DE2146355A1 - Process for steel finishing - Google Patents

Description

Andrejewski, Honke & Gesthuysen patent attorneys Physicist Dr. Walter Andrejewski Graduate engineer Dr.-Ing. Manfred Honke

_. . Graduate engineer

Attorney's file: 57 554 / Na-th _{Hans Dieter} Gesthuysen

4300 Essen, September 14, 1971 Theaterplatz 3

Patent application

NATIONAL RESEARCH
DEVELOPMENT CORPORATION

Kingsgate House,
66-74, Victoria Street,
London, SW 1 / England

Process for steel finishing.

In all steel finishing processes, regardless of whether they are in the converter, are carried out in a Siemens Martin furnace or in an electric furnace, an essential process step is decarburization by oxidation, further oxidizable elements, in particular silicon, manganese and phosphorus being removed at the same time will. Hydrogen and nitrogen are also removed as a result of the flushing action of the flowing hot melt bath (carbon boil). the Amount of carbon to be removed and the speed

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its removal controls the speed of the process and also the final hydrogen and nitrogen content, so that usually at least 0.20 % carbon is removed from ferrite steels and 0.1-0.25% carbon from austenitic stainless steels. As a result, however, a correspondingly high carbon content is required in the molten bath, regardless of the composition of the charge, ie whether it consists of scrap steel, hot metal or cold pig iron or the aforementioned substances in different proportions. In the case of a batch of 100 % steel scrap, carbon usually has to be added because of the high carbon content required for refining, for example in the form of ground electrodes, anthracite or coke.

The refinement is usually carried out until the steel has the desired carbon content, although this is true It is also known to first refine a batch to a carbon content that is equal to or lower than that value required for stainless steel if the steel inevitably has less carbon than desired after finishing will. In this case, the refined steel is usually decarburized to the required carbon content

The speed at which the carbon is removed varies with the type of oxidation carried out. At the smelting plant (ore boiling), i.e. the addition of iron ore or hammer blow to the weld pool by hand, the reaction proceeds as follows Equation in front of you

C + FeO - ** Fe + CO

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and in the same way with other iron oxides such as Pe ₂ O ,, Fe ^ (K and in the oxidation of silicon and other of the aforementioned elements can be easily removed by smoke cleaners, there are several basic disadvantages, namely:

1. the reaction is slow and consequent is

2. The removal of hydrogen and nitrogen by flushing the "boiling" bath is not guaranteed.

In addition, the process does not generally work with stainless steel Apply steel batches.

The endeavors of the steelmakers to drive decarburization further and above all to accelerate it ultimately led to what is now considered the most successful route to rapid steel refinement is considered, i.e. for oxygen pricking, in which oxygen gas is blown into the weld pool. The effect that oxygen prish is that

1. the entire heat balance of the reaction is exothermic,

2. The reaction is quick and as a result

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3. the removal of hydrogen and nitrogen is guaranteed due to the rinsing effect in the "boiling" molten bath.

This process is also suitable for stainless steel batches. However, as the reaction proceeds, this process will dense brown iron oxide smoke clouds are emitted, so that expensive smoke cleaners have to be installed to remove the Prevent pollution of the environment.

This emission of the brown oxide smoke can be reduced or even avoided if an oxygen-fuel burner is used (with oil or gas) is used, but the rate of carbon removal is generally slower than in oxygen prischarging, the cost increases, in particular by the fuel consumption, the increased oxygen consumption and the cost of the burner cooling water. In addition, this can only be done with carbon steels and low perform alloy steels.

It has already been proposed to use a strongly oxidizing P carrier gas such as pure oxygen or at least 45 vol- # enriched with oxygen? * ρ air metal oxide particles under the Blowing in the surface of the molten bath (US Pat. No. 2,502,259). In comparison to the conventional fresh process, this results in an acceleration of the finishing process. The injection of oxide particles has heretofore been mainly carried out in order to reduce the Lower the bath temperature and thus reduce the wear and tear on the furnace lining. It was also believed that the in

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oxide particles blown into a carrier gas such as oxygen or oxygen-enriched air due to their cooling effect would reduce the emission of brown oxide fumes on the melt. However, this may be the case to a lesser extent, but result from the relatively large amounts of oxygen in the carrier gas inevitably the same conditions as in the Oxygen prish, so that brown iron oxide vapors in such a way A lot arise that large and expensive smoke cleaners are required.

