EP0620288B1 - Feuille laminee a froid, eventuellement galvanisee a chaud, aux qualites de sechage de peinture a chaud, de non-vieillissement a froid et de formage excellentes, et procede de production - Google Patents

Feuille laminee a froid, eventuellement galvanisee a chaud, aux qualites de sechage de peinture a chaud, de non-vieillissement a froid et de formage excellentes, et procede de production Download PDF

Info

Publication number
EP0620288B1
EP0620288B1 EP93919599A EP93919599A EP0620288B1 EP 0620288 B1 EP0620288 B1 EP 0620288B1 EP 93919599 A EP93919599 A EP 93919599A EP 93919599 A EP93919599 A EP 93919599A EP 0620288 B1 EP0620288 B1 EP 0620288B1
Authority
EP
European Patent Office
Prior art keywords
cold
temperature
rolled steel
hot
annealing
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.)
Expired - Lifetime
Application number
EP93919599A
Other languages
German (de)
English (en)
Other versions
EP0620288A1 (fr
EP0620288A4 (fr
Inventor
Naoki; Yoshinaga
Kohsaku; Ushioda
Osamu; Akisue
Yoshikazu; Matsumura
Kunio Nishimura
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.)
Filing date
Publication date
Priority claimed from JP5044108A external-priority patent/JP2980785B2/ja
Application filed by Nippon Steel Corp filed Critical Nippon Steel Corp
Publication of EP0620288A1 publication Critical patent/EP0620288A1/fr
Publication of EP0620288A4 publication Critical patent/EP0620288A4/fr
Application granted granted Critical
Publication of EP0620288B1 publication Critical patent/EP0620288B1/fr
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
    • C21D8/0426—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
    • C21D8/0436—Cold rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
    • C21D8/0473—Final recrystallisation annealing

