US3920487A - Press forming cold rolled steel sheet and a producing method thereof - Google Patents

Press forming cold rolled steel sheet and a producing method thereof Download PDF

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Publication number
US3920487A
US3920487A US399530A US39953073A US3920487A US 3920487 A US3920487 A US 3920487A US 399530 A US399530 A US 399530A US 39953073 A US39953073 A US 39953073A US 3920487 A US3920487 A US 3920487A
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Prior art keywords
overageing
temperature
cold rolled
soaking
rolled steel
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US399530A
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Hisashi Gondo
Hiroshi Takechi
Mitsunobu Abe
Norimasa Uehara
Kunihiko Komiya
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Nippon Steel Corp
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Nippon Steel Corp
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Priority claimed from JP9572872A external-priority patent/JPS5341613B2/ja
Priority claimed from JP9572972A external-priority patent/JPS5338685B2/ja
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
    • C21D8/0473—Final recrystallisation annealing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length

Definitions

  • FIG. 2 4Z mmm 01/524 6.97/76 6'0/Y0/T/0 Y5 FIG. 2
  • the most important property required for the press forming steel sheet is a high 7 value.
  • the wrinkle preventive force is remarkably increased, and only a slight portion of the steel sheets are pressed into the dies and only portions contacting the punch are expanded and pressed.
  • the most important characteristic is a high Erichsen value, and additionally it is desired that yield stress is low both for deep drawability and stretchability, and elongation is large.
  • Cold rolled steel sheets subjected to the press forming are generally annealed after the cold rolling, but the steel sheets as annealed have high yield point elongation so that when the sheets are press formed, stretcher strain is caused and the surface appearance is damaged. For this reason, the sheets after the annealing are subjected to a temper rolling to eliminate the yield point elongation.
  • the cold rolled steel sheet in which the yield point elongation is not restored even when the sheet is left for a long time after the temper rolling, are called non-ageing steel sheets and the steel sheets in which the restoration of the yield point elongation is slow, are called a slow ageing steel sheets.
  • the steel sheets for press forming have non-ageing, or at least a slow ageing property, deep drawability and stretchability.
  • the cold rolled non-ageing or slow ageing steel sheets having above mentioned properties for auto bodies have been commercially produced by applying a box annealing to Al-killed steel.
  • the Al-killed steel contains aluminium in such an amount as to be enough to form AlN during the heating of the annealing and is effective to improve the 7value in the cource of the AlN formation, and fixes the solid solution nitrogen as AlN, thus improving the ageing property.
  • the Al-killed steel pipes are formed during the ingot making in the head portion of the ingot, which cause inner defects in the final product, and thus it is necessary to cut off the head portions.
  • annealing requires normally more than 60 hours and thus is not desirable for the production efficiency.
  • one of the object of the present invention is to provide a cold rolled steel sheet having an excellent press formability and ageing properties for auto bodies, especially improved stretchability and slow ageing properties.
  • Another object of the present invention is to provide a method for producing the cold rolled steel sheet having an excellent press formability and ageing property for auto bodies, especially improved stretchability and slow ageing property, by means of a continuous annealing method.
  • a cold rolled steel sheet for press forming having a chemical composition comprising not more than 0.1% carbon and not more than 0.30% manganese in which 0.002. (ppm) -0.03 s K s 0.17 +0.002N(ppm) where,
  • a method for producing a press forming cold rolled steel sheet comprising not more than 0.1% C and not more than 0.30% Mn and satisfying the conditions 0.002 X N ppm 0.03 s K S 0.17 +0.002 X N pp where which comprising an ordinary hot rolling step, a cold rolling step and a continuous annealing step;
  • a method for producing cold rolled steel sheet having good press formability comprising passing a cold rolled steel strip containing not more than 0.1% carbon through a continuous annealing furnace composed of a heating and a soaking zone, a primary cooling zone, an overageing zone, and a secondary cooling zone arranged in series, in which 30 seconds to 5 minutes heating and soaking is effected at a temperature between 650 and 900C in the heating and soaking zone, cooling down to the starting temperature of overageing or below is effected in the primary cooling zone, and overageing with starting temperature between 400 and 500C and then stepwisely or continuously lowering temperature between 200 and 500C is effected for 2 to 10 minutes and the overageing is completed between 200 and 350C; and
