EP0462380A2 - Procédé pour la fabrication de tôles d'acier laminées à froid ayant une résistance élevée et apte au formage - Google Patents

Procédé pour la fabrication de tôles d'acier laminées à froid ayant une résistance élevée et apte au formage Download PDF

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Publication number
EP0462380A2
EP0462380A2 EP91106841A EP91106841A EP0462380A2 EP 0462380 A2 EP0462380 A2 EP 0462380A2 EP 91106841 A EP91106841 A EP 91106841A EP 91106841 A EP91106841 A EP 91106841A EP 0462380 A2 EP0462380 A2 EP 0462380A2
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EP
European Patent Office
Prior art keywords
steel
less
rolling
cold
condition
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP91106841A
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German (de)
English (en)
Other versions
EP0462380B1 (fr
EP0462380A3 (en
Inventor
Susumu c/o Technical Research Division Okada
Tojiro c/o Chiba Works Ikeda
Susumu C/O Technical Research Division Satoh
Hideo C/O Technical Research Division Abe
Jun-ichi c/o Chiba Works Mano
Norio c/o Mizushima Works Kawasaki Steel Ohta
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
JFE Steel Corp
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Kawasaki Steel Corp
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Publication date
Application filed by Kawasaki Steel Corp filed Critical Kawasaki Steel Corp
Publication of EP0462380A2 publication Critical patent/EP0462380A2/fr
Publication of EP0462380A3 publication Critical patent/EP0462380A3/en
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Publication of EP0462380B1 publication Critical patent/EP0462380B1/fr
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for drawing, e.g. for deep-drawing
    • C21D8/0421—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for drawing, e.g. for deep-drawing characterised by the working steps
    • C21D8/0431—Warm rolling
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for drawing, e.g. 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for drawing, e.g. for deep-drawing
    • C21D8/0421—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for drawing, e.g. for deep-drawing characterised by the working steps
    • C21D8/0436—Cold rolling

