EP1411140B1 - Process for manufacturing of cold-rolled steel strips or sheets having excellent formability - Google Patents

Process for manufacturing of cold-rolled steel strips or sheets having excellent formability Download PDF

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EP1411140B1
EP1411140B1 EP03018184A EP03018184A EP1411140B1 EP 1411140 B1 EP1411140 B1 EP 1411140B1 EP 03018184 A EP03018184 A EP 03018184A EP 03018184 A EP03018184 A EP 03018184A EP 1411140 B1 EP1411140 B1 EP 1411140B1
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Prior art keywords
hot
process according
rolling
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last
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EP03018184A
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German (de)
French (fr)
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EP1411140A1 (en
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Bernhard Dr.-Ing. Engl
Klaus-Dieter Horn
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ThyssenKrupp Steel Europe AG
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ThyssenKrupp Steel AG
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    • 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
    • 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
    • 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
    • C21D8/0447—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
    • 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
    • C21D9/48—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals deep-drawing sheets
    • 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
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • 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
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • 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
    • C21D8/0478—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 involving a particular surface treatment

Definitions

  • the invention relates to a method for producing a cold-rolled steel strip or sheet.
  • such tape or sheet is used for the production of body parts required in vehicle construction.
  • a good formability is characterized by a high n-value characterizing the iron drawability and a likewise high r value characterizing the deep drawability.
  • a method for producing a hot-rolled steel strip having a high r-value in which a not more than 0.015 wt .-% C, 1.0 - 2.0 % By weight of Mn, 0.005 to 0.10% by weight of Al, 0.01 to 0.06% by weight of Nb, 0.01 to 0.1% by weight of Ti and the remainder containing iron and unavoidable impurities Steel in a reheating furnace to a temperature of not less than 1150 ° C is heated.
  • the thus heated steel is pre-rolled, wherein the rough rolling is carried out in a temperature range of 980 ° C to 1100 ° C with a reduction in thickness of not less than 20% per pass.
  • the pre-rolled steel is hot rolled in a temperature range of Ar 3 to 930 ° C while maintaining a total reduction of not less than 90% before being coiled at 600 ° C to 800 ° C.
  • the hot strip thus produced should have a high formability, the essential feature of the known from DE 37 04 828 C2 method is seen in that the developed IF steel has a high Mn content and is free of dissolved C and N and that the steel thus composed undergoes a large reduction within a certain temperature range, then cooled and then rewound within a certain temperature range.
  • a process for the production of fine formable metal sheet with a cold strip final thickness of at most 0.3 mm is known from DE 101 17 118 C1.
  • slabs or thin slabs are then reheated after cooling to a temperature ranging from 1080 ° C to 1150 ° C for a maximum of eight hours holding time.
  • the reheated slabs or slabs are then hot rolled into a hot strip at a number of passes in a hot rolling mill at a final rolling temperature above the Ar 3 temperature and coiled at temperatures ranging from 590 ° C to 660 ° C. After coiling, the hot strip obtained is cold rolled to cold strip and subjected to a continuous annealing.
  • JP 07-018381 A discloses a method for producing an excellent deep-drawable cold-rolled steel sheet in which a steel other than iron (in% by weight) is subjected to an ultra-low C content by Max. 0.015%, a Mn content of max. 0.40%, a P content of max. 0.020%, an Al content of max. 0.080%, an N content of max. 0.005%, a Ti content of 0.005-0.020% and an S content of max. 0.015%.
  • N, S, Mn and Ti must simultaneously satisfy the condition 3.42 N + S / 16 (Mn + 0.10) ⁇ Ti ⁇ 10 N + S / 8 (Mn + 0.10) to obtain the To allow formation of TiN precipitates, which decisively influence the thermoformability of the steel processed in the known manner.
  • the thus composed steel is continuously cast at a certain take-off speed and then hot rolled.
  • a degree of deformation of at least 40% and in the final stage of finish hot rolling a degree of deformation of at least 20% is to be achieved.
  • the hot rolling temperatures are in the known method in each case above the Ar 3 temperature in order to ensure the lowest possible property dispersion in the bands obtained after hot rolling. Hot rolling is followed by targeted cooling of the hot strip, at which cooling rates of at least 30 ° C./s must be achieved.
  • the object of the invention was therefore to provide a method by which can be produced at low production cost effort cold strips or sheets with widely dispersed composition that have a compared to conventionally manufactured products further improved formability.
  • the invention is based on the knowledge that a decisive improvement in the formability of steel strips and steel sheets of the type in question can be achieved not only by a suitable, the finished hot rolling upstream processing of each used precursor, but in particular by the inventive choice of hot rolling.
  • cold sheets produced according to the invention are distinguished by outstanding r values and, correspondingly, excellent deep drawability.
  • an embodiment of the invention provides that a soft steel alloy is processed, each containing (in wt .-%) 0.01 - 0.1% C, 0.1 - 0.5% Mn, up to 0.03% P, up to 0.03% S, 0.01-0.1% Al, less than 0.005% Ti, less than 0.005% Nb and up to 0.01% B, and the remainder iron and unavoidable impurities may contain.
  • an IF steel may typically contain (in% by weight) less than 0.01% C, less than 0.2% Mn, less than 0.02% S, less than 0.02% P less than 0.05% Al, less than 0.005% N, 0.02-0.1% Ti, up to 0.05% Nb, and less than 0.001% B.
  • the individual alloy components can be coordinated with one another within the ranges generally specified by the invention in such a way that an optimum work result is achieved.
  • the suitably alloyed molten steel is poured into a hot-rolling starting material, such as slabs or thin slabs. These are heated to a preheating temperature, which is preferably in the range of 1000 ° C to 1300 ° C. Subsequently, the starting material is fed into a hot rolling mill, where it is rolled into hot strip.
  • This hot rolling comprises a multi-stage finish rolling, which may be preceded by rough rolling if necessary.
  • the improvement sought by the invention is achieved in each case that in the last four stages of Fertigwarmwalzens the remaining, over these four stages to be handled Bacumformgrad as high as possible.
  • the invention requires that over the last four stands of the hot roll stand the Retroformgrad should be at least 80%. In the case of a classic rolling scale comprising seven stands, it is therefore necessary, via the stands 4, 5, 6 and 7, to set a total degree of deformation of at least 80%, preferably 85%, in order to achieve the desired increase in the r value.
  • the division of the individual thickness decreases on the individual last of the hot strip traversed rolling stands is not arbitrary, but follows a precisely graded plan.
  • the invention still stipulates that the overall degree of transformation to be handled over the last three rolling stands is still at least 65%, preferably 75%, which is at least 50% above the last two stands of the rolling scale 60% and the degree of deformation reached over the last frame of the squadron must be at least 25%, preferably at least 30% or even at least 35%.
  • the effect of the procedure according to the invention is all the more favorable, the higher the overall conversion remaining for the last four scaffolds.
  • the temperature at which the hot rolling is carried out in the last four continuous stands of the hot rolling stand is of importance. This should be chosen according to the invention so that the relevant passes of the hot rolling are carried out in deep austenite. Therefore, the invention contemplates rolling the last four passes at temperatures ranging from 950 ° C to 880 ° C in close proximity to the Ar 3 transformation temperature. In this case, roller temperatures which are particularly close to the Ar 3 temperature, which range from 930 ° C. down to the Ar 3 temperature, are advantageous. In this case, the respective hot rolling temperatures are within a range in which the steel being processed is still certainly austenitic, but at the same time is at a level which ensures that work is done in the deep austenite favorable for the effects of the invention.
  • An operating parameter also to be considered according to the invention which is of importance for the properties of the product obtained, is the tape end speed.
  • This is at least 10 m / s, for unalloyed very soft steel, but preferably at least 15 m / s, in order to avoid recrystallization in the finishing scale between the rolling passes.
  • the high rolling or rolling speed is required, so that there is no recrystallization in the finishing scale, especially in very rekristallisationsfreudigem steel after the rolling passes between the individual Walgerüsten. In this way, a high cumulative degree of hot deformation is achieved, whereby the Texture base for the very high r-values on the hot strip produced according to the invention is set.
  • the cold strip is to be recrystallized after cold rolling in a continuous furnace, it has proven to be advantageous in view of the desired high r-values of steel sheets or strips produced according to the invention if the coiling temperature is at least 700 ° C. If, on the other hand, a "pan-cake microstructure" favorable for certain deformation tasks is to be produced in the cold-rolled sheet by a recrystallizing annealing carried out in the bundle under the hood, it is favorable to choose a reel temperature which is as low as possible and which does not exceed 550 ° C. "Pan-cake texture" is characterized by a stretched, relatively coarse grain.
  • the fabric of this nature and the texture associated therewith are particularly favorable if high degrees of deformation must be achieved during the cold forming of the cold sheet into a component.
  • a high reel temperature causes coarse, a low coiler temperature on the other hand fine carbides and nitrides. In principle, a few coarse precipitates are more favorable for cold strip recrystallization than many fine ones, since they have a less disturbing effect on the recrystallization process.
  • hot rolling scale slabs were hot rolled to hot strip W consisting of a 0.025 wt .-% C, 0.15 wt .-% Mn, each less than 0.01 wt .-% P and S, 0.04 wt. % Al, 0.003 wt .-% N, balance iron and unavoidable impurities containing mild steel have been poured.
  • the slabs were thoroughly warmed to a preheat temperature of 1250 ° C before being finish hot rolled in hot roll 8 to hot strip W at a hot rolling end temperature of 900 ° C.
  • the resulting hot strip was then coiled at a reel temperature of 520 ° C and rolled at a cold rolling degree of 75% to cold strip.
  • the cold strip in the coil in the annealing furnace at 700 ° C was annealed recrystallizing.
  • the slabs were heated to a preheating temperature of 1100 ° C, hot rolled in the hot rolling stand 8 at a hot rolling end temperature of 900 ° C to hot strip W.
  • the hot strip W has been coiled at a temperature of 720 ° C., cold-rolled with a cold rolling degree of 75% and recrystallized at 800 ° C. in a continuously passed continuous furnace.
  • the forming degrees ⁇ h1 to ⁇ h7 to be achieved over the individual respective rolling stands 1, 2, 3, 4, 5, 6, 7 are each set such that the for the last four rolling stands 4 , 5,6,7 of the rolling scale remaining remainders were significantly higher than in conventional production.
  • three erfindunsupplementarye hot rolling variants Ea, Eb and Ec have been compared to a conventionally performed hot rolling K compared to setting the highest possible for the last four rolling stands 4,5,6,7 remaining forming effects according to the invention.

