US3615356A - Basic steelmaking process - Google Patents

Basic steelmaking process Download PDF

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US3615356A
US3615356A US776417A US3615356DA US3615356A US 3615356 A US3615356 A US 3615356A US 776417 A US776417 A US 776417A US 3615356D A US3615356D A US 3615356DA US 3615356 A US3615356 A US 3615356A
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oxygen
fuel
percent
refining
stage
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Hugh W Grenfell
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British Steel Corp
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British Steel 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
    • 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
    • C21C5/30—Regulating or controlling the blowing
    • C21C5/32—Blowing from above

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  • White Attorney-Buell, Blenko & Ziesenheim ABSTRACT A basic steelmaking process for refining a charge of steel scrap, molten pig iron and basic slag-making material in a converter-type vessel employing hot refining gases comprising products of combustion and uncombined oxygen directed downwardly toward the charge at high velocity from a burner-type lance comprising the successive stages: (I) a fuel-fired slag-making, bath-conditioning and preliminaryrefining stage employing a stream of'hot refining gas relatively rich in combustion products and a relatively poor in uncombined oxygen; (11) a fuel-fired decarburization-refining stage employing a stream of hot refining gas relatively poor in combustion products and relatively rich in uncombined oxygen; and (III) a fuel-fired terminal-refining and regulating stage employing a stream of hot refining gas relatively rich in combustion products and relatively poor in uncombined oxygen.
  • This invention relates to a basic steelmaking process, that is a steelmaking process which requires the presence of a basic slag for the removal of phosphorus and sulfur impurities present in molten crude iron.
  • the three basic steelmaking processes most widely heretofore employed for the refining of molten crude iron into steel are the basic open hearth process, the Thomas or basic Bessemer process, and the basic oxygen (BOF") process.
  • open hearth practice the heat required for refining is supplied by combustion of a liquid or gaseous hydrocarbon fuel with air.
  • the Thomas and BOF processes are autogenous, that is the heat required for refining is supplied by the heat of reac tion of iron impurities with oxygen.
  • Each of the foregoing basic steelmaking processes has characteristic advantages and disadvantages.
  • conventional open hearth practice where the heat required for refining the charge is supplied externally by the combustion of a fuel with air, a high degree of process control over tapping temperature and molten metal bath composition is attainable.
  • the open hearth practice permits the use of a high percent of scrap in the charge, typically 50-65 percent by weight.
  • Basic open hearth steelmaking has the disadvantage that the time per heat is long, 6 to 10 hours, with correspondingly large fuel consumption.
  • an elaborate refractory checkerwork is required for efficient energy utilization, and charging the furnace is a time consuming and tedious operation.
  • the Thomas or basic Bessemer process is an autogenous process wherein a molten ferrous metal charge is refined into steel in a converter type vessel usually by passing air into the charge through tuyeres in the bottom of the vessel.
  • the Thomas process is limited for practical purposes to the refining of high phosphorus crude iron (pig iron).
  • the process requires a two-slag practice in which a first slag is employed during a decarburization blow and a second slag with ferromanganese is employed during he dephosphorization blow.
  • the Thomas process scrap is used to control the temperature of the refining, and scrap practice is therefore critical with time of scrap-addition varying with the type of scrap available.
  • Thomas steel generally has a higher oxygen content and definitely has a higher nitrogen content than steels produced by the other basic steelmaking processes. It is therefore, inadequate for certain applications because of lower ductility and susceptibility to strain-aging.
  • a charge of molten crude iron and steel scrap in an open-top converter is refined into steel by subject ing it to a cold jet of oxygen directed downwardly from a lance at supersonic velocity toward the charge.
  • the BOF process has a considerable advantage over the open hearth process in that it is possible to refine a charge comparable to that in an open hearth furnace, e.g. 200 tons, in a about to minutes with an overall tap-to-tap time of about 50 minutes.
  • the BOF process has however certain disadvantages. BOF scrap charge is limited to about 27 percent to 32 percent by weight (compared to 50 percent to 65 percent) typically in an open hearth furnace) and many BOF facilities produce more scrap internally than can be used in their own in-shop converters.
  • the BOP process does not provide control over the proportions of metals such as manganese, in the steel produced.
