CN103088187B - Method of producing steel - Google Patents

Method of producing steel Download PDF

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Publication number
CN103088187B
CN103088187B CN201210270203.3A CN201210270203A CN103088187B CN 103088187 B CN103088187 B CN 103088187B CN 201210270203 A CN201210270203 A CN 201210270203A CN 103088187 B CN103088187 B CN 103088187B
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molten steel
slag
steel
mgo
ladle
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CN201210270203.3A
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CN103088187A (en
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冈本真吾
井上畅
荒牧则亲
锦织正规
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JFE Engineering Corp
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NKK Corp
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    • 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
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04—Removing impurities by adding a treating agent
    • C21C7/06—Deoxidising, e.g. killing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/10—Supplying or treating molten metal
    • B22D11/108—Feeding additives, powders, or the like
    • 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
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • 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
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04—Removing impurities by adding a treating agent
    • 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
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/10—Handling in a vacuum

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • Treatment Of Steel In Its Molten State (AREA)
  • Continuous Casting (AREA)

Abstract

The present invention provides a method of producing steel, wherein cast sheet which has the advantages of small inclusion matter and high cleanness can be manufactured through high-speed casting. Steel is directly discharged from a converter to a ladle in a nondeoxidization state. After steel discharge, metal Al or Al dross is added into slag in the ladle for reducing low-grade oxide in the slag. Furthermore block-shaped composition which comprises hydroxide and carbon oxide, namely MgO source, is added into the slag, so that the MgO concentration in the slag reaches 6-15mass%. Then, in a vacuum degassing device, reaction between carbon and dissolved oxygen in the molten steel is caused for reducing the concentration of the dissolved oxygen to less than 0.050mass%. After the concentration of the dissolved oxygen is less than 0.050mass%, metal Al is used for performing oxygen removal on the molten steel, and Mn is not added into the molten steel without oxygen removal. When Mn concentration adjustment to the molten steel is required, Mn metal is added after Al oxygen removal for performing Mn concentration adjustment, and then a continuous casting machine is used for casting the molten steel to steel blanks.

Description

The manufacture method of steel
Technical field
The present invention relates to the manufacture method of the High Clean Steel Melts that oxide based non-metallic inclusion is few.
Background technology
With regard to Al killed steel, when from converter tapping or after tapping, add metal A l as reductor, remove the oxygen in the molten steel raising due to the oxidation refining in converter (Decarburising and refining), then, utilize continuous casting machine casting to cause as the raw-material slab of rolling.By adding this metal A l, in molten steel, generate the Al as deoxidation products 2o 3, this Al 2o 3can not be from molten steel emersion, separation and while remaining in slab, steel work can produce by Al 2o 3the crackle causing and surface imperfection.
Therefore, in order to reduce the Al remaining in steel 2o 3adopted with the following method: add metal A l or Al scum silica frost to accommodating in the ladle of the molten steel after tapping in the past, the lower oxyde (easily-reductive oxide) (FeO, MnO) of the slag that exists on hot molten steel face of reduction and reduce the lower oxyde in slag, then carries out Al deoxidation (for example, with reference to patent documentation 1).In addition, Al scum silica frost is for the oxide compound of aluminium and the mixture of nitride that generate, that contain the metal A l of the 30 quality %～approximately 40 quality % that have an appointment of the stage in fusing again using recycling as the aluminum metal of the uses such as tank, material of construction or car aluminum wheel for beverage.
In addition, in order to reduce deoxidation products, the kind of restriction reductor, the technology of order of addition have also been proposed.For example, in patent documentation 2, the order that has proposed to increase progressively by deoxidizing capacity is added the method for reductor, particularly, has proposed the method for adding by the order of Mn → Si → Al.According to patent documentation 2, add reductor by the order increasing progressively by deoxidizing capacity, the cohesion of deoxidation products is carried out, and forms the deoxidation products being made up of multiple compounds, thereby promotes emersion, separation from molten steel.But, in the method, there is the problem that forms a large amount of MnO and make the MnO concentration in slag increase.MnO is lower oxyde, reacts with the Al in the strong molten steel of the deoxidizing capacity adding afterwards, forms constantly Al in molten steel 2o 3thereby, be difficult to obtain the steel that cleanliness factor is high.
With respect to this, following method is proposed in patent documentation 3: first so that the residual mode of dissolved oxygen regulates addition to add Al scum silica frost, then add successively Mn, Si, finally add metal A l, thereby carry out deoxidation.In this method of deoxidation, although can reduce the growing amount of MnO, just before utilizing Al to carry out deoxidation, add Mn in this point, same with patent documentation 2, existence can not suppress the problem of the generation of MnO completely.
