US3668016A - Process for producing cold-rolled steel plate high in the cold-formability - Google Patents

Process for producing cold-rolled steel plate high in the cold-formability Download PDF

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Publication number
US3668016A
US3668016A US803669A US3668016DA US3668016A US 3668016 A US3668016 A US 3668016A US 803669 A US803669 A US 803669A US 3668016D A US3668016D A US 3668016DA US 3668016 A US3668016 A US 3668016A
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Prior art keywords
steel
cold
value
molten steel
ingot
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Expired - Lifetime
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US803669A
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English (en)
Inventor
Mineo Shimizu
Hiroshi Takechi
Hiroyuki Kajioka
Minoru Kawaharada
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Nippon Steel Corp
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Nippon 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
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04—Removing impurities by adding a treating agent
    • C21C7/076—Use of slags or fluxes as treating agents
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • 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
    • 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
    • C21D8/041—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 involving a particular fabrication or treatment of ingot or slab
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

Definitions

  • Cold-rolled steel having excellent cold-formability is made by pouring into a mold a molten steel having a composition of C0.07 wt. percent, 0.04 to 0.20 wt. percent Mn, 0.004 to 0.020 wt. percent S, the ratio of Mn to S being at least 7, not more than 0.0030% N, and the balance iron and impurities.
  • the molten steel is allowed to rim in the mold for a time interval.
  • the core of the molten steel is killed by adding Al to the molten steel after the time interval, such that the acid-soluble Al in the remaining molten steel is more than 0.010% to obtain an ingot.
  • the ingot is then subjected to hotrolling, cold-rolling recrystallizing and annealing.
  • This invention relates to a cold-rolled steel plate having few surface flaws and excellent cold-formability and a process for producing the same.
  • the steel plate In the case of forming a cold-rolled steel plate by a pressing operation, it is required that the steel plate should be nonageable and should have good deep-drawability and extrudability depending on the use.
  • the main cause of such ageing phenomenon is considered to be N solid-dissolved in the steel and can be prevented by adding an element which will combine with N.
  • cheap Al is used in most cases.
  • An aluminum-killed steel containing more than 0.02% acid-soluble Al (which shall be referred to as sol. Al hereinafter) is typical thereof.
  • the present invention seeks to solve the above described problem and has for an object to provide a rimstabilized steel which has favorable surface properties and excellent cold-forrnability.
  • FIG. 1 shows influences of the Mn content on the '1 value of the final product when only the Mn content was varied
  • FIG. 2 shows influences of the absolute values and combination of the Mn and S contents on the F and n values of the final product when both the Mn and S contents were varied;
  • FIG. 3 is a photograph of a corner sample of an ingot made by a conventional method and having an Mn content of 0.30%;
  • FIG. 4 is a photograph of a corner sample of an ingot according to the present invention.
  • a rim-stabilized steel In producing a rim-stabilized steel, according to an ordinary ingotting method wherein Al is added immediately or several minutes after a molten steel to be made a rimmed steel is poured, it is possible to prevent A1 0 from mainly gathering near the skin of an ingot and the surface defect from being caused by A1 0 In this case the thickness and soundness of the rim layer coagulated before Al is added are important in relation to the surface flaws. It is considered that a range of 0.07 to 0.10% C is desirable to obtain a sound rim layer.
  • the rimming action is weak and there remain many small bubbles as shown in the photograph (steel with 0.050% C, 0.30% Mn and 0.018% S) in FIG. 3, whereby the soundness of the rim layer is remarkably reduced.
  • the bubbles distributed near the ingot skin are subjected to an oxidation during the soaking heating and cannot be pressed into contact, causing thereby the formation of surface flaws of the rolled product.
  • 0 content should be as low as possible and is required to be below 0.07%
  • the present inventors have discovered that, when the C content is reduced, only the Mn value in the ladle is related with the removal of the generated bubbles and that, when the Mn content is held to a low value which is not conceivable in the usual conventional cold-rolled steel plate, that is, less than 0.2%, the bubbles near the skin of the ingot (steel with 0.052% C, 0.17% Mn and 0.016% S) vanish as shown in the photograph in FIG. 4, thus the problem of the surface flaws in the product may be solved.
  • FIG. 1 shows the relation between the F value and the Mn content of a product manufactured from an ingot of rim-stabilized steel of 0.006% S, said steel ingot being prepared by melting so that the Mn content thereof may be varied, but other chemical components not intentionally varied, by subjecting said ingot to following steps: blooming, hot-rolling, cold-rolling at a reduction rate of 70% and to recrystallization annealing at 700 C. for 4 hours.
  • the F value which is also called a plastic strain ratio, is a mechanical characteristic represented by the ratio of the width strain to the thickness strain of a tension test piece and is known to show a very favorable correlation with the deep-drawability of a metal plate.
  • F value is a mean value in each direction in the plane of the plate.
  • the F value of the materials on the low Mn side in FIG. 1 is that converted from a measured value for a final product obtained from a material partly cracked in hot-rolling as a mother material, said measured value being obtained by quantitatively measuring the crystal surface parallel with the plate plane of the final product by X-rays. Because the sample to be used for the X-ray measurement is large even though it is smaller than that needed for a mechanical test, even a. partly cracked material can be used as a sample, while avoiding the cracked part. Further, as is described in detail, for instance, in the Japan Metal Society Journal, vol. 29, No. 4, 1965, the relation between the value measured with X-rays and the F value measured from the mechanical test is very close.