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

Abstract

Production of a steel strip or sheet comprises casting a steel melt into slabs or thin slabs, heating to at least 1000degrees C, hot rolling using a strip end speed of at least 10 m/s into a hot strip, coiling, cold rolling to form a cold strip, and recrystallization annealing. The steel melt contains (in wt.%) less than 0.1, less than 0.5 Mn, less than 0.03 P, less than 0.03 S, less than 0.1 Al, less than 0.01 N, less than 0.1 Ti, less than 0.05 Nb and less than 0.01 B with a balance of Fe and the usual impurities.

Description

Die Erfindung betrifft ein Verfahren zum Herstellen eines kaltgewalzten Stahlbands oder -blechs. Beispielsweise wird derartiges Band oder Blech für die Herstellung von im Fahrzeugbau benötigten Karosserieteilen verwendet.The invention relates to a method for producing a cold-rolled steel strip or sheet. For example, such tape or sheet is used for the production of body parts required in vehicle construction.

An die Umformeigenschaften derartiger Stahlflachprodukte werden immer höhere Anforderungen gestellt, um auch komplexe Formgestaltungen bei vermindertem Arbeitsaufwand verwirklichen zu können. Eine gute Umformbarkeit ist dabei gekennzeichnet durch einen hohen, die Streckziehbarkeit charakterisierenden n-Wert und einen gleichfalls hohen, die Tiefziehbarkeit kennzeichnenden r-Wert.At the forming properties of such flat steel products ever higher demands are made in order to realize even complex designs with reduced workload can. A good formability is characterized by a high n-value characterizing the iron drawability and a likewise high r value characterizing the deep drawability.

Aus der Fachliteratur ("Herstellung von warmgewalzten Flacherzeugnissen", Verein deutscher Eisenhüttenleute, 1972, Seiten 271 - 303; "Herstellung von kaltgewalztem Band", Verein deutscher Eisenhüttenleute, 1970, Teil 2, Seiten 33 - 54; "Werkstoffkunde der gebräuchlichen Stähle", Verein deutscher Eisenhüttenleute, 1977, Teil 1, Seiten 237 - 258) ist es bekannt, dass bei konventioneller Herstellweise neben der Auswahl einer geeigneten Stahlzusammensetzung die Verformungseigenschaften entscheidend durch die Einstellung der Bedingungen beim Vorwalzen der Brammen beeinflusst werden können. In der Praxis zeigt sich jedoch, dass auch mit Stahlblechen, die unter Anwendung dieser Maßnahmen erzeugt worden sind, die gesteigerten Anforderungen nicht ohne weiteres erfüllt werden können.From the specialist literature ("Production of hot-rolled flat products", Association of German iron and steel workers, 1972, pages 271-303; "Production of cold rolled strip", Association of German iron and steel industry, 1970, Part 2, pages 33-54, "Material Science of common steels", Verein deutscher Eisenhüttenleute, 1977, Part 1, pp. 237-258), it is known that in conventional production, in addition to the selection of a suitable steel composition, the deformation properties can be decisively influenced by adjusting the conditions during rough rolling of the slabs. In practice, however, it has been found that even with steel sheets produced using these measures, the Increased requirements can not be met easily.

Neben dem voranstehend erläuterten Stand der Technik ist aus der DE 37 04 828 C2 ein Verfahren zur Herstellung eines warmgewalzten Stahlbandes mit einem hohen r-Wert bekannt, bei dem ein nicht mehr als 0,015 Gew.-% C, 1,0 - 2,0 Gew.-% Mn, 0,005 - 0,10 Gew.-% Al, 0,01 - 0,06 Gew.-% Nb, 0,01 - 0,1 Gew.-% Ti und als Rest Eisen sowie unvermeidliche Verunreinigungen enthaltender Stahl in einem Nachwärmofen auf eine Temperatur von nicht weniger als 1150 °C erwärmt wird. Anschließend wird der so erwärmte Stahl vorgewalzt, wobei das Vorwalzen in einem Temperaturbereich von 980 °C bis 1100 °C bei einer Dickenreduktion von nicht weniger als 20 % pro Durchgang durchgeführt wird. Anschließend wird der vorgewalzte Stahl in einem Temperaturbereich von Ar3 bis 930°C bei Beibehaltung einer Gesamtreduktion von nicht weniger als 90 % warmendgewalzt, bevor er bei 600 °C bis 800 °C gehaspelt wird. Das derart erzeugte Warmband soll eine hohe Umformbarkeit aufweisen, wobei das wesentliche Merkmal des aus der DE 37 04 828 C2 bekannten Verfahrens darin gesehen wird, dass der erarbeitete IF-Stahl einen hohen Mn-Gehalt aufweist und frei von gelöstem C und N ist und dass der derart zusammengesetzte Stahl innerhalb eines bestimmten Temperaturbereichs einer großen Reduktion unterzogen, anschließend gekühlt und danach innerhalb eines bestimmten Temperaturbereichs wieder aufgewickelt wird.In addition to the prior art described above, from DE 37 04 828 C2 a method for producing a hot-rolled steel strip having a high r-value is known in which a not more than 0.015 wt .-% C, 1.0 - 2.0 % By weight of Mn, 0.005 to 0.10% by weight of Al, 0.01 to 0.06% by weight of Nb, 0.01 to 0.1% by weight of Ti and the remainder containing iron and unavoidable impurities Steel in a reheating furnace to a temperature of not less than 1150 ° C is heated. Subsequently, the thus heated steel is pre-rolled, wherein the rough rolling is carried out in a temperature range of 980 ° C to 1100 ° C with a reduction in thickness of not less than 20% per pass. Subsequently, the pre-rolled steel is hot rolled in a temperature range of Ar 3 to 930 ° C while maintaining a total reduction of not less than 90% before being coiled at 600 ° C to 800 ° C. The hot strip thus produced should have a high formability, the essential feature of the known from DE 37 04 828 C2 method is seen in that the developed IF steel has a high Mn content and is free of dissolved C and N and that the steel thus composed undergoes a large reduction within a certain temperature range, then cooled and then rewound within a certain temperature range.