Similar conditions prevail when using a device for blowing in oxide powder, such as iron ore powder by means of a carrier gas from compressed air (cf. GB-PS 970 990). Such a device was, however, developed in order to be able to introduce iron oxide into the melt in such an amount that it makes up about 20 % of the total weight of the melt. With such a device, the metal oxide powder is therefore blown in by the ton, which inevitably requires such large amounts of carrier gas, i.e. compressed air, that an amount of oxygen is blown into the melt that practically causes the same difficulties as with oxygen pricking, i.e. the emission is denser brown iron oxide fumes. Although it has already been proposed to use an inert carrier gas instead of compressed air, the large amount of inert gas results in an undesirable, disadvantageous cooling of the melt.

The object of the invention is to provide a method for refining steel to create by means of which carbon and other oxidizable

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Items can be removed as soon as possible to get a to achieve maximum economy and performance without however, as with oxygen pricking, an excessive emission dense brown iron oxide fumes or excessive cooling the melt takes place, while at the same time a reduction in the hydrogen and nitrogen proportions can be achieved by degassing target.

) The method according to the invention for steel finishing is identified essentially by the fact that for the purpose of faster removal of the carbon with flushing of nitrogen and Hydrogen from a molten metal into the molten bath by means of oxide particles of a metal desired in the finished steel be blown in such an amount of a carrier gas that the oxygen content of the carrier gas is insufficient to to allow dense brown iron oxide vapors to form, and also the amount of carrier gas does not cause excessive cooling of the Melt pool leads.

It has been found that if the amount of oxygen delivered by the carrier gas is not greater, preferably even "is less than the amount of carbon monoxide resulting from the reaction of carbon with the metal oxide, the process is practically smokeless.

The amount of carrier gas is preferably 0.2 m / kg of oxide particles. If circumstances permit, even an amount of carrier gas of 0.1-0.06 nr / kg metal oxide can be used.

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Essentially, the invention is based on the position that carbon and other oxidizable elements can be obtained from the molten metal by means of a metal oxide powder which carries out the main decarburization. In fact, the fact that a carrier gas is used to blow the oxide particles into the molten bath only in such a composition and quantity that it does not itself act as an oxidizing agent prevents the creation of an oxidizing atmosphere over the molten bath, which in turn is the cause of the dense browns Iron oxide fumes is. Naturally, the greater the proportion of oxygen in the carrier gas, the lower the probability that a smokeless process can be carried out for given amounts of carrier gas. The maximum amounts of oxygen that are still acceptable for a certain injection amount in the unit of time can be determined by simple experiments for each special furnace. Air, carbon dioxide or any gas whose oxidation potential is at most equal to that of air enriched with oxygen to an extent of about ^ O - 55% can therefore be used as the carrier gas. By limiting the amount of carrier gas per kg of oxide particles, if the carrier gas contains free or bound oxygen or consists of an inert gas, there is no excessive cooling of the melt, which could lead to its solidification, which must be avoided at all costs.

Surprisingly, it was therefore found that if you keep the amount of carrier gas close to the minimum amount of what for blowing in the oxide is required, a satisfactory decarburization and degassing, i.e. also removal of Hydrogen and nitrogen, is achieved without becoming dense

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Brown iron oxide vapors arise, even if the carrier gas has an oxidation potential which corresponds to that of oxygen-enriched air, which contains about 50-55 % pure oxygen.

By blowing in the oxide by means of a carrier gas according to the method according to the invention, the carbon becomes sufficient quickly removed so that the hydrogen and nitrogen can also be removed from the bath. As a special advantage of this kind the carbon removal results in the process either runs smokeless or at most a very small amount of brown iron oxide vapor is produced.

The invention has therefore recognized for the first time that the amount of carbon monoxide formed during the oxidation of carbon can be used to prevent the formation of dense brown iron oxide vapors during a refining process, its speed of decarburization with oxygen freshening is comparable.

