EP2297367A1 - Method for producing a formed steel part having a predominantly ferritic-bainitic structure - Google Patents

Method for producing a formed steel part having a predominantly ferritic-bainitic structure

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Publication number
EP2297367A1
EP2297367A1 EP09741994A EP09741994A EP2297367A1 EP 2297367 A1 EP2297367 A1 EP 2297367A1 EP 09741994 A EP09741994 A EP 09741994A EP 09741994 A EP09741994 A EP 09741994A EP 2297367 A1 EP2297367 A1 EP 2297367A1
Authority
EP
European Patent Office
Prior art keywords
max
steel
temperature
time
bainitization
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
EP09741994A
Other languages
German (de)
French (fr)
Other versions
EP2297367B9 (en
EP2297367B1 (en
Inventor
Jian Bian
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 Steel Europe AG
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Publication of EP2297367A1 publication Critical patent/EP2297367A1/en
Application granted granted Critical
Publication of EP2297367B1 publication Critical patent/EP2297367B1/en
Publication of EP2297367B9 publication Critical patent/EP2297367B9/en
Active legal-status Critical Current
Anticipated expiration legal-status Critical

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • 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
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/185—Hardening; Quenching with or without subsequent tempering from an intercritical temperature
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
    • C21D1/20—Isothermal quenching, e.g. bainitic hardening
    • 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
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite

Definitions

  • DJ e invention relates to a method for producing a steel molding with a predominantly ferritic-bainitic Gefuge.
  • hot-press molded components produced from high-strength steel are nowadays used in those areas of the body which may be exposed to particularly high loads in the event of a crash .
  • Examples of such steel moldings are the A and B pillars, called the Stoßfanger and Turaufpralltrager a passenger car.
  • the sheet metal blanks concerned are heated to a generally above the Austenitmaschinestemperatur of the respective steel deformation temperature and placed in the heated state in the tool of a forming press.
  • the sheet metal blank or the component formed from it experience a contact with the cool tool rapid cooling, which results in hardened components in the component. It may be sufficient if the component cools without aktxve cooling only by the contact with the tool. However, rapid cooling can also be supported by the fact that the tool itself is actively cooled.
  • Em steel comparable to steel 22MnB5 is known from JP 2006104526A.
  • This known steel contains in addition to Fe and unavoidable impurities (xn wt .-%) 0.05 - 0.55% C, max. 2% Si, 0.1-3% Mn, max. 0.1% P and max. 0.03% S.
  • additional amounts of 0.0002 - 0.005% B and 0.001 - 0.1% Ti can be added to the steel.
  • the respective Ti content serves to bind the nitrogen present in the steel. In this way, the boron present in the steel can develop its strength-increasing effect as completely as possible.
  • sheets made of the composite steel in this way are first produced be preheated 950 0 C, lying temperature - then to an above the AEC 3 temperature, typically in the range of 850th During the subsequent rapid cooling in the pressing tool, starting from this temperature range, the martensitic joint, which ensures the desired high strength, is formed in the component molded from the respective sheet metal blank. It has a favorable effect that the sheet metal parts heated to the stated temperature level can be formed into complex shaped components at relatively low forming forces. This is especially true for such sheet metal parts, which are made of high-strength steel and provided with a corrosion protection coating.
  • the components produced from boron-alloyed steels in the above-described manner achieve strengths of more than 1,500 MPa.
  • the required complete martensitic structure of the components has the result that the components have an insufficient residual elongation at break of 5-6% for many applications.
  • the relatively low residual elongation at break is associated with a low toughness. In the case of applications in which good deformation behavior is required in the event of a crash, this leads to components made of boron-alloyed steel in the known manner frequently no longer meeting these requirements. This applies in particular when the components to be produced are parts for an automobile body.
  • a board or a preformed mold component each consisting of a steel of the above type, heated in a heating device to an austenitizing and then fed via a transport path to a hardening process.