  • a method for producing a slow ageing cold rolled steel plate for press forming comprising hot rolling a steel slab having a chemical composition comprising not more than 0.1% carbon and not more than 0.30% manganese, in which 0.002.N(PPm) 0.002.N(ppm) where,
  • FIG. 1 a, b and c respectively show a graph of heat cycles of isothermal overageing and stepwise overageing.
  • FIG. 2 is a graph showing Erichsen values of steel materials subjected to isothermal overageing and stepwise overageing.
  • FIG. 3 is a graph showing a heat cycle in the continuous annealing furnace.
  • metal materials having a larger grain size are softer and more suitable for cold working and show larger Erichsen values, elongation, and T values and lower yield stress with good ageing properties.
  • the size of the grains depend on the chemical composition and the heating history in the production process.
  • Mn, S and O are elements which harden the steel and lower deep drawability and stretchability by their solid solution hardening effects orv by grain refinement due to their recrystallization preventing effects or by both.
  • Mn combines with S and O to form MnS and MnO, the grain refinement-tendency due to the solid solution hardening and the recrystallization preventing effects disappear and large grains are obtained, thus improving deep drawability and stretchability.
  • Mn or any or both of S and 0 remains excessively in a large amount, they are harmful.
  • MnS and MnO are present in alarge amount, they by themselves cause fractures during the press forming operation, and it is necessary to maintain MnS and MnO as low as possible.
  • the carbon content more than 0.1% carbon causes material hardening, and thus the carbon content should be not more than 0.1%.
  • the chemical composition of the slow ageing cold rolled steel sheet for press forming according to the present invention is limited so as to satisfy the following conditions.
  • N content less than 25 ppm improves some mechanical properties such as drawability and ageing property.
  • the cold rolled steel sheet to which the method of the present invention is directed may be produced from any of a rimmed steel, a capped steel, a killed steel and other steels containing various alloying elements and impurities, so far as the carbon content is not more than 0.1% and the desired results of the present invention can be obtained.
  • the feature of the present invention lies in the uses of the continuous annealing method as specified.
  • steel coils or cut sheets are heated for soaking and then cooled in a piled condition and the heat capacity of the piled steel coils or cut plates is so large that it takes about 10 hours to heat the whole of the piled coils or cut plates to a predetermined annealing temperature, and the cooling after the soaking is very slow and it usually takes more than one day to cool the coil or the plate to a room temperature from the soaking temperature.
  • the steel strip is once uncoiled into a strand form and supplied to an annealing furnace so that the heat capacity of the material to be annealed is so small that it is possible to heat the material to the soaking temperature in a short time, that is recrystallization can be completed by 30 seconds to 5 minutes soaking at a temperature between a recrystallization temperature and 900C, with similar results as in the box annealing method.
  • the recrystallization is not enough, while when the soaking temperature is higher than 900C and the soaking time is longer than 5 minutes, no substantial improvement of the material is obtained with only lowering of the production efficiency and also 7 value remarkably decreases.
  • the carbon atoms in solid solution present at the beginning of the cooling gradually pre- 1 ;cipitate as carbides during the cooling in corresponproving the stretchability and the ageing property of the material.
  • the continuous annealing As the heat capacity of the material passing through the heating and soaking zone of the furnace is so small that the material is rapidly cooled down to the room temperature within minutes. Therefore, a considerable part of the solid solution carbon which was present in the material at the beginning of the cooling is retained in the solid solution and thus the stretchability and the ageing property of the material are deteriorated by the solid solution hardening.
  • the material is cooled down to the overageing temperature or below and then the material is subjected to an overageing treatment at a temperature below the soaking temperature to precipitate the excessive solid solution carbon as carbides.
  • the overageing temperature When the overageing temperature is high, the diffusion rate of the carbon is rapid and thus the carbide precipitation is completed in a short time, but the solid solution limit of carbon is so high that the amount of the residual solid solution carbon is large. Therefore, the overageing is not complete.
  • the overageing temperature when the overageing temperature is low, the diffusion rate of carbon is so slow that a long time is required for the completion of the carbide precipitation, but the solid solution limit of carbon is so small that the,