During rapid refining, is thrown, a fine spray of nearly pure iron regardless of the manner of its implementation W from the surface of the molten bath, the oxidation of the dense brown iron oxide vapor are formed lHßt. This fine drizzle respectively. Fog is only present directly above the molten pool, since at a greater distance there is a compaction to form larger particles which, if oxidized, would only have an outer layer and would most likely fall back into the slag layer. If therefore

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the carrier gas has less than about 30-35 vol- # of oxygen and the amount of the carrier gas, e.g., air, is preferably substantially not greater than that for blowing the metal oxide particles is required, i.e. below about 0.2 nr / kg oxide, then the amount of that produced by the reaction is Carbon monoxide is greater than the amount of blown oxygen and a thick layer of carbon monoxide forms over the Melt bath, the non-oxidizing nature of which is not disturbed by the relatively small amounts of pure oxygen, which escapes from the carrier gas on the bath surface. As a result, prevail in the area of the furnace atmosphere in which The fine spray of pure iron exists, non-oxidizing conditions exist, making the process practical runs completely without the previously usual dense brown iron oxide vapors.

In the case of the carrier gas used for the method according to the invention it is therefore a gas which essentially only serves as a means of transport for the metal oxide to be introduced, while this metal oxide is the actual agent for converting carbon in the melt to carbon monoxide. That However, to a small extent, carrier gas can also take part in the oxidation by introducing some oxygen into the weld pool be involved as long as the values already mentioned with regard to the oxidation potential and the quantitative ratio between Carrier gas and metal oxide are observed. Gases with a higher content of oxygen result in even the smallest ratio Carrier gas / oxide unavoidable brown iron oxide vapors.

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Further advantages of the method according to the invention are, in particular when using air as the carrier gas, that;

1. the process is relatively inexpensive;

2. Bring the molten bath to a boil at a relatively low bath temperature and am Cooking can be kept or by means of

"External heating is intensified and at

any desired temperature can be continued so that

J3. particularly favorable conditions for the

Oxidation and removal of any elements can be created;

4. any desired speed at the

Carbon removal in consecutive Operations can be achieved;

5. some of the oxide in the slag above that

Bath can be blown in to form cinder blocks, which not only helps To remove carbon from the weld pool, it also increases the metal yield, and

6. Not having to worry about serious damage to the furnace lining by blowing in often with oxygen prish or with

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Use of oxygen fuel burners, and that no water is required, as is the case for cooling such burners.

The equipment for dispensing and injecting the oxide is inexpensive to install and operate. So this can Equipment simply consist of a funnel, the outlet of which communicates with the line for the carrier gas, wherein Arrangements for controlling the powder throughput in the outlet can be provided and the line in connection with a lance stands in order to be able to blow the powder into the weld pool. The powder addition is preferably carried out by means of arrangements controlled, which enable a pulsating feed into the carrier gas line, for which purpose e.g. a paddle wheel can be provided in the bottom of a funnel, the compartments formed between each two blades an effective Measure the amount of oxide to the carrier gas line. Preferably two funnels attached to a central spindle provided, one of which is connected to the carrier gas line. When this funnel is empty it just goes off the pipe finished, swiveled the whole thing around the spindle to connect the other full funnel to the carrier gas line after which the empty hopper is refilled while the second is emptied.

The process also allows the original carbon content of the molten bath to be changed. Therefore, if the carbon content of the batch from which the weld pool was made is greater than that required in the refined steel,

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the blowing is continued until the carbon by oxidation · is so far removed that the result is a value equal to the value in the finished steel, within this time also hydrogen and nitrogen and other undesirable elements such as silicon, manganese and phosphorus removed respectively. oxidized became. On the other hand, if the batch has a lower carbon content than that used to make the desired one refined steel is required is only blown in for so long until so much carbon has been removed that hydrogen and nitrogen are properly removed and others unwanted elements are oxidized, whereupon the refined steel is then converted to the desired in a manner known per se Carbon content is re-carbonized.

