FI61724C - FRAMEWORK FOR THE FRAMEWORK OF ENCLOSURES - Google Patents

Description

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National Board of Patents and Research (44) Date of publication of NihtivUulpanon I ». - 31.05.82

Patani och ragictaratyraltan Amekan utiagd odi uti.ikitft «i pubik« rad (32) (33) (31) FyydKty Muoikau · —Begird priorltet l6.08.73

27.OU.7U Federal Republic of Germany-Förbunds-republiken lyskland (DE) P 23U1238.6, p 2U20527.U

(71) Fried. Krupp Gesellschaft mit beschränkter Haftung, Altendorfer Strasse 103, D-U3 Essen, Federal Republic of Germany (DE) (72) Kurt Borowski, Essen, Dietrich Radke, Essen, Federal Republic of Germany, Germany (DE), Germany (DE), Germany (DE) Natal, South Africa - South Africa (ZA) (7U) Oy Jalo Ant-Wuorinen Ab (5U) Method for the production of low carbon Ferro-chromium alloy - Förfarande för framställning av en ferrochromlegering med l & g kolhalt

The invention relates to a process for the preparation of a low-carbon Ferro-chromium alloy (FeCr-Affin§) / with a chromium content of more than 60%, in the form of a melt of high-carbon Ferro-chromium (FeCr-carbur6) by oxygen slurry under slag.

Ferro-chromium alloys generally include chromium-iron alloys having a chromium content of at least 60% and more and a carbon content of less than 0.5-10%. According to the carbon content, a distinction is made between so-called Fe-Cr-carbur§ (having a high carbon content) with 2-10% carbon and FeCr-affino (having a low carbon content) with 1-2% carbon. Very soft grades of FeCr with less than 1% carbon are called FeCr-curaffin§.

In the preparation of FeCr-affinS, oxygen slurry has hitherto been worked on using slag, in which case all the following disadvantages must still be taken into account. Methods are also known for the preparation of FeCr affine from FrCr carburo in which the necessary carbon removal takes place in an arc furnace. These methods also have the great disadvantage that the refractory lining of the furnace 2,61724 is subjected to high wear (compared to the method according to the invention).

A process which does not involve the production of a low-carbon Ferro-chromium alloy but the production of a high-chromium steel from an oxygen-annealed melt is known from DT-OS 2 100 115. This process is characterized by further annealing by the addition of solid slag additives. so as to achieve a near-maximum rate of carbon removal relative to the amount of oxygen added. The presence of solid slag throughout the annealing distinguishes this method from other annealing methods known in the art, which always work with running slag.

However, the use of running slag has several drawbacks. The main disadvantages are the relatively high combustion of chromium when using slag, which in practice means the loss of chromium and the fact that due to the high reactivity of the slag the refractory lining of the annealing vessel is exposed to high consumption. All these disadvantages are avoided by using solid slag during the rioting process.

It is an object of the present invention to make the advantages associated with solid slag useful in other methods as well.

This is achieved according to the invention by using the method mentioned at the outset, in which the simultaneous melting of the melt with oxygen is carried out by adding solid slag-forming additives such as chromite and / or magnesite, the composition and amount of additives being melted 1800 ° C and that the temperature of these substances during the annealing process is in each case kept below this melting temperature.

The method according to the invention achieves high temperature ranges, 1800-2000 ° C, mainly 1900-2000 ° C. These high temperatures of the metal melt advantageously mainly affect the removal of carbon and the avoidance of the formation of chromium slag. The control of such a high temperature is also economically advantageous in the new method, since the presence of 3,61724 solid slag is an essential condition for achieving the desired goal. Only under these conditions can a refractory lining of magnesite or chromium magnesite last, which already achieves the good economy of the method.

Some preferred embodiments of the invention are set out in the subclaims.

By adding magnesite and / or chromite as claimed in claims 3-5, it is achieved that carbon removal elements are formed locally at a higher temperature (flash point), while at the same time small particles can immediately convert the liquid SiO 2 slag formed here into a solid slag with a melting point of 1950 ° C or higher. advanced.

When carrying out the process according to the invention, the silicon content of the slag to be spent must be as low as possible, since the silicic acid formed promotes the formation of liquid slag. Thus, FeCr-carburS1 with a correspondingly low silicon content can also be used. When producing a FeCr-carbur6 starting melt, for example in a reduction furnace with a low gap, this has the great advantage that the reduction energy required for a high silicon content can be saved by using the lowest possible silicon content.

