DE1758765A1 - Process for the production of very pure steels - Google Patents

Description

Process for the production of very pure steels

The invention relates to a method of manufacture very pure steels, to which aluminum is added, in order to have an extremely low oxygen content achieve. .

It has long been known that metals, in particular Ferrous metals, when smelting in contact with air or another atmosphere containing oxygen, oxygen absorbed, so that undesirable conditions arise that further treatment of these metals affect and reduce the quality of the products made from these metals. Examples of adverse effects of oxygen in rolled steel products are oxide fractures, non-metallic inclusions, formation of cavities

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near the surface of the ingots that crack
during the rolling process.

The best known method so far, this absorbed
Treating oxygen has consisted of introducing into the metal one or more metallic elements, for example manganese, silicon or aluminum, which, although in
Added in small amounts, have a greater affinity for oxygen than the metal to which they are added and form oxides that float upwards and separate from the rietall as a slag layer. In most previous processes, however, the metal, such as steel, “while still liquid, can continue to absorb oxygen from the air or some other source. Generally there will be an excess of beoxed dation elements that have been drawn so that oxygen will continue to enter the metal when it is in the liquid state. The excess deoxidizer then continues to “ react with the oxygen.” The resulting oxides are often trapped and formed in the cast steel
Defects

In practice, the earlier method is deoxidation
lower carbon steels were only suitable » one
To remove part of the oxygen present, with calibration

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the reaction continued until the steel had completely solidified. This also leads to oxide inclusions, which are all cracks in the surface or as not express metallic inclusions.

The reaction between dissolved oxygen in liquid ferrous metals and yellow aluminum, which is added as a deoxidizing agent, is known to result in massive amounts of oxide particles, which always contain some aluminum oxide. These are generally associated with other oxides, for example iron oxides. There have been many recent reports in the literature relating to a compound called hercynite (FeO.Al ₂ O-).

Under certain conditions, crystals of hercynite or Similar types of oxides, which are defined below, can seep inside liquid iron as tiny Form particles that rise upwards and group together to form masses or crusts of hercynite-like particles If, however, hercynite-like particles precipitate, the reaction seems incomplete, and oxygen And aluminum remain in solution in the liquid metal » to then knock down later in the course of the proceedings.

469

The words hercynite and hercynite-like oxides, as used herein, "refer to the compound FeO.AIpO, or FeO.AIpO, with some manganese oxide (MnO) or FeO.Al ₂ O, with some aluminum oxide (AIpO,), the some iron oxide (FeO) in solid solution in a range from about 0.0 to about 3.5 i "contains or combinations of any or all of the above-mentioned compounds or of AIPO, in combination with other oxides of elements such as silicon. chromium , Vanadium, molybdenum or nickel, similar to FeO or MnO. This combination, although in contact with liquid steel, tends to increase the oxygen activity in the liquid steel to a level and even above that which would be present in the steel if it were only in contact with the compound AIpO- Compounds of various compositions can exist and can be characterized quite generally by the formula (Z) _x ^ AIgO,), in which Z means one or more has another of the above-mentioned oxides.

The expression "testing of external influences" used in this specification relates to a known method to improve metal production in a controlled external atmosphere using a harmless one Gas.

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_ 5 -

The term "ceramic alloy" refers to a Combination of two or more ceramic oxides in solid solution in one another or in one or more solid solutions with one or more chemical compounds, which consist of one or more metallic oxides *

The procedure for testing external influences, such as it described here can be used along with any Metal casting processes are used, according to which the liquid ferrous metal is converted into a solid metal product However, this method is particularly useful and necessary in many cases for the so-called continuous casting of low carbon steels, where it is believed that a method of controlling oxygen to a deeper and more even-

a / 'ren level in the liquid metal so far / desired,

but has not been achievable improvement.

The present invention has the following advantages:

1. It creates opportunities for making liquid Steel using aluminum as a deoxidizer without hercynite forming in the final stages.

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2. It creates means for the production of liquid steels from extremely low oxygen content in an environmentally controlled system, so that the re-entry of oxygen in the metal after the first deoxidation is prevented. '

3. It creates strong steels that are essentially free from oxide defects in the surface, from non-metallic ones

• Oxide inclusions or other disturbances that relate to oxygen are due.

4. It creates the possibility of low carbon steels continuously cast, which are of a slightly high quality, and aluminum as an oxidizing agent use, refines the grain structure and prevents aging due to dissolved nitrogen.

5. She creates a process by which an accurate chemisee Control of the composition for oxidizable alloy elements such as carbon, silicon, manganese, and chromium Vanadium is possible.

6. It creates a process that will significantly improve the life of refractory linings Containers for liquid metals brings with it.

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According to the present invention, the method for Production of ferrous metals that are essentially free of undesirable oxide impurities, thereby achieved that first the molten metal undergoes pre-oxidation is subjected. So that the dissolved oxygen in the metal to no more than the value

Log # 0 = -7640 / T ( ⁰ K) + 2.84 10

where $ 0 means weight percent dissolved oxygen and T ( ⁰ K) temperature in Kelvin degrees, so that a relationship is established with any aluminum present in the metal, which is no more than an amount which is given by the following equation

is expressed:

2 4

Log [(^ Al) * (# 0)] = -79600 / T ( ⁰ K) + 32.15, 10

whereupon the pre-deoxidized molten metal from the Deoxidation product is separated.

