EP1709208B1 - Steel sheet for containers, and manufacturing method therefor - Google Patents

Steel sheet for containers, and manufacturing method therefor Download PDF

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Publication number
EP1709208B1
EP1709208B1 EP04807042.9A EP04807042A EP1709208B1 EP 1709208 B1 EP1709208 B1 EP 1709208B1 EP 04807042 A EP04807042 A EP 04807042A EP 1709208 B1 EP1709208 B1 EP 1709208B1
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steel sheet
thickness
nitriding
layer
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German (de)
English (en)
French (fr)
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EP1709208A1 (en
Inventor
Hidekuni c/o Nippon Steel Corporation MURAKAMI
Shigeru c/o Nippon Steel Corporation HIRANO
Akihiro c/o Nippon Steel Corporation ENOMOTO
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Nippon Steel Corp
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Nippon Steel and Sumitomo Metal Corp
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    • CCHEMISTRY; METALLURGY
    • C23COATING 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
    • C23CCOATING 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
    • C23C8/00Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/02Pretreatment of the material to be coated
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING 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
    • C21D8/00Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0236Cold rolling
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING 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
    • C21D8/00Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0257Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment with diffusion of elements, e.g. decarburising, nitriding
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/001Ferrous alloys, e.g. steel alloys containing N
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/02Ferrous alloys, e.g. steel alloys containing silicon
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/04Ferrous alloys, e.g. steel alloys containing manganese
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/06Ferrous alloys, e.g. steel alloys containing aluminium
    • CCHEMISTRY; METALLURGY
    • C23COATING 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
    • C23CCOATING 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
    • C23C8/00Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/08Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
    • C23C8/24Nitriding
    • C23C8/26Nitriding of ferrous surfaces
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING 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
    • C21D8/00Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0273Final recrystallisation annealing

Definitions

  • JP-A-2001-107189 discloses an extra-thin steel sheet excellent in homogeneity of material in coil and its production method, in which nitriding treatment is performed to obtain uniform properties in a coil.
  • JP-A-2001-107148 discloses a method for producing a high strength and high ductility steel sheet for vessels remarkably good in flange formability, in which nitriding treatment is performed to obtain uniform properties in a coil.
  • JP-A-08-176788 discloses a method for producing a steel sheet for vessels excellent in can forming properties, in which nitriding and carbonising treatment are performed.
  • JP-A-11-310829 and JP-A-07-3429 disclose a method for producing a cold rolled steel sheet for deep drawing, excellent in dent resistance and surface strain resistance, in which nitriding treatment is performed.
  • One of the objects of the present invention is to overcome the problems in containers manufactured using ultra-thin sheet materials by providing a specialized steel sheet and manufacturing method therefor, with respect to the color tone, surface coating adhesion and weldability of containers, which depend on the state of the steel sheet surface.
  • Another object of the present invention is to provide improvements by certain state controlled in both of the surface and mid-thickness layer of the material through the application of nitriding, which can allow both of controlling the state of the steel sheet surface and avoiding to add any special processing that would obstruct productivity.
  • Japanese Patent Application Publications 2004-323905 and 2004-218061 describe techniques of nitriding steel sheet in a post-annealing process and appropriately controlling the nitriding condition in the thickness direction of the sheet. Such techniques are provided, e.g., for the purpose of significantly improving the deformation resistance of containers without overly degrading the ductility of the steel sheet. In the course of evaluating the weldability, etc. of these materials, it was ascertained that there exist conditions under which the surface condition of the steel sheet becomes favorable, making it possible to greatly improve the color tone, surface coating adhesion and weldability of containers.
  • a steel sheet for containers is the steel sheet for containers with a sheet thicknesses of 0.400 mm or less, distinguished in that it contains, in terms of mass%, C: 0.0800% or less, N: 0.600% or less, Si: 2.0% or less, Mn: 2.0% or less, P: 0.10% or less, S: 0.05% or less and Al: 2.0% or less; (steel sheet cross-sectional mean Vickers hardness of 1/8 thickness surface layer) - (steel sheet cross-sectional mean Vickers hardness of 1/4 thickness mid-thickness layer) > 10 points, or (steel sheet cross-sectional maximum Vickers hardness of 1/8 thickness surface layer) - (steel sheet cross-sectional mean Vickers hardness of 1/4 thickness mid-thickness layer) > 20 points, the surface roughness is 0.90 ⁇ m or less in terms of Ra, and PPI, which is the number of concavo-convex peaks per one inch of length, is 250 or more.
