EP0900857B1 - Tole d'acier galvanise a chaud presentant peu de defauts par suite d'un placage defectueux, ainsi que d'excellentes caracteristiques d'adherence de depot par contact, et son procede de production - Google Patents

Tole d'acier galvanise a chaud presentant peu de defauts par suite d'un placage defectueux, ainsi que d'excellentes caracteristiques d'adherence de depot par contact, et son procede de production Download PDF

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Publication number
EP0900857B1
EP0900857B1 EP97900126A EP97900126A EP0900857B1 EP 0900857 B1 EP0900857 B1 EP 0900857B1 EP 97900126 A EP97900126 A EP 97900126A EP 97900126 A EP97900126 A EP 97900126A EP 0900857 B1 EP0900857 B1 EP 0900857B1
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Prior art keywords
zinc
hot
steel sheet
dip
coated
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German (de)
English (en)
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EP0900857A4 (fr
EP0900857A1 (fr
Inventor
Nobue Kawasaki Steel Corporation Fujibayashi
Kazuaki Kawasaki Steel Corporation Kyono
Motonori Kawasaki Steel Corporation MIYAOKA
Nobuo Instit. Nuclear Safety System Inc. TOTSUKA
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JFE Steel Corp
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JFE Steel Corp
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Classifications

    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/06—Zinc or cadmium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
    • B05D3/002—Pretreatement
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
    • B05D3/007—After-treatment
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C18/00—Alloys based on zinc
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
    • C23C2/0224—Two or more thermal pretreatments
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/024—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by cleaning or etching
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/26—After-treatment
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
    • C23C2/36—Elongated material
    • C23C2/40—Plates; Strips
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
    • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
    • C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
    • C23G1/08—Iron or steel
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
    • C25F1/00—Electrolytic cleaning, degreasing, pickling or descaling

