GB2057509A - Steel making in top-blown converter - Google Patents
Steel making in top-blown converter Download PDFInfo
- Publication number
- GB2057509A GB2057509A GB8027215A GB8027215A GB2057509A GB 2057509 A GB2057509 A GB 2057509A GB 8027215 A GB8027215 A GB 8027215A GB 8027215 A GB8027215 A GB 8027215A GB 2057509 A GB2057509 A GB 2057509A
- Authority
- GB
- United Kingdom
- Prior art keywords
- steel
- molten steel
- noble gas
- nitrogen
- oxygen
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
- C21C5/28—Manufacture of steel in the converter
- C21C5/30—Regulating or controlling the blowing
- C21C5/32—Blowing from above
Abstract
In conventional processes of making steel by blowing with oxygen in an LD vessel, the dissolved oxygen that is produced in the steel can increase the requirement for addition of alloying metals such as manganese. In order to reduce such requirement, after blowing with oxygen, the steel is blown with noble gas or nitrogen to create turbulence within the main body of the molten steel. A sample of the steel is then taken to determine whether or not the steel meets a predetermined specification. If, say, its carbon content is too high, the steps of blowing with oxygen and then nitrogen and/or noble gas are repeated as necessary. For producing steel with a low nitrogen content, noble gas rather than nitrogen is used. Moreover, each reblow with oxygen may be preceded by displacing, with noble, air which enters the steel making vessel during sampling.
Description
SPECIFICATION
Steel making
This invention relates to a steel making or refining process in which molten steel is blown with oxygen. In particular, it is concerned with a top-blown converter process in which molten steel is blown by a jet or jets of oxygen.
Current methods in which steel is refined by being blown from above with an oxygencontaining gas includes the LD process (also known as the BOP, BOS or BOF process). In this process, the oxygen-containing gas (preferably substantially pure oxygen) may, for instance, be introduced through a lance extending downwardly from the top of the converter and it is caused to penetrate the surface of the melt.
Blowing oxygen onto molten steel in a converter has the effect of reducing the content of carbon in the steel and makes possible production of steel requiring a low nitrogen content.
Top blowing of oxygen does, however, suffer from certain drawbacks. Typically, at the end of blowing there may be a dissolved oxygen concentration in the steel of 800 ppm (by weight).
It is frequently desirable to remove some or all of this oxygen depending on the end use of the steel.
The oxygen blowing also oxidisss some of the iron in the steel and also some of the manganese present in the hot metal charged to the vessel. The oxides of iron and manganese are held in the slag above the metal. Since most steels include manganese in their specification, manganese (in the form of ferromanganese) is added after the steel making process.
In addition, deoxidisers such as aluminium and/or silicon are typically added to the molten steel. Such additions may be made while the molten steel is in the converter or other steelmaking vessel or after the molten steel has been poured into a ladle. Such additions are however relatively expensive and they result in the molten steel being reduced in temperature. In addition, alumina and/or silica are formed and if left in the
steel when solid will adversely affect its quality.
Attempts to remove oxygen from the steel by treating the steel in a vacuum degasser have given rise to considerable operating difficulties.
Another solution which has been proposed is to blow the steel in the ladle with argon. In this proposal the argon is introduced from the bottom of the ladle. This proposal has not found favour in practice as it leads to rapid heat loss, and consequently it is necessary to superheat the steel in the steel making vessel so as to compensate for this heat loss. In addition, precautions need to be taken to prevent carry-over of slag from the steel making vessel to the ladle since such slag tends to attack the refractory lining of the ladle and cause undesirable elements such as phosphorus to reenter the steel.
In recent years, a new oxygen-steel making process in which oxygen is injected into the bottom of the melt has been adopted by some steel makers. This process is known as the 'OBM' or'O--BOP' process. In plants which operate this process it is usual to blow nitrogen or argon through the steel from the bottom of the steel making vessel just before tapping the steel from the vessel. This step reduces the partial pressure of carbon monoxide in the steel in the converter.
Consequently the dissolved oxygen reacts with carbon in the molten steel to form carbon monoxide. The carbon monoxide diffuses into bubbles of argon or nitrogen in the steel and is carried out of the steel in such bubbles. The steel produced in the vessel has consequently a very low dissolved oxygen concentration. This results in a number of advantages being attained in comparison with top blowing processes: a greater yield of steel: longer refractory life as a result of lower concentrations of iron oxide in the slag; and a reduced requirement for aluminium and silicon additions and a concommitant increase in the cleanliness of the steel and an increase in manganese content.Accordingly, operators of top-blown steel converters have attempted to inject argon or nitrogen into the bottom of their converters so as to purge at least some of the dissolved oxygen from the molten steel before it is poured from the converter into a ladle and thereby obtain the advantages of the OBM or O--BOP process. This has necessitated fitting the vessel or converter with tuyeres or porous refractory members at its bottom so that nitrogen or a noble gas such as argon can be injected into the molten steel from the bottom. This practice may give rise to safety problems, and is also, we believe, unnecessarily cumbersome.
