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
  • C21C7/04—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
  • C21C1/00—Refining of pig-iron; Cast iron
  • C21C1/04—Removing impurities other than carbon, phosphorus or sulfur
• • 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
  • C21C5/42—Constructional features of converters
  • C21C5/46—Details or accessories
  • C21C5/4606—Lances or injectors
• • 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
  • C21C7/0056—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00 using cored wires
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F27—FURNACES; KILNS; OVENS; RETORTS
  • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
  • F27D3/00—Charging; Discharging; Manipulation of charge
  • F27D3/0025—Charging or loading melting furnaces with material in the solid state
  • F27D3/0026—Introducing additives into the melt
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F27—FURNACES; KILNS; OVENS; RETORTS
  • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
  • F27D3/00—Charging; Discharging; Manipulation of charge
  • F27D3/18—Charging particulate material using a fluid carrier

Definitions

• This invention relates in general to the field of metallurgical processing, and more specifically to processes for adding materials, such as fluxes, into molten metal such as liquid steel.
• nitrogen is generally considered to be an unwanted element in steel.
• Nitrogen enters into liquid steel from the air and from contaminants, such as oil, that may find their way into the raw and recycled material from which steel is made.
• the nitrogen changes the mechanical properties of steel, making it harder and less ductile. It can also chemically combine with aluminum, or other elements, to form inclusions, affecting the quality of the product.
• Combined compounds can also migrate to grain boundaries in the steel's microstructure, weakening the steel at elevated temperatures, giving rise to inter-granular cracks.
• Nitrogen levels are particularly a problem in steel that is produced by the so-called "mini-mills," which generally use electric arc furnaces to melt the steel and that also tend to use a relatively high level of metal scrap as source material. It is not uncommon to see steels that are produced at such facilities as having a nitrogen content that is within the range of about 60 parts per million (ppm) to about 120 ppm. Steels that are made in mills having a basic oxygen furnace, on the other hand, have a nitrogen content that is commonly within the range of about 30 ppm to about 50 ppm. Some specialty applications, such as for the automotive body, however, require nitrogen levels that are as low as 20 ppm.
• top slag process which is also in common practice for desulfurizing steel, involves heating the steel within the ladle for an extended period of time and to circulate the steel, thereby exposing all the molten metal over time to the liquid metal-slag reaction interface. While denitrogenization with top ladle slag is promising in the sense that it permits reduction of nitrogen to levels otherwise not achievable by other processes, it has several practical limitations and consequently it is not in wide practice at this point.
• the top ladle slag denitrogenizing treatment would require skimming of carried over furnace slag from the ladle and introduction of a synthetic denitrogenizing ladle flux of a specific composition on top of liquid steel. Adding of such flux to the ladle already containing other slag would not be desired and effective due to the dilution effect by the other slag. Effects of nitrogen removal by doing so would be questionable due to variability of composition of diluted ladle slag.
• the skimming operations which are not uncommon in some practices such as special desulfurization processes, are very time consuming and not energy efficient. Temperature loss of steel in the ladle not covered with slag can amount to 100-150 degrees F depending on the type of operation. Addition of solid slag fluxing mix requires extended heating to melt and bring the mix into solution. This requires a great deal of time and energy, both of which are expensive factors in the overall cost of production.
• a method of introducing a denitrogenizing flux to an amount of molten metal includes, according to a first aspect of the invention steps of: (a) encasing the denitrogenizing flux with an outer layer of a metallic material of equal of lower melting point in comparison to the liquid metal; and (b) introducing the flux so encased into the molten metal, whereby the outer layer will melt, thereby introducing the flux into the molten metal.
• an article for introducing a denitrogenizing flux to an amount of molten metal includes an outer layer of a metallic material that has a melting point that is beneath the anticipated temperature of the amount, of molten metal; and a denitrogenizing flux that is encased within the molten metal, whereby the outer layer will melt after the article has been introduced into the molten metal for a predetermined period of time, thereby permitting introduction of the denitrogenizing flux into the molten metal at a depth below the top surface of the molten metal.
• a method of denitrogenizing an amount of molten metal includes steps of: (a) providing an amount of molten metal; and (b) introducing a denitrogenizing flux into the molten metal in such a way that the flux becomes exposed to the molten metal at a location that is at a depth that is substantially below the top surface of the molten metal, thereby promoting more efficient mixing of the flux into the molten metal.
• a method of introducing a denitrogenizing flux to an amount of molten metal includes, according to a fourth aspect of the invention, steps of: (a) supplying an amount of denitrogenizing flux into a lance assembly of the type that includes a nozzle that is constructed and arranged to be immersed in molten metal; and (b) using the lance assembly to introduce the flux into the molten metal.