Definitions

  • the present invention relates to a zinc and zinc-alloy hot-dip-coated steel sheet having a decreased number of bare spots and excellent coating adhesion, and a method for manufacturing the same.
  • Zinc and zinc-alloy hot-dip-coated steel sheets are mainly used for automobile bodies because of low cost and excellent corrosion resistance, and in addition to the corrosion resistance due to coating, coating adhesion during press working is required for applying the steel sheets to automobile bodies.
  • coating adhesion deteriorates, coated layers peel as a powder or blocks, which phenomenon sometimes causes galling in press forming or deteriorates corrosion resistance of the portions from which the coated layer peels; and also, peeled fragments disadvantageously inflict the steel sheet.
  • Japanese Patent Laid-Open No. 61-276961 discloses a technique in which alloying Fe with Zn at a high temperature ranging from 700 to 850°C is performed after zinc hot-dip-coating.
  • alloying at a high temperature lead to not only higher costs but also increased expenses for equipment such as rolls.
  • steel contains at least one of Zr, La, Ce, Y, and Ca, and the cooling rate from recrystallization annealing to coating is set to not less than 50°C/sec.
  • the cost is raised due to the addition of Zr or the like to steel and productivity deteriorates because the sheet-feeding rate has to be lowered due to the cooling capacity.
  • the O, Al, and N contents in steel are set to not more than 0.0045 wt%, (25 x N wt%) to 0.15 wt%, and not more than 0.0030%, respectively.
  • restrictions on the Ti, Si, and P contents, and Si (wt%) + P (wt%) ⁇ Ti (wt%) must be satisfied according to Japanese Patent Laid-Open No. 6-81101.
  • the desired steel-sheet properties such as strength and drawing cannot be always achieved by such content restrictions, and there is a possibility that coating adhesion will deteriorate because of deviations from a predetermined composition range.
  • recrystallization annealing at a high temperature ranging from approximately 700 to 900°C is necessary to attain excellent material characteristics.
  • CGL recrystallization annealing is generally carried out under a nitrogen atmosphere in the presence of hydrogen (hereinafter referred to as reduction annealing), and although this atmosphere is a reducing atmosphere for Fe, it is an oxidizing atmosphere for some elements such as Si, Mn, and P.
  • reduction annealing a nitrogen atmosphere in the presence of hydrogen
  • this atmosphere is a reducing atmosphere for Fe
  • this atmosphere is a reducing atmosphere for Fe
  • it is an oxidizing atmosphere for some elements such as Si, Mn, and P.
  • elements such as Si, Mn, and P (referred to as readily oxidizable elements) which are more oxidizable than Fe externally diffuse during reduction annealing and bond to oxygen on the surface of steel sheets to form oxides (called as "surface segregated layer”). Since these oxides significantly impede wettability between molten zinc and the steel sheets,
  • Japanese Patent Examined Publication No. 61-9386 proposes a method of pre-plating the surface of steel sheets with Ni before the zinc hot-dip-coating process.
  • Ni plating when steel contains at least Si and one more element among 0.2 to 2.0 wt% of Si, 0.5 to 2.0 wt% of Mn, and 0.1 to 20 wt% of Cr, Ni plating of not less than 10 g/m 2 is necessary, resulting in an increased cost.
  • Ni plating of not less than 10 g/m 2 is necessary, resulting in an increased cost.
  • such a large quantity of Ni plating improves the wettability between the zinc hot-dip-coating and the steel sheet, disadvantageously, defects caused by Si and Ni on the coated surface frequently appear during the alloying process.
  • Japanese Patent Laid-Open No. 57-70268 proposes a method of pre-plating the surface of steel sheets with Fe before the zinc hot-dip-coating process. According to this method, bare spots in Si-containing steel are preventable by pre-plating, however, not less than 5 g/m 2 of Fe plating is required, which fact is extremely uneconomical.
  • Japanese Patent Laid-Open No. 6-158172 discloses a method in which a steel containing Si ⁇ 0.2 and Mn ⁇ 1.5 by wt% is wound at a temperature not less than 650°C followed by acid washing, cold-rolling, annealing, and zinc hot-dip-coating; and Japanese Patent Laid-Open No.
  • 6-179943 discloses a method in which a steel containing 0.10 to 1.5 wt% of Si and 1.00 to 3.5 wt% of Mn is wound at a temperature ranging from 500°C to 680°C, both inclusive, followed by acid washing, cold-rolling, annealing, and zinc hot-dip-coating.
  • JP-A-7-216 524 discloses a high tensile strength hot rolled steel plate which is subjected to descaling pickling, desmutting treatment, weak oxidation, and reduction heating. Then, hot dipping is applied.
  • the oxide film of Fe, resulting from weak oxidation and having 500-10000 - film thickness, is reduced to active metal Fe by reduction heating while preventing Si and Mn in the steel from being selectively oxidized and concentrated in the surface layer part.
  • the atmosphere for reduction heating is regulated so that it has a reducing power reducing the oxide film of Fe but causing no selective oxidation of the Si and Mn in the steel by controlling hydrogen concentration to 3-25 vol.%.
