not dissolve in the melt. and is delivered to a second chamber and thereafter to a final chamber provided with the continuous-casting mold. the latter two chambers being maintained under superatmospheric pressure by the soluble gas.  
 5 Claims, 1 Drawing Figure Ill I l |l E PATENTEnAPnzsms METHOD FOR&#39;CONTINUOUS CASTING OF METALS CROSS-REFERENCE TO RELATED,  
 APPLICATIONS The present application is related to our copending application Ser. No. 811,450 filed Mar. 1969 (now US. Pat. No. 3,693,698) and extending the principles set forth in then-pending application Ser. No. 667,409 of Sept. 13. 1967. That application. in turn, represented a further development of the system described 1 in an application Ser. No. 173,052 issued as U.S. Pat. No. 3,196,501, and itself has issued as US. Pat. No, 3,532,154. The application is also related to copending application Ser. No.&#34; 863.153, now US. Pat. No. 3.650, 1 3.  
 FIELD OF THE INVENTION Our present invention relates to a method of and an apparatus for the continuous casting of metal bodies and, more particularly. to the continuous or semi eontinuous casting of elongated metal&#39;bodies from-a melt containing a dissolved gas affecting the properties-of the metals. I I  
 BACKGROUND OF THE INVENTION- The aforementioned applications&#39; &#39;and patents describe our prior developments in the fieldof intermittent casting wherein a melt of metal or some other&#39;material such as a synthetic resingis maintained under pressure to avoid evaporation (volatilization) and spontaneous decomposition which may occur with heating at low pressures. The melt is generally induced to flow from the superatmospheric&#39;melt chamber to a superatmospheric mold chamber, e.g.. through a syphon or by gravity, and is thus maintained under pressure in both chambers while a pressure differential is applied between the mold and the melt to induce the&#34; metal to flow. Such systems are generally directed to the production of individual casting in a inold cavity of predetermined volume and configuration.  
  It is also known to provide continuous casting systems in which an open-ended mold is charged from one extremity with the molten metal and a solidified or semisolidified elongated body is drawn out of the other end. Continuous-cast ingots may be rolled, forged, drawn or otherwise shaped to produce rod; tube, wire, strip and like elongated articles and such articles of a well-defined cross section may be&#39;made without subsequent handling by the continuous-casting method. It should benoted that the term continuous casting&#34; is not used to suggest that the casting operation is never interrupted or that molten metal is poured into the receiving end of the mold without cessation. The term is one of convenience used, as is known in the art. to indicate the formation of an ingot, bar, bloom, billet or the like which is elongated and generally is of greater length than the mold in which it is formed. Hence the production of any solidifying metal body which emerges from a mold as additionally metal is cast into it, will be defined hereinafter as a continuously cast ingot&#34;. I  
  In the continuous casting of molten metals. attempts have bcen made to use metal melts which are&#39;solutions containing, in addition to a pure metal and an alloy, sol-&#39; uble gases which in some way affect the characteristics of the solidified metal. For example, it is&#39; k&#39;no&#39;wn&#39; that steel can be modified to improve some of its characteristics by treating it with nitrogen to the point that at &#34;least-some-of the nitrogen is solubilized in the steel.  
  Efforts to apply gas-solubilizing techniques to continuous casting has generally proved ineffective and it has heretofore been the practice to confine solubilization approaches to inte&#39;rrupted casting operations while avoiding any use of ga&#39;s in association with continuous casting. T&#39;helatter &#39;avoidancederives, it is believed, from the&#39;experience of many workers in the field that the association of gas withcontinuously-cast molten metafrest&#39;ilts in gas inclusions and the formation of large&#39;gas-filled pockets in the molten metal.  
 OBJ ECTS OF THE INVENTION It is the principal object of the present invention to provide an improved method of and apparatus for the continuous casting of molten metals.  
  It isanother object of the invention to provide a method of continuously casting rod, tube, wire. strip and like elongated articles or a precursor therefor (ingot or bar) which will avoid the above-mentioned disadvantages and can be constituted from a metal containing dissolved gas which remains dissolved even in the solidifiedstate of the metal.  
  -Still another object of the invention is the provision ofa system for the continuous casting ofa molten metal containing dissolved gas in such manner as to avoid intercrystalline gas evolution. separation or porosity as has resulted in the past with metals containing gas as a result of the sharp decrease in solubilityduring the solidification process.  