If the deoxidation products are solids, this can be done by letting them float and that liquid metal pours out from under the layer of solid oxides. If the deoxidation products are gaseous, the separation is even easier because the gas is then only released from the Near the metal dissipated. One sees a chamber that contains the molten metal and is lined with a refractory material that is essentially nonexistent

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Gives off oxygen to the molten metal, but contains aluminum as a deoxidizer. A harmless inert gas is introduced into the chamber so that an atmosphere is maintained which is substantially free of undesirable constituents and which gives substantially no oxygen to the molten metal which contains aluminum as a deoxidizer. A stoichiometric excess of aluminum over the theoretical amount required to react with all of the oxygen to form AlpO- * in the metal to be treated is maintained in the metal of the chamber. The already pre-deoxidized metal is poured into the chamber and the chamber is kept at a temperature above the melting point of the metal and so much aluminum is made available that it reacts with the oxygen in the metal and can form aluminum oxides to such an extent that no more than 0.006 ia oxygen remains dissolved in the metal, preferably even no more than 0.003 1 ° oxygen. The insoluble material, essentially Al _? O ,, can then be separated from the deoxidized molten metal by allowing it to float and pouring the liquid metal out from under this oxide layer. Continuation of this process results in a progressive build-up of a top layer of metal containing a concentration of oxide particles

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contains and which is skimmed off or stripped from time to time must become.

During preoxidation or the first process stage, aluminum or carbon can be used for deoxidation, if necessary under a reduced partial pressure of 00 or other deoxidizing gases * In any case, a stoichiometric excess of aluminum should be present in the chamber or in the second stage of the last deoxidation process be. The. The amount of aluminum to be added in the second stage depends on a number of circumstances including the aluminum and oxygen level of the metal with which it enters the chamber, the temperature, the amount of residual aluminum and oxygen, which may be contained in the metal, if maximum purity of the metal is required, of the refractory material, the grain size of the steel product and the fixation of nitrogen in order to prevent aging in the steel product. In addition, the precipitation and separation of the solid particles of AlpO in the chamber can be promoted by adding aluminum in the second stage, preferably to an extent of at least 0.025% , based on the total weight of the metal to be treated. It is desirable that mixing be carried out well, and for other reasons before or during the addition of the metal to be treated.

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Such an addition increases the driving force of the reaction 2 Al + 30 = AlpO ,. As already mentioned, this can be done Pour molten metal from the solid oxide particles and transfer it to the chamber for the second deoxidation or for the transfer the second stage of the procedure. In the event of solid waste products or floating deoxidation products does the? rennuhg. Although adhering to the above cited formula is essential in the first or pre-oxidation step, it is desirable that the content of the dissolved oxygen in the metal to no more than 0.06 weight percent, and preferably no more than 0.058 Weight percent is reduced. The deoxidized molten metal from the second stage of the process can be used in can be further treated in various ways, or it can be allowed to cool and solidify without further treatment, in any case, however, it must not be exposed to the oxygen present which can penetrate the metal and again increases the oxygen content of the metal above the desired level. The procedure as it is above is particularly suitable for treating low carbon steels. Such Steels contain no more than 0.15 # carbon and generally less than 0.12 $ carbon. Should that be To solidify metal after the second stage of the process, it is desirable to take it out of the chamber through a pouring channel

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pouring into a mold without contacting it with the oxygen of the atmosphere as mentioned above. Aluminum can be added to this pouring stream and it is perhaps the best way to get good mixing and grain formation. Another possible method is to add the aluminum to the chamber before adding the pre-deoxidized molten metal c

The invention will now be explained with reference to the drawing, for example. In the drawing show:

Pig. 1 is a graph showing the percentage of oxygen dissolved in iron versus the aluminum dissolved in the metal is applied at different temperatures .-. ^ t,

2 shows a phase diagram of the iron oxide aluminum oxide system,

Fig. 3 results from Fig. 1 and shows the relationship between oxygen and aluminum in iron at 1600 °,

Fig. 4 is a further part of Fig. 3 and shows more clearly the relationship between aluminum-oxygen-iron and

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Pig!> Ate a part of Fi ₍ > 3 in more detail, namely the relative between Almainiuiri-E'auerntoff-Lisen.

L'n ict been mentioned, äa 'under gcwicBon ideal hodingun ^ en dio leaktion awiochcxi ^ olüoteia aluminum untl golöotom!. ". Aueratoff ir. Ctalii Al ₂ O- results otatt I'ercynit and that dao

;:. the Cauorutoff in the i'otal! aktivoara vcrringort and for all purposes practically complete · Ob * rleicli Qolcho idealon Lc: Iin, jiin.; cu for "iher ia small LoborntoriuconiaCstab received before cincl, v; ar cc not known _f ca '; nian oolche ideal conditions auo: i la ^ ro-teehntechen. "a ctob bei der je - .. erbliolien rtnhlhcrrtclluiu; vrirtlo eirJialton can _t εο da 'flic 3il <iunt; of Ifercynit and its unconcerned effects in IJorctellun «-: before. fecten ^cr ti-hien could be avoided

uoll zunticiiüt liezu ^; jem: nsen v / ground on ^ U "· 11 in the

the urven 1 and 2 of the!? ciiiehuns Loß ₁₀ U? 'Al) ^? . ('-' O) -79600 / T ( ⁰ K) + 3.:. 15 cntcrechner and the horcynitartlee Gxidbilrlur ^; in flUooi.'en ^ ieen _t v / elehec Tauerrtoff and aluminum contains It, vriedcr _t ; e cn, \ Hhrend the curves 3 and the AlgCU-üildunc i. '^ Fluot.i-.en ^ ioon, doo Gnuerotoff and

ii contains it, at the ani; egg; flat door doors again-In each:? nll lot Oie Verwr.ndtoch :: ft zvdcchcn dissolved aluminum (Al) and celöBten oxygen (0) in the liquid Te. temperature dnr,; unrolled.

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In Fig. 1, a horizontal line has been drawn on the 0.065 > 0 plane, which corresponds to about the amount of oxygen normally found in a non-deoxidized, low carbon steel of about 0.06% carbon in solution. Lines A and B have been drawn to show what happens when an amount of 1.5 and 2.0 pounds of aluminum per ton of steel is added. Starting at "S" on line A, 1.5 pounds of aluminum are added per ton of steel at a temperature of 1600 ° Celsius and this addition results in a precipitate I of Hercynite until the aluminum and oxygen content in solution at point S * and at this point the metal, it appears, is essentially in equilibrium with the solid hercynite at 1600 ° C.

