US3879232A - Method for producing non-ageing cold rolled steel sheets having good press-formability by continuous annealing - Google Patents

Method for producing non-ageing cold rolled steel sheets having good press-formability by continuous annealing Download PDF

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Publication number
US3879232A
US3879232A US416059A US41605973A US3879232A US 3879232 A US3879232 A US 3879232A US 416059 A US416059 A US 416059A US 41605973 A US41605973 A US 41605973A US 3879232 A US3879232 A US 3879232A
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United States
Prior art keywords
cold rolled
rolled steel
ageing
formability
steel
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Expired - Lifetime
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US416059A
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English (en)
Inventor
Hisashi Gondo
Hiroshi Takechi
Mitsunobu Abe
Kazuo Namba
Hiroaki Masui
Norimasa Uehara
Kunihiko Komiya
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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
    • 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
    • C21D8/0421—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 working steps
    • C21D8/0426—Hot rolling

Definitions

  • Press forming grades of cold rolled steel sheets. for applications such as auto bodies are required to have excellent deep drawability and stretchability and further good ageing property.
  • Cold rolled steel sheets for subjection to press forming are generally annealed after cold rolling. but when usually subjected to temper rolling to reduce the yield point elongation. Even in this case. however. if the sheets are left for a long time before press forming. the yield point elongation is gradually restored to its former high value. due to the ageing of carbon and nitrogen in solid solution. and thus stretcher strains are again caused during press forming.
  • Cold rolled steel sheet in which the yield point elongation does not return to its original value. even when the sheet is left for a long time after temper rolling. is called non-ageing steel sheet. and higher press-forming grades of cold rolled steel sheet must be non-ageing.
  • Cold rolled non-ageing steel sheets having deep drawability and stretchability for automobile bodies have been conventionally produced on commercial scale by box annealing an Al-killed steel in sheet form.
  • box annealing requires normally more than 60 hours to complete. even in case when low grades of cold rolled steel sheets which cannot be press-formed are treated. and in case of higher grades of cold rolled steel sheet for press-forming of automobile bodies.
  • slow heating is necessary in order to improve 'Fvalue through precipitation of AlN during annealing. thus further elongating the treating time and lowering the production efficiency.
  • non-ageing property of the steel can be obtained even when Al addition is small.
  • the coiling temperature after hot coiling is low. and descaling is easier.
  • the method of the present invention is characterized in that a steel containing not more than 0.015 percent of carbon. and containing manganese. aluminium. sulfur. oxygen and nitrogen so as to satisfy the following condition:
  • cold rolled steel sheet is hot rolled with a finishing temperature between 650 and 980C. at coiling temperature between 300 and 600C. then cold rolled. and thus obtained cold rolled steel sheet is subjected to continuous annealing.
  • the steel contains impurities such as S. O. N etc.. and it is natural that the steel shows better press-formability when these impurities are smaller. However. it is not desirable to reduce these impurities to extremely low contents in a commercial production because it increases production cost remarkably.
  • the basic inventive idea of the present invention is to render the impurities as harmless as possible and to utilize these impurities for improvement of the steel.
  • Molten steel obtained by an ordinary steel making method contains about 500 ppm of oxygen.
  • 0.5 2.0 kg of Al per ton of molten steel is added before ingot making or before continuous casting.
  • A1 0 is formed. which is removed.
  • the oxygen content can be reduced to about 50 ppm.
  • Al fixes N as AlN at low temperatures after the ingot solidification. thus improving the steel quality. Therefore it is necessary that Al is retained additionally in an amount corresponding to the amount of nitrogen.
  • the steel ingot to which the present invention is applied must contain Al in an amount determined by the following formula 2Xlatomic weight of Al) 3 (atomic weight of 0) atomic weight of Al AHr/l) atomic weight of N 2 by vacuum degassing etc. in order to improve the 7 value.
  • the carbon content is lowered to 0.008 per cent or less.
  • Al may be added to the steel during the last stage of the ingot making or may be added dividedly before the ingot making and during the last stage of the ingot making, whereby a steel ingot having a rim layer or a similar layer in the surfacial thin portion. and a core portion of the composition defined by the present invention is obtained. and when this steel ingot is processed into a cold rolled steel sheet. the surface of the cold rolled steel sheet is covered by the rim layer which contains substantially no aluminium. and thus a cold rolled steel sheet having excellent coating adhesion for zinc-plating can be obtained.
  • the present invention is completely different from the conventional method in which the combination of AlN is attained by a high temperature coiling after the hot rolling.
  • the hot rolling finishing temperature is defined between 650 and 980C.
  • the steel is rapidly cooled to the coiling temperature. and coiled at a temperature between 300 and 600C.
  • the above finishing temperature range includes A transformation point. and when the finishing is done above the A, transformation point. the steel is cooled rapidly through the transformation point to increase the intergranular area so as to provide the precipitation site of AlN. and when the finishing is done below the A;, transformation point. the dislocation increased by the rolling is partially retained by the subsequent rapid cooling so as to provide the precipitation site of AlN.
  • finishing temperature When the finishing temperature is higher than 980C. grain growth takes place during the cooling just above the transformation point. so that it is impossible to increase the intergranular area even after the passthrough of A transformation point. On the other hand if the finishing temperature is lower than 650C the retained dislocation is excessive so that AlN becomes too fine during the subsequent steps and falls outside the appropriate range of the present invention.
  • the hot rolling finishing temperature range is defined from 650 to 980C. and the hot coiling temperature range is defined from 300 to 600C and the fine Al-N cluster which is a pre-stage of the AlN precipitate is densely distributed.
  • the most desirable conditions are the hot rolling finishing temperature range from 700 to 880C; the cooling rate from l0 to l00C/second down to the hot coiling temperature. and the hot coiling temperature range from 400 to 550C.
  • the cooling rate after the hot rolling finishing is below 10C/second.
  • the effect of increasing the intergranular area during the passage through the A transformation point is weakened, and the restoration of the discolation formed during the rolling progresses to some degrees and the results of the present invention are less remarkable.
  • the cooling rate is higher than l00C/second. the cooling is too rapid to obtain uniform cooling for a commercial production and the shape quality of the steel sheet is some times deteriorated.
  • AlN can be easily and densely formed even by continuous annealing in which short time heating and soaking are applied to the cold rolled steel sheet. and nitrogen can be fixed as AlN completely by Al. Also there are many lattice defects at the intersurface between AlN and the matrix which serve as the precipitation site for carbon. and AlN having such intersurface is densely distributed so that the precipitation of carbon during the rapid cooling after the soaking or during overageing can be completed in a very short time. It is most desirable that tensile stress or repeated bending stress or both which gives l to 3 percent permanent strain is given to the steel sheet during heating and soaking in the continuous annealing. and that the heating rate from 300C to a temperature higher than the recrystallization temperature is maintained between 3 and 10C/second. These measures can be done in single or in combination. and are most efficient conditions for forming the AlN precipitate from the MN cluster.
  • FIG. 1 (a) and (b) are respectively a graph showing the r value and the strain ageing index of the products obtained according to Example 2.
  • EXAMPLE 1 Steel ingot prepared by steel making in a convertor and vacuum degassing and having the composition shown in Table l was hot rolled with a finishing temperature of 780C. an average cooling rate of 23C/second to a coiling temperature and a hot coiling temperature of 450C. acid-pickled. and cold rolled with a reduction of 80 percent to obtain 0.8mm thick cold rolled steel sheets.
  • the steel sheet thus obtained was subjected to recrystallization annealing at 700C for 1 minute and over-ageing at 350C for 3 minutes in a continuous annealing furnace. while repeated bending by a hearth, roll and 2.5- percent.
  • a method for producing a cold rolled steel sheet 5 having non-ageing properties and press-formability comprising hot rolling a steel containing not more than 0.015% of carbon. and containing manganese. aluminum. sulfur. oxygen and nitrogen and wherein with a finishing temperature between 650 and 980C. coiling at a temperature between 300 and 600C. cold rolling and then continuously annealing the cold rolled steel sheet.
  • finishing temperature is between 700 to 880C.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Heat Treatment Of Sheet Steel (AREA)
  • Heat Treatment Of Steel (AREA)
US416059A 1972-11-20 1973-11-15 Method for producing non-ageing cold rolled steel sheets having good press-formability by continuous annealing Expired - Lifetime US3879232A (en)