• FIGURE 1 is a schematic depiction of a conventional wire feed machine, which is shown in operation according to the invention
• FIGURE 2 is a cross-sectional view taken along lines 2-2 in FIGURE 1;
• FIGURE 3 is a schematic depiction of a system constructed according to an alternative embodiment of the invention.
• FIGURE 4 is a schematic control diagram.
• an improved system 10 for producing steel that has a low nitrogen content includes a source 12 of a wire vector 14 that is constructed and arranged to introduce a denitrogenizing flux into molten metal such as steel.
• System 10 utilizes a conventional wire feed machine of the type that includes feeding structure 16 for feeding the wire vector into a guide chute 18 at a controlled velocity so as to cause the wire vector 14 to penetrate into the molten steel 22 at a predetermined speed and direction.
• the wire vector 14 includes an outer layer 24 of a material, such as steel, that has a melting point that is at or beneath the temperature of the molten metal 22.
• the outer layer 24 is fabricated from steel a material with equal or lower melting point than the liquid melt, preferably the outer layer can be made of steel or aluminum. Outer layer 24 thus encases the nonmetallic substance in an elongated, tube-like hollow cladding of metallic material that is designed to melt after being introduced into the molten metal 22.
• Wire vector 14 further includes an inner body of a powdered denitrogenizing flux material 26, which includes calcium oxide (CaO) and at least one compound selected from the group consisting of oxides, silicates, carbonates of alkali and alkaline earth metals and oxides, fluorides, silicates and carbonates of metals selected from the group consisting of Calcium (Ca), Silicon (Si), Magnesium (Mg), Boron (B), Titanium (Ti), Barium (Ba) and Aluminum (Al).
• the most preferred flux materials are CaO-BaO-TiO -(Al 2 O 3 ), CaO-TiO 2 -(Al 2 O 3 ) and Calcium - Boron oxide bearing fluxes.
• any other flux that is capable of achieving the desired denitrogenization could be substituted.
• a process according to one embodiment of the invention involves encasing the denitrogenizing flux 26 with the outer layer of metallic material 24 and introducing the flux 26 so encased into the molten metal 22, whereby the outer layer will melt, thereby introducing the flux into the molten metal.
• a system 30 for introducing a denitrogenizing flux 20 to an amount of molten metal 32 that is constructed according to a preferred embodiment of the invention includes a container 34, such as a ladle, for holding an amount of molten metal 32 such as . liquefied steel.
• System 30 further includes a lance assembly 36 that is preferably inclusive of a container or hopper 38 of a supply of denitrogenizing flux 40, and a lance 42 for introducing the flux 40 into the molten metal 32.
• the flux material 40 is a powdered denitrogenizing flux material which includes calcium oxide (CaO) and at least one compound selected from the group consisting of oxides, silicates, carbonates of alkali and alkaline earth metals and oxides, fluorides, silicates and carbonates of metals selected from the group consisting of Calcium (Ca), Silicon (Si), Magnesium (Mg), Boron (B), Titanium (Ti), Barium (Ba) and Aluminum (Al).
• the most preferred flux materials are CaO-BaO-TiO 2 -(Al 2 O 3 ), CaO-TiO 2 -(Al 2 O 3 ) and Calcium - Boron oxide bearing fluxes.
• any other flux that is capable of achieving the desired denitrogenization could be substituted.
• a second end of the lance 42 terminates in a nozzle 48, which during operation of the system 30 is immersed in the molten metal 32.
• the portion of the lance 42 that is expected to be immersed in the molten metal 32 during operation is encased in a protective refractory sleeve 54, as is shown in FIGURE 3.
• a conveyor 50 that is powered by a motor 52 is positioned to supply flux material from the hopper 38 into the lance 42 at a location that is between the valve 46 and the nozzle 48.
• System 30 includes a control system having a CPU 56 that controls operation of the motor 52 and the valve 56.
• system 30 is operated to introduce the denitrogenizing flux 40 into the molten metal 32 by CPU 56 instructing motor 52 to cause conveyor 50 to move flux into the lance 42, and by opening valve 46, thus causing the flux 40 to become entrained in the flow of inert gas that is provided by the pressure source 44.
• the flux is then injected into the molten metal 32 at a preselected depth and velocity that is chosen to promote fast, efficient mixing of the flux 40 with the molten metal 32.
• the invention adds denitrogenizing flux in a manner that is less time consuming and less wasteful of energy than methods of flux addition and mixing that are in conventional use.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Treatment Of Steel In Its Molten State (AREA)
• Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)
• Furnace Charging Or Discharging (AREA)

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Cited By (1)

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Citations (4)

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• 1998
  • 1998-05-29 AU AU77239/98A patent/AU743299B2/en not_active Ceased
  • 1998-05-29 CN CN98805650A patent/CN1084793C/zh not_active Expired - Fee Related
  • 1998-05-29 WO PCT/US1998/011528 patent/WO1998054369A1/en not_active Application Discontinuation
  • 1998-05-29 BR BR9809184-0A patent/BR9809184A/pt not_active Application Discontinuation
  • 1998-05-29 KR KR19997011163A patent/KR20010013178A/ko not_active Application Discontinuation
  • 1998-05-29 CA CA002292591A patent/CA2292591A1/en not_active Abandoned
  • 1998-05-29 DE DE19882438T patent/DE19882438T1/de not_active Withdrawn
  • 1998-05-29 JP JP50105999A patent/JP2002501578A/ja active Pending
  • 1998-12-03 ES ES009950067A patent/ES2168934B1/es not_active Expired - Lifetime
• 1999
  • 1999-11-26 GB GB9927865A patent/GB2340132A/en not_active Withdrawn
  • 1999-11-29 FI FI992549A patent/FI19992549A/fi unknown

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