Ein Verfahren zur Herstellung von gut umformfähigem Feinstblech mit einer Kaltband-Enddicke von höchstens 0,3 mm ist aus der DE 101 17 118 C1 bekannt. Bei diesem Verfahren wird ein Stahl der 0,0015 bis 0,008 Masse-% C, 0,15 - 0,25 Masse-% Mn, ≤ 0,02 Masse-% P, 0,005 - 0,03 Masse-% S, ≤ 0,02 Masse-% Si, 0,0080 - 0,06 Masse-% Al, 0,0010 - 0,020 Masse-% N, ≤ 0,05 Masse-% Ca, ≤ 0,5 Masse-% Ni, ≤ 0,05 Masse-% Cu, ≤ 0,02 Masse-% Sn, ≤ 0,01 Masse-% Mo, ≤ 0,0005 Masse-% Ti, ≤ 0,0005 Masse-% Mb, ≤ 0,002 Masse-% V, ≤ 0,007 Masse-% B und ≤ 0,05 Masse-% Co, sowie wahlweise weitere Elemente und als Rest Eisen und unvermeidbare Verunreinigungen enthält, zu Brammen oder Dünnbrammen vergossen. Diese Brammen oder Dünnbrammen werden anschließend nach einer Abkühlung auf eine Temperatur, die im Bereich von 1080 °C bis 1150 °C liegt einer maximal acht Stunden betragenden Haltezeit wiedererwärmt. Die wiedererwärmten Brammen oder Dünnbrammen werden dann mehreren Stichen in einer Warmwalzstraße bei einer oberhalb der Ar3-Temperatur liegenden Endwalztemperatur zu jeweils einem Warmband warmgewalzt und bei Temperaturen, die im Bereich von 590 °C bis 660 °C liegen, gehaspelt. Nach dem Haspeln wird das erhaltene Warmband zu Kaltband kaltgewalzt und einer im Durchlauf erfolgenden Glühung unterzogen.A process for the production of fine formable metal sheet with a cold strip final thickness of at most 0.3 mm is known from DE 101 17 118 C1. In this method, a steel of 0.0015 to 0.008 mass% C, 0.15 to 0.25 mass% Mn, ≤ 0.02 mass% P, 0.005 to 0.03 Mass% S, ≤ 0.02 mass% Si, 0.0080-0.06 mass% Al, 0.0010-0.020 mass% N, ≤ 0.05 mass% Ca, ≤ 0.5 mass -% Ni, ≤ 0.05 mass% Cu, ≤ 0.02 mass% Sn, ≤ 0.01 mass% Mo, ≤ 0.0005 mass% Ti, ≤ 0.0005 mass% Mb, ≤ 0.002% by mass V, ≤ 0.007% by mass B and ≤ 0.05% by mass of Co, and optionally other elements and the remainder containing iron and unavoidable impurities, cast into slabs or thin slabs. These slabs or thin slabs are then reheated after cooling to a temperature ranging from 1080 ° C to 1150 ° C for a maximum of eight hours holding time. The reheated slabs or slabs are then hot rolled into a hot strip at a number of passes in a hot rolling mill at a final rolling temperature above the Ar 3 temperature and coiled at temperatures ranging from 590 ° C to 660 ° C. After coiling, the hot strip obtained is cold rolled to cold strip and subjected to a continuous annealing.

Neben dem voranstehend erläuterten Stand der Technik ist aus der JP 07-018381 A ein Verfahren zur Herstellung eines hervorragend tiefziehbaren kaltgewalzten Stahlblechs bekannt, bei dem ein Stahl verarbeitet wird, der außer Eisen (in Gew.-%) einen ultra-niedrigen C-Gehalt von max. 0,015 %, einen Mn-Gehalt von max. 0,40 %, einen P-Gehalt von max. 0,020 %, einen Al-Gehalt von max. 0,080 %, einen N-Gehalt von max. 0,005 %, einen Ti-Gehalt von 0,005 - 0,020 % und einen S-Gehalt von max. 0,015 % aufweist. Dabei müssen die Gehalte an N, S, Mn und Ti gleichzeitig die Bedingung 3,42 N + S/16(Mn+0,10) < Ti < 10 N + S/8(Mn+0,10) erfüllen, um die Bildung von TiN-Ausscheidungen zu ermöglichen, die die Tiefziehfähigkeit des in der bekannten Weise verarbeiteten Stahls entscheidend beeinflussen.Besides the above-mentioned prior art, JP 07-018381 A discloses a method for producing an excellent deep-drawable cold-rolled steel sheet in which a steel other than iron (in% by weight) is subjected to an ultra-low C content by Max. 0.015%, a Mn content of max. 0.40%, a P content of max. 0.020%, an Al content of max. 0.080%, an N content of max. 0.005%, a Ti content of 0.005-0.020% and an S content of max. 0.015%. The contents of N, S, Mn and Ti must simultaneously satisfy the condition 3.42 N + S / 16 (Mn + 0.10) <Ti <10 N + S / 8 (Mn + 0.10) to obtain the To allow formation of TiN precipitates, which decisively influence the thermoformability of the steel processed in the known manner.

Gemäß der JP 07-018381 A wird der derart zusammengesetzte Stahl mit einer bestimmten Abzugsgeschwindigkeit stranggegossen und anschließend warmgewalzt. In der vorletzten Stufe des Fertig-Warmwalzens soll dabei ein Verformungsgrad von mindestens 40 % und in der letzten Stufe des Fertig-Warmwalzens ein Verformungsgrad von mindestens 20 % erzielt werden. Die Warmwalztemperaturen liegen bei dem bekannten Verfahren jeweils oberhalb der Ar3-Temperatur, um eine möglichst geringe Eigenschaftsstreuung bei den nach dem Warmwalzen erhaltenen Bändern sicherzustellen. An das Warmwalzen schließt sich eine gezielte Kühlung des Warmbandes an, bei der Abkühlraten von mindestens 30 °C/s erzielt werden müssen.According to JP 07-018381 A, the thus composed steel is continuously cast at a certain take-off speed and then hot rolled. In the penultimate stage of finish hot rolling a degree of deformation of at least 40% and in the final stage of finish hot rolling a degree of deformation of at least 20% is to be achieved. The hot rolling temperatures are in the known method in each case above the Ar 3 temperature in order to ensure the lowest possible property dispersion in the bands obtained after hot rolling. Hot rolling is followed by targeted cooling of the hot strip, at which cooling rates of at least 30 ° C./s must be achieved.