In addition, also proposed not use metal A l and use Ti, the Ca technology (for example, with reference to patent documentation 4) as main reductor, this is that Ti, than Al costliness, cannot be applied to common steel grade using the technology as object containing Ti steel.
On the other hand, as for making the innoxious technology of deoxidation products, in patent documentation 5 and patent documentation 6, proposed to add the technology in MgO source in the slag on steel bath face.According to patent documentation 5 and patent documentation 6, adding behind MgO source, when slag and molten steel are stirred, the Al of deoxidation products 2o 3react with MgO source and form MgO-Al 2o 3spinel, MgO-Al 2o 3cohesion, the associativity of spinel are little, can make deoxidation products remain on fine level, thereby can carry out innoxious.
In addition, as the technology of adding MgO source in slag or molten steel, following technology is proposed: after the refining in RH vacuum degasser starts in patent documentation 7, immediately MgO source is added in the molten steel in vacuum tank, between molten steel in ladle and slag, form MgO enriched layer, suppress reacting of molten steel and slag by this MgO enriched layer.In addition, following technology is disclosed in patent documentation 8: in ladle, add slag properties-correcting agent and the slag in ladle is carried out to modification, then, in the slag in ladle, adding MgO source, slag in ladle is solidified, thereby the slag suppressing in ladle flow out to tundish from ladle.
Patent documentation 1: Japanese kokai publication hei 5-230516 communique
Patent documentation 2: Japanese kokai publication sho 54-94422 communique
Patent documentation 3: TOHKEMY 2009-120930 communique
Patent documentation 4: TOHKEMY 2000-144330 communique
Patent documentation 5: TOHKEMY 2004-169147 communique
Patent documentation 6: TOHKEMY 2003-171714 communique
Patent documentation 7: Japanese kokai publication hei 6-116623 communique
Patent documentation 8: TOHKEMY 2008-240136 communique
In recent years, from the viewpoint of boosting productivity, the casting speed of continuous caster realizes high speed, even in the past only by the fully high steel work of cleanliness that adopts the slag method of modifying proposing in patent documentation 1 to obtain, also can produce the defect being caused by oxide based non-metallic inclusion (following, to be only designated as " inclusion ").Particularly, with regard to the slab in the time that the ladle that is equivalent to many stoves continuous casting (being called " sequence casting ") exchanges, observe the defect being caused by inclusion.
This be due to, realize in the operation of high speed in casting speed, inclusion in the molten steel of the slag in ladle and near existence this slag (CaO in deoxidation products and converter slag or add CaO in the unslaked lime in ladle to as slag former cohesion occurs and form) is rolled into and is injected into from ladle at molten steel the eddy current forming in ladle in latter stage of tundish, the frequency that flows out to tundish increases, in addition, the residence time of molten steel in tundish also shortens relatively, therefore, there is no emersion, the frequency being directly injected under the state separating in mold increases.It should be noted that, if increase the injection rate (time per unit) that is injected into the molten steel of tundish from ladle, in ladle, produce the time advance of eddy current., start to produce eddy current from many moment of the residual molten steel amount in ladle.
For the cleanliness that makes molten steel improves, effectively reduce the lower oxyde in slag, but in patent documentation 2 and patent documentation 3, as mentioned above, generated MnO, thereby not talkative its effect is sufficient.
In addition, in order not make the slag in ladle be rolled in eddy current, effectively make the slag in ladle solidify, the technology to adding MgO source in slag proposing in patent documentation 5～8 is effective, but, when excessive interpolation, although slag occurs to solidify, but can damage the receptivity of the deoxidation products of slag, make on the contrary the situation of cleanliness variation.In addition, solidify in order to carry out slag, need to make the MgO source of adding react with slag, in citing document 5 ~ 8, use MgO grog (clinker) is as MgO source, and need to carry out the processing that MgO grog to interpolation and slag stir etc.But, at molten steel not deoxidation in the situation that, as conventionally carried out when blasting gas in molten steel slag stirred, for the equilibrium relationship of the oxygen concn in approaching and molten steel, the concentration of the lower oxyde such as FeO, MnO in slag raises, therefore, thus the problem that exists molten steel after deoxidation to make cleanliness factor reduce because slag reoxidizes.In addition, the emersion region that is blown into the gas in molten steel is local, and therefore, there are the following problems: gas blasts speed when insufficient, slag cannot be stirred, thereby remain the reduction of lower oxyde or the curing inadequate region of slag.