  • the exemplary embodiment(s) of the steel sheet according to the present invention may furthermore contain, in terms of mass%, one, two, or more of Ti: 0.05% or less, Nb: 0.05% or less, and B: 0.015% or less.
  • the steel sheet may contain one, two, or more of Ti: 4 ⁇ C + 1.5 ⁇ S + 3.4 ⁇ N or more, Nb: 7.8 ⁇ C + 6.6 ⁇ N or more, and B: 0.8 ⁇ N or more.
  • the steel sheet may contain, in terms of mass%; one, two, or more of Cr: 20% or less, Ni: 10% or less, and Cu: 5% or less.
  • the steel sheet may furthermore contain, in terms of mass%, a total of 0.1% or less of Sn, Sb, Mo, Ta, V, and W.
  • Exemplary steel sheet components may furthermore be composed of, in terms of mass%, one, two, or more of Ti: 0.05% or less, Nb: 0.05% or less, and B: 0.015% or less.
  • Ti 0.05% or less
  • Nb 0.05% or less
  • B 0.015% or less.
  • Ti 4 ⁇ C + 1.5 ⁇ S + 3.4 ⁇ N or more
  • Nb 7.8 ⁇ C + 6.6 ⁇ N or more
  • B 0.8 ⁇ N or more
  • Further exemplary steel sheet components may be composed of, in terms of mass%, one, two, or more of Cr: 20% or less, Ni: 10% or less, and Cu: 5% or less.
  • a steel sheet components may also be composed of, in terms of mass%, a total of 0.1% or less of Sn, Sb, Mo, Ta, V and W.
  • the steel sheet can be held for no less than 1 second and no more than 360 seconds in an atmosphere comprising of 0.02% or more ammonia gas with the sheet temperature being 550 to 800 °C, making the product of temperature (°C) and time (seconds) in the thermal history in the 550 °C or higher temperature range after nitriding 48000 or less, or else making the mean rate of cooling from 550°C to 300 °C 10°C/second or greater.
  • a re-cold rolling reduction ratio after recrystallization annealing and before or after nitriding can be made 20% or less.
  • a particular upper limit to the C content before annealing is preferable to avoid degradation of workability, and is set at C: 0.0800%.
  • the upper limit can be set to 0.0600% or less, or more preferably, 0.0400% or less.
  • the steel according to an exemplary embodiment of the present invention wherein the content of N, which has properties similar to C, can be increased by nitriding after annealing, can have a low content of C, which is preferable from the perspective of ensuring strength and the like.
  • the strength can be ensured even with C: 0.0050% or less, with 0.0020% or less being permissible as well. At 0.0015% or less, it is possible to manufacture an ultra-soft material that would be outside the standard for normal container material, depending on the balance with the amount of nitriding.
  • an upper limit to the N content before annealing is preferable to avoid degradation of workability, and is set at N: 0.0300% or less.
  • N: 0.0200% or less can be preferable, N: 0.0150% or less can be more preferable, N: 0.0100% is even more preferable, N: 0.0050% or less is yet more preferable, and N: 0.0030% is further preferable.
  • the N incorporated by nitriding after annealing is there to provide a beneficial effect with regard to the color tone, surface coating adhesion and weldability of the can, and has a different effect from the N present before annealing.
  • Mn can be added to adjust strength. Too much of Mn will degrade workability, so it is set at 2.0% or less.
  • S can degrade hot ductility, and may obstruct casting and hot rolling, so it is set at 0.05% or less.
  • Al is an element which can be added for deoxidation. Too high content of Al makes being casted more difficult and causes damage such as increased surface flaws, so Al can be made 2.0% or less.
  • Ti can increase the recrystallization temperature of steel sheet, and degrade annealing pass-through of ultra-thin steel sheet, which is one of the objects of the present invention.
  • Ti can be made 0.050% or less. In normal applications which do not require a high r value in particular, there is no need to add Ti, and it is preferably made 0.03% or less, and more preferably 0.02% or less.
  • Nb has a similar effect to Ti, raising the recrystallization temperature of the steel sheet and markedly degrading annealing pass-through of ultra-thin steel sheet, which is one of the objects of the present invention.
  • Nb is preferably made 0.050% or less. In normal applications which do not need a high r value in particular, there is not requisite, so much, to add Nb, and it is preferably made 0.03% or less, more preferably 0.01 % or less.
