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
• • 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
• • 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
• • 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
  • 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

Definitions

• the invention relates to a method for producing a cold-rolled, high-strength steel sheet or strip with good formability, in particular stretch-pullability, for the production of pressed parts with high buckling stiffness.
• the pressed parts should have a high basic material strength and, after an additional heat treatment, as is usually used in painting, should receive additional material hardening ("bake hardening"). This gives excellent buckling stiffness properties.
• Pressed parts with a high proportion of drawn parts are e.g. flat body parts in the automotive industry, such as doors, hoods, roofs.
• Recrystallization temperature an additional annealing, the so-called aging annealing, applied to ensure aging resistance.
• An aging-resistant material is characterized in that no significant changes in the material properties occur even after prolonged storage times, and error-free, flow figure-free processing is possible. In a continuous furnace, this treatment can take place in an aging section of the line. Subsequent external annealing, usually in the bundle, must be carried out on strips that are produced in a conventional fire coating system.
• the carbon content is included the AI-calmed unalloyed deep-drawing steels, also called "low-carbon" (LC) steels, in the range 0.02 to 0.08%.
• the use of the thinnest possible sheet metal is desirable in order to save weight.
• higher strengths are necessary.
• Bake hardening steels are increasingly used for this. Steels with bake hardening properties are characterized by an additional increase in the yield strength on the drawn component. This is achieved in that the material, in addition to the deformation hardening that occurs during pressing ("work hardening"), also undergoes an additional increase in strength when baked-on, "bake hardening".
• the physical cause is a controlled carbon aging. For bake-hardening steels and their field of application, sufficient aging resistance for faultless surfaces after pressing is also necessary.
• An unalloyed LC steel can also be produced as bake-hardening steel in continuous furnaces that have an aging part in line by precisely matching the chemical steel composition, cooling rate and aging condition. This process is already being used on an industrial scale. Optimization of the production conditions is described, for example, by Haya ⁇ hida et al. (T. Hayashida, M. Oda, T. Yamada, Y. Mat ⁇ ukawa, J. Tanaka: "Development and applications of continuous-annealed low-carbon Al-killed BH steel Sheets", Poe. Of the Symp. On High-Strength Sheet steels for the Automotive Industry, Baltimore, October 16-19, 1994, p.135).
• the aim is the complete setting of the nitrogen in titanium nitrides, although a small amount of carbon must remain in solution to ensure the bake-hardening effect. Generation in vacuum degassing plants is necessary.
• the advantage of this process is that the annealing annealing is no longer necessary, which makes it suitable for hot-dip coating systems.
• the bake-hardening parameters determined in the tensile test after 2% pre-stretching (BH 2 value) reach approximately 40 N / mm 2 for the steels produced in this way.
• the yield strengths are around 200 N / mm 2
• the values for the mean vertical anisotropy (r-value) are around 1.8.
• EP 0 620 288 A1 discloses a process for producing only cold-rolled or fire-coated cold-rolled steel strip in continuous strip lines, which, in addition to being resistant to aging, has high bake hardening properties and good deep-drawing properties due to high r values.
• a ULC steel itself or a ULC steel with either a titanium or a niobium alloy is annealed above the Ac 3 conversion temperature, ie in the austenite area.
• the bake-harding values reach 100 N / mm 2 .
• An aging glow is not necessary.
• ULC steel the steel production must take place in a vacuum degassing plant. Difficulties with regard to strip flatness are caused by the necessary high annealing temperatures. A large-scale application of this method is not known.
• processes previously used or described in the literature for the production of readily deformable cold thin sheet with bake-hardening properties in continuous strip systems either include the additional annealing treatment described above for the case of using a soft, unalloyed, AI-soaked deep-drawing steel, which results in production not allowed in a common fire coating system, or must the more complex to produce ULC steels with very low carbon contents can be used.
• the above-described methods based on ULC steels mainly include steels with yield strengths in the lower range up to 240 N / mm 2 . Because of the high average r values (> 1.5), they are suitable for pressed parts with a high proportion of deep-drawn parts.