At S ¹ , the liquid steel contains a significant amount of

Aluminum and oxygen in solution at 1600 ° G, and the Most of the oxygen forms hercynite or AIoO *

with further cooling and solidification, so that in the

Set steel non-metallic inclusions or oxide streaks in the rolled products.

Under normal working conditions, in which the liquid metal is always kept in contact with the hercynite, the relationship between oxygen and aluminum will follow curve 2, and only to a comparatively modest extent

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-H-

A further deoxidation can be calibrated by adding more Achieve amounts of aluminum. For example, note line "C" where a total of 3 pounds of aluminum per Ton of steel has been added.

If, on the other hand, contact with the hercynite is prevented and the environment of the metal is changed so that with an additional 0.5 pfunö aluminum per ton, the metal under ideal conditions shifts from "S" to ^M L "momentarily, and a v / Further deoxidation takes place up to "L", so that essentially all of the remaining oxygen is precipitated as AIpO ^.

The explanation of the method should begin with understanding the FeG-AloO ^ equilibrium weight diagram shown in FIG. On the right in the diagram, a solid solution is present at a temperature of 1600 ° G, which contains up to 3.5 # FeO in the Al ₃ O ₅ . Are more available than 3.5 ^ PeO in such a ceramic alloy), there is the excess completely in the form of Rarcynit to PeO about 4-1: 'o exceeds the ceramic alloy. It follows that refractory containers lined with A ^ O-, which is in contact with liquid metal, must contain less than about 3.5% FeO in order to avoid the formation of Hercynite, ia the refractory material. Oxygen content of pure liquid Fe of 0.058 # at 1600 ° C in agreement

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with the relation Log ₁₀ $ 0 = -7640 / [P ( ⁰ K) + 2.84 appear to be in equilibrium with solid hercynite at a temperature of 1600 C and also in equilibrium with both hercynite and the solid solution of AlpO, with 3 » $ 5 FeO. Thus, a refractory lining, initially made of pure AlpO-, in a container containing liquid Fe, which contains a little more than 0.058 $ 0, would convert to hercynite under the liquid metal and the solid solution of AlpÖ_ with 3> Saturate 5 -i ° FeO. The relative amounts of these two phases could variie- ä ren both up and down, if only the total amount produced of the two equal $ 100. At times when more than 0.058 ti 0 is present, the relative amount of hercynite would increase, whereas at times when less than 0.058 fo 0 is present, the relative amount would decrease.

Curve 2 in FIG. 1 shows a relationship between 0 and Al, which continues below $ 0.058. The curve 4

shows an Al-O relationship, which is curve 2 for the ™

the same Al content overlaps. As will be shown, the overlap can be explained by a careful study of the "ceramic alloy" of the diagram of FIG. In Fig. 3 , the curve 4 of Fig. 1 is from above from point "E" to point "B", where the relationship with the

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Hercynit takes place, has been extended. In Pig. 3 places the lines ALO-O and HER-O represent the ratios of oxygen to aluminum in the compounds AIpO and FeO.AIpO ,, respectively. The precipitation of AIpO, and PeO.AIpO, from the liquid Pe would be done along lines parallel to these lines.

Like Pig. 3 shows, only a relationship between Al and 0 results from the curved line "A - B", that is, additional Al or 0 forms PeO.Al ₀ O ,. At point "B" you can

έ 3

. two relationships exist. Below point "B" would be in ideal system where the environmental conditions are completely harmless, that is, neither the atmosphere nor the refractory materials (for example pure AIpO-) or any solids present in the material can give off oxygen to the metal, one Adding aluminum theoretically causes a drop of 0 on the "B - E" line and no formation of

Instead of starting the consideration at point "B" in such an ideal system, consider the situation which arises if one ^{starts at point M} A "At this point the container will be covered with PeO.AIpO, or impregnate by absorbing 0 and PeO from the metal.Aluminum, which is added, will react with 0 and form PeO.Al ₂ O, which is suspended as a contaminant, floats and is in contact with the metal

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or adheres to the walls of the container. If when it reaches point "B", the system has been contaminated with a supply of available oxygen, and if Al is still present at "B", the relationship follows Al-O of curve "B-C-D".

For example, at point ^ S "to point" T "would be aluminum added another hercynite would be on the "T-W" line, like Jig. ' 4 shows fail if in the system Germs of pure AIpO were present, this "

very quickly in Hercynite due to the excess of Pe and O be converted because Fe and 0 are always in the system available. As long as a significant amount of hercynite is present in the system, the relationship between follows Aluminum and oxygen of the curve "A-B-C-D", although the atmosphere itself does not supply oxygen. In this description, the term "available oxygen" can be referred to as the oxygen that is able to interact with the molten metal or with the deoxidation | to combine means, regardless of whether it is atmospheric oxygen, dissolved oxygen or chemically bound oxygen, and which is capable of being released so that it can combine with the metal or deoxidizer.

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To understand the nature of the relationships which occur on the "BE" line, consider further the earlier statement that at "B" the 3.5 # FeO are in solid solution and in equilibrium with hercynite as well as the liquid Fe, which at 1600 ° G contains 0.058 $> oxygen. On the other hand, not far from point "E" is nearly pure AlpO, in equilibrium with liquid Fe, which contains oxygen on the order of about 0.0025 #. It follows that between "B" and "E" there is a whole ψ series of solid solutions of FeO and AlpO in equilibrium with the metal, and the right-hand scale in FIG. 3 shows the theoretically calculated connections of these equilibria.