  • transport portions of the first type of board or of the molded component which are intended to have higher ductility properties in the final component, are quenched from a predetermined cooling start temperature which is above the ⁇ - ⁇ transformation temperature. This quenching is terminated when a predetermined cooling stop temperature is reached, before conversion to ferrite and / or pearlite has taken place or after a slight conversion in ferrite and / or perlite.
  • the board or the respective molded part is held isothermally to convert the austenite into ferrite and / or perlite.
  • the tempering temperature of the areas of the second kind which should have relatively lower ductile properties in the final component, is kept just high enough for sufficient martensite formation to take place in the areas of the second type during a hardening process.
  • the cooling is carried out.
  • the resulting molded part is immersed in a separate operation in a quenching tank or the like to form the desired martensitic Hartegefuge.
  • This procedure also requires a Prozeßbowung that can be incorporated only with great effort in a modern production plant.
  • there is also the problem with the components produced by this known method that while they have a high strength, they are at the same time so brittle that they do not meet the requirements for their deformability which are set in practice.
  • the object of the invention was to provide a method with which it is possible to produce in a process-technically simple manner Stahlformtei Ie in which a high strength is combined with a good residual elongation at break.
  • a steel shaped part is produced with a predominantly ferritic-Bavarian mesh.
  • a starting material in the form of a steel plate or a preformed steel part is provided. If a hitherto undeformed steel plate is processed as a starting material, the entire process is referred to as a "one-step" process. If, on the other hand, a preformed steel part is processed, this is referred to as a two-stage process, whereby in the first stage a previously undeformed blank is deformed so that the steel component thus obtained has not yet reached its final shape.
  • the respective starting material consists of a steel of a known composition which, in addition to iron and unavoidable production-related impurities (in% by weight) C: 0.02-0.6%, Mn: 0.5-2.0%, Al : 0.01 - 0.06%, Si: up to 0.4%, Cr: up to 1.2%, P: up to 0.035%, S: up to 0.035% and optionally one or more elements from the group "Ti, B, Mo, Ni, Cu, N", wherein - if present - Ti in a content of up to 0.05%, Cu in a content of up to 0.01%, B in contents of 0 , 0008 - 0.005%, Mo in contents of up to 0.3%, Ni in contents of up to 0.4%, N m contents of up to 0.01%.
  • the as-assembled starting material (steel plate or preformed steel part) is soaked through at a heating temperature lying between the AcI and the Ac3 temperature of the steel such that incomplete austenitisation of the starting material occurs. Accordingly, at the end of the austenitizing phase, the microstructure of the starting material consists of ferrite and austenite.
  • Vormate ⁇ al is placed in a press mold and molded therein to the steel molding. Press-hardening takes place in a temperature range in which the microstructure of the primary material in the two-phase region is composed of ferrite and austenite.
  • the steel mold part according to the invention is kept substantially isothermally on the Bainit Siegstemperatur over a bainitization time until a Gefuge has set in the steel mold part, the majority of ferrite and bainite exists.
  • the bainitization temperature to be set in each case depends on the bainite transformation temperature, which is differentiated upward in each case according to the chemical composition of the enriched austenite by the martensite start temperature and perlite transition temperature.
  • Press hardening is significantly influenced by the austenitizing and mold temperature. This must be so fast that the board is cooled without conversion to the Bainitumwandlungstemperatur and kept constant at this temperature.
  • a Gefuge which has in addition to the ferritic and Bavarian constituent parts minor amounts of retained austenite and possibly below 5% levels of martensite.
  • the residual austenite contents in the resulting component which are essentially determined by the carbon content, can be up to 10%.
  • the steel mold is cooled to room temperature.
  • the temperature control is controlled with respect to the austenitizing process and the subsequent press-hardening in such a way that a mixture of ferrite, bainite and a proportion of retained austenite in the component is established.
  • the erfmdungsgelaute method thus provides a steel component whose Gefuge is characterized by a fer ⁇ tisch-bainitician microstructure.
