DE2250710A1 - METHOD OF GENERATING LARGE BLOCKS OF STEEL USING THE MELTING OF AN ELECTRODE - Google Patents

Description

Dr.-1 ng. E. BERKENFELD · Dipl.-Ing. H. BERKENFELD, patent attorney ·, Cologne

! 225Q710

Anlage AktMizsidtan ______

.urEi _nB from October 13, 1972 vA // _Na mdAnm. HEPPENSTAIX COMPANY

Method of creating large steel blocks using the Peeling off an electrode

(Addition to P 21 38 662.9-24)

The invention relates to methods of making large steel billets and, more particularly, to a method of making large steel billets using electrode reflow to obtain a large compact billet free of a central cavity or funnel cavity, which is well known Problem with casting large blocks.

When producing steel blocks for later forging or Rolling operations is the usual method that the liquid Steel in cooled iron molds with the desired cross-sectional area and height is poured to receive the molten steel, and that a compact steel block is produced which can be heated and handled for the forging or rolling process.

The change in volume of steel during the transition from the liquid to the solid state is known as the result of shrinkage cavities and voids in the steel blocks. «To be arranged at the end of the block. by a minute of fluid vision
to des. liquid steel wa

the producers vasi

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This effort to produce flawless steel blocks with no shrinkage voids is not always successful, even when the refractory insulated heating hood at the top of the cast iron mold containing the steel block accounts for up to 25 or 30% of the total cast block weight. This is especially true if the weight and cross-section of the block are increased and the times required for complete solidification are increased accordingly.

Various methods are used to keep the steel in the container sufficiently hot during the extended solidification period and keep it flowing. These methods include insulating covers over the top of the warming hood, exothermic powders, and / or exothermic linings in the warming hood for the purpose of introducing additional heat to maintain the liquid state, electrical induction around the warming hood, an electric arc at the top of the molten steel or electric current passing through the liquid slag at the top of the liquid steel (electroslag)

These procedures are “effective in varying degrees by they introduce liquid steel into the solidifying ingot for the required time. Have all the procedures used however, some harmful properties in common. The first is that while maintaining the liquid state in the container it is subject to oxidation and chemical change. This applies with or without the liquid slag layer and becomes particularly worrying when progressively larger Blocks require the availability of a container of liquid steel for ten hours, twenty hours or more.

A second major disadvantage of conventional warming hood processes is in that the liquid metal for the volume of the heating mantle must be provided as part of the liquid steel that is melted and poured for the product. This is true even though it is it is known that the product is obtained only from the block, and

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that the metal provided for the volume of the heating hood of the entire Block weight is cut off and thrown away as scrap steel.

The invention described below relates to the use a consumable steel electrode with the same composition as the cast block, which is inserted into the upper The liquid surface of the "cast block" is melted off. The melting rate is controlled so that shrinkage of the Blocks is fully compensated by the molten steel that is peeled off by the consumable electrode.

The use of arc melting a consumable Electrode for block head heating of a large steel block has already been described. Other Process of melting a self-consuming metal electrode, such as electroslag melting, plasma light or arc melting, Electron beam ablation and the like can be used with equally satisfactory results if they are controlled so that a continuous supply of molten metal to the molten one Body of the casting takes place at a speed which is substantially equal to the volume loss due to shrinkage on cooling until the body of the metal is in the shape has solidified.

The invention therefore relates to a method for preventing Shrinkage cavities and blowholes in steel blocks due to the formation of a body of degassed molten steel in a block shape and continuously supplying molten steel by melting an electrode into the molten steel body at a controlled rate substantially equal to the volume loss due to shrinkage on cooling until the steel body has solidified.