It is now to be investigated what happens when such a solid solution as it is shown at the point "TJ", is present and aluminum is added at point "V" (Fig. 5). At this point the first precipitation consists of of the solid solution containing FeO at the level of "U", and ^ the precipitation continues on the line "V-X", the The concentration of FeO decreases to the level of the point "X" in the precipitate. In the meantime, the refractories remain Walls at "U" level in terms of FeO until fusion can take place. When the merger takes place, it seems the concentration of the system to reach an equilibrium at point "Y", which can vary up and down, depending on what relative amounts of liquid metal

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and refractories are present.

The end result of the continuous addition of aluminum to a system in areas "B" and "E" is the conversion of the oxygen in the metal and in the refractory to an aluminum oxide precipitate which is eventually almost pure at point "E". However, this high theoretical purity is only possible when the relative amount of liquid metal is large compared to the amount of oxygen available in the refractory material. | When the refractories are able to soak up oxygen as FeO almost to point "B", there is no longer a reservoir of oxygen to diffuse into the system for several hours, until it is finally almost completely as Al ₂ O, with a relatively small amount of oxygen low PeO gohalt could be put down.

However, the situation that has just been described is even better than the situation that occurs when the refractories are saturated with Hycernit Bind, because then would " the "reservoir" has at least 10 times more available oxygen and the presence of the fercynite would also guarantee that the gradient would take place on the "A-B-C-D" line on the line "A-B-E-P" occurs when aluminum is added to the system is added.

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There are two types, as with a refractory system Materials and precipitated oxides that are saturated with Hercynite can be guaranteed that the Existence of hercynite on the line "A-B-C-D" and "C-I)" and thus it is essentially impossible for it to be on the line "A-B-E-P". One of those ways is related to the. Surface energy at the interface between the solid hercynite and the liquid metal, The crystal geometry of the hercynite at the interface between

™ see the solid and the liquid seems better iff the Al and O atoms to match than with AIpO ,. The other way is that the hercynite continues to introduce available oxygen into the system so that it follows the line "A-B-C-D" follows even when aluminum is in excess. An important conclusion from the above analysis is that the presence of a significant amount of hercynite in refractories or precipitated oxides or in both tends to continue "even as more and more aluminum is added and no additional one." Oxygen from external sources is more available. Adding aluminum only beats oxygen out of the Metal or forms further hercynite. Obviously, unless a very large excess is added, there is less tendency to remove more oxygen from the hercynite that is already present. Too big aluminum -

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But excess leads to additional deoxidation of the Slag and refractory material with excess aluminum.

Even if there is a tendency to get oxygen out of that already It takes a long time to remove existing hercynite because a diffusion process in the solid state takes place see goes. Tests have shown that it takes 8 to 10 hours takes time to equilibrate in small laboratory pots

has hired _e ^

As for the source of oxygen, which is only hercynite, it is easy to see that low carbon steels, in which the oxygen content is normally 0.065 ° , tend to make the difference between 0.065 and 0.058% oxygen in refractories in the form of feed dissolved FeO and hercynite. In practical terms, the operation of a steel plant is always something FeQ-rich slag present, which enters into the container and this addition of oxygen available to-i leads. In any system except a high vacuum system and with at least some carbon in the metal or a fully controlled environment, oxygen from the atmosphere is always available at some stage. A container lined with refractory material, which contained liquid iron and which is placed in contact with air, is inevitably filled with hercynite.

»■

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saturates due to the iron droplets that stick to the lining or are embedded in it when it is still at high temperatures or when it is reheated for a new use. These iron droplets quickly transform into FeO and are absorbed by the refractory materials as PeO in solid solution or as Hercynite. Another important factor to consider is the surface energy which, even when aluminum is added to a system that does not contain hercynite _{, is greater to form Al 2} O than to form hercynite. Therefore, a driving force must be created to get over this "hump", which provides additional energy for the formation of AIpO-. Preferably the oxygen level of the iron should be well below the transformation point of hercynite and the system should be free of hercynite compounds in the refractories or of hercynite suspended in or floating on the metal. To generate additional nucleation forces for AIgO, a pure Fe-C alloy should be deoxidized to approximately 0.045 # oxygen so that it is sufficiently below the transformation point of Hercynite. This point is well below 0.065% oxygen, which is normally found in low-carbon sections.

In summary, it can be said that it is practically impossible to # | f bjti <f§n earlier syi? Tejpn _f 'the aluminum ^ l | :

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Deoxidizer related to find a condition in which at least a portion of the refractory material of the container containing the liquid steel is not included Hercynite becomes saturated. It's even harder to find an earlier system in which pure Al ^ O, that Represents reaction product in which curve 4 predominates.

It is now apparent that a practically useful system, in which the formation of hercynite is avoided, must provide means in which the liquid Ä

Metal goes through a multi-stage process, of which the first stage results in the following: 1. The metal is pre-deoxidized, so that excess oxygen is below the transition point of Hercynite to Pig. 3 is lowered so that a Relationship to any aluminum that occurs in or below this curve, line "S-D" in FIG. 3. 2. Separating essentially all suspended or floating hercynite-like substances and preventing that these enter the second stage. The separation of the suspended or floating slag or the hercynite-like ™ Substances in the first stage should create time for this, so that they can rise to the surface layer and the metal can be poured into a second container.

The second stage of the procedure must always be sufficient Aluminum must be present so it will react with the remaining oxygen and prove to be essentially pure

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AIpO- can knock down. This should also be sufficient Time to. Are available for the AIpO to float up and can be retained by the metal which passes from under the oxide in a further stage or in a Mold poured.

The second assistant in the process must have total control of environmental influences in the following Way: 1. The gas atmosphere must not be able to

"Put a noticeable amount of oxygen in the liquid iron to convert at the desired low oxygen content. 2. The refractory wall of the second stage container must essentially always be out of contact with available oxygen and thus free from any hercynite infiltration being held. 3 ° The refractory wall must be made of stable oxides, for example AlpO, which themselves cannot be decomposed by iron of low oxygen activity in the presence of aluminum. 4. It must

^ an excess of aluminum can always be maintained in the metal which is above - e & - the stoichiometric amount of oxygen present in the metal.