  • the material is cooled from the soaking temperature to the starting temperature of the overageing or below, and overageing with starting temperature between 400 and 500C is effected for 2 to 10 minutes with the temperature stepwisely or continuously lowering between 200 and 500C and the overageing is completed between 200 .and 350C, thereby the advantages that the carbide precipitation is completed rapidly by a high temperature overageing and that the residual solid solution carbon is remarkably reduced by a low temperature overageing are assured while the defects of the high and low temperature overageing are eliminated, thus maintaining the stretchability, preventing the ageing due to the solid solution carbon, and improving the productivity.
  • the cooling from the soaking temperature to a temperature below the starting temperature of the overageing is conducted at a rate of 5 to C/second. Even during the cooling from the soaking temperature, the diffusion rate of the carbon is remarkably high immediately below the soaking temperature, it is not desirable that the cooling rate in the primary cooling zone exceedes 30C/second in order to utilize also the carbide precipitate in this stage. Also with a cooling rate more than 30C/second, the over saturation degree of special advantage is not obtained, and the productivity is lowered.
  • the cooling rate of 5 to 30C/second from the soaking temperature to a temperature below the overageing temperature is a preferable range and not an essential range. The desired results of the present invention can be obtained even when the cooling rate is outside the above range.
  • the solid solution of carbon becomes relatively large and the overageing is meaningless.
  • carbides are formed at the grain boundaries when the above primary cooling rate is applied.
  • the solid solution limit at 700 and 400C is respectively 0.02% and 0.0036% and thus most of the solid solution carbon precipitates as grain boundary carbides at this stage, but a small amount of solid solution carbide remains. The residual solid solution carbon even in such a small amount is harmfull to the stretchability and the ageing property.
  • the residual solid solution carbon precipitates as fine carbides in the grains and the residual solid solution carbon is reduced to a negligible amount, for example to about 0.004% which is a solubility limit for carbon at without damaging the stretchability and this can not be expected in the box annealing and one of the features of the present invention.
  • the precipitation hardening as mentioned before is caused and thus the stretchability is deteriorated, although advantageous for the slow ageing.
  • 2 to 10 minutes are given from the beginning of the overageing (400 to 500C) to the completion of the overageing (200 to 350C) during which the overageing temperature is lowered stepwisely or continuously.
  • the most desired conditions of the overageing are: the beginning of the overageing between 400 and 450C, the completion of the same between 250 and 300C, and the total period of the overageing of 3 to 6 minutes.
  • the overageing with the continuously lowering temperature used herein means the case where the temper ature lowering rate at each position in the overageing zone is within i 30% of the average temperature lowering rate obtained by dividing the difference between the beginning temperature and the completing temperature of the overageing by the total overageing time.
  • the overageing with the stepwisely lowering temperatures and used herein means as under.
  • the overageing zone is divided into two or more isothermal overageing zones, where the overageing temperature stepwisely lowers, each of the isothermal times is maintained within i 30% of the average isothermal overageing time obtained by equally dividing the total passing time in the total isothermal zones by the number of the isothermal overageing zones and the temperature range in each of the isothermal overageings is maintained within i 30% of the average overageing temperature difference obtained by dividing the difference between the beginning temperature and the completing temperature of the overageing by the number of the isothermal overageing zones and the transition zone between the isothermal overageing zones is passed through in time shorter than 50% of average isothermal overageing time.
  • the secondary cooling zone it is desirable to cool the material down to near the room temperature as rapid as possible for improvement of the productionefficiency.
  • the slow ageing cold rolled steel sheets for press forming according to a purpose of the present invention will have more desirable properties by applying the continuous annealing method as described hereinbefore. In this case, however, the hot coiling temperature is important.
  • a hot rolled steel strip is prepared from a rimmed capped or killed steel having the following chemical compositions;
  • the hot coiling temperature is limited as under in order to promote the reactions of Mn S -r MnS and Mn MnO for the reasons mentioned hereinbefore.
  • the cooling rate after the hot rolling is very slow, so that the strip is maintained at the high temperature for a long time, and particularly when the coiling is done at a temperature not lower than 600C, more preferably not lower than 650C, the formation of MnS and MnO by the above reaction is remarkably promoted.
  • the coiling temperature is too high, coarse carbides are formed, which promote the fracture during the press forming.
  • the upper limit of the coiling temperature is limited to [850 2.1 X 10 x C(%)]C.