  • JP-A-7-090 529 discloses a steel sheet having an Si content of ⁇ 0.2 wt.% which is subjected to cold rolling by using work rolls which are distributed with grinding grains of the rolls in the axial direction of the rolls in average and which have the surface roughness (Ra ⁇ ) in the circumferential direction thereof of 0.1 to 0.6 ⁇ m and the diameter of ⁇ 200 mm, thereafter, the surfaces of the steel sheet are heated in an oxidizing atmosphere (an atmosphere containing, for example, O 2 , H 2 O, CO 2 , CO, etc.), and in succession, the steel sheet is heated in a reducing atmosphere (for example, gaseous nitrogen in which H 2 is included at 2 to 10 vol.%). The steel sheet is then subjected to galvanizing or further to galvannealing.
  • an oxidizing atmosphere an atmosphere containing, for example, O 2 , H 2 O, CO 2 , CO, etc.
  • a reducing atmosphere for example, gaseous nitrogen in which H 2 is included at 2 to 10
  • the inventors of the present invention have found that bare spots and coating adhesion are remarkably improved by providing oxides of readily oxidizable elements just under a coated layer of a zinc and zinc-alloy hot-dip-coated steel sheet.
  • the present invention provides a zinc and zinc-alloy hot-dip-coated hot-rolled steel sheet comprising oxides inside of and near the surface of the steel sheet surface just under a coated layer, said oxides being formed with elements more oxidizable than iron, wherein said zinc and zinc-alloy hot-dip-coated hot-rolled steel sheet is obtainable from a process comprising:
  • the oxygen concentration is preferably not less than 1 ppm, more preferably, 2 to 200 ppm, and further more preferably, 3 to 100 ppm, in a region of from the surface layer of a steel-sheet substrate just under the coated layer to 3 ⁇ m deep in the sheet-thickness direction.
  • such hot-dip-coated hot-rolled steel sheets are preferably further subjected to heat-alloying after zinc hot-dip-coating, and excellent alloyed zinc and zinc-alloy hot-dip-coated hot-rolled steel sheets are thereby obtained.
  • the oxygen concentration is preferably not less than 1 ppm, more preferably, 2 to 200 ppm, and further more preferably, 3 to 100 ppm, in a region of from the surface layer of a steel-sheet substrate just under the coated layer to 3 ⁇ m deep in the sheet-thickness direction.
  • each of the zinc and zinc-alloy hot-dip-coated hot-rolled steel sheets and alloyed zinc and zinc-alloy hot-dip-coated steel sheets preferably contains at least one element selected from the group consisting of Si, Mn, and P as a steel component in the following ranges: 0.001 ⁇ Si ⁇ 3.0 Wt% 0.05 ⁇ Mn ⁇ 2.0 Wt% 0.005 ⁇ P ⁇ 0.2 Wt%
  • the present invention provides a method for producing the above-mentioned zinc and zinc-alloy hot-dip-coated hot-rolled steel sheets or the alloyed zinc-alloy hot-dip-coated hot-rolled steel sheets according to claim 6, both of which show a decreased number of base spots and excellent coating adhesion.
  • the present invention provides a method having:
  • the oxides formed in the step A preferably remain after a pre-treatment step carried out after the step A until treatment conducted in an annealing furnace immediately before the step B.
  • a slab subjected to hot rolling preferably contains at least one element selected from the group consisting of Si, Mn, and P as a steel component in the following ranges: 0.001 ⁇ Si ⁇ 3.0 Wt% 0.05 ⁇ Mn ⁇ 2.0 Wt% 0.005 ⁇ P ⁇ 0.2 Wt%
  • an alloyed zinc and zinc-alloy hot-dip-coated steel sheet can be produced by employing heat-alloying treatment after the step B.
  • oxides of readily oxidizable elements are formed during hot-rolling, in particular, the oxides are grown when the temperature (hereinafter referred to as "CT" ) during coiling is high and the cooling rate after coiling is low.
  • CT temperature
  • the oxides formed during hot-rolling are observed just under the scale, as is shown in figure 6. Meanwhile, in a conventional hot-rolled sheet, no oxide is observed just under the scale, as is shown in figure 7.
  • the oxides observed during hot-rolling are analyzed by using an electron probe microanalyzer (hereinafter referred to as "EPMA") and the results are shown in figure 1. Since Mn, P, Al, and 0 show peaks, it is understood that oxides of these elements are formed.
  • Steel sheets shown in figures 6 and 1 contain 0.1 wt% of Mn, 0.006 wt% of P, and 0.03 wt% of Al, and they do not contain a particularly large amount of Mn, P, or Al.
  • the oxides positioned inside of and near the surface of the steel sheet surface just under a coated layer of a zinc hot-dip-coated hot-rolled steel sheet or an alloyed zinc hot-dip-coated hot-rolled steel sheet of the present invention are produced such that oxides formed inside of and near the surface of the steel sheet surface just under the scale during the hot-rolling process remain even after post-treatment steps such as pickling and coating.
  • the mechanism of producing oxides just under the scale is as follows: oxygen in a scale layer essentially consisting of iron oxide which has been formed during hot-rolling internally diffuses into steel during or after the coiling process, and then, forms an oxide of a readily oxidizable element in the steel. Therefore, oxides are produced even when only a trace amount of readily oxidizable elements is contained in the steel.