Summary of the invention
The present invention In view of the foregoing completes, its object is to provide a kind of manufacture method of High Clean Steel Melts, even if it does not stir etc., also can make the slag in ladle fully solidify and can not be rolled into the eddy current of formation in latter stage that is injected into tundish at molten steel from ladle, and, compared with the conventional method, the cleanliness of molten steel is further improved, even under high-speed casting, also can obtain the good slab of cleanliness that inclusion is few.
As follows for the purport of the present invention addressing the above problem.
[1] manufacture method for steel, is characterized in that,
Have:
By the molten steel that molten iron is carried out to Decarburising and refining and obtain under the state of not deoxidation directly from converter to the operation of tapping in ladle;
After tapping, in the slag existing on the molten steel in ladle, add metal A l or Al scum silica frost, then add MgO source, in the lower oxyde in reduction slag, by the operation of MgO concentration adjustment to the 6 ~ 15 quality % in slag;
Then, in vacuum degasser, make the carbon in molten steel under reduced pressure react and dissolved oxygen concentration is reduced to below 0.050 quality % with the dissolved oxygen in molten steel, after dissolved oxygen concentration in molten steel reaches below 0.050 quality %, make the operation of deoxidation of molten steel to adding metal A l in the molten steel under decompression; And
Then utilize continuous caster molten steel to be cast as to the operation of steel billet,
Wherein, above-mentioned MgO contains oxyhydroxide and oxycarbide in source, and it is more than 5 moles with respect to the above-mentioned MgO of every 1kg source that this MgO source is heated to the gas that 1000 DEG C and thermolysis generate,
From start from converter tapping later to vacuum degasser to the interpolation of not implementing Mn till adding metal A l in molten steel, in the time need to regulating the Mn concentration of molten steel, make after deoxidation of molten steel with metal A l, contain Mn metal and carry out the adjusting of Mn concentration to adding in the lower molten steel of decompression.
[2] manufacture method of the steel as described in above-mentioned [1], is characterized in that, at the initial stage in the stage of under reduced pressure reacting with the dissolved oxygen in molten steel at the carbon making in molten steel, in molten steel, adds carbon material.
[3] manufacture method of the steel as described in above-mentioned [1] or [2], is characterized in that, is more than 4.5 tons/minute in the molten steel casting amount of the single current of the stable casting region of continuous caster.
[4] manufacture method of the steel as described in any one in above-mentioned [1] ~ [3], is characterized in that, by the Dissolved Oxygen concentration Control in the molten steel when the converter tapping below 0.075 quality %.
Invention effect
According to the present invention, in the slag existing, add metal A l or Al scum silica frost on the bath face of the molten steel of converter tapping, then, the MgO source of containing oxyhydroxide and oxycarbide is added in the slag in ladle, in the lower oxyde such as ferriferous oxide and the Mn oxide reduction making in slag, make the Melting point elevation of slag and at least make a part for slag solidify, therefore, the content of the lower oxyde of the slag in ladle reduces, and, the rising of the slag fusing point causing along with the MgO source of containing oxyhydroxide and oxycarbide due to interpolation is solidified, the discharge that makes thus slag flow to tundish from ladle reduces.In addition, the H being generated by pyrolysis by the MgO source of containing oxyhydroxide and oxycarbide of adding in slag 2o gas and CO 2gas is stirred slag, and therefore, even if do not carry out action of forced stirring, the metal A l that also can first drop into efficiently or Al scum silica frost react with slag, and can promote MgO in MgO source dispersion and the fusing in slag.Now, H 2o gas produced in the stage of the lesser temps that is heated to approximately 400 DEG C, CO 2gas produced in the stage of the comparatively high temps that is heated to approximately 700 DEG C, therefore, can utilize the gas that the initial stage from dropping into starts to continue to produce effectively slag to be stirred.In addition, in the case of the block MgO source of use, the MgO source of input especially easily invades in molten slag layer and disperses.By these effects, even exist a little bias in the distribution of input, also can stably control the composition of slag.