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In the foregoing general description of the invention are given certain problems of the known and certain objects, features and advantages of the invention relative to these problems Further objects, features and advantages of the invention will become apparent from the following description with reference to FIG Drawings in which shows:

Fig. 1 is a vertical longitudinal section through a block mold and vacuum chamber with a pouring ladle for pouring a block according to the invention,

FIG. 2 shows a vertical longitudinal section through the mold and chamber of FIG. 1 with a self-consuming electrode in place the ladle,

3 shows a vertical longitudinal section through the mold and chamber of FIG. 1 with a self-consuming electrode in place the ladle, with the consumable electrode in a molten electrically conductive slag is immersed on top of the metal of the block body,

4 shows a vertical longitudinal section through the unit of FIG. 2 with a water-cooled copper jacket or melting crucible, which is arranged at the upper end of the cast iron mold and which the molten electrically conductive slag contains,

5 shows a vertical longitudinal section through the unit of FIG. 3, but with the water-cooled copper crucible, containing the molten electrically conductive slag, placed on the inside of the cast iron mold is,

6 is a vertical longitudinal section through the mold and chamber

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of Figure 1 with a self-consuming electrode instead the ladle and a series of plasma arc guns aimed at the electrode to melt the same, as well as to the top of the molten steel body, around it during the solidification period keep melted, and

7 shows a vertical longitudinal section through the mold and chamber of FIG. 1 with a self-consuming electrode in place the ladle and with a series of electron beam guns aimed at the electrode, to melt it, as well as to the upper end of the molten steel body, around it during the solidification period keep melted.

In the drawings there is shown a typical manufacturing process according to the invention. A cast iron mold 10 is on top of a Cast iron plate 11 arranged within a housing 12 which forms a chamber around the mold 10. The housing 12 is with an opening 13 connected to a vacuum pump of conventional shape used in vacuum flow degassing and is therefore not shown. A lid 14 is arranged in a sealed manner on the housing 12 and a pan 15 * containing molten metal to be poured into the mold 10 is placed on the lid. The chamber inside the case 12 is evacuated to a desired low pressure and liquid steel 16 is poured into the cast iron mold 10 after known vacuum flow degassing methods. Vacuum flow degassing is a well known technique and is used here to illustrate one of the methods of casting a large block of vacuum degassed liquid steel

After the steel 16 has been poured into the mold 10, the chamber within the housing 12 is restored to atmospheric pressure and the pan 15 is removed. A furnace body

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per 17, which can carry a vacuum-tight pressure piston 18 and a holder 19 for an electrode 20, is placed on the cover 14. The electrode 20 is made of the same material as the steel 16. The pressure in the housing 12 is reduced again to the desired output range (for example to a pressure of 0.3 to 0.6 mm mercury column), the electrode 20 is applied to the surface of the steel 22 in the mold 10 is lowered and the arc is created which melts steel from the lower end of the electrode which falls into the body of liquid steel that forms the block 22. The melting of the electrode 20 is continued all the time until the block 22 has completely solidified at a rate which is necessary to compensate for the shrinkage in the block body. The level of the molten steel bath at the upper end of the block body is monitored through appropriate viewing openings 23 or by television cameras and screens. The current supplied to the consumable electrode 20 is the same as is commonly used for consumable arc melting, namely direct current with straight polarity (electrode negative) of 25 to 65 V. It is also possible that the polarity is reversed in polarity (Electrode positive) is changed to generate additional heat in the molten steel bath. The diameter of the electrode is preferably about 25 to 35 % of the diameter of the block body and it is centered above the block body in order to keep the molten molten bath in the central axial zone of the block body which solidifies last. For example, a block body 2.55 m in diameter (in a round corrugated cast iron shape) weighing 157.644 tons would preferably use an electrode 6.25 to 8.75 cm in diameter. Such an electrode would weigh at least 7.882 tons (5 % of the weight of the cast block body) to provide enough metal to compensate for the shrinkage of the solidifying block. With a diameter of 6.25 to 8.75 cm, this electrode would generate electrical energy in the form of direct current of 25 to 50 V and 15,000 to 25,000 A.

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erf order. corresponding to the known self-consuming vacuum arc deposition process, with a current decrease towards the end of the cycle. At the end of the freezing period, if No more steel is needed in the block body, the process becomes brought to a standstill and the atmospheric pressure re-established within the housing 12. The furnace body 17 is removed, the cover 14 is removed and the block 22 is removed from the mold 10 taken out. The subsequent treatment of the block 22 depends on the particular steel produced and the desired th end product.