Die mit dem aus der JP 07-018381 A bekannten Verfahren erzeugten Stahlbleche und -bänder weisen zwar r-Werte auf, die sie als für eine Tiefziehverarbeitung besonders geeignet ausweisen. Dazu ist allerdings nicht nur eine bestimmte Art und Weise des Stranggießens erforderlich, sondern es kann mit dem gewünschten Erfolg auch nur ein eng begrenztes Spektrum von Stahlsammensetzungen verarbeitet werden.Although the steel sheets and strips produced by the method known from JP 07-018381 A have r values which make them particularly suitable for deep-drawing processing. But not just one certain manner of continuous casting is required, but it can be processed with the desired success even a narrow range of steel compositions.

Die Aufgabe der Erfindung bestand daher darin, ein Verfahren zu schaffen, mit dem sich bei geringem fertigungstechnischen Aufwand Kaltbänder oder -bleche mit weit gestreuter Zusammensetzung erzeugen lassen, die eine gegenüber konventionell hergestellten Produkten weiter verbesserte Umformbarkeit besitzen.The object of the invention was therefore to provide a method by which can be produced at low production cost effort cold strips or sheets with widely dispersed composition that have a compared to conventionally manufactured products further improved formability.

Diese Aufgabe ist gemäß der Erfindung durch ein Verfahren zum Herstellen von kaltgewalztem Stahlband oder -blech gelöst worden, welches folgende Schritte umfasst:

  • Vergießen einer (in Ges.-%) ≤ 0,1 % C, ≤ 0,5 % Mn, < 0,03 % P, < 0,03 % S, ≤ 0,1 % Al, < 0,01 % N, < 0,1 % Ti, < 0,05 % Nb, ≤ 0,01 % B, Rest Eisen und übliche Verunreinigungen enthaltenden Stahlschmelze zu einem Vormaterial, wie Brammen oder Dünnbrammen,
  • Durchwärmen des Vormaterials auf eine mindestens 1000 °C betragende Vorwärmtemperatur,
  • Warmwalzen des Vormaterials in einer mindestens vier Walzgerüste umfassenden Fertigwarmwalzstaffel zu einem Warmband, wobei
  • der über die letzten vier vor dem Verlassen der Warmwalzstaffel passierten Walzgerüste erzielte Gesamtumformgrad εh4 mindestens 80 %,
  • der über die letzten drei vor dem Verlassen der Warmwalzstaffel passierten Walzgerüste erzielte Gesamtumformgrad εh3 mindestens 65 %,
  • der über die letzten beiden vor dem Verlassen der Warmwalzstaffel passierten Walzgerüste erzielte Gesamtumformgrad εh2 mindestens 50 %,
  • der über das letzte vor dem Verlassen der Warmwalzstaffel passierten Walzgerüste erzielte Gesamtumformgrad εh1 mindestens 25 %,
  • das Warmwalzen in den letzten vier vor dem Verlassen der Warmwalzstaffel passierten Walzgerüsten bei einer 880 °C bis 950 °C betragenden Walztemperatur erfolgt,
  • das Warmwalzen bei Warmwalzendtemperatur beendet wird, die ≥ der Ar3-Temperatur ist, und
  • die Bandendgeschwindigkeit des erhaltenen Warmbands beim Verlassen der Warmwalzstaffel mindestens 10 m/s beträgt,
  • Haspeln des Warmbandes,
  • Kaltwalzen des Warmbandes zu einem Kaltband,
  • Rekristallisationsglühen des Kaltbands.
This object has been achieved according to the invention by a method for producing cold-rolled steel strip or sheet, comprising the following steps:
  • Casting a (in% by weight) ≤ 0.1% C, ≤ 0.5% Mn, <0.03% P, <0.03% S, ≤ 0.1% Al, <0.01% N , <0.1% Ti, <0.05% Nb, ≤ 0.01% B, balance iron and common impurities containing molten steel to a starting material, such as slabs or thin slabs,
  • Heating the starting material to a preheating temperature of at least 1000 ° C,
  • Hot rolling of the starting material in a complete at least four rolling stands Fertigwarmwalzstaffel to a hot strip, wherein
  • the total degree of deformation ε h4 achieved at least 80% over the last four mill stands passed before leaving the hot rolling mill
  • the total degree of deformation ε h3 achieved at least 65% over the last three mill stands passed before leaving the hot rolling mill,
  • the total degree of deformation ε h2 achieved by the last two stands passed before leaving the hot roll stand at least 50%,
  • the total degree of deformation ε h1 achieved by the last mill stands passed before leaving the hot rolling stand at least 25%,
  • the hot rolling in the last four stands passed before leaving the hot rolling mill is at a rolling temperature of 880 ° C to 950 ° C,
  • the hot rolling is terminated at hot rolling end temperature which is ≥ the Ar 3 temperature, and
  • the strip end speed of the hot strip obtained when leaving the hot rolling train is at least 10 m / s,
  • Coiling the hot strip,
  • Cold rolling the hot strip to a cold strip,
  • Recrystallization annealing of the cold strip.

Die Erfindung geht von der Erkenntnis aus, dass nicht nur durch eine geeignete, dem Fertigwarmwalzen vorgeschaltete Bearbeitung des jeweils eingesetzten Vorproduktes, sondern insbesondere durch die erfindungsgemäße Wahl der Warmwalzbedingungen eine entscheidende Verbesserung der Umformbarkeit von Stahlbändern und Stahlblechen der in Rede stehenden Art erreicht werden kann. So zeichnen sich erfindungsgemäß erzeugte Kaltbleche durch hervorragende r-Werte und eine dementsprechend ausgezeichnete Tiefziehbarkeit aus.The invention is based on the knowledge that a decisive improvement in the formability of steel strips and steel sheets of the type in question can be achieved not only by a suitable, the finished hot rolling upstream processing of each used precursor, but in particular by the inventive choice of hot rolling. Thus, cold sheets produced according to the invention are distinguished by outstanding r values and, correspondingly, excellent deep drawability.

Dabei lässt sich das erfindungsgemäße Verfahren basierend auf konventionell zusammengesetzten weichen Kohlenstoffstählen oder IF-Stählen durchführen. Dementsprechend sieht eine Ausgestaltung der Erfindung vor, dass eine weiche Stahllegierung verarbeitet wird, die jeweils (in Gew.-%) 0,01 - 0,1 % C, 0,1 - 0,5 % Mn, bis zu 0,03 % P, bis zu 0,03 % S, 0,01 - 0,1 % Al, weniger als 0,005 % Ti, weniger als 0,005 % Nb und bis zu 0,01 % B sowie als Rest Eisen und unvermeidbare Verunreinigungen enthalten kann. Wird ein IF-Stahl verarbeitet, so kann dieser (in Gew.-%) typischerweise jeweils weniger als 0,01 % C, weniger als 0,2 % Mn, weniger als 0,02 % S, weniger als 0,02 % P, weniger als 0,05 % Al, weniger als 0,005 % N, 0,02 - 0,1 % Ti, bis zu 0,05 % Nb und weniger als 0,001 % B enthalten. Selbstverständlich lassen sich die einzelnen Legierungskomponenten dabei innerhalb der durch die Erfindung allgemein vorgegebenen Bereiche so aufeinander abstimmen, dass ein optimales Arbeitsergebnis erzielt wird. So kann es in einzelnen Fällen günstig sein, jeweils nur eine der in den abhängigen Ansprüchen angegebenen Modifikationen der Legierung aufzugreifen, um die durch das jeweilige Element beeinflusste Eigenschaft besonders hervorzuheben bzw. zu unterdrücken, während die anderen Legierungselemente nach wie vor in den weiter gefassten Bereichen variiert werden.In this case, the method according to the invention can be carried out based on conventionally composed soft carbon steels or IF steels. Accordingly, an embodiment of the invention provides that a soft steel alloy is processed, each containing (in wt .-%) 0.01 - 0.1% C, 0.1 - 0.5% Mn, up to 0.03% P, up to 0.03% S, 0.01-0.1% Al, less than 0.005% Ti, less than 0.005% Nb and up to 0.01% B, and the remainder iron and unavoidable impurities may contain. If an IF steel is processed, it may typically contain (in% by weight) less than 0.01% C, less than 0.2% Mn, less than 0.02% S, less than 0.02% P less than 0.05% Al, less than 0.005% N, 0.02-0.1% Ti, up to 0.05% Nb, and less than 0.001% B. Of course, the individual alloy components can be coordinated with one another within the ranges generally specified by the invention in such a way that an optimum work result is achieved. Thus, it may be favorable in individual cases to take up only one of the modifications of the alloy specified in the dependent claims in order to particularly emphasize or suppress the property influenced by the respective element, while the other alloying elements remain in the broader ranges be varied.

