EP3963114A1 - Procédé de production d'une bande laminée sur mesure à recuit discontinu - Google Patents

Procédé de production d'une bande laminée sur mesure à recuit discontinu

Info

Publication number
EP3963114A1
EP3963114A1 EP20719642.9A EP20719642A EP3963114A1 EP 3963114 A1 EP3963114 A1 EP 3963114A1 EP 20719642 A EP20719642 A EP 20719642A EP 3963114 A1 EP3963114 A1 EP 3963114A1
Authority
EP
European Patent Office
Prior art keywords
strip
tailor
coating
temperature
tailor rolled
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.)
Pending
Application number
EP20719642.9A
Other languages
German (de)
English (en)
Inventor
Bernard Leo Ennis
Richard MOSTERT
Steven Celotto
Theo Arnold Kop
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.)
Tata Steel Ijmuiden BV
Original Assignee
Tata Steel Ijmuiden BV
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
Application filed by Tata Steel Ijmuiden BV filed Critical Tata Steel Ijmuiden BV
Publication of EP3963114A1 publication Critical patent/EP3963114A1/fr
Pending legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • 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
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • 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
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0236—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
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0273—Final recrystallisation annealing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/06—Zinc or cadmium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/12—Aluminium or alloys based thereon
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/62—Quenching devices
    • C21D1/673—Quenching devices for die quenching
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite

Definitions

  • the invention relates to a process for producing batch annealed tailor rolled steel.
  • the invention also relates to a tailor rolled strip produced thereby, and a tailor rolled blank cut from the tailor rolled strip.
  • a tailor rolled strip is cut into parts having at least one thicker and one thinner portion, as is known in the art.
  • the tailor rolled strip is produced from cold rolled steel having a standard thickness, which strip is differentially rolled to provide alternating different thicknesses over the length of the strip. After the differential rolling the strip is usually batch annealed, because it is difficult to continuous anneal a strip having different thicknesses. The batch annealing normally does not lead to high yield strength.
  • a process for producing batch annealed tailor rolled steel strip comprising the following steps:
  • the invention shows that control of the hot-rolling process is vital to the microstructural development during batch-annealing.
  • a high finishing rolling temperature is required to ensure that the structure remains in the austenite state during rolling to avoid unfavourable development in texture leading to poor formability [Bodin et. Al, Metal Mater Trans. A. (2000) 33. A. 1589-1603] and to retain precipitating elements such as Nb, Ti, Mo and V from forming dynamic precipitates during rolling. It is essential that these elements remain in solid solution so that they can form precipitates of the small size required for strengthening during the batch- annealing process. For this reason, the cooling rate after hot-rolling should be sufficient to avoid the formation of precipitates during cooling (31 °C/s) where these elements are present. Thus a finish rolling temperature between 910 and 1100 °C is needed.
  • Cooling at a moderate rate ( ⁇ 1 to ⁇ 20°C/s) to a fairly high coiling temperature (600 - 750°C) results in a ferrite-pearlite hot-rolled microstructure.
  • the ferrite is polygonal and free from carbides and there are pearlite colonies distributed throughout, such that all of the carbon available is contained within the randomly distributed pearlite colonies.
  • Manganese has a stabilising effect on pearlite, so these colonies will be predominately associated with areas where the local manganese content is increased, due to segregation and/or normal variability. Both manganese and carbon serve to reduce the ferrite to austenite transformation temperature so that during batch annealing, the first austenite to be formed will nucleate within the pearlite colonies.
  • This austenite will become further stabilised due to manganese and carbon partitioning and will eventually transform to martensite during cooling after annealing.
  • the resultant microstructure will be a dual phase mixture of polygonal ferrite with randomly distributed martensite islands. Due to the long annealing times, there is significant ferrite grain growth which leads to a reduction in yield strength with respect to that in the hot-rolled condition.
  • the cold-rolling reduction of the hot rolled strip is at least 30% to different thicknesses with in the same coil.
  • the batch annealing temperature must be between 650 °C and the Ac3 temperature of the strip, preferably during a time of at least 2 hours and at most 24 hours.
  • composition of the steel that is used in the process is chosen for the following reasons.