  • This bainitic microstructure gives a component produced erfxndungsgeINE improved Verformungsei properties, in particular an improved residual elongation at break.
  • steel moldings produced according to the invention have an improved crash behavior, without the need for separate tempering treatment, since bainite can be regarded as a type of tempered martensite.
  • the erfmdungsge64e method allows the steel component to cool more slowly than in the conventional method in which the cooling takes place in the tool with the aim to produce martensitic Hartegefuge. Therefore, in a erfI ndungsgedorfen process, the risk of the formation of component distortion is minimized and the components produced according to the invention are characterized by a particularly high dimensional stability.
  • the pressing tool can also be specifically heated to carry out the method according to the invention.
  • the ferrite and Baimtanteile should be in the Gefuge of the steel molding at the end of Bainitmaschineszeit Jn sum at least 90%, the ferrite and bainite each should be at least 30%.
  • the curing according to the invention is prevented as completely as possible, it is fundamentally advantageous if, at the end of the bainitization time, the martensite portion of the steel molding is less than 1%, in particular limited to tracks.
  • the alloy of the steel from which the starting material to be processed according to the invention is conventional
  • tempered steel has in addition to iron and unavoidable impurities (in wt .-%) C:
  • MnB steels which are suitable for the process according to the invention have C: 0.25-0.6
  • the austenitizing temperature of the steels which is made of processed accordance with the invention starting material, in the range 750-810 0 C.
  • the intended for the fürerwarmen at the warming temperature heating time is typically in the range 6 - 15 minutes.
  • the starting material is provided with a corrosion-protecting metallic coating.
  • This coating also protects the respective starting material (steel plate, preformed steel part) from the press mold during transport from the oven, in which it is preheated to the austenitizing temperature.
  • the corrosion protection coating can be designed so that it protects an oxidation of the hot steel substrate with the ambient oxygen even when transported in air.
  • a particularly practical variant of the method according to the invention is characterized in that the press forming and the bainitization of the steel component produced in the course of the press forming takes place in the press forming tool.
  • a particularly advantageous variant of the invention provides that after the compression molding of the starting material, the steel mold part then obtained remains in the compression mold and brought there to the Bamit avoirstemperatur and kept for the Bamitmaschineszeit.
  • the press mold is preferably tempered so that the starting material, starting from one above the Bainitisi tion temperature lying temperature during their compression deformation to the steel component to the Ba Lnitmaschinestemperatur be cooled.
  • the tool closing time of the pressing tool, within which the shaping, Abkluhlung and Bainitmaschine of the steel molding takes place in this case is usually 5 - 60 seconds, especially 20 - 60 seconds.
  • the typical range of the bainitization temperature at which the baintization according to the invention with the aim of Formation of a ferritic / bainitic Gefuges is preferably carried out, is typically bounded below by the martensite [respective steel composition of the raw material, while it may be adjusted upwardly in each case lower than 500 0 C in order to avoid the formation of pearlite.
  • steel blanks which have been divided off from a hot-rolled or cold-rolled flat product such as strip or sheet, are suitable. It is likewise possible to apply the method according to the invention to a steel part which has been preformed in a previous work step. The latter is useful, for example, when the shape of the steel component to be produced is so complex that several shaping steps are required for its production.
  • steel components produced according to the invention are particularly suitable for use as crash-relevant parts of an automobile body.
  • the inventive method is particularly suitable for the production of Longitudinal and bottom crossbeams, which in practice should have a particularly good energy absorption capacity.
  • FIG. 1 shows a typical course of the temperature T over the time t, which is maintained during the execution of a method according to the invention. Accordingly, as a starting material to be deformed in each case to a steel component, for example, provided with a corrosion-protective AlSi coating steel plate first heated to an austenitizing TA, which is below the Ac3 temperature but above the AcI temperature of the steel, from which the steel plate respectively is made. In the case of this
  • Austenitizing temperature TA the Stahlplatme is held for a time tA until the steel plate is completely soaked through, so that there is an existing austenite and ferrite Mischgefuge.
