EP0032583A1 - Verfahren zur kontinuierlichen Wärmebehandlung eines kaltgewalzten Stahlbandes - Google Patents

Verfahren zur kontinuierlichen Wärmebehandlung eines kaltgewalzten Stahlbandes Download PDF

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Publication number
EP0032583A1
EP0032583A1 EP80108148A EP80108148A EP0032583A1 EP 0032583 A1 EP0032583 A1 EP 0032583A1 EP 80108148 A EP80108148 A EP 80108148A EP 80108148 A EP80108148 A EP 80108148A EP 0032583 A1 EP0032583 A1 EP 0032583A1
Authority
EP
European Patent Office
Prior art keywords
steel strip
process according
cooling
temperature
overaging
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
EP80108148A
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English (en)
French (fr)
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EP0032583B1 (de
Inventor
Hajime Nitto
Hiromitsu Naito
Takao Saito
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.)
Nippon Steel Corp
Original Assignee
Nippon Steel Corp
Priority date (The priority date 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 date listed.)
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Priority claimed from JP16682779A external-priority patent/JPS5933172B2/ja
Priority claimed from JP16682679A external-priority patent/JPS5933171B2/ja
Application filed by Nippon Steel Corp filed Critical Nippon Steel Corp
Publication of EP0032583A1 publication Critical patent/EP0032583A1/de
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Publication of EP0032583B1 publication Critical patent/EP0032583B1/de
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Classifications

