DE1803377A1 - Process for reducing molten steel gear drive means, particularly for mechanical toys - Google Patents

Description

PATENT LAWYERS H. LEINWEBER dipling. H. ZIMMERMANN PotUchatk account: tank account: Telephone Tal.-Adr. MOnchenHMS Dresden tank AO. ftHtadM · (MII) M1f »Utapat MMkImm Manchen 2, Marlenplatz, account no. 927W Our reference: Lw / XIII / C s M (iMi »ii2, Roseatai7, zA _U f _g .

(Kuitermann-Pa »* ag ·)

^{d # n} October 16, 1968

NIPPON KOKAN KABUSHIKI KAISHA, Tokyo / Japan Process for reducing molten steel

The invention relates to a method of making steel of greater purity. In this procedure, Calcium or a calcium alloy to the molten one Steel added, whereby the productivity of the calcium is effectively improved. This makes some non-metallic Inclusions are removed from the molten steel and this is also desulfurized and degassed.

So far, Mn, Si, Al, Ti and Cr have been largely used for ilinguction in the ladle during tapping. The amount of oxygen in a molten steel is general higher than an equilibrium with metallic Mn, Si or Al in the melt. It was therefore difficult to produce a steel with only a few inclusions; in order to keep the amount of inclusions as low as possible, was previously a lot of reducing agent added, since the

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liquid steel present reduction products and the erosion of visually fusible materials and through Oxide inclusions formed by slag accounted for a considerable proportion. One with Si, Al, Ti or the like Reduced steel can contain disadvantageous macro-inclusions, so that defects occur in the steel even if when the amount of inclusions is negligibly small.

Many processes for reducing steel with calcium are already known which solve these problems tried. It has been known for 50 years that alloyed calcium is a very powerful reducing and desulfurizing agent and that it can be used to refine steel. Goldschmidt published one Work showing the use of Ca-Si to remove oxygen and sulfur from molten liquid Steel with the formation of molten slag is suitable, which is then easily removed from the molten slag Steel can be severed. Many other experiments in the laboratory or in the

'· Technical scale. The enormous influence of calcium on "! the shape and amount of inclusions in steel is in many

j publications. In contrast, Sims et al deny the effect of calcium by comparing a reduction with Ca-Si and one with Si alone. One

Number of authors is of the opinion that calcium does not t
is effective.

ORlQIWAL IMSPiCTED

One of the reasons for such inconsistent results due to the fact that calcium unstable and its yield is low in steel, because the melting point of calcium is 85O ⁰ C and the boiling point of 1440 C. Calcium therefore easily evaporates when it is added to the surface of the steel bath. Various attempts have therefore been made to obtain better results. For example, by using an alloy based on Fe-Ca, the formation of oxide inclusions is reduced; however, the efficiency is low in view of the large amount of calcium (over 0.2 $) required as (a)) as shown in Table 1. Furthermore, the amount of inclusions remaining after the addition is large. The analysis of the inclusions as well as the reproducibility of the results is also difficult.

B0

ORIGINAL INSPSCTED

Table 1: Analysis of oxide inclusions

Oxide inclusions, wt #

No. Al-Fe-Ca sum

Addition of the alloy FeO MnO SiOp AlpO * of the oxides

I -. none 0.0120 0.0027 0.0056 0.0075 0.0178

0.5 0.0051 0.0005 0.0036 0.0030 0.0122

II - none 0.0045 0.0013 0.0120 0.0074 0.0252

1, Ό 0.0053 0.0022 0.0090- 0.0037 0.0202

III - none 0.0055 0.0023 0.0097 0.0075 .0.0250

1.5 0.051 0.0009 0.0055 0.0068 0.0183

IV 0.02 none 0.004 0.003 0.001 0.017 0.025

1.0 0.004 0.001 0.0008 0.015 0.0208

V 0.05 none 0.004 0.0042 0.0002 0.018 0.0262

1.0 0.006 0.0005 0.0007 0.014 0.0212

VI 0.10 none 0.004 0.001 0.0015 0.014 0.0205

1.0 0.004 0.0008 0.0009 0.010 0.0157

VII 0.16 none 0.003 <Η> 0.0014 0.016 0.0204

1.0 0.005 Lr 0.0001 0.006 0.0111

On a technical scale, the calcium alloy generally used in an amount of 5.2 kg / ton. This is both in terms of manufacturing cost as well an undesirably large amount to the desired steel composition.