  • a in Fig. 1 The area where the steel has a groove is indicated by A in Fig. 1, while the area of the mixed ferrite and austenite core is indicated by "A + F”.
  • the steel plate After the end of the austenitizing time tA, the steel plate is transported to a press forming tool.
  • the transfer time required until the mold is closed is designated tT in FIG.
  • the temperature TW at which the steel plate enters the die is still within the temperature range Ac3 - AcI.
  • the press mold is equipped with a tempering device, which keeps it at a constant temperature, which corresponds to the Ba mitleitersstemperatur TB.
  • the shaped steel part formed from the steel plate and coming into direct contact with the press mold is accordingly cooled to the bainitizing temperature TB over a cooling time tK.
  • the bainitization temperature TB is above the martensite start temperature Ms but below the pearlite transformation temperature.
  • M m Fig. 1 marked with P.
  • F indicates the area where pure ferrite is present and M denotes the area in which martensite is present.
  • the steel component still sitting in the die is kept isothermal at the bainitizing temperature TB for a period of time tB.
  • the Baimtleiterszeit tB is dimensioned so that at its end the Gefuge of the steel component is substantially completely baimtisch.
  • the cooling of the steel plate in the tempered pressing tool takes place within the cooling time tK so fast that the steel passes through the two-phase mixing area A + F and conversion in the martensite area M and perlite area P is prevented, wherein the martensite formation is avoided as completely as possible.
  • the tool closing time tW which comprises the cooling time tK and the bainitization time tB, is 5 to 60 seconds, depending on the complexity of the shape of the steel component to be produced and the sheet thickness of the respectively processed steel plate.
  • the first steel plate SPl has been heated to an austenitizing temperature TA of 780 0 C and maintained at this temperature TA for a Austenitmaschineszeit tA of 6 min.
  • the steel plate SPI has been transported in a 6 to 12 s transfer time tT in air in a press mold, which has been heated to a bainitization temperature TB of 400 0 C and kept constant at this temperature TB.
  • Pressing tool has been press-formed over a tool closing time tW of 40 s.
  • the total press temperature t comprised the cooling time IK in which the steel plates SPl had been cooled from the tool inlet temperature TW to the Bamitis release temperature TB, and the bittitization time tB in which the bamit fusion was formed in the steel component hot-press-forged in the press forming tool.
  • the pressing tool has been opened and the steel component has been cooled to room temperature in still air.
  • the Gefuge of the thus obtained steel molding had a Fer ⁇ tantei] of 50%, a Baimtanteil of 40%, a Restauustemtanteil of 6% and a Martensitanteil of 4%.
  • the inventive baini tables press hardening is thus a process for hot pressing, in which instead of the usually produced Martensitgefuges a predominantly consisting of ferrite and bainite Gefuge is set by an isothermal conversion during press-hardening on each press-formed steel component.
  • the resulting ferritic / bainitic structure has improved residual elongation at high strength compared to martensite.

Abstract

In order to produce formed steel parts in a simple process, said parts having high strength and good residual elongation at break, according to the invention a primary steel material is provided which (in % by weight) comprises C: 0.02 - 0.6%, Mn: 0.5 - 2.0%, Al: 0.01 - 0.06%, Si: max. 0.4%, Cr: max. 1.2%, P: max. 0.035%, S: max. 0.035%, and optionally one or more of the elements of the "Ti, Cu, B, Mo, Ni, N" group, with the proviso that Ti: max. 0.05%, Cu: max. 0.01%, B: 0.0008 - 0.005%, Mo: max. 0.3%, Ni: max. 0.4%, N: max. 0.01%, and the remainder as iron and inevitable contamination. The primary material is heated through at a heating temperature (TA) ranging between the AcI and Ac3 temperature such that at best incomplete austenitization of the primary material takes place, is placed into a press-form tool and formed therein into the formed steel part. The formed steel part is then heated to a bainite forming temperature (TB), which is above the martensite starting temperature (Ms), however below the perlite transformation temperature of the steel from which the primary material is produced in each case. After cooling, it is maintained for an austempering period (tB) at the bainite forming temperature (TB) in a substantially isothermic manner until the formed steel part has produced a structure comprising predominantly ferrite and bainite, the martensite content thereof being < 5%, wherein residual austenite contents of ≤ 10% may be present. After the end of the austempering period (tB), the formed steel part is brought to room temperature. ..