This method can be used with all of the aforementioned types of steel. Depending on the specific type of steel desired, the appropriate oxides such as iron oxide, nickel oxide, chromium oxide, molybdenum oxide, copper oxide, cobalt oxide and tungsten oxide are added. For example, for carbon steels, an oxide is used in the mold hammer blow, iron ore or iron oxide dust added by dust cleaners, while for corrosion-resistant steels oxides of nickel, chromium, molybdenum, copper, cobalt or tungsten or any combination of these, possibly with an iron oxide, to set the oxidation reactions in motion and at the same time for at least some of the metallic components of the steels to form a cheaper raw material.

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"Oxide particles" in this context are intended to mean all grain sizes be understood from relatively coarse grain with a diameter of about 5.75 mm up to dust-fine grain. The grain size must of course not be so coarse that it cannot be blown in through the lance; but she may also not be too fine so as not to be carried away by the carrier gas through the weld pool and simply into the Oven atmosphere to be blown. The following grain size limits have proven to be particularly suitable:

Maximum grain less than 6.35 mm; At most about 30 % below 0.0104 mm.

To avoid the slag forming part of the refining process / To facilitate and accelerate metal reactions, slag formers such as lime powder, limestone or fluorspar are made with the Blown metal oxide or the metal oxides, either continuously with the same or during one or more selected periods during the course of the procedure.

The method according to the invention is described below with the aid of some are only explained as reference Durohführungbeispiele.

Example II carbon steel

An electric arc furnace with a capacity of k to was filled with steel scrap, ^{heated to a temperature of 155O 0} C and a slag in well-known catfish on the

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Melt pool formed. The weld pool was then ready for that Oxidation and powdered hammer blow in the following grain size was added:

Grit 2.41 Weight% (mm) 1.685 3.17 - 1.395 6.1 2.41 - 1.193 13.4 1.685 - 0.99 3.5 1.395 - 0.863 6.1 1.193 - 0.0687 6.1 0.99 - 0.508 4.5 0.863 - 0.356 6.1 0.687 - 0.356 11.8 0.508 - 11.8 under 30.6

From this hammer punch powder, a Lance immersed in the molten bath, using compressed air as the carrier gas, was blown in at 22.7 kg / min for 2 minutes. At Carrier gas was consumed at normal temperature and pressure of 2.83 nr air P.

An examination of the molten bath immediately before and immediately after blowing in resulted in the following table, column 1 being the Weight percentages before and column 2 the weight percentages after blowing:

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C. ο, Mn 0, Si 0, S. O, P. O, Ni 0, Cr 0, N ₂ H ₂
ppm 1 0.39 ο, 32 0, 02 0, 033 O, 015 O, 15th 0, 09 0, 012 5.3 2 0.24 25th 00 032 13th 15th 09 oo8 2.4

This steel should have a carbon content of 0.24 % , so that no recarburization was necessary. The molten bath was then cleared of slag, deoxidized, a reduction slag formed in a manner known per se and then drained off.

As the table shows, the carbon was removed so quickly that the content of nitrogen and hydrogen was noticeably reduced became. The process proceeded with no visible emission of brown fumes.

Example II; Carbon steel

The process was initially carried out as described in Example I and the molten bath was again oxidized by blowing in hammer powder with a grain size of -5 BSS using compressed air as the carrier gas, but in this case 45.36 kg / min were blown in for 3.5 minutes, for what purpose a total amount of compressed air of 10.62 m at normal temperature and pressure was required. An examination of the weld pool immediately before and after the injection resulted in the following

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Values given in the table, column 1 again showing the percentages by weight before and column 2 indicates the percent by weight after blowing.

ο, C. 0 Mn ο., S. ο, P. _N 2 H ₂
ppm 1 ο, 40 0 , 29 0, 034 ο, 004 O, Oil 3.0 2 24 , 23 025 002 ο, 010 2.7

In this case the steel should have 0.30 % C so that it was re-carbonized by adding 127 kg of pig iron, which was known to contain 4% C.