Die in geeigneter Weise legierte Stahlschmelze wird zu einem warmwalzbaren Vormaterial, wie Brammen oder Dünnbrammen, vergossen. Diese werden auf eine Vorwärmtemperatur erwärmt, die bevorzugt im Bereich von 1000 °C bis 1300 °C liegt. Anschließend wird das Vormaterial in eine Warmwalzstaffel geleitet, in der es zu Warmband gewalzt wird. Dieses Warmwalzen umfasst ein in mehreren Stufen durchgeführtes Fertigwalzen, dem erforderlichenfalls ein Vorwalzen vorgeschaltet sein kann.The suitably alloyed molten steel is poured into a hot-rolling starting material, such as slabs or thin slabs. These are heated to a preheating temperature, which is preferably in the range of 1000 ° C to 1300 ° C. Subsequently, the starting material is fed into a hot rolling mill, where it is rolled into hot strip. This hot rolling comprises a multi-stage finish rolling, which may be preceded by rough rolling if necessary.

Unabhängig davon, welche der im erfindungsgemäß vorgegebenen Rahmen möglichen Legierungen eingesetzt werden, wird die durch die Erfindung angestrebte Verbesserung jeweils dadurch erreicht, dass in den letzten vier Stufen des Fertigwarmwalzens der verbleibende, über diese vier Stufen zu bewältigende Gesamtumformgrad möglichst hoch ist. Unter dem "Gesamtumformgrad εh4" wird allgemein in diesem Zusammenhang das Verhältnis der Differenz aus der Warmbanddicke de4 beim Einlaufen in das viertletzte Gerüst und der Warmbanddicke de7 beim Verlassen des letzten Gerüstes zur Warmbanddicke de4 beim Einlaufen in das viertletzte Gerüst verstanden (εh4 = (de4-de7) / de4).Regardless of which of the inventively given framework possible alloys are used, the improvement sought by the invention is achieved in each case that in the last four stages of Fertigwarmwalzens the remaining, over these four stages to be handled Gesamtumformgrad as high as possible. In this context, the term "overall degree of deformation ε h4 " generally refers to the ratio of the difference between the hot strip thickness d e4 when entering the fourth-last stand and the hot strip thickness d e7 when leaving the last stand to the hot strip thickness d e4 when entering the fourth-last stand (ε h4 = (d e4 -d e7 ) / d e4 ).

Die Erfindung schreibt vor, dass über die letzten vier Gerüste der Warmwalzstaffel der Gesamtumformgrad mindestens 80 % betragen soll. Bei einer klassischen, sieben Walzgerüste umfassenden Walzstaffel ist gemäß der Erfindung daher über die Gerüste 4, 5, 6 und 7 ein Gesamtumformgrad von mindestens 80 %, bevorzugt 85 % einzustellen, um die gewünschte Steigerung des r-Wertes zu erreichen.The invention requires that over the last four stands of the hot roll stand the Gesamtumformgrad should be at least 80%. In the case of a classic rolling scale comprising seven stands, it is therefore necessary, via the stands 4, 5, 6 and 7, to set a total degree of deformation of at least 80%, preferably 85%, in order to achieve the desired increase in the r value.

Die Aufteilung der einzelnen Dickenabnahmen auf die einzelnen zuletzt vom Warmband durchlaufenen Walzgerüste ist jedoch nicht beliebig, sondern folgt einem exakt abgestuften Plan. So schreibt die Erfindung neben der über die letzten vier Gerüste zu erzielenden Gesamtumformung vor, dass der über die letzten drei Walzgerüste insgesamt zu bewältigende Gesamtumformgrad immer noch mindestens 65 %, bevorzugt 75 %, der über die letzten beiden Gerüste der Walzstaffel mindestens 50 %, bevorzugt 60 % und der über das letzte Gerüst der Staffel erreichte Umformgrad mindestens 25 %, bevorzugt mindestens 30 % oder sogar mindestens 35 %, betragen muss. Überraschend hat sich gezeigt, dass die Auswirkung der erfindungsgemäßen Vorgehensweise umso günstiger ist, je höher die für die letzten vier durchlaufenen Gerüste jeweils verbleibende Gesamtumformung ist.However, the division of the individual thickness decreases on the individual last of the hot strip traversed rolling stands is not arbitrary, but follows a precisely graded plan. Thus, in addition to the total conversion to be achieved over the last four stands, the invention still stipulates that the overall degree of transformation to be handled over the last three rolling stands is still at least 65%, preferably 75%, which is at least 50% above the last two stands of the rolling scale 60% and the degree of deformation reached over the last frame of the squadron must be at least 25%, preferably at least 30% or even at least 35%. Surprisingly, it has been shown that the effect of the procedure according to the invention is all the more favorable, the higher the overall conversion remaining for the last four scaffolds.

Neben dem hohen über die einzelnen Warmwalzgerüste jeweils zu bewältigenden Gesamtumformgrad ist die Temperatur von Bedeutung, bei der das Warmwalzen in den letzten vier durchlaufenen Gerüsten der Warmwalzstaffel durchgeführt wird. Diese soll gemäß der Erfindung so gewählt werden, dass die betreffenden Stiche des Warmwalzens im tiefen Austenit durchgeführt werden. Daher sieht die Erfindung vor, die letzten vier Stiche bei Temperaturen zu walzen, die im Bereich von 950 °C bis 880 °C in enger Nachbarschaft zur Umwandlungstemperatur Ar3 angesiedelt sind. Vorteilhaft sind dabei besonders eng an der Ar3-Temperatur angesiedelte Walztemperaturen, die von 930 °C bis herab zur Ar3-Temperatur reichen. In diesem Fall liegen die jeweiligen Warmwalztemperaturen in einem Bereich, in dem der jeweils verarbeitete Stahl noch sicher austenitisch ist, der gleichzeitig aber auf einem Niveau liegt, welches gewährleistet, dass im für die Effekte der Erfindung günstigen tiefen Austenit gearbeitet wird.In addition to the high overall degree of deformation to be overcome by the individual hot rolling stands, the temperature at which the hot rolling is carried out in the last four continuous stands of the hot rolling stand is of importance. This should be chosen according to the invention so that the relevant passes of the hot rolling are carried out in deep austenite. Therefore, the invention contemplates rolling the last four passes at temperatures ranging from 950 ° C to 880 ° C in close proximity to the Ar 3 transformation temperature. In this case, roller temperatures which are particularly close to the Ar 3 temperature, which range from 930 ° C. down to the Ar 3 temperature, are advantageous. In this case, the respective hot rolling temperatures are within a range in which the steel being processed is still certainly austenitic, but at the same time is at a level which ensures that work is done in the deep austenite favorable for the effects of the invention.

