US3420657A - Oxygen treatment of chromium alloys - Google Patents

Oxygen treatment of chromium alloys Download PDF

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Publication number
US3420657A
US3420657A US527214A US3420657DA US3420657A US 3420657 A US3420657 A US 3420657A US 527214 A US527214 A US 527214A US 3420657D A US3420657D A US 3420657DA US 3420657 A US3420657 A US 3420657A
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Prior art keywords
chromium
carbon
alloy
oxygen
pressure
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US527214A
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English (en)
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Donald J Hansen
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Elkem Metals Co LP
Umetco Minerals Corp
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Union Carbide Corp
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Assigned to ELKEM METALS COMPANY, A NEW YORK GENERAL PARTNERSHIP reassignment ELKEM METALS COMPANY, A NEW YORK GENERAL PARTNERSHIP ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: UNION CARBIDE CORPORATION, A NY CORP.
Assigned to UMETCO MINERALS CORPORATION reassignment UMETCO MINERALS CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: UNION CARBIDE CORPORATION
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C27/00—Alloys based on rhenium or a refractory metal not mentioned in groups C22C14/00 or C22C16/00
    • C22C27/06—Alloys based on chromium
    • 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
    • C21C7/068—Decarburising
    • C21C7/0685—Decarburising of stainless steel
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B9/00—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals
    • C22B9/04—Refining by applying a vacuum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys

Definitions

  • a process for rernOVing carbon from iron-chromiumcarbon alloys without substantial loss of chromium which comprises: providing a substantially slag-free molten mass of iron-chromium-carbon alloy, adjusting the starting composition of the alloy to provide between 75% and 15% chromium and a silicon content of less than about 3% and treating the molten alloy 'by blowing oxygen on the surface of said alloy, the pressure conditions at all times during oxygen treatment, for a particular metal temperature, being in the volume of the graph of the drawing which extends to the left of th plane corresponding to the chromium content of the alloy and in front of the plane corresponding to the desired final carbon content of the alloy.
  • the present invention relates to the oxygen treatment of chromium allows. More particularly, the present invention relates to the oxygen treatment of chromiumiron-carbon alloys to provide such alloys with a predetermined chromium-carbon content.
  • a process in accordance with the present invention for adjusting the chromium-carbon content of iron-chromiumcarbon alloys to provide at least a predetermined minimum chromium-to-carbon ratio in the final alloy comprises providing a substantially slag-free molten mass of ironchromium-carbon alloy at a temperature of at least about 50 C. above its melting point; adjusting the composition of the alloy to the extent necessary to provide a chromium content in the range of about to 75% and a silicon content of not more than 3 treating the molten alloy by blowing oxygen on the surface of said alloy and reducing the ambient pressure below atmospheric pressure to cause reaction of the oxygen and alloy, and
  • the alloys which can be effectively treated range from about 15 to Cr, up to 10% C balance iron and incidental amounts of other elements such as Mn, S, Si, P, Ni, Cb, Ta, and Mo.
  • the silicon content, if any, of the alloy to be treated be less than about 3% by weight. If necessary, the silicon content can be adjusted by the addition of suitable amounts of chromium, iron, or low-silicon iron-chromium alloy when the alloy is in the molten state and prior to oxygen treatment.
  • the broad reason for maintaining the silicon content below the aforesaid value is to substantially avoid the formation of slag on the surface of the alloy during oxygen treatment.
  • recovery of chromium is improved because any chromium that is inadvertently oxidized will not be dissolved in a slag with resultant loss in activity.
  • any chromium oxide formed can be readily redissolved with liberation of CO by suitable pressure reduction.
  • a further increase in chromium recovery can be realized since no fine metal droplets will be lost as suspended particles in a slag.
  • the absence of a slag allows the surface of the molten metal to be completely exposed to the reduced pressure which promotes escape of CO gas with resultant lowering of the carbon content.
  • CO gas can be trapped between the metalslag interface resulting in a higher CO partial pressure and less effective decarburization.
  • Another important consideration favoring a slagless operation is the effect on maximum temperature of operation. The maximum temperature of an oxygen blowing operation is usually limited by the vessel refractories. When a slag cover is present, eutectics form between slag and the refractory lining lowering the maximum temperature of operation.
  • the figures of the drawing represent relationships between chromium and carbon content for various temperature and pressure conditions during oxygen treatment which have been found to be effective only when the silicon content of the alloy being treated is below 3%.
  • FIGURE 1 shows an orthogonal, three dimensional graph in which the surfaces indicated as 1 and 1 correspond to the chromium contents desired in the final product and are referred to herein as chromium planes.
  • the two chromium planes illustrated in FIGURE 1 represent 70% Cr and 15% Cr which substantially covers the range of alloys suitably treated in accordance with the present invention.
  • FIGURE 1 also shows at 3 and 3 the intersection of temperature planes with the chromium planes for various temperatures from 1600 C. to 2000 C.
  • FIGURE 2 shows the 70% chromium plane of FIG- URE 1 and the intersection therewith of carbon planes corresponding to carbon contents of 0.01%, 0.05% and 0.1% and exemplary temperature planes.
  • the remaining FIGURES 3-5 show the chromium planes for 50%, 30% and chromium and the relationships therewith of carbon content, temperature, and pressure. Chromium planes for other Cr values can be readily obtained by interpolation or extrapolation.
  • a molten chromium-iron-carbon alloy is heated to initially provide a temperature about 50 C. or more above its melting point.
  • the metal is transferred to a suitable vessel, for example a magnesia lined reactor which is placed within a vacuum chamber and fitted with H a vacuum cover and oxygen is blown onto the surface of the molten metal for example using to 70 s.c.f.m. per sq. ft. of molten metal surface.
  • a suitable vessel for example a magnesia lined reactor which is placed within a vacuum chamber and fitted with H a vacuum cover and oxygen is blown onto the surface of the molten metal for example using to 70 s.c.f.m. per sq. ft. of molten metal surface.
  • the pressure is reduced to below atmospheric and controlled, together with the temperature of the molten metal surface as hereinafter described.
  • the ambient pressure over the metal bath can be adjusted by controlling the rate at which gases are exhausted from the system, using conventional vacuum equipment, preferably steam ejectors.
  • the temperature of the metal surface is adjusted by altering the rate at which oxygen is reacted with the surface of the metal knowing the initial temperature and the heat transfer characteristics of the reactor.
  • the temperature can be suitably measured by an immersion type thermocouple or by a suitably adapted optical pyrometer.
  • suitable pressure conditions employed during oxygen treatment lie in the volume of the graph of the drawing which is to the left of the 70% chromium plane at a particular operating temperature and in front of the carbon plane corresponding to 0.05 carbon.
  • oxygen treatment of a 70% Cr alloy at a metal temperature of 1800 C., and a pressure of 0.022 atmospheres provides the selective oxidation and removal of carbon to 0.05% without significant oxidation of chromium i.e., not more than 5% of the chromium is oxidized.
  • Operation at a lower pressure, e.g. 0.01 atmospheres can provide an even lower carbon content, as indicated at 5, before chromium is significantly oxidized, or permit the use of a lower temperature, as indicated at 7, to obtain a carbon content of 0.05 without chromium oxidation.
  • operation at a higher temperature will permit the use of a higher pressure.
  • the pressure should be to the left of the intersection of the chromium plane and in front of the carbon plane corresponding to the carbon content of the alloy. This means that initial pressure can be higher than the final pressure, but that under such circumstances, as the carbon content is decreased, the pressure must be decreased in accordance with the relationship shown in the drawing.
  • chromium oxidation in preference to carbon oxidation can be detected by a sharp decrease in the evolution of CO and CO from the surface of the molten alloy, regardless of the oxygen flow rate.
  • oxygen flow rate held constant, when chromium begins to oxidize in preference to carbon, the decreased amount of reaction gases will cause a sudden noticeable decrease in pressure, and this phenomena may be used in conjunction with the diagrams to control the composition of the desired alloy.
  • the conditions of temperature and pressure are controlled so that they coincide with the intersection of the desired final carbon and chromium planes, and oxygen treatment is terminated when a sudden pressure drop is observed since further oxygen treatment would lead to additional oxidation of chromium.
  • FIGURES 3 through 5 illustrate chromium planes for 50%, 30% and 15 chromium respectively. Also shown in FIGURES 35 are carbon plane intersections for 0.1%, 0.05% carbon and 0.01% carbon.
  • the graphs of these figures, and FIGURE 2 can be used following the aforedescribed procedure to define oxygen treatment operating conditions for other alloys merely by interpolating or extrapolating when the chromium contents or intended operating temperatures do not correspond to the particular values illustrated.
  • the chromium/carbon ratio of an iron-chromium-carbon alloy can be adjusted by the oxidation of chromium.
  • the starting alloy can contain 16% chromium and 0.05% carbon, and the desired alloy is one containing 15% chromium and 0.05% maximum carbon.
  • Molten alloy is provided at an initial temperature of about 1600 C., the pressure above the molten metal surface is reduced to below atmospheric, and oxygen is blown onto the surface of the alloy. As a result of the oxygen treatment, the temperature of the surface of the metal rises. Since it is desired to reduce the chromium content of the alloy, the temperature and ambient pressure are controlled in accordance with the present invention so as to be to the right of a 16% chromium plane and substantially coincident with the intersection of the 15% chromium plane and the 0.05% carbon plane.
  • chromium is oxidized and removed from the alloy in preference to carbon. That is to say, the chromium will be preferentially oxidized until the chromium content of the alloy is about 15%, then chromium oxidation will abruptly cease and carbon will be oxidized. The commencement of carbon oxidation will be evidenced by the evolution of CO and CO from the surface of the molten alloy.
  • EXAMPLE 1 Two thousand six hundred twenty pounds of molten iron-chromium-carbon alloy at 1710 C. contained in a magnesia-lined reactor were positioned in a vacuum shell. The analysis of the alloy was 66.8% chromium, 4.4% carbon, less than 0.5% silicon, balance iron. The pressure in the vessel was reduced to 0.44 atmosphere by means of steam ejectors, and 600 cubic feet of oxygen were introduced to the surface (3.40 sq. ft.) of the molten alloy through a water-cooled lance at a rate of c.f.m. causing the temperature of the alloy to increase. The pressure was reduced during the oxygen blow from 0.44 atmosphere to 0.21 atmosphere, after which the vacuum vessel was backfilled with air and the product sampled. The product analysis was 67.6% chromium, 2.7% carbon, less than 0.5 silicon, balance iron. Not more than 1.3% of the original chromium was lost through oxidation.
  • EXAMPLE 3 Into a magnesia-lined reactor was poured 2100 pounds of slag-free high-carbon ferrochrome analyzing 8.9% carbon, 63.5% chromium, less than 1% silicon, balance iron. The shell was closed and evacuated to 500 mm. Hg pressure using steam ejectors. Approximately 400 cubic feet of oxygen were introduced to the surface of the metal through a water-cooled lance according to the following schedule which was selected first to keep the pressure of the shell to the left of the chromium plane in FIGURE 2, second to reduce the amount of gases being evolved at lower pressures to minimize splashing, and third to provide an oxygen rate to bring the temperature of the alloy to about 1800 C.
  • a process for removing carbon from iron-chromiumcarbon alloys without substantial loss of chromium which comprises:

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Treatment Of Steel In Its Molten State (AREA)
US527214A 1966-02-14 1966-02-14 Oxygen treatment of chromium alloys Expired - Lifetime US3420657A (en)

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US52721466A 1966-02-14 1966-02-14

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US (1) US3420657A (de)
DE (1) DE1533950B1 (de)
FR (1) FR1511298A (de)
GB (1) GB1176731A (de)
NO (1) NO122378B (de)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2061122A1 (de) * 1970-01-05 1971-07-15 Allegheny Ludlum Ind Inc Verfahren zur kontrollierten Entkohlung von Metall-,insbesondere Stahlschmelzen unter vermindertem Druck in geschlossenen Gefaessen
US3773496A (en) * 1970-02-18 1973-11-20 Maximilianshuette Eisenwerk Process for producing chrome steels and a converter for carrying out the process
US3816100A (en) * 1970-09-29 1974-06-11 Allegheny Ludlum Ind Inc Method for producing alloy steel
US3850617A (en) * 1970-04-14 1974-11-26 J Umowski Refining of stainless steel
US4001009A (en) * 1969-04-03 1977-01-04 Hannsgeorg Bauer Process for the manufacture of steels with a high chromium content

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2114600B2 (de) * 1971-03-25 1981-05-07 Vacmetal Gesellschaft für Vakuum-Metallurgie mbH, 4600 Dortmund Verfahren zur gezielten Vakuumentkohlung hochlegierter Stähle
FR2343050A1 (fr) * 1976-03-05 1977-09-30 Nickel Sln Ste Procede perfectionne pour la fabrication d'aciers contenant du nickel
US5123957A (en) * 1988-11-11 1992-06-23 Nkk Corporation Method for manufacturing low carbon ferrochrome with high chromium content
US9210651B2 (en) 2005-10-27 2015-12-08 Qualcomm Incorporated Method and apparatus for bootstraping information in a communication system

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2093666A (en) * 1934-11-23 1937-09-21 Wacker Chemie Gmbh Process for treating iron and iron alloys
FR1343235A (fr) * 1962-12-21 1963-11-15 Nippon Kokan Kk Procédé pour la production de ferrochrome sans carbone

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2093666A (en) * 1934-11-23 1937-09-21 Wacker Chemie Gmbh Process for treating iron and iron alloys
FR1343235A (fr) * 1962-12-21 1963-11-15 Nippon Kokan Kk Procédé pour la production de ferrochrome sans carbone

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4001009A (en) * 1969-04-03 1977-01-04 Hannsgeorg Bauer Process for the manufacture of steels with a high chromium content
DE2061122A1 (de) * 1970-01-05 1971-07-15 Allegheny Ludlum Ind Inc Verfahren zur kontrollierten Entkohlung von Metall-,insbesondere Stahlschmelzen unter vermindertem Druck in geschlossenen Gefaessen
US3773496A (en) * 1970-02-18 1973-11-20 Maximilianshuette Eisenwerk Process for producing chrome steels and a converter for carrying out the process
US3850617A (en) * 1970-04-14 1974-11-26 J Umowski Refining of stainless steel
US3816100A (en) * 1970-09-29 1974-06-11 Allegheny Ludlum Ind Inc Method for producing alloy steel

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Publication number Publication date
NO122378B (de) 1971-06-21
GB1176731A (en) 1970-01-07
DE1533950B1 (de) 1971-03-11
FR1511298A (fr) 1968-01-26

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Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:UNION CARBIDE CORPORATION, A NY CORP.;REEL/FRAME:003882/0838

Effective date: 19810618

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Effective date: 19850402