US3837841A - Process for controlled removal of carbon under vacuum from highly alloyed steels - Google Patents

Process for controlled removal of carbon under vacuum from highly alloyed steels Download PDF

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Publication number
US3837841A
US3837841A US00235506A US23550672A US3837841A US 3837841 A US3837841 A US 3837841A US 00235506 A US00235506 A US 00235506A US 23550672 A US23550672 A US 23550672A US 3837841 A US3837841 A US 3837841A
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melt
temperature
oxygen
carbon
percent
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US00235506A
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English (en)
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H Kutscher
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Vacmetal Gesellschaft fuer Vakuum Metallurgie mbH
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Vacmetal Gesellschaft fuer Vakuum Metallurgie mbH
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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
    • C21C7/068—Decarburising
    • C21C7/0685—Decarburising of stainless steel
    • 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

Definitions

  • ABSTRACT In a process for removing carbon from a highlyalloyed steel, such as a chrome steel, the steel is treated by blowing oxygen into or on to the molten steel in a vacuum vessel to remove carbon from the melt. The temperature of the gases extracted from the vessel is monitored to detect an abrupt drop in the gas temperature, at which point the oxygen treatment is arrested and the temperature of the melt is immediately measured. The composition of the melt is then corrected on the basis of the known equilibrium concentration of carbon and chrome, or other constituent, which occurs at that measured melt temperature. The composition of the melt may be corrected either by adding further alloying substances thereto, or by further oxygen treatment, as the situation requires.
  • This invention relates to a process for removing carbon from highly-alloyed steels by blowing gaseous oxygen on to or into the molten steel under vacuum.
  • a high carbon alloy steel which has been refined in the conventional manner is introduced into a vacuum vessel and carbon is removed until the extracted gases show an abrupt temperature drop, whereupon th melt temperature is measured and the composition of the melt is corrected on the basis of the known equilibrium concentrations of carbon and chromium or other constituent at the measured melt temperature.
  • the concentrations of chromium, nickel, phosphorous and sulphur being adjusted approximately to the desired values.
  • the carbon concentration in the melt is considerably higher than the desired final concentration, to prevent excessive loss of chromium.
  • the carbon concentration can, for example, be between 0.2 and 1 percent.
  • the absolute pressure over the melt decreases down to ap proximately Torr.
  • oxygen is introduced into the vacuum vessel by means of a lance, the oxygen being blown either on to the surface of the melt or into the body of melt.
  • the resulting reaction raises the temperature of the melt by an amount which depends on the rate of feed of oxygen.
  • the rise in the temperature of the extracted gas is utilised for monitoring the process of carbon removal.
  • the vacuum pumps can, for example, be dimensioned so as to ensure that, in spite of the CO produced, the pressure in the vacuum vessel remains between 10 Torr and 30 Torr. It has been found by making tests that, in large scale production, if the pressure is held between these two values the carbon concentration in the melt is brought down with economically tolerable rapidity to a value at which the CO equilibrium corresponds to a pressure of approximately 50 Torr. At this pressure, the carbon concentration in the melt depends on the oxygen concentration in the melt and this depends on the melt temperature and on the chromium concentration in the melt.
  • the highest oxygen concentration which is possible without losing chromium into the slag increases with melt temperature. Consequently the final carbon concentration is lower as the melt temperature increases.
  • the desired equilibrium final carbon concentration is reached only after blowing with oxygen and evacuating the gases produced for long enough to complete the CO reaction. When equilibrium is reached, the CO reaction ceases. Further blowing then results in loss of chromium into the slag. The attainment of equilibrium is indicated by an abrupt temperature fall in the extracted gases, due to the fact that the exothermal reaction between the carbon and the oxygen, with evolution of CO, has ceased.
  • the carbon concentration in the melt is monitored by measuring the melt temperature at the instant of the temperature fall in the evacuated gases. If the carbon concentration is too low, that is to say if it is below the desired final value, carbon can be added without delay to the melt under vacuum. On the other hand, if the carbon concentration is too high there is added to the melt under vacuum an element which has a high affinity for oxygen and reacts with oxygen strongly exothermally, for example silicon.
