EP1399598A1 - Method for producing high-strength cold-formed steel products from a hot rolled strip, said products exhibiting good malleability - Google Patents

Method for producing high-strength cold-formed steel products from a hot rolled strip, said products exhibiting good malleability

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Publication number
EP1399598A1
EP1399598A1 EP02738172A EP02738172A EP1399598A1 EP 1399598 A1 EP1399598 A1 EP 1399598A1 EP 02738172 A EP02738172 A EP 02738172A EP 02738172 A EP02738172 A EP 02738172A EP 1399598 A1 EP1399598 A1 EP 1399598A1
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EP
European Patent Office
Prior art keywords
cold
hot
temperature
strip
product
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.)
Granted
Application number
EP02738172A
Other languages
German (de)
French (fr)
Other versions
EP1399598B1 (en
EP1399598B2 (en
Inventor
Thomas Heller
Bernhard Engl
Günter STICH
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.)
ThyssenKrupp Steel Europe AG
Original Assignee
ThyssenKrupp Stahl AG
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Classifications

    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226Hot rolling
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0236Cold rolling
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0273Final recrystallisation annealing
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0278Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular surface treatment

Definitions

  • the invention relates to a method for producing a high-strength, cold-formed steel product from a hot strip with good formability.
  • This formability can be according to the
  • the hot strip treated in this way is suitable for cold rolling, in which a degree of deformation of at least 30% is achieved.
  • a cold-formed sheet product of high strength, further improved yield strength ratio and good hardening behavior can be produced.
  • this object is achieved by a method for producing a high-strength, cold-formed product from a hot strip with good ductility, in which a steel with (in% by weight) 0.01-0.25% C, 0.01-1.50% Si, 0.50-2.00% Mn, ⁇ 0.08% P, ⁇ 0.01% S, 0.001
  • Microalloying elements remain essentially dissolved, hot-rolled to hot strip, in which the hot strip is coiled at a coiling temperature of less than 600 ° C., in which the hot strip is then cold-formed into a product with a degree of cold deformation of at least 2% and at most corresponding to the limit deformation, and in which the product produced by cold working at temperatures and times below that for the complete
  • the temperatures and times required for recrystallization are annealed.
  • the invention is based on the surprising finding that the strength-increasing properties of the microalloying elements contained in steels according to the invention are activated when the hot strip is produced according to the invention by annealing the product obtained from the hot strip after coiling by cold deformation, and cold-formed products with particularly high strengths and one Allow good forming properties to be produced even in the cold-formed state, without requiring a technically complex remuneration.
  • the method according to the invention is particularly suitable for producing components whose dimensional and dimensional stability are just as demanding as their strength in use.
  • a typical example of such an application are frames for screens which have to hold the shadow mask in a tube of television sets or computer monitors due to the heat load during their assembly and their operation under uniform tension in a defined level.
  • the required high strength is then given to the cold-formed component in the course of the heat treatment carried out according to the invention after the cold-forming, so that the result is an exactly shaped, high-strength component with a high yield strength. Additional compensation, which can lead to warpage of the component and impairment of the surface, is then no longer necessary.
  • the steel alloy used according to the invention comprises steel compositions from which, depending on the particular composition and the production conditions, dual-phase steels, bainitic steels or complex-phase steels can be produced.
  • the aim is to have steels with a fine-grained, multi-phase structure, in which bainite, ferrite, martensite and residual austenite are contained, depending on the respective type of steel.
  • this starting material After a starting material has been produced from a steel with a composition used according to the invention, this starting material is hot-rolled into hot strip.
  • the hot rolling starting temperature is chosen so that the micro-alloying elements remain largely dissolved in the steel so that they are available for the effects brought about in the last step of the method according to the invention.
  • the initial rolling temperature should be at least 1050 ° C for this purpose.
  • thin slab or thin strip casting processes are particularly suitable for the production of the primary material, with which it is possible with particular reliability due to the fact that there is no need to reheat the primary material or a solution of the microalloying elements and on the other hand the cooling rates of the strand can be high. the To keep micro-alloy elements largely dissolved until the start of the hot rolling process.
  • the hot rolling end temperature should preferably be in the austenite region, that is to say above the Ar 3 temperature, in order to maintain the fine-grained, multi-phase structure sought after according to the invention.
  • composition of the structure of the hot strip obtained is determined by the chemical properties, the heating, rolling and cooling conditions and the reel temperatures. It has been shown that the effect of increasing the strength and formability achieved with dual-phase steels achieved according to the invention is particularly reliable when the reel temperature is at most 300 ° C. In steels with a predominantly bainitic structure, this effect is reliably achieved at reel temperatures that are 350 ° C to 450 ° C. Complex phase steels should preferably be coiled at temperatures from 450 ° C to 550 ° C.
  • steels of the type used according to the invention have a high strength of at least 550 N / mm 2 .
  • the steels harden very strongly.
  • the elongation decreases significantly, so that a product that is high-strength but difficult to deform is obtained.
  • cold-formed components of this type have only a small forming reserve and a correspondingly reduced energy absorption capacity. As such, for example, they are only suitable to a limited extent for the production of components which are used as bumpers in crash endangered areas of an automobile.
  • the yield strength of the steel used is further increased, on the one hand, by the fact that the product obtained is cold annealed.
  • the annealing increases the elongation values almost to the level at which the ductility of the hot strip was before the cold working.
  • the products that were originally difficult to form immediately after cold forming can be made into components that are not only high-strength but also have a high formability due to their good elongation properties. As such, they are suitable for those applications for which they were not suitable before the annealing treatment.
  • Typical annealing temperatures during the annealing following the cold deformation are in the range from 450 ° C. to 700 ° C., preferably in the range from 550 ° C. to 650 ° C.
  • the annealing time and annealing temperature are interchangeable to a limited extent. This means that at high temperatures only short holding times are required and vice versa. Accordingly, the heat treatment can be carried out as a separately carried out treatment step in a hood or in a continuous annealing. Annealing treatment in a conventional manner under conditions that would lead to complete recrystallization would nullify the effect achieved by the invention.
  • This step can be, for example, a zinc coating or another method for coating or passivating the surface of the cold-formed product, which is carried out at the range of the temperatures provided for the annealing treatment.
  • the degrees of deformation achieved in the course of cold deformation amount to at least 2% up to the change in limit shape, the effects achieved by the procedure according to the invention having an effect particularly when the degree of cold deformation is 5% to 20%, in particular 5% to 10%.
  • Cold forming can be carried out, for example, as roll profiling, drawing, pressing or hydroforming. Cold rolling with relatively low degrees of deformation is also suitable for this.
  • At least one of the elements Ti, Nb and / or V is used as the microalloying element in steel according to the invention.
  • these elements can be added combined in amounts sufficient to trigger the excretion process effected at the end of the method according to the invention.
  • it is particularly preferred to use Ti which is distinguished by a particularly favorable excretion behavior.
  • Ti is used as the only microalloying element according to a preferred embodiment of the invention, its content should be at least 3.4 times the content of N in order to have a sufficient solution potential of the Ensure microalloying element.
  • the Ti content of the steel for this purpose is preferably in the range 0.07 to 0.15% by weight, while the nitrogen content is preferably less than 0.007% by weight. With Ti contents of this size, the formation of fine deposits with a hardening effect is optimally supported.
  • the Al content is preferably in the range from 0.015 to 0.08% by weight. or 0.5 to 1.5% by weight.
  • a steel composed according to Table 1 was cast on a continuous casting plant to a pre-slab, which was then hot-rolled as a starting material at a temperature of 1125 ° C. in a hot strip mill to a hot strip.
  • the hot rolling end temperature was 925 ° C.
  • the reel temperature was 475 ° C. After coiling, the hot strip is pickled and delivered to a cold rolling mill in the pickled state.
  • the plates of group G1 have not been subjected to any annealing following the cold deformation, while the plates of group G2 at 500 ° C, the plates of group G3 at 550 ° C, the plates of group G4 at 600 ° C and the plates Group G5 were annealed at 650 ° C in a bell-type furnace for one hour each and then cooled in air.
  • the strength values obtained in each case are markedly improved compared to the only cold-formed and not heat-treated sheets Gl.l-G1.5.