The present invention aims at providing a process for steel making or refining in an LD vessel which includes the step of removing dissolved oxygen from the steel therein, but which avoids the need to instal tuyeres or porous refractory members in or near the base of the vessel, and which thereby provides an elegant and at least partial solution to the long-outstanding problem of dealing with dissolved oxygen in steel produced in an LD vessel.
According to the present invention, there is provided a method of refining or making steel in an LD vessel, wherein after the step of blowing (or reblowing) the steel (in molten state) from above its surface with oxygen or a gas mixture containing oxygen, the molten steel is blown from above its surface with nitrogen and/or noble gas, said nitrogen and/or noble gas penetrating beneath the surface of the molten steel and creating turbulence within the main body of molten steel and then taking a sample of the molten steel so as to determine whether the steel meets a predetermined specification and may be poured into a ladle or other vessel or needs further blowing with oxygen or a gas mixture containing oxygen.
The sample may be taken by means of an automatic sampling device with the-vessel in an upright position. Many if not most LD steel making vessels are not equipped with such automatic sampling devices. It is usual to sample the steel with the vessel is in a horizontal position.
Accordingly, with the vessel in such position, a sampling spoon (or like device) is typically inserted into the vessel and a sample taken. This procedure inevitably allows air to flow into the steel-making vessel.
If it is found that the carbon content of the steel is not above specification and its temperature not below a predetermined minimum, then it is not generally necessary to blow the molten steel again with oxygen and the steel may be poured into a ladle or other collecting device. If, on the other hand, the carbon content is too high or the temperature is too low it will be necessary to reblow with oxygen, sometimes more than one reblow may be necessary. After each such reblow it is desirable to blow with noble gas, or nitrogen, or mixture thereof, from above, in such a manner that the surface of the molten steel is penetrated by the gas and turbulence created within the main body of the molten steel.
If it is desired to produce a steel having a low nitrogen content, such reblow may give rise to difficulties as the oxygen will tend, we believe, to entrain nitrogen from the air that enters the vessel during sampling and consequently a steel
containing an undesirably high concentration of
nitrogen may be produced. In order to overcome this problem, or at least to reduce its seriousness,
our UK published patent application 2 041 412
provides a method of refining or making steel by the LD process, wherein, after the steps of blowing the steel (in molten state) of oxygen and then sampling the molten metal, but before the step of
reblowing with oxygen, a noble gas heavier than
air is introduced into the steel containing vessel in the space above the molten steel so as to displace air from the said space. Typically, the noble gas is argon.Subsequent reblowing with oxygen will therefore not give rise to so great a pick-up of nitrogen as it would have, had the noble gas not been introduced. After reblowing, the steel is resampled and if its analysis is satisfactory, it is poured from the steel making vessel into a ladle or other receptacle. If the analysis is unsatisfactory in that the steel still contains too much carbon or is at too low a temperature, then the step of introducing argon into the space above the molten metal may be repeated and a further reblow with oxygen conducted. It is a feature of the process according to our published patent application No.
2 041 412 that no argon or other nitrogen-free gas is mixed with the oxygen used for blowing and reblowing the molten metal.
It is desirable to employ an analogous 'noble gas purging step' in the method according to this invention.
Accordingly, there is provided a method of making or refining molten metal in a LD vessel, wherein:
(i) the steel in molten state is blown from above its surface with oxygen;
(ii) the molten steel is blown from above its surface with noble gas, the noble gas penetrating beneath the surface of the molten steel and creating turbulence within the main body of the molten steel;
(iii) a sample of the molten steel is taken by means which allow the ingress of air into the space in the LD vessel above the molten steel; and
(iv) either (a) the molten steel is poured into a ladle or other receptacle, or (b) a noble gas heavier than air is introduced into the said space so as to displace air therefrom, and then steps (i) to (iv) are repeated.
If after sampling it is found that the molten steel meets a predetermined specification it may be poured into a ladle or other receptacle. If it is found, for example, that the steel has too high a carbon content or if its temperature is too- low it is desirably reblown with oxygen. Although the original blowing with oxygen may typically last for from 10 to 1 5 minutes, any subsequent reblowing with oxygen may typically be conducted for about one minute. The step of displacing air from the space above the molten steel may typically be conducted for a period of from 0.5 to 2 minutes.