 SUMMARY OF THE INVENTION These objects and others which will become apparent hereinafter are attained, in accordance with the present invention, in a system for the continuous casting of a molten metal containing a dissolved gas capable of modifying the metallurgical properties of the cast (solidified product) wherein the melt .is-treated under a gas pressure produced by a mixture of the soluble metallurgically effective gas and a gas inertwith respect to metallurgical properties. Subsequent to this treatment and preferably at a location spatially removed from the treatment location, the melt is solidified-under gas containing a higher partial pressure of the soluble gas. The apparatus for carrying out the method of the present invention thus may&#39;comprise a first chamber wherein the&#39;moltenmetal is treated with gas under pressure (i.e., the mixture of the soluble gas having metallurgical propertiesat a first partial pressure) and the inert gas, and a second chamber connected to the first and receiving the melt therefrom. A thirdor. final chamber provided with or communicating with the continuouscasting mold is connected to the second or intermediate chamber and means is provided for maintaining the second and third chambers under a superatmospheric pressure of the soluble or dissolving gas so that the latter lias a higher partial pressure in these chambers than in the first chamber.  
  According to a more specific feature of the invention, the first or treatment chamber comprises a housing above a ladle for the melt which may be pressurized and is connected by a syphon tube reaching into the melt to a second vessel also maintained under pressure via a housing above this ladle or pan. The pressure differential between the chambers above the melts in these vessels serves to displace the molten metal from the first chamber to the second through the syphon tube in accordance with principles discussed in the prior applications and patents mentioned above. The third chamber, preferably located below the-second vessel is provided with a continuous casting mold which, advantageously, is elongated and is provided with cooling means along the mold wall to solidify the mold cast therein. The chamber above the mold is advantageously connected with the chamber above the second vessel for control of a pressure differential therebetween to regulate the rate at which the molten metal is introduced into the mold. lt has been found to be advantageous, moreover, to provide in the syphon tube a one-way valve system for mechanically blocking molten-metal communicating between the first and second vessels. Furthermore, we may provide a direct connection between the first vessel (e.g., via the syphon tube) and the mold chamber as will become apparent hereinafter.  
 DESCRIPTlON OF THE DRAWING The above and other objects, features and advantages of the present invention will become more readily apparent from the following description reference being made to the accompanying drawing in which the sole FIGURE is a diagram of an apparatus embodyingthe principles of the invention.  
 SPEClFlC DESCRlPTlON AND EXAMPLE In the drawing, we show an apparatus for carrying out the method of the present invention, the apparatus comprising a ladle la received in a mass of insulating material lb of the treatment vessel 1, the ladle being heated by a coil 2 surrounding it within the insulating mass and preferably constituting an induction coil of conventional construction. The vessel 1 is closed by a cover 6 defining a gas space 60 above the melt 3 therein and having a flap 6b openable to afford access to the ladle. A perforated pipe 4 reaches downwardly into the melt and is connected via a throttle or pressurereducing valve 5&#39; and a cut-off valve 8 with a source 7 of gas under pressure The gas may thus be bubbled through the melt which may have a layer 3a of slag thereabove. For venting the space 6a, a futher valve and conduit 21 is provided which may open to the atmosphere. A control device 7a may be provided to connect the gas-pressure source 7 with a gas pressure source 14 to be described subsequently so that the molten metal may be induced to flow through a syphon tube 11a through a conduit ll, 12 to the second vessel Pressurized gas source 7 serves to supply the soluble gas (nitrogen) capable of affecting the metallurgy of the melt (steel) in mixture with an inert gas (argon) having no substantial metallurgical effect. The respective partial pressures may be established by a conventional flow or pressure controller 7b connected to the respective gas bottles 7c and 7d. A further valve 9 and its conduit supplies the gas mixture to the chamber 611 above the melt.  
  The syphon ll, 12, comprises a valve 1112 which is of the one-way type to prevent return of the melt to the ladle 1a.  