  • a uniform expansion Agi is achieved by the heat treatment carried out after the cold deformation, which corresponds approximately to the uniform expansion Agi of the non-cold-formed and non-heat-treated sheet Gll.O. Accordingly, the cold-formed and subsequently heat-treated steels produced according to the invention have particularly good formability and an equally good energy absorption capacity.
  • Table 3 shows a second example of a steel composition used according to the invention.
  • a correspondingly alloyed steel was melted and cast into slabs.
  • the slabs are then reheated to a temperature of more than 1150 ° C and with a hot rolling temperature of at least 850 ° C has been hot rolled.
  • T2.1 for one with a degree of cold deformation of 10 % only cold-rolled strip sample T2.2 and for a strip sample T2.3 cold-rolled in the manner according to the invention with a degree of cold deformation of 10%, then annealed for 30 minutes at 580 ° C. and then cooled in air
  • the mechanical properties R p o, 2 , R m , Re / R m , A 5 , A so or A 80 have been determined.
  • the determined values of the mechanical properties are given in Table 4.
  • the steel composed according to the alloy specified in Table 5 was also melted and cast into slabs.
  • these slabs were reheated to a temperature of more than 1150 ° C., with a hot rolling temperature of at least 850 ° C. and at a temperature of less than 600 ° C. Then six tape samples T3.0 to T3.5 were then taken.
  • the strip sample T3.2 clearly shows that high-strength cold-formed sheet products can be obtained with the procedure according to the invention, which, as a comparison of the ductility values shows, are superior in their formability to the undeformed strip sample T3.0.
  • the procedure according to the invention which, as a comparison of the ductility values shows, are superior in their formability to the undeformed strip sample T3.0.
  • Another advantageous application of the method according to the invention consists in the production of galvanized side impact beams or other crash-relevant components for vehicle bodies.
  • the respective component is cold formed from hot strip produced according to the invention, for example by a deep-drawing operation.
  • the cold-formed component is then subjected to piece galvanizing at temperatures in the range of 470 ° C.
  • the component is also kept at a temperature level at which the increase in ductility and strength achieved according to the invention occurs.
  • the side impact beam obtained in this way has a particularly high energy absorption capacity due to its good elasticity and high strength, by means of which it converts a large part of the kinetic energy released in the event of a collision with another vehicle into deformation energy and that required for the survival of the occupants Can secure space.

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

Abstract

The invention relates to a method for producing a high-strength cold-formed product from a hot-rolled strip, said product exhibiting good malleability. According to said method, a steel comprising (in wt.%): C: 0.01 0.25 %, Si: 0.01 1.50 %, Mn: 0.50 2.00 %, P: <= 0.08 %, S: <= 0.01 %, Al: 0.001 1.50 %, Cr: <= 0.60 %, Mo: <= 0.60 %, N: < 0.02 %, at least one micro-alloy element from the group Ti: <= 0.20 %, Nb: <= 0.06 %, V: <= 0.15 %, the remainder being iron and the usual impurities is cast to form an input stock such as slabs, thin slabs or a cast strip. Starting from an initial hot-roll temperature, at which the micro-alloy elements remain essentially dissolved, the input stock is hot-rolled to form a hot-rolled strip. Said strip is firstly wound at a winding temperature of less than 600 DEG C and then cold formed into a product at a cold formation degree which is not less than 2 % and not greater than the deformation limit. The cold-formed product is annealed at a temperature and for a period which are less those required for complete recrystallization. The inventive method enables a cold formed product to be produced, said product exhibiting high strength, malleability and plasticity in the cold formed state.

Description

Verfahren zum Herstellen von hochfesten, aus einem Warmband kaltverformten Stahlprodukten mit guter Process for the production of high-strength, cold-formed steel products from a hot strip with good
Dehnbarkeitductility
Die Erfindung betrifft ein Verfahren zum Herstellen eines hochfesten, aus einem Warmband kaltverformten Stahlprodukts mit guter Umformbarkeit .The invention relates to a method for producing a high-strength, cold-formed steel product from a hot strip with good formability.
Ein Verfahren zum Herstellen von eine hohe Festigkeit aufweisendem Warmband ist aus der DE 197 10 125 AI bekannt. Gemäß dem bekannten Verfahren wird ein (in Gew.-%) 0,1 - 0,2 % C, 0,3 bis 0,6 % Si, 1,5 bis 2,0 % Mn, ≤ 0,08 % P, 0,3 bis 0,8 % Cr, < 0,4 % Mo, < 0,2 % Ti,A method for producing high-strength hot strip is known from DE 197 10 125 AI. According to the known method, a (in% by weight) 0.1-0.2% C, 0.3-0.6% Si, 1.5-2.0% Mn, ≤ 0.08% P, 0.3 to 0.8% Cr, <0.4% Mo, <0.2% Ti,
< 0,08 % Nb und als Rest Eisen sowie unvermeidbare Verunreinigungen enthaltender Complexphasenstahl erschmolzen, zu Brammen abgegossen und anschließend zu Warmband ausgewalzt, wobei die Warmwalzendtemperatur oberhalb von 800 °C liegt. Anschließend wird das erhaltene Warmband bei einer Abkühlgeschwindigkeit von mindestens 30 °C/s abgekühlt und dann bei einer Haspeltemperatur von höchstens 600 °C gehaspelt. Bei so erhaltenem Warmband beträgt die Festigkeit aufgrund der relativ niedrigen Haspeltemperatur mindestens 900 MPa. Darüber hinaus besitzt das nach dem bekannten Verfahren erzeugte Warmband eine gute Kaltumformbarkeit .<0.08% Nb and the rest iron and complex phase steel containing unavoidable impurities were melted, poured into slabs and then rolled out into hot strip, the hot rolling end temperature being above 800 ° C. The hot strip obtained is then cooled at a cooling rate of at least 30 ° C./s and then coiled at a coiling temperature of at most 600 ° C. With hot strip obtained in this way, the strength is at least 900 MPa due to the relatively low coiling temperature. In addition, the hot strip produced by the known method has good cold formability.
Diese Umformbarkeit kann gemäß dem aus derThis formability can be according to the
DE 197 10 125 AI bekannten Verfahren dadurch noch gesteigert werden, dass das Warmband nach dem Haspeln einer Glühung im Temperaturbereich von 500 °C bis 850 °C unterzogen wird. Durch diese Glühung wird ein Werkstoffzustand erreicht, der Vorteile für Bauteile bietet, die insgesamt noch eine hohe Festigkeit, vor allem Streckgrenze, bei guter Umformbarkeit besitzen müssen. Durch die Wahl höherer Glühtemperaturen können dabei besonders hohe Festigkeiten bei außerordentlich niedrigen Streckgrenzenverhältnissen oder gleichbedeutend hoher Verfestigung bei guten Dehnungswerten erreicht werden.DE 197 10 125 AI known methods can be further increased in that the hot strip after coiling subjected to annealing in the temperature range from 500 ° C to 850 ° C. This annealing achieves a material condition that offers advantages for components that, overall, must still have high strength, especially the yield strength, and good formability. By choosing higher annealing temperatures, particularly high strengths can be achieved with exceptionally low yield strength ratios or the same amount of hardening with good elongation values.
Gemäß der DE 197 10 125 AI eignet sich das derart glühbehandelte Warmband zum Kaltwalzen, bei dem ein Umformgrad von mindestens 30 % erreicht wird. Indem das derart kaltverformte Band anschließend bei Temperaturen von 700 °C bis 900 °C rekristallisierend durchlaufgeglüht wird, kann ein kaltverformtes Blechprodukt von hoher Festigkeit, weiter verbessertem Streckgrenzenverhältnis und gutem Verfestigungsverhalten erzeugt werden.According to DE 197 10 125 AI, the hot strip treated in this way is suitable for cold rolling, in which a degree of deformation of at least 30% is achieved. By subsequently annealing the cold-formed strip in such a way that it recrystallises at temperatures of 700 ° C. to 900 ° C., a cold-formed sheet product of high strength, further improved yield strength ratio and good hardening behavior can be produced.