Investigations were also carried out with regard to the reduction with calcium by adding calcium or a calcium alloy undertaken on the surface of the molten steel. However, since a large amount of calcium evaporates, no effect can be achieved until a large amount of calcium has been added.

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I »ι- U. '

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Vacuum melting process, vacuum degassing process and electroslag processes are used to avoid the To decrease the amount of inclusions in the steel. However, this requires cumbersome devices and experience, making mass production difficult.

The disadvantages of using calcium can be summarized as follows:

(1) The fertility of calcium in the molten liquid Steel is quite low if you have calcium or a calcium alloy used for reduction purposes. This low yield is all the more important, the larger the size Amount of molten metal is.

(2). Small amounts of calcium added are therefore not effective.

(3) The effect after adding a large amount of calcium is remarkable. (The decrease in oxidation inclusions is small and the remaining amount is large).

(4) Calcium is generally added to steel in alloy form and the maximum allowable amount is a matter of course limited depending on the desired steel composition. The addition of a large amount of calcium results therefore does not produce a noticeable effect.

(5) Since the reaction of calcium on addition is unknown there is no specific procedure for primary reduction or timing of calcium addition.

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ORIGINAL INSPECTED

(6) Because of the evaporation of calcium on the bath surface and the violent reaction due to the low melting and boiling points can reduce the amount evaporated or the reaction at the time of addition cannot be regulated.

(7) So there is no effective reduction method

to reduce the amount of inclusions or the oxygen content by adding a small amount of calcium.

(8) An improvement in steel properties by calcium is not to be expected because of the low yield of calcium in the molten steel.

Mn, Si or Al can be used for reduction without calcium. If those with metallic Mn, Si or Al in equilibrium in the molten bath the total amount of oxygen is quite small, however, the total concentration of oxygen in the steel is (sum of free oxygen and oxide inclusions, as well as the oxygen found by oxygen analysis) is quite high. Because inclusions are not removed from the molten bath it is difficult to keep total oxygen below $ 0.004 regardless of the amount of reductant. Due to various circumstances in the reduction, the inclusions remaining in the steel become unstable and form macro-inclusions which adversely affect steel properties.

The invention provides a method for reducing molten steel, in which calcium or a calcium-containing material in the lower part of a

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liquid bath can be added, this bath beforehand
was subjected to a reduction.

The invention will now be further explained with reference to the following description and the drawings. In the drawings mean

1 shows an embodiment of the invention;

Fig. 2 is a graph showing the decrease in the! Oxygen content in the steel according to the method according to the invention; ' ^!

FIGS. 3 and 4 graphical representations of the removal of \ total oxygen content depending on the j addition of the calcium during the Si reduction; ₍

FIGS. 5 and 6 are graphs similar to FIG

3 and 4, which were obtained in a different series of experiments (aluminum reduction). j

According to FIG. 1, a calcium alloy is produced by a
Hollow cylinder or a tube 3 in the lower part of the melting \

liquid bath 5 added. The calcium alloy is used in

Tank 1 is stored and its flow is controlled by adjusting

Valve 2 is regulated while gas is being blown into the cylinder. The cylinder or tube 3 is off

the entrance to the bath 5 is provided with a fireproof cladding I 4. The calcium rises rapidly to the surface, where- removed or prevented by inclusions in the bath ■;

ι or the occurrence of macro inclusions is reduced.

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However, it must be already a prior reduction to reduce \ to the value of the dissolved oxygen in the steel below the predetermined distance. This reduction must be carried out before or during the calcium addition.

Since the calcium has a melting point of 85O ⁰ C and a boiling point of 144O ⁰ C, it liquefies or vaporizes immediately as it rises to the surface when it is introduced into the lower part of the molten pool; the calcium molten in the bath reacts with free oxygen and oxide inclusions. The inclusions reacted with the added calcium rise rapidly to the surface due to their changed composition and are carried away, so that the total amount of oxygen present in the steel is reliably reduced.

By adjusting the valve 2 at the bottom of the tank 1, as shown in Fig. 1, the supplied Control the amount of calcium and thus the reaction in the molten bath.

Instead of the single cylinder shown in FIG. 1, several hollow cylinders made of refractory material can also be used at the same time.