  • the Mn content is defined to be 0.25 to 0.45%.
  • it. can be said to be advantageous to the F value to further reduce the Mn content.
  • FIG. 2 shows the relationships of the F value and 11 value with the Mn and S contents, when treating in the same manner as in the case of the material of FIG. 1, 57 rim-stabilized steel ingots obtained by various combinations within ranges of 0.02 to 0.40% Mn and 0.003 to 0.030% S.
  • the F value and n value are influenced by both Mn and S.
  • the F value and the n value are represented respectively by round and square marks on the same material.
  • the position of the round mark indicates the right position.
  • the square mark is drawn to show the n value is placed beside the corresponding round mark.
  • the round mark having no square mark therebeside represents that the material was broken due to red-hot brittleness and the n value could not be measured.
  • the n value so called here is also called a work hardening index and is known to have a good relation with the extrudability of the metal plate.
  • the steel of the present invention is made so that the sol. A1 contained in the steel may be more than 0.01%. However, this is about the same as in an ordinary aluminum-killed steel and is suflicient to make the steel nonageable.
  • conventional steels of the same kind contain Mn and S in the ranges of about 0.30 to 0.40% and 0.010 to 0.025% respectively and have an F value of 1.4 to 1.8 and an 11 value of 0.20 to 0.25, which clearly demonstrates the superiority of the present method, when compared with the above-mentioned values of the steel of the present invention.
  • red-hot embrittlement in which an embrittlement of a steel is caused when it is hot-rolled. This is considered to be caused by the fact that S in the steel is reticulately deposited as FeS around an initial crystal.
  • S in the steel is reticulately deposited as FeS around an initial crystal.
  • the C content as a ladle composition has an influence on the formability, as abovementioned, and should be as low as possible. Therefore, the C content as a ladle composition is made 0.07%. However, in consideration of the economy of the steel producing operation and the surface quality of the product, the C content as a ladle composition is made more than 0.03%. In order to improve the workability of rimmed steel, such steel has been decarburized by an open coil annealing system. But, it is a feature of the method of the present invention that, without subjecting the steel of the present invention to such a decarburization treatment, a very high press-formability can be obtained.
  • a conventional aluminumkilled steel usually contains more than 0.020% acid-soluble Al. This is, of course, an amount too large for the putrhprge of making the steel plate nonageable by combining W1 However, this amount is based on the idea of simultaneously elevating the F value by forming AlN in an op timum amount. Therefore, in the case of the present invention in which the F value is increased by the balance of Mn and S, and Al is added only for the purpose of obtaining the nonageability of steel, the content of more than 0.010% acid-soluble Al in the product is sufiicient for the said purpose.
  • a molten steel made in a converter or open-hearth furnace and having a ladle composition of C 0.07% and Mn and S within the designated range of FIG. 2 is toppoured or bottom-poured so as to be a rimmed steel.
  • some shot Al is used in response to the state of the rimming action.
  • Al is added into the molten steel in the mold so that the sol.
  • Al in the remaining molten steel may be more than 0.02% and the molten steel is coagulated.
  • a cold-rolled steel plate is made from it through respective blooming, hot-rolling, cold-rolling and annealing steps by a conventional process. That is to say, it is hot-rolled at a temperature above the Ar point, is coldrolled at a reduction rate in a range of 50 to 90% and is then annealed at a temperature above the recrystallizing temperature.
  • Al is added after a desired rim layer has been obtained when making a rimmed steel from the molten steel, which prevents the formation of any surface fiaw to be caused by A1 partially gathering near the ingot skin by the sound rim layer which is first obtained by making Mn 0.20% as described above.
  • the amount of Al to be added difi'ers depending on the property of the molten steel, the pouring condition and the time used for adding Al. However, in case sol. Al is 0.02%, it is necessary to add more than 0.7 kg./ton of Al.
  • the time of adding Al is somewhat different depending on such pouring method as top-pouring or bottom-pouring and on the pouring rate but is generally determined by taking into consideration both the thickness of the rim layer required when rolling an ingot and the refloating of A1 0 series impurities.
  • the thus produced product contains C in the range of 0.06 to 0.02% and Mn and S in the ranges substantially not varied, but still such that the ratio of Mn to S 57, that is, in the designated range of FIG. 2. Therefore, the object is attained thereby. Even if C is made less than 0.02%, the product cannot be expected to improve in quality. Therefore, C is defined to be than 0.02%.
  • EXAMPLE 9 tons of a molten steel of 0.06% C, 0.14% Mn and 0.010% S made in a converter were bottom-poured into a downwardly expanding flat mold and 0.9 kg./ton of Al was added thereto immediately before the completion of the pouring to produce an ingot.
  • This ingot was hot-rolled, was then cold-rolled to be 0.8 mm. thick at a reduction rate of 68% and was annealed at 710 C. for 5 hours to obtain a cold-rolled steel plate of 0.050% C, 0.14% Mn, 0.01% S, 0.038% acid-soluble Al and 0.014% P, the rest being Fe and impurities.
  • the surface test result and coldformability in this case as compared with those in a conventional method are shown in Table 1.
  • the conventional method here designates a treatment of a rim-stabilized ingot containing 0.07% C, 0.31% Mn and 0.015% S by the same process as is mentioned above. By the following comparison the effect of the method of the present
  • a process for producing cold-rolled steel plates having excellent cold-formability comprising the steps of pouring into a mold a molten steel made in a converter or open-hearth furnace and consisting essentially of a composition of C 50.07 Wt. percent, 0.04 to 0.20 wt. percent Mn, 0.004 to 0.020 wt.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • Heat Treatment Of Sheet Steel (AREA)
  • Heat Treatment Of Steel (AREA)
US803669A 1968-03-02 1969-03-03 Process for producing cold-rolled steel plate high in the cold-formability Expired - Lifetime US3668016A (en)