Allerdings zeigt sich, dass das Dehnungsverhalten der gemäß den bekannten Verfahren durch Kaltverformung erzeugten Produkte für viele Anwendungsfälle nicht ausreicht. So ist es beispielsweise schwer, mit aus einem solchen Stahl hergestellten Bauteilen, die zum Schutz der Insassen eines Fahrzeugs im Fall eines Unfalls eingesetzt werden sollen, die an derartige Teile hinsichtlich der Festigkeit einerseits und des Energieaufnahmevermögens andererseits gestellten Anforderungen zu erfüllen. Die nach dem bekannten Verfahren erzeugten Bauteile besitzen nach der Kaltverformung auch dann nicht die notwendige Verformbarkeit. Wenn sie nach der Kaltverformung einer rekristallisierenden Glühung unterzogen werden, nimmt zwar die Umformbarkeit zu, die Festigkeit ist dann allerdings nicht mehr ausreichend.However, it has been shown that the elongation behavior of the products produced by cold working in accordance with the known processes is not sufficient for many applications. For example, it is difficult with components made from such steel, which are to be used to protect the occupants of a vehicle in the event of an accident, to meet the requirements imposed on such parts with regard to strength on the one hand and energy absorption capacity on the other. The components produced by the known method do not have the necessary deformability even after the cold forming. If they undergo recrystallizing annealing after cold working, increases Although the formability increases, the strength is then no longer sufficient.
Die Aufgabe der Erfindung bestand darin, ein Verfahren zum Herstellen eines kaltverformten Produkts zu schaffen, das bei erhöhter Festigkeit im kaltverformten Zustand eine hohe Dehnbarkeit und eine dementsprechend gute Umformbarkeit besitzt.The object of the invention was to provide a method for producing a cold-formed product which, with increased strength in the cold-formed state, has high ductility and, accordingly, good formability.
Ausgehend von dem voranstehend erläuterten Stand der Technik wird diese Aufgabe durch ein Verfahren zum Herstellen eines hochfesten, aus einem Warmband kaltverformten Produkts mit guter Dehnbarkeit gelöst, bei dem ein Stahl mit (in Gewichts-%) 0,01 - 0,25 % C, 0,01 - 1,50 % Si, 0,50 - 2,00 % Mn, < 0,08 % P, < 0,01 % S, 0,001Starting from the prior art explained above, this object is achieved by a method for producing a high-strength, cold-formed product from a hot strip with good ductility, in which a steel with (in% by weight) 0.01-0.25% C, 0.01-1.50% Si, 0.50-2.00% Mn, <0.08% P, <0.01% S, 0.001
- 1,50 % AI, < 0,60 % Cr, < 0,60 % Mo, < 0,02 % Mo, sowie mindestens einem Mikrolegierungselement aus der Gruppe Ti, Nb, V, wobei der Gehalt an Ti < 0,20 %, der Gehalt an Nb < 0,06 % und der Gehalt an V < 0,15 % ist, Rest Eisen und übliche Verunreinigungen, zu einem Vormaterial, wie Brammen, Dünnbrammen oder gegossenes Band, vergossen wird, bei dem das Vormaterial ausgehend von einer Warmwalzanfangstemperatur, bei der die- 1.50% Al, <0.60% Cr, <0.60% Mo, <0.02% Mo, and at least one microalloying element from the group Ti, Nb, V, the content of Ti <0.20 %, the content of Nb <0.06% and the content of V <0.15%, balance iron and usual impurities, is cast into a raw material, such as slabs, thin slabs or cast strip, in which the raw material starts from a hot rolling starting temperature at which the
Mikrolegierungselemente im wesentlichen gelöst bleiben, zu Warmband warmgewalzt wird, bei dem das Warmband bei einer weniger als 600 °C betragenden Haspeltemperatur gehaspelt wird, bei dem das Warmband anschließend bei einem mindestens 2 % betragenden und höchstens der Grenzformänderung entsprechenden Kaltverformungsgrad zu einem Produkt kaltverformt wird, und bei dem das durch Kaltverformung erzeugte Produkt bei Temperaturen und Zeiten, die unterhalb der zur vollständigen Rekristallisation erforderlichen Temperaturen und Zeiten liegen, geglüht wird.Microalloying elements remain essentially dissolved, hot-rolled to hot strip, in which the hot strip is coiled at a coiling temperature of less than 600 ° C., in which the hot strip is then cold-formed into a product with a degree of cold deformation of at least 2% and at most corresponding to the limit deformation, and in which the product produced by cold working at temperatures and times below that for the complete The temperatures and times required for recrystallization are annealed.
Die Erfindung basiert auf der überraschenden Feststellung, dass sich die festigkeitssteigernden Eigenschaften der in erfindungsgemäßen Stählen enthaltenen Mikrolegierungselemente bei erfindungsgemäßer Erzeugung des Warmbandes durch eine Glühung des aus dem Warmband nach dem Haspeln durch KaltVerformung erhaltenen Produktes aktivieren und sich dabei kaltverformte Produkte mit besonders hohen Festigkeiten und einem auch im kaltverformten Zustand guten Umformvermögen herstellen lassen, ohne dass dazu eine verfahrenstechnisch aufwendige Vergütung erforderlich wäre.The invention is based on the surprising finding that the strength-increasing properties of the microalloying elements contained in steels according to the invention are activated when the hot strip is produced according to the invention by annealing the product obtained from the hot strip after coiling by cold deformation, and cold-formed products with particularly high strengths and one Allow good forming properties to be produced even in the cold-formed state, without requiring a technically complex remuneration.
Durch die erfindungsgemäß nach der KaltVerformung durchgeführte Wärmebehandlung wird der mit der Kaltverformung regelmäßig einhergehende Verlust an Verformungsfähigkeit ohne Festigkeitseinbußen ausgeglichen. Dies gilt beispielsweise auch für Aufhärtungen im Bereich der Schnittkanten beim Schneiden oder Stanzen sowie die damit einhergehende ansteigende Empfindlichkeit gegen Rissbildung. Statt dessen zeigt sich, dass es im Zuge der nach der Kaltverformung durchgeführten Wärmebehandlung zu einer weiteren Steigerung der Festigkeit kommt, so dass bei einem erfindungsgemäß erzeugten kaltverformten Produkt eine hohe Festigkeit gezielt mit einem hohen Umformvermögen kombiniert ist. Diese Kombination vorteilhafter Eigenschaften ermöglicht es beispielsweise, das kaltverformte und anschließend wärmebehandelte Produkt nochmals kaltzuverformen, um es so in seine Endform zu bringen. Zudem steht das gute Umformvermögen beispielsweise bei crash-relevanten Bauteilen, wie Stoßfänger, Seitenaufprallträger, Verstärkungselemente, im vollen Umfang zur Verfügung, um im Falle eines Zusammenpralls mit anderen Gegenständen im großen Umfang kinetische Energie in Umformenergie umwandeln zu können.As a result of the heat treatment carried out according to the invention after cold working, the loss of deformability which is regularly associated with cold working is compensated for without loss of strength. This also applies, for example, to hardening in the area of the cut edges when cutting or punching and the associated increasing sensitivity to crack formation. Instead, it is shown that in the course of the heat treatment carried out after the cold working there is a further increase in strength, so that high strength is specifically combined with high forming capacity in a cold-formed product produced according to the invention. This combination of advantageous properties makes it possible, for example, to cold-deform the cold-formed and then heat-treated product in order to bring it into its final shape. In addition, the good formability, for example, is relevant for crash-relevant components such as Bumpers, side impact beams, reinforcing elements, are available in full in order to be able to convert kinetic energy into forming energy on a large scale in the event of a collision with other objects.
Ebenso eignet sich das erfindungsgemäße Verfahren besonders zur Erzeugung von Bauteilen, an deren Maß- und Formhaltigkeit ebenso hohe Anforderungen gestellt werden wie an ihre Festigkeit im Einsatz. Ein typisches Beispiel für eine solche Anwendung stellen Rahmen für Bildschirme dar, die in Bildröhren von Fernsehern oder Computermonitoren die Schattenmaske aufgrund der Wärmebelastung während ihres Zusammenbaus und ihres Betriebes unter gleichmäßiger Spannung in einer fest definierten Ebene halten müssen. Die geforderte hohe Festigkeit erhält das so kaltverformte Bauteil dann im Zuge der nach der Kaltverformung erfindungsgemäß durchgeführten Wärmebehandlung, so dass im Ergebnis ein exakt geformtes, hochfestes Bauelement mit hoher Dehngrenze zur Verfügung steht. Eine zusätzliche Vergütung, die zum Verzug des Bauteils und einer Beeinträchtigung der Oberfläche führen kann, ist dann nicht mehr notwendig.Likewise, the method according to the invention is particularly suitable for producing components whose dimensional and dimensional stability are just as demanding as their strength in use. A typical example of such an application are frames for screens which have to hold the shadow mask in a tube of television sets or computer monitors due to the heat load during their assembly and their operation under uniform tension in a defined level. The required high strength is then given to the cold-formed component in the course of the heat treatment carried out according to the invention after the cold-forming, so that the result is an exactly shaped, high-strength component with a high yield strength. Additional compensation, which can lead to warpage of the component and impairment of the surface, is then no longer necessary.