In this way, an excellent utilization of the calcium or the calcium alloy in the bath (in some cases over

In the following table 2 the calcium amounts remaining in the steel are given in percent, which with the addition of 0, M> calcium at the surface of 50 kg

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ORKälNAL IMSPiCTED

a molten bath according to the known method and by adding the same amount of calcium according to the invention Process in the steel remained;

Table 2: Calcium analysis in steel, #

Known procedure 0.0015 # Method according to the invention 0

It follows from this that the amount of calcium to be added is small compared to the known method. (In the known method, more than 0.2 # calcium were used. In the method according to the invention, however, is an addition of $ 0.05 is perfectly adequate). The larger the amount of molten steel, the more the contact time of calcium in the liquid or gaseous state becomes longer. In some cases it is static Pressure of the molten bath greater than the vapor pressure of calcium, whereby the invention Procedure becomes even more effective.

The calcium or the calcium alloy can be used in the process according to the invention as a powder or granulate or in the form of small chunks. Except for calcium, a calcium alloy or a calcium compound Magnesium, sodium or potassium or their alloys and compounds can be added.

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The calcium or the calcium alloy are usually contained in a molten steel Added pouring ladle; it can also be added in an open oven, converter, electric oven or mold take place.

Inert gases such as argon or nitrogen can be used when adding the calcium or calcium alloy will. In the case of adding nitrogen, the formation of nitrides can be effectively achieved. Other additions to the Formation of nitrides can also be added together with the calcium or the calcium alloy. In this Case, the partial pressure of oxygen in the molten liquid in contact with gaseous nitrogen Bath lowered very effectively as a result of absorption by calcium and nitrogen.

As a result of the exothermic reaction that occurs when calcium or a calcium alloy is added the reducing agent can be added without a Temperature decrease occurs.

The molten steel rises to the surface of the bath as the calcium evaporates and rises well rested so that a uniform bathroom composition is created.

As can be seen from Table 2, the content of the calcium remaining in the steel is lower, so that the Calcium improves the properties of the steel considerably.

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ORIGINAL INSPECTED

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Lots of inclusions in the molten bath which up to now could not rise to the bath surface migrate with the addition of calcium according to the invention Move to the bath surface quickly and under stable conditions. The percentage decrease in the in- ' Conclusion is great this way and the final grade is low and stable.

If you give 0.05 $ calcium to 50 kg of one beforehand Manganese, Si or Al reduced molten steel can keep the oxygen concentration below $ 0.002. In the known method, however, it is difficult to keep the oxygen content below $ 0.005. The composition the inclusions remaining in the steel are of such a nature that the formation of disadvantageous macro-inclusions is prevented. Therefore, the size of inclusions in a steel ingot is extremely small.

Any desired fuel composition can be used in accordance with the invention can be achieved in a simple manner, since the amount of calcium added is small (in general, the amount of amount of calcium to be added determined according to the desired composition; this lies with the invention Amount in this area from the start).

Compared to the known vacuum melting process, the vacuum degassing process or the electron slagging process the device to be used according to the invention is extremely simple and does not require any experienced Operating personnel and is therefore suitable for mass production.

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The invention will now be explained in more detail with reference to FIGS.

In Fig. 2 curves 1, 2, 3 and 4 are shown;

0 means the oxygen content in the molten steel before reduction. Curve 1 corresponds to the course of the concentration of the total amount of oxygen when the reduction is carried out in the normal way at time T ₁ ; Curve 2 shows the course of the concentration of free oxygen under the same conditions. According to curve 3 · calcium was added at time T ^ and the total oxygen content corresponds to curve 3, while the course of the concentration of free oxygen under the same conditions is shown in curve 4. The difference between curves 1 and 2 and curves 3 and 4 corresponds to the oxygen content present as an inclusion in the molten steel.

From Fig. 3 and 4 the concentration profile of the total amount of oxygen in a sample of

1 kg electrolytic iron was melted in a high frequency furnace and held at 1600 ⁰ C, · wherein 0.0596 Calcium after reduction with 0.3? * Silicon was added. According to Fig. 3, the total oxygen content reaches a constant value of about $ 0.015 1 minute after adding the calcium. Under the same conditions, but without the addition of calcium, the oxygen content also reaches the value of $ 0.015 6 to 8 minutes after the addition of the Si (cf. FIG. 4). With these

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In experiments, metallic Si was present in an amount of $ 0.10 and the amount of oxygen in equilibrium was $ 0.015. The free oxygen content during the Si reduction decreases approximately in equilibrium with the increase in the metallic Si content found that most of the oxygen content of $ 0.065 one minute after the addition of Si consists of SiOr ₁ , the primary reduction product. This migrates rapidly to the surface of the molten bath and is removed by the addition of calcium The addition of calcium is very small and corresponds to a different composition than before the addition,

In Fig. 4 an embodiment is shown, in which the calcium only after the primary reduction product SiOp has risen to the surface and the removal of which was admitted. In this example it was found that the total oxygen content was constant of about $ 0.015 in about 6 minutes. In the case of Si reduction, there is therefore an addition of calcium useful during the reduction.