The control of the environmental influences, as mentioned above, must be maintained at all subsequent process stages and also during the casting process itself, so that no noticeable amount of oxygen can enter the metal,

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as long as it is still in the liquid state.

The first stage of the process can be carried out in a number of ways including, deoxidation using carbon with or without reduced partial pressure of carbon monoxide, using other controlling gas spheres, or using aluminum, or other suitable deoxidizing agents. Palis carbon, vacuum, or a gas is used in the first stage of the process, preferably some aluminum should be added * before the first stage is completed, and then time should be allowed for separation or precipitation of hereynite to occur. Adding aluminum in this way will help reduce attack on the refractories.

If aluminum as a deoxidizer in the first stage is used, the first stage need not necessarily be completely controlled in its atmosphere. It can be seen that in the 1. Level a lot of hereynite and the benefit of a controlled atmosphere would be that Saving a part of aluminum »

The transition point of the hereynite and the curve in Fig. 3 are subject to changes for the pure iron-oxygen-aluminum system, which are caused by the presence of other oxides in the ·

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System, which is mostly the Pall, depends. ■ ¹ Venn, for example, the manganese content of the metal is between about 0.25 to 0.50 fo, is the point "B" 0.058 <£ 0) maybe 0.020 $ 0 or even lower, and therefore the rest of the curve should be adjusted according to will. Other oxide-forming elements can, in small amounts, change the conversion synm of Hercynite and the control curve. These include titanium, zirconium, silicon, Ohron, magnesium, vanadium, molybdenum, nickel and copper. Some of these compounds were expected to decrease the conversion point "3" while others increase it. In the presence of manganese it may be necessary to lower the oxygen level, and the relationship between Al and oxygen would then of course change in such a way that a lower oxygen content occurs for a given aluminum content. The complex oxides (Z). (Al ₀ O-.) Would now be the product of the

X c. j

Deoxidation in the first stage.

fc In practice, all low carbon steels always contain some manganese, and due to its degrading effect on the transformation point of Hercynite and the additional driving force that may be required to get AIpO * nucleation in the second stage, the oxygen content should be in the first stage is reduced to 0.015 ° / ° oxygen or even further

will.

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It is interesting to note that the hercynite problem is related to the carbon content of steels and can become a significant problem at very low carbon contents. For example, a steel containing 0.30 fo carbon will normally contain no more than 0.02 <fo oxygen. Such steel would not form hercynite in a container lined with refractory if manganese was absent. But is Hercynit already present, the carbon (dissolved carbon) in the steel with oxygen is expected to react, the like of the Hercynit

is supplied so that at least a partial oxygen depletion of the refractory metal occurs. Thus, the present invention is particularly advantageous for treating steel containing less than about 0.13 ° F carbon.

Carbon does more to change type than grade according to regarding hercynite. Increased carbon seems to bring up the oxygen concentration, but one abrupt change occurs when the oxygen level drops Conversion point of Hercynit reached and the control curve, for example at point "B", the latter by the Presence of other alloying elements. for example manganese, is affected.

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If the second and subsequent process steps are carried out correctly, the metal can be converted into a highly pure state and contain very little oxygen or are available to the metal in its environment. It is therefore possible to introduce any desired oxidizable alloying element into the metal in the second stage, thereby making one to obtain essentially 100% addition without losing any appreciable amount of the alloying elements. Through this

^ Not only is metal saved itself, but it is too very precise chemical control of the analysis of the finished metal is possible. That is why they are used in the manufacture of steels such oxidizable elements as manganese, silicon, chromium and vanadium preferably in the low carbon content second stage added. A final addition of carbon can also take place after the addition of aluminum in the second stage, to precisely adjust the carbon content. Other oxidizable elements can also be found in the second stage for effective for special purposes. For the purpose of

W sulphurization z. B. can be calcium, magnesium or rare earths

be added or titanium or zirconium to achieve other

Advantages, for example for the removal of nitrogen or

to achieve an extremely low oxygen content.

One reason that extremely precise chemical control of the metal can be achieved is because peelings

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■ or "layers of Hercynlt-like materials attached to the Fireproof. Slipping of the container would be avoided · Sable -shells tend to, as with the earlier ones Procedure on the G-r-enz surface solid-liquid between PeO in the refractory materials and the metal oxide forming elements such as manganese, in the metal chemical Reäsfcionen trigger. Manganese — hercynite pods can become damaged when heated form so that little manganese is found, but the lost manganese can re-enter the metal when it is heated later. Such conditions lead to indeterminable Manganese content

■ With respect to the control atmosphere in the second and subsequent stages, the chamber may be purged with argon alone, which has a dew point lower owns and preferably lower than minus 5O ⁰ C, which supplies the metal no significant amounts of oxygen from minus 35 ° C or higher. The second stage is preferably carried out so that a sump or a quantity of liquid metal is always present in the container.

Oxygen in the refractories of the chamber or during the second stage of the process during the first commissioning the plant can be controlled by gate melting of an iron-aluminum alloy or an iron alloy with a high carbon content or an «» iron

■ - 30 209815/0351

metal that contains carbon and silicon, all of the Keep oxygen activity very low. A liquid metal of such a composition is poured into the container and forms the first liquid metal sump.

With regard to the design of the container or containers for the system, instead of two or more containers, each set up for decanting, one or more elongated containers can be used which contain partition walls or dams made of refractory materials and thus form the individual steps in the process, or any other system may be used. A suitable design for the system would include a gravel chute having a tap opening or bung in the first stage in its bottom surface. The aluminum is added to the metal stream when the container is filled. The container of the first stage is then drained down into the tank of the second stage, the channel-like shape may have, and is disposed in an induction furnace, wherein the container below the I ¹ IUSSigkeitsoberflache a Spundoffnung be emptied. The metal sump that remains in the first stage vessel and the oxides that are concentrated in it are returned to steelmaking where they can be reused. The second stage container is drained down into a channel-like induction-heated tundish,

209815/0351

between the and the adjoining. Casting mold is gas-tight Extend jacket in which argon gas is contained.