Description

Verfahren zum Herstellen eines Stahlformteils mit einem überwiegend ferritisch-bainitischen Gefüge Process for producing a steel molding having a predominantly ferritic-bainitic structure
DJ e Erfindung betrifft ein Verfahren zum Herstellen eines Stahlformteils mit einem überwiegend ferritisch- bainitischen Gefuge.DJ e invention relates to a method for producing a steel molding with a predominantly ferritic-bainitic Gefuge.
Um die sich im modernen Karosseriebau bestehende Forderung nach geringem Gewicht bei gleichzeitig maximaler Festigkeit und Schutzwirkung zu erfulien, werden heutzutage in solchen Bereichen der Karosserie, die im Fall eines Crashs besonders hohen Belastungen ausgesetzt sein können, warmpressgeformte Bauteile eingesetzt, die aus hochfesten Stahlen erzeugt sind. A] s Beispiele für solche Stahlformteile sind die A- und B- Saule, die Stoßfanger und Turaufpralltrager eines Personenkraftfahrzeugs zu nennen.In order to satisfy the requirement for low weight with maximum strength and protective effect that exists in modern body construction, hot-press molded components produced from high-strength steel are nowadays used in those areas of the body which may be exposed to particularly high loads in the event of a crash , Examples of such steel moldings are the A and B pillars, called the Stoßfanger and Turaufpralltrager a passenger car.
Beim Warmpressharten von Stahlplatinen, die von kalt- oder warmgewalztem Stahlband abgeteilt sind, werden die betreffenden Blechzuschnitte auf eine in der Regel oberhalb der Austenitisierungstemperatur des jeweiligen Stahls liegende Verformungstemperatur erwärmt und im erwärmten Zustand in das Werkzeug einer Umformpresse gelegt. Im Zuge der anschließend durchgeführten Umformung erfahrt der Blechzuschnitt bzw. das aus ihm geformte Bauteil durch den Kontakt mit dem kühlen Werkzeug eine schnelle Abkühlung, durch die sich im Bauteil Hartegefuge ergibt. Dabei kann es ausreichend sein, wenn das Bauteil ohne aktxve Kühlung alleine durch den Kontakt mit dem Werkzeug abkühlt. Unterstutzt werden kann eine schnelle Abkühlung jedoch auch dadurch, dass das Werkzeug selbst aktiv gekühlt wird.In the hot press hardening of steel blanks, which are separated from cold or hot rolled steel strip, the sheet metal blanks concerned are heated to a generally above the Austenitisierungstemperatur of the respective steel deformation temperature and placed in the heated state in the tool of a forming press. In the course of the subsequently carried out deformation, the sheet metal blank or the component formed from it experience a contact with the cool tool rapid cooling, which results in hardened components in the component. It may be sufficient if the component cools without aktxve cooling only by the contact with the tool. However, rapid cooling can also be supported by the fact that the tool itself is actively cooled.