    • 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

  • the present invention relates to a process for continuously annealing a cold rolled steel strip. More particularly, the present invention relates to a process for continuously annealing a cold rolled steel strip, which process is capable of completing the annealing operation within a short time and, also, capable of obtaining a cold rolled steel strip having an excellent workability, especially formability and an excellent surface quality, at a low cost.
  • the continuous annealing method can exhibit an extremely high efficiency in comparison with the conventional batch type annealing method. However, it is strongly desired to increase the efficiency of the continuous annealing method to such an extent that the continuous annealing operation is completed within a few minutes.
  • the heating and cooling operations result in the formation of a considerably large thickness of the oxide layer, and this large thickness causes the time necessary for completing the elimination of the oxide layer to be undesirably long.
  • the sheet surface is coarsened due to the pickling for removing the oxide layer.
  • the elimination of the oxide layer from the steel strip is carried out during the reheating overaging operation at a relatively low temperature. Therefore, in order to effectively attain the elimination of the oxide layer, the reducing operation should be carried out by using a strictly controlled reducing atmosphere having a special concentration of hydrogen and dew point. Also, in the processes (1) and (2), in order to overage the steel strip after the rapid cooling, it is necessary to reheat the steel strip to an overaging temperature thereof.
  • the combustion air ratio is adopted as a parameter of the combustion condition in the direct fired furnace.
  • the oxidation tendency of the sheet surface is dependent upon the combustion air ratio.
  • the present invention involves a concept of combining the following:
  • the process without the overaging step of the present invention can be applied to cold-rolled non-aging low carbon steel strips, for example, cold-rolled, extremely low carbon aluminum killed steel strips, and cold-rolled non- or retarded-aging extremely low carbon steel strips containing a small amount of Ti, Nb, V or B, which are capable of forming carbonitrides.
  • the process of the present invention can be applied to various cold-rolled low carbon steel strips which include the usual type of cold-rolled low carbon steel strips having a drawing quality and a deep drawing quality, for example, bodies of automobiles, high tensile strength cold-rolled low carbon steel strips and other types of cold-rolled low- carbon steel strips suitable for various surface-treating processes, for example, metal plating and coating processes. Since, there is no necessity of overaging in the non- or retarded-aging steels, the steel strips are directly pickled after cooling, so as to remove the oxide layer.
  • the primary cooling operation is followed by an overaging operation.
  • the overaging operation is usually applied to them.
  • the cooling operation must be terminated when the temperature of the steel strip reaches a level near an overaging temperature of the steel strip, the cooled steel strip may be overaged and, then, the overaged steel strip may be additionally cooled to a desired temperature.
  • the peripheral surface of the cold-rolled steel strip may be cleaned to remove grease or rolling oil therefrom by a conventional surface-cleaning method. Otherwise, the process of the present invention may be applied to the cold rolled steel strip without surface-cleaning it.
  • radiation heating means such as a radiant-tube heating and other appropriate heating means, are employed for heating the steel strip to a temperature within the range of from the recrystallization temperature to the A C3 point of the steel strip and also for holding the steel strip within the temperature range of from the recrystallization temperature to the Ac 3 point over a period of at least 10 seconds, preferably from 10 to 60 seconds.
  • the present invention is characterized as compared with the prior arts in the combination use of the radiation heating furnace for heating steel strip to and holding it within the requisite annealing temperature range, cooling the steel strip by a cooling medium consisting of a mixture of gas and liquid, a pickling removal of the oxide layer formed by the cooling and overaging without reheating, if overaging is necessary.
  • the holding temperature depends on the composition and the other properties of the steel strip, as well as the objective properties of the final product.
  • the holding temperature is not always constant but may be varied in the direction of the holding zone so as to adapt the heat cycle for recrystallization and growth of crystal grains.
  • the heating rate is lower than that of the direct fired heating, but the surface deterioration due to the direct contact of flame with the sheet surface is prevented.
  • the pickling time in the final step is shortened as compared with that of steel strips heated in the direct fired furnace, and also a surface quality problem involved in the pickling is mitigated.
  • a non-oxidizing or reducing atmosphere inert to the steel is employed for the furnace atmosphere and is maintained during the heating and holding zones, the oxidation of the sheet surface in these zones is prevented.
  • the pickling at the final step is carried out at an extent sufficient to remove only a thin oxide layer formed at this cooling step or the primary cooling step.
  • the reducting atmosphere preferably comprises a mixture of 4% by volume or more of hydrogen gas, with the balance consisting of nitrogen gas, and preferably exhibits a dew point of 10°C or less.
  • the steel strip which is subjected to the holding in a radiation heating furnace, is then rapidly cooled at a cooling rate from 10 to 300°C/second which is preferable from the view points of the metallurgical properties of the annealed steel strip.
  • the steel strip may be directly rapid-cooled from the holding temperature, or may be slow-cooled from the holding temperature to a temperature of preferably 600°C at the lowest and then rapid-cooled, if necessary.
  • the rapid cooling must start at a temperature between the above holding temperature and 600°C from the view points of shortening the overaging time period.
  • the steel strip can be rapidly cooled by immersing it into water, e.g. boiled water
  • a cooling medium consisting of a mixture of gas and liquid hereinafter referred to as a gas-liquid cooling medium
  • a gas-liquid cooling medium not only realizes the rapid cooling but also provides such advantages as, good shape of the cooled steel strip, and easiness in controlling the cooling rate.
  • gas-liquid cooling medium herein is preferably a fluid which is produced through such a process that a high speed gas stream and a liquid stream of a predetermined pressure are injected from their respective nozzles as jet streams and these streams are then mixed with each other by intersecting with each other so that the liquid (e.g., water) reduces itself to fine particles mixed in the gas in the form of a mist, or in a form almost equivalent to spray.
  • liquid e.g., water
  • the liquid is preferably water and the gas is usually selected from inert gases, such as nitrogen gas, and mixtures of nitrogen and hydrogen.
  • the gas-liquid cooling medium consists of a mixture of nitrogen gas with water.
  • the overaging operation is carried out for the purpose of precipitating carbon in the steel matrix which has been super-saturated with a solid solution carbon.
  • the overaging operation is preferably carried out in a temperature range of from 300 to 550°C, more preferably, from 350 to 450°C, for 3 minutes or less, more preferably 2 minutes or less. It is not always necessary that the steel strip be maintained at a constant temperature throughout the overaging operation. That is, the overaging temperature in an initial stage of the overaging operation may be higher than that in a final stage of the overaging operation.
  • the temperature profile from the entry to withdrawal ends of the overaging equipment may be gradual or may decrease stepwise.
  • the peripheral surface portion of the steel strip cannot be prevented from oxidation. That is, the resultant layer of oxides causes the appearance of the steel strip surface to be unsatisfactory, and the surface property of the steel strip to be unsuitable to the surface treatments. Therefore, it is necessary to eliminate the layer of oxides from the peripheral surface of the steel strip.
  • the elimination of the oxide layer is effected by any conventional pickling methods effective for eliminating various oxides.
  • the oxide layer can be removed by treating the peripheral surface of the steel strip with, for example, an acid aqueous solution of an inorganic acid, such as hydrochloric acid, sulfuric acid or phosphoric acid, or of an organic acid, such as formic acid or oxalic acid.
  • the treatment may be effected by immersing the steel strip in an acid aqueous solution, by spraying the acid aqueous solution onto a peripheral surface of the steel strip, or by subjecting the steel strip to an electrolytic pickling with an acid aqueous solution.
  • the oxide layer formed in the cooling and, optionally, overaging operations is very thin. Therefore, the oxide layer can be readily eliminated by the above-mentioned methods.
  • the pickled steel strip is linsed with water. However, since the peripheral surface of the acid-cleaned steel strip is reactive to oxygen and easily rusts, it is preferable that the linsed steel strip be neutralized with a diluted alkali aqueous solution. This neutralization is effective for preventing rust and discoloration of the peripheral surface of the steel strip.
  • the cold rolled steel strip for example, to be used for producing an automobile body, is coated before the working process.
  • the surface of steel strip is treated with zinc phosphate.
  • the quality of the zinc phosphate film formed on the surface of the steel strip can be improved by applying the following treatment to the steel strip after the pickling operation.
  • an aqueous suspension containing water-insoluble phosphate for example, Zn 3 (P0 4 ) 2
  • a thin film of Ni, Zn or Mn is flash-coated on the pickled steel strip surface by means of electroplating.
  • the surface of steel strip is treated with the zinc phosphate.
  • the above-mentioned surface pre-treatment is effective for promoting the formation of crystal nuclei of the zinc phosphate and for providing a dense film of the zinc phosphate. Therefore, the above-mentioned surface pre-treatment is very effective for enhancing the bonding strength of the zinc phosphate layer to the coating layer and for increasing the resistance of the coating layer to corrosion.
  • the process of the present invention can exhibit the following advantages.
  • 0.8 mm thick cold rolled steel strips were processed under the conditions given in Table 1.
  • the oxide film thickness in the comparative examples 1 and 2 was determined by preliminary experiments, in which the steel strips were heated under the same condition as in these examples by a direct fired furnace followed by a rapid cooling by means of blowing nitrogen gas on the strips in the next zone. Samples were cut from the strips and pickled in a 5% hydrochloric acid aqueous solution. The weight decrease of samples due to pickling was reduced to the thickness of the oxide layer of FeO.
  • the 0.8 mm thick cold rolled steel strips were processed under the conditions given in Table 2.
  • the oxide layer thickness was determined by the same procedure as described above.