  • Carbon (C) is added to form carbide and/or carbo-nitride precipitates, optionally together with Ti, Nb, V and Mo.
  • the amount of C depends on the amount of Ti, Nb, V and/or Mo used. However, the maximum content is 0.20 wt.% to prevent excessive segregation and to prevent a too high fraction of cementite and/or pearlite.
  • a more preferable C content range for the present invention is between 0.001 and 0.15 wt.%, or most preferably between 0.002 and 0.12 wt.%.
  • Si Silicon
  • Si provides significant solid-solution strengthening, which can be used as its contribution to strength is not compromised by the thermal cycle of the batch annealing process. Furthermore, it retards the formation of cementite and pearlite, thus suppressing the formation of coarse carbides.
  • too high Si will lead to an undesired increase in rolling loads and may lead to surface issues and reduced fatigue properties. For these reasons, the Si content may not exceed 1.0 wt.%.
  • a more preferable Si content range for the present invention is at most 0.7 wt.%, or more preferably at most 0.60 or 0.50 wt.%.
  • Mn Manganese
  • Mn content should be at least 2.0 wt.%.
  • a too high Mn content may lead to excessive segregation, which can promote delamination or splitting during shearing operations.
  • a too high Mn content will suppress the ferritic transformation temperature and promote hardenability, leading to hard carbon-rich phase constituents in the intermediate hot-rolled feedstock (e.g., martensite and retained-austenite) which in turn can lead to unacceptable high strength and too high rolling loads for the cold mill.
  • a suitable maximum Mn content for the present invention is 4.0 wt.%.
  • a more preferable Mn content range for the present invention is between 2.1 and 3.8 wt.%, or most preferably between 2.2 and 3.7 wt.%.
  • Phosphorus (P) provides solid-solution strengthening, However, at high levels, P segregation will promote delamination or splitting during shearing operations and impair hole-expansion capacity. Therefore, the P content should be at most 0.05 wt.%, or preferably at most 0.04 wt.%, and more preferably at most 0.02 wt.%. Due to the production process of steel there will always be some P present, at least 0.001 wt.%.
  • S Sulphur
  • the S content should be at most 0.01 wt.%, or preferably at most 0.005 wt.%, or more preferably at most 0.003 wt.%. Due to the production process of steel there will always be some S present, at least 0.001 wt.%.
  • Al is added as a deoxidizer.
  • a suitable minimum Al content is 0.01 wt.%.
  • too high Al can be deleterious as it forms AIN particles during solidification of the molten steel, which can provoke surface issues during casting.
  • the Al content should be at most 0.10 wt.%.
  • a suitable Al content range for the present invention is between 0.01 and 0.10 wt.%, or more preferably between 0.02 and 0.09 wt.%, and most preferably between 0.04 and 0.08 wt.%.
  • N Nitrogen
  • Nb aluminium and other nitrides
  • V, Nb, Ti aluminium and other nitrides
  • grain refinement due to the presence of nitride precipitates.
  • nitrogen can also be present in more complex precipitate species in combination with carbon and/or boron e.g. carbo-nitrides, boro-nitrides etc. Small amount of nitrogen present as precipitates have a beneficial effect on impact properties.
  • Nitrides of aluminium, vanadium, niobium and titanium result in the formation of fine grained ferrite.
  • N content of more than 0.02 wt.% (200 ppm) may result in inconsistent mechanical properties in hot rolled steels, embrittlement of the heat affected zone (HAZ) of welded steels, and poor cold formability.
  • HZ heat affected zone
  • nitrogen can result in strain ageing and reduced ductility of cold rolled and annealed low carbon aluminium killed steels.
  • a more preferable range for N content for the present invention is at most 0.012 wt.%, or most preferably between 0.002 and 0.010 wt.%.
  • Titanium (Ti) can be used in the present invention to realise precipitation strengthening and to some degree grain refinement.
  • Ti is an optional element in the alloy composition of the present invention to achieve a desired strength level for the steel strip or sheet after batch annealing.
  • a suitable maximum Ti content is 0.04 wt.%.
  • a more preferable Ti maximum content for the present invention is 0.02 wt.
  • no Ti needs to be added.