Definitions

  • the present invention relates to a cold-rolled steel sheet and a hot-dip galvanized cold-rolled steel sheet having excellent bake hardenability, non-aging properties at room temperature and good formability and a process for producing the same.
  • the cold-rolled steel sheet according to the present invention is subjected to press molding before use in automobiles, domestic electric appliances, buildings, etc. It includes both a cold-rolled steel sheet in a narrow sense, which has an untreated surface, and a cold-rolled steel sheet subjected to surface treatments, such as galvanizing or alloyed galvanizing, for rust preventive purposes. Since the steel sheet according to the present invention has a combination of strength with formability, use thereof enables the sheet thickness to be reduced to a greater extent than with conventional steel sheets. In other words, a reduction in weight is possible. Therefore, the steel sheet of the present invention can be expected to contribute to the protection of the environment.
  • extra low carbon steel sheets having a good formability.
  • extra low carbon steel sheets disclosed in, for example, JP-A 59-31827 and JP-A-59-38337, wherein Ti and Nb are added in combination have a combination of very good formability and paint-bake hardenability (BH) and are also excellent in hot-dip galvanizing properties, so that they hold an important position in this field.
  • BH paint-bake hardenability
  • the BH level of these sheets does not exceed the level of the conventional BH steel sheets, and an attempt to further enhance the BH level unfavorably makes it impossible to ensure that non-aging properties at room temperature.
  • numerous extra low carbon steel sheets containing neither Ti or Nb and having an excellent formability have been disclosed, and examples thereof include those disclose in JP-B-53-22052 and JP-A-58-136721 and JP-A-58-141335.
  • JP-A-59-31827 and JP-A-59-38337 disclose a production process in which Si and P are mainly added to an extra low carbon steel sheet containing Ti and Nb to produce a high-strength cold-rolled steel sheet having a tensile strength up to 45 kgf/mm 2 .
  • JP-B-57-57945 discloses a representative prior art technique in which P is added to an extra low carbon steel containing Ti to produce a high-strength cold-rolled steel sheet. Further, with respect to extra low carbon steels containing neither Ti nor Nb, JP-B-58-57492 and JP-A-58-48636 disclose a technique in which P is added to enhance the strength, and JP-A-57-43932 discloses a technique in which Si is utilized.
  • P has hitherto been most extensively used as a reinforcing element with Si being the second most extensively used reinforcing element.
  • Si have been considered to have a very high solid solution strength capability, enable the strength to be increased by addition thereof in a minor amount, cause no significant lowering in ductility and deep drawability and further incur no significant increase in cost derived from the addition of these elements.
  • an attempt to attain the increase in strength by addition of these elements alone causes not only strength but also yield strength to be remarkably increased, which renders the face shape unsatisfactory, so that use thereof in panels for automobiles is often limited.
  • Si induces a failure in plating or P and Si remarkably lower the alloying rate, so that the productivity is lowered.
  • JP-A-63-190141 and JP-A-64-62440 disclose a technique in which Mn is added to an extra low carbon steel sheet containing Ti
  • JP-B-59-42742 and the above-described JP-B-57-57945 disclose a technique in which Mn and Cr are added to an extra low carbon steel sheet containing Ti
  • JP-A-62-40352 discloses a technique in which Mn is added to an extra low carbon steel containing neither Ti nor Nb.
  • JP-A-2-111841 discloses a cold-rolled steel sheet and a hot-dip galvanized steel sheet having a bake hardenability and a good formability, comprising a Ti-containing extra low carbon steel and, added thereto, from 1.5 to less than 3.5% of Mn.
  • an improvement in operating stability of hot rolling and in the homogeneity of the metallic structure through a lowering in Ar 3 transformation point is intended by the addition of a large amount of Mn.
  • the addition of Cr and V in amounts in the range of from 0.2 to 1.0% is also disclosed with a view to further improving the ductility.
  • DP steel dual phase steel
  • YR very low yield ratio
  • JP-B-3-2224 and JP-B-3-21611 and JP-A-3-277741 disclose steel sheets having a composite structure comprising an extra low carbon steel as a raw material.
  • large amounts of Nb and B in combination with Ti are added to an extra low carbon steel to bring the structure after annealing to a composite structure comprising a ferritic phase and a phase formed by low-temperature transformation, thereby providing a cold-rolled steel sheet having a combination of a high r value, a high BH level, a high ductility with non-aging properties at room temperature.
  • the present inventors have found that the above technique has the following problems. Specifically, in a steel comprising a composite structure having a percentage volume of not more than 5% in the second phase, it is difficult to impart a BH property on a level comparable or superior to the conventional level, that is, on the level of not less than 5 kgf/mm 2 . Further, even though the BH level could exceed 5 kgf/mm 2 , the YP-El after artificial aging unfavorably exceeds 0.2%, so that it is very difficult to ensure the non-aging properties at room temperature. This problem is considered attributable to a low percentage volume of the second phase which results in a unsatisfactory movable dislocation density introduced into ferrite.
  • the steel sheet after press molding is required to have denting resistance.
  • denting resistance is intended to mean resistance of the steel sheet to permanent depression deformation when stones or the like hit against assembled automobiles or the like. Assuming the sheet thickness is constant, the denting resistance becomes better with increasing the deformation stress after press molding and painting/baking. Therefore, when steels sheets have the same yield strength, the denting resistance improves with increasing the paint-bake hardenability and increasing the work hardenability.
  • steel sheets desirable for use in panels for automobiles are those having a combination of such properties that the yield strength is not very high, work hardening is significant and paint-bake hardenability is high. It is a matter of course that they should be excellent also in formability in respect of the average r value (deep drawability) and elongation (punch stretchability). Further, they should have substantially non-aging at room temperature.
  • An object of the present invention is to provide a cold-rolled steel sheet and a hot-dip galvanized cold-rolled steel sheet unattainable by the prior art, which can satisfy the above-described demands, particularly with respect to the paint-bake hardenability, can impart a BH property on a high level of not less than 5 kgf/mm 2 depending upon purposes and also have a non-aging properties at room temperature, and a process for producing the same.
  • the present inventors have made extensive and intensive studies with a view to attaining the above-described object and, as a result, have obtained the following novel finding.
  • Mn, B and Cr were added to a base material comprising an extra low carbon steel containing neither Nb nor Ti or a base material comprising an extra low carbon steel and, added thereto, one or a combination of Nb and Ti (for example, a steel having a composition of 0.003%C-0.01%Si-0.15%Mn-0.008%P-0.003%S-0.05%Al-0.012%Ti-0.02%Nb-0.0015%B), and studies have been made on the structure and tensile properties after cold rolling, annealing and temper rolling, particularly a difference in the structure and tensile properties between annealing in a two-phase region of ⁇ + ⁇ and annealing in a ⁇ single-phase region.
  • annealing in a ⁇ single-phase region has the following features as compared with annealing in an ( ⁇ + ⁇ ) two-phase region.
  • the present inventors have conducted further studies on the relationship between these elements and the amount of Mn added and, as a result, have found that, when the Mn content is less than 0.3%, in order to improve the non-aging properties, addition of Ti or Nb is necessary and it is preferred to satisfy the requirement represented by the above formula.