Ein gemäß der Erfindung ebenfalls zu beachtender Betriebsparameter, der von Bedeutung für die Eigenschaften des erhaltenen Produktes ist, ist die Bandendgeschwindigkeit. Diese beträgt mindestens 10 m/s, bei unlegiertem sehr weichen Stahl, bevorzugt jedoch mindestens 15 m/s, um eine Rekristallisation in der Fertigstaffel zwischen den Walzstichen zu vermeiden. Die hohe Walz- bzw. Walzendgeschwindigkeit ist erforderlich, damit es besonders bei sehr rekristallisationsfreudigem Stahl nach den Walzstichen zwischen den einzelnen Walgerüsten zu keiner Rekristallisation in der Fertigstaffel kommt. Auf diese Weise wird ein hoher kumulativer Warmverformungsgrad erreicht, wodurch die Texturgrundlage für die sehr hohen r-Werte am erfindungsgemäß erzeugten Warmband eingestellt wird.An operating parameter also to be considered according to the invention, which is of importance for the properties of the product obtained, is the tape end speed. This is at least 10 m / s, for unalloyed very soft steel, but preferably at least 15 m / s, in order to avoid recrystallization in the finishing scale between the rolling passes. The high rolling or rolling speed is required, so that there is no recrystallization in the finishing scale, especially in very rekristallisationsfreudigem steel after the rolling passes between the individual Walgerüsten. In this way, a high cumulative degree of hot deformation is achieved, whereby the Texture base for the very high r-values on the hot strip produced according to the invention is set.

Soll das Kaltband nach dem Kaltwalzen in einem Durchlaufofen rekristallisierend geglüht werden, so hat es sich im Hinblick auf die angestrebten hohen r-Werte erfindungsgemäß erzeugter Stahlbleche oder -bänder als vorteilhaft erwiesen, wenn die Haspeltemperatur mindestens 700 °C beträgt. Soll dagegen ein für bestimmte Verformungsaufgaben günstiges "Pan-Cake-Gefüge" in dem kaltgewalzten Blech durch eine im Bund unter der Haube erfolgende rekristallisierende Glühung erzeugt werden, so ist es günstig, eine möglichst niedrige, maximal 550 °C betragende Haspeltemperatur zu wählen. "Pan-Cake-Gefüge" zeichnet sich durch ein gestrecktes, verhältnismäßig grobes Korn aus. Das derart beschaffene Gefüge und die damit verbundene Textur ist insbesondere dann günstig, wenn bei der Kaltverformung des Kaltbleches zu einem Bauteil hohe Umformgrade erreicht werden müssen. Eine hohe Haspeltemperatur bewirkt grobe, eine niedrige Haspeltemperatur dagegen feine Karbide und Nitride. Für die Kaltbandrekristallisation sind grundsätzlich wenige grobe Ausscheidungen günstiger als viele feine, da sie beim Rekristallisationsablauf weniger störend wirken. Zur Erzeugung eines Pan-Cake-Gefüges auf Kaltband über die Haubenglühung ist es allerdings erforderlich, dass die Nitridausscheidungen (AlN) am Warmband durch eine tiefe Haspeltemperatur unterdrückt werden, da die AlN-Ausscheidung bei der Kaltbandrekristallisationsglühung während der langsamen Aufheizphase als Störung zur Kornorientierung benötigt wird und sich auf diese Weise noch höhere r-Werte einstellen. Die Glühung des Stahlbands in einer Durchlaufglühe erweist sich dann als besonders wirtschaftlich, wenn eine solche Durchlaufglühe mit einer Schmelztauchveredelungsanlage, insbesondere einer Bandfeuerverzinkungsanlage, gekoppelt ist.If the cold strip is to be recrystallized after cold rolling in a continuous furnace, it has proven to be advantageous in view of the desired high r-values of steel sheets or strips produced according to the invention if the coiling temperature is at least 700 ° C. If, on the other hand, a "pan-cake microstructure" favorable for certain deformation tasks is to be produced in the cold-rolled sheet by a recrystallizing annealing carried out in the bundle under the hood, it is favorable to choose a reel temperature which is as low as possible and which does not exceed 550 ° C. "Pan-cake texture" is characterized by a stretched, relatively coarse grain. The fabric of this nature and the texture associated therewith are particularly favorable if high degrees of deformation must be achieved during the cold forming of the cold sheet into a component. A high reel temperature causes coarse, a low coiler temperature on the other hand fine carbides and nitrides. In principle, a few coarse precipitates are more favorable for cold strip recrystallization than many fine ones, since they have a less disturbing effect on the recrystallization process. To produce a pan-cake microstructure on cold strip via bell annealing, however, it is necessary for the nitride precipitates (AlN) on the hot strip to be suppressed by a deep reel temperature, since the AlN precipitation in the cold strip recrystallization annealing during the slow heating phase requires as a disturbance to the grain orientation and thus get even higher r-values. The annealing of the steel strip in a continuous annealing then proves to be special economically, if such a continuous annealing is coupled with a hot dip finishing plant, in particular a belt fire galvanizing plant.

Zudem ist es möglich, das rekristallisationsgeglühte Band einer elektrolytischen Oberflächenveredelung zu unterziehen.In addition, it is possible to subject the recrystallization annealed strip to an electrolytic surface refinement.

Nachfolgend wird die Erfindung anhand von Ausführungsbeispielen näher erläutert.The invention will be explained in more detail by means of exemplary embodiments.

In der beigefügten Figur sind schematisch eine sieben Walzgerüste 1,2,3,4,5,6,7 umfassende Warmwalzstaffel 8, ein in Förderrichtung F hinter der Warmwalzstaffel 8 angeordneter Rollgang 9 und eine am Ende des Rollgangs 9 angeordnete Haspeleinrichtung 10 dargestellt.In the attached figure schematically a seven rolling stands 1,2,3,4,5,6,7 comprehensive hot rolling stand 8, arranged in the conveying direction F behind the hot rolling stand 8 roller table 9 and arranged at the end of the roller table 9 reeling device 10 are shown.

In der Warmwalzstaffel sind Brammen zu Warmband W warmgewalzt worden, die aus einem 0,025 Gew.-% C, 0,15 Gew.-% Mn, jeweils weniger als 0,01 Gew.-% P und S, 0,04 Gew.-% Al, 0,003 Gew.-% N, Rest Eisen und unvermeidbare Verunreinigungen enthaltenden Weichstahl abgegossen worden sind.In the hot rolling scale slabs were hot rolled to hot strip W consisting of a 0.025 wt .-% C, 0.15 wt .-% Mn, each less than 0.01 wt .-% P and S, 0.04 wt. % Al, 0.003 wt .-% N, balance iron and unavoidable impurities containing mild steel have been poured.

In einem ersten Versuch sind die Brammen auf eine Vorwärmtemperatur von 1250 °C durchgewärmt worden, bevor sie in der Warmwalzstaffel 8 zu Warmband W bei einer Warmwalzendtemperatur von 900 °C fertig warmgewalzt worden sind. Das erhaltene Warmband ist dann bei einer Haspeltemperatur von 520 °C gehaspelt und bei einem Kaltwalzgrad von 75 % zu Kaltband gewalzt worden. Nach dem Kaltwalzen ist das Kaltband im Bund im Haubenglühofen bei 700 °C rekristallisierend geglüht worden.In a first attempt, the slabs were thoroughly warmed to a preheat temperature of 1250 ° C before being finish hot rolled in hot roll 8 to hot strip W at a hot rolling end temperature of 900 ° C. The resulting hot strip was then coiled at a reel temperature of 520 ° C and rolled at a cold rolling degree of 75% to cold strip. After this Cold rolling, the cold strip in the coil in the annealing furnace at 700 ° C was annealed recrystallizing.