From Fig. 5 it can be seen that the total oxygen content is $ 0.0016 and less if calcium is added became. Under the same conditions, but without the addition of calcium, the oxygen content is 6 to 8 minutes about $ 0.004 after the aluminum addition, but does not drop below this value (see FIG. 6). With these

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ORlG!. \ 'A

The amount of metallic aluminum added was 0.14 ? * and the amount of oxygen in equilibrium with aluminum was about $ 0.0001. In the case of the reduction with aluminum, the fine particles formed in the primary reduction do not rise to the bath surface even if the. Amount of free oxygen decreases. The total oxygen content therefore remains much higher than the free oxygen content and does not decrease. The total oxygen content of $ 0.046 one minute after the addition of aluminum is mainly due to the primary reduction product A ^ O ^. This rises quickly to the bath surface and can be removed there when calcium is added. The total amount of oxygen here almost corresponds to the amount of free oxygen.

Fig. 6 gives an example of the addition of calcium to the molten steel, with Al 0 in a substantial amount Measure remains as the primary product. It can be seen from this figure that the amount of oxygen decreases rapidly and the total amount of oxygen approximates the value of free oxygen.

In the examples according to FIGS. 5 and 6, the size is the inclusions in steel after the addition of calcium extremely low and the composition of the inclusions is different from before the encore. AIpO * generally tends to Droplet formation; however, this phenomenon does not occur with inclusions to which calcium has been added. From this it follows that the effective addition of calcium the formation of macro-inclusions, especially with regard to on AIpO ,, prevented.

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ORIGINAL INSPECTED

The use of a calcium alloy leads to similar results if this alloy has an equivalent one Has calcium content.

The results described above were not previously known. It follows that a calcium addition to the molten bath after or during the reduction to lower the free oxygen content below the desired volume and to a rapid and severe reduction in the content of primary Reduction products leads.

In Figs. 3 to 6 are the results of laboratory tests reproduced with 1 kg of molten steel; but one achieves in the execution on an industrial scale same or similar results. The process is very effective because it escapes into the atmosphere Calcium amount by the type ': r addition extremely kept low and the contact time of the calcium in the liquid state or in vapor form by adding in the lower Part of the bathroom is extended. So the larger the amount of molten steel, the longer it is Contact time. In some cases the static pressure of the molten bath is greater than the vapor pressure of the Calcium, which makes the process even more effective. This has been demonstrated in particular through experiments on an industrial scale confirmed.

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The amount of reducing agent with which the content of free oxygen is kept below 0 * 004 $, in the case of metallic aluminum is about 0.QÖO4 $ and in the case of metallic titanium according to Chipman et al, about £ 2 $. One can therefore check the total oxygen content press down to below $ 0.004 when adding calcium or a calcium alloy to molten steel, which was previously reduced by adding over $ 0.0004 metallic aluminum or over $ 0.02 metallic titanium became.

: In this case the composition changes

of inclusions so that the formation of adverse! Macro inclusions in the steel is prevented.

In the above-described method of adding calcium or a calcium alloy, not only use the procedure described above, but also blowing and adding through a hole at the bottom of the jar.

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Claims (1)

- 17 patent claims j Ί. Method of reducing molten Steel, characterized in that calcium or a calcium alloy in the lower part of a bath of molten Steel by means of an appropriate device with gas being blown in after or during the reduction of the bathroom admits. 2. The method according to claim 1, characterized in that the primary reduction with aluminum, silicon or titanium. 5. The method according to claims 1 or 2, characterized characterized by adding 0.05% by weight of calcium, based on the weight of the steel. 4. The method according to any one of the preceding claims, characterized in that one simultaneously introduces nitrogen or argon with the calcium or calcium-containing material. 5. The method according to any one of the preceding claims, characterized in that the calcium or the calcium alloy is added through a refractory hollow cylinder. - 18 - 9 ο 9 ^ 2 σ / (Tff τα 6. The method according to any one of the preceding claims, characterized in that the reduction executes in a ladle into which the molten steel has been poured. 7. The method according to any one of the preceding claims, characterized in that the primary Carries out reduction so that the free oxygen content falls below a desired value. 9Uaö2ü / üö7Ü