  • the manganese content of the melt atturn down is on the order of 0.0l percent by weight.
  • a proportion of 0.3 percent to 0.4 percent by weight of manganese is desirable in the steel to improve the rolling properties, and it is necessary to add considerable quantities of ferromanganese to the ladle before casting a good rolling grade steeL'The ferromanganese addition is expensive and also can result in nitrogen contamination of the metal which has a detrimental effect on the steel quality.
  • My basic steelmaking process substantially obtainsthe advantages yet does not suffer from the disadvantages of the basic steelmaking processes heretofore known. It is a versatile basic steelmaking process having high capacity, short tap-totap time controllable fume emission, variable scrap accommodation, and ability to reach. with regularity desired predetermined carbon and temperature end-points without the necessity of an end-point correction.
  • My process is a basic steelmaking process for refining into steel a charge comprising molten crude iron and steel scrap in a converter vessel employing hot refining gases directed downwardly to the charge at high velocity from a burner-type lane fed by oxygen and a liquid hydrocarbon fuel to provide a hot refining gas stream consisting of combustion products and uncombined oxygen and which process comprises (l) a slagforming, bath-conditioning, and prelimiary-refining stage wherein the refining gas stream is relatively rich in combustion products and relatively poor in uncombined oxygen: (ll) a decarburization-refining stage wherein the refining gas stream is relatively poor in combustion products and relatively rich in uncombined oxygen; and (III) a terminal-refining and regulating stage in which the refining gas stream is relatively rich in combustion products and relatively poor in uncombined oxygen.
  • the refining gas stream is essentially nitrogen-free since the components of the stream are combustion products of a hydrocarbon fuel
  • FIG. l is a flow diagram of the process of my invention
  • FIG. 2 is a sectional view of an open-top converter-type vessel having a lance suitable for use in the practice of my invention
  • FIG. 3 is a lance used in the practice of a present preferred embodiment of the process of my invention.
  • FIG. l in the steelmaking process of my invention there is first charged to a converter type vessel molten crude iron (pig iron) and solid scrap.
  • the converter vessel is equipped with a burner-type lance movable vertically into and out from the open top of the vessel as shown in FIG. 2.
  • the process of the invention comprises three successive refining stages hereinafter referred to for convenience as Stage I" "Stage ll, and Stage lll.”
  • Stage I Stage ll, and Stage lll
  • After charging the vessel streams of oxygen and fuel oil are fed to the lance, mixed within a lance mixing nozzle, and ejecting from the lance. Ignition of the fuel oil is instantaneous and ignition of the metal occurs almost immediately thereafter.
  • streams of liquid carbonaceous fuel and highpurity oxygen are fed with a burner-type lance having a mixing nozzle for mixing the streams of fuel and oxygen to provide a flame surrounded by a substantially pure oxygen envelope.
  • the surrounding envelope presents uncombusted fuel from contacting the melt or reactive portions of the slag thereby preventing the introduction of fuel-contained impurities into the charge.
  • Slag forming materials may be part of the initial charge but usually are added to the charge 1 or 2 minutes after ignition.
  • the slag-forming materials may be, e.g. lime, limestone, dolomitic lime or mixtures thereof.
  • Stage I of the process is essentially a slag-forming, bath-conditioning, and preliminary stage in which streams of oxygen and liquid carbonaceous fuel are flowed to the lance in proportions to produce a stream of hot gas relatively rich in combustion products and relatively poor in uncombined oxygen.
  • Stage I oxygen is flowed to the lance in a quantity in excess of that required for complete combustion of the fuel, thereby providing uncombined oxygen in the refine gases.
  • the excess oxygen flowed to the lance in State I while small when compared to the excess employed in Stage II, insures complete combustion of the fuel, prevents introduction of fuel-contained impurities into the charge, and provides uncombined oxygen for preliminary refining. The excess is not so great as to initiate a vigorous early carbon boil as in the BOF process.
  • the hot refining gases of Stage I are oxygen-starved relative to BOF refining as (undiluted oxygen) and the typical early refining reactions of silicon and carbon therefore proceed at a greatly reduced rate in comparison with BOF refining.
  • the hot (typically 4000-6000 F.) refining gases of Stage I aid of fiuxing the slag-making materials to provide a reactive fluid slag within the first few minutes of refining.