Wie im Artikel "Potenziale für den Karosserieleichtbau" , erschienen in der Messezeitung der ThyssenKrupp Automotiv AG zur 61. Internationalen Automobilausstellung in Frankfurt, 15.-25. Sept. 2005, berichtet, wird das Warmpressharten in der Praxis insbesondere für die Herstellung von hochfesten Karosseriebauteilen aus borlegierten Stahlen angewendet. Ein typisches Beispiel für einen solchen Stahl ist der unter der Bezeichnung 22MnB5 bekannte Stahl, der im Stahlschlussel 2004 unter der Werkstoffnummer 1.5528 zu finden ist.As in the article "Potentials for lightweight body construction", published in the fair newspaper of ThyssenKrupp Automotiv AG for the 61st International Motor Show in Frankfurt, 15.-25. Sept. 2005, reports that hot press-hardening is used in practice in particular for the production of high-strength body components made of boron-alloyed steel. A typical example of such a steel is the steel known under the name 22MnB5, which can be found in the steel key 2004 under the material number 1.5528.
Em mit dem Stahl 22MnB5 vergleichbarer Stahl ist aus der JP 2006104526 A bekannt. Dieser bekannte Stahl enthalt neben Fe und unvermeidbaren Verunreinigungen (xn Gew.-%) 0,05 - 0,55 % C, max. 2 % Si, 0,1 - 3 % Mn, max . 0,1 % P und max. 0,03 % S. Zur Hartesteigerung können dem Stahl zusatzlich Gehalte von 0,0002 - 0,005 % B und 0,001 - 0,1 % Ti zugegeben werden. Der jeweilige Ti- Gehalt dient dabei zum Abbinden des in dem Stahl vorhandenen Stickstoffs. Auf diese Weise kann das im Stahl vorhandene Bor seine festigkeitssteigernde Wirkung möglichst vollständig entfalten.Em steel comparable to steel 22MnB5 is known from JP 2006104526A. This known steel contains in addition to Fe and unavoidable impurities (xn wt .-%) 0.05 - 0.55% C, max. 2% Si, 0.1-3% Mn, max. 0.1% P and max. 0.03% S. To increase the hardness, additional amounts of 0.0002 - 0.005% B and 0.001 - 0.1% Ti can be added to the steel. The respective Ti content serves to bind the nitrogen present in the steel. In this way, the boron present in the steel can develop its strength-increasing effect as completely as possible.
Gemäß der JP 2006104526 A werden aus dem derart zusammengesetzten Stahl zunächst Bleche gefertigt, die dann auf eine oberhalb der ÄC3-Temperatur, typischerweise im Bereich von 850 - 950 0C, liegende Temperatur vorgewärmt werden. Bei der anschließend im Presswerkzeug erfolgenden, von diesem Temperaturbereich ausgehenden schnellen Abkühlung bildet sich im aus dem jeweiligen Blechzuschnitt pressgeformten Bauteil das die angestrebten hohen Festigkeiten gewahrleistende martensitische Gefuge. Gunstig wirkt sich dabei aus, dass sich die auf das genannte Temperaturniveau erwärmten Blechteile bei relativ geringen Umformkraften zu komplex geformten Bauteilen umformen lassen. Dies gilt insbesondere auch für solche Blechteile, die aus hochfestem Stahl gefertigt und mit einer Korrosionsschutzbeschichtung versehen sind.According to JP 2006104526 A, sheets made of the composite steel in this way are first produced be preheated 950 0 C, lying temperature - then to an above the AEC 3 temperature, typically in the range of 850th During the subsequent rapid cooling in the pressing tool, starting from this temperature range, the martensitic joint, which ensures the desired high strength, is formed in the component molded from the respective sheet metal blank. It has a favorable effect that the sheet metal parts heated to the stated temperature level can be formed into complex shaped components at relatively low forming forces. This is especially true for such sheet metal parts, which are made of high-strength steel and provided with a corrosion protection coating.