  • the recrystallization temperature of the steel sheet may be increased and the annealing pass-through of ultra-thin steel sheet, which is the object of the present invention, are markedly degraded.
  • the recrystallization temperature can actually be lowered, thus enabling recrystallization annealing at a lower temperature.
  • B since B has the effect of improving annealing pass-through, it can even be actively added.
  • the upper limit is preferably set at 0.015%.
  • N content before nitriding B/N 0.6 to 1.5.
  • Cr solid-dissolved in the steel prior to nitriding binds with N which penetrates into the steel sheet due to nitriding, and has the effect of forming fine Cr nitrides in the steel, especially at the steel sheet surface, thus making it possible to utilize these nitrides to increase the effect of the present invention.
  • Cr also can increase the recrystallization temperature of the steel sheet, and excessive addition of it can markedly degrade the annealing pass-through of the ultra-thin steel sheet, which is one of the objects of the present invention.
  • a total of 0.1% or less of Sn, Sb, Mo, Ta, V and W may be incorporated to impart characteristics not explicitly specified by exemplary embodiments of the present invention without in any way detracting from the effect of the present invention.
  • P, B, Sn and Sb may, under certain conditions, lower the efficiency of nitriding, which is an important requirement for the present invention, thus it is preferable to consider to limit their maximum content in balance with the nitriding conditions.
  • “1/8 thickness surface layer” represents the corresponding area in FIG. 1 .
  • “1/4 thickness mid-thickness layer” represents the corresponding area in FIG. 1 .
  • An area corresponding to the "1/8 thickness surface layer” can be present on both surfaces of the steel sheet, and according to the exemplary embodiment of the present invention may apply to any material, whereof at least one such surface falls within the scope of the present invention.
  • the nitrogen distribution or hardness distribution between the top and bottom can be changed by the method of nitriding and by surface treatment before nitriding, as well as by various types of treatment after nitriding.
  • the exemplary embodiments of the present invention also applies to such steel sheet with different top and bottom surface layers. This is because it is possible to achieve the color tone; surface adhesion and weldability that are some of the objectives of the present invention, e.g., just on one surface.
  • N content of 1/8 thickness surface layer can be determined by analysis after polishing the steel sheet to leave only the area of interest.
  • an analytical value is used which is obtained by analysis after polishing away both surfaces to leave only the area of interest.
  • Vickers hardness values can be used which are measured at positions in the thickness direction and with a load that leaves a sufficiently small impression to allow suitable evaluation of the hardness distribution in the thickness direction of the steel sheet cross-section.
  • the measurement positions in the thickness direction can be set so as to obtain at least two measurement positions within 1/8 thickness and are equidistantly spaced in the thickness direction.
  • the mean of the values measured in each area is then taken as the respective cross-sectional mean hardness.
  • the distance between the indentations calls for care, but usually, for Vickers hardness determination, a suitable distance from the nearest impression can be provided according to the size of the indentations.
  • displacing while leaving an appropriate distance along the direction of the sheet surface makes it possible to maintain an appropriate distance between the indentations.
  • the influence of the sheet surface may become a problem; for such cases; measured values of cross-sectional hardness taken on steel sheet with equivalent stacked and tied thereto will be used.
  • “steel sheet cross-sectional maximum Vickers hardness of 1/8 thickness surface layer” and “steel sheet cross-sectional maximum Vickers hardness of 1/4 thickness mid-thickness layer” indicate the maximum hardness for each area in the hardness distribution obtained from the above-described "steel sheet cross-sectional mean Vickers hardness of 1/8 thickness surface layer” and “steel sheet cross-sectional mean Vickers hardness of 1/4 thickness mid-thickness layer", respectively.
  • Analytical values and hardness distribution normally exhibit some errors and variations due to local segregation of component elements and structural non-uniformities, and can be determined through trials with suitable quantities sufficient to exclude outliers.
  • nitriding which is an important condition for an exemplary embodiment of the present invention, including N increase due to nitriding and the content of N after annealing, is described below.
  • the exemplary embodiment according to the present invention provides that a difference in N content may be created between the surface layer part and the mid-thickness layer part of steel sheet.
  • This difference is specified as (N content of 1/8 thickness surface layer) - (N content of 1/4 thickness mid-thickness layer).
  • Such value can be set at 100 ppm, preferably 200 ppm, more preferably 300 ppm, even more preferably 500 ppm, still more preferably 1000 ppm, yet more preferably 2000 ppm, and even more preferably 3000 ppm.