The selection of the refractory materials is of great importance for the second stage and for the subsequent stages. In the first stage the refractory material will be coated with Herzynite, and therefore any useful refractory material is suitable Refractory material in the second stage be very stable, for example made of Al ₂ ⁰ - * or if possible a MgO.AlpO-- ™ Spinel, so that the refractory material itself to the iron, which contains in the order of 0.0005 $ oxygen , cannot give off oxygen, if magnesium oxide is used in the first stage, it will become coated with Herzynit.

The temperature control is ensures in the first stage of particular importance, because the lowest appropriate temperature for the subsequent steps of the process like a maximum distance of oxygen in the first stage. Under some conditions it may be desirable to reheat the metal to a slightly higher temperature in the second stage and also in the subsequent stages, so that the growth in size of the ΑΙρΟ, -particles is supported and good conditions for casting result. Particle growth in the second stage

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also supports the floating of the Al ₂ O, particles in an upper layer in which the particles are concentrated and thus supports the separation of the oayd from the purest metal in the subsequent stages.

The nucleation of the AIpO, in the second and in the subsequent ones Stages can, if desired, by adding pure ΑΙρΟ, -particles (for example minus 200 mesh corundum or fc ■ = «- aluminum oxide) to the metal, if aluminum is added, take place. The aluminum may conveniently be associated or mixed with the seed compound.

Considerable study was required to determine what amount of aluminum was considered to be excess in the second stage Oxygen quantity of the metal that is introduced into this stage should be present. As mentioned above, a Number of considerations to be taken into account here.

The first thing to do is to clarify whether aluminum is in the first Stage has been used as a deoxidizer, if aluminum has been used then it is already a stoichiometric one Contain excess aluminum in the metal as it enters the second stage. Next can be practical Advantages result, for example reduced amounts of oxides that have to be separated in the second stage,

- 33 20981 5/0351

in terms of separating as great an amount of oxides as possible from the metal in the first stage, where it is easiest is to be accomplished, for example, when the launder with which aluminum is used in the first stage. Such Considerations also arise when a vacuum is used or in the first stage a deoxidation is carried out using gas.

One reason not to have an excess amount "| To add aluminum is present ^ if one has an excessive Desires to avoid deoxidation of any existing slag or the refractory material, which only leads to a " damming of aluminum and unnecessary attack on the refractory material. A waste of aluminum can also be avoided if the time in the first Process stage is not dimensioned excessively large because an excessively long period of time for oxygen diffusion from the solid oxides and refractories into the metal. The period of time in the first stage should ' 20 minutes for an effective use of the aluminum and for the longest possible service life of the refractory materials do not exceed. It is also, as mentioned above, desirable to add some aluminum in the second stage, so that if an excess had already been used in the first stage, then the total amount would be unnecessarily large.

■ - ■ 34 209815/0351

Another reason to avoid an excess of aluminum in the first stage is that in the second stage Sufficient oxygen should be available so that there is sufficient oxygen for the nucleation and growth of the AIpOV particles Driving force is available so that the best possible separation of the oxide particles is achieved

if aluminum was not used in the first stage, aluminum must of course be pulled at the beginning of the second stage the amount of which must be at least a stoic-biometric excess of the oxygen present

Even if a stoichiometric excess of aluminum is already present in the metal entering the second stage, some additional aluminum should be added in the second stage _{to aid in the nucleation of Al 2} O by the addition of nucleating agents, if the aluminum defuses into the oxygen-containing liquid iron.

The consideration which is of the greatest importance in determining the stoichiometric excess of aluminum is perhaps the fact that a driving force is maintained in the second stage should be that the deoxidation proceeds to such an extent that the oxygen dissolved in the iron

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becomes very low. This is especially significant when that Material should be poured continuously. The stoichiometric The excess also depends on the temperature. The higher the temperature, the greater the stoichiometric should be Be an excess in order to achieve the lowest possible oxygen content.

Table 1 is attached to show how much aluminum is should be added in the first stage and in the second stage depending on the temperature. As from Table 1 It is apparent that a stoichiometric excess of aluminum, based on the oe, is theoretically necessary to use the total to react when it is in oxygen contained in your metal the second stage is necessary when carrying out the process according to the invention.

Although the better setting of dissolved oxygen in the liquid iron to an even and very low level Level is a very important characteristic for casting purposes is (J.

This process is especially important to the continuous Casting of low carbon steels. This continuous casting of such steels brings namely the Combination of a solidifying or freezing system which tends to concentrate continuously, namely the impurities in the liquid phase to the same extent as that