However, by using the feature of claim 6, these effects of silicon can be offset by the dosing of the slag additive. For example, higher amounts of silicon require a larger amount of additive, such as magnesite and chromite. By adding these substances at certain intervals when blowing air, the non-metallic components, such as C

The melting point of MgO, SiO 2, etc. rises above 1950 ° C, for example.

4,61724

The method according to the invention will be explained in more detail in connection with the following embodiment.

An oxygen converter lined with magnesite rocks and preheated to 1000 ° C by means of a burner is filled with 2.4 tonnes of flowing FeCr-carbur6 with a composition of 67.5% Cr, 6.7% C, 0.105% S and 0.2% Si, and then oxygen injection is started in a known manner. After ignition, finely ground magnesite and chromite are added to avoid the formation of flowing slag. For example, the composition of the magnesite was as follows:

MgO 91%

CaO 1.3% Al 2 O 3 0.03%

Fe 2 O 3 0.09%

SiO 2 3.1% so2 0.1%

Glow loss 4.2% and composition of chromite added as follows

Cr203 53%

FeO 12% Al 2 O 3 8.6%

CaO 0.4%

MgO 18.5%

SiO2 6.5%

The amount of addition and the time of addition depend in each case on the components of the starting melt which, when oxygen is added, cause the formation of fluid slag, such as silicon. higher than the temperature.

With a constant flow of oxygen, the maximum rate of carbon removal with respect to the amount of oxygen added is achieved within this framework. Thus, the distance between the spray nozzles must also be kept as constant as possible.

When a C content of 1.25% is reached, the temperature of the metal melt settles to about 1910 ° C. In this case, the blowing of oxygen is stopped and the metal is poured slag-free for desulfurization treatment into a magnesite-lined vessel.

Depending on the rate of decarbonisation rate, the final carbon content of the melted melt obtained from the starting melt with a known chromium content can be adjusted to ± 0.3%, without any significant loss of chromium combustion. The desired final carbon content is reached when the abrasion of chromium sharply increases, which is manifested by a sudden decrease in the continuously measured carbon removal rate. At the same time, a certain temperature is stabilized and then the oxygenation is terminated as already described above.

The working method according to the invention has achieved a fire loss of chromium of less than 1% when the initial chromium concentrations are on average 69% and the final carbon contents are 1.2-1.5%.

A further significant advantage of the method according to the invention is that the slag obtained from the annealing does not have to be treated afterwards to reduce the fire loss of chromium, because the chromium contents of the metal are already at the desired level due to low chromium loss and the amount of slag is small.

The solid slag obtained at the end of the blowing step can be fed back to the ore charge of the low shaft furnace. The process according to the invention makes it possible to obtain a solid slag having the best possible properties for use in a low-shaft furnace.

The quenching according to the invention using solid slag can also be considered very advantageous when processing other suitable ferrol alloys, for example ferromanganese.

Claims (7)

1. A process for the preparation of a low-carbon Ferro-chromium alloy (FeCr-affine§) with a chromium content of more than 60% from a high-carbon Ferro-chromium (FeCr-carburS) in the form of a melt by oxygen scavenging under slag, characterized in that oxygenation of the melt is carried out by the addition of solid slag-forming additives such as chromite and / or magnesite, the amount and composition of the additives being metered so that the melting point of all non-metallic substances in the annealing vessel is at least above 1800 ° C and the temperature during the annealing process kept below this melting point. Method according to Claim 1, characterized in that the composition and the amount of these additives are metered in such a way that the melting point of all non-metallic substances in the annealing vessel is in each case above 1950 ° C. Process according to Claim 1 or 2, characterized in that the additives are added in finely divided form. Method according to Claim 3, characterized in that the average particle size of the finely divided additives is less than 3 mm. Method according to one of the preceding claims, characterized in that the oxygen-quenching stream pneumatically feeds the finely divided additive into the vessel. Process according to one of the preceding claims, characterized in that the amount of substance added is made dependent, inter alia, on the silicon content of the high-carbon Ferro-chromium starting melt, namely by adding higher amounts of additives due to the higher amount of silicon. 6 61724 Method according to one of the preceding claims, characterized in that the quenching is interrupted when the loss of chromium sharply increases.