  • the upper limit of (N content of 1/8 thickness surface layer) can be set at 20000 ppm.
  • a mean of 20000 ppm can be specified for the 1/8 thickness surface layer because the N content of the outermost layer will become 20000 ppm or greater under normal conditions of the exemplary embodiment of the present invention, which can readily cause surface problems such as plating defects.
  • the upper limit of (N content of 1/8 thickness surface layer) is preferably set at 6000 ppm, more preferably, 3000 ppm.
  • an appropriate state before nitriding should also be provided.
  • the N content of the steel sheet before nitriding is preferably made 0.0300% or less, as described above. If a large content ofN is already contained before nitriding, it becomes difficult to produce the effect of the present invention. Furthermore, in order to increase the N content by nitriding while avoiding degradation of workability, an upper limit to the N content after nitriding is needed, which is set at N: 0.600% or less.
  • the N content is preferably made N: 0.300% or less, more preferably N: 0.150% or less, even more preferably N: 0.100% or less, still more preferably N: 0.050% or less, and even more preferably 0.030% or less.
  • a higher N content is preferable not just in order to further harden the areas hardened by nitriding but also to stably obtain the effect of nitriding.
  • the exemplary embodiment of the present invention can be distinguished in that Ra is 0.90 ⁇ m or less and PPI is 250 or more. If Ra is too high or PPI is too low, the properties of color tone, surface coating adhesion, weldability etc, which are the objective of the present invention, will degrade due to the concavo-convexity of the surface.
  • Ra is preferably 0.80 ⁇ m or less, more preferably 0.70 ⁇ m or less, even more preferably 0.60 ⁇ m or less, still more preferably 0.50 pm or less.
  • PPI is preferably 300 or more, more preferably 350 or more, even more preferably 400 or more, still more preferably 450 or more, and yet more preferably 500 or more.
  • One exemplary method of segregating N toward the surface is to perform nitriding for a relatively short time in an ammonia atmosphere.
  • the surface state can also be affected by the previously existing steel components and crystal grain diameter, the annealing temperature and cold rolling conditions, as well as the reduction ratio, number of passes and roll roughness during temper rolling after nitriding, the plating conditions when plating is performed, etc. Therefore, while it is difficult to specify the surface state to a particular range, the basic control is the same as that conventionally performed, and can be achieved without problem by a person skilled in the art after several tests.
  • the concavo-convexities of the roll conventionally, since the concavo-convexities of a roll are worn off by rolling, in order to keep the concavo-convexities of the steel sheet surface within a desirable range, it was necessary to frequently perform roll replacement or machining of concavo-convexities, which produced an excessive burden on productivity and labor, such as having to stop production for roll maintenance.
  • the surface state of the steel sheet is hardly affected by the method of temper rolling, and there is not much need to manage the wearing of the concavo-convexities of the roll, making it possible to perform mass processing.
  • the thickness of the hardened layer in the surface layer, the material quality, especially the ductility, of the surface layer part, the ratio between the surface layer and mid-thickness layer parts, etc, may affect the concavo-convexity of the surface layer which is preferable according to the present invention. Therefore, if there are no extreme conditions deviating from the present invention, such as uniform nitriding on the entire sheet thickness, extreme increase of surface layer nitride concentration or formation of excessive Ti nitrides due to high Ti content of the steel sheet, and if the steel sheet is manufactured under conditions according to the present invention, the roughness of the steel sheet surface will be in a desirable range.
  • temper rolling is generally, to a large extent, performed after annealing, a desirable surface state can be obtained in the steel sheet according to the exemplary embodiment of the present invention without performing special control, but since bending of hearth rolls when passing the sheet through a conventional continuous annealing line causes fine cracking to form in the steel sheet surface, temper rolling is not considered essential.
  • coating may adhere finely and uniformly, and assume a desirable morphology and distribution according to the concavo-convexities of the steel sheet, even if fine control of the coating conditions or the like is not performed in the coating process.
  • the nitriding process according to the exemplary embodiment of the present invention can be advantageously performed simultaneously with or after the recrystallization annealing that follows cold rolling, continuously with the recrystallization annealing, but it is not limited to this.
  • the annealing method both batch and continuously annealing can be employed.
  • continuous annealing is advantageous.