As described above, a furnace body 17 is shown the upper end of the cover 14 and placed on the housing 12 "The furnace body 17 with an adapter plate or a special" formed furnace body could also be placed directly on the upper end of the mold 10 and evacuated ^ whereupon the electrode 20 would be melted in the manner described above

The above overview describes the use of "the self-consuming vacuum arc hot hood with a steel block ^ which is degassed and poured off after the vacuum _{flow degassing process. Other degassing processes can also be used, such as the tap degassing 9} the vacuum ladle degassing, the degassing of Ladle to ladle © the other, including degassing the steel poured into the ingot mold during the pump down cycle over the top of the mold prior to the self-consuming valaium-arc hood operation. This latter degassing process of otherwise ungassed steel in the ingot mold results in a rapid and usually violent development of Gases from the liquid steel and requires a high, free edge area of the block form, so that the same can hold the entire actively moving liquid steel during the degassing.

In the method illustrated in FIG. 3, the molten

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zene metal poured into the mold, preferably in a vacuum, like has been described above in connection with FIGS. 1 and 2.

After the steel has been vacuum-poured into the mold, the chamber is restored to atmospheric pressure and the ladle 15 is removed. A furnace body 30, which can carry a vacuum-tight pressure piston 31 and a holder 32 for an electrode 33, is placed on the cover 14. The electrode is nominally made of the same material as the metal in the block body. Slag 34 having the correct chemical composition for electroslag melting is placed on top of the molten metal of the ingot body. This slag can be composed of calcium fluoride (CaF ₂ ), calcium oxide (CaO) and / or silicon dioxide (SiOp) and / or aluminum oxide (AlpO,) and / or other materials, as is desired according to the known methods for electroslag melting. The electrode 33 is lowered into position within the slag coating 34 and the electrical current turned on which melts metal from the lower end of the electrode which falls into the body of the liquid metal that forms the ingot. The melting of the electrode continues for the entire time necessary for the complete solidification of the block at a rate which is necessary to overcome the shrinkage in the block body.

In the process of melting the electrode, the electrical energy that is applied can be alternating current or direct current according to the known state of the art for this melting process. In Fig. 3 the electrical circuit of the electrode can be closed by the cast iron plate 11 of the mold. In Fig. 4 and in Fig. 5, the electrical circuit the electrode can either be closed by the cast iron plate 11 of the mold or by a water-cooled copper jacket

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35 or crucible at the top of the block body.

During the period of electroslag meltdown of the electrode for the block head heating, the pressure above the slag can be kept at or close to an atmosphere that consists of dried Air or dried inert gas (such as argon), or the pressure can be adjusted by appropriate pumping equipment can be reduced to the absorption of hydrogen or other harmful gases by the molten slag and accordingly to prevent the molten metal of the solidifying block body.

The use of plasma arc ablation of an electrode for block head heating of a large block is illustrated in Figure 6 of the drawings.

In the plasma arc process, the electrode 40 is held in a holder 41 on the plunger 42, so that the electrode can be moved in the vertical direction to a corresponding position above the molten metal 22 in the mold 10 to take. A number of plasma arc guns 45 are arranged in the cover 14, which the plasma arc 46 on the Point the electrode to melt it as well as to the top of the molten block body to melt it during the To keep the solidification period melted.

In Fig. 7, the electron beam method is illustrated. Even here the electrode 50 is held in a holder 51 on the plunger 52 so that the electrode is relatively vertical to the molten metal 22 in the mold 10 can be adjusted. A number of electron beam guns 55 are in the lid 14, which direct an electron beam 54 onto the electrode "" to melt the same as well as onto the upper end of the molten ingot body to keep the same molten during the solidification period.

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Both in the plasma lip arc melting process and in the Electron beam ablation is the pressure in the chamber reduced according to the known methods of operating these meltdown systems. When electron beam melting can this pressure must be very low (less than 1 mm of mercury) and attention must be paid to avoiding losses Manganese and other elements that must be present in the block body.