  • a reactive basic slag is thus formed in my process in advance of excessive said silica formation, thereby reducing silica attack of the converter's basic refractory lining.
  • the foregoing is in contrast to the autogenous BOF process wherein slag development is dependent upon heat produced by exothermic refining reactions of cold oxygen with impurities in the crude iron charged to the converter.
  • the excess oxygen employed in Stage I may be within the range 25 percent to 300 percent in excess of the quantity of oxygen theoretically required for complete combustion of the fuel. it is preferred an oxygen excess of 50to l50percent is employed and typicallyan oxygen excess of 60to 70 percent is used.
  • An excess of uncombined oxygen in Stage I greater than about 300 percent results in relatively poor slag making and bathconditioning since a cooler flame is obtained in the higher excess range and also since higher excesses cause excessive refining reactions, especially silicon refining reactions, at a point too early in the process.
  • An excess of less than 25 percent results in unnecessary lengthening of refining time, and in poor heat transfer efficiency of the oil burnt.
  • the low excess can cause a high percentage of iron oxide to remain in the slag, thereby decreasing the yield due to a "soft" blow.
  • the preferred excesses may vary, however, in the case that there is employed in the process a fuel of substantially different heating value and/or an oxygen supply rate substantially different from those as discussed in the examples.
  • the hot gas issuing from the flame at the lower end of the lance in Stage I is usually itself sufficient to flux the slag making' material such as lime, limestone or dolomitic lime without the use of additional fluxing agents.
  • Conventional fiuxing agents, such as fiuorspar or millscale may however be added to further accelerate formation of the fluid slag and to assist in an early phosphorus removal in the process.
  • Stage I generally is of duration about 4-l0 minutes during which time a considerable quantity of phosphorus and sulfur impurities present in the charge and some carbon and silicon are refined.
  • a manganese-content of 0.30 percent to 0.40 percent by weight improves the rolling properties of the steel considerably. In other applications it is desirable to have as low a manganese content as possible. Even in the case of crude iron having a fairly high concentration of manganese, normal BOF refining reduces the manganese content in the steel produced to typically less than 0.15 percent and the balance has to be made up by the addition of ferromanganese in the ladle.
  • the manganese content in the steel produced by my process may be effected by varying the duration of Stage 1. Generally, if a high manganese content is desired then a short Stage I will provide a steel having a manganese content relatively high when compared to steel produced in BOF refining of the same crude iron charge. If a low manganese content is desired a long Stage I will provide a steel relatively low in manganese content when compared to steel produced in BOF refining of the same crude iron charge. Thus the duration of Stage I may be selected to control the manganese in the steel produced.
  • Stage II of my process a major decarburization of the molten crude iron takes place.
  • fuel and oxygen are flowed to the burner-type lance in proportions to produce a hot refining gas rich in uncombined oxygen and poor in combustion products.
  • the excess is about 1000 percent-1300 percent over that required to effect complete combustion of the fuel.
  • the great excess of uncombined oxygen present in the refining gas of Stage ll initiates a vigorous carbon boil in the melt and a major portion of the carbon refining in the process occurs during this stage.
  • the refining gas stream issuing from the burner-type lance in Stage ll is comprised of about percent to percent by weight hot uncombined oxygen the remaining portion being combustion products.
  • the hot refining gases typically at a temperature of the order of 2500 F. to 3000 F. in Stage ll, assist in maintaining the slag fluid by preventing slag chilling, which can occur in the BOF process where oxygen at a temperature of l50 F. is blown onto the charge.
  • Stage ll is generally within the range 8 to 15 minutes, more or less, depending for example upon the desired carbon and temperature end points. Also, Stage ll duration is dependent on the proportion of scrap included in the charge. In general the higher the proportion of scrap in the charge the shorter the duration of Stage II.
  • Stage III is a terminal refining and regulating stage.
  • fuel and oxygen are flowed to the burner-type lance in proportions to produce a hot refining gas relatively rich in combustion products and relatively poor in uncombined oxygen.
  • the excess of oxygen flowed to the lance is about 25 percent -200 percent in excess of that quantity required for complete combustion of the fuel.