  • the nitriding time and the subsequent thermal history may be disadvantageous for the nitriding time and the subsequent thermal history to become too long, and in this regard as well, it is preferable for at least the nitriding process to be conducted with continuous annealing equipment. In the absence of a special reason, the use of continuously annealed sheet is assumed. There are many merits in particular to conducting the continuous annealing process by controlling the atmosphere in the furnace in sections to perform recrystallization in the first half and nitriding in the latter half, such as productivity, uniformity of material quality, ease of controlling the nitriding state, etc.
  • the nitriding process should be determined by taking into consideration not only the increase in N content of the steel sheet due to nitriding, but also the steel sheet components and recrystallization annealing conditions, as well as the thermal history after nitriding and the like, and by looking at the diffusion ofN from the steel sheet surface to the inner area and at the changes in hardness along the sheet cross-section.
  • the color tone, surface coating adhesion and weldability that are the objective of the present invention cannot be obtained if one simply uses material quality determined by Rockwell hardness as an indicator.
  • the conditions here need to be determined with reference to an appropriate number of tests, but the fundamental idea is as follows, and the exemplary embodiment of the present invention can thus be specified.
  • nitriding should be performed with the steel sheet temperature of 550 to 800 °C. This can be achieved by setting the nitriding atmosphere to this temperature as in conventional annealing, passing the steel sheet through this atmosphere to bring the sheet temperature into this range, and simultaneously performing nitriding.
  • the nitriding atmosphere can be set to a lower temperature, and nitriding can be carried out by inserting steel sheet heated to this temperature range into that atmosphere.
  • the steel sheet nitriding efficiency may in some cases deterioration due to variation and breakdown of the atmosphere unrelated to nitriding of the steel sheet, so it may be specified as 550 to 750 °C. It is preferably made 600 to 700 °C, more preferably 630 to 680 °C.
  • the nitriding atmosphere may contain, by volumetric ratio, 10% or more nitrogen gas, preferably 20% or more, more preferably 40% or more, even more preferably 60% or more, and as necessary, it may contain 90% or less hydrogen gas, preferably 80% or less, more preferably 60% or less, still more preferably 20% or less; it may also contain 0.02% or more ammonia gas as necessary.
  • the rest can be oxygen gas, hydrogen gas, carbon dioxide gas, hydrogen carbide gas and various inert gases.
  • Ammonia gas in particular is highly effective in raising the nitriding efficiency and makes it possible to obtain a specific amount of nitriding within a short period of time, thus preventing diffusion of N into the steel sheet mid-thickness and providing an effect favorable to the exemplary embodiment of the present invention.
  • nitriding generally does not take place in an atmosphere which mainly consists of nitrogen gas and hydrogen gas
  • a person skilled in the art would be able to modify the atmosphere to where nitriding took place after suitable trials, not only by admixture of ammonia gas as describe above, but also by modifying the dew point, by admixture of trace amounts of gases, modification of gas ratios, etc.
  • the exemplary embodiment of the present invention covers atmospheres for which it can be detected based on modem analytical capabilities that nitriding took place due to heat treatment including annealing at least.
  • the holding time in the nitriding atmosphere is generally not restricted, but in conjunction with the 550 °C or higher temperature conditions of the present invention, considering the steel sheet thickness of 0.400 mm maximum, in consideration of the fact that, if N, penetrating from the steel sheet surface due to nitriding by diffusion ofN in the steel sheet, reaches the steel sheet mid-thickness layer while it is held in the nitriding atmosphere, it may not be possible to obtain the N distribution or hardness distribution which is the objective of the present invention, the upper limit is set at 360 seconds. Furthermore, even if nitriding efficiency is improved, 1 second is required to obtain the amount of nitriding and the nitrogen and hardness distribution in the thickness direction of the steel sheet that are required by the present invention.
  • 2 to 120 seconds may be preferable, 3 to 60 seconds more preferable, 4 to 30 seconds even more preferable, and 5 to 15 seconds more preferable still.
  • the nitriding efficiency should be increased by increasing the ammonia concentration or the like when controlling in a short time period.
  • the thermal history of the steel sheet after nitriding is also important for controlling the nitrogen distribution in the thickness direction of the steel sheet. Considering the thickness of the steel sheets in question and the diffusion of nitrogen in the steel, holding for a long time at a high temperature may not be desirable.