The described block head heating method according to the invention achieves two main advantages. The first and most important The advantage is that the steel block is under optimal conditions for medium flawlessness and a minimum of chemical Segregation can freeze. As a result of the vacuum arc melting With the self-consuming electrode it is possible to ensure that the container keeps liquid steel during the whole Time period required for the block body to completely solidify is maintained. The maintenance this liquid melt pool at the upper end of the block body ensures that no intervening solidification or bridging takes place in the block body itself. As a result, secondary funnel cavities or shrinkage cavities can be eliminated will"

A second important advantage of this block head heating process is that in the production of ingots of maximum size, which usually takes up all of the smelting and refining capacity use a melting plant, the £ * $ size range of available blocks can be increased. If, for example, a special melting plant with several furnaces is programmed in this way can be that it produces a total of 181.2 tons of steel, which by normal casting and block head heating devices could be combined into a block weighing 181.2 tons, the block body would weigh approximately 135.9 tons. The rest would be in the block header. A resulting forging would be a

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proportion of this block body of 155.9 t. With the described invention, however, the entire capacity of the melting plant of 181.2 tons can be poured into a cast iron mold to form the block body and the steel melted off by the consumable electrode is used to compensate for the normal shrinkage in this block body. In this way, all of the steel in the tendon line is used to produce the usable body of the ingot, and the resulting forging that can be obtained from this ingot body would have a correspondingly greater weight 30 % without changing the size of the equipment ^ that is used to create the molten steel o This is a very important benefit »

The invention is not limited to the exemplary embodiments shown and described, which differ Changes can be made, oime the katoaen of the invention leaving.

Claims

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Claims (1)

Attachment file number lur input, from October 13, 1972 VA // Nam.d.Nm. HEPPENSTALL COMPANY PATENT CLAIMS 1 · Method for preventing shrinkage voids and blowholes in metal blocks, characterized by the following Steps: a) pouring a body of degassed molten metal into a block shape and b) the continuous supply of molten metal of the same composition to the molten body before The poured metal completely solidifies, by melting an electrode in the body of the molten one Metal at a controlled rate substantially equal to the loss in volume due to shrinkage on cooling until the metal body has solidified in the ingot shape, increasing the level of the molten metal is kept substantially constant in the block shape until solidification is complete. 2, method according to claim 1, characterized in that the Bodies degassed molten metal in a block shape within a vacuum chamber by vacuum flow degassing is formed and that molten metal is melted down by electroslag an electrode is continuously fed into the metal body from a furnace arranged on the chamber will. 3. Method according to claim 1, characterized in that the body of degassed molten metal is in a block form is formed within a vacuum chamber by vacuum flow degassing and that molten metal is melted off by flasinal arc an electrode in the metal body made of a H 108/5 309851/0742 no continuously fed to the furnace arranged on the chamber will. 4, method according to claim 1, characterized in that the Body of degassed molten metal formed in a block shape within a vacuum chamber by vacuum flow degassing and that molten metal is melted off by electron beam an electrode is continuously fed into the metal body from a furnace arranged on the chamber will· 5. The method according to claim 1, characterized in that all of the available molten metal with a particular composition is poured into a block mold which has no heating hood , and that molten metal is continuously fed to an electrode with essentially the same composition by means of electroslag peeling · 6. The method according to claim 1, characterized in that the whole available molten metal with a special composition is poured into a block mold, which does not have any Has a heating hood, and that molten metal by plasma arc melting an electrode with substantially the the same composition is continuously fed 7 «Method according to claim 1, characterized in that the whole available molten metal with a special composition is poured into a block mold, which does not have any Has a heating hood, and that molten metal by electron gas t rahlab tend to be an electrode with essentially the same composition is fed continuously. 8 «Method according to claim 1, characterized in that the diameter of the electrode is approximately 25 to 35 % of the diameter of the block body« H 108/5 309851/0742 9. The method according to claim 1, characterized in that the Electrode is essentially centered above the bath of molten metal in the font. 10. A method for preventing shrinkage cavities and blowholes in metal blocks according to claim 1, wherein at the same time the normal segregation of chemical elements in the central zone of metal blocks is avoided, characterized in that all available molten metal with a particular composition is poured into a block form which does not have any Värmhaube, and that molten metal is continuously supplied by melting an electrode with a correspondingly different composition in order to compensate for the heterogeneous effects of the optional Brstarrena. H 108/9 309851/0742 Blank page