Die auf die voranstehend erläuterte Weise aus borlegierten Stahlen erzeugten Bauteile erreichen Festigkeiten von über 1.500 MPa. Allerdings hat das dazu benotigte vollständig martensitische Gefuge der Bauteile zur Folge, dass die Bauteile eine für viele Anwendungen unzureichende Restbruchdehnung von 5 - 6 % besitzen. Die relativ geringe Restbruchdehnung geht mit einer geringen Zähigkeit einher. Diese führt bei Anwendungen, bei denen es auf ein gutes Verformungsverhalten im Falle eines Crashs ankommt, dazu, dass aus borlegierten Stahlen in der bekannten Weise hergestellte Bauteile, diese Anforderungen häufig nicht mehr erfüllen. Dies gilt insbesondere dann, wenn es sich bei den herzustellenden Bauteilen um Teile für eine Automobilkarosserie handelt.The components produced from boron-alloyed steels in the above-described manner achieve strengths of more than 1,500 MPa. However, the required complete martensitic structure of the components has the result that the components have an insufficient residual elongation at break of 5-6% for many applications. The relatively low residual elongation at break is associated with a low toughness. In the case of applications in which good deformation behavior is required in the event of a crash, this leads to components made of boron-alloyed steel in the known manner frequently no longer meeting these requirements. This applies in particular when the components to be produced are parts for an automobile body.
In der DE 10 2005 054 847 B3 ist vorgeschlagen worden, durch eine nachgeschaltete Wärmebehandlung das Crashvcrhalton von durch Warmpressharten erzeugten Stahlbauteilen zu verbessern, die neben Eisen und unvermeidbaren Verunreinigungen (m Gew.-%) 0,18 - 0,3 % C, 0,1 - 0,7 % Si, 1,0 - 2,50 % Mn, max. 0,025 % P, 0,1 - 0,8 % Cr, 0,1 - 0,5 % Mo, max. 0,01 % S, 0,02 - 0,05 % Ti, 0,002 - 0,005 % B und 0,01 - 0,06 % Al enthalten. Im Zuge der Wärmebehandlung werden die warmpressgeharteten Bauteile bei 320 - 400 0C gehalten. Abgesehen davon, dass ein solcher Warmebehand] ungsschritt nur mit großem Aufwand in die für die Herstellung von warmpressgeharteten Stahl bauten len etablierte Prozesskette eingegliedert werden kann, haben praktische Untersuchungen gezeigt, dass die Bruchdehnung von auf diese Weise warmebehandelten Bauteilen sich deutlich verschlechtert .In DE 10 2005 054 847 B3 has been proposed by a downstream heat treatment the To improve crash resistance of steel components produced by hot press hardening, which besides iron and unavoidable impurities (m% by weight) 0.18-0.3% C, 0.1-0.7% Si, 1.0-2.50% Mn, max. 0.025% P, 0.1-0.8% Cr, 0.1-0.5% Mo, max. 0.01% S, 0.02-0.05% Ti, 0.002-0.005% B and 0.01-0.06% Al. In the course of heat treatment, the warmpressgeharteten components at 320 to - 400 0 C maintained. Apart from the fact that such a heat treatment step can only be incorporated with great effort into the process chain established for the production of hot-press-hardened steel, practical investigations have shown that the elongation at break of components heat-treated in this way deteriorates markedly.