- 36 209815 / 03Bt

1 Available 20th Temp Table I. % Al -0- % O CONTROL METHOD SECOND STAGE Added % T Al .085 5 " .q .001 Total aluminum .9 0. % (a
Cs.
j Oxygen 10 oc TWO-STAGE ENVIRONMENTAL Remain. -0- Remain. Aluminum 025 Remain. .085 Remain. .001 .4 0. 245 % 065 1700 0.09 -0- 0.028 Lbs / tone 0. 025 0 .085 0 .001 Added .9 0. 170 5 0. 20th
10 1700 0.09 -0- 0.028 Temp 0.5 0. 025 0 .04
.04 0 .0005
.0005 Lbs / tone .1
.5 0.
0. 145 0. 065 1700 FIRST STAGE 0.09 -O ^ 0.028 ⁰ C 0.5 0. 025
025 0 .04 0 .0005 4th .0 0. 205
125 - * 0. 20th 1600
1600 Aluminum Added 0.027
0.027 0.013
0.013 1700 0.5 0.
0. 025 0
0 .026 0
0 .001 3 .12 0. 100 0.
ro
ο 0.
CD 10 1600 Lbs / Ton% 0.033 0.013 1700 0.5
0.5 0. 056 0 .026 0 .001 2 .12 0. 09 co 10 »0. 065 1700 4.4 0.22 Carbon, gaseous -0-
or Vacuum
Deoxidation 0.028 1700 0.5 0. 056 0 .026 0 .001 4th
2 .12 0. 09 CD
αϊ ^ ο.
CD
to
«N 20th 1700 2.9 0.145 do 0.028 1600
1600 1.12 0. 056 0 .025 0 .0005 2 .8th 0. 09 -*O. 10 1700 2.4 0.120 do 0.028 1,600 1.12 0. 040 0 .025 0 .0005 1 .8th 0. 034 0. 065 1600 3.6 0.180
2.0 0.100 do 0.013 1700 1.12 0. 040 0 .025 0 .0005 1 .8th 0. 034 L5 0. 1600 1.5 0.075 do 0.013 1700 0.8 0. 040 0 0 1 034 0. 1600 do 0.013 1700 0.8 0. 0 0 0 0. 1600 0.8 0 1600 0 1600

Freezing progresses, convicting, and a ... pollution, namely, oxygen, to accumulate in the remaining liquid phase, with itself.

Although the maximum segregation only in real balance-weight conditions is possible, for which time is required, but the fact remains that with an oxygen content of the liquid starting material at higher amounts, which correspond to the formation of hercynite, a considerable and harmful enrichment of the oxygen content in the liquid Metal occurs during continuous casting. When carbon * is present and aluminum or another deoxidizer If not used, there can be violent unrest in the steel arise because carbon also accumulates in the remaining liquid metal phase · If, on the other hand, residual aluminum is present, form the hercynite conditions and the segregation of oxygen in the remaining liquid phase has high concentrations of hercynite reaction products, and so can cause severe damage in the continuously poured Product.

has already been mentioned above with reference to FIG. 1, curve 2 the ratio of Hercynite to aluminum and oxygen is responsible for the relatively incomplete removal of Oxygen through aluminum from the liquid steel. Even at

■ '.; ■■■ - 38 -

209815/0351

BATH ORIGINAL

With a substantial excess of residual aluminum, the concentration of oxygen remaining in the steel is high. Since the oxygen solubility in the solid metal is very low, almost all of the oxygen remains after the Herzynitreaktion in the liquid metal and appear as precipitated oxides during cooling and solidification that in the casting process takes place.

Table II shows the significant improvement in deoxidation by aluminum, which is obtained in the control of the environmental influences compared to the known method. It is not only requires less aluminum, but you also get a much lower oxygen content

Table II

EFFECTIVENESS OF ALIMIiTIOM DEOXIMTION FROM STEELS LOW

KOHIENSTOPi ¹ SALARY WITH 0.20 Ί * AVAILABLE OXYGEN suggest Chem "
* 0 Final analysis
$ Al Al. J Cumulative
Lbs./ton gemp.
C Ibs./Ton 0.028
0.020 0.09
0.15 Known procedure: 5.70 0.010
0.005 0.05
0.15 1700 First stage
Additional stage 4.4-0
1.30 5.90 1600 First stage
Additional stage 3.90
2.00

According to the invention, the method;

1700 First stage 4.4 0.028 0.09

Second stage O ₅ Jj 4.9 0.001 0.085

1600 First stage 3.6 0.013 0.027

Second stage 0 ^ 5 4Jj 0.0005 0.04

20981S / 03S1

BAD OftiGiNÄL

_ 39 -

There are at least three types of undesirable conditions in the known methods during casting that include the
Maintain undesirable curve 2 conditions
These are: The metal flows through an atmosphere, aie
Contains oxygen * The metal flows through a tundish,
lined with oxidized refractories, and the metal itself contains particles of solid hercynite when the solidification interface of the steel containing 0.25 # of manganese contains more than about 0.02% of oxygen.

The formation of large and extensive oxide crusts can lead to serious oxide cracks, especially on the surfaces of rolled products. These conditions are in.-the known methods in practice by hitting the blocks and plates to remove the surface skins where these large ones can be found
Often and mainly found, oxide build-up has been eliminated.

Non-metallic inclusions that are very finely distributed
Oxide particles can exist, have various harmful effects
Influences on steel products. Here the invention shows its great progress in practice - in that such inclusions are almost completely eliminated.

It can be assumed that no massive oxides are alike what kind will be forming. It is therefore not a hitting

- 40 2098 15/03 51

of the blocks to remove the surface today is necessary in the practice of the present invention. In addition, the amount of non-metallic inclusions is believed to have decreased on the order of 1/10 or less by weight resulting from other processes, and these inclusions are expected to be well-dispersed particles of almost pure Al ₂ O and extremely smaller Size.

Another advance achieved by the invention is the extension of the life of the refractories Fabrics. There are at least five ways in which the hercynite affects the life of the refractory lining.

The first influence results from the formation of a ceramic alloy with Al ₂ O ,. Hercynite reduces the fire resistance of Al ₂ O, because the ceramic alloy has a lower melting point than the pure one

2 »The dissolution of FeO in Al ₂ O causes a change in volume, which can lead to cracks and, in general, to the destruction of the refractory lining.

3. When oxidized refractories are reduced to a lower degree of oxidation by contact with the liquid metal,

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just one. Deoxidizer has been added, reduced the deoxidizer and metal attack the refractory lining by reducing JeO to Pe will. Pe particles in the refractory mass can subsequently oxidize again, so that expansion cracks and cracks occur,

4. As mentioned above, Hercynitschalen or - Form layers according to the old method on the lining of the container, which can lead to the refractory The lining of the container must be replaced at an early stage. ™

A fifth possible harmful effect on the refractory. Lining results when looking at Figure 1, ■ by liquid metal at "I" on curve 2 is able to produce a Dissolve noticeable amount of aluminum and oxygen from the refractory lining when the temperature is up to curve 1 increases. On the other hand, under the conditions of curves 3 and 4 this solution effect is very small.