  • the hot refining gases provided in Stage III have sufficient uncombined oxygen to complete the refining of the charge at a rate whereby the carbon and temperature end points are approached at a gradual, controllable rate. This is in contrast with the autogenous BOF blow in which a cold stream of oxygen is blow into the charge throughout refining, affording no means of close process control.
  • the duration of Stage Ill depends upon the overall heat balance of the process and also upon the duration of Stages l and ll. For example, a given quantity' of heat is required for refining, scrap-melting and reaching a desired turndown temperature (typically 2900-3000" F.) in a Steelmaking process. Part of the heat for melting the scrap and reaching the desired turndown temperature in my process is supplied by way of exothermic refining reactions and part is supplied as sensible heat in the hot refining gases. For example, after a total required amount of heat for refining a given charge has been determined, the amount of additional heat required to be added to the bath by way of fuel combustion can be calculated. Whatever part of the calculated fuel requirement is not burned in Stage I and ll is burned in Stage llll. Stage III generally endures from the end of Stage ll until the refining is complete and typically may be about -15 minutes.
  • the total refining time of my process is generally 20 to 30 minutes, but can be varied as necessary or desirable and depends to a degree on such factors as available oxygen, capacity of converter vessel, fuel characteristic and lance characteristics. Generally, the greater the oxygen availability, the shorter will be the overall refining time.
  • streams of hydrocarbon fuel, preferably a liquid carbonaceous fuel, and substantially pure oxygen are in each of the refining stages flowed to a burner-type lance having means for contacting and mixing the fuel and oxygen to form a fuel-oxygen stream, and means for ejecting the fuel-oxygen stream from the lance at supersonic velocity to eliminate or reduce turbulance in the stream.
  • Turbulance is generally to be avoided since a nonturbulant stream is important for effectively delivering the hot refining gases to the charge being refined.
  • the radiant heat from the vessel walls and charge is sufficient to cause ignition of the mixed fuel-oxygen stream to produce a flame (c.f. FIG. 2) extending from the discharge orifices of the lance.
  • the hot refining gases emitting from the flame comprise combustion products and oxygen and are directed generally downwardly and outwardly from the lance toward the charge at a high velocity.
  • the lance comprises an elongate body member 11 which is provided with a combined delivery and burner nozzle 12 at the lower end thereof.
  • the interior of the body member ll of the lance is built up with a number of annular passageways and conduits by which oxygen and liquid fuel are supplied to a plurality of discharge orifices 13 formed in the combined delivery and burner nozzle 12.
  • the number of nozzles is determined to some extent by the size of the refining vessel. For example, with small converters, e.g.
  • a fuel oil supply conduit comprising a pipe M is preferably located centrally of the body member 11 of the lance 2.
  • a plurality of pipes 16 are welded at 15 to the lower end of the pipe 14 and extend downwardly therefrom, the pipes 16 corresponding in number to the number of discharge orifices 113.
  • Nozzle 12 has a plurality of oxygen supply pipes 21 disposed at an angle to the longitudinal axis of the lance communicating with oxygen supply conduit 18 and incorporating means such as venturi 33 for accelerating the oxygen.
  • the fuel supply conduit is preferably provided with an annular jacket disposed between the oil conduit and the oxygen supply con duit to insulate preheated fuel in the fuel supply conduit. This is necessary since when using heavy grades of fuel oil, the low temperature of the oxygen passing down the oxygen supply conduit 18 chills the oil and may prevent oil flow.
  • the fuel supply conduit 14 is provided at its outlet end with a plurality of fuel supply pipes 23 extending therefrom and each having its end portion secured in the corresponding oxygen supply pipe Zll so that oxygen flowing through said supply pipes to the discharge orifices will flow in an annulus around the end of the corresponding fuel supply pipes whereby fuel will be entrained in the oxygen supplies when discharged from the discharge orifices.
  • the lance-nozzle arrangement provides for the entrainment of fuel in a substantially pure stream of oxygen which when ejected from the lance nozzle will ignite to provide a short process of the present invention.
  • EXAMPLE An open-top converter was charged with 269,000. lbs. of molten pig iron (crude iron), 176,000 lbs. of steel scrap and 15,600 lbs. of cold pig iron (corresponding to 58.5 percent, 38.3 percent and 3.2 percent respectively by weight of the charge).