  • the effect of the exemplary embodiment of the present invention is pronounced by making the nitrogen distribution appropriately gradual through heat treatment
  • the history in the 550 °C or higher temperature region is important, and the product of temperature (°C) and time (seconds) in this temperature region is preferably made 48000 or lower. This corresponds to 80 seconds at 600 °C or 60 seconds at 800 °C, but when the temperature is continuously changing, the effect thereof can be suitably evaluated by recording the temperature changes in approximately 5-second time slices and finding the sum of the products of temperature (°C) and time (seconds) for each time slice.
  • the rate of cooling after nitriding greatly can influence the effect of the present invention.
  • differences in the cross-sectional hardness distribution may be observed because the state of formation of nitrides changes greatly in the cooling process, even at low temperature and in a short period of time, when there is hardly any change in the nitrogen distribution.
  • Making the mean rate of cooling from 550 ° to 300 °C 10 °C/s or greater will leave more solid-dissolved nitrogen, make the surface layer part relatively harder as compared to the mid-thickness layer, and improve the color tone, surface coating adhesion and weldability.
  • it is made 20 °C/s or more, with 50 °C/s or more being more preferable.
  • re-cold rolling can be performed after recrystallization annealing for hardness adjustment and sheet thickness adjustment.
  • the reduction ratios employed here range from 1%, close to that of skin passing performed for shape adjustment, to 50% or more, the same as for cold rolling.
  • the same sort of re-cold rolling can be employed as for conventional steel sheet.
  • re-cold rolling is carried out in the range of about 0.5% to 2.5%.
  • the steel sheet of the present invention may also be normally subjected to this extent of rolling.
  • the re-cold rolling rather preferentially hardens the hard surface layer part with a high N content, making the hardness difference between the surface and mid-thickness layers formed in the steel sheet of the present invention more pronounced.
  • the surface layer is more susceptible to work hardening due to the large content of solid-dissolved N and nitrides, while the mid-thickness layer is constrained by the surface layer, so it cannot preferentially deform and does not selectively harden to greatly exceed the hardening of the surface layer.
  • the reduction ratio is preferably made up to about 70%.
  • re-cold rolling ratios are desirable, being preferably 6% or greater, more preferably 10% or greater, even more preferably 20% or greater, yet more preferably 30% or greatly, and more preferably still, 40% or greater.
  • lower reduction ratios of re-cold rolling are desirable from the viewpoint of ductility, with 50% or less being preferable, 40% or less being more preferable, 30% or less being even more preferable, 20% or less being yet more preferable, 10% or less being still more preferable, and 5% or less being even more preferable.
  • the reduction ratio is preferably made 0.8 to 45%, with 4 to 35% being more preferable, 6 to 30% being even more preferable, and 8 to 25% being more preferable still.
  • the time of re-cold rolling would be after the nitriding, but if recrystallization annealing and nitriding are performed in separate processes, re-cold rolling can also be performed before nitriding.
  • the time of re-cold rolling would be after the nitriding, but if recrystallization annealing and nitriding are performed in separate processes, re-cold rolling can be performed before nitriding.
  • the slab, bloom, or billet in cases where hot rolling is performed is not limited to any manufacturing method such as the ingot method or continuous casting method, and the effect of the present invention can be obtained with the slab reheating method, the CC-DR method, whereby hot rolling is performed directly without reheating the cast slab, or with thin slab casting whereby rough rolling and the like is omitted, since the effect of the present invention does not depend on the thermal history before annealing.
  • the effect of the exemplary embodiment of the present invention furthermore does not have to depend on the hot rolling conditions and can be obtained with two-phase region rolling with an ⁇ + y two-phase region finishing temperature, or with continuous hot rolling whereby rough bars are joined and rolled.
  • the steel sheet of the exemplary embodiment of the present invention is used as a material for containers with the welding area, softening of the heat affected zone is suppressed and the surface layer area with especially high N concentration rapidly cools and hardens, which has the effect of increasing the weld strength. This becomes more marked when elements such as B and Nb are added, which are conventionally used to control softening of heat affected zones.
  • the steel sheet of the exemplary embodiment of the present invention includes cases where surface treatment of whatever sort is carried out. Namely, in steel sheets used by the customers after surface treatment, color tone and weldability are necessary for the steel sheet after surface treatment, and the favorable state of the steel sheet surface which is necessary for these characteristics is not damaged by surface treatment in the case of steel sheet manufactured as described above.
  • the absolute value of PPI or Ra may change significantly due to the surface treatment, but the function which provides a favorable surface state for the steel sheet by controlling the hardness of the steel sheet in the thickness direction, i.e. the state wherein numerous low concavo-convexities are formed, can be adequately detected on the steel sheet even after surface treatment. This effect provides good color tone and weldability for the surface-treated steel sheet.