  • the quantity of silicon added to the melt is chosen so that, in its reaction with the oxygen fed into the melt, sufficient heat is produced to raise the temperature of the melt to the temperature which corresponds to the desired carbon concentration.
  • oxygen is blown briefly, raising the melt temperature and lowering the carbon concentration down to the desired value. Once more the attainment of equilibrium is indicated by an abrupt drop in the temperature of the extracted gas.
  • the process described above can, of course, if desired be conducted in a different way.
  • the required initial melt temperature at the beginning of the vacuum treatment can be calculated from the final melt temperature corresponding to the desired carbon concentration, the heat which can be expected to be lost during the degassing without oxygen feed, and the heat which will be released by the CO reaction.
  • the initial melt temperature is adjusted. If the melt in the furnace is too hot, its temperature can be adjusted downwards during the tapping off procedure. If the melt in the furnace is too cool, its temperature can be adjusted upwards, either before or during the vacuum treatment by adding the quantity of silicon necessary to give the correct final melt temperature, at the end of the vacuum treatment, corresponding to the desired final carbon concentration.
  • the initial melt temperature, at the beginning of the vacuum treatment can be calculated in the known way from the following equation:
  • T is the calculated tapping temperature.
  • T is the final temperature corresponding to the de' sired final carbon concentration, as represented in the diagram.
  • T is the temperature drop occurring during tapping off from the furnace.
  • T is the loss of temperature in the melt in the vacuum pan between the end of the tapping procedure and the end of the blow period.
  • the blow period can be assumed with sufficient accuracy to be between and minutes.
  • the quantity T is the sum of several operational quantities which can easily be measured.
  • T is the total heat of reaction released by the reaction between oxygen and carbon and by the reactions between oxygen and other elements.
  • the quantity T can be calculated from the following equation:
  • Example 1 A 50 tonne melt of the following composition was tapped from a furnace:
  • a melt was tapped at a temperature of 1,630C.
  • the ladle was introduced into a vacuum vessel and a vacuum applied.
  • the melt contained a certain concentration of oxygen and consequently a slight CO reaction took place, resulting in the carbon concentration decreasing by approximately 0.02 percent.
  • an oxygen lance was introduced into the vacuum vessel over the surface of the melt.
  • Oxygen was fed at a rate of 1,800 kg/h. A strong CO reaction took place, the effluent gas temperature rising from an initial 300C up to approximately 500C. At the end of approximately 12 minutes, the effluent gas temperature abruptly dropped. The oxygen feed was immediately cut off. The temperature of the melt was found to be 1,770C. From the diagram this corresponds to a carbon concentration in the melt of 0.01 percent.
  • the composition of the melt was corrected by adding:
  • Example 2 A 50 tonne melt tapped from the furnace had the composition:
  • the tapping temperature was 1,600C.
  • the pressure in the vacuum vessel was brought down to 10 Torr, whereupon oxygen was fed at the rate of l .000 kg/ h.
  • the effluent gas temperature dropped, the melt now showing a temperature of 1,670C. From the diagram this corresponds to a carbon concentration of 0.022 percent.
  • the specification called for a carbon concentration of at most 0.03 percent, with at least 17.5 percent chromium. It was therefore necessary to add at least 1 percent of chromium.
  • Ferrochrome was added containing 1.5 percent carbon, involving an increase of the order of0.021 percent in the carbon concentration. There were therefore added to the melt 750kg of ferrochrome (70 percent Cr) and 130 kg of ferrosilicon (75 percent Si).
  • the process therefore makes it possible to control the vacuum treatment in such a way that the desired low carbon concentration is obtained, without timeconsuming analyses and without serious chromium losses.
  • the process is therefore particularly suitable for application in high output technology.
  • the process is also applicable to other types of highly-alloyed steels, besides the chrome steel described above.
  • a process of removing excess carbon from alloy steel containing an excess amount of carbon which comprises:

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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)
US00235506A 1971-03-25 1972-03-17 Process for controlled removal of carbon under vacuum from highly alloyed steels Expired - Lifetime US3837841A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE2114600A DE2114600B2 (de) 1971-03-25 1971-03-25 Verfahren zur gezielten Vakuumentkohlung hochlegierter Stähle

Publications (1)

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US3837841A true US3837841A (en) 1974-09-24