In addition, in vacuum degasser, make the carbon in molten steel under reduced pressure react with dissolved oxygen and dissolved oxygen concentration is reduced to below 0.050 quality %, then, add metal A l and make deoxidation of molten steel, therefore, can suppress the growing amount of deoxidation products, and then, in unkilled steel water, do not add Mn, and in the time need to regulating the Mn concentration of molten steel, after making deoxidation of molten steel with metal A l to adding containing Mn metal and carry out the adjusting of Mn concentration in molten steel, therefore, dissolved oxygen concentration while adding Mn is fully low, can not cause because adding Mn the generation of MnO, thereby can prevent the rising of the MnO concentration of slag.
; in the present invention; it is overlapping that the cleanliness raising effect that the cleanliness raising effect reducing based on the lower oxyde in slag, the discharge flowing out from ladle based on slag reduce and the few cleanliness of the growing amount based on deoxidation products improve effect, can manufacture the few High Clean Steel Melts of inclusion.
Embodiment
Below, the present invention is described particularly, but be not limited thereto.
Molten iron is encased in converter, to oxygen gas-supplying in molten iron, molten iron is carried out to Decarburising and refining and melting molten steel by top-blown spray gun or bottom blowing blast orifice.In this converter Decarburising and refining, for by the basicity of the slag generating in stove (quality %CaO/ quality %SiO 2) be adjusted to and in 3 ~ 5 scope, add unslaked lime, and as required, for prevent converter body refractory body melting loss and add rhombspar.In addition, can also in stove, add the Mn source of manganese ore as molten steel composition adjusting use.In a word, use the converter Decarburising and refining method conventionally carrying out to carry out Decarburising and refining to molten iron.
But, the object of the invention is to manufacture the Clean Steel that inclusion is few, the growing amount of deoxidation products is fewer, and to purifying more favourable, therefore, the Dissolved Oxygen concentration Control in molten steel when preferably Decarburising and refining end is below 0.075 quality %.At this, dissolved oxygen is not to be suspended the oxygen in molten steel with oxide form, but is dissolved in molten steel and the oxygen that exists.
Carbon concentration in dissolved oxygen concentration and molten steel when Decarburising and refining finishes is inversely proportional to, therefore, if be more than 0.035 quality %, preferably finish Decarburising and refining under state more than 0.040 quality % at carbon concentration, can be by Dissolved Oxygen concentration Control below 0.075 quality %.On the other hand, the present invention is taking soft steel (carbon concentration: approximately 0.02 quality % ~ approximately 0.07 quality %) and ultra-low carbon steel (carbon concentration: 0.0030 quality % is following) as object, when in molten steel in the time that Decarburising and refining finishes, carbon concentration exceedes 0.10 quality %, Decarburising and refining under decompression in the vacuum degasser of a rear operation extends and productivity is reduced, therefore in molten steel when, preferably Decarburising and refining finishes, carbon concentration is below 0.10 quality %.
Not to add any reductors such as Si, Al, Ti, Ca in ladle in the situation that, obtained molten steel is directly tapped in ladle from converter under the state of not deoxidation.In the moment to the steel discharge reduction in latter stage, the converter of tapping in ladle from converter, in the molten steel in stove, form eddy current, the slag in converter is rolled in eddy current, flows out in ladle, and be trapped on the molten steel in ladle together with molten steel.As mentioned above, in the time of tapping, can not add reductor, but can add unslaked lime (CaO purity is about 95 quality %).By adding this unslaked lime, the slag flowing out in ladle is diluted, thereby can reduce the concentration of the lower oxyde such as ferriferous oxide and Mn oxide in slag.
First, to adding in the slag in this ladle for reducing metal A l or the Al scum silica frost of the lower oxyde such as ferriferous oxide and Mn oxide of slag.The addition of guaranteeing metal A l or Al scum silica frost is to utilize Al be enough to the amount of the ferriferous oxide in slag and Mn oxide Restore All or be enough to the part in them to be reduced to the amount of innoxious degree.Particularly, infer ferriferous oxide in slag and the amount of Mn oxide by carbon concentration in the dissolved oxygen content in the molten steel of bessemerizing while finishing or the molten steel after tapping, thereby determine the addition of metal A l or Al scum silica frost.Conventionally, dissolved oxygen content few (in the molten steel after tapping, carbon concentration is high) in molten steel, the tendency that exists the amount of the lower oxyde in slag to reduce, on the other hand, dissolved oxygen content many (in the molten steel after tapping, carbon concentration is low) in molten steel, the tendency that exists the amount of the lower oxyde in slag to increase.But the concentration of the lower oxyde in slag is subject to the impact of operation format and changes, therefore, the slag analysis of preferably carrying out termly in ladle keeps precision.