  • oxides of elements more oxidizable than iron exist inside of and near the surface of the steel sheet surface just under the zinc and zinc-alloy hot-dip-coating according to the present invention
  • an oxide of an element less oxidizable than iron oxide or iron may also be contained.
  • such an oxide is preferably formed in grain boundaries of a hot-rolled steel sheet.
  • the inventors of the present invention have found oxides of Si-O, Mn-O, Al-O, P-O, and Fe-Si-O in the steel sheets.
  • Figure 2 shows the result of elemental analysis of a conventional steel sheet and figure 3 shows that of an unannealed cold-rolled steel sheet wherein oxides were observed, which analysis was carried out in a region of from the surface of each steel sheet to approximately 10 ⁇ m in the depth direction by glow-discharge spectroscopy (hereinafter referred to as "GDS").
  • GDS glow-discharge spectroscopy
  • Figure 4 shows the result of elemental analysis of a conventional steel sheet and figure 5 shows that of an annealed cold-rolled steel sheet wherein oxides were observed, which analysis was carried out by GDS in a region of from the surface of each steel sheet to approximately 10 ⁇ m in the depth direction.
  • GDS GDS
  • a large amount of surface segregated substances generated by reduction annealing is observed in the conventional steel sheet of figure 4, meanwhile the generation of surface segregation products is suppressed and hardly observed in the steel sheet with oxides produced during hot-rolling.
  • oxides of the present invention which exist in a surface layer of a steel sheet (surface layer of a steel-sheet substrate) just under a coated layer can optical-microscopically be observed by etching the steel sheet with a 1% nital solution for several to several dozen of seconds.
  • Figure 8 (photograph) and figure 9 (photograph) show a conventional alloyed zinc hot-dip-coated steel sheet not containing oxide and an alloyed zinc hot-dip-coated steel sheet containing oxides incorporated in the present invention, respectively.
  • Figures 8 and 9 are cross-sectional optical micrographs of alloyed zinc hot-dip-coated steel sheets taken at a magnification of x1,000. Black ribbon-like materials observed just under the coated layer are oxides (shown by arrows).
  • oxides can also be confirmed by analyzing oxygen contained in steel.
  • Concerning technique oxygen in steel is analyzed in the total sheet-thickness direction using a hot-rolled steel sheet whose scale layer has been removed by pickling after coiling, a steel sheet obtained by dissolving only a coated layer of a zinc and zinc-alloy hot-dip-coated steel sheet, an unannealed cold-rolled steel sheet, or an annealed steel sheet, and the resulting values are compared with those of steel sheets obtained by grinding the surface layer in which oxides are formed.
  • the steel sheets in which oxides are formed have larger oxygen values analyzed in the total sheet-thickness direction as compared with those of the ground sheets.
  • This phenomenon is assumed to be due to following: the amount of readily oxidizable elements in the surface layer decreases because the readily oxidizable elements already precipitate as oxides during or after coiling; the formed oxides impede transfer (external diffusion) of the readily oxidizable elements from bulk steel to the steel sheet surface; and oxidation-reduction occurs inside the steel sheet, in other words, a Fe-containing oxide produced during or after coiling changes to an oxide of readily oxidizable element during reduction annealing.
  • the surface segregated substances of the readily oxidizable elements which substances impede wettability between molten zinc and the steel sheet, extremely decrease, thereby remarkably improving bare spots.
  • a steel sheet having oxides inside of and near the surface of the steel sheet surface just under a coated layer i.e. a steel sheet of the present invention
  • a steel sheet of the present invention has spaces between oxide crystals
  • zinc more readily penetrates into the steel sheet as compared with conventional steel sheets not containing oxides.
  • the interface between the coated layer and the steel sheet is significantly roughened so that the coated layer can tightly adhere to the steel sheet.
  • a zinc hot-dip-coated steel sheet and an alloyed zinc hot-dip-coated steel sheet both incorporated in the present invention acquire excellent coating adhesion during press forming.
  • Figures 10 and 11 show the observation results obtained from a steel sheet using a SEM, a coated layer of which steel sheet has been forcibly dissolved to the iron potential according to a galvanostatic process (4% methyl salicylate, 1% salicylic acid, and 10% potassium iodide/methanol solution; 5 mA/cm 2 ) so as to expose the steel sheet. It is understood that the interface between the coated layer and the steel sheet is apparently more roughened as compared with the conventional steel sheet not containing oxides.