Voraussetzung für den durch die Erfindung erzielten Erfolg ist, dass während der Warmverarbeitung des erfindungsgemäß verwendeten Stahls die Betriebsparameter einschließlich der Haspeltemperatur so gewählt werden, dass die durch die Anwesenheit einer ausreichenden Menge von Mikrolegierungselementen an sich mögliche Härtesteigerung im Zuge des Haspeins nicht erreicht wird, sondern dass die Mikrolegierungselemente nach dem Haspeln im nicht ausgeschiedenen, gelösten Zustand vorliegen. Aus diesem Grund wird die Haspeltemperatur erfindungsgemäß stets so gewählt, dass sie mit einem deutlichen Abstand unterhalb der Temperatur liegt, bei der das Ausscheidungsmaximum der Mikrolegierungselemente erreicht würde .A prerequisite for the success achieved by the invention is that during the hot processing of the steel used according to the invention, the operating parameters, including the coiling temperature, are selected such that the hardness increase per se due to the presence of a sufficient amount of microalloying elements is not achieved in the course of coiling, but rather that the microalloying elements are present in the undissolved, dissolved state after reeling. For this reason, the reel temperature is according to the invention always chosen so that it lies at a clear distance below the temperature at which the maximum precipitation of the microalloying elements would be reached.
Die gemäß der Erfindung verwendete Stahllegierung umfasst StahlZusammensetzungen, aus denen sich abhängig von der jeweiligen Zusammensetzung und den Produktionsbedingungen Dualphasenstähle, bainitische Stähle oder Complexphasenstähle herstellen lassen. Angestrebt werden dabei grundsätzlich Stähle mit einem feinkörnigen mehrphasigen Gefüge, in dem Bainit, Ferrit, Martensit und Restaustenit in abhängig vom jeweiligen Typ des Stahles abhängigen Umfang enthalten sind.The steel alloy used according to the invention comprises steel compositions from which, depending on the particular composition and the production conditions, dual-phase steels, bainitic steels or complex-phase steels can be produced. Basically, the aim is to have steels with a fine-grained, multi-phase structure, in which bainite, ferrite, martensite and residual austenite are contained, depending on the respective type of steel.
Nachdem aus einem Stahl mit einer erfindungsgemäß verwendeten Zusammensetzung ein Vormaterial erzeugt worden ist, wird dieses Vormaterial zu Warmband warmgewalzt. Die Warmwalzanfangstemperatur wird dabei so gewählt, dass die Mikrolegierungselemente weitestgehend in dem Stahl gelöst bleiben, damit sie für die im letzten Schritt des erfindungsgemäßen Verfahrens bewirkten Effekte zur Verfügung stehen.After a starting material has been produced from a steel with a composition used according to the invention, this starting material is hot-rolled into hot strip. The hot rolling starting temperature is chosen so that the micro-alloying elements remain largely dissolved in the steel so that they are available for the effects brought about in the last step of the method according to the invention.
Bei konventionell vergossenen Brammen sollte die Walzanfangstemperatur zu diesem Zweck mindestens 1050 °C betragen. Besonders eignen sich zur Herstellung des Vormaterials allerdings Dünnbrammen- oder Dünnbandgießverfahren, mit denen es aufgrund des Umstandes, dass die Notwendigkeit einer Wiedererwärmung des Vormaterials bzw. einer Lösung der Mikrolegierungselemente nicht besteht und andererseits die Abkühlgeschwindigkeiten des Stranges hoch sein können, besonders sicher möglich ist, die Mikrolegierungselemente bis zum Beginn des Warmwalzprozesses weitgehend gelöst zu halten.For conventionally cast slabs, the initial rolling temperature should be at least 1050 ° C for this purpose. However, thin slab or thin strip casting processes are particularly suitable for the production of the primary material, with which it is possible with particular reliability due to the fact that there is no need to reheat the primary material or a solution of the microalloying elements and on the other hand the cooling rates of the strand can be high. the To keep micro-alloy elements largely dissolved until the start of the hot rolling process.
Die Warmwalzendtemperatur sollte bevorzugt im Austenitgebiet, also oberhalb der Ar3-Temperatur liegen, um die erfindungsgemäß angestrebte feinkörnige, mehrphasige Gefügestruktur zu erhalten.The hot rolling end temperature should preferably be in the austenite region, that is to say above the Ar 3 temperature, in order to maintain the fine-grained, multi-phase structure sought after according to the invention.
Die genaue Zusammensetzung der Gefügestruktur des erhaltenen Warmbands wird durch die chemischen Eigenschaften, die Aufwärm-, Walz- und Abkühlbedingungen sowie die Haspeltemperaturen bestimmt. Es hat sich gezeigt, dass sich die erfindungsgemäß erzielte Wirkung der Steigerung von Festigkeit und Umformbarkeit bei Dualphasenstählen besonders sicher dann einstellt, wenn die Haspeltemperatur maximal 300 °C beträgt. Bei Stählen mit überwiegend bainitischem Gefüge wird diese Wirkung bei Haspeltemperaturen sicher erreicht, die 350 °C bis 450 °C betragen. Complexphasenstähle sollten bevorzugt bei Temperaturen von 450 °C bis 550 °C gehaspelt werden.The exact composition of the structure of the hot strip obtained is determined by the chemical properties, the heating, rolling and cooling conditions and the reel temperatures. It has been shown that the effect of increasing the strength and formability achieved with dual-phase steels achieved according to the invention is particularly reliable when the reel temperature is at most 300 ° C. In steels with a predominantly bainitic structure, this effect is reliably achieved at reel temperatures that are 350 ° C to 450 ° C. Complex phase steels should preferably be coiled at temperatures from 450 ° C to 550 ° C.
Schon im warmverformten Zustand besitzen Stähle der gemäß der Erfindung eingesetzten Art eine hohe Festigkeit von mindestens- 550 N/mm2. Im Zuge der anschließenden Kaltverformung verfestigen die Stähle sehr stark. Gleichzeitig nimmt die Dehnung stark ab, so dass ein zwar hochfestes, jedoch nur schwer verformbares Produkt erhalten wird. Derart beschaffene kaltgeformte Bauteile besitzen aufgrund ihrer verminderten Umformbarkeit nur eine geringe Umformreserve und ein dementsprechend vermindertes Energieaufnahmevermögen. Sie sind als solche beispielsweise nur eingeschränkt für die Herstellung von Bauelementen geeignet, die als Stoßfänger in crash- gefährdeten Bereichen eines Automobils eingesetzt werden sollen.Even in the hot-formed state, steels of the type used according to the invention have a high strength of at least 550 N / mm 2 . In the course of the subsequent cold forming, the steels harden very strongly. At the same time, the elongation decreases significantly, so that a product that is high-strength but difficult to deform is obtained. Because of their reduced formability, cold-formed components of this type have only a small forming reserve and a correspondingly reduced energy absorption capacity. As such, for example, they are only suitable to a limited extent for the production of components which are used as bumpers in crash endangered areas of an automobile.