If add metal A l or Al scum silica frost, in the slag in ladle, add the MgO source of containing oxyhydroxide and oxycarbide immediately.The MgO source of containing oxyhydroxide and oxycarbide by adding this, rises in the scope of 6 ~ 15 quality % the MgO concentration of slag.The MgO concentration of slag is during lower than 6 quality %, and in ladle, the curing of slag becomes insufficient, cannot suppress the increase of the inclusion defects in molten steel.In addition, when the MgO concentration of slag exceedes 15 quality %, although slag solidifies, the deoxidation products receptivity of slag suffers damage, and makes on the contrary cleanliness variation.The MgO concentration of slag shown here refers to the value calculating when the MgO in the MgO source of interpolation is made as in the slag being evenly melted in ladle, part MgO does not melt, or reach locally MgO concentration more than this concentration, include within the scope of this.The standard of the concrete addition in the MgO source of containing oxyhydroxide and oxycarbide is confirmed as with MgO purity and is counted about 0.15kg/ molten steel-ton ~ about 0.4kg/ molten steel-ton in experience, but the discharge and the addition of unslaked lime in ladle that flow out in ladle with slag change, therefore, need to increase and decrease according to their amount.
The slag adding in the ladle after metal A l or Al scum silica frost consists of CaO-Al 2o 3system or CaO-Al 2o 3-SiO 2system, the MgO that reason MgO brings in source and make slag fusing point rise.Rise by the fusing point that makes slag, the curing beginning of slag, thus make the area decreases of molten state.In addition, when the MgO source of containing oxyhydroxide and oxycarbide produces gas by thermolysis, absorb a large amount of heat, therefore, utilize the cooling performance being produced by MgO source, the medial temperature of slag reduces quickly compared with using the situation of MgO grog, affected by this, carry out solidifying of the interior slag of ladle.
In addition, absorb heat and generate H in the MgO source of containing oxyhydroxide and oxycarbide of putting in ladle from slag 2o gas and CO 2gas.Utilize the H being generated by this decomposition reaction 2o gas and CO 2gas stirs the slag in ladle, and therefore, even if molten steel or slag are not implemented to action of forced stirring, the metal A l that also can first drop into efficiently or Al scum silica frost react with slag.In order effectively slag being stirred, preferably to use and be heated to 1000 DEG C and gas that thermolysis generates is 5 moles of above MgO sources with respect to the above-mentioned MgO of every 1kg source.At this, the condition that the test temperature of 1000 DEG C is measured with reference to common burning decrement (ignition loss, ig.loss) adopts.The gas generating by above-mentioned thermolysis does not need capping especially, but in the time of the foaming (foaming) that need to suppress slag etc., suitably capping (for example with respect to the above-mentioned MgO of every 1kg source be 40 moles with inferior).
In addition, preferably use oxyhydroxide thermolysis and the H that generates 2o is 3 moles of CO that oxycarbide thermolysis above, that contain generates with respect to the MgO source of every 1kg 2be 2 moles of above MgO sources with respect to the MgO source of every 1kg.Now, H 2o gas produced in the stage of the lesser temps that is heated to approximately 400 DEG C, CO 2gas produced in the stage of the comparatively high temps that is heated to approximately 700 DEG C, therefore, can utilize the gas that the initial stage from dropping into starts to continue to produce effectively slag to be stirred.In the case of using not containing the MgO source of oxyhydroxide, from putting into slag, until activating, γ-ray emission needs spended time afterwards, and therefore, slag sometimes solidifies under the state on slag at MgO source emersion and cannot effectively stir.
In addition, in the case of the block MgO source of use, the MgO source of input especially easily invades in molten slag layer and disperses.
By these effects, even exist a little bias in the distribution of input, also can stably control the composition of slag.
As long as block size makes not limit fast to the intrusion in molten slag layer, more than preferably counting about 2cm with intermediate value (median) particle diameter.From promoting the viewpoint of fusing in MgO source, preferred about 5cm is as the upper limit.
As used MgO source, the MgO concentration being preferably defined as in the MgO source after the burning decrement that is heated to 1000 DEG C is MgO sources more than 50 quality %.Its reason is, for CaO, Al 2o 3, SiO 2the material that equal size is many, the effect that makes fusing point increase is little, in order to improve fusing point, must increase the addition in MgO source.