  • Niobium can be used in the present invention to realise a certain degree of precipitation strengthening as well as to achieve grain refinement and hence strength via the Hall-Petch effect.
  • the use of Nb is considered as optional for the present invention.
  • a suitable maximum Nb content is 0.04 wt.%, more preferably 0.02 wt.%.
  • the total of Ti + Nb is set at max 0.05 wt.%.
  • Vanadium (V) acts as an agent to stimulate recrystallization during batch annealing, providing grain refinement, and provides precipitation strengthening.
  • the former i.e., the aspect of recrystallization - is achieved by the formation of V-based carbide precipitates during the initial stages of batch annealing which nucleate on dislocations and hence pin dislocations, reducing their mobility and suppressing recovery.
  • the driving force for the onset of recrystallization is increased as the pool of surviving dislocations at the start of recrystallization increases.
  • a suitable maximum of V is 0.20 wt.%.
  • the maximum V content is 0.10 wt.%.
  • Molybdenum (Mo) is known to be a carbide-forming element and can form together with Ti, Nb and/or V composite carbide and/or carbo-nitride precipitates. These composite precipitates comprising Mo are reported to be more thermally stable than their counterparts without Mo and hence more resistant to coarsening during exposure to a thermal cycle at temperatures above 600°C. Hence, Mo is beneficial to suppress precipitate coarsening during batch annealing at top temperatures above 600°C and to reduce the loss in precipitation strengthening due to batch annealing above 600°C. The desired strength level of the final batch annealed steel in the end will determine to what extent Mo, which is an expensive alloy element, is required. For the present invention, a suitable Mo content is at most 0.10 wt.%. However, there is no need to add Mo.
  • V + Mo Since V and Mo result in the same effects in the steel, the total of V + Mo is set at at most 0.15 wt.%.
  • Chromium is an element that can be added as a replacement of Mn to provide solid-solution strengthening. Since Cr can have detrimental effects for the end product, Cr should be added in an amount of at most 1.0 wt.%. Since it is a replacement of Mn, the total of Cr + Mn should be between 2.0 and 4.0 wt.% and follow the preferred ranges for Mn.
  • Calcium is an optional element for the present invention and may be used to modify MnS-type of inclusions to improve formability and/or to modify Al x O y -type of inclusions to reduce the risk of clogging and to improve castability of the steel during steel making.
  • a too high Ca content can lead to excessive wear of the refractory lining in the installations of the steel-making plant.
  • a suitable maximum Ca content is 50 ppm, or more preferable maximum 35 ppm.
  • a suitable minimum Ca content in the steel is 20 ppm.
  • the Ca content in the steel is at most 20 ppm, or preferably at most 10 ppm, or most preferably at most 5 ppm.
  • the strip that is produced has a strength between 570 and 750 MPa, lower amounts of C, Mn and Si can be used, and there is no need to add Ti, Nb, V or Mo.
  • the annealing temperature can be lower, that is between 650 and 760 °C.
  • the strip that is produced has a strength between 700 and 900 MPa, so the amounts of C, Mn and Si can be somewhat higher than according to the previous embodiment. Moreover, it is an option to add Ti, Nb, V and/or Mo. Furthermore, the annealing temperature can be slightly higher, between 670 and 790 °C.
  • the strip produced according to this third embodiment has a high strength between 900 and 1200 MPa, for which higher amounts of C, Mn and Si can be added. It is also possible to add Ti, Nb, V and/or Mo. Here as well the annealing temperature can be slightly higher then for the first embodiment.
  • the coiling temperature of the hot rolled strip is at least 300 °C, preferably at least 400 °C, more preferably at least 500 °C. Since the higher limit for the coiling temperature is most relevant, it is advantageous to coil the strip at a higher temperature.
  • the composition contains B £ 0.003 wt%. There is no specific need to add more boron.
  • the batch annealed tailor rolled dual phase steel strip is coated with an organic coating or a metallic coating, preferably by heat-to-coat, electro-galvanising, PVD or CVD.
  • this coating is preferably a zinc or zinc alloy coating or an aluminium or aluminium alloy coating, such as a Gl coating, a GA coating, a AlSi coating or a ZnAIMg coating. These are the coatings mainly used for automotive purposes.