  • the state of the steel sheet surface before surface treatment may be important. For this characteristic as well, creating a favorable steel sheet surface state by controlling the hardness of the steel sheet in the thickness direction as disclosed according to the exemplary embodiment of the present invention, e.g., creating a state wherein numerous low concavo-convexities are formed, may provide a good adhesion.
  • For the surface treatment in the case of metal plating, conventionally used tin, chrome (tin-free), Ni, zinc, aluminum or the like is applied. Not only the adhesion of these coatings, but also the color tone and weldability after formation of the coating are improved. Adhesion can be improved by the effect of the present invention also in the case of substrates for laminated steel sheet coated with an organic film, which has come into use in recent years, and in cases where the steel sheet is painted directly or after metal plating or the like.
  • the exemplary embodiment of the present invention can be used for containers in general, whether they be two-piece cans or three-piece cans, and it goes without saying that it can be used in cases where the problem to be solved is similar to that described above, for whatever application.
  • an evaluation of color tone, surface coating adhesion and weldability was conducted using an Sn-plated steel sheet, which is one of the most commonly used types of steel sheet for containers.
  • L values obtained using a spectrocolorimeter after applying 10 ⁇ m transparent polyester resin and drying were used as an indicator. Higher L values indicate superior color tone, and these values were used to grade the samples.
  • the L value also depends on conditions other than steel components and the manufacturing conditions for obtaining the present invention, and the required level differs depending on the application and the like, so determining suitability solely on the basis of absolute values may in some respects not always conform to practical utility. Nonetheless, less than 60 was taken as "improvement required,” 60 to 75 was taken as “usable,” 75 to 90 was taken as "good” and 90 or greater was taken as "very good.”
  • the weldable current range was determined based on the occurrence of splash (occurrence of spatter) during welding, the weld strength based on a peel test (Hein test), and the welded surface damage due to arc current between the steel sheet surface and an electrode ring during welding, and the decision was made based on the width of that range and the lower limit value.
  • the decision was made by taking a wider range as being desirable in terms of higher manufacturing stability, and taking a lower minimum as desirable in terms of being less prone to material quality change and peeling of plating due to temperature increase of the welding area.
  • Productivity was evaluated based on productivity during temper rolling.
  • the "productivity" referred to here does not merely signify the volume of production per unit time, but also includes the ease of personnel and equipment management for maintaining the desired line operation.
  • the reason for focusing on temper rolling is that surface control, which is a distinguishing feature of the steel of the present invention, is mainly performed in the state of the art through management of roll roughness and rolling conditions during temper rolling. In terms of categories, an investigation was conducted based primarily on the number of rolling passes and the management relating to roll roughness; basically, cases where rolling at low roughness is possible, roll roughness management tolerances are wide and the number of rolling passes is small are preferable.
  • the change in elements in the thickness direction before nitriding is extremely small, being of a negligible extent with regard to the effect of the exemplary embodiment of the present invention.
  • the N content of the 1/8 thickness surface layer and the N content of the 1/4 thickness mid-thickness layer were assumed to be the same in the steel sheet before nitriding.
  • temper rolling was performed to manufacture steel sheet.
  • the rolling conditions, final sheet thickness, nitrogen content analysis results and property evaluation results for these steels are shown in Tables 5 through 8. It was possible to confirm that good color tone, surface coating adhesion and weldability could be obtained by controlling the state in the sheet thickness direction to be within the range of the present invention by the manufacturing method of the present invention. In some of the cases, an attempt was made to adjust the surface roughness by means of special temper rolling conditions on materials which were not nitrided, but efficient production was obstructed due to roll wear, the number of passes, etc.
  • the steel sheet for containers and manufacturing method thereof according to the exemplary embodiment of the present invention allows the color tone, surface coating adhesion and weldability of containers to be improved while avoiding complicated treatment after nitriding and hindrance of productivity due to such complicated treatment. Therefore, the productivity of ultra-thin steel sheet for containers can be improved, providing a remarkable industrially useful effect.
  • the steel sheet for containers according to exemplary embodiments of the present invention and the manufacturing method therefor make it possible to improve the color tone, surface coating adhesion and weldability of containers while avoiding complicated processing after nitriding and obstruction of productivity due to this complicated processing. Therefore, it becomes possible to keep as high productivity as of conventional sheet and method with complicated processing for steel sheet for ultra-thin containers and provide an industrially-useful effect.