  • the technique disclosed by the present invention exhibits more excellent effects when a steel sheet contains at least one component selected from the group consisting of Si, Mn, and P as a steel component in the following ranges: 0.001 ⁇ Si ⁇ 3.0 Wt% 0.05 ⁇ Mn ⁇ 2.0 Wt% 0.005 ⁇ P ⁇ 0.2 Wt% Problems such as bare spots and decreased coating adhesion hardly occur in steel sheets not containing the above elements, thus the lower limits for these elements are preferably 0.001 wt% for Si, 0.05 wt% for Mn, and 0.005 wt% for P. Meanwhile, the upper limit for each element is determined considering the preferable ranges for both the maximum effect for strengthening and cost.
  • the technique disclosed by the present invention exhibits sufficient effects on both bare spots and coating adhesion when even a small amount of oxides is observed by an optical microscope in a cross-section of a zinc and zinc-alloy hot-dip-coated steel sheet etched by 1% nital.
  • the temperature for coiling after hot-rolling must be 600°C or more to produce oxides and the cooling rate up to 540°C after coiling must be not more than the following: (CT - 540) 0.9 ö 40 (°C/min) Oxides are not formed at not more than 540°C even when slow-cooling is further carried out.
  • Zinc and zinc-alloy hot-dip-coating of the present invention is a general term for molten zinc containing zinc and may include not only zinc hot-dip-coating but also galfan and galvalume, in both of which Si is contained in zinc. Moreover, Pb, Mg, Mn, etc. may be further contained. Therefore, conditions for a zinc bath are not particularly restricted.
  • the preferred amount of zinc and zinc-alloy coating is approximately 25 to 90 g/m 2 and the preferred iron content.in a coated layer in an alloyed zinc hot-dip-coated steel sheet is 8 to 13 wt%.
  • hot-rolled steel sheets and cold-rolled steel sheets can be used as a material for coating.
  • Each sample shown in Table 1 was melted by a converter and formed into a slab by continuous casting.
  • Each of the resulting slabs was hot-rolled to 1.2 to 3.5 mm thick at a slab-heating temperature of 1150 to 1200°C, and with a finishing temperature of 900 to 920°C, and a coiling temperature and a cooling rate which are shown in Table 2.
  • the resulting sheets were pickled for 5 to 15 seconds at 80°C in an aqueous 5% HCl solution to remove scale layers, and then, divided into two groups one of which was directly subjected to the CGL and the other was cold-rolled into 0.7 mm thick.
  • the following methods were also used in combination as a pre-treatment for removing the surface layer of a steel sheet, if required.
  • Electrolytic degreasing electrolysis at 60°C in an aqueous 3% NaOH solution for approximately 10 seconds.
  • Brushing roll a brushing roll with abrasive grains.
  • both the hot-rolled sheet and the cold-rolled sheet were zinc hot-dip-coated at 470°C after annealing at 800 to 850°C.
  • alloyed zinc hot-dip-coated steel sheets were obtained by successively subjecting the annealed sheets to an alloying process conducted at 480 to 530°C for 15 to 30 seconds.
  • a cross section of each hot-rolled sheet with the scale was ground and, without being etched, subjected to optical-microscopic observation so as to measure the depth of oxide invasion.
  • the preferred magnification of the optical microscopy was 1,000.
  • each of the coated sheets was immersed in the solutions shown below until the end of the dissolving reaction of coating and then the concentration of the oxide-derived oxygen in a region of from the surface of the steel sheet to 3 ⁇ m in the sheet-thickness direction was calculated according to the following formula: (oxygen in a steel sheet whose coating was peeled by a hydrochloric acid ⁇ antimony method) - (oxygen in a steel sheet whose coating was peeled by a hydrochloric acid ⁇ antimony method and whose surface layer was then ground to remove 3 ⁇ m thereof)
  • Each of the coated sheets was subjected to a Dupont impact test using a 1/2-inch punch and occurrence of peeling was confirmed by macroscopic observation.
  • Each alloyed zinc alloy hot-dip-coated steel sheet was bent to 90°, bent back, and then the compressed side of the steel sheet was peeled by a tape so as to measure the peeled amount of zinc by fluorescent X ray.
  • Table 3 shows the results of the zinc hot-dip-coated steel sheet and Table 4 shows those of the alloyed zinc hot-dip-coated steel sheets.
  • Table 1 Sample-Steel Composition Symbol C wt% Si wt% Mn wt% P wt% A 0.105 0.010 0.08 0.008 B 0.070 0.10 0.10 0.01 C 0.070 0.50 2.0 0.07 D 0.010 1.50 0.10 0.05 E 0.003 0.003 0.05 0.005 F 0.003 0.01 0.20 0.01 G 0.003 0.30 0.50 0.04 H 0.003 0.05 1.95 0.20 Table 2 Coiling conditions, depth of oxide invasion into hot-rolled sheet, and oxide amount in hot-rolled sheet Sample steel CT °C Mean cooling rate to 540°C °C/min Depth of oxide invasion into hot-rolled sheet ⁇ m Oxide amount in hot-rolled sheet ppm Sample steel No.
  • a 540 1.0 0 0 1 A 600 1.0 1 1 2 A 600 1.5 0 ⁇ 1 3 A 700 2.0 7 5 4 B 650 1.5 8 8 5 C 650 1.5 6 7 6 D 580 1.0 0 0 7 D 620 1.2 ⁇ 1 ⁇ 1 8 E 650 1.2 5 5 9 E 650 1.6 ⁇ 1 1 10 E 650 1.8 0 ⁇ 1 11 F 650 1.0 10 11 12 G 650 1.0 12 15 13 H 600 1.8 0 0 14 H 650 1.0 12 18 15
  • the technique disclosed by the present invention relates to a zinc hot-dip-coated steel sheet and an alloyed zinc hot-dip-coated steel sheet showing a decreased number of bare spots and excellent coating adhesion, and are appropriately used mainly for steel sheets of automobile bodies.