Indem erfindungsgemäß nach der KaltVerformung eine Glühung des erhaltenen Produkts bei Temperaturen und für Zeiten durchgeführt wird, durch welche die vollständige Rekristallisation sicher vermieden wird, , wird einerseits die Streckgrenze des verwendeten Stahls weiter angehoben. Andererseits werden durch die Glühung dessen Dehnungswerte wieder annähernd bis auf das Niveau angehoben, auf dem sich die Dehnbarkeit des Warmbandes vor der Kaltverformung befand. Auf diese Weise lassen sich die unmittelbar nach der Kaltverformung ursprünglich nur schwer umformbaren Produkte zu Bauteilen machen, die nicht nur hochfest sind, sondern aufgrund ihrer guten Dehnungseigenschaften auch ein hohes Umformvermögen besitzen. Sie eignen sich als solche für diejenigen Anwendungen, für die sie vor der Glühbehandlung gerade nicht geeignet gewesen sind.By annealing the product obtained at temperatures and for times during which the complete recrystallization is reliably avoided, the yield strength of the steel used is further increased, on the one hand, by the fact that the product obtained is cold annealed. On the other hand, the annealing increases the elongation values almost to the level at which the ductility of the hot strip was before the cold working. In this way, the products that were originally difficult to form immediately after cold forming can be made into components that are not only high-strength but also have a high formability due to their good elongation properties. As such, they are suitable for those applications for which they were not suitable before the annealing treatment.
Typische Glühtemperaturen während des auf die Kaltverformung folgenden Glühens liegen im Bereich von 450 °C bis 700 °C, vorzugsweise im Bereich von 550 °C bis 650 °C. Glühzeit und Glühtemperatur sind dabei im begrenzten Rahmen gegeneinander austauschbar. D.h., bei hohen Temperaturen sind nur geringe Haltezeiten erforderlich und umgekehrt. Dementsprechend kann die Wärmebehandlung als separat durchgeführter Behandlungsschritt in einer Haube oder in einer Durchlaufglühe erfolgen. Eine in konventioneller Weise bei Bedingungen, die zu einer vollständigen Rekristallisation führen würde, erfolgende Glühbehandlung würde die durch die Erfindung erreichte Wirkung zunichte machen. Besonders günstig ist es, den Glühschritt einzubinden in eine Wärmebehandlung, der das aus dem Warmband kaltverformte Produkt im Zuge seiner Weiterverarbeitung ohnehin unterzogen wird. Bei diesem Schritt kann es sich beispielsweise um eine Verzinkung oder ein anderes Verfahren zur Beschichtung oder Passivierung der Oberfläche des kaltverformten Produktes handeln, das bei im Bereich der für die Glühbehandlung vorgesehenen Temperaturen durchgeführt wird.Typical annealing temperatures during the annealing following the cold deformation are in the range from 450 ° C. to 700 ° C., preferably in the range from 550 ° C. to 650 ° C. The annealing time and annealing temperature are interchangeable to a limited extent. This means that at high temperatures only short holding times are required and vice versa. Accordingly, the heat treatment can be carried out as a separately carried out treatment step in a hood or in a continuous annealing. Annealing treatment in a conventional manner under conditions that would lead to complete recrystallization would nullify the effect achieved by the invention. It is particularly advantageous to incorporate the annealing step into a heat treatment to which the product cold-formed from the hot strip is subjected in any case in the course of its further processing. This step can be, for example, a zinc coating or another method for coating or passivating the surface of the cold-formed product, which is carried out at the range of the temperatures provided for the annealing treatment.
Die im Zuge der KaltVerformung erzielten Verformungsgrade betragen mindestens 2 % bis zur Grenzformänderung, wobei sich die durch die erfindungsgemäße Vorgehensweise erzielten Effekte insbesondere dann auswirken, wenn der Kaltverformungsgrad 5 % bis 20 %, insbesondere 5 % bis 10 %, beträgt. Die Kaltverformung kann beispielsweise als Rollprofilieren, Ziehen, Pressen oder Innenhochdruckumformen durchgeführt werden. Ein Kaltwalzen bei verhältnismäßig niedrigen Verformungsgraden ist dazu ebenfalls geeignet.The degrees of deformation achieved in the course of cold deformation amount to at least 2% up to the change in limit shape, the effects achieved by the procedure according to the invention having an effect particularly when the degree of cold deformation is 5% to 20%, in particular 5% to 10%. Cold forming can be carried out, for example, as roll profiling, drawing, pressing or hydroforming. Cold rolling with relatively low degrees of deformation is also suitable for this.
Als Mirkolegierungselement kommt in erfindungsgemäßem Stahl mindestens eines der Elemente Ti, Nb und / oder V zum Einsatz. Selbstverständlich können diese Elemente kombiniert in Mengen zugegeben werden, die zur Auslösung der am Ende des erfindungsgemäßen Verfahrens bewirkten Ausscheidungsvorganges ausreichend sind. Besonders bevorzugt ist allerdings die Verwendung von Ti, das sich durch ein besonders günstiges Ausscheidungsverhalten auszeichnet. Wird Ti gemäß einer bevorzugten Ausgestaltung der Erfindung als einziges Mikrolegierungselement verwendet, so sollte sein Gehalt mindestens das 3, 4-fache des Gehalts an N betragen, um ein ausreichendes Lösungspotential des Mikrolegierungselementes sicherzustellen. Bevorzugt liegt der Ti-Gehalt des Stahls zu diesem Zweck im Bereich 0,07 bis 0,15 Gew.-%, während der Stickstoffgehalt vorzugsweise weniger als 0,007 Gew.-% beträgt. Bei Ti- Gehalten in dieser Größenordnung wird die Bildung von Feinstauscheidungen mit aushärtender Wirkung optimal unterstützt .At least one of the elements Ti, Nb and / or V is used as the microalloying element in steel according to the invention. Of course, these elements can be added combined in amounts sufficient to trigger the excretion process effected at the end of the method according to the invention. However, it is particularly preferred to use Ti, which is distinguished by a particularly favorable excretion behavior. If Ti is used as the only microalloying element according to a preferred embodiment of the invention, its content should be at least 3.4 times the content of N in order to have a sufficient solution potential of the Ensure microalloying element. The Ti content of the steel for this purpose is preferably in the range 0.07 to 0.15% by weight, while the nitrogen content is preferably less than 0.007% by weight. With Ti contents of this size, the formation of fine deposits with a hardening effect is optimally supported.
Abhängig vom Typ des jeweils verarbeiteten Stahls liegt der Al-Gehalt bevorzugt im Bereich von 0,015 bis 0,08 Gew.-%. bzw. 0,5 bis 1,5 Gew.-%.Depending on the type of steel processed, the Al content is preferably in the range from 0.015 to 0.08% by weight. or 0.5 to 1.5% by weight.
Erfindungsgemäß erzeugte Stahlbleche eignen sich bevorzugt für die Kaltverformung zu Bauteilen, an deren Festigkeit bei gleichzeitig gutem Dehnungsverhalten und dementsprechend gutem Verformungsverhalten sowie hoher geometrischer Maßhaltigkeit hohe Anforderungen gestellt sind. Dabei zeichnen sich aus erfindungsgemäßen Blechen erzeugte Bauelemente durch geringes Gewicht und hohes Energieauf ahmevermögen aus .Steel sheets produced according to the invention are preferably suitable for cold forming into components, the strength of which, along with good elongation behavior and, accordingly, good deformation behavior and high geometric dimensional stability, are subject to high demands. Components produced from sheet metal according to the invention are notable for their low weight and high energy absorption capacity.
Ein Beispiel für eine vorteilhafte Verwendung erfindungsgemäß erzeugter Stahlbleche ist die Herstellung von Rahmen für Flachbildschirme. Ebenso lassen sich aus erfindungsgemäß hergestellten Stahlblechen Bauelemente für Karosserien von Kraftfahrzeugen oder Anbauteile herstellen, die einerseits besonders fest und andererseits beispielsweise im Fall eines Zusammenstoßes mit einem anderen Fahrzeug die beim Aufprall frei werdenden kinetischen Energien in Verformungsenergie umwandeln müssen. Dies sind u.a. Längsträger, sog. "Crashboxen", Fahrwerksteile, Hohlstrukturteile und Verstärkungsteile, wie die A- , B- oder C-Säule der Automobilkarosserie . Erfindungsgemäß erzeugtes Warmband ist grundsätzlich zur Verzinkung geeignet. Dabei ist jedoch eine bei relativ niedrigen Temperaturen stattfindende, insbesondere stückweise erfolgende, Feuerverzinkung vorzuziehen, Verzinkungen, bei denen Temperaturen über 750 °C anfallen, sind dazu weniger geeignet, da dabei die hinsichtlich des erfindungsgemäß erzielten Effekts kritischen Temperaturen im jeweils verarbeiteten Werkstück überschritten werden können.An example of an advantageous use of steel sheets produced according to the invention is the production of frames for flat screens. Likewise, components for bodywork of motor vehicles or add-on parts can be produced from steel sheets produced according to the invention, which on the one hand have to be particularly strong and on the other hand, in the event of a collision with another vehicle, must convert the kinetic energies released in the event of an impact into deformation energy. These include longitudinal members, so-called "crash boxes", chassis parts, hollow structure parts and reinforcement parts, such as the A, B or C pillar of the automobile body. Hot strip produced according to the invention is basically suitable for galvanizing. However, hot-dip galvanizing, which takes place at relatively low temperatures, in particular piecewise, is preferable, galvanizing at temperatures above 750 ° C. is less suitable for this, since the critical temperatures with regard to the effect achieved according to the invention can be exceeded in the workpiece being processed ,
Nachfolgend wird die Erfindung anhand von Ausführungsbeispielen näher erläutert.The invention is explained in more detail below on the basis of exemplary embodiments.