In einem zweiten Versuch sind die Brammen auf eine Vorwärmtemperatur von 1100 °C erwärmt, in der Warmwalzstaffel 8 bei einer Warmwalzendtemperatur von 900 °C zu Warmband W warmgewalzt worden. Das Warmband W ist bei einer 720 °C betragenden Temperatur gehaspelt, mit einem Kaltwalzgrad von 75 % kaltgewalzt und bei 800 °C in einem kontinuierlich durchlaufenen Durchlaufofen rekristallisierend geglüht worden.In a second experiment, the slabs were heated to a preheating temperature of 1100 ° C, hot rolled in the hot rolling stand 8 at a hot rolling end temperature of 900 ° C to hot strip W. The hot strip W has been coiled at a temperature of 720 ° C., cold-rolled with a cold rolling degree of 75% and recrystallized at 800 ° C. in a continuously passed continuous furnace.

Im Zuge des Warmwalzens in der Warmwalzstaffel 8 sind die über die einzelnen jeweils verbleibenden Walzgerüste 1,2,3,4,5,6,7 zu erzielenden Umformgrade εh1 bis εh7 jeweils so eingestellt worden, dass die für die letzten vier Walzgerüste 4,5,6,7 der Walzstaffel verbleibenden Restumformungen deutlich höher lagen als bei konventioneller Fertigung. Dabei sind zum Nachweis der sich bei erfindungsgemäßer Einstellung einer möglichst hohen für die letzten vier Walzgerüste 4,5,6,7 verbleibenden Restumformung einstellenden Effekte jeweils drei erfindungemäße Warmwalzvarianten Ea, Eb und Ec einem konventionell durchgeführten Warmwalzversuch K gegenüber gestellt worden. In der nachfolgenden Tabelle sind die betreffenden für die Umformung über die letzten vier Walzgerüste 4,5,6,7 jeweils verbleibenden Umformgrade εh4, εh5, εh6, εh7 für die erfindungsgemäß durchgeführten Versuche Ea,Eb,Ec und den konventionell durchgeführten Versuch K eingetragen. Gesamtumformgrad Restliche zu absolvierende Walzgerüste Versuch Ea Versuch Eb Versuch Ec Versuch K εh4 4,5,6,7 ca. 80 % ca. 85 % > 85 % ca. 75 % εh5 5,6,7 ca. 65 % ca. 75 % > 75 % ca. 55 % εh6 6,7 ca. 50 % ca. 60 % > 60 % ca. 35 % εh7 7 ca. 25 % ca. 30 % > 35 % ca. 15 % In the course of hot rolling in the hot rolling stand 8, the forming degrees ε h1 to ε h7 to be achieved over the individual respective rolling stands 1, 2, 3, 4, 5, 6, 7 are each set such that the for the last four rolling stands 4 , 5,6,7 of the rolling scale remaining remainders were significantly higher than in conventional production. In this case, three erfindungemäße hot rolling variants Ea, Eb and Ec have been compared to a conventionally performed hot rolling K compared to setting the highest possible for the last four rolling stands 4,5,6,7 remaining forming effects according to the invention. In the following table, the respective deformation degrees ε h4 , ε h5 , ε h6 , ε h7 remaining for the conversion over the last four rolling stands 4, 5, 7, 7 are for the experiments Ea, Eb, Ec and the conventionally carried out according to the invention Attempt K registered. total degree Remaining rolling stands to be completed Try Ea Try Eb Try ec Try K ε h4 4,5,6,7 about 80% about 85% > 85% about 75% ε h5 5,6,7 about 65% about 75% > 75% about 55% ε h6 6.7 approx. 50 % about 60% > 60% about 35% ε h7 7 about 25% about 30% > 35% about 15%

In Diag. 1 sind die für die konventionell erzeugten Warmbänder ermittelten r-Werte r0° (r-Wert in Walzrichtung), r45° (r-Wert diagonal zur Walzrichtung), r90° (r-Wert quer zur Walzrichtung), rm (rm = (r0°+2r45+r90°)/4) den r0°, r45°, r90°, rm°-Werten gegenübergestellt, die bei den erfindungsgemäß erzeugten Kaltblechen festgestellt werden konnten. Es zeigt sich eine deutliche Überlegenheit der erfindungsgemäß erzeugten Bleche.In Diag. 1 are the r values determined for the conventionally produced hot strips r 0 ° (r value in the rolling direction), r 45 ° (r value diagonal to the rolling direction), r 90 ° (r value transversely to the rolling direction), r m ( r m = (r 0 ° + 2r 45 + r 90 ° ) / 4) compared with the r 0 ° , r 45 ° , r 90 ° , r m ° values that could be found in the cold plates produced according to the invention. It shows a clear superiority of the sheets produced according to the invention.

Ein weiterer Beleg für die im Hinblick auf die gewünscht gute Kaltverformbarkeit, insbesondere die Tiefziehbarkeit, überlegenen Eigenschaften erfindungsgemäß erzeugter Stahlbleche und -bänder liefert Diag. 2, in dem das Ergebnis der Texturanalyse der erfindungsgemäß erzeugten Bleche der Texturanalyse der konventionell hergestellten Bleche gegenübergestellt ist. Aufgetragen ist die Belegungsdichte entlang bestimmter "Fasern", auf denen die wichtigsten Kornorientierungen liegen. Insgesamt sind starke Belegungen auf der γ-Faser bei den Orientierungen <111>|| Blechnormale, besonders bei (111) [110], zu erkennen. Diese Texturkomponenten sind für hohe r-Werte erwünscht. Dementsprechend lassen sich die höheren r-Werte der erfindungsgemäß erzeugten Bleche gegenüber den konventionell erzeugten Blechen auf eine stärkere Belegung zurückführen. Die Texturergebnisse erklären damit die erzielten r-Werte. Darüber hinaus wurde aufgezeigt, dass die für einen kontigeglühten Al-beruhigten Tiefziehstahl sehr hohen r-Werte von ca. 2,0 am erfindungsgemäß erzeugten Kaltband mit einer Verschärfung der <111>-Glühstruktur im Zusammenhang stehen. Auch hier weisen die erfindungsgemäß hergestellten Bleche deutlich bessere Eigenschaften auf als die konventionell hergestellten Bleche.Another proof of the desired good cold workability, especially the deep drawability, superior properties according to the invention produced steel sheets and strips provides Diag. 2, in which the result of the texture analysis of the sheets produced according to the invention is compared with the texture analysis of the conventionally produced sheets. Plotted is the occupation density along certain "fibers", on which the most important grain orientations lie. Overall, strong occupancies on the gamma fiber are at the orientations <111> || Standard forks, especially at (111) [110]. These texture components are desirable for high r values. Accordingly, the higher r-values of the sheets produced according to the invention can be more heavily used compared to the conventionally produced sheets traced. The texture results thus explain the r-values achieved. In addition, it was shown that the very high r values of about 2.0 for the cold-rolled strip calendered according to the invention for a continuous-flow-hardened deep-drawing steel are associated with a worsening of the <111> glass structure. Again, the sheets according to the invention have significantly better properties than the conventionally produced sheets.