  The second vessel or chamber 10 comprises an insulating body 100 carrying a ladle or trough 10b communicating with the treatment ladle In via the syphon ll,  
 12. The space above the vessel b is represented at 10c and is closed by a cover 10d. This space is connected via a control valve 16 with the source 14 of soluble gas. A further valve 15 supplies this gas under pressure to valve 16 mentioned earlier and a valve 17 communicating with the third or mold chamber 13. A discharge tube l0e leads from the bottom of the vessel 10b into the mold chamber 13 which is disposed above a continuous-casting mold 130 surrounded by a mass 13b of thermal insulation and a cooling coil 13c. The mold 13a in the solidification region 18 is capable of forming an elongated body or billet 19 which is drawn downwardly at a controllable rate by the drawing device 20 Y which operates to controlledly resist the gravitational descent of the billet. A seal 22 prevents escape of gas around the cast billet. Since the pressure differential defined by control unit 7a regulates the rate of flow between chambers 1 and 10, through the syphon ll, 12, the control 7a also synchronizes the actuating device 20 which may be of conventional construction. lt has been found to be advantageous to provide, in some cases, a bypass for the intermediate chambers 10 in the form of a conduit 12 which, with its valve 12&#34;, communicates directly between the first and third chambers. In this case a line 17 is used in place of valves 17 and 16 to deliver the gas with high partial pressure of soluble gas to the third chamber.  
  In operation, the soluble gas/inert gas mixture is bubbled through a melt in ladle la for a treatment period sufficient to effect the desired homogeneity of the melt and dissolution of gas therein. Usually this time suffices for steady state to be achieved. The valve 9 is briefly opened to establish the desired pressure differential between chambers 10c and 6a to drive the molten metal through the syphon 11, 12 into the vessel 10b past the automatically open check valve 11b. This briefincrease in pressure does not appreciably alter the degree of dissolution of the gas since it acts upon the slag or flux layer 10g and to deliver the molten metal to this bath below the slag layer. After a portion of the metal is I transferred as described, the pressure in space 60 can be returned to its usual value by venting through valve 21.  
  The pressure in chamber 10 is maintained at the level necessary to control the flow via conduit 10e into the mold and the gas is of a higher partial pressure of the soluble component than the gas used in vessel 1. The absolute pressure in this part of the apparatus can also be considerably higher than that at which the melt is saturated with the soluble gas in the first vessel 1. In this manner we have been able to compensate the billet for the normal decrease in the solubility of the gas during solidifaction to maintain the concentration of the gas in the end product 19.  
  When a constant absolute pressure is required in the entire apparatus, we omit the intermediate chamber and directly connect the first vessel 1 with the final vessel 13 via conduit 12&#39; so that the atmosphere in the casting chamber is at the same pressure as the atmosphere in the treatment chamber (except for the moment of transfer) but the partial pressure of the soluble gas is greater in the casting chamber than in the treatment chamber.  
  Various measuring, controlling and regulating devices, known to the art, may be provided for controlling the levels of metal in the various vessels, regulating temperatures and gas pressures and for establishing the metal and melt compositions. The gas may be maintained dissolved in the melt through solidification to appear in solid solution in the cast billet without separation in the form of intercrystalline pores.  
 We claim:  
 1. A method of making a metal body comprising the steps of:  
 a. treating a melt of molten metal with a gas mixture consisting of at least one soluble gas capable of modifying a metallurgical characteristic of said body at a relatively low partial pressure and an inert gas;  
 b. continuously casting the melt treated in step (a) and solidifying the cast melt into an elongated body; and  
 c. maintaining the solubilized gas dissolved in the molten metal in solution during the continuous casting and solidification in step (b) by providing thereabove a gas atmosphere having a relatively high partial pressure of said soluble gas.  
  2. The method defined in claim 1 wherein said molten metal is treated in step (a) and is continuously cast and solidified in step (b) at two spatially separated locations. further comprising the step of temporarily storing the molten metal treated in step (a) under an atmosphere containing said soluble gas at a higher partial pressure than said relatively low partial pressure prior to continuously casting and solidifying the molten metal in step (b).  
  3. The method defined in claim 2, further comprising the step of displacing the molten metal between said locations at least in part by applying gas pressure differentials thereacross.  
  4, The method defined in claim 2 wherein the molten metal is treated in step (a) by bubbling gas therethrough below a slag layer.  
  5 The method defined in claim 2 wherein said molten metal is stored subsequent to step (a) below a slag layer.