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Claims (10)

  1. Tôle d'acier laminée à chaud, galvanisée au zinc et à l'alliage de zinc par immersion à chaud, comprenant des oxydes à l'intérieur et près de la surface de la tôle d'acier juste en dessous d'une couche déposée, lesdits oxydes étant formés d'éléments plus oxydables que le fer, dans laquelle ladite tôle d'acier laminée à chaud, galvanisée au zinc et à l'alliage de zinc par immersion à chaud peut être obtenue par un procédé comprenant :
    une étape A de formation d'oxydes à l'intérieur et près de la surface de la tôle d'acier juste au-dessous de la calamine, lesquels oxydes étant formés d'éléments plus oxydables que le fer, en établissant une température d'une bande en acier à pas moins de 600°C et en établissant le taux de refroidissement lent moyen jusqu'à 540°C à pas plus de (CT (température de refroidissement) - 540)0,9 + 40 (°C/min) au cours du refroidissement de ladite bande d'acier laminée à chaud ; et
    une étape B pour galvaniser au zinc et à l'alliage de zinc par immersion à chaud ladite bande d'acier.
  2. Tôle d'acier laminée à chaud, galvanisée au zinc et à l'alliage de zinc par immersion à chaud selon la revendication 1, dans laquelle la concentration en oxygène n'est pas inférieure à 1 ppm dans une région allant de la couche superficielle d'un substrat de tôle d'acier juste en dessous de ladite couche déposée à 3 µm de profondeur dans la direction de l'épaisseur de la tôle.
  3. Tôle d'acier laminée à chaud, galvanisée au zinc et à l'alliage de zinc par immersion à chaud selon la revendication 1, dans laquelle ladite tôle d'acier est en outre soumise à une opération d'alliage à chaud.
  4. Tôle d'acier laminée à chaud, galvanisée au zinc et à l'alliage de zinc par immersion à chaud selon la revendication 3, dans laquelle la concentration en oxygène n'est pas inférieure à 1 ppm dans une région allant de la couche superficielle d'un substrat de tôle d'acier juste en dessous de ladite couche déposée à 3 µm de profondeur dans la direction de l'épaisseur de la tôle.
  5. Tôle d'acier laminée à chaud, galvanisée au zinc et à l'alliage de zinc par immersion à chaud selon l'une quelconque des revendications 1 à 4, dans laquelle au moins un élément choisi parmi le groupe constitué de Si, Mn et P est présent en tant que composant acier dans les plages suivantes : 0,001 ≤ Si ≤ 3,0 % en poids 0,05 ≤ Mn ≤ 2,0 % en poids 0,005 ≤ P ≤ 0,2 % en poids
  6. Procédé de production d'une tôle d'acier laminée à chaud, galvanisée au zinc et à l'alliage de zinc par immersion à chaud comprenant :
    une étape A de formation d'oxydes à l'intérieur et près de la surface de la tôle d'acier juste au-dessous de la calamine, lesquels oxydes étant formés d'éléments plus oxydables que le fer, en établissant une température d'une bande en acier à pas moins de 600°C et en établissant le taux de refroidissement lent moyen jusqu'à 540°C à pas plus de (CT (température de refroidissement) - 540)0,9 + 40 (°C/min) au cours du refroidissement de ladite bande d'acier laminée à chaud ; et
    une étape B pour galvaniser au zinc et à l'alliage de zinc par immersion à chaud ladite bande d'acier.
  7. Procédé de production d'une tôle d'acier laminée à chaud, galvanisée au zinc et à l'alliage de zinc par immersion à chaud selon la revendication 6, dans lequel lesdits oxydes formés dans ladite étape A restent après une étape de prétraitement réalisée après ladite étape A et jusqu'à ce que le traitement de recuit soit réalisé dans un four immédiatement avant ladite étape B.
  8. Procédé de production d'une tôle d'acier laminée à chaud, galvanisée au zinc et à l'alliage de zinc par immersion à chaud selon l'une quelconque des revendications 6 et 7, dans lequel une ébauche soumise au laminage à chaud contient au moins un élément choisi parmi le groupe constitué de Si, Mn et P en tant que composant acier dans les plages suivantes : 0,001 ≤ Si ≤ 3,0 % en poids 0,05 ≤ Mn ≤ 2,0 % en poids 0,005 ≤ P ≤ 0,2 % en poids
  9. Procédé de production d'une tôle d'acier laminée à chaud, galvanisée au zinc et à l'alliage de zinc par immersion à chaud selon l'une quelconque des revendications 6 et 7, dans lequel ladite tôle d'acier laminée à chaud, galvanisée au zinc et à l'alliage de zinc par immersion à chaud est traitée avec alliage à chaud après ladite étape B.
  10. Procédé de production d'une tôle d'acier laminée à chaud, galvanisée au zinc et à l'alliage de zinc par immersion à chaud selon la revendication 9, dans lequel une ébauche soumise au laminage à chaud contient au moins un élément choisi parmi le groupe constitué de Si, Mn et P en tant que composant acier dans les plages suivantes : 0,001 ≤ Si ≤ 3,0 % en poids 0,05 ≤ Mn ≤ 2,0 % en poids 0,005 ≤ P ≤ 0,2 % en poids
EP97900126A 1997-01-13 1997-01-13 Tole d'acier galvanise a chaud presentant peu de defauts par suite d'un placage defectueux, ainsi que d'excellentes caracteristiques d'adherence de depot par contact, et son procede de production Expired - Lifetime EP0900857B1 (fr)