As the block MgO source of containing oxyhydroxide and oxycarbide, can use block composition (composition of matter), for example, use to the powder of the complex chemical compound of the magnesiumcarbonate that adds sodium carbonate in the aqueous solution of magnesium salts and separate out and magnesium hydroxide and be shaped to briquette (briquet) shape and MgO source of obtaining etc.Like this, while using the MgO source that uses the tackiness agents such as cement to be shaped to bulk the small primary particle of magnesium compound and to obtain, compared with the situation of the sintering particle that the particle diameter such with using magnesium oxide grog is larger, specific surface area is larger, bonding force between primary particle also disappears in the process of temperature rise, therefore, fusing and dispersion in slag are promoted, thereby solidifying of slag carried out more equably.In addition, not necessarily magnesium compound of the oxyhydroxide comprising in MgO source or oxycarbide, as long as being selected from more than one oxyhydroxide or the oxycarbide in Mg, Ca, Al, gas can similarly be produced and for slag is stirred, therefore, they can be mixed with magnesium oxide powder and lump (agglomeration) and as MgO source.
If add the MgO source of containing oxyhydroxide and oxycarbide in the slag in ladle, the ladle that contains molten steel be delivered in RH vacuum degasser or DH vacuum degasser equal vacuum de-gassing vessel.
In vacuum degasser, at least make a part for molten steel be exposed in the atmosphere under decompression.In the present invention, molten steel is deoxidation state not, therefore, by molten steel being exposed in the atmosphere under decompression, the CO partial pressure of the atmosphere under decompression is low, therefore, carbon in molten steel reacts with the dissolved oxygen in molten steel, causes the reaction (C+O → CO) that generates CO gas.By this reaction (being called " boiling reaction "), the carbon concentration in molten steel and dissolved oxygen concentration reduce, and molten steel reaches the state after decarburization and deoxidation.In the present invention, proceed boiling reaction, until the dissolved oxygen concentration in molten steel reaches below 0.050 quality %, preferably reaches below 0.030 quality %.Carbon and oxygen reduce pro rata with nucleidic mass separately respectively.
When carbon concentration in molten steel reduces because of boiling reaction, be difficult to cause boiling reaction, therefore, preferably cause boiling reaction stage initial stage moment to decompression under molten steel in add carbon material (coke, graphite etc.), make the carbon concentration in molten steel increase, thereby promote boiling reaction.But, the addition of carbon material becomes too much and during higher than the carbon concentration of the molten steel composition of target, need to follow to supplying with oxygen source in molten steel and carry out carbonization treatment, become the reason that inclusion content in melting steel is increased, therefore, the addition of the carbon material adding in moment of boiling reaction need to be set in to the molten steel after boiling reaction in carbon concentration be no more than in the scope of carbon concentration of the molten steel composition of target.
Like this, proceed boiling reaction, making the dissolved oxygen concentration in molten steel is below 0.050 quality %, and any time in the scope of carbon concentration in the molten steel steel grades that is target, makes deoxidation of molten steel to adding metal A l in the molten steel under decompression.Dissolved oxygen concentration for example can utilize and measure as the determinator of sensor using the deep or light battery of oxygen.By adding metal A l, cause (2Al+3O → the Al that reacts of added Al and dissolved oxygen 2o 3), dissolved oxygen is reduced to the concentration of approximate number ppm quickly, and boiling reaction stops.As long as adding the dissolved oxygen concentration in the moment of metal A l is that 0.050 quality % specified with next needs, but dissolved oxygen concentration is lower, the growing amount of deoxidation products is fewer, therefore, preferably reduces as much as possible dissolved oxygen concentration.The addition of metal A l has the mode of the Al of 0.01～0.07 quality % to set with fusing make molten steel on the basis of removing dissolved oxygen in.
From start from converter tapping later to vacuum degasser to till adding metal A l in molten steel, do not implement the interpolation of Mn.Preferably Si also with Mn similarly until do not added by metal A l deoxidation.
But the steel grades standard of the molten steel based on melting, in the situation that needs regulate Mn or Si, is utilizing metal A l to carry out after deoxidation treatment, to adding Mn source in molten steel or constituent adjustment is implemented in Si source.In this case, use high carbon ferromanganese (FMnH) or manganese metal etc. to regulate as Mn source containing Mn metal, but contain the carbon of the 7 quality % that have an appointment containing high carbon ferromanganese the most cheap in Mn metal, by adding high carbon ferromanganese, the carbon concentration in molten steel rises.Therefore, consider the rise of the carbon concentration being caused containing Mn metal by interpolation high carbon ferromanganese etc., in molten steel when boiling reaction is finished, carbon concentration regulates.Because manganese metal does not contain carbon, therefore, in the situation that using manganese metal as Mn source, do not need to consider the rise of carbon concentration.In addition, need to regulate in the situation of the trace additives such as Nb, V, B, Ca, Ti, also after the deoxidation treatment of utilizing metal A l to carry out, implement.