Definitions

  • the present invention relates to a method of producing a high-strength cold-rolled steel sheet suitable for various types of working such as press working, bulging and so forth and adaptable also to deep drawing.
  • high-strength cold-rolled steel sheets are used not only for the inner panels but also for outer panels such as engine hoods, trunk lid and fenders. As a consequence, high-strength cold-rolled steel sheet is required to have an excellent workability.
  • Japanese Patent Laid-Open Publication No. 63-317648 discloses a cold-rolled steel sheet in which Ti, Nb and B are added to a low-carbon steel for the purpose of improving press-workability and spot-weldability. It has also been proposed to add strengthening elements such as P and Mn to the above-mentioned steel system. For instance, Japanese Patent Publication No.
  • 61-11294 discloses a method of producing a high-strength steel sheet having a superior workability in which a steel enriched with P is continuously annealed after a cold rolling.
  • Japanese patent Publication No. 1-28817 discloses a method in which a steel enriched with P and Mn is continuously annealed to form a high-strength cold-rolled steel sheet.
  • An object of the present invention is to provide a method of producing, from a low-carbon steel having an extremely small carbon content, a high-strength cold-rolled steel sheet suitable for working, and more particularly a steel sheet having a superior workability, specifically a Lankford value ( r ) of 1.8 or greater, a tensile strength T.S.) of 40 kgf/mm2 or greater, an elongation (El) of 40 % or greater, and a truncated-cone height of 40 mm or greater in the conical cup test.
  • a method of producing a high-strength cold-rolled steel sheet suitable for working comprising the steps of: preparing a steel consisting essentially of not more than 0.02 wt% of C, not more than 1.0 wt% of Si, not more than 2.0 wt% of Mn, and not less than 0.01 wt% but not more than 0.10 wt% of Ti, the Ti, C and N contents being determined to meet the condition of Ti > (48/12) C wt% + (48/14) N wt%, said steel also consisting essentially of not less than 0.0010 wt% but not more than 0.0100 wt% of Nb, not less than 0.0002 wt% but not more than 0.0020 wt% of B, not less than 0.03 wt% but not more than 0.20 wt% of P, not more than 0.03 wt% of S, not less than 0.010 wt% but not more than 0.100 w
  • Fig. 1 is a graph which shows the relationship between rolling reductions and various characteristics of the steel sheet.
  • a high-strength cold-rolled steel sheet having a superior workability specifically a Lankford value ( r ) of 1.8 or greater, a tensile strength T.S.) of 40 kgf/mm2 or greater, an elongation (El) of 40 % or greater and a truncated-cone height of 40 mm or greater, can be obtained by selecting the strain-imparting condition in the cold rolling of a very-low-carbon steel which is rich in P and small in oxygen content.
  • the present invention is based upon the above-described discovery. A description will be given first of the reason why the condition is posed that the sum of the rolling reductions of passes which meet the condition of T ⁇ ⁇ ⁇ 50,000°C S ⁇ 1 between the sheet temperature (T °C) and the strain rate ⁇ (S ⁇ 1) is 50 % or greater.
  • Three types of continuous-cast steel slabs A,B and C having the compositions shown in Table 1 were prepared by a converter.
  • Each slab was heated to 1250°C and rough-rolled at a rolling reduction of 88 %, followed by a hot finish-rolling at a rolling reduction of 88 % (hot-rolling finish temperature : 880°C, coiling temperature: 500°C) so as to be formed into a hot coil of 4.0 mm thick. Then, an ordinary cold rolling was effected at a rolling reduction of 82.5 % so that the steel was formed into a sheet 0.7 mm thick. Subsequently, a continuous annealing was conducted at 810°C followed by a temper rolling at a rolling reduction of 0.8 %, thereby producing a rolled steel sheet.
  • the cold rolling was conducted while varying the sheet temperature within the range of 30°C to 300°C, while varying the reduction rate, i.e,, the strain rate ⁇ within the range between 10 S ⁇ 1 to 2,000 S ⁇ 1.
  • the sheet temperature was controlled by varying the initial sheet temperature for the cold rolling and the flow rate of the cooling water.
  • the Lankford value (r), elongation, tensile strength and truncated-cone height were measured for each of the sample steel sheets.
  • the truncated-cone height which is an index indicative of the workability approximating that in actual working was measured by a conical cup test conducted under the following conditions:
  • Fig. 1 shows the relationship between these measured values and the sum of the rolling reductions of the passes which meet the condition of the product of the cold rolling sheet temperature and the strain rate being not smaller than 50,000°C S ⁇ 1.
  • the low-oxygen steel material A rich in P exhibited a tensile strength (T.S.) which is smaller than that of the steel B which has a small P content.
  • T.S. tensile strength
  • the truncated-cone height indicative of the workability approximating that of actual working is remarkably improved to a value approximating that of the steel B which has a large tensile strength, while the elongation(El) and the Lankford value ( r ) increase only slightly.
  • the steel C which is rich both in P and C does not show remarkable improvement in the properties indicative of the workability such as the Lankford value ( r ), elongation (El) and the truncated-cone height.
  • the sum of the rolling reductions of passes which meet the condition of the product of the sheet temperature and the strain rate being 50,000 °C S ⁇ 1 or greater is generally around 30 %.
  • suitable measures such as an increase in the rolling speed, control of flow rate of cooling water, or elevation of the initial cold rolling temperature through a continuous change from the preceding step, which is usually pickling.
  • the segregation zone does not produce any substantial unfavorable effect on the elongation Lankford value ( r ) which is measured in tensile test. In the actual use of the material, however, the segregation zone reduces the uniformity of the steel sheet in the thicknesswise direction and, hence, is considered to cause a reduction in the workability.
  • the cold rolling conducted under the specified condition produces a working effect which serves to break the segregation zone, so that the uniformity of the structure in the thicknesswise direction of the steel sheet is improved so as to improve the workability as confirmed through the conical cup test which simulates the actual condition of use.
  • the oxygen content in the steel is large, however, the large quantity of the inclusions impedes the cold-rolling straining of P in the segregation zone so as to reduce the effect of improving the workability.
  • C serves, when added to the steel material together with Ti, to strengthens the steel without impairing workability.
  • the upper limit of C content,therefore is determined to be 0.02 wt%.
  • the C content is preferably below 0.006 wt%.
  • Si The upper limit of Si content is set to be 1.0 wt%, since the drawing characteristic of the steel is impaired when the Si content exceeds 1.0 wt%.
  • Mn This element is effective in raising the strength without impairing the drawing characteristic.
  • This element serves to fix C and N in the steel so as to prevent deterioration of the material caused by solid solution of C.
  • this element impedes formation of BN so as to prevent reduction in the amount of solid solution of B.
  • this element should be added in an amount exceeding the sum of the C equivalent [(48/12) C wt%] and N equivalent [(48/14) N wt%].
  • Ti content below 0.01 wt% is too low to enable Ti to produce any appreciable effect.
  • addition of Ti in excess of 0.10 wt% reduces the strength.
  • the Ti content should be not less than 0.01 wt% and not more that 0.10 wt% and be determined to exceed the value of [(48/12) C wt% + (48/14) N wt%].