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PCT/JP1997/000045 WO1998030729A1 (fr) 1997-01-13 1997-01-13 Tole d'acier galvanise a chaud presentant peu de defauts par suite d'un placage defectueux, ainsi que d'excellentes caracteristiques d'adherence de depot par contact, et son procede de production

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EP0900857A1 EP0900857A1 (fr) 1999-03-10
EP0900857A4 EP0900857A4 (fr) 2000-08-02
EP0900857B1 true EP0900857B1 (fr) 2004-03-31

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EP (1) EP0900857B1 (fr)
KR (1) KR100325755B1 (fr)
CA (1) CA2215110C (fr)
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WO (1) WO1998030729A1 (fr)

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CA2330010C (fr) * 1999-02-25 2008-11-18 Kawasaki Steel Corporation Plaque d'acier, plaque d'acier obtenue par immersion a chaud et alliage de plaque d'acier obtenue par immersion a chaud et leurs procedes de production
JP4886118B2 (ja) * 2001-04-25 2012-02-29 株式会社神戸製鋼所 溶融亜鉛めっき鋼板
MXPA04006178A (es) * 2002-03-01 2004-12-06 Jfe Steel Corp Lamina de acero con superficie tratada y metodo para la produccion de la misma.
CN104388870B (zh) 2009-12-29 2017-04-12 Posco公司 一种热压模塑部件
JP6694511B2 (ja) 2015-12-23 2020-05-13 ポスコＰｏｓｃｏ 延性、穴加工性、及び表面処理特性に優れた高強度冷延鋼板、溶融亜鉛めっき鋼板、並びにそれらの製造方法
KR102330604B1 (ko) 2019-12-03 2021-11-24 주식회사 포스코 전기저항 점용접부의 피로강도가 우수한 아연도금강판 및 그 제조방법

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JPH0790529A (ja) * 1993-09-24 1995-04-04 Sumitomo Metal Ind Ltd 珪素含有鋼溶融亜鉛めっき鋼板および合金化溶融亜鉛めっき鋼板の製造方法
JP3277063B2 (ja) * 1994-01-25 2002-04-22 日新製鋼株式会社 高張力熱延鋼板の溶融めっき方法

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KR19980702926A (ko) 1998-09-05
EP0900857A4 (fr) 2000-08-02
EP0900857A1 (fr) 1999-03-10
DE69728389T2 (de) 2005-02-24
CA2215110A1 (fr) 1998-07-13
WO1998030729A1 (fr) 1998-07-16
KR100325755B1 (ko) 2002-07-18
CA2215110C (fr) 2001-08-14
DE69728389D1 (de) 2004-05-06

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