Like this, even in the case of regulating the Mn concentration of molten steel, containing interpolation period of Mn metal be also the extremely low moment of dissolved oxygen concentration after Al deoxidation, therefore, can not cause containing the reacting of the Mn in Mn metal and dissolved oxygen, adding while containing Mn metal, prevent the generation as the MnO of lower oxyde.
If the degassed refining in vacuum degasser finishes, the ladle that contains molten steel is delivered in continuous-casting of steel billet machine, utilize continuous caster to cast and manufacture steel billet.In continuous caster, from the viewpoint that productivity is improved, preferably by being that more than 4.5 tons/minute high-speed casting is cast in the molten steel casting amount of single current of stablizing casting region.
Along with the carrying out of the casting in continuous caster, molten steel in ladle reduces, before the ladle exchange that is about to carry out sequence casting, the molten steel height in ladle is extremely low, and the steel flow that flows to tundish from the ladle molten steel near the ladle of of (ladle nozzle) that portals forms eddy current.Inclusion in the molten steel of the slag in ladle and near existence this slag is rolled in this eddy current, and flows out to tundish, and a part that flows out to tundish does not have complete emersion and flows out in mold, becomes the inclusion of slab.Under high-speed casting, being injected into molten steel tundish from ladle, to inject flow many, therefore, the many moment of residual molten steel in ladle start to form eddy current in ladle, and the inclusion in the molten steel of the slag in ladle and near existence this slag is rolled into the increase frequency in eddy current.
But, in the present invention, the MgO source of containing oxyhydroxide and oxycarbide by interpolation, slag in ladle is solidified, therefore, slag in ladle is difficult for being rolled in eddy current, and, the lower oxyde that adds metal A l or Al scum silica frost and reduce in slag, and after Al deoxidation, carry out the adjusting of the Mn of molten steel composition, therefore, can prevent newly-generated MnO, reduce the oxygen current potential of slag, inclusion near the molten steel existing slag tails off, in addition, because at dissolved oxygen concentration being moment below 0.050 quality % carries out Al deoxidation, therefore, the growing amount of deoxidation products itself reduces, by the overlapping cleanliness of guaranteeing molten steel of above-mentioned effect, result, even the molten steel casting amount of single current is 4.5 tons of/minute above high-speed castings, also can manufacture the good steel billet of cleanliness that inclusion is few.
Embodiment
Based on embodiment, the present invention is given the account in greater detail.Be that the molten steel of the top blast bottom-blown converter melting of 300 tons carries out refining in RH vacuum degasser by utilizing furnace capacity, then, in the operation application the present invention who manufactures steel sheet steel billet with the double discharge type continuous-casting of steel billet machine that for cast thickness is 235mm, the width steel billet that is 1100mm.In addition, as a comparison, also carry out the operation outside scope of the present invention.Using four stoves as a unit, under identical conditions, carry out melting, in continuous casting, implement the sequence casting of above-mentioned four stoves, test as a unit using four stoves.
The slab of manufacturing is carried out to hot rolling in the situation that not implementing surfacing, make steel sheet, obtained steel sheet is carried out to cleanup acid treatment, then, carry out cold rollingly, the steel plate after cold rolling is carried out zinc-plated, investigate the surface imperfection being caused by oxide based inclusion of this steel plate after zinc-plated.
The surface imperfection index that operational condition in the inventive example and comparative example and steel-sheet are caused by oxide based inclusion has been shown in table 1.At this, the surface imperfection index shown in table 1 is to go forward side by side row index and the value that illustrates as benchmark (1.00) not adding the degradation ratio being caused by defect in the comparative example 1 that the block composition that contains oxyhydroxide and oxycarbide is MgO source.Being the MgO ball that MgO source is used as the block composition that contains oxyhydroxide and oxycarbide, is to contain magnesium hydroxide, magnesiumcarbonate and magnesium oxide and Mg (OH) 2content is that approximately 20 quality % are above, MgCO 3content is that approximately 20 quality % are above, burning decrement (1000 DEG C of processing) for the MgO concentration in the residue after approximately 20 quality %, burning decrement be that more than 80 quality % powder composition is shaped to the block fusing assistant that the briquette of diameter 30mm obtains.While being heated to 1000 DEG C, the H generating by thermolysis 2o is more than 3.4 moles with respect to the MgO source of every 1kg, the CO generating by thermolysis 2be more than 2.4 moles with respect to the MgO source of every 1kg.
In all embodiment and comparative example, after the molten steel of not deoxidation is tapped to ladle, on the slag in ladle, add Al scum silica frost, in all embodiment and a part of comparative example, and then add MgO ball and carry out the control of slag.In addition, in comparative example 8, on the slag in ladle, drop into after Al scum silica frost and MgO grog, the spray gun that is coated with refractory body is flooded to about 2m in molten steel, with about 1Nm 3/ minute the speed that blasts blast the Ar gas of 3 minutes and stir.The MgO grog using in comparative example 8, by the magnesium hydroxide calcining extracting from seawater is obtained, contains MgO more than 90 quality %, and contains the SiO as impurity 2, CaO, Al 2o 3, Fe 2o 3etc. a small amount of oxide compound.
In the inventive example 1～5, compared with comparative example 1, inclusion can be reduced to below 1/3.With respect to this, the addition of the MgO ball that contains oxyhydroxide and oxycarbide in interpolation is many, MgO content in slag exceeds the comparative example 2 of scope of the present invention and the addition of MgO ball is few, MgO content in slag does not reach in the comparative example 4 of scope of the present invention, is not reduced fully the effect of inclusion.In addition, in the boiling reaction of utilizing RH vacuum outgas, do not add Mn source but do not add in the comparative example 3 of MgO ball, not reduced fully the effect of inclusion.In comparative example 6, although control slag composition with MgO ball, the dissolved oxygen concentration before Al adds, higher than 0.050 quality %, therefore, is not reduced the effect of inclusion fully.In addition, in comparative example 7, added Mn source although control slag composition with MgO ball in boiling reaction, therefore, the MnO concentration in slag rises, and is not reduced fully the effect of inclusion.In addition, replace and add MgO ball and carry out bubbling and stir, in the comparative example 8 of the control of carrying out slag, also not reduced fully the effect of inclusion at interpolation MgO grog.
As above can confirm, by application the present invention, even be under more than 4.5 tons/minute high-speed castings in the molten steel casting amount of single current, also can manufacture the good steel of cleanliness that inclusion is few.

Claims (5)

1. a manufacture method for steel, is characterized in that,
Have:
By the molten steel that molten iron is carried out to Decarburising and refining and obtain under the state of not deoxidation directly from converter to the operation of tapping in ladle;
After tapping, in the slag existing on the molten steel in ladle, add metal A l or Al scum silica frost, then add MgO source, in the lower oxyde in reduction slag, by the operation of MgO concentration adjustment to the 6～15 quality % in slag;
Then, in vacuum degasser, make the carbon in molten steel under reduced pressure react and dissolved oxygen concentration is reduced to below 0.050 quality % with the dissolved oxygen in molten steel, after dissolved oxygen concentration in molten steel reaches below 0.050 quality %, make the operation of deoxidation of molten steel to adding metal A l in the molten steel under decompression; And
Then utilize continuous caster molten steel to be cast as to the operation of steel billet,
Wherein, described MgO contains oxyhydroxide and oxycarbide in source, and it is more than 5 moles with respect to MgO source described in every 1kg that this MgO source is heated to the gas that 1000 DEG C and thermolysis generate, with slag described in described gas stirring,
From start from converter tapping later to vacuum degasser to the interpolation of not implementing Mn till adding metal A l in molten steel, in the time need to regulating the Mn concentration of molten steel, make after deoxidation of molten steel with metal A l, contain Mn metal and carry out the adjusting of Mn concentration to adding in the lower molten steel of decompression.
2. the manufacture method of steel as claimed in claim 1, is characterized in that, at the initial stage in the stage of under reduced pressure reacting with the dissolved oxygen in molten steel at the carbon making in molten steel, in molten steel, adds carbon material.
3. the manufacture method of steel as claimed in claim 1 or 2, is characterized in that, is more than 4.5 tons/minute in the molten steel casting amount of the single current of the stable casting region of continuous caster.
4. the manufacture method of steel as claimed in claim 1 or 2, is characterized in that, by the Dissolved Oxygen concentration Control in the molten steel when the converter tapping below 0.075 quality %.
5. the manufacture method of steel as claimed in claim 3, is characterized in that, by the Dissolved Oxygen concentration Control in the molten steel when the converter tapping below 0.075 quality %.
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