(This step shall be referred to hereinafter as the 'noble gas purging step', whereas the aforesaid step of blowing the molten steel with noble gas or nitrogen shall be referred to as the 'noble gas blowing step').
The noble gas is preferably argon, though at least one other noble gas such as krypton, neon or xenon may be used instead of or in addition to the argon. Nitrogen is a desirable alternative to argon if high levels of dissolved nitrogen can be tolerated in the steel. (If nitrogen can be tolerated it will not generally be necessary to perform a 'noble-gas purging step' before any reblowing with oxygen.)
Such use of nitrogen also makes possible the formation of steel whose specification requires a higher-than-normal nitrogen concentration.
To perform a noble gas blowing step, it is generally preferred to introduce the nitrogen or noble gas (or mixture thereof) into the steelmaking vessel through at least one lance which is also used, in a different part of the steel making process, to blow oxygen or gas mixture containing oxygen at the surface of the molten metal.
If desired, for the noble gas blowing step, the supply of nitrogen or noble gas (or mixture thereof) may be pulsed. This helps to create turbulence throughout the molten metal. A suitable valve may be employed to effect pulsing.
If desired, the lance or lances through which the nitrogen and/or noble gas are blown at the surface of the molten metal may be oscillated. The oscillation may have a vector component in the horizontal direction and in the vertical direction as well, or may be entirely in a horizontal plane or a vertical plane.
The or each lance may have an outlet nozzle with a single orifice or with more than one orifice.
The nitrogen or noble gas, or mixture thereof, is preferably directed at the surface of the molten metal in one or more jets. The or each jet preferably has such a velocity that it creates a gas pocket extending below the surface of the molten metal. This will typically create turbulence throughout the molten steel down to the bottom of the steel making vessel. Such turbulence stirs the molten metal, preventing thermal and chemical stratification from occurring. The consequential advantage is that when a sample is taken from the molten steel it will be substantially typical of the composition of the steel irrespective of the level in the steel making vessel at which it is taken.
The nitrogen or noble gas, or mixture thereof, will tend to leave the gas pocket in the form of large bubbles which rise to the surface of the melt owing to their natural buoyancy. This gas will therefore pass into the head-space of the steelmaking vessel and purge oxygen from such headspace. Thus, the partial pressure of carbon monoxide in the steel and the head-space is reduced. There will thus be a consequential tendency for dissolved oxygen in the molten steel to react with carbon to form carbon monoxide.
The so-formed carbon monoxide will pass into the head-space. Thus, the concentration of dissolved oxygen in the molten steel is reduced. Moreover, the stirring of the molten steel produced by the nitrogen or noble gas, or mixture thereof, will prevent the phenomenon of oxygen coming out of solution being confined to a top layer of the molten steel.
The or each lance from which the noble gas or nitrogen, or mixture thereof, is blown at the surface of the molten metal is typically positioned from 1 to 2 metres above the surface of the bath.
Typically, the nitrogen or noble gas, or mixture thereof, is blown at the surface of the melt for a period of time from half a minute to two minutes.
Typically, from 3 to 5 cubic metres at (NTP) per tonne of noble gas or nitrogen, or mixture thereof, may be employed. Thus, for example, a 135 tonne heat may be blown with argon at 540 cubic metres (NTP) per minute for one minute from a single lance whose tip is from 1 to 2 metres above the surface of the melt. The height of the lance and the rate at which the argon is blown at the surface may be varied so as to alter its penetration into the molten steel in accordance with the level of dissolved oxygen in the steel.
Typically, if a steel containing 0.03% by weight of carbon after normal oxygen blowing is blown with argon a reduction in dissolved oxygen concentration from about 800 ppm to 600 ppm and a reduction in the concentration of carbon to from 0.03% to about 0.01% by weight would be achieved. This carbon content would be suitable for some end users of the steel, but for others, additional carbon may need to be added. The reduced dissolved oxygen content of the metal will produce a reduced requirement for deoxidant. For example, the removal of 200 ppm of dissolved oxygen will reduce the requirement for aluminium by approximately 0.2 kg per tonne of steel. This will also lead to a cleaner steel as less alumina will be produced.In addition, the reduction in the dissolved oxygen concentration in the steel will lead to a reduction in the concentration of oxygen in the slag, and hence a lower iron content. This will give a less corrosive slag thus increasing the life of the refractory lining of the steel making vessel. In addition, manganese recovery will also, we believe, be increased thereby reducing the quantity of ferro-manganese that needs to be added.