Ein gemäß Tabelle 1 zusammengesetzter Stahl ist auf einer Stranggießanlage zu einer Vorbramme vergossen worden, welches anschließend als Vormaterial mit einer Temperatur von 1125 °C in einer Warmbandstraße zu einem Warmband warmgewalzt worden ist. Die Warmwalzendtemperatur betrug 925 °C. Die Haspeltemperatur lag bei 475 °C. Nach dem Haspeln ist das Warmband gebeizt und im gebeizten Zustand an ein Kaltwalzwerk geliefert worden.A steel composed according to Table 1 was cast on a continuous casting plant to a pre-slab, which was then hot-rolled as a starting material at a temperature of 1125 ° C. in a hot strip mill to a hot strip. The hot rolling end temperature was 925 ° C. The reel temperature was 475 ° C. After coiling, the hot strip is pickled and delivered to a cold rolling mill in the pickled state.
Tabelle 1Table 1
Dort sind verschiedene Bandproben des Warmbands bei Kaltwalzgraden von 5 %, 10 %, 20 %, 30 %, 40 % kaltgewalzt worden. Aus den so erhaltenen Kaltbändern sind anschließend Gruppen Gl bis G5 zusammengestellt worden, wobei jeder Gruppe Gl bis G5 jeweils ein nicht kaltverformtes (Kaltverformungsgrad = 0 %) , ein mit 5 %, ein mit 10 %, ein mit 20 %, ein mit 30 % und ein mit 40 % Kaltverformungsgrad kaltverformtes Kaltband zugeordnet worden ist . Die Bleche der Gruppe Gl sind zu Vergleichszwecken keiner auf die Kaltverformung folgenden Anlassglühung unterzogen worden, während die Bleche der Gruppe G2 bei 500 °C, die Bleche der Gruppe G3 bei 550 °C, die Bleche der Gruppe G4 bei 600 °C und die Bleche der Gruppe G5 bei 650 °C in einem Haubenofen für jeweils eine Stunde anlassgeglüht und anschließend an Luft abgekühlt worden sind.There, various strip samples of the hot strip were cold rolled at cold rolling degrees of 5%, 10%, 20%, 30%, 40%. Groups G1 to G5 were then put together from the cold strips obtained in this way, each group G1 to G5 not having one Cold-formed (cold deformation degree = 0%), one with 5%, one with 10%, one with 20%, one with 30% and one with 40% cold deformation degree cold-formed cold strip has been assigned. For comparison purposes, the plates of group G1 have not been subjected to any annealing following the cold deformation, while the plates of group G2 at 500 ° C, the plates of group G3 at 550 ° C, the plates of group G4 at 600 ° C and the plates Group G5 were annealed at 650 ° C in a bell-type furnace for one hour each and then cooled in air.
In Tabelle 2 sind für jedes der Bleche der Gruppen Gl - G5 die im Zugversuch ermittelten Werkstoffeigenschaften eingetragen.The material properties determined in the tensile test are entered in Table 2 for each of the sheets in groups Gl - G5.
") Bei den in der Spalte A80 mit "E" gekennzeichneten Beispielen kam es zum Endbruch. ") The examples marked" E "in column A 80 resulted in a final break.
Tabelle 2Table 2
Es zeigt sich, dass sich bei den in erfindungsgemäßer Weise verarbeiteten Blechen in Folge der nach der Kaltverformung durchgeführten Wärmebehandlung gegenüber den nur kaltverformten und nicht wärmebehandelten Blechen Gl.l - G1.5 jeweils deutlich verbesserte Festigkeitswerte einstellen. Gleichzeitig wird durch die nach der KaltVerformung durchgeführte Wärmebehandlung eine Gleichmaßdehnung Agi erreicht, die jeweils annähernd der Gleichmaßdehnung Agi des nicht kaltverformten und nicht wärmebehandelten Blechs Gll.O entspricht. Dementsprechend weisen die erfindungsgemäß erzeugten kaltverformten und anschließend wärmebehandelten Stähle eine besonders gute Umformbarkeit und ein ebenso gutes Energieaufnahmevermögen auf.It can be seen that in the sheets processed in the manner according to the invention, as a result of the heat treatment carried out after the cold deformation, the strength values obtained in each case are markedly improved compared to the only cold-formed and not heat-treated sheets Gl.l-G1.5. At the same time, a uniform expansion Agi is achieved by the heat treatment carried out after the cold deformation, which corresponds approximately to the uniform expansion Agi of the non-cold-formed and non-heat-treated sheet Gll.O. Accordingly, the cold-formed and subsequently heat-treated steels produced according to the invention have particularly good formability and an equally good energy absorption capacity.
In Tabelle 3 ist ein zweites Beispiel einer erfindungsgemäß verwendeten StahlZusammensetzung angegeben.Table 3 shows a second example of a steel composition used according to the invention.
Tabelle 3Table 3
Ein entsprechend legierter Stahl wurde erschmolzen und zu Brammen vergossen. Anschließend sind die Brammen auf eine Temperatur von mehr als 1150 °C wiedererwärmt und mit einer mindestens 850 °C betragenden Warmwalztemperatur warmgewalzt worden. Nach dem Haspeln bei einer Temperatur von weniger als 600 °C sind für eine erste unbehandelte Bandprobe T2.0 des Bandes, für eine 30 Minuten bei 580 °C geglühte und anschließend an Luft abgekühlte Bandprobe T2.1, für eine bei einem Kaltverformungsgrad von 10 % nur kaltgewalzte Bandprobe T2.2 und für eine in erfindungsgemäßer Weise bei einem Kaltverformungsgrad von 10 % kaltgewalzte, anschließend für 30 Minuten bei 580 °C geglühte und dann an Luft abgekühlte Bandprobe T2.3 die mechanischen Eigenschaften Rpo,2, Rm, Re/Rm, A5, Aso bzw. A80 ermittelt worden. Die festgestellten Werte der mechanischen Eigenschaften sind in Tabelle 4 angegeben.A correspondingly alloyed steel was melted and cast into slabs. The slabs are then reheated to a temperature of more than 1150 ° C and with a hot rolling temperature of at least 850 ° C has been hot rolled. After coiling at a temperature of less than 600 ° C, for a first untreated strip sample T2.0 of the strip, for a strip sample annealed at 580 ° C for 30 minutes and then cooled in air, there is T2.1 for one with a degree of cold deformation of 10 % only cold-rolled strip sample T2.2 and for a strip sample T2.3 cold-rolled in the manner according to the invention with a degree of cold deformation of 10%, then annealed for 30 minutes at 580 ° C. and then cooled in air, the mechanical properties R p o, 2 , R m , Re / R m , A 5 , A so or A 80 have been determined. The determined values of the mechanical properties are given in Table 4.