Eine andere Möglichkeit der Herstellung eines geharteten metalli sehen Bauteils ist aus der DE 102 08 216 Cl bekannt. Bei diesem bekannten Verfahren wird eine Platine oder ein vorgeformtes Formbauteil, die jeweils aus einem Stahl der voranstehend angegebenen Art bestehen, in einer Erwarmungseinrichtung auf eine Austenitisierungstemperatur erwärmt und anschließend über einen Transportweg einem Harteprozess zugeführt. Wahrend des Transports werden Teilbereiche erster Art der Platine oder des Formbauteils, die im Endbauteil höhere Dukti litatseigenschaften aufweisen sollen, von einer vorbestimmten Abkuhl-Starttemperatur abgeschreckt, die oberhalb der γ-α-Umwandlungstemperatur liegt. Dieses Abschrecken wird beendet, wenn eine vorgegebene Abkuhl-Stopptemperatur erreicht ist, und zwar bevor eine Umwandlung in Ferrit und/oder Perlit stattgefunden hat oder nachdem erst eine geringe Umwandlung in Ferrit und/oder Perlit stattgefunden hat. Anschließend wird die Platine oder das jeweilige Formteil isotherm zur Umwandlung des Austenits in Ferrit und/oder Perlit gehalten. Währenddessen wird m den Bereichen zweiter Art, die im Endbauteil im Verhältnis geringere Duktili tatseigenschaften aufweisen sollen, die Hartetemperatur gerade so hoch gehalten, dass eine ausreichende Martensitbildung in den Bereichen zweiter Art wahrend eines Harteprozesses stattfinden kann. Abschließend wird dann die Abkühlung durchgeführt. Dazu wird das erhaltene Formteil in einem separaten Arbeitsgang in ein Abschreckbecken oder desgleichen getaucht, um das gewünschte martensitische Hartegefuge auszubilden. Auch diese Verfahrensweise bedingt eine Prozessfuhrung, die nur mit großem Aufwand in einen modernen Produktionsbetrieb eingegliedert werden kann. Darüber hinaus besteht auch bei den nach diesem bekannten Verfahren hergestellten Bauteilen das Problem, dass sie zwar eine hohe Festigkeit besitzen, gleichzeitig aber so spröde sind, dass sie den in der Praxis sich stellenden Anforderungen an ihre Verformbarkeit nicht gerecht werden.Another way of producing a hardened metalli see component is known from DE 102 08 216 Cl. In this known method, a board or a preformed mold component, each consisting of a steel of the above type, heated in a heating device to an austenitizing and then fed via a transport path to a hardening process. During transport portions of the first type of board or of the molded component, which are intended to have higher ductility properties in the final component, are quenched from a predetermined cooling start temperature which is above the γ-α transformation temperature. This quenching is terminated when a predetermined cooling stop temperature is reached, before conversion to ferrite and / or pearlite has taken place or after a slight conversion in ferrite and / or perlite. Subsequently, the board or the respective molded part is held isothermally to convert the austenite into ferrite and / or perlite. In the meantime, the tempering temperature of the areas of the second kind, which should have relatively lower ductile properties in the final component, is kept just high enough for sufficient martensite formation to take place in the areas of the second type during a hardening process. Finally, then the cooling is carried out. For this purpose, the resulting molded part is immersed in a separate operation in a quenching tank or the like to form the desired martensitic Hartegefuge. This procedure also requires a Prozeßfuhrung that can be incorporated only with great effort in a modern production plant. In addition, there is also the problem with the components produced by this known method, that while they have a high strength, they are at the same time so brittle that they do not meet the requirements for their deformability which are set in practice.
Vor dem Hintergrund des voranstehend erläuterten Standes der Technik bestand die Aufgabe der Erfindung darin, ein Verfahren anzugeben, mit dem es möglich ist, auf prozesstechnisch einfache Weise Stahlformtei Ie herzustellen, bei denen eine hohe Festigkeit mit einer guten Restbruchdehnung kombiniert ist.Against the background of the prior art described above, the object of the invention was to provide a method with which it is possible to produce in a process-technically simple manner Stahlformtei Ie in which a high strength is combined with a good residual elongation at break.
Diese Aufgabe ist erfi ndungsgemaß durch das in Anspruch 1 angegebene Verfahren gelost worden. Vorteilhafte Ausgestaltungen dieses Verfahrens sind in den auf Anspruch 1 ruckbezogenen Ansprüchen angegeben.This object has been erfi ndungsgemaß solved by the method specified in claim 1. advantageous Embodiments of this method are given in the claims based on claim 1.
Gemäß der Erfindung wird ein Stahlformteil mit einem überwiegend ferritisch-baimtischen Gefuge hergestellt.According to the invention, a steel shaped part is produced with a predominantly ferritic-Bavarian mesh.
Dazu wird ein Vormaterial in Form einer Stahlplatine oder