  • annealing in a ⁇ region enabled a BH property on a level of not less than 5 kgf/mm 2 to be stably imparted.
  • samples were prepared in the same manner as that of Example 1 using sample No. 4-1 (steel of the present invention) and sample No. 4-4 (comparative steel) specified in Table 1 and used to examine the relationship between the deep drawability (r value) and the annealing temperature of the samples.
  • the results are given in Fig. 3.
  • the present inventors have found that the steel of the present invention is advantageous also as a hot-dip galvanized cold-rolled steel sheet. Specifically, addition of large amounts of Si or P to steels is known to deteriorate the platability of the steels in the hot-dip galvanizing and, further, causes delay of the subsequent alloying reaction. By contrast, steels containing Mn or Cr cause no deterioration in platability in the hot-dip galvanizing even when they contain large amounts of Si and P. The present inventors have also carried out studies on the influence of B and, as a result, have found that a large amount of B has an adverse effect on platability in the hot-dip galvanizing and the alloying reaction.
  • a lowering in the P and Si Contents is advantageous also from the viewpoint of lowering the Ac 3 point.
  • the present invention provides a novel steel sheet based on the above-described idea and novel finding, and The objects of the present invention are solved by the features specified in the claims.
  • This property is characteristic of steel sheets having a single-phase structure of a low-temperature transformation product and cannot be provided in steel sheets having a ferritic single-phase structure and steel sheets having a composite structure provided by adding a large amount of B. What is more important is as follows.
  • the conventional steels are commonly known to cause a remarkable deterioration in the r value when annealed in a ⁇ single-phase region. For this reason, the annealing temperature has been limited to the Ae 3 or Ac 3 point or lower temperature.
  • the r value is hardly deteriorated even when annealing is effected in a ⁇ single-phase region.
  • Mn is a solid solution strengthening element useful for increasing the strength without causing a significant increase in yield strength and also has the effect of improving the conversion treatability or improving the platability in hot-dip galvanizing.
  • the lower limit is 0.01% from the viewpoint of steelmaking techniques.
  • Mn is added in an amount of 0.6% or more, it becomes possible to most significantly attain the effect of lowering the annealing temperature necessary for the formation of a single-phase structure of a low-temperature transformation product, the effect of improving the non-aging properties and other effects.
  • the amount of Mn added exceeds 4.0%, the cost becomes high and the formability is deteriorated.
  • Ti, Nb, B and Cr are useful for attaining excellent BH properties and non-aging properties when annealing is effected in a ⁇ region. They are also useful for maintaining a high r value.
  • Mn content is less than 0.3% by weight, an addition of Ti or Nb is necessary.
  • Ti and Nb it is preferred for Ti and Nb to be added in respective amounts capable of satisfying the requirement: 10(Ti + Nb) + 100B + Cr ⁇ 0.1.
  • the upper limit of the content of the above elements is 0.1% by weight for Ti and Nb, 0.0030% by weight for B and 3.0% by weight for Cr.
  • the lower limit of the content of the above elements is a minimum value necessary for attaining the intended effect.
  • the strength all the steel sheets having a strength of not less than 25 kgf/mm 2 fall within the scope of the present invention. However, in order to provide a good r value as the single-phase structure of a low-temperature transformation product, it is preferred for the strength to be 35 kgf/mm 2 .
  • a slab having the above-described composition is heated in the temperature range of from 900 to 1,400°C and then hot-rolled.
  • the finishing temperature of the hot rolling should be not less than (Ar 3 - 100)°C from the viewpoint of ensuring the formability of the product sheet.
  • the coiling temperature for the hot-rolled steel strip is in the range of from room temperature to 750°C.
  • the present invention is characterized in that the quality of the product is not significantly influenced by the coiling temperature in the hot rolling.
  • the upper limit of the coiling temperature is determined from the viewpoint of preventing a lowering in yield attributable to a deterioration in the quality at both ends of the coil.
  • the hot-rolled steel strip is then cold-rolled.
  • the rolling is effected with a reduction ratio of not less than 60% from the viewpoint of ensuring the deep drawability after annealing.
  • the cold-rolled steel strip thus obtained is transferred to a continuous annealing furnace while uncoiling the steel strip and annealed at the Ac 3 transformation point or above.
  • the annealing temperature is below the Ac 3 transformation point, it is impossible to provide the single-phase structure of a low-temperature transformation product characteristic of the present invention.
  • cooling is preferably effected at an average rate of 30°C/sec or less until the temperature is lowered from the annealing temperature to 600 to 700°C.
  • cooling is preferably effected at an average rate of 30°C/sec or more until the temperature is lowered from the annealing temperature to 600 to 700°C.
  • one of these conditions is essential.
  • the steel strip When hot-dip galvanizing is effected after the annealing, the steel strip is cooled from the above-described annealing temperature and immersed in a galvanizing bath (temperature: 420 to 520°C, Al concentration of the bath: 0.05 to 0.3%) to galvanize the surface of the steel strip. Thereafter, the galvanized steel strip may be subjected to an alloying treatment commonly effected in the conventional galvanizing.
  • a cold-rolled steel strip and a hot-dip galvanized steel strip are produced. Thereafter, if necessary, the steel strip is subjected to temper rolling with a reduction ratio of 0.2 to 3% for the purpose of correcting the shape. In the present invention, the temper rolling for improving the aging property is not necessary.
  • a steel sheet which has a combination of a high paint-bake hardenability and non-aging properties at room temperature and is also excellent in formability in respect of average r value (deep drawability) and elongation (punch stretchability).
  • a BH property on a high level of not less than 5 kgf/mm 2 can be stably imparted according to need, and it is possible to provide a cold-rolled steel sheet which also has non-aging properties at room temperature.
  • Steels having compositions specified in Table 1 were prepared by a melt process and hot-rolled under conditions of a slab heating temperature of 1,200°C, a finishing temperature of 920°C and a coiling temperature of 700°C to form steel strips having a thickness of 4.0 mm. After pickling, the steel strips were cold-rolled with a reduction ratio of 80% to form cold-rolled sheets having a thickness of 0.8 mm and then subjected to continuous annealing under conditions of a heating rate of 10°C/sec, a soaking of 860 to 980°C for 50 sec, an average rate of cooling to 650°C of 3°C/sec and an average rate of cooling from 650°C to room temperature of 80°C/sec.
  • the annealed sheet was subjected to temper rolling with a reduction ratio of 1.0%, and a JIS No. 5 tensile specimen was extracted therefrom and subjected to a tensile test.
  • the results of the tensile test are summarized in Table 2.
  • the WH value is the level of work hardening when a 2% tensile strain is applied in the rolling direction. This value is determined by subtracting the yield stress (YP) from a 2% deformation stress.
  • the BH property is the level of an increment of the stress when the tensile test is again effected after a 2% prestrained material is subjected to a heat treatment corresponding to painting baking at 170°C for 20 min (that is, a value determined by subtracting 2% deformation stress from lower yield stress in the retensile test).