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JP11564972A JPS5338690B2 (sv) 1972-11-20 1972-11-20

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JP (1) JPS5338690B2 (sv)
BR (1) BR7309085D0 (sv)
DE (1) DE2357443B2 (sv)

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4019929A (en) * 1974-06-24 1977-04-26 Nippon Kokan Kabushiki Kaisha Enameling cold rolled steel sheet with a high enamel adhesive property
US4026729A (en) * 1974-12-05 1977-05-31 Nippon Kokan Kabushiki Kaisha Method of making a soft steel sheet by continuous annealing
US4313770A (en) * 1979-06-28 1982-02-02 Sumitomo Metal Industries, Ltd. Method of producing cold rolled steel strip having improved press formability and bake-hardenability
US4315783A (en) * 1978-10-21 1982-02-16 Nippon Steel Corporation Method of producing non-ageing cold rolled steel strip with excellent deep-drawability by continuous heat treatment
US4478649A (en) * 1982-02-09 1984-10-23 Nippon Steel Corporation Method for producing a cold-rolled steel sheet having excellent formability
US4576657A (en) * 1982-02-19 1986-03-18 Kawasaki Steel Corporation Process of manufacturing a cold rolled steel sheet having excellent press formability
US4576656A (en) * 1982-10-08 1986-03-18 Kawasaki Steel Corporation Method of producing cold rolled steel sheets for deep drawing
US4591395A (en) * 1983-05-05 1986-05-27 Armco Inc. Method of heat treating low carbon steel strip
US5078809A (en) * 1986-09-27 1992-01-07 Nippon Kokan Kabushiki Kaisha Method for producing cold-rolled steel sheet
US5405463A (en) * 1980-10-24 1995-04-11 Nippon Kokan Kabushiki Kaisha Continuous annealing process of producing cold rolled mild steel sheet excellent in deep drawability and aging resistibility
WO2000014288A1 (de) * 1998-09-08 2000-03-16 Thyssen Krupp Stahl Ag Verfahren zur erzeugung von kaltgewalzten bändern oder blechen
US20090020196A1 (en) * 2003-11-10 2009-01-22 Posco Cold Rolled Steel Sheet Having Aging Resistance and Superior Formability, and Process for Producing the Same