• the task derived from this is to produce a readily deformable, high-strength cold-rolled steel sheet or strip in a continuous strip line without a subsequent aging annealing treatment, which also has good bake-hardening properties.
• the combination of the high basic material strength and the bake-hardening potential should lead to excellent buckling stiffness of the pressed parts.
• Balance iron and unavoidable impurities including max. 0.08% P and max. 0.02% S, proposed, consisting of preheating the cast slab to a temperature above 1050 ° C, hot rolling with a final temperature in the range from above the Ar 3 temperature to 950 ° C, preferably in the range from 870 to 950 ° C, reeling the hot-rolled strip a temperature in the range of 550 to 750 ° C, cold rolling with a total cold rolling degree of 40 to 85%, recrystallizing annealing of the cold strip in a continuous furnace at a temperature of at least 720 ° C with subsequent high cooling rates of 5 to 70 K / s and final skin training.
• the steel achieves its aging resistance by adding titanium to the nitrogen content. This leads to an early complete setting of the nitrogen, which is known to be an element which has a severe adverse effect on aging resistance.
• the nitrogen in excess of the nitrogen setting, so that the formation of a minimum amount of titanium carbides is ensured.
• the volume fraction and the number of titanium carbides must not be too high, however, so that the steel has the hardening characteristics necessary for the high forming demands and sufficient elongation and toughness properties. Therefore, the amount of the nitride former not bound to nitrogen should be 0.003 to 0.015% Ti or 0.0015 to 0.008% Nb.
• niobium can also be used to form nitride and carbide.
• the silicon content should preferably be max. 0.15% may be limited.
• the economic advantage of the method according to the invention consists in the fact that the additional process step of the aging annealing to achieve the aging resistance is eliminated, although the steel composition is based on the analysis of soft, unalloyed Al-alloyed (LC) steels. On the basis of this analysis concept, steel production can take place without complex metallurgical production processes. In addition, titanium or niobium are only required in small quantities, so that the steel can also be produced inexpensively with regard to the addition of alloys.
• the steel manufacturing process includes this
• the cold strip should preferably be heated to the temperature of the recrystallization annealing at a speed in the range from 5 to 10 K / s.
• the recrystallizing annealing can preferably be carried out in line with a hot-dip galvanizing plant.
• the steel strips or sheets produced by the process according to the invention are distinguished by a high initial yield strength (greater than 240 N / mm 2 ) and a high strengthening capacity in the range of small plastic expansions. Together with low values of the vertical anisotropy, which characterize a preferred flow from the thickness, pressed parts with a high proportion of drawn parts, for example automobile outer skin parts, are the ideal area of application.
• the strong solidification of this material which occurs even with small plastic deformations and is expressed in very high work hardening values, is an essential point for the properties of the product.
• the strong solidification favors the transmission of force to neighboring material areas, as a result of which local material failure, eg constriction, is avoided.
• Tables 2 and 3 show the mechanical properties and grain sizes of strips A and B determined in the tensile test, measured at an angle of 90 ° to the rolling direction. Only the r values and the values for the planar anisotropy are calculated as follows from three tensile specimens, which were taken in the angular positions 0 °, 45 ° and 90 ° to the rolling direction
• the BH 0 value corresponds to the increase in the lower yield point after a heat treatment of 20 minutes at 170 ° C.
• the size WH indicates the amount of deformation hardening when the tensile test is stretched by 2%. She is calculated by subtracting the yield strength Rp c: from the measured stress at 2% deformation.
• the size BH 2 corresponds to the increase in the lower yield strength after a heat treatment of 20 minutes at 170 ° C, measured on the 2% pre-stretched tensile test.
• the hot-dip galvanized cold-rolled strips made of steels A and B show an almost unchanged level of the lower or upper yield strength after artificial aging of 60 minutes at 100 ° C (Table 3).
• the extent of the yield point elongation also remains below 0.5%, which means that the aging resistance is sufficient for processing without flow figures, even after long periods of storage.
• the course of the differential (momentary) hardening exponent (n value) over the total elongation is in Fig. 1 for the steel AI (reel temperature 730 ° C) and in Fig. 2 for the steel A2 (coil temperature 600 ° C) applied.