  • the fabrication embrittlement transition temperature is a ductility-embrittlement transition temperature determined by punching a blank having a diameter of 50 mm from a temper-rolled steel sheet, molding a cup using a punch having a diameter of 33 mm and subjecting the cup to a drop weight test at various temperatures.
  • the annealing temperature necessary for the formation of a single-phase structure of a low-temperature transformation product is considerably lower than that in the case of the comparative steels. Therefore, the steels can be produced without applying an excessive burden on continuous annealing equipment.
  • the steels of the present invention have a higher BH property than the conventional steel sheets having a tensile strength on the same level as the steel sheets of the present invention, and additionally have a very excellent non-aging properties at room temperature.
  • This advantage is considered largely attributable to a better dislocation density of the steel sheet of which the single-phase structure of a low-temperature transformation product has been formed using Mn or Cr as compared with other steel sheets.
  • Another feature of the present invention is that substantially no deterioration in r value occurs despite annealing in a ⁇ single-phase temperature region.
  • the steels of the present invention have a low yield strength, an excellent retention of face shape and a high WH value. Therefore, the steels of the present invention are suitable as a material, for example, for an outer or inner plate panel of automobiles.
  • the influence of soaking temperature on continuous annealing was studied using steel No. 2-2 specified in Table 1.
  • Conditions for hot rolling and cold rolling were the sane as those of Example 1.
  • the cold rolled steel sheet was subjected to continuous annealing as follows. It was heated at a rate of 10°C/sec, held at a temperature in the range of from 840 to 940°C for 50 sec, cooled to 650°C at an average rate of 60°C/sec and then cooled from 650°C to room temperature at an average rate of 80°C/sec. Further, the annealed sheet was subjected to temper rolling with a reduction ratio of 1.0%, and a JIS No. 5 tensile specimen was extracted therefrom and subjected to a tensile test. The results of the tensile test are summarized in Table 3.
  • the appearance of plating was evaluated based on the following criteria.
  • the plated sheet was bent at 180°C for close overlapping, and an adhesive tape was adhered to the bent portion and then peeled off to measure the amount of peeled plating to evaluate the peeling of the galvanized coating.
  • the evaluation was made based on the following five grades.
  • the concentration of Fe in the plating was determined by X-ray diffractometry.
  • the alloyed galvanized steel sheets of the present invention had good plating appearance and powdering resistance. Further, the concentration of Fe in the alloy layer corresponds to that of ⁇ 1 phase considered as a desired phase. In the present invention, the above properties are considered to be attained by reducing the amount of P and Si, which deteriorates plating adhesion and delays alloying reaction, and adding Mn or Cr. Further, it is apparent that, when Mn or Cr is added, the platability is not deteriorated even though P and Si are contained in a certain amount. Sample No.
  • Steels having compositions specified in Table 5 were prepared by a melt process and hot-rolled under conditions of a slab heating temperature of 1,180°C, a finishing temperature of 910°C and a coiling temperature of 600°C to form steel strips having a thickness of 4.0 mm. After pickling, the steel strips were cold-rolled with a reduction ratio of 80% to form cold-rolled sheets having a thickness of 0.8 mm and then subjected to continuous annealing under conditions of a heating rate of 10°C/sec, a soaking of 830 to 980°C for 50 sec, an average rate of cooling to 650°C of 5°C/sec and an average rate of cooling from 650°C of 80°C/sec.
  • the annealed sheet was subjected to temper rolling with a reduction ratio of 0.5%, and a JIS No. 5 tensile specimen was extracted therefrom and subjected to a tensile test.
  • the results of the tensile test are summarized in Table 6.
  • the BH value is the level of an increment of the stress when the tensile test is again effected after a 2% prestrained material is subjected to a heat treatment corresponding to painting baking at 170°C for 20 min (that is, a value determined by subtracting 2% deformation stress from lower yield stress in the retensile test).
  • the fabrication embrittlement transition temperature is a ductility-embrittlement transition temperature determined by punching a blank having a diameter of 50 mm from a temper-rolled steel sheet, molding a cup using a punch having a diameter of 33 mm and subjecting the cup to a drop weight test at various temperatures.
  • the steels of the present invention have a higher BH property than the conventional steel sheets having a tensile strength on the same level as the steel sheets of the present invention, and additionally have a excellent non-aging properties at room temperature.
  • This advantage is considered largely attributable to a better dislocation density of the steel sheet having a single-phase structure of a low-temperature transformation product as compared with other steel sheets.
  • the steels of the present invention are excellent also in r value. Therefore, the steels of the present invention are suitable as a material for an outer or inner plate panel of automobiles, for example.
  • the structure was brought to a single phase of a low-temperature transformation product by annealing in a ⁇ single-phase region, whereas in the comparative examples, the annealing was effected in an a single-phase or ( ⁇ + ⁇ ) two-phase region, so that the structure was not a single-phase structure of a low-temperature transformation product.
  • Example 2 The influence of soaking temperature in continuous annealing was studied using steel No. 3-2 specified in Table 5. Conditions for hot rolling and cold rolling were the same as those of Example 1. Thereafter, the cold-rolled steel sheet was subjected to continuous annealing as follows. It was heated at a rate of 10°C/sec, held at a temperature in the range of from 840 to 930°C for 50 sec, cooled at an average rate of 60°C/sec.
  • the annealed sheet was subjected to temper rolling with a reduction ratio of 0.5%, and a JIS No. 5 tensile specimen was extracted therefrom and subjected to a tensile test.
  • the results of the tensile test are summarized in Table 7.
  • Sample Nos. 3-1 to 3-4 and 4-1 to 4-4 specified in Table 5 were hot-rolled under conditions of a slab heating temperature of 1220°C, a finishing temperature of 900°C and a coiling temperature of 500°C to form steel sheets having a thickness of 3.8 mm.
  • the steel sheets were cold-rolled to form cold-rolled sheets having a thickness of 0.75 mm, heated at a heating rate of 15°C/sec to a maximum heating temperature in the range of from 840 to 980°C, cooled at a rate of about 70°C/sec, subjected to conventional hot-dip galvanizing at 460°C (Al concentration of bath: 0.11%), further heated at 520°C for 20 sec to effect alloying and then cooled to room temperature at about 20°C/sec.
  • the resultant alloyed galvanized steel sheets were subjected to measurement of appearance of plating, powdering resistance and concentration of Fe in plating. The results are summarized in Table 8. Sample No.
  • the alloyed galvanized steel sheets of the present invention had good plating appearance and powdering resistance. Further, the concentration of Fe in the alloy layer corresponds to that of ⁇ 1 phase considered as a desired phase.
  • the present invention it is possible to provide a cold-rolled steel sheet having a combination of BH property with non-aging properties at room temperature unattainable by the prior art techniques.
  • the steel of the present invention has an excellent press moldability and is excellent also in platability in hot-dip galvanizing, so that it can exhibit also a rust preventive property. Therefore, use of the steel of the present invention in bodies or frames of automobiles enables the thickness of the sheet, that is, the weight of the automobile bodies, to be reduced, which can greatly contribute to environmental protection which has attracted attention in recent years. Thus, the present invention is very valuable from the viewpoint of industry.