Tabelle 4Table 4
Auch diese Beispiele belegen, dass durch die erfindungsgemäße Kombination von Kalt erformung und anschließender Wärme hochfeste Stähle erzeugt werden, die aufgrund ihrer guten Dehnbarkeit ein besonders hohes Umformvermögen besitzen. So ist die Festigkeit der erfindungsgemäß erzeugten Bandprobe T2.3 der Festigkeit der unbehandelten Bandprobe T2.0 weit überlegen, während seine Dehnungswerte denen der unverformten Bandprobe T2.0 entsprechen. Ebenso weist die nur kaltverformte Bandprobe T2.2 gegenüber der erfindungsgemäß erzeugten Bandprobe T2.3 nicht nur eine weit unterlegene Dehnbarkeit, sondern auch eine geringere Festigkeit auf. Bei der nur wärmebehandelten Bandprobe T2.1 liegt zwar die Dehnbarkeit auf einem mit der erfindungsgemäß erzeugten Bandprobe T2.3 vergleichbaren Niveau. Gleichzeitig ist aber die Festigkeit der Bandprobe T2.1 der Festigkeit der erfindungsgemäß erzeugten Bandprobe weit unterlegen.These examples also demonstrate that the combination of cold forming and subsequent heat according to the invention produces high-strength steels which, because of their good ductility, have a particularly high formability. The strength of the tape sample T2.3 produced according to the invention is far superior to the strength of the untreated tape sample T2.0, while its elongation values correspond to those of the undeformed tape sample T2.0. Likewise, the only cold-deformed tape sample T2.2 not only exhibits inferior extensibility compared to the tape sample T2.3 produced according to the invention, but also also lower strength. With the only heat-treated tape sample T2.1, the extensibility is at a level comparable to the tape sample T2.3 produced according to the invention. At the same time, however, the strength of the tape sample T2.1 is far inferior to the strength of the tape sample produced according to the invention.
Der entsprechend der in Tabelle 5 angegebenen Legierung zusammengesetzte Stahl ist ebenfalls erschmolzen und zu Brammen vergossen worden.The steel composed according to the alloy specified in Table 5 was also melted and cast into slabs.
Tabelle 5Table 5
Anschließend sind diese Brammen wie beim im Zusammenhang mit dem in den Tabellen 3/4 angegebenen Beispiel auf eine Temperatur von mehr als 1150 °C wiedererwärmt, mit einer mindestens 850 °C betragenden Warmwalztemperatur und bei einer Temperatur von weniger als 600 °C gehaspelt worden. Anschließend sind dann sechs Bandproben T3.0 bis T3.5 genommen worden.Subsequently, as in the example given in Tables 3/4, these slabs were reheated to a temperature of more than 1150 ° C., with a hot rolling temperature of at least 850 ° C. and at a temperature of less than 600 ° C. Then six tape samples T3.0 to T3.5 were then taken.
Die mit den betreffenden Bandproben T3.0 bis T3.2 durchgeführten weiteren Verarbeitungsschritte sind ebenso wie die zugehörigen Werte der mechanischen Eigenschaften für eine der Bandmitte entnommene Probe in Tabelle 6 angegebe . The further processing steps carried out with the relevant tape samples T3.0 to T3.2 as well as the associated values of the mechanical properties for a sample taken from the tape center are given in Table 6.
1) Glühdauer jeweils 30 Minuten, Abkühlung an Luft 1 ) Annealing time 30 minutes each, cooling in air
2) Bei den in der Spalte A80 mit "E" gekennzeichneten Beispielen kam es zum Endbruch. 2 ) The examples marked with "E" in column A 80 resulted in a final break.
Tabelle 6Table 6
Auch in diesem Fall belegt die Bandprobe T3.2 deutlich, dass sich bei erfindungsgemäßer Vorgehensweise hochfeste kaltverformte Blechprodukte erhalten lassen, die, wie ein Vergleich der Dehnbarkeitswerte zeigt, hinsichtlich ihrer Umformbarkeit der unverformten Bandprobe T3.0 überlegen sind. Ebenso werden erfindungsgemäßeIn this case too, the strip sample T3.2 clearly shows that high-strength cold-formed sheet products can be obtained with the procedure according to the invention, which, as a comparison of the ductility values shows, are superior in their formability to the undeformed strip sample T3.0. Likewise, according to the invention
Eigenschaf sverbesserungen erzielt, wenn kaltgewalztes Band über sehr viel längeren Zeiten bei vergleichsweise niedrigen Temperaturen, z.B. 450 °C bis 550 °C, in einer Haube geglüht werden.Property improvements are achieved when cold rolled strip is used for much longer times at comparatively low temperatures, e.g. 450 ° C to 550 ° C, can be annealed in a hood.
Ein Beispiel für eine besonders vorteilhafte Verwendung eines erfindungsgemäß erzeugten Stahls besteht in der Herstellung von Rahmen, in denen die Schattenmasken von Fernsehröhren gehalten werden. Zum Schwärzen der in einem derartigen Rahmen gespannten Schattenmaske wird der Rahmen mit der Schattenmaske über eine ausreichende Zeit einer Temperatur ausgesetzt, die typischerweise ca. 570 °C beträgt. Indem der Rahmen aus einem in erfindungsgemäßer Weise erzeugten Warmband unter Ausnutzung der in diesem Zustand hervorragenden Verformbarkeit des Warmbands durch Kaltverformung erzeugt und anschließend im Zuge des Schwärzens der von ihm gehaltenen Schattenmaske über eine ausreichende Zeit bei der zum Schwärzen erforderlichen Temperatur gehalten wird, erhöht sich die Festigkeit des Rahmens auf ein Niveau, bei welchem der Rahmen sicher und formstabil die während der Herstellung und des Betriebs der Fernsehröhre auf ihn ausgeübte Wärmebelastung ertragen und Verzugsfreiheit der Schattenmaske gewährleisten kann.An example of a particularly advantageous use of a steel produced according to the invention consists in the production of frames in which the shadow masks are held by television tubes. In order to blacken the shadow mask stretched in such a frame, the frame with the shadow mask is exposed to a temperature which is typically approximately 570 ° C. for a sufficient time. By producing the frame from a hot strip produced in the manner according to the invention, taking advantage of the deformability of the hot strip which is outstanding in this state, by cold working and then in the course of the blackening of the shadow mask held by it for a sufficient time the temperature required for blackening, the strength of the frame increases to a level at which the frame can safely and dimensionally bear the heat load exerted on it during the manufacture and operation of the television tube and can ensure that the shadow mask is free from distortion.
Eine andere vorteilhafte Anwendung des erfindungsgemäßen Verfahrens besteht in der Herstellung von verzinkten Seitenaufprallträgern oder anderen crashrelevanten Bauelementen für Fahrzeugkarosserien. Dabei wird zunächst aus erfindungsgemäß erzeugtem Warmband das jeweilige Bauteil beispielsweise durch eine Tiefziehoperation kaltgeformt. Das kaltgeformte Bauteil wird dann bei Temperaturen im Bereich von 470 °C einer Stückverzinkung unterzogen. Im Zuge dieses Verzinkungsvorgangs wird das Bauteil ebenfalls auf einem Temperaturniveau gehalten, bei dem sich die erfindungsgemäß erreichte Steigerung der Dehnbarkeit und Festigkeit einstellt. Der so erhaltene Seitenaufprallträger weist aufgrund seiner guten Dehnbarkeit und gleichzeitig hohen Festigkeit ein besonders hohes Energieaufnahmevermδgen auf, durch welches er im Fall eines Zusammenstoßes mit einem anderen Fahrzeug einen großen Teil der dabei frei werdenden kinetischen Energie in Verformungsenergie umwandeln und den für das Überleben der Insassen erforderlichen Raum absichern kann. Another advantageous application of the method according to the invention consists in the production of galvanized side impact beams or other crash-relevant components for vehicle bodies. First, the respective component is cold formed from hot strip produced according to the invention, for example by a deep-drawing operation. The cold-formed component is then subjected to piece galvanizing at temperatures in the range of 470 ° C. In the course of this galvanizing process, the component is also kept at a temperature level at which the increase in ductility and strength achieved according to the invention occurs. The side impact beam obtained in this way has a particularly high energy absorption capacity due to its good elasticity and high strength, by means of which it converts a large part of the kinetic energy released in the event of a collision with another vehicle into deformation energy and that required for the survival of the occupants Can secure space.