The process according to UK published patent application No. 2 041 412 is an alternative to blowing the molten steel with an argon/oxygen mixture. The process according to this invention may also be performed with advantage when the steel is blown with an argon/oxygen mixture rather than with pure oxygen.
The same equipment used to perform the noble gas blowing step may be used to perform the noble gas purging step.
A typical procedure for performing the method according to the invention is now described by way of example.
With a steel-making vessel in its charging position a charge of steel scrap is charged into the vessel through its mouth. Typically, it takes from 1 to 2 minutes to charge the vessel with scrap. The steel-making vessel is then returned to an upright position so as to rock the scrap into its bottom.
When this has been done, the vessel is returned to a tilted position and is charged with molten iron typically at a temperature 14500 C. Charging the vessel with molten iron typically takes about 3 minutes. The vessel is then returned to an upright position. A single lance through which oxygen is blown at the surface of the steel is then lowered into a blowing position from 1 to 2 metres above the surface. Blowing is started.
Once ignition has taken place slag forming materials may, if desired, be added. All aluminium, ferromanganese etc. additions are made after all oxygen blowing has been completed, usually, but not always to the steel in the ladle.
The oxygen blow agitates the surface of the metal and the metal comes into contact with the oxygen. The oxygen reacts with such constituents as carbon, silicon, phosphorus and manganese in the molten metal. During the blow the lance may be lowered progressively closer to the bath or in one step from a high to a low position closer to the bath. During blowing with oxygen a slag forms above the metal. As a result of the chemical reactions taking place between the slag and the molten metal and as a result of the gas passing through the slag, there is frothing of the slag and-it rises inside the steel-making vessel. Other consequences of the reaction are generation of iron oxide fume and formation of carbon monoxide which passes out of the vessel with the waste gas.
Once the maximum rate of removal of impurities from the steel has been achieved and this rate is beginning to fall, more iron is oxidised creating more fume and iron oxide pick up in the slag. In addition, the reaction between the slag and the molten metal tends to become less pronounced and the frothing of the slag begins to subside. When it is estimated the desired carbon level has been reached, the oxygen flow is shut off and argon is blown at the molten metal for a chosen time at a chosen rate through the same lance as is used to blow oxygen at the steel. When the oxygen is shut off, slag/metal reactions cease and the slag returns to a compact layer. It is thus possible to supply the argon at a rate and velocity such that the slag layer will be penetrated and the molten steel adequately stirred. The blowing with argon may typically continue for up to 2 minutes.
Blowing with argon reduces the dissolved oxygen concentration of the molten steel with the consequences that have been discussed hereinbefore. An additional consequence is that the equilibrium between oxides in the slag and dissolved oxygen in the steel is disturbed and consequently there will be a reversion of some of these oxides to metal. This thus results in reversion of manganese oxide and iron oxide to manganese and iron respectively.
Once blowing with argon is stopped, the lance may be retracted and the making vessel tilted into a horizontal position for sampling.
Claims (12)
1. A method of refining or making steel in an LD vessel, wherein after the step of blowing (or reblowing) the steel (in molten state) from above its surface with oxygen or a gas mixture containing oxygen, the molten steel is blown from above its surface with nitrogen and/or noble gas, said nitrogen and/or noble gas penetrating beneath the surface of the molten metal and creating turbulence within the main body of molten steel, and then taking a sample of the molten steel so as to determine whether the steel meets a predetermined specification and may be poured into a ladle or other vessel or needs further blowing with oxygen or a gas mixture containing oxygen.
2. A method of refining or making steel in an
LD vessel, wherein:
(i) the steel in molten state is blown from above its surface with oxygen;
(ii) the molten steel is blown from above its surface with noble gas, the noble gas penetrating beneath the surface of the molten steel and creating turbulence within the main body of the molten steel;
(iii) a sample of the molten steel is taken by means which allow the ingress of air into the space in the LD vessel above the molten steel; and
(iv) either (a) the molten steel is poured into a ladle or other receptacle, or (b) noble gas heavier than air is introduced into the said space so as to displace air therefrom, and then steps (i) to (iv) are repeated.
3. A method as claimed in claim 2, in which the step of displacing air from the space above the molten steel is conducted for 0.5 to 2 minutes.
4. A method as claimed in any one of the preceding claims, in which the noble gas is argon.
5. A method as claimed in any one of the preceding claims, in which in blowing the molten steel, the supply of nitrogen or noble gas (or mixture thereof) is pulsed.
6. A method as claimed in any of the preceding claims, in which in blowing the molten steel, the nitrogen or noble gas (or mixture thereof) is introduced into the steel-making vessel through at least one lance.