Claims (5)

  1. Tôle en acier laminée à froid présentant d'excellentes aptitude au durcissement par cuisson et propriétés de non-vieillissement à température ambiante, caractérisée en ce qu'elle comprend en termes de % en poids de 0,0005 à 0,0070% de C, de 0,001 à 0,8 % de Si, de 0,3 à 4,0% de Mn, de 0,002 à 0,15 % de P, de 0,0005 à 0,015 % de S, de 0,005 à 0,2 % de Al, de 0,0003 à 0,0060 % de N, facultativement au moins un élément choisi parmi de 0,003 à 0,1 % de Ti, de 0,003 à 0,1 % de Nb, B dans une quantité capable de satisfaire une exigence inférieure à 0,0030 % en poids et B/N ≤ 1,5 et de 0,01 à 3,0 % en poids de Cr avec le reste étant constitué de Fe et d'impuretés inévitables et consistant en une microstructure d'un produit de transformation critique à faible température formé par recuisson de la tôle en acier laminée à froid à une température d'au moins le point Ac3 et supérieure à 900°C dans une région monophasique γ, dans laquelle la microstructure du produit de transformation critique à faible température comprend au moins un élément choisi parmi la ferrite massive, la bainite, la ferrite Widmanstätten, la martensite et la ferrite aciculaire, à l'exception de la ferrite polygonale.
  2. Tôle en acier laminée à froid présentant d'excellentes aptitude au durcissement par cuisson et aptitude au moulage, caractérisée en ce qu'elle comprend en termes de % en poids de 0,0005 à 0,0070 % de C, de 0,001 à 0,8 % de Si, de 0,01 à 4,0% de Mn, de 0,002 à 0,15 % de P, de 0,0005 à 0,015 % de S, de 0,005 à 0,2 % de Al, de 0,0003 à 0,0060 % de N, au moins un élément supplémentaire choisi parmi de 0,003 à 0,1 % de Ti et de 0,003 à 0,1 % de Nb, et facultativement au moins un élément choisi parmi moins de 0,0030 % en poids de B et de 0,01 à 3,0 % en poids de Cr avec le reste étant constitué de Fe et d'impuretés inévitables et consistant en une microstructure d'un produit de transformation critique à faible température formé par recuisson de la tôle en acier laminée à froid à une température d'au moins le point Ac3 et supérieure à 900°C dans une région monophasique γ, dans laquelle la micro structure du produit de transformation critique à faible température comprend au moins un élément choisi parmi la ferrite massive, la bainite, la ferrite Widmanstätten, la martensite et la ferrite aciculaire, à l'exception de la ferrite polygonale.
  3. Tôle en acier laminée à froid galvanisée par immersion à chaud présentant d'excellentes aptitude au durcissement par cuisson et propriétés de non-vieillissement à température ambiante, caractérisée en ce qu'une tôle en acier laminée à froid selon la revendication 1 ou 2 est galvanisée par immersion à chaud.
  4. Procédé de production d'une tôle en acier laminée à froid selon la revendication 1 ou 2 caractérisé en ce qu'il comprend les étapes consistant : à chauffer une plaque comprenant lesdits constituants, à laminer à chaud la plaque chauffée à une température de laminage à chaud de finition d'au moins (Ar3 - 100)°C ; à enrouler la bande en acier laminée à chaud à une température d'au plus 750°C ; à laminer à froid la bande en acier laminée à chaud avec un rapport de réduction d'au moins 60 % ; et à soumettre la bande en acier laminée à froid à une recuisson continue à une température de recuisson d'au moins le point de transformation critique Ac3 et supérieure à 900°C dans une région monophasique γ.
  5. Procédé de production d'une tôle en acier laminée à froid galvanisée par immersion à chaud présentant d'excellentes aptitude au durcissement par cuisson et propriétés de non-vieillissement à température ambiante caractérisé en ce qu'il comprend les étapes consistant à soumettre la bande en acier laminée à froid selon la revendication 4 à une galvanisation par immersion à chaud de type recuisson en ligne à une température de recuisson d'au moins le point de transformation critique Ac3 et supérieure à 900°C dans une région monophasique γ à la place de ladite recuisson continue.
EP93919599A 1992-08-31 1993-08-31 Feuille laminee a froid, eventuellement galvanisee a chaud, aux qualites de sechage de peinture a chaud, de non-vieillissement a froid et de formage excellentes, et procede de production Expired - Lifetime EP0620288B1 (fr)