Landscapes

  • 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 Strip Materials And Filament Materials (AREA)
EP80108148A 1979-12-24 1980-12-22 Verfahren zur kontinuierlichen Wärmebehandlung eines kaltgewalzten Stahlbandes Expired EP0032583B1 (de)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
JP166826/79 1979-12-24
JP16682779A JPS5933172B2 (ja) 1979-12-24 1979-12-24 冷延鋼板の連続焼鈍処理方法
JP16682679A JPS5933171B2 (ja) 1979-12-24 1979-12-24 冷延鋼板の連続焼鈍方法
JP166827/79 1979-12-24

Publications (2)

Publication Number Publication Date
EP0032583A1 true EP0032583A1 (de) 1981-07-29
EP0032583B1 EP0032583B1 (de) 1984-08-01

Family

ID=26491070

Family Applications (1)

Application Number Title Priority Date Filing Date
EP80108148A Expired EP0032583B1 (de) 1979-12-24 1980-12-22 Verfahren zur kontinuierlichen Wärmebehandlung eines kaltgewalzten Stahlbandes

Country Status (4)

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EP (1) EP0032583B1 (de)
BR (1) BR8008511A (de)
CA (1) CA1152870A (de)
DE (1) DE3068827D1 (de)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0049729A1 (de) * 1980-10-09 1982-04-21 Nippon Steel Corporation Verfahren und Vorrichtung zum Kühlen eines kaltgewalzten Stahlbandes
EP0157708A2 (de) * 1984-04-05 1985-10-09 Stein Heurtey Entfettungsverfahren für kaltgewalztes Stahlband
FR2562563A1 (fr) * 1984-04-05 1985-10-11 Stein Heurtey Procede de degraissage d'une bande metallique laminee a froid
CN112111638A (zh) * 2020-09-27 2020-12-22 攀钢集团研究院有限公司 低碳冷轧钢板的分级生产方法
CN112593051A (zh) * 2020-12-07 2021-04-02 山东钢铁集团日照有限公司 一种预防氧化铁皮生成的退火炉快速点炉升温的方法
CN115058582A (zh) * 2022-07-14 2022-09-16 上海曙佳科技发展有限公司 一种连退炉炉内可视化及工件温度管理方法