  • Nb This element is essential since it improves the Lankford value ( r ) and strengthens the steel when added together with B. Nb content below 0.0010 wt%, however,does not produce any remarkable effect. On the other hand,addition of Nb in excess of 0.0100 wt% reduces the workability so as to impair the balance between strength and workability.
  • the Nb content,therefore, is determined to be not less than 0.0010 wt% but not more than 0.0100 wt%.
  • the Nb content is preferably not less than 0.0075 wt%.
  • B This element is indispensable since it improves the strength when added together with Nb. B content below 0.0002 wt% does not produce any remarkable effect, while addition of B in excess of 0.002 wt% seriously degrades the material. The B content, therefore, is determined to be not less than 0.0002 wt% but not more than 0.002 wt%. Preferably, B content is determined to be not more than 0.0012 wt%.
  • P This element is an important strengthening element. The effect of this element is remarkable particularly when the content is 0.03 wt% or more.
  • the content of P is determined to be not less than 0.03 wt% but not more than 0.20 wt%, more preferably not less than 0.04 wt% but not more than 0.15 wt%.
  • S A reduction in S content in the steel is necessary for improving deep drawability.
  • the undesirable effect on the workability produced by S is not so serious when the S content is reduced down below 0.03 wt%.
  • the upper limit of the S content is therefore set to be 0.03 wt%.
  • Al This element is necessary for improving yield of carbonitride formers through deoxidation and for eliminating generation of surface defects caused by formation of TiO2.
  • the effect of addition of this element is not appreciable when the content is below 0.010 wt%.
  • the deoxidation effect is saturated when the Al content is increased beyond 0.10 wt%.
  • increase in the Al content tends to cause surface defect due to generation of Al2O3.
  • the Al content therefore, is determined to be not less than 0.01 wt% but not more than 0.10 wt%.
  • N This element degrades deep drawability of the steel and, in addition, reduces anti-secondary working embrittlement due to bonding with B, unless it is fixed by Ti.
  • the N content should be not more than 0.008 wt%, preferably not more than 0.006 wt%.
  • O In order to improve workability which is the critical requirement in the present invention, it is necessary to reduce O concentration. When the O content exceeds 0.0045 wt%, the cold-rolling straining to the segregation zone is impeded by a large amount of inclusions as explained before. As a consequence, the effect of improving workability produced by the cold straining is impaired and, in addition, an effect which is not negligible is caused on the brittleness.
  • the upper limit of O content is set to be 0.0045 wt%, preferably to 0.004 wt%.
  • Reduction in the oxygen content in the steel is effected by controlling the length of time of killed treatment in degassing step in ordinary steel making process.
  • the steel making process and a subsequent hot rolling can be carried out in the same manner as the known process, except that the oxygen content is reduced by the method described above.
  • a material having satisfactory properties can be obtained when the coiling temperature of the steel after the hot rolling falls within the range of ordinary process, e.g., between 400°C and 700°C.
  • the coiling temperature is comparatively low, e.g., 550°C or less, in order to avoid any deterioration in pickling property caused by the thickening of scale and to prevent excessive softening of the product.
  • the cold rolling may be conducted by using an ordinary cold rolling mill, provided that the aforementioned cold rolling condition is met. Namely, it is necessary that the sum of the rolling reductions of passes which meets the condition of the product of the sheet temperature and the strain rate being not smaller than 50,000 °C S ⁇ 1 is 50 % or greater. There is no restriction in the total rolling reduction, i.e.,the sum of the reductions of all passes employed, provided that the above-described condition is met.
  • the cold rolling sheet temperature has to be not higher than 300°C because a cold rolling at higher temperature causes concentration of shear deformation to the surface region of the steel sheet, making it difficult to work the central segregation zone.
  • the steel having the described composition When the steel having the described composition is annealed by batch-type box annealing method, the steel tends to become brittle due to grain boundary segregation of P due to high P content, particularly when the cooling rate is small.
  • a continuous annealing method which enables rapid heating and cooling.
  • the annealing temperature may be not lower than recrystallization temperature but not higher than A3 transformation temperature, as in the case of ordinary steel annealing process.
  • the temper rolling subsequent to the annealing may be effected under ordinary steel tempering condition with a rolling reduction corresponding to the sheet thickness (mm), for the purpose of, for example, obtaining optimum shape of the sheet.
  • Ten types of steels including 7 types meeting the composition condition of the invention and 3 types as reference examples, were prepared in a converter and were continuously cast into slabs. Each slab was hot-rolled to form a hot coil of 3,0 mm thick and cold-rolled to a thickness of 0.72 mm. Subsequently, a continuous annealing was conducted under ordinary condition. Then, the steel sheets other than the type No. 3 were subjected to a temper rolling with a rolling reduction of 0.7 %, whereby 10 types of steel sheets including one which has not been subjected to temper rolling were prepared.
  • the roll used in the cold rolling had a diameter of 600 mm.
  • the cold rolling speed was 1500 to 2500 m/min at the outlet side of the cold rolling stand.
  • each of type Nos. 1 and 2 were subjected to three different production conditions with different cold-rolling and continuous annealing conditions,so that three samples were produced for each of the steel type Nos. 1 and 2. Similarly, two samples were prepared from the steel type No. 1 through different production conditions. Only one sample was prepared for each of the remainder steel types.
  • Table 3 shows the hot-rolling and continuous annealing conditions
  • Table 4 shows the cold rolling conditions
  • Table 5 shows the result of examination of the properties of the cold-rolled sample steel sheets.
  • Sample No. 3 was subjected to a galvannealing instead of the continuous annealing.
  • This galvannealed steel sheet also showed excellent workability as in the cases of other samples meeting the conditions of the invention.
  • Sample No. 6 was cold-rolled at a cold-rolling sheet temperature exceeding 300°C, although the sum of the rolling reductions of the passes having the product of the sheet temperature and the strain rate exceeding 50,000°C S ⁇ 1 was greater than 50 %. Consequently, this sample showed a too small workability which was 20 mm in terms of truncated-cone height.
  • a method has been established by the present invention which enables production of a high-strength cold-rolled steel sheet having superior workability by processing a low-oxygen low-carbon steel rich in P under specific cold-rolling conditions.
  • the cold-rolled steel sheet produced by the method of the invention is suitable for use as a material of products which are produced through press-forming, bulging, deep-drawing and other plastic works.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Sheet Steel (AREA)
  • Heat Treatment Of Steel (AREA)
EP91106841A 1990-06-20 1991-04-26 Procédé pour la fabrication de tÔles d'acier laminées à froid ayant une résistance élevée et apte au formage Expired - Lifetime EP0462380B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP2159856A JPH0756051B2 (ja) 1990-06-20 1990-06-20 加工用高張力冷延鋼板の製造方法
JP159856/90 1990-06-20