  • a tailor rolled strip obtained by using the process in accordance with the process described above, wherein the strip has alternating portions having a high thickness and portions having a low thickness, wherein the variation in thickness between the high thickness and the low thickness is at least 15%.
  • this strip has an ultimate tensile strength Rm between 570 and 750 MPa, a 0.2% proof strength Rp0.2 between 270 and 400 MPa and a total elongation A80 of at least 18%.
  • Such a strip can be used as a DP600 dual phase tailor rolled strip.
  • this strip has an ultimate tensile strength Rm between 700 and 900 MPa, a 0.2% proof strength Rp0.2 between 350 and 550 MPa and a total elongation A80 of at least 14%.
  • Such a strip can be used as a DP800 dual phase tailor rolled strip.
  • this strip has an ultimate tensile strength Rm between 900 and 1200 MPa, a 0.2% proof strength Rp0.2 between 500 and 700 MPa and a total elongation A80 of at least 8%, preferably a total elongation of at least 10%, more preferably a total elongation of at least 12%.
  • a strip can be used as a DP1000 dual phase tailor rolled strip.
  • DP1000 has a total elongation of at least 12%.
  • the strip according to the second aspect of the invention can also be a multiphase steel.
  • Usually the total elongation of multiphase steel is somewhat lower than the total elongation of dual phase steel.
  • the steel of the tailor rolled strip according to the first embodiment of the second aspect of the invention has a microstructure consisting of at most 10% bainite and at most 15% martensite, the remainder being ferrite.
  • the ferrite fraction is acicular ferrite. With this microstructure, the strength and elongation of the batch annealed strip according to the first embodiment are sufficient. In dual phase steel usually no bainite is present.
  • the steel of the tailor rolled strip according to the second or third embodiment of the second aspect of the invention has the microstructure consisting of 10 - 20% martensite, 0 - 20% bainite, the remainder being ferrite.
  • the ferrite fraction is acicular ferrite. With this microstructure, the strength and elongation of the batch annealed strip according to the second and third embodiment are sufficient. In dual phase steel usually no bainite is present.
  • a tailor rolled blank (TRB) cut from a tailor rolled strip according to the second aspect of the invention wherein the TRB has at least one portion having a high thickness and at least one portion having a low thickness.
  • This TRB has a strength and elongation in accordance with that of the tailor rolled strip from which it is cut. This combination of strength and elongation makes the TRB very suitable for use in automotive products.
  • the tailor rolled strip or TRB according to the third aspect of the invention has a zinc or zinc alloy coating or an aluminium or aluminium alloy coating, such as a Gl coating, a GA coating, a AlSi coating or a ZnAIMg coating.
  • the TRB with a metallic coating is especially suitable for automotive purposes.
  • Table 1 shows the composition of 21 different steels types in accordance with the present invention.
  • Table 2 shows the process conditions for producing these steel types, and the resulting mechanical properties thereof.
  • composition of and process conditions for the steel types 1 to 9 result in steel types according to the first embodiment as described above. All these nine steel types a DP600 steels.
  • composition of and process conditions for the steel types 10 to 18 result in steel types according to the second embodiment as described above.
  • These nine steel types are DP800 steels.
  • composition of and process conditions for the steel types 19, 20 and 20 result in steel types according to the third embodiment as described above.
  • These nine steel types are DP1000 or multiphase steels having a strength level of a DP1000 steel.
  • Nb can be added instead of or in combination with Ti, since it results in the same effects for the steel. This is common knowledge for the skilled person.
  • Mo can be added instead of or in combination with V.
  • Chromium can be added instead of Mn, though this is not exemplified.
  • Table 2 shows that with a finish rolling temperature (FRT) of at least 910 °C and a coiling temperature (CT) of at most 650 °C, these steel types result in the required mechanical properties, when the reduction (CR red., cold rolling reduction) is at least 30% and the batch annealing temperature (Soak) is more than 650 °C.
  • FRT finish rolling temperature
  • CT coiling temperature
  • Soak batch annealing temperature
  • the cooling rate for the strip on the run-out table is at least 20 °C/s
  • the heating rate before batch annealing was approximately 40 °C/s
  • the cooling rate after batch annealing was approximately 30 °C/s.