7. A method as claimed in claim 6, in which the lances are oscillated during the blowing of the molten steel with nitrogen or noble gas (or mixture thereof).
8. A method as claimed in any one of the preceding claims, in which in blowing the molten steel the nitrogen or noble gas (or mixture thereof) is directed at the surface of the molten steel in one or more jets.
9. A method as claimed in claim 8, in which the or each met preferably has such velocity that it creates a gas pocket extending below the surface of the molten steel.
10. A method as claimed in any one of the preceding claims, in which in blowing the molten steel, the nitrogen or noble gas (or mixture thereof) stirs the molten steel and thereby prevents thermal stratification from occurring.
11. A method as claimed in any one of the preceding claims, in which the or each blowing with nitrogen or noble gas (or mixture thereof) lasts for 0.5 to 2 minutes.
12. A method or refining or making steel in an
LD vessel, substantially as herein described.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8027215A GB2057509A (en) | 1979-08-30 | 1980-08-21 | Steel making in top-blown converter |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB7930000 | 1979-08-30 | ||
| GB8027215A GB2057509A (en) | 1979-08-30 | 1980-08-21 | Steel making in top-blown converter |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB2057509A true GB2057509A (en) | 1981-04-01 |
Family
ID=26272712
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8027215A Withdrawn GB2057509A (en) | 1979-08-30 | 1980-08-21 | Steel making in top-blown converter |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2057509A (en) |
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102220448A (en) * | 2011-06-02 | 2011-10-19 | 首钢总公司 | Method for smelting uniform end-point molten steel composition with converter |
| CN102732665A (en) * | 2012-03-29 | 2012-10-17 | 鞍钢股份有限公司 | Method for adding nitrogen in molten steel in last phase of steel making |
| CN103160637A (en) * | 2013-02-26 | 2013-06-19 | 首钢总公司 | Low-phosphorous steel smelting method of mixed blowing of oxygen and nitrogen of top blowing oxygen lance of converter |
| CN103451350A (en) * | 2013-08-13 | 2013-12-18 | 攀钢集团攀枝花钢铁研究院有限公司 | Method for controlling nitrogen content in molten steel |
| CN104774992A (en) * | 2015-05-04 | 2015-07-15 | 北京佰能电气技术有限公司 | Control device for converter steelmaking nitrogen-oxygen combined blowing |
| CN104928432A (en) * | 2015-06-11 | 2015-09-23 | 江苏永钢集团有限公司 | Method for removing phosphorus in converter through blowing nitrogen |
| CN115044736A (en) * | 2022-06-16 | 2022-09-13 | 莱芜钢铁集团银山型钢有限公司 | Converter steel tapping hole with argon blowing function and whole-process slag stopping method |
-
1980
- 1980-08-21 GB GB8027215A patent/GB2057509A/en not_active Withdrawn
Cited By (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102220448A (en) * | 2011-06-02 | 2011-10-19 | 首钢总公司 | Method for smelting uniform end-point molten steel composition with converter |
| CN102732665A (en) * | 2012-03-29 | 2012-10-17 | 鞍钢股份有限公司 | Method for adding nitrogen in molten steel in last phase of steel making |
| CN103160637A (en) * | 2013-02-26 | 2013-06-19 | 首钢总公司 | Low-phosphorous steel smelting method of mixed blowing of oxygen and nitrogen of top blowing oxygen lance of converter |
| CN103451350A (en) * | 2013-08-13 | 2013-12-18 | 攀钢集团攀枝花钢铁研究院有限公司 | Method for controlling nitrogen content in molten steel |
| CN103451350B (en) * | 2013-08-13 | 2015-04-29 | 攀钢集团攀枝花钢铁研究院有限公司 | Method for controlling nitrogen content in molten steel |
| CN104774992A (en) * | 2015-05-04 | 2015-07-15 | 北京佰能电气技术有限公司 | Control device for converter steelmaking nitrogen-oxygen combined blowing |
| CN104928432A (en) * | 2015-06-11 | 2015-09-23 | 江苏永钢集团有限公司 | Method for removing phosphorus in converter through blowing nitrogen |
| CN115044736A (en) * | 2022-06-16 | 2022-09-13 | 莱芜钢铁集团银山型钢有限公司 | Converter steel tapping hole with argon blowing function and whole-process slag stopping method |
| CN115044736B (en) * | 2022-06-16 | 2023-06-09 | 莱芜钢铁集团银山型钢有限公司 | Converter tapping hole with argon blowing function and whole-course slag blocking method |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |