WO2012163849A1 - Process for producing clean steels and clean steel produced thereby - Google Patents

Process for producing clean steels and clean steel produced thereby Download PDF

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Publication number
WO2012163849A1
WO2012163849A1 PCT/EP2012/059881 EP2012059881W WO2012163849A1 WO 2012163849 A1 WO2012163849 A1 WO 2012163849A1 EP 2012059881 W EP2012059881 W EP 2012059881W WO 2012163849 A1 WO2012163849 A1 WO 2012163849A1
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WO
WIPO (PCT)
Prior art keywords
molten steel
alloys
furnace
liquid additive
elements
Prior art date
Application number
PCT/EP2012/059881
Other languages
French (fr)
Inventor
Wouter Karel Tiekink
Willem Van Der Knoop
Original Assignee
Tata Steel Nederland Technology Bv
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Tata Steel Nederland Technology Bv filed Critical Tata Steel Nederland Technology Bv
Priority to EP12724955.5A priority Critical patent/EP2714943A1/en
Publication of WO2012163849A1 publication Critical patent/WO2012163849A1/en

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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
    • 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
    • C21C7/076—Use of slags or fluxes as treating agents
    • 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
    • C21C7/0006—Adding metallic additives
    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

Definitions

  • This invention relates to a method of producing clean steel by means of an oxygen converter process or an electric furnace to produce a molten steel wherein the molten steel is further processed in a secondary steelmaking process.
  • the steel After the primary steelmaking in the oxygen converter or the electric furnace, the steel has not yet reached its final qual ity. Certain operations which have an essential bearing on final product quality are performed during the various secondary or ladle refining treatment: the analytical quality of the liquid metal is adjusted, including compositional trimming. Not only of metallic alloying elements, but also the control of metal loids (C, H , N, O, P, S) to different degrees depending on the g rade. The type and content of oxide inclusions is controlled, by deoxidation (or killing) of the steel, generally by the add ition of aluminium and/or silicon, by calcium treatment to modify their compositions, and by controlled flotation . Other elements like manganese can be used for deoxidation, but aluminium and silicon are the most commonly used elements.
  • the temperature is controlled by management of heat losses during the various operations, by reheating, or where necessary by cooling with the aid of suitable amounts of scrap.
  • additive alloys To obtain the desired chemical composition of the steel, other elements are added to the steel, usually in the form of additive alloys. There are three moments in the known steelmaking processes where the addition of additive alloys can be done relatively easily:
  • DE10164610 discloses a method to produce TWIP steels comprising up to 30% manganese, silicon and up to 1% carbon . During production of these exotic steels so-called brown smoke develops as a result of the evaporation and subsequent oxidation of manganese and iron and the formation of CO- bubbles which wildly agitate the melt thereby throwing droplets into the air. In DE10164610 an excess of aluminium is added to deoxidise the steel melt to prevent CO-formation in combination with adding the manganese and silicon alloying elements in molten form thus allowing to keep the temperature low thereby counteracting evaporation of volatile elements.
  • the invention relates to a method of producing clean steel by means of an oxygen converter process or an electric furnace to produce a molten steel wherein the molten steel is further processed in a secondary steelmaking process characterised in that the secondary steelmaking process involves the add ition of add itive al loying elements which are l iq u id at the moment of addition to the molten steel wherein the liquid additive alloying elements to be added to the molten steel have been subjected to a purification treatment prior the moment of addition to the molten steel and wherein the purification treatment involves reducing the contamination of the liquid additive alloys by removing unwanted elements such as Al from FeSi, Ca from FeSi, Zr from FeTi and/or S from FeMn.
  • the advantage of the process according to the invention is that the additive alloying elements added to the molten steel are optimally suited to perform their task without introducing unwanted elements in the molten steel .
  • Th is resu lts i n a steel with out ad d itiona l elements in the molten state immediately prior to casting, and therefore also in a steel with a smaller amount of unwanted elements in the solidified steel.
  • These unwanted elements usually manifest themselves in the form of inclusions or precipitates in the solid matrix. These inclusions or precipitates affect the formability of the steel , for instance during deep d rawing or wire drawing, or they result in surface defects which is unacceptable for appl ications where the surface quality of the steel is one of the important properties.
  • the purification treatment is performed in an electric induction furnace or an electric arc furnace or in any other device that can heat the additive alloys to a temperature higher than their melting point.
  • these additive alloys are melted in a melting facility which is provided with means to shield the (molten) additive alloys from the surround ing atmosphere .
  • this shield ing is performed by gas- shielding, such as argon or nitrogen shielding .
  • the invention is therefore also embodied in a method wherein the additive alloys, molten or otherwise, are shielded from the surrounding atmosphere, preferably by gas-shielding, such as argon or nitrogen shielding .
  • the pu rification treatment involves red ucing the amou nt of strong ly oxid isi ng elements from the add itive al l oys thereby creating the correct oxygen potential in the argon or nitrogen shielded furnace after melting, so that the oxidising elements react with the oxygen.
  • the purification treatment involves reducing the amount of oxides and sulphides which do not dissolve in the liquid additive alloys by flotation in the furnace after melting the additive alloys.
  • the slag on the liquid additive alloys is skimmed just before the liquid additive alloys are added to the molten steel . This also diminishes the amount of unwanted elements added to the molten steel.
  • the sulphur content of the liquid additive alloys is reduced by adding a desulphurising slag onto the melted alloy in a fully argon or nitrogen shielded furnace and/or the addition of some additional Al, Ti or Si to enable the desulphurisation reaction.
  • the liquid is added to or into the molten steel while the latter is held in a ladle which is usually gas-agitated or gas-stirred .
  • the bubble breakthrough region at the upper surface of the molten steel is commonly referred to as spout region or the plume eye.
  • the stirring may also be performed by means of electromag netic stirring in which case there is no plume eye as defined above.
  • a ladle shroud can be used or any other refractory tube, which is fitted below a small tundish, as illustrated in figure 1.
  • the small tundish serves as a temporary holder of the liquid additive alloys prior to being added to the molten steel.
  • this embodiment can also be used in a ladle which is not gas-agitated . It is the preferred embodiment of the two adding methods.
  • FIG. 1 shows a schematic representation of the embodiment in which the liquid additive alloying elements are added in the plume eye.
  • Vessel 1 represents the vessel or furnace in which the additive alloys are melted .
  • the liquid add itive al loying elements 2 are subsequently poured into a tund ish 3, which serves as a temporary holder of the liq uid additive alloying elements.
  • a tube 5 usually a ceramic tube, the alloying elements are poured through the ladle slag 4 into the plume eye 8 which is caused by the rising bubbles 7 of the gas-stirring 9 into the molten steel 6.
  • figure 1 A variant of figure 1 is presented in figure 2 where the exit of the tube 5 is suspended just above the pl ume eye. This way any pressure d ifference between the liquid alloy and molten steel is avoided.
  • FIG. 3 shows a schematic representation of the embodiment in which the liquid additive alloying elements are added through the nozzle though the slag in the molten steel .
  • Vessel 1 represents the vessel or furnace in which the additive alloys are melted .
  • the liquid additive alloying elements 2 are subsequently poured into a tundish 3, which serves as a temporary holder of the liquid additive alloying elements.
  • a tube 5 usually a ceramic tube, the alloying elements are poured through the ladle slag 4 away from the plume eye 8 which is caused by the rising bubbles 7 of the gas-stirring 9 into the molten steel 6.

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

Abstract

Method of producing clean steel by means of an oxygen converter process or an electric furnace to produce a molten steel wherein the molten steel is further processed in a secondary steelmaking process characterised in that the secondary steelmaking process involves the addition of additive alloying elements which are liquid at the moment of addition to the molten steel.

Description

PROCESS FOR PRODUCI NG CLEAN STEELS AND CLEAN STEEL PRODUCED THEREBY
This invention relates to a method of producing clean steel by means of an oxygen converter process or an electric furnace to produce a molten steel wherein the molten steel is further processed in a secondary steelmaking process.
After the primary steelmaking in the oxygen converter or the electric furnace, the steel has not yet reached its final qual ity. Certain operations which have an essential bearing on final product quality are performed during the various secondary or ladle refining treatment: the analytical quality of the liquid metal is adjusted, including compositional trimming. Not only of metallic alloying elements, but also the control of metal loids (C, H , N, O, P, S) to different degrees depending on the g rade. The type and content of oxide inclusions is controlled, by deoxidation (or killing) of the steel, generally by the add ition of aluminium and/or silicon, by calcium treatment to modify their compositions, and by controlled flotation . Other elements like manganese can be used for deoxidation, but aluminium and silicon are the most commonly used elements.
The temperature is controlled by management of heat losses during the various operations, by reheating, or where necessary by cooling with the aid of suitable amounts of scrap.
To obtain the desired chemical composition of the steel, other elements are added to the steel, usually in the form of additive alloys. There are three moments in the known steelmaking processes where the addition of additive alloys can be done relatively easily:
• at the moment of tapping the molten steel from the BOF-converter or from the electric arc furnace (EAF) into a ladle,
• during ladle metallurgy where very exact adjustments to steel by the addition of the additive alloys can be made, or
• in the casting tundish so that for instance several grades can be made out of one converter- or EAF-heat.
The addition of additive alloys is usually performed in the form of pellets of the additive alloy(s) or broken iron-alloy metals. DE10164610 discloses a method to produce TWIP steels comprising up to 30% manganese, silicon and up to 1% carbon . During production of these exotic steels so-called brown smoke develops as a result of the evaporation and subsequent oxidation of manganese and iron and the formation of CO- bubbles which wildly agitate the melt thereby throwing droplets into the air. In DE10164610 an excess of aluminium is added to deoxidise the steel melt to prevent CO-formation in combination with adding the manganese and silicon alloying elements in molten form thus allowing to keep the temperature low thereby counteracting evaporation of volatile elements.
The invention relates to a method of producing clean steel by means of an oxygen converter process or an electric furnace to produce a molten steel wherein the molten steel is further processed in a secondary steelmaking process characterised in that the secondary steelmaking process involves the add ition of add itive al loying elements which are l iq u id at the moment of addition to the molten steel wherein the liquid additive alloying elements to be added to the molten steel have been subjected to a purification treatment prior the moment of addition to the molten steel and wherein the purification treatment involves reducing the contamination of the liquid additive alloys by removing unwanted elements such as Al from FeSi, Ca from FeSi, Zr from FeTi and/or S from FeMn.
In this way very pure alloys can be added to the steel to make clean steels that will not be affected by residuals or oxides or sulphides originally present in the solid as bought alloys.
The advantage of the process according to the invention is that the additive alloying elements added to the molten steel are optimally suited to perform their task without introducing unwanted elements in the molten steel . Th is resu lts i n a steel with out ad d itiona l elements in the molten state immediately prior to casting, and therefore also in a steel with a smaller amount of unwanted elements in the solidified steel. These unwanted elements usually manifest themselves in the form of inclusions or precipitates in the solid matrix. These inclusions or precipitates affect the formability of the steel , for instance during deep d rawing or wire drawing, or they result in surface defects which is unacceptable for appl ications where the surface quality of the steel is one of the important properties. This is particularly the case fo r o ute r pa n el s fo r a uto m o b i l e a p p l i cati o n s . W i re b rea ka g e o r contamination of wire by inclusions is of particular interest in the case of steel cast as bl ooms o r bi l lets for a ppl ications su ch as wel d i n g wi re, or fo r automotive tyres etc. Clean billets or blooms will lead to fewer occurrences of wire breakage during wire drawing . The purification treatment diminishes the amount of unwanted elements added to the molten steel .
In an embodiment the purification treatment is performed in an electric induction furnace or an electric arc furnace or in any other device that can heat the additive alloys to a temperature higher than their melting point.
Preferably these additive alloys are melted in a melting facility which is provided with means to shield the (molten) additive alloys from the surround ing atmosphere . Preferably this shield ing is performed by gas- shielding, such as argon or nitrogen shielding . The invention is therefore also embodied in a method wherein the additive alloys, molten or otherwise, are shielded from the surrounding atmosphere, preferably by gas-shielding, such as argon or nitrogen shielding .
In an embod iment the pu rification treatment involves red ucing the amou nt of strong ly oxid isi ng elements from the add itive al l oys thereby creating the correct oxygen potential in the argon or nitrogen shielded furnace after melting, so that the oxidising elements react with the oxygen.
In an embodiment the purification treatment involves reducing the amount of oxides and sulphides which do not dissolve in the liquid additive alloys by flotation in the furnace after melting the additive alloys.
In a preferable embod iment the slag on the liquid additive alloys is skimmed just before the liquid additive alloys are added to the molten steel . This also diminishes the amount of unwanted elements added to the molten steel.
In an embodiment the sulphur content of the liquid additive alloys is reduced by adding a desulphurising slag onto the melted alloy in a fully argon or nitrogen shielded furnace and/or the addition of some additional Al, Ti or Si to enable the desulphurisation reaction.
In adding the liquid additive alloying elements a special way is needed to add the liquid to the molten steel without causing re-oxidation and in order to have a reproducible and high recovery of the alloying element.
The liquid is added to or into the molten steel while the latter is held in a ladle which is usually gas-agitated or gas-stirred . The bubble breakthrough region at the upper surface of the molten steel is commonly referred to as spout region or the plume eye. The stirring may also be performed by means of electromag netic stirring in which case there is no plume eye as defined above.
In an embodiment a ladle shroud can be used or any other refractory tube, which is fitted below a small tundish, as illustrated in figure 1. The small tundish serves as a temporary holder of the liquid additive alloys prior to being added to the molten steel.
Two ways of adding can be employed :
1. to add the liquid additive alloying elements to the steel in the plume eye by adjusting the tube just above the plume eye to avoid dragging in ladle slag or,
2. to put through the tube through the ladle slag into the molten steel, so that a plume eye is not necessary.
Consequently this embodiment can also be used in a ladle which is not gas-agitated . It is the preferred embodiment of the two adding methods.
In the following, non-limitative and schematic figures, the invention is further explained .
Figure 1 shows a schematic representation of the embodiment in which the liquid additive alloying elements are added in the plume eye. Vessel 1 represents the vessel or furnace in which the additive alloys are melted . In this embod iment the liquid add itive al loying elements 2 are subsequently poured into a tund ish 3, which serves as a temporary holder of the liq uid additive alloying elements. By means of a tube 5, usually a ceramic tube, the alloying elements are poured through the ladle slag 4 into the plume eye 8 which is caused by the rising bubbles 7 of the gas-stirring 9 into the molten steel 6.
A variant of figure 1 is presented in figure 2 where the exit of the tube 5 is suspended just above the pl ume eye. This way any pressure d ifference between the liquid alloy and molten steel is avoided.
Figure 3 shows a schematic representation of the embodiment in which the liquid additive alloying elements are added through the nozzle though the slag in the molten steel . Vessel 1 represents the vessel or furnace in which the additive alloys are melted . In this embodiment the liquid additive alloying elements 2 are subsequently poured into a tundish 3, which serves as a temporary holder of the liquid additive alloying elements. By means of a tube 5, usually a ceramic tube, the alloying elements are poured through the ladle slag 4 away from the plume eye 8 which is caused by the rising bubbles 7 of the gas-stirring 9 into the molten steel 6.

Claims

1. Method of producing clean steel by means of an oxygen converter process or an electric furnace to produce a molten steel wherein the molten steel is further processed in a secondary steelmaking process wherein the secondary steelmaking process involves the addition of additive alloying elements which are liquid at the moment of addition to the molten steel wherein the liquid additive alloying elements to be added to the molten steel have been subjected to a purification treatment prior the moment of addition to the molten steel and wherein the purification treatment involves reducing the contamination of the liquid additive alloys by removing unwanted elements such as Al from FeSi, Ca from FeSi, Zr from FeTi and/or S from FeMn.
2. Method according to claim 1 wherein the purification treatment is performed in an electric induction furnace or an electric arc furnace or in any other device that can heat the additive alloys to a temperature higher than their melting point.
3. Method according to claim 1 or 2 wherein the additive alloys are shielded from the surrounding atmosphere, preferably by gas-shielding, such as argon or nitrogen shielding .
4. Method according to claim 1 or 3 wherein the purification treatment involves reducing the amount of strongly oxidising elements from the liquid additive alloys thereby creating the correct oxygen potential in the argon or nitrogen shielded purification furnace after melting, so that the oxidising elements react with the oxygen.
5. Method according to any one of claim 1 to 4 wherein the purification treatment involves decreasing the amount of oxides and sulphides which do not dissolve in the liquid additive alloys by flotation in the furnace after melting the additive alloys.
6. Method according to any one of claim 1 to 5 wherein the slag on the liquid additive alloys is skimmed just before the liquid additive alloys are added to the molten steel.
7. Method according to any one of claim 1 to 5 wherein the sulphur content of the liquid additive alloys is reduced by adding a desulphurising slag onto the melted alloy in a fully argon or nitrogen shielded furnace and/or the addition of some additional Al, Ti or Si to enable the desulphurisation reaction.
8. Clean steel produced by the method of any one of claims 1 to 7.
PCT/EP2012/059881 2011-05-27 2012-05-25 Process for producing clean steels and clean steel produced thereby WO2012163849A1 (en)

Priority Applications (1)

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EP12724955.5A EP2714943A1 (en) 2011-05-27 2012-05-25 Process for producing clean steels and clean steel produced thereby

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
EP11167992.4 2011-05-27
EP11167992 2011-05-27

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WO2012163849A1 true WO2012163849A1 (en) 2012-12-06

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2001057280A1 (en) * 2000-01-31 2001-08-09 Elkem Asa Method for grain refining of steel, grain refining alloy for steel and method for producing grain refining alloy
DE10164610C1 (en) 2001-12-27 2003-07-17 Thyssenkrupp Stahl Ag Producing a steel melt comprises melting a process material into a melt, deoxidizing the melt with aluminum, adding manganese and silicon to the deoxidized melt, and treating the melt
WO2007062680A1 (en) * 2005-12-02 2007-06-07 Sms Demag Ag Method and foundry for producing high-manganese, low-carbon steel

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2001057280A1 (en) * 2000-01-31 2001-08-09 Elkem Asa Method for grain refining of steel, grain refining alloy for steel and method for producing grain refining alloy
DE10164610C1 (en) 2001-12-27 2003-07-17 Thyssenkrupp Stahl Ag Producing a steel melt comprises melting a process material into a melt, deoxidizing the melt with aluminum, adding manganese and silicon to the deoxidized melt, and treating the melt
WO2007062680A1 (en) * 2005-12-02 2007-06-07 Sms Demag Ag Method and foundry for producing high-manganese, low-carbon steel

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