  • the hot rolled steel strip thus obtained is cold rolled and then continuously annealed by passing the strip through the continuous annealing furnace in which a heating and soaking zone, a primary cooling zone, an overageing zone and a secondary cooling zone, are arranged in series.
  • the soaking time should be limited to not more than 5 minutes, when the annealing temperature is too high, coarse carbides are formed, which promote the fracture during press forming.
  • the upper limit of temperature should be determined in relation to the hot coiling temperature. In this way, the soaking condition of the present invention is limited as between 650C and [1680 4.6 X 10 X C(%) the hot coiling temperature (C)]C for 30 seconds to 5 minutes.
  • the secondary cooling should be done as rapidly as possible to 40C. This is desirable for the improvement of the production efficiency.
  • the steel strip cooled down below 40C which has been passed through the secondary cooling zone is, if necessary, subjected continuously 1.0 to 1.5% temper rolling to eliminate the yield point elongation and to prevent the stretcher strain and subjected to levelling for shape correction, and then coated with rust preventive oil or solid lubricating oil for the press forming, finally coiled for shipment.
  • EXAMPLE 1 A capped steel refined in a convertor and comprising 0.04% C, 0.23% Mn, 0.010% S, 0.011% P, 0.01% Si, 0.042% 0 and 15 ppm N, with the balance being iron and unavoidable impurities was made into slabs by an ordinary method. After soaking at 1200C for 5 hours, the slab was hot rolled into 2.6 mm thickness with a finishing temperature of 890C and coiled at 710C. After acid pickling for scale removal, the hot rolled strip was cold rolled into 0.8 mm thickness and electrically cleaned, and subjected to a recrystallization annealing at 700C for 2 minutes in a salt bath furnace.
  • an isothermal overageing and a stepwise overageing as shown in FIG. 1 were conducted for 5 minutes of overageing using salt baths maintained at 600, 500, 400 and 300C, an oil bath maintained at 200C.
  • the cooling rate from the annealing temperature to the starting temperature of the overageing was 10 to 15C/second.
  • Erichsen values of the samples are shown in FIG. 2, and the samples G, H and J, which are within the scope of the present invention show particularly high Erichsen values, which are similar to that of the sample X which was box annealed for 4 hours at 700C for comparison.
  • EXAMPLE 2 Three rimmed steel ingots refined in a convertor and comprising 0.04% C, 0.22% to 0.24% Mn, 0.01% Si, 0.008% to 0.012% S, 0.010 to 0.012% P, 0.032 to 0.041% 0, 9 to 12 ppm N, with the balance being iron and unavoidable impurities were processed in the same way as in Example 1 up to the cold rolling, passed through a vertical continuous annealing furnace provided with an electrical cleaning device in the front and a temper leveller and an oil coater in the rear, where annealing cycles (a), (b) and (c) shown in FIG. 3 were applied and 1.5% temper rolling was conducted.
  • the properties of the products thus obtained are shown in Table 1 together with the properties of the product obtained by a box annealing of a coil of the above composition at 700C for 4 hours and 1.5% temper rolling.
  • EXAMPLE 3 Cold rolled steel strip of 0.8 mm thickness obtained from hot rolled steel strip of 2.6 mm thickness coiled at 680C, having a chemical composition of 0.04% C, 0.015% Mn, 0.01% Si, S, 0.013% P, 0.040% 0 and l 15 ppm N with the balance being iron and unavoidable 1.5% temper rolling.
  • the capped steel No. 7, and the Alkilled steel No. 8 were box annealed at 700C for 4 hours and 16 hours respectively and were subjected to 1.5% temper rolling.
  • the results of tests on the mechanical properties for these comparison samples are shown in Table 4.
  • the yield stress, the elongationthe r value and the Erichsen value are all on the same level to that of the box annealed Al-killed steel No. 8 and the press formability is better than that of the steel No. 8.
  • the ageing property is somewhat lower than that of the Al-killed steel No. 8, the yield point elongation after the ageing is remarkably smaller as compared with the box annealed capped steel No. 7 and a slow ageing property is completely obtained.
  • a method for producing a slow ageing cold rolled steel plate for press forming comprising hot rolling a steel slab having a chemical composition comprising not more than 0.1% carbon and not more than 0.30% manganese in which coiling the hot rolled strip at a temperature between 600 and [850 2.1 X 10 X C(%) ]C, cold rolling the hot rolled strip by a conventional method, and passing the cold rolled strip thus obtained continuously through a continuous annealing furnace composed of a heating and soaking zone, a primary cooling zone, an overageing zone, and a secondary cooling zone arranged in series, in which 30 seconds to 5 minutes heating and soaking is effected at a temperature between 650 and [1680 4.6 X 10 X C(%) the hot coiling temperature (20 C) C in the heating and soaking zone, cooling down to the starting temperature of overageing or below is effected in the primary cooling zone, and overageing with a starting temperature between 400 and 500C and then step-wisely or continuously lowering the temperature at the starting temperature of overage