Claims

P AT E N T AN S P R Ü C H E P AT E N T AN S P RÜ C H E
Verfahren zum Herstellen eines hochfesten, aus einem Warmband kaltverformten Produkts mit gutem Umformvermogen bei dem ein Stahl mit (in Gewichts-%) :Process for producing a high-strength, cold-formed product from a hot strip with good forming capacity, in which a steel with (in% by weight):
C: 0,01 - 0,25 %C: 0.01-0.25%
Si: 0,01 - 1,50 %Si: 0.01 - 1.50%
Mn: 0,50 - 2,00 %Mn: 0.50 - 2.00%
P: < 0,08 %P: <0.08%
S: < 0,01 %S: <0.01%
AI: 0,001 - 1,50 %AI: 0.001 - 1.50%
Cr: < 0,60 %Cr: <0.60%
Mo: < 0,60 %Mo: <0.60%
N: < 0,02 % sowie mindestens einem Mikrolegierungselement aus der GruppeN: <0.02% and at least one microalloying element from the group
Ti: < 0,20 %,Ti: <0.20%,
Nb: < 0,06 %,Nb: <0.06%,
V: < 0,15 %, Rest Eisen und übliche Verunreinigungen, zu einem Vormaterial, wie Brammen, Dünnbrammen oder gegossenes Band, vergossen wird, bei dem das Vormaterial ausgehend von einer Warmwalzanfangstemperatur, bei der die Mikrolegierungselemente im wesentlichen gelöst bleiben, zu Warmband warmgewalzt wird, bei dem das Warmband bei einer weniger als 600 °C betragenden Haspeltemperatur gehaspelt wird, bei dem das Warmband anschließend bei einem mindestens 2 % betragenden und höchstens der Grenzformänderung entsprechendenV: <0.15%, remainder iron and usual impurities, is cast into a starting material, such as slabs, thin slabs or cast strip, in which the starting material is hot-rolled into hot strip starting from a hot rolling starting temperature at which the microalloying elements remain essentially dissolved becomes, in which the hot strip is coiled at a coiling temperature of less than 600 ° C, in which the hot strip is subsequently at a change of at least 2% and at most corresponding to the limit shape change
Kaltverformungsgrad zu einem Produkt kaltverformt wird, und bei dem das durch KaltVerformung erzeugte Produkt Temperaturen und Zeiten, die unterhalb der zur vollständigen Rekristallisation erforderlichen Temperaturen und Zeiten liegen, geglüht wird.Degree of cold deformation into a product is cold worked, and at which the product produced by cold working is annealed at temperatures and times which are below the temperatures and times required for complete recrystallization.
2. Verfahren nach Anspruch 1, d a d u r c h g e k e n n z e i c h n e t, d a s s der Stahl als einziges Mikrolegierungselement Ti enthält und d a s s das Verhältnis des Gehalts an Ti bezogen auf den Gehalt an N mindestens 3 , 4 beträgt .2. The method of claim 1, d a d u r c h g e k e n n z e i c h n e t, that the steel as the only microalloying element contains Ti and that the ratio of the content of Ti based on the content of N is at least 3.4.
3. Verfahren nach einem der voranstehenden Ansprüche, d a d u r c h g e k e n n z e i c h n e t, d a s s die Warmwalzendtemperatur mindestens gleich der Ar3- Temperatur ist.3. The method according to any one of the preceding claims, characterized in that the hot rolling end temperature is at least equal to the Ar 3 temperature.
4. Verfahren nach einem der voranstehenden Ansprüche, d a d u r c h g e k e n n z e i c h n e t, d a s s die Haspeltemperatur weniger als 300 °C beträgt.4. The method according to any one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t, that the reel temperature is less than 300 ° C.
5. Verfahren nach einem der Ansprüche 1 bis 3, d a d u r c h g e k e n n z e i c hn e t, d a s s die Haspeltemperatur 350 °C - 450 °C beträgt. 5. The method according to any one of claims 1 to 3, dadurchgekennzeic hn et that the reel temperature is 350 ° C - 450 ° C.
6. Verfahren nach einem der Ansprüche 1 bis 3, d a d u r c h g e k e n n z e i c h n e t, d a s s die Haspeltemperatur 450 °C - 550 °C beträgt.6. The method according to any one of claims 1 to 3, d a d u r c h g e k e n n z e i c h n e t, that the reel temperature is 450 ° C - 550 ° C.
7. Verfahren nach einem der voranstehenden Ansprüche, d a d u r c h g e k e n n z e i c h n e t, d a s s der Kaltverformungsgrad 5 % - 20 %, insbesondere 5 % bis 10 %, beträgt.7. The method according to any one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t, that the degree of cold deformation is 5% - 20%, in particular 5% to 10%.
8. Verfahren nach einem der voranstehenden Ansprüche, d a d u r c h g e k e n n z e i c h n e t, d a s s die Glühtemperatur 550 °C - 600 °C beträgt.8. The method according to any one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t, that the annealing temperature is 550 ° C - 600 ° C.
9. Verfahren nach einem der voranstehenden Ansprüche, d a d u r c h g e k e n n z e i c h n e t, d a s s die Glühung im Durchlauf durchgeführt wird.9. The method according to any one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t, that the annealing is carried out in one pass.
10. Verfahren nach einem der Ansprüche 1 bis 8, d a d u r c h g e k e n n z e i c h n e t, d a s s die Glühung im Haubenofen durchgeführt wird.10. The method according to any one of claims 1 to 8, d a d u r c h g e k e n n z e i c h n e t, that the annealing is carried out in the hood furnace.
11. Verfahren nach einem der voranstehenden Ansprüche, d a d u r c h g e k e n n z e i c h n e t, d a s s das Vormaterial als gegossenes Band auf einer Gießwalzanläge erzeugt wird.11. The method according to any one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t, that the primary material is produced as a cast strip on a casting and rolling plant.
12. Verfahren nach einem der voranstehenden Ansprüche, d a d u r c h g e k e n n z e i c h n e t, d a s s das durch KaltVerformung hergestellte Produkt ein Rahmen für Flachbildschirme ist. 12. The method according to any one of the preceding claims, characterized in that the product produced by cold working is a frame for flat screens.
13. Verfahren nach einem der Ansprüche 1 bis 11, d a d u r c h g e k e n n z e i c h n e t, d a s s das durch Kalt erformung hergestellte Produkt ein Bauelement für die Herstellung von Kraftfahrzeugkarosserien oder ein Anbauteil ist.13. The method according to any one of claims 1 to 11, d a d u r c h g e k e n n z e i c h n e t that the product produced by cold forming is a component for the production of motor vehicle bodies or an add-on part.
14. Verfahren nach einem der voranstehenden Ansprüche, d a d u r c h g e k e n n z e i c h n e t, d a s s das Produkt durch kalt erfolgendes Innenhochdruckumformen erzeugt wird.14. The method according to any one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t that the product is produced by cold internal high pressure forming.
15. Verfahren nach einem der voranstehenden Ansprüche, d a d u r c h g e k e n n z e i c h n e t, d a s s das kaltverformte Produkt einer Verzinkung unterzogen wird.15. The method according to any one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t, that the cold-formed product is subjected to galvanizing.
16. Verfahren nach Anspruch 15, d a d u r c h g e k e n n z e i c h n e t, d a s s die Verzinkung als Feuerverzinkung durchgeführt wird.16. The method according to claim 15, d a d u r c h g e k e n n z e i c h n e t, that the galvanizing is carried out as hot-dip galvanizing.
17. Verfahren nach Anspruch 15 oder 16, d a d u r c h g e k e n n z e i c h n e t, d a s s die Verzinkung bei Temperaturen um 460 °C stattfindet. 17. The method of claim 15 or 16, d a d u r c h g e k e n n z e i c h n e t, that the galvanizing takes place at temperatures around 460 ° C.
EP02738172A 2001-06-26 2002-06-21 Method for producing high-strength cold-formed steel products from a hot rolled strip, said products exhibiting good malleability Expired - Lifetime EP1399598B2 (en)

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DE10130774A DE10130774C1 (en) 2001-06-26 2001-06-26 Production of a high strength cold-formed product comprises pre-casting a steel to a pre-material, hot rolling into a hot strip so that the micro-alloying elements remain dissolved, coiling, cold-forming to a product, and annealing
DE10130774 2001-06-26
PCT/EP2002/006870 WO2003002772A1 (en) 2001-06-26 2002-06-21 Method for producing high-strength cold-formed steel products from a hot rolled strip, said products exhibiting good malleability

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