  • the pig iron analysis was: carbon 4.56 percent, manganese 0.95 percent, phosphorus 0.09 percent and silicon 0.70 percent.
  • the molten iron was at a temperature of 2450 F.
  • a burner-type lance of the character shown in FIG. 3 and described hereinabove having four discharge orifices was lowered into the vessel to a height of inches above the quiescent bath surface. There was flowed to the lance during Stage I a Bunker C fuel oil having a.
  • Stage I was: ended and the fuel rate was reduced to 4 gallons per minute.
  • the oxygen flow rate was left unchanged to provide an excess of 1300 percent over that quantity required for complete combustion of the fuel in Stage II. With the decrease in oil rate the decarburization of the molten metal proceeded vigorously.
  • Stage ll refining was continued for 8 minutes after which the fuel oil rate was increased to 35 U.S. gallons per minute (65 percent of excess of oxygen) and held at that rate for 16 more minutes in Stage III to give a total blowing time of 28 minutes.
  • Oxygen flow was left unchanged in Stage ill. The vessel was turned down at a tem perature of 2920 F.
  • a basic steelmaking process for refining to steel a charge of molten crude iron, steel scrap and basic slagmaking material in a converter vessel employing hot refining gases directed downwardly to the charge at a high velocity from a burner-type lance comprising successively:
  • a basic steelmalting process comprising:
  • said lance being movable into and out-from said vessel through said open-top;
  • said lance having a delivery nozzle at one end thereof through which fluids may pass;
  • said delivery nozzle having a plurality of discharge orifices
  • discharge orifices being positioned whereby fluids passing therethrough are directed generally downwardly and outwardly;
  • said first refining stage being bath-conditioning and preliminary refining stage wherein said stream of liquid carbonaceous fuel and high-purity oxygen are flowed to the lance with oxygen in the range of about 25 percent to 300 percent in excess of the quantity theoretically required for complete combustion of the fuel to produce a stream of hot gas relatively rich in combustion products and relatively poor in uncombined oxygen and continuing the stage substantially until a desired slag layer is formed;
  • said second refining stage being a decarburization-refining stage wherein said streams of hot liquid carbonaceous fuel and high-purity oxygen are flowed to the lance with oxygen in the range of about 1000 percent to 1300 percent in excess of that theoretically required for combustion of the fuel to produce a stream of hot gas relatively poor in combustion products and relatively rich in uncombined oxygen, and continuing the stage substantially until major and substantial decarburization takes place; and
  • said third blowing stage being a terminal-refining and regulating stage wherein said streams of liquid carbonaceous fuel and high-purity oxygen are flowed to said lance with oxygen in the range of about 25 percent to 200 percent in excess of that theoretically required for complete combustion of the fuel to produce a stream of hot gas relatively rich in combustion products and relatively poor in uncombined oxygen, and continuing the stage substantially until refining is completed.
  • said oxygen is flowed to said lance in said first stage in a quantity of from about 50 percent to l50 percent in excess of quantity of oxygen theoretically required for complete combustion of the fuel
  • said oxygen is flowed to said lance in said second refining stage in a quantity of from about 1000 percent-1300 percent in excess of that quantity of oxygen theoretically required for complete combustion of the fuel;
  • said oxygen is flowed to said lance in said third stage in a quantity from about 25 percent-200 percent in excess of that quantity of oxygen theoretically required for complete combustion of the fuel.
  • a process according to claim 4 wherein the charge entered into the converter comprises molten pig iron, ferrous scrap, and slag-forming materials.
  • a process for the refining of a ferrous metal charge to steel in a converter vessel by employing hot refining gases directed downwardly to the charge at high velocity from a nozzle fed by oxygen and fuel to provide a refining gas stream comprising combustion products and uncombined oxygen which process comprises a first slag forming stage in which oxygen is supplied in the range of about 25 percent to 300 percent in excess of the quantity theoretically required for complete combustion of the fuel and the gas is relatively poor in uncombined oxygen; a second decarburising stage in which oxygen is supplied in the range of about 1000 percent to 1300 percent in excess of the quantity theoretically required for combustion of the fuel and the gas stream is relatively rich in uncombined oxygen; and a third correction stage in which oxygen is supplied in the range of about 25 percent to 200 percent in excess of the quantity theoretically required for complete combustion of the fuel and the gas stream is relatively poor in uncombined oxygen.