Applications Claiming Priority (10)

Application Number Priority Date Filing Date Title
JP23230192 1992-08-31
JP23231992 1992-08-31
JP232319/92 1992-08-31
JP232301/92 1992-08-31
JP23231992 1992-08-31
JP23230192 1992-08-31
JP4410893 1993-03-04
JP5044108A JP2980785B2 (ja) 1992-08-31 1993-03-04 焼付硬化性と成形性とに優れた冷延鋼板あるいは溶融亜鉛メッキ冷延鋼板およびそれらの製造方法
JP44108/93 1993-03-04
PCT/JP1993/001231 WO1994005823A1 (fr) 1992-08-31 1993-08-31 Feuille laminee a froid, eventuellement galvanisee a chaud, aux qualites de sechage de peinture a chaud, de non-vieillissement a froid et de formage excellentes, et procede de production

Publications (3)

Publication Number Publication Date
EP0620288A1 EP0620288A1 (fr) 1994-10-19
EP0620288A4 EP0620288A4 (fr) 1995-01-25
EP0620288B1 true EP0620288B1 (fr) 2000-11-22

Family

ID=27291785

Family Applications (1)

Application Number Title Priority Date Filing Date
EP93919599A Expired - Lifetime EP0620288B1 (fr) 1992-08-31 1993-08-31 Feuille laminee a froid, eventuellement galvanisee a chaud, aux qualites de sechage de peinture a chaud, de non-vieillissement a froid et de formage excellentes, et procede de production

Country Status (4)

Country Link
EP (1) EP0620288B1 (fr)
KR (1) KR0121737B1 (fr)
DE (1) DE69329696T2 (fr)
WO (1) WO1994005823A1 (fr)

Families Citing this family (19)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5855696A (en) * 1995-03-27 1999-01-05 Nippon Steel Corporation Ultra low carbon, cold rolled steel sheet and galvanized steel sheet having improved fatigue properties and processes for producing the same
DE19622164C1 (de) * 1996-06-01 1997-05-07 Thyssen Stahl Ag Verfahren zur Erzeugung eines kaltgewalzten Stahlbleches oder -bandes mit guter Umformbarkeit
TW515847B (en) * 1997-04-09 2003-01-01 Kawasaki Steel Co Coating/baking curable type cold rolled steel sheet with excellent strain aging resistance and method for producing the same
US6143100A (en) * 1998-09-29 2000-11-07 National Steel Corporation Bake-hardenable cold rolled steel sheet and method of producing same
JP3958921B2 (ja) * 2000-08-04 2007-08-15 新日本製鐵株式会社 塗装焼付硬化性能と耐常温時効性に優れた冷延鋼板及びその製造方法
KR100544538B1 (ko) * 2001-12-21 2006-01-24 주식회사 포스코 가공성이 우수한 비시효 소부경화형 냉연고장력강판과 그제조방법
KR20030083276A (ko) * 2002-04-20 2003-10-30 현대자동차주식회사 소부경화형 고장력강판 및 이것의 제조방법
KR101105025B1 (ko) * 2003-12-29 2012-01-16 주식회사 포스코 면내이방성이 작은 소부경화형 고강도 냉연강판과 그제조방법
KR101105132B1 (ko) * 2003-12-23 2012-01-16 주식회사 포스코 소부경화형 고강도 냉연강판과 그 제조방법
KR101105098B1 (ko) * 2003-12-29 2012-01-16 주식회사 포스코 가공성이 우수한 소부경화형 고강도 냉연강판과 그 제조방법
KR101104981B1 (ko) * 2003-12-23 2012-01-16 주식회사 포스코 내2차가공취성이 우수한 소부경화형 고강도 냉연강판과 그제조방법
KR101105007B1 (ko) * 2003-12-23 2012-01-16 주식회사 포스코 소부경화형 냉연강판과 그 제조방법
KR20140129150A (ko) 2012-02-20 2014-11-06 타타 스틸 네덜란드 테크날러지 베.뷔. 고강도 소부경화형 저밀도 강 및 상기 강의 제조방법
EP2836615B1 (fr) 2012-04-11 2016-04-06 Tata Steel Nederland Technology B.V. Acier haute résistance à faible densité sans interstitiel et procédé de production de cet acier
KR101505293B1 (ko) * 2013-05-31 2015-03-23 현대제철 주식회사 강판
KR101505269B1 (ko) * 2013-03-28 2015-03-23 현대제철 주식회사 강판 및 그 제조 방법
KR101758557B1 (ko) * 2015-06-05 2017-07-18 주식회사 포스코 드로잉성 및 소부경화성이 우수한 고강도 박강판 및 그 제조방법
KR101795918B1 (ko) 2015-07-24 2017-11-10 주식회사 포스코 내시효성 및 소부경화성이 우수한 용융아연도금강판, 합금화 용융아연도금강판 및 그 제조방법
KR102045654B1 (ko) 2017-12-26 2019-11-15 주식회사 포스코 고온 특성과 상온 가공성이 우수한 냉연강판 및 그 제조방법