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  • Mechanical Engineering (AREA)
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  • Metallurgy (AREA)
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  • Physics & Mathematics (AREA)
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  • Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
EP04807042.9A 2003-12-09 2004-12-08 Steel sheet for containers, and manufacturing method therefor Active EP1709208B1 (en)

Applications Claiming Priority (2)

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JP2003409918 2003-12-09
PCT/JP2004/018683 WO2005056841A1 (en) 2003-12-09 2004-12-08 Steel sheet for containers, and manufacturing method therefor

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EP1709208B1 true EP1709208B1 (en) 2014-08-06

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JP (1) JP4299859B2 (ko)
KR (2) KR100895347B1 (ko)
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EP1806420A4 (en) * 2004-09-09 2008-04-23 Nippon Steel Corp STEEL PLATE FOR EXTREMELY THIN CONTAINERS AND RELATED MANUFACTURING METHOD
US8518501B2 (en) 2010-03-10 2013-08-27 Restaurant Technology, Inc. Food holding device, method of making, and method of storing cooked food
US9777353B2 (en) * 2011-11-21 2017-10-03 Nippon Steel & Sumitomo Metal Corporation Hot-rolled steel sheet for nitriding, cold-rolled steel sheet for nitriding excellent in fatigue strength, manufacturing method thereof, and automobile part excellent in fatigue strength using the same
DE102014112286A1 (de) 2014-08-27 2016-03-03 Thyssenkrupp Ag Verfahren zur Herstellung eines aufgestickten Verpackungsstahls
DE102014116929B3 (de) * 2014-11-19 2015-11-05 Thyssenkrupp Ag Verfahren zur Herstellung eines aufgestickten Verpackungsstahls, kaltgewalztes Stahlflachprodukt und Vorrichtung zum rekristallisierenden Glühen und Aufsticken eines Stahlflachprodukts
JP6108044B2 (ja) * 2015-03-31 2017-04-05 Jfeスチール株式会社 缶蓋用鋼板およびその製造方法
JP6421772B2 (ja) * 2016-02-29 2018-11-14 Jfeスチール株式会社 缶用鋼板の製造方法
EP3875626B1 (de) * 2020-03-06 2024-07-17 ThyssenKrupp Rasselstein GmbH Verpackungsblecherzeugnis
DE102020112485B3 (de) 2020-05-08 2021-08-12 Thyssenkrupp Rasselstein Gmbh Stahlblech und Verfahren zur Herstellung eines Stahlblechs für Verpackungen
DE102021129191A1 (de) 2021-11-10 2023-05-11 Thyssenkrupp Rasselstein Gmbh Stahlblech mit einem zweischichtigen Kristallisationsgefüge und Verfahren zur Herstellung eines solchen Stahlblechs
DE102023103708A1 (de) 2023-02-15 2024-08-22 Thyssenkrupp Rasselstein Gmbh Verfahren zur Herstellung eines Stahlblechs für Verpackungen mit einem mehrschichtigen Kristallisationsgefüge sowie Stahlblech mit einem mehrschichtigen Kristallisationsgefüge

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JP3105380B2 (ja) * 1993-06-21 2000-10-30 新日本製鐵株式会社 耐デント性ならびに耐面ひずみ性に優れた深絞り用冷延鋼板の製造方法
JP3448380B2 (ja) * 1994-12-27 2003-09-22 新日本製鐵株式会社 容器用鋼板の製造方法
JP3777049B2 (ja) * 1998-04-30 2006-05-24 新日本製鐵株式会社 耐デント性ならびに耐面ひずみ性に優れた深絞り用bh冷延鋼板の製造方法
JP4249860B2 (ja) * 1999-10-01 2009-04-08 新日本製鐵株式会社 容器用鋼板の製造方法
JP2001107189A (ja) * 1999-10-06 2001-04-17 Nippon Steel Corp コイル内の材質の均質性に優れる極薄鋼板およびその製造方法

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WO2005056841A1 (en) 2005-06-23
CN1890389A (zh) 2007-01-03
EP1709208A1 (en) 2006-10-11
KR20060096465A (ko) 2006-09-11
JP4299859B2 (ja) 2009-07-22
JP2007519818A (ja) 2007-07-19
CN100427614C (zh) 2008-10-22
KR100895347B1 (ko) 2009-04-29

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