  • a process as claimed in claim 7 wherein the oxygen excess during the first stage of the process is about 60 percent to percent of the quantity of oxygen theoretically required for complete combustion of the fuel.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Carbon Steel Or Casting Steel Manufacturing (AREA)
  • Nozzles For Spraying Of Liquid Fuel (AREA)
  • Gas Burners (AREA)
  • Pre-Mixing And Non-Premixing Gas Burner (AREA)
US776417A 1968-09-26 1968-11-18 Basic steelmaking process Expired - Lifetime US3615356A (en)

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JP (1) JPS5412405B1 (enrdf_load_stackoverflow)
BE (1) BE730471A (enrdf_load_stackoverflow)
CH (1) CH516641A (enrdf_load_stackoverflow)
DE (1) DE1914645B2 (enrdf_load_stackoverflow)
FR (1) FR2018884A1 (enrdf_load_stackoverflow)
GB (1) GB1209987A (enrdf_load_stackoverflow)
LU (1) LU58299A1 (enrdf_load_stackoverflow)
NL (1) NL6904586A (enrdf_load_stackoverflow)
NO (1) NO125893B (enrdf_load_stackoverflow)
SE (1) SE364728B (enrdf_load_stackoverflow)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5322547A (en) * 1992-05-05 1994-06-21 Molten Metal Technology, Inc. Method for indirect chemical reduction of metals in waste
US5374297A (en) * 1993-01-05 1994-12-20 Steel Technology Corporation Lance for fuel and oxygen injection into smelting or refining furnace
RU2272078C1 (ru) * 2005-08-16 2006-03-20 ЗАО "Патентные услуги" Способ получения стали
US20120060650A1 (en) * 2009-05-15 2012-03-15 Istc Co., Ltd Method for manufacturing molten iron

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1003514A (en) * 1961-05-10 1965-09-02 Steel Co Of Wales Ltd Improvements in steel manufacture
GB1119833A (en) * 1963-11-11 1968-07-17 British Iron Steel Research Improvements in or relating to steelmaking processes
FR1422692A (fr) * 1964-01-27 1965-12-24 Steel Co Of Wales Ltd Perfectionnements apportés à la fabrication de l'acier
GB1148601A (en) * 1966-02-16 1969-04-16 Steel Co Of Wales Ltd Improvements in and relating to the refining of metals

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5322547A (en) * 1992-05-05 1994-06-21 Molten Metal Technology, Inc. Method for indirect chemical reduction of metals in waste
US5324341A (en) * 1992-05-05 1994-06-28 Molten Metal Technology, Inc. Method for chemically reducing metals in waste compositions
US5358549A (en) * 1992-05-05 1994-10-25 Molten Metal Technology, Inc. Method of indirect chemical reduction of metals in waste
US5374297A (en) * 1993-01-05 1994-12-20 Steel Technology Corporation Lance for fuel and oxygen injection into smelting or refining furnace
RU2272078C1 (ru) * 2005-08-16 2006-03-20 ЗАО "Патентные услуги" Способ получения стали
US20120060650A1 (en) * 2009-05-15 2012-03-15 Istc Co., Ltd Method for manufacturing molten iron
US8771400B2 (en) * 2009-05-15 2014-07-08 Istc Co., Ltd. Method for manufacturing molten iron

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NO125893B (enrdf_load_stackoverflow) 1972-11-20
NL6904586A (enrdf_load_stackoverflow) 1970-04-01
SE364728B (enrdf_load_stackoverflow) 1974-03-04
DE1914645B2 (de) 1971-12-16
LU58299A1 (enrdf_load_stackoverflow) 1969-07-15
JPS5412405B1 (enrdf_load_stackoverflow) 1979-05-23
FR2018884A1 (enrdf_load_stackoverflow) 1970-06-26
BE730471A (enrdf_load_stackoverflow) 1969-09-01
GB1209987A (en) 1970-10-28
DE1914645A1 (de) 1971-02-11
CH516641A (fr) 1971-12-15

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