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US00235506A Expired - Lifetime US3837841A (en) 1971-03-25 1972-03-17 Process for controlled removal of carbon under vacuum from highly alloyed steels

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US (1) US3837841A (de)
JP (1) JPS5428370B1 (de)
CS (1) CS216653B2 (de)
DE (1) DE2114600B2 (de)
FR (1) FR2130350B1 (de)
GB (1) GB1329216A (de)
IT (1) IT952335B (de)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2551089A1 (fr) * 1983-08-26 1985-03-01 Lenin Kohaszati Muvek Procede de fabrication d'aciers a faible teneur en carbone par reglage du point de decarburation et de la temperature de soufflage
US4732607A (en) * 1985-11-26 1988-03-22 Sumitomo Metal Industries, Ltd. Method of controlling the stirring strength and flow rate of a jet of gas blown through a lance onto a molten metal surface
AU622678B2 (en) * 1988-06-21 1992-04-16 Kawasaki Steel Corporation Process for vacuum degassing and decarbonization with temperature drop compensating feature

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5394214A (en) * 1977-01-31 1978-08-18 Kawasaki Steel Co Denitriding method of high chrome molten steel with small chrome loss
ATE203778T1 (de) * 1995-11-17 2001-08-15 Sms Demag Ag Verfahren zur entkohlung von stahlschmelzen

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3003865A (en) * 1959-09-10 1961-10-10 Cameron Iron Works Inc Decarburizing process for alloy steels containing chromium
US3450867A (en) * 1966-03-14 1969-06-17 Leeds & Northrup Co Estimated tap temperature calculator for basic oxygen furnace
US3528800A (en) * 1966-02-14 1970-09-15 Leeds & Northrup Co Optimized blowing control for basic oxygen furnaces
US3640119A (en) * 1966-02-14 1972-02-08 Leeds & Northrup Co Carbon content measurement in a basic oxygen furnace
US3645718A (en) * 1967-10-09 1972-02-29 Crucible Inc Method for making steel
US3666439A (en) * 1970-03-02 1972-05-30 Allegheny Ludlum Ind Inc Method of decarburizing alloy steels
US3669645A (en) * 1966-05-23 1972-06-13 Nippon Steel Corp Method for operating an oxygen top-blowing converter

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3420657A (en) * 1966-02-14 1969-01-07 Union Carbide Corp Oxygen treatment of chromium alloys

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3003865A (en) * 1959-09-10 1961-10-10 Cameron Iron Works Inc Decarburizing process for alloy steels containing chromium
US3528800A (en) * 1966-02-14 1970-09-15 Leeds & Northrup Co Optimized blowing control for basic oxygen furnaces
US3640119A (en) * 1966-02-14 1972-02-08 Leeds & Northrup Co Carbon content measurement in a basic oxygen furnace
US3450867A (en) * 1966-03-14 1969-06-17 Leeds & Northrup Co Estimated tap temperature calculator for basic oxygen furnace
US3669645A (en) * 1966-05-23 1972-06-13 Nippon Steel Corp Method for operating an oxygen top-blowing converter
US3645718A (en) * 1967-10-09 1972-02-29 Crucible Inc Method for making steel
US3666439A (en) * 1970-03-02 1972-05-30 Allegheny Ludlum Ind Inc Method of decarburizing alloy steels

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2551089A1 (fr) * 1983-08-26 1985-03-01 Lenin Kohaszati Muvek Procede de fabrication d'aciers a faible teneur en carbone par reglage du point de decarburation et de la temperature de soufflage
US4732607A (en) * 1985-11-26 1988-03-22 Sumitomo Metal Industries, Ltd. Method of controlling the stirring strength and flow rate of a jet of gas blown through a lance onto a molten metal surface
AU622678B2 (en) * 1988-06-21 1992-04-16 Kawasaki Steel Corporation Process for vacuum degassing and decarbonization with temperature drop compensating feature

Also Published As

Publication number Publication date
GB1329216A (en) 1973-09-05
CS216653B2 (en) 1982-11-26
FR2130350A1 (de) 1972-11-03
FR2130350B1 (de) 1976-08-06
DE2114600A1 (de) 1972-10-05
IT952335B (it) 1973-07-20
JPS5428370B1 (de) 1979-09-17
DE2114600B2 (de) 1981-05-07

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