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2401381B2 (de) * 1973-01-11 1975-02-20 Nippon Kokan K.K., Tokio Durchziehofen
DE2133411B2 (de) * 1970-07-03 1975-07-03 Nippon Kokan K.K., Tokio Verfahren und Vorrichtung zum kontinuierlichen Abschrecken eines Metallbandes
DE2159597B2 (de) * 1970-12-01 1975-08-07 Nippon Steel Corp., Tokio Anlage zur kontinuierlichen Wärmebehandlung eines kaltgewalzten Stahlbleches
DE2061726B2 (de) * 1969-12-16 1978-01-19 Nippon Kokan ICK, Tokio Vorrichtung zur kontinuierlichen behandlung von stahlbaendern und verfahren zu ihrem betrieb

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1336490A (en) * 1970-12-28 1973-11-07 Nippon Kokan Kk Method and apparatus for quenching metal stocks

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2061726B2 (de) * 1969-12-16 1978-01-19 Nippon Kokan ICK, Tokio Vorrichtung zur kontinuierlichen behandlung von stahlbaendern und verfahren zu ihrem betrieb
DE2133411B2 (de) * 1970-07-03 1975-07-03 Nippon Kokan K.K., Tokio Verfahren und Vorrichtung zum kontinuierlichen Abschrecken eines Metallbandes
DE2159597B2 (de) * 1970-12-01 1975-08-07 Nippon Steel Corp., Tokio Anlage zur kontinuierlichen Wärmebehandlung eines kaltgewalzten Stahlbleches
DE2401381B2 (de) * 1973-01-11 1975-02-20 Nippon Kokan K.K., Tokio Durchziehofen

Non-Patent Citations (7)

* Cited by examiner, † Cited by third party
Title
PATENTS ABSTRACTS OF JAPAN Vol, 4, No. 22, 23 February 1980 page 128C74 & JP-A-54 162614. *
PATENTS ABSTRACTS OF JAPAN Vol. 1, No. 4, 10 March 1977 page 46C76 & JP-A-51 112413. *
PATENTS ABSTRACTS OF JAPAN Vol. 1, No. 64, 22 June 1977 page 995C77 & JP-A-52 028411. *
PATENTS ABSTRACTS OF JAPAN Vol. 2, No. 59, 27 April 1978 page 431C78 & JP-A-53 017518. *
PATENTS ABSTRACTS OF JAPAN Vol. 3, No. 7, 24 January 1979 page 160C34 & JP-A-53 132418. *
PATENTS ABSTRACTS OF JAPAN Vol. 3, No. 7, 24 January 1979 page 60C34 & JP-A-53 130219. *
PATENTS ABSTRACTS OF JAPAN Vol. 4, No. 38, 27 March 1980 page 50C4 & JP-A-55 011155. *

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0049729A1 (de) * 1980-10-09 1982-04-21 Nippon Steel Corporation Verfahren und Vorrichtung zum Kühlen eines kaltgewalzten Stahlbandes
EP0157708A2 (de) * 1984-04-05 1985-10-09 Stein Heurtey Entfettungsverfahren für kaltgewalztes Stahlband
FR2562563A1 (fr) * 1984-04-05 1985-10-11 Stein Heurtey Procede de degraissage d'une bande metallique laminee a froid
EP0157708A3 (en) * 1984-04-05 1987-05-20 Stein Heurtey Degreasing process for cold-rolled metal strip
CN112111638A (zh) * 2020-09-27 2020-12-22 攀钢集团研究院有限公司 低碳冷轧钢板的分级生产方法
CN112111638B (zh) * 2020-09-27 2022-05-24 攀钢集团研究院有限公司 低碳冷轧钢板的分级生产方法
CN112593051A (zh) * 2020-12-07 2021-04-02 山东钢铁集团日照有限公司 一种预防氧化铁皮生成的退火炉快速点炉升温的方法
CN115058582A (zh) * 2022-07-14 2022-09-16 上海曙佳科技发展有限公司 一种连退炉炉内可视化及工件温度管理方法
CN115058582B (zh) * 2022-07-14 2024-06-11 上海曙佳科技发展有限公司 一种连退炉炉内可视化及工件温度管理方法

Also Published As

Publication number Publication date
EP0032583B1 (de) 1984-08-01
BR8008511A (pt) 1981-07-21
CA1152870A (en) 1983-08-30
DE3068827D1 (en) 1984-09-06

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