Family Cites Families (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0757892B2 (ja) * 1983-01-28 1995-06-21 新日本製鐵株式会社 ２次加工性と表面処理性の優れた深絞り用冷延鋼板の製造方法
JPS59143027A (ja) * 1983-02-07 1984-08-16 Kawasaki Steel Corp 延性および加工性の良好な高強度鋼板の製造方法
JPS60103128A (ja) * 1983-11-11 1985-06-07 Kawasaki Steel Corp 複合組織冷延鋼板の製造方法
JPS60174852A (ja) * 1984-02-18 1985-09-09 Kawasaki Steel Corp 深絞り性に優れる複合組織冷延鋼板とその製造方法
JPS61281852A (ja) * 1985-06-07 1986-12-12 Kawasaki Steel Corp 焼付硬化性に富む遅時効性深絞り用冷延鋼板
JPH06102816B2 (ja) * 1990-03-28 1994-12-14 川崎製鉄株式会社 加工性、常温非時効性及び焼付け硬化性に優れる複合組織冷延鋼板とその製造方法
JPH04214820A (ja) * 1990-12-14 1992-08-05 Nippon Steel Corp 焼付硬化性に優れる自動車用鋼板の製造方法
JP3365632B2 (ja) * 1991-03-15 2003-01-14 新日本製鐵株式会社 成形性の良好な高強度冷延鋼板と溶融亜鉛メッキ高強度冷延鋼板およびそれらの製造方法
JPH0578783A (ja) * 1991-09-12 1993-03-30 Nippon Steel Corp 成形性の良好な高強度冷延鋼板
JP3016636B2 (ja) * 1991-09-12 2000-03-06 新日本製鐵株式会社 成形性の良好な高強度冷延鋼板

Also Published As

Publication number Publication date
KR0121737B1 (ko) 1997-12-04
EP0620288A1 (fr) 1994-10-19
DE69329696T2 (de) 2001-06-13
EP0620288A4 (fr) 1995-01-25
WO1994005823A1 (fr) 1994-03-17
DE69329696D1 (de) 2000-12-28

Similar Documents

Publication Publication Date Title
US5690755A (en) Cold-rolled steel sheet and hot-dip galvanized cold-rolled steel sheet having excellent bake hardenability, non-aging properties at room temperature and good formability and process for producing the same
EP0608430B1 (fr) Tole laminee a froid representant une trempabilite pour peinture au four et des caracteristiques de vieillissement et une aptitude au moulage autrement qu'a froid excellentes, et tole zinguee laminee a froid et procede de fabrication
US5855696A (en) Ultra low carbon, cold rolled steel sheet and galvanized steel sheet having improved fatigue properties and processes for producing the same
EP0620288B1 (fr) Feuille laminee a froid, eventuellement galvanisee a chaud, aux qualites de sechage de peinture a chaud, de non-vieillissement a froid et de formage excellentes, et procede de production
EP0612857B1 (fr) Tole d'acier laminee a froid a phase unique de ferrite ou tole d'acier plaquee au zinc par fusion pour emboutissage profond a froid inalterable par vieillissement et procede de fabrication
EP0816524B1 (fr) Tôle d'acier ayant un aspect de surface et une résistance à la déformation après formage excellents
US5846343A (en) Cold rolled steel sheet exhibiting excellent press workability and method of manufacturing the same
EP1616971A1 (fr) Feuille d'acier lamine a froid a resistance elevee et procede de production de celle-ci
JP3365632B2 (ja) 成形性の良好な高強度冷延鋼板と溶融亜鉛メッキ高強度冷延鋼板およびそれらの製造方法
EP1932932A1 (fr) Feuille d acier laminée à froid excellente en termes de capacité à durcir le revêtement lors de la cuisson et de propriété de vieillissement lent à froid et son procédé de production
EP0406619A1 (fr) Procédé pour la fabrication de tôles d'acier laminées à froid, galvanisées non vieillissantes et ayant une bonne aptitude au formage, dans une ligne de galvanisation continue
JP3238211B2 (ja) 焼付硬化性と非時効性とに優れた冷延鋼板あるいは溶融亜鉛メッキ冷延鋼板の製造方法
JP2800541B2 (ja) 深絞り用高強度溶融亜鉛メッキ鋼板の製造方法
JPH02111841A (ja) 焼付け硬化性を有する良加工性冷延鋼板および溶融亜鉛めっき鋼板
JP2980785B2 (ja) 焼付硬化性と成形性とに優れた冷延鋼板あるいは溶融亜鉛メッキ冷延鋼板およびそれらの製造方法
JPH06122940A (ja) 優れた焼付硬化性と常温非時効性を兼備した冷延鋼板と溶融亜鉛メッキ冷延鋼板およびその製造方法
JPH0530900B2 (fr)
JPH06116648A (ja) 焼付硬化性と非時効性とに優れた冷延鋼板あるいは溶融亜鉛メッキ冷延鋼板の製造方法
JPH0657337A (ja) 成形性に優れた高強度合金化溶融亜鉛めっき鋼板の製造方法
JP3350096B2 (ja) 焼付硬化性と成形性とに優れた冷延鋼板あるいは溶融亜鉛メッキ冷延鋼板およびそれらの製造方法
JPH11193419A (ja) 成形性に優れた合金化溶融亜鉛めっき高強度冷延鋼板の製造方法
JPH05255807A (ja) 成形性に優れた高強度冷延鋼板と溶融亜鉛メッキ高強度冷延鋼板およびそれらの製造方法
JP2000144261A (ja) 延性の優れた熱延下地溶融亜鉛めっきおよび合金化溶融亜鉛めっき高張力鋼板の製造方法
JPH05263189A (ja) 成形性の良好な高強度冷延鋼板と溶融亜鉛メッキ高強度冷延鋼板およびそれらの製造方法
JPH05263185A (ja) 成形性の良好な高強度冷延鋼板と溶融亜鉛メッキ高強度冷延鋼板およびそれらの製造方法