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FR (1) FR2003109B1 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
GB (1) GB1260405A (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
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
US3865643A (en) * 1972-08-31 1975-02-11 United States Steel Corp Deep drawing sheet steel
US3926692A (en) * 1974-09-30 1975-12-16 United States Steel Corp Drawability of deoxidized steels by the addition of phosphorus and silicon
US4092179A (en) * 1976-12-27 1978-05-30 Jones & Laughlin Steel Corporation Method of producing high strength cold rolled steel sheet
EP0132365A3 (en) * 1983-07-20 1988-08-31 Armco Inc. Process of making aluminum killed low manganese deep drawing steel

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1096525A (en) * 1963-12-14 1967-12-29 Fuji Iron & Steel Company Ltd Improvements in or relating to enameling-grade steel and materials and methods used in its production

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
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
US3865643A (en) * 1972-08-31 1975-02-11 United States Steel Corp Deep drawing sheet steel
US3926692A (en) * 1974-09-30 1975-12-16 United States Steel Corp Drawability of deoxidized steels by the addition of phosphorus and silicon
US4092179A (en) * 1976-12-27 1978-05-30 Jones & Laughlin Steel Corporation Method of producing high strength cold rolled steel sheet
EP0132365A3 (en) * 1983-07-20 1988-08-31 Armco Inc. Process of making aluminum killed low manganese deep drawing steel

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FR2003109B1 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) 1973-02-02
FR2003109A1 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) 1969-11-07
GB1260405A (en) 1972-01-19
DE1910762B1 (de) 1970-10-29

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