  • these heating and cooling rates are not decisive, as long as the cooling rate on the run out table is more than 20 °C.
  • Example 19 provides a T.EI of 12,5 %, so this example shows that a DP1000 with the required strength and elongation can be provided by the invention.
  • Examples 20 and 21 show multiphase steel types having the same strength as a DP1000, but having a slightly lower total elongation.
  • Table 1 Composition of 21 steel types in weight%, only N and B in ppm (parts per million).
  • Table 2 Process conditions and mechanical properties of the 21 steel types of Table 1.

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Abstract

L'invention concerne un procédé de fabrication d'une bande d'acier laminée sur mesure à recuit discontinu, comprenant les étapes suivantes consistant à : a) couler une brame ayant la composition suivante (en % en poids) : C = 0 à 0,2 ; Mn = 2,0 à 4,0 ; Si ≤ 1,0 ; P = 0,001 à 0,05 ; S = 0,001 à 0,01 ; N ≤ 0,02 ; Al = 0,01 à 0,10 ; éventuellement : Ti ≤ 0,04 ; Nb ≤ 0,04 ; V ≤ 0,20 ; Mo ≤ 0,10 ; b ≤ 0,005 ; Cr ≤ 1,0 ; Ca ≤ 0,005, Ti + Nb ≤ 0,05, V + Mo ≤ 0,15, et 2,0 ≤ Cr + Mn ≤ 4,0, le reste étant constitué de Fe et des impuretés inévitables ; b) laminer à chaud la brame jusqu'à une température de laminage de finition comprise entre 910 et 1 100 °C ; c) refroidir la bande laminée à chaud jusqu'à une température de bobinage comprise entre 200 et 700 °C ; d) laminer à froid la bande laminée à chaud avec une réduction d'au moins 30 % en utilisant un laminage différentiel pour produire différentes épaisseurs à l'intérieur de la bande, de manière à produire une bande d'acier laminée sur mesure, à découper en ébauches laminées sur mesure ; e) recuire de manière discontinue la bande laminée à froid différentielle à une température comprise entre 650 °C et la température Ac3 de la bande, pour obtenir une bande d'acier laminée sur mesure à recuit discontinu ayant une Rm d'au moins 570 MPa.
EP20719642.9A 2019-04-30 2020-04-21 Procédé de production d'une bande laminée sur mesure à recuit discontinu Pending EP3963114A1 (fr)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2031081B1 (fr) * 2007-08-15 2011-07-13 ThyssenKrupp Steel Europe AG Acier en phase double, produit plat à partir d'un tel acier en phase double et son procédé de fabrication
EP2025771A1 (fr) * 2007-08-15 2009-02-18 Corus Staal BV Procédé de production de bande d'acier revêtu pour produire des éléments taylorisés adaptés à la mise en forme thermomécanique, bande produite, et utilisation d'une telle bande revêtue
DE102009051673B3 (de) * 2009-11-03 2011-04-14 Voestalpine Stahl Gmbh Herstellung von Galvannealed-Blechen durch Wärmebehandlung elektrolytisch veredelter Bleche
RU2661692C2 (ru) * 2014-04-23 2018-07-19 Ниппон Стил Энд Сумитомо Метал Корпорейшн Горячекатаный стальной лист для прокатанной заготовки переменной толщины, прокатанная заготовка переменной толщины и способы для их производства
KR20180025852A (ko) * 2015-07-01 2018-03-09 타타 스틸 이즈무이덴 베.뷔. 고강도 용융 침지 아연도금 강 스트립
DE102015112889A1 (de) * 2015-08-05 2017-02-09 Salzgitter Flachstahl Gmbh Hochfester manganhaltiger Stahl, Verwendung des Stahls für flexibel gewalzte Stahlflachprodukte und Herstellverfahren nebst Stahlflachprodukt hierzu
DE102016117502A1 (de) * 2016-09-16 2018-03-22 Salzgitter Flachstahl Gmbh Verfahren zur Herstellung eines Warm- oder Kaltbandes und/oder eines flexibel gewalzten Stahlflachprodukts aus einem hochfesten manganhaltigen Stahl und Stahlflachprodukt hiernach

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