Schließlich ist in Diag. 3 für die im Haubenglühofen und die im Durchlaufglühofen rekristallisierend geglühten, erfindungsgemäß erzeugten Bleche der rm-Wert über den im Zuge des Warmwalzens erreichten Gesamtumformgrad aufgetragen, um den Einfluss der Art der Rekristallisationsglühung und die Höhe der Umformung über den akkumulierten Austenitverformungsgrad des Warmwalzens auf den rm-Wert des erhaltenen Kaltbandes zu demonstrieren. Es zeigt sich, dass hohe Umformgrade zu einer deutlichen Steigerung des rm-Wertes führen. Gleichzeitig zeigt sich, dass die haubengeglühten Bleche aufgrund des sich bei dieser Art der Glühung einstellenden Pan-Cake-Gefüges gegenüber den im Durchlauf geglühten Blechen weiter gesteigerte r-Werte aufweisen.Finally, in Diag. 3 for the annealing annealing furnace annealed in the continuous annealing annealed, inventively produced sheets of r m value over the achieved during hot rolling Gesamtumformgrad to the influence of the type of recrystallization and the amount of deformation on the accumulated Austenitverformungsgrad of hot rolling on the r m value of the resulting cold strip to demonstrate. It turns out that high degrees of deformation lead to a significant increase in the r m value. At the same time it can be seen that the hood-annealed sheets have further increased r-values as compared to the pan-annealed sheets in the course of annealing in this type of annealing.

Claims (25)

  1. Process for manufacturing cold-rolled steel strip or steel sheet, comprising the following steps:
    - casting a steel melt containing (in wt.%)
    C: ≤ 0.1%
    Mn: ≤ 0.5%
    P: < 0.03%
    S: < 0.03%
    Al: ≤ 0.1%
    N: < 0.01%
    Ti < 0.1%
    Nb: < 0.05%
    B: ≤ 0.01%
    the remainder being iron and the usual impurities to an input stock, such as slabs or thin slabs,
    - heating the input stock to a pre-heat temperature of at least 1,000°C,
    - hot-rolling the input stock in a finish hot-rolling line comprising at least four roll stands to a hot-rolled strip, wherein
    - the total strain εh4 obtained over the last four roll stands passed through leaving the hot-rolling line, is at least 80%
    - the total strain εh3 obtained over the last three roll stands passed through leaving the hot-rolling line is at least 65%,
    - the total strain εh2 obtained over the last two roll stands passed through leaving the hot-rolling line is at least 50%,
    - the total strain εh1 obtained over the last roll stand passed through leaving the hot-rolling line is at least 25%,
    - hot-rolling in the last four roll stands passed through leaving the hot-rolling line takes place at a rolling temperature of 880° - 950°C,
    - hot-rolling is terminated at a final hot-rolling temperature, which is ≥ the Ar3 temperature, and
    - the final strip speed of the finished hot-rolled strip when leaving the hot-rolling line is at least 10 metres per second
    - coiling the hot-rolled strip,
    - cold-rolling the hot-rolled strip to cold-rolled strip,
    - re-crystallization-annealing of the cold-rolled strip.
  2. Process according to Claim 1, characterized in that the steel melt contains at least 0.01 wt.% C.
  3. Process according to Claim 1, characterized in that the steel melt contains less than 0.01 wt.% C.
  4. Process according to any one of the preceding claims, characterized in that the steel melt contains at least 0.1 wt.% Mn.
  5. Process according to any one of the preceding claims, characterized in that the steel melt contains less than 0.2 wt.% Mn.
  6. Process according to any one of the preceding claims, characterized in that the steel melt contains less than 0.02 wt.% P and/or less than 0.02 wt.% S.
  7. Process according to any one of the preceding claims, characterized in that the steel melt contains less than 0.05 wt.% Al.
  8. Process according to any one of the preceding claims, characterized in that the steel melt contains less than 0.005 wt.% N.
  9. Process according to any one of the preceding claims, characterized in that the steel melt contains less than 0.005 wt.% Ti.
  10. Process according to any one of Claims 1 to 8, characterized in that the steel melt contains at least 0.02 wt.% Ti.
  11. Process according to any one of the preceding claims, characterized in that the steel melt contains less than 0.005 wt.% Nb.
  12. Process according to any one of the preceding claims, characterized in that the steel melt contains less than 0.001 wt.% B.
  13. Process according to any one of the preceding claims, characterized in that hot-rolling takes place in the last four roll stands passed through leaving the hot-rolling line at a rolling temperature which is at least the same as the Ar3 temperature and at most equivalent to 930°C.
  14. Process according to any one of the preceding claims, characterized in that the total strain εh4 obtained over the last four roll stands passed through leaving the hot-rolling line is at least 85%.
  15. Process according to any one of the preceding claims, characterized in that the total strain εh3 obtained over the last three roll stands passed through leaving the hot-rolling line is at least 75%.
  16. Process according to any one of the preceding claims, characterized in that the total strain εh2 obtained over the last two roll stands passed through leaving the hot-rolling line is at least 60%.
  17. Process according to any one of the preceding claims, characterized in that the total strain εh1 obtained over the last roll stand passed through leaving the hot-rolling line is at least 35%.
  18. Process according to any one of the preceding claims, characterized in that the final strip terminal speed of the finished hot-strip when leaving the hot-rolling line is at least 15 metres per second.
  19. Process according to any one of the preceding claims, characterized in that the coiling temperature is at least 700°C.
  20. Process according to any one of Claims 1 to 18, characterized in that the coiling temperature is less than 550°C.
  21. Process according to any one of the preceding claims, characterized in that the cold-rolling strain obtained by the cold-rolling is at least 40%.
  22. Process according to any one of the preceding claims, characterized in that the re-crystallization-annealing takes place in the tunnel furnace.
  23. Process according to Claim 22, characterized in that the re-crystallization-annealed strip is subsequently hot dip surface finished.
  24. Process according to any one of Claims 1 to 21, characterized in that the re-crystallization-annealing takes place in the coil in a batch furnace.
  25. Process according to any one of Claims 1 to 22 or 24, characterized in that electrolytic surface finishing takes place after the re-crystallization-annealing.
EP03018184A 2002-10-15 2003-08-09 Process for manufacturing of cold-rolled steel strips or sheets having excellent formability Expired - Lifetime EP1411140B1 (en)

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DE10247998 2002-10-15
DE10247998A DE10247998B4 (en) 2002-10-15 2002-10-15 Process for producing a particularly well deformable cold-rolled steel strip or sheet

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EP1411140B1 true EP1411140B1 (en) 2006-10-25

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CN104831207A (en) * 2015-04-16 2015-08-12 河北钢铁股份有限公司邯郸分公司 Thin gauge 600MPa grade hot galvanized plate production method
US11453923B2 (en) 2016-09-20 2022-09-27 Thyssenkrupp Steel Europe Ag Method for manufacturing flat steel products and flat steel product
CN111996463B (en) * 2020-07-31 2021-12-14 马鞍山钢铁股份有限公司 Low-cost low-alloy steel coil and manufacturing method thereof

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US3772091A (en) * 1969-08-27 1973-11-13 Bethlehem Steel Corp Very thin steel sheet and method of producing same
US3849209A (en) * 1972-02-01 1974-11-19 Nippon Steel Corp Manufacturing method of high tension, high toughness steel
JPS62192539A (en) * 1986-02-18 1987-08-24 Nippon Steel Corp Manufacture of high gamma value hot rolled steel plate
JP3273383B2 (en) * 1993-06-30 2002-04-08 新日本製鐵株式会社 Cold rolled steel sheet excellent in deep drawability and method for producing the same
EP0662523B1 (en) * 1993-07-28 1999-04-28 Nippon Steel Corporation Steel sheet of high stress-corrosion-cracking resistance for cans and method of manufacturing the same
DE19725434C2 (en) * 1997-06-16 1999-08-19 Schloemann Siemag Ag Process for rolling hot wide strip in a CSP plant
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DK1411140T3 (en) 2007-02-26
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DE10247998B4 (en) 2004-07-15
PL361945A1 (en) 2004-04-19

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