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
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  • Crystallography & Structural Chemistry (AREA)
  • Mechanical Engineering (AREA)
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  • Metallurgy (AREA)
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  • Heat Treatment Of Sheet Steel (AREA)
US399530A 1972-09-26 1973-09-21 Press forming cold rolled steel sheet and a producing method thereof Expired - Lifetime US3920487A (en)

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JP9572872A JPS5341613B2 (enrdf_load_stackoverflow) 1972-09-26 1972-09-26
JP9572972A JPS5338685B2 (enrdf_load_stackoverflow) 1972-09-26 1972-09-26

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US (1) US3920487A (enrdf_load_stackoverflow)
AU (1) AU470116B2 (enrdf_load_stackoverflow)
CA (1) CA1019169A (enrdf_load_stackoverflow)
DE (1) DE2348062C3 (enrdf_load_stackoverflow)
ES (1) ES419110A1 (enrdf_load_stackoverflow)
FR (1) FR2200359B1 (enrdf_load_stackoverflow)
GB (1) GB1443466A (enrdf_load_stackoverflow)
IT (1) IT995496B (enrdf_load_stackoverflow)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4023987A (en) * 1974-12-20 1977-05-17 Toyo Kohan Co., Ltd. Method of producing soft thin steel sheet by continuous annealing
US4050959A (en) * 1974-11-18 1977-09-27 Nippon Kokan Kabushiki Kaisha Process of making a high strength cold reduced steel sheet having high bake-hardenability and excellent non-aging property
US4191600A (en) * 1977-05-02 1980-03-04 Centre De Recherches Metallurgiques-Centrum Voor Research In De Metallurgie Method of continuously heat-treating steel sheet or strip
US4292097A (en) * 1978-08-22 1981-09-29 Kawasaki Steel Corporation High tensile strength steel sheets having high press-formability and a process for producing the same
US4443272A (en) * 1981-09-19 1984-04-17 Nippon Steel Corporation Process for producing cold rolled steel sheets having excellent press formability and ageing property
RU2238988C1 (ru) * 2003-08-28 2004-10-27 Открытое акционерное общество "Магнитогорский металлургический комбинат" Способ производства холоднокатаной полосы
RU2258749C1 (ru) * 2004-08-18 2005-08-20 Липецкий государственный технический университет Способ производства стали