Example III: Austhenitic Corrosion Resistant Steel

The procedure described in Example 1 was oxidized again in an electric arc furnace with a batch of 1/2 to w performed and the molten bath by injecting hammer powder having a particle size of -5 BSS, wherein compressed air was used as carrier gas. The powder was blown in an amount of 9 kg / min for 3.5 minutes using a total amount of 2.97 nr air (at normal temperature and pressure). There was no visible brown smoke. A review of the weld pool immediately before and immediately after the oxidation

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showed the following composition in percent by weight, column 1 again showing the values and column 2 the values after blowing in.

1 C. 0 Si 0, S. 0, P. 8th Ni Cr 0, N ₂ 1 0 ,1 0 , 52 0, 022 0, 041 7th , 66 16.1 0, 053 2 , 05 , 42 019 050 , 48 9.1 020

The table clearly shows the reduction in the oxidizable elements due to the oxidation. The chromium content of the steel was reduced to such an extent that it was too low for the desired final analysis of the steel, so that reducing agents such as Perro-silicon were added to the slag, as a result of which chromium was released from the slag back into the bath. After checking, it was found that the chromium content had increased to 14 % . The melt was then freed from slag and a reducing slag was formed, whereupon the melt was finally drained. Palis for the desired type of steel, the other alloy elements have to be present in larger quantities, one could also add suitable aggregates of such elements after the reduction slag had been formed .

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Example IVt Austhenitic Corrosion Resistant Steel

The same procedure as in Example I was carried out again, However, nickel oxide powder in a grain size similar to that of the grain size of the hammer blow according to Example I for the oxidation was used and again compressed air was used as the carrier gas and the powder for 2 minutes in an amount of 4.5 kg / min was blown. In this case, the compressed air was 0.85 no used up and there was no visible brown smoke. A review of the melt immediately before and after oxidation resulted in the following composition in percent by weight, with column 1 the values before and column 2 the values after Blowing in.

0, C. Si 0, S. 0, P. Mn Cr Ni 49 Mon 73 1 0, 26th 0.28 0, 005 0, 054 0.76 10.8 5, 06 0, 77 2 20th 0.10 001 057 0.58 8.16 9, 0,

During the oxidation, the increase in nickel content indicated that 95 % of the nickel was recovered from the nickel oxide. Chromium and other alloying elements were modified according to the desired steel composition in the same way as in Example III »

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Example V: Austhenitic Corrosion Resistant Steel

Here, too, the same procedure was carried out as in Example I, a mixture of 50 % chromite sand (ground chrome ore) and 50 % hammer blow in the same grain size as in Example I being used. The molten bath was checked immediately before the oxidation and the result was a carbon content of 0.75 % and a chromium content of 6.18 %. After the oxidation, the melt contained 0.65% carbon and 5.80 & chrome, so a value that was well within the range required for the desired steel chromium content of 5 to 6%. This shows that the chromite sand used was an inexpensive source of chromium for the melt and effectively compensated for the reduction in the chromium content caused by oxidation of the chromium, so that the addition of expensive chromium in the reduction stage was no longer necessary.

Example VI: carbon steel

An electric arc furnace was charged with 37.95 tons of steel scrap and heated to a temperature of 1500 ° C., with in a slag was formed in a manner known per se. The bath was then ready for oxidation and abrasion by one Iron ore sintering equipment passed through a 6.35 mm mesh screen was placed in the bath for 3 minutes with a throughput of 169 kg / min by means of a into the weld pool into the immersed lance. Compressed air was used as the carrier gas in an amount of 12.74 nr under a pressure of 3.5 kg / cm

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used. The oxidation took place with no visible brown fumes,

The molten bath was checked immediately before and immediately after it was blown in and contained in percent by weight:

C. 0 Mn Si 0, S. 0, P. 0 Cr 0 N ₂ 415 0 , 33 0, OJ 0, 047 0, 021 0 , 21 0 , 015 O, 265 , 20 0.02 045 OI5 , 18 , 007

The bath was then purged, deoxidized, in a known manner Way, a reducing slag formed and finally drained.