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19858073C2 (de) * 1998-12-16 2003-04-24 Max Planck Inst Eisenforschung Verfahren zur Erzeugung von dünnen Warmbändern aus Stahl mit verbesserter Tiefziehfähigkeit
FR2798871B1 (fr) * 1999-09-24 2001-11-02 Usinor Procede de fabrication de bandes d'acier au carbone, notamment d'acier pour emballages, et bandes ainsi produites

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3239390A (en) * 1961-04-12 1966-03-08 Yawata Iron & Steel Co Method of producing non-ageing special low carbon iron sheets
US3248270A (en) * 1961-07-18 1966-04-26 Bethlehem Steel Corp Method of producing deep drawing steel
US3492173A (en) * 1967-07-21 1970-01-27 Jones & Laughlin Steel Corp Recovery-annealed cold-worked titanium steels
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 (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3239390A (en) * 1961-04-12 1966-03-08 Yawata Iron & Steel Co Method of producing non-ageing special low carbon iron sheets
US3248270A (en) * 1961-07-18 1966-04-26 Bethlehem Steel Corp Method of producing deep drawing steel
US3492173A (en) * 1967-07-21 1970-01-27 Jones & Laughlin Steel Corp Recovery-annealed cold-worked titanium steels
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

Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4019929A (en) * 1974-06-24 1977-04-26 Nippon Kokan Kabushiki Kaisha Enameling cold rolled steel sheet with a high enamel adhesive property
US4026729A (en) * 1974-12-05 1977-05-31 Nippon Kokan Kabushiki Kaisha Method of making a soft steel sheet by continuous annealing
US4315783A (en) * 1978-10-21 1982-02-16 Nippon Steel Corporation Method of producing non-ageing cold rolled steel strip with excellent deep-drawability by continuous heat treatment
US4313770A (en) * 1979-06-28 1982-02-02 Sumitomo Metal Industries, Ltd. Method of producing cold rolled steel strip having improved press formability and bake-hardenability
US5405463A (en) * 1980-10-24 1995-04-11 Nippon Kokan Kabushiki Kaisha Continuous annealing process of producing cold rolled mild steel sheet excellent in deep drawability and aging resistibility
US4478649A (en) * 1982-02-09 1984-10-23 Nippon Steel Corporation Method for producing a cold-rolled steel sheet having excellent formability
US4576657A (en) * 1982-02-19 1986-03-18 Kawasaki Steel Corporation Process of manufacturing a cold rolled steel sheet having excellent press formability
US4576656A (en) * 1982-10-08 1986-03-18 Kawasaki Steel Corporation Method of producing cold rolled steel sheets for deep drawing
US4591395A (en) * 1983-05-05 1986-05-27 Armco Inc. Method of heat treating low carbon steel strip
US5078809A (en) * 1986-09-27 1992-01-07 Nippon Kokan Kabushiki Kaisha Method for producing cold-rolled steel sheet
WO2000014288A1 (de) * 1998-09-08 2000-03-16 Thyssen Krupp Stahl Ag Verfahren zur erzeugung von kaltgewalzten bändern oder blechen
US6582537B1 (en) 1998-09-08 2003-06-24 Thyssen Krupp Stahl Ag Method for producing cold-rolled bands or sheets
CZ300683B6 (cs) * 1998-09-08 2009-07-15 Thyssen Krupp Stahl Ag Zpusob výroby za studena válcovaných pásu nebo tabulí
US20090020196A1 (en) * 2003-11-10 2009-01-22 Posco Cold Rolled Steel Sheet Having Aging Resistance and Superior Formability, and Process for Producing the Same
US9297057B2 (en) * 2003-11-10 2016-03-29 Posco Cold rolled steel sheet having aging resistance and superior formability, and process for producing the same

Also Published As

Publication number Publication date
JPS4974615A (sv) 1974-07-18
BR7309085D0 (pt) 1974-08-29
DE2357443A1 (de) 1974-05-30
DE2357443B2 (de) 1978-05-18
JPS5338690B2 (sv) 1978-10-17

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