Publications (3)

Publication Number Publication Date
EP0462380A2 true EP0462380A2 (fr) 1991-12-27
EP0462380A3 EP0462380A3 (en) 1993-10-06
EP0462380B1 EP0462380B1 (fr) 1996-11-13

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EP91106841A Expired - Lifetime EP0462380B1 (fr) 1990-06-20 1991-04-26 Procédé pour la fabrication de tÔles d'acier laminées à froid ayant une résistance élevée et apte au formage

Country Status (6)

Country Link
EP (1) EP0462380B1 (fr)
JP (1) JPH0756051B2 (fr)
KR (1) KR930004809B1 (fr)
AU (1) AU632228B2 (fr)
CA (1) CA2041403C (fr)
DE (1) DE69123088T2 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0780482A1 (fr) * 1995-12-20 1997-06-25 Sollac S.A. Acier laminé à froid présentant une bonne aptitude au soudage et au brasage

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19915633A1 (de) * 1999-04-07 2000-10-12 Volkswagen Ag Schwenklager
KR100729125B1 (ko) * 2005-12-28 2007-06-14 현대하이스코 주식회사 소성 변형비가 우수한 고강도 냉연강판 및 그 제조 방법
CN116815059A (zh) * 2023-07-06 2023-09-29 湖南华菱涟源钢铁有限公司 镀锌低碳钢及其制备方法和制品

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5884923A (ja) * 1981-11-16 1983-05-21 Nippon Steel Corp 高磁束密度低鉄損一方向性電磁鋼板の圧延方法
JPS6045689B2 (ja) * 1982-02-19 1985-10-11 川崎製鉄株式会社 プレス成形性にすぐれた冷延鋼板の製造方法
US4676844A (en) * 1985-03-06 1987-06-30 Kawasaki Steel Corporation Production of formable thin steel sheet excellent in ridging resistance
JPS61276927A (ja) * 1985-05-31 1986-12-06 Kawasaki Steel Corp 深絞り性の良好な冷延鋼板の製造方法
US4889566A (en) * 1987-06-18 1989-12-26 Kawasaki Steel Corporation Method for producing cold rolled steel sheets having improved spot weldability

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0780482A1 (fr) * 1995-12-20 1997-06-25 Sollac S.A. Acier laminé à froid présentant une bonne aptitude au soudage et au brasage
FR2742769A1 (fr) * 1995-12-20 1997-06-27 Lorraine Laminage Acier lamine a froid presentant une bonne aptitude au soudage et au brasage

Also Published As

Publication number Publication date
DE69123088T2 (de) 1997-03-06
AU632228B2 (en) 1992-12-17
KR930004809B1 (ko) 1993-06-08
JPH0756051B2 (ja) 1995-06-14
EP0462380B1 (fr) 1996-11-13
AU7597191A (en) 1992-01-02
EP0462380A3 (en) 1993-10-06
DE69123088D1 (de) 1996-12-19
CA2041403A1 (fr) 1991-12-21
CA2041403C (fr) 1997-04-22
JPH0452230A (ja) 1992-02-20
KR920000957A (ko) 1992-01-29

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