• the maxima of the differential n values are listed in Table 2; They reach at least 0.170 for steels A and B for both reel temperature classes, and even at least 0.180 for high reel temperatures.
• the maximum n value of steels A and B is in the range of low total strains between 2 and 5%.
• the yield strengths are about 50 N / mm 2 larger for the higher-coiled variants AI and B1 than for the low-coiled variants A2 and B2, so that the starting position of the yield strength can be determined by the choice of the coiler temperature.
• the values for the mean vertical anisotropy for the steels AI, A2, B1 and B2 according to the invention are low at 1.0-1.1. Regardless of the reel temperature, they have isotropic properties with ⁇ r values between 0 and 0.3.
• the work hardening values which represent a measure of the hardening by plastic deformation, are very high at approx. 50 N / mm 2 .
• the Characteristic values for bake-hardening with or without pre-deformation in all cases at least 45 N / mm 2 .
• the increase in yield strength after the painting treatment of a pressed part can be estimated by the sum WH + BH 2 .
• these values are at least 100 N / mm 2 .
• the sum WH + BH 2 with at least 60 N / mm 2 is still favorable.
• Tables 1, 2 and 3 additionally list steels C to E for comparison, which, in contrast to steels A and B, either contain no titanium (steel E) or have titanium contents which are substoichiometric in relation to the nitrogen content (steels C and D with Ti / N ⁇ 3.4).
• the values of the initial state, ie not aged, relate to the extracted state.
• the increase in the lower yield strength (R el ) and the yield strength expansions after artificial aging are significantly higher for these comparative steels than for steels A and B produced according to the invention. Above all, the upper yield strength (deer) increases up to 70 N / mm 2 . Correct processing after long aging is not possible with steels C to E.
• Steel F contains no titanium, but niobium. Due to the reel temperature of 600 ° C and the alloying with niobium, its yield strength is very high at 350 N / mm 2 .
• the mean r value is 1.0 and the ⁇ r value is - 0.20, which is favorable for uniform forming behavior.
• the lower and upper yield strength of the Nb-alloyed steel is also stable and the yield strength elongation is less than 1%, so that here too, processing without flow lines after longer storage times of the Material is possible.
• the forming behavior of the steels AI and Bl produced according to the invention was extensively investigated in a practical large-scale test using molded automobile bonnets. With regard to the shape accuracy and surface of the pressed parts, perfect pressing results were achieved, which were reproducible even after processing after a storage period of 5 months.
• the tensile tests were carried out on samples with measuring lengths of 80 mm.
• ⁇ Reh after aging indicates the increase in the upper yield strength after artificial aging of the tensile samples (100 ° C, 60 minutes).
• ⁇ n max is the total strain at which the maximum of the n value occurs.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Organic Chemistry (AREA)
• Metallurgy (AREA)
• Materials Engineering (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Heat Treatment Of Sheet Steel (AREA)
• Lubricants (AREA)
• Continuous Casting (AREA)

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• 1996
  • 1996-06-01 DE DE19622164A patent/DE19622164C1/de not_active Expired - Lifetime
• 1997
  • 1997-04-26 WO PCT/EP1997/002169 patent/WO1997046720A1/fr not_active Application Discontinuation
  • 1997-04-26 JP JP50012198A patent/JP3875725B2/ja not_active Expired - Fee Related
  • 1997-04-26 ES ES97922915T patent/ES2229352T3/es not_active Expired - Lifetime
  • 1997-04-26 PL PL97330318A patent/PL183911B1/pl unknown
  • 1997-04-26 AT AT97922915T patent/ATE278040T1/de active
  • 1997-04-26 CA CA002251354A patent/CA2251354A1/fr not_active Abandoned
  • 1997-04-26 US US09/171,837 patent/US6162308A/en not_active Expired - Fee Related
  • 1997-04-26 KR KR1019980709882A patent/KR20000016309A/ko not_active Application Discontinuation
  • 1997-04-26 BR BR9709633A patent/BR9709633A/pt not_active IP Right Cessation
  • 1997-04-26 DE DE59711972T patent/DE59711972D1/de not_active Expired - Lifetime
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