One way to counter the fifth effect is by Metal to keep a residual amount of aluminum always dissolved. The mass action of the aluminum atoms acts to dissolve opposite,

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The first four. Effects seem to be to some extent to be present in the first stage of the procedure. But since the conditions of the refractory mass, including temperature, are essentially constant, it is believed that the life of the refractory mass to that of the conventional systems Handling of liquid iron with low carbon content is far superior. The life of the refractory The mass in the second and further process stages is extremely good.

Another reason to maintain a residual concentration of aluminum in the metal is used to combine with nitrogen to make the steel resistant to aging, and another purpose of residual aluminum is its known effect on grain structure and physical properties.

Taking into account all of these factors affected by the W aluminum to oxygen ratio in the first stage, in the second stage and of those relating to the quality of the steel product, there should be a stoichiometric excess of aluminum over the amount available Oxygen for the formation of Al ₂ O ^ must be present at the beginning of the second stage. Normally the oxygen in the metal with a manganese content in the first stage should be $ 0.015>

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or less. In the second stage, aluminum should further be added in an amount of about 0.025 % or more. After the deoxidation reaction in the second stage, the preferred chemical analysis would be: Aluminum 0.02 to 0.09 Ψ * Oxygen less than 0.003 #

The following remarks are intended to help explain the reasons for these requirements, as set out above, if the metal cannot be brought to an oxygen content in the first stage which is well below the. If the hercynite transformation point is and is on or below the control curve, there is a tendency for the nucleation and growth of solid hercynite particles in the metal or the hercynite to penetrate the refractory lining in the second stage and thus the purpose of the method according to the invention is not achieved second step, a stoichiometric excess of aluminum in relation is not maintained on the amount of available oxygen ia the metal, then the driving force may be too low, the aluminum ä oxygen ratio in this and subsequent stages maintain, so that again the intended purpose is not achieved Finally, any oxygen that gets into the second and subsequent stages, for example due to significant amounts of entrained hercynite particles from the first stage, or oxygen from the atmosphere or the refractory lining, can cause the undesirable hercynite damage.

set the ratio in the system again.

209815/0351

- Expectations -

Claims (1)

Expectations 1. A process for the preparation of very pure steels, which are free of oxygen impurities is essentially characterized in that the molten metal is subjected to a Vordeoxydation, so that the dissolved Sauerstoffgebalt of the metal to the value of at most ₁₀ IOG? 5O "-7640 / T ( ⁰ K) +2.84 is lowered, in which $ 0 is dissolved oxygen in percent by weight and T ( ⁰ K) is the temperature in degrees Kelvin, and that a relationship to any aluminum present in the metal is established which is no more than IOg ₁ Q [_ ($ A1) · ($ 0) *] m -79600 / T ( ⁰ K) ♦ 52.15, where in this equation (^ Al) means dissolved aluminum in percent by weight, and that the pre-deoxidized molten metal is separated from the dooxidation products and that a chamber is provided which is lined with a refractory metal that does not release oxygen to the aluminum contained as a deoxidizer in the molten metal, whereupon an inert Ga The atmosphere is introduced into the chamber so that an atmosphere is obtained which is essentially free of undesirable constituents which give off oxygen to the molten metal, with a stoichlometric excess of aluminum being maintained, based on the theoretically required aluminum value which is necessary for the Reaction with the oxygen contained in the metal is required, whereupon the pre-deoxidized metal is transferred into the chamber and the chamber door is kept at a temperature above the melting point. 20981 5/0351 - A 2 - of the metal so that the aluminum is in the metal with the Oxygen of the metal and aluminum oxide react in one so that no more than 0.006 # oxygen remains in the molten metal, whereupon the insoluble material is separated from the deoxidized molten metal. 2. The method according to claim 1, characterized in that the In the pre-oxidation stage of the molten metal Alumlniua is used as an oxidizing agent. 3. The method according to claim 1, characterized in that the Aluminum the metal in the Sammer in the la Metal contained oxygen corresponding stolohlometrieobea Amount for the formation of AIgO, is added and about 0.025 Jf the total weight of the pre-deoxidized metal, which is treated 4 »Method according to claim 1, characterized in that the (| molten metal from those produced by pre-oxidation Products in the chamber is separated by decanting 5 · The method according to claim 1, characterized in »daö bei Preoxidation of the dissolved oxygen content of the metal is reduced to below about 0.058 percent by weight 209 8 1 5/0351 6. The method according to claim 1, characterized in that The liquid metal solidifies in a fora against the action of oxygen is gosobUtst. 7. The method naob claim 1, characterized in that the metal to be treated contains no more than about 0.12 % carbon. 8. The method according to Anspruob 1, characterized in that the the metal to be treated does not contain more than 0.10 # carbon 9. The method according to claim 1, characterized in that Hydrogen as an oxidizing agent to pre-deoxidize the Metal is used. 10. The method according to claim 1, characterized in that Aluminum is entered into the chamber before the red-oxidized molten metal is poured into the chamber. 11. The method according to claim 1, characterized in that dadurob Aluminum on the same side as the pre-deoxidized metal Chamber is registered. 12. The method according to claim 1, characterized in that the ferrous metal to be treated not much than about 0, SiO jC Contains manganese, and that contained in the metal · content of 209815/0351. _{A 4} _ HY golöotea oxygen in the pre-oxidation stage to a maximum about 0.02 percent by weight is reduced 13. The method according to claim 1, characterized in that the deoxidized Ho tall contains about 0.04 percent by weight Re ortaluQiniua « 14. Method according to claim 1, characterized in that «da8 Eoblenstoff with carbon monoxide under reduced pressure: as Deoxidationoaittol in the pre-oxidation of the metal is used.