Legal Events

Date Code Title Description
PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

Free format text: ORIGINAL CODE: 0009012

17P Request for examination filed

Effective date: 19940527

AK Designated contracting states

Kind code of ref document: A1

Designated state(s): DE FR GB IT

A4 Supplementary search report drawn up and despatched
AK Designated contracting states

Kind code of ref document: A4

Designated state(s): DE FR GB IT

17Q First examination report despatched

Effective date: 19980407

GRAG Despatch of communication of intention to grant

Free format text: ORIGINAL CODE: EPIDOS AGRA

GRAG Despatch of communication of intention to grant

Free format text: ORIGINAL CODE: EPIDOS AGRA

GRAG Despatch of communication of intention to grant

Free format text: ORIGINAL CODE: EPIDOS AGRA

GRAH Despatch of communication of intention to grant a patent

Free format text: ORIGINAL CODE: EPIDOS IGRA

RTI1 Title (correction)

Free format text: COLD-ROLLED SHEET AND HOT-GALVANIZED COLD-ROLLED SHEET, BOTH EXCELLENT IN BAKE HARDENING, COLD NONAGING AND FORMING PROPERTIES, AND PROCESS FOR PRODUCING THE SAME

GRAH Despatch of communication of intention to grant a patent

Free format text: ORIGINAL CODE: EPIDOS IGRA

GRAA (expected) grant

Free format text: ORIGINAL CODE: 0009210

AK Designated contracting states

Kind code of ref document: B1

Designated state(s): DE FR GB IT

REF Corresponds to:

Ref document number: 69329696

Country of ref document: DE

Date of ref document: 20001228

ITF It: translation for a ep patent filed

Owner name: STUDIO TORTA S.R.L.

ET Fr: translation filed
PLBE No opposition filed within time limit

Free format text: ORIGINAL CODE: 0009261

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: NO OPPOSITION FILED WITHIN TIME LIMIT

26N No opposition filed
REG Reference to a national code

Ref country code: GB

Ref legal event code: IF02

PGFP Annual fee paid to national office [announced via postgrant information from national office to epo]

Ref country code: GB

Payment date: 20120829

Year of fee payment: 20

PGFP Annual fee paid to national office [announced via postgrant information from national office to epo]

Ref country code: FR

Payment date: 20120823

Year of fee payment: 20

Ref country code: IT

Payment date: 20120813

Year of fee payment: 20

Ref country code: DE

Payment date: 20120829

Year of fee payment: 20

REG Reference to a national code

Ref country code: DE

Ref legal event code: R082

Ref document number: 69329696

Country of ref document: DE

Representative=s name: VOSSIUS & PARTNER, DE

Effective date: 20130227

Ref country code: DE

Ref legal event code: R081

Ref document number: 69329696

Country of ref document: DE

Owner name: NIPPON STEEL & SUMITOMO METAL CORPORATION, JP

Free format text: FORMER OWNER: NIPPON STEEL CORP., TOKIO/TOKYO, JP

Effective date: 20130227

REG Reference to a national code

Ref country code: DE

Ref legal event code: R071

Ref document number: 69329696

Country of ref document: DE

REG Reference to a national code

Ref country code: GB

Ref legal event code: PE20

Expiry date: 20130830

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: DE

Free format text: LAPSE BECAUSE OF EXPIRATION OF PROTECTION

Effective date: 20130903

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: GB

Free format text: LAPSE BECAUSE OF EXPIRATION OF PROTECTION

Effective date: 20130830