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU575730B2 (en) * 1985-01-31 1988-08-04 Kawasaki Steel Corporation Continuous annealing extra-low carbon steel

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3607456A (en) * 1969-04-15 1971-09-21 Bethlehem Steel Corp Deep drawing steel and method of manufacture
US3666569A (en) * 1969-06-18 1972-05-30 Republic Steel Corp Production of deep drawing steel
US3765874A (en) * 1972-05-19 1973-10-16 Armco Steel Corp Vacuum degassed, interstitial-free, low carbon steel and method for producing same
US3798076A (en) * 1971-04-27 1974-03-19 Nippon Steel Corp METHOD FOR PRODUCING Al-KILLED DEEP DRAWING COLD ROLLED STEEL PLATE BY CONTINUOUS ANNEALING
US3806376A (en) * 1969-12-30 1974-04-23 Nippon Steel Corp Method for producing low-carbon cold rolled steel sheet having excellent cold working properties and an apparatus for continuous treatment thereof

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3607456A (en) * 1969-04-15 1971-09-21 Bethlehem Steel Corp Deep drawing steel and method of manufacture
US3666569A (en) * 1969-06-18 1972-05-30 Republic Steel Corp Production of deep drawing steel
US3806376A (en) * 1969-12-30 1974-04-23 Nippon Steel Corp Method for producing low-carbon cold rolled steel sheet having excellent cold working properties and an apparatus for continuous treatment thereof
US3798076A (en) * 1971-04-27 1974-03-19 Nippon Steel Corp METHOD FOR PRODUCING Al-KILLED DEEP DRAWING COLD ROLLED STEEL PLATE BY CONTINUOUS ANNEALING
US3765874A (en) * 1972-05-19 1973-10-16 Armco Steel Corp Vacuum degassed, interstitial-free, low carbon steel and method for producing same

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4050959A (en) * 1974-11-18 1977-09-27 Nippon Kokan Kabushiki Kaisha Process of making a high strength cold reduced steel sheet having high bake-hardenability and excellent non-aging property
US4023987A (en) * 1974-12-20 1977-05-17 Toyo Kohan Co., Ltd. Method of producing soft thin steel sheet by continuous annealing
US4191600A (en) * 1977-05-02 1980-03-04 Centre De Recherches Metallurgiques-Centrum Voor Research In De Metallurgie Method of continuously heat-treating steel sheet or strip
US4292097A (en) * 1978-08-22 1981-09-29 Kawasaki Steel Corporation High tensile strength steel sheets having high press-formability and a process for producing the same
US4443272A (en) * 1981-09-19 1984-04-17 Nippon Steel Corporation Process for producing cold rolled steel sheets having excellent press formability and ageing property
US4981531A (en) * 1981-09-19 1991-01-01 Nippon Steel Corporation Process for producing cold rolled steel sheets having excellent press formability and ageing property
RU2238988C1 (ru) * 2003-08-28 2004-10-27 Открытое акционерное общество "Магнитогорский металлургический комбинат" Способ производства холоднокатаной полосы
RU2258749C1 (ru) * 2004-08-18 2005-08-20 Липецкий государственный технический университет Способ производства стали

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DE2348062B2 (de) 1979-12-20
DE2348062C3 (de) 1980-08-28
ES419110A1 (es) 1976-03-16
CA1019169A (en) 1977-10-18
DE2348062A1 (de) 1974-04-04
FR2200359B1 (enrdf_load_stackoverflow) 1976-04-30
AU6063273A (en) 1975-05-08
GB1443466A (en) 1976-07-21
FR2200359A1 (enrdf_load_stackoverflow) 1974-04-19
AU470116B2 (en) 1976-03-04
IT995496B (it) 1975-11-10

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