Example VII:

An open hearth furnace with a capacity of 240 tons was charged with 145 tons of scrap and 95 tons of hot metal from a blast furnace. After the end of the melting process, the metal contained 0.70 % carbon, this carbon content falling to 0.45 % 48 minutes after the melting process had ended. In this state, 1422.5 kg of iron oxide powder was obtained by means of 39.64 in air

at a pressure of 3.5 kg / cm by means of a into the weld pool into the immersed lance.

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The blown iron oxide had the following grain size:

Particle size 1,590 Wt% (mm) 0.060 3,390 - 0.025 o, 7 1.590 - 0.018 15.7 0.060 - 0.015 24.5 0.025 - 0.0105 3.8 0.018 - 0.0075 11.6 0.015 - 10.5 0.0105- 24.7

Samples taken from the weld pool at different times during refining gave the following results:

Sample ^ C $ C. Decrease / h.

At the end of melting 0.70

; 0.31

18 min after melting 0.45 51.5 "" "" Start of blowing

\ 0.60

57.5 "" "" End of blow 60 "" "" 0.25 117 "" "" 0.08

The steel was then drained in the usual manner and made into ingots poured.

The oxidation occurred with no visible brown steam over the weld pool.

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Example VIII and IX:

Examples VIII and IX were carried out to the limit for the oxygen content of the carrier gas to prevent the formation of brown iron oxide vapors must be adhered to.

^ In each example, powdered hammer was blown into a ™ Resistance furnace with a capacity of 204 kg under Use of compressed air blown in as the carrier gas. The air was then enriched with oxygen until the first time brown oxide vapor was observed, the proportion of oxygen is set out in the following table in the carrier gas at this point in time:

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From the table above it can be seen that with a throughput of hammer blows between 4.54 and 9.07 kg / min and one Ratio of about 1: 1 between carrier gas and oxide causes smoke formation began when the oxygen content in the carrier gas approached about 30%.

Example Xt carbon steel

A 204 kg resistance furnace was used with Steel scrap charged and at a temperature of 1540 C heated, in a manner known per se on the molten bath a slag was formed. The weld pool was then ready for oxidation and powdered hammer blow roughly that The same grain size as in the previous examples was immersed in the bath for 1 minute by means of a Lance blown in at an amount of 4.54 kg / min, with carbon dioxide was used as the carrier gas. The total amount of carbon dioxide consumed was converted to normal temperature and pressure 1.42 m.

The molten bath was tested immediately before and immediately after the blowing process and resulted in the following composition Weight percent:

1, C. Mn Si 0, S. P. 035 1 0, 03 0.65 0.01 0, 024 0, 024 2 85 0.23 0.01 036 O,

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where column 1 gives the values before and column 2 the values after the blowing process.

This reaction gave the steel the required carbon content, so that no recooling was necessary.

The weld pool was then made free of flakes, deoxidized, a reducing slag is formed in a manner known per se and finally drained.

The speed of decarburization was completely sufficient to also noticeably reduce the nitrogen and hydrogen content, while the process proceeded with no brown vapors showing over the weld pool.

Of course, the invention is not limited to those described above The information contained in the examples is limited, but can be modified in a number of ways.

Claims ι

209813/1139

Claims (6)

Andrejewski, Honke & Gesthuysen, patent attorneys, 4300 Essen, Theaterplatz 3 claims. 1. A method for steel finishing, characterized in that for the purpose of faster removal of the carbon with flushing of nitrogen and hydrogen from a molten metal into the molten bath Oxide particles of a metal desired in Pertigstahl are blown in by means of such an amount of a carrier gas that the oxygen content of the carrier gas is insufficient, to create dense brown iron oxide vapors, w and, moreover, the amount of carrier gas does not lead to excessive cooling of the melt pool. 2. The method according to claim 1, characterized in that an amount of carrier gas of 0.06-0.2 m is used for 1 kg of oxide particles will. 3. The method according to claim 1 or 2, characterized in that the oxidation potential of the carrier gas is at most equal which is about 30 - 35 # oxygenated air. 4. The method according to claim 3 * characterized in that as Carrier gas atmospheric air is used. 5. The method according to claim 3 # characterized in that as Carrier gas carbon dioxide is used. 6. The method according to claim 3 # characterized in that as Carrier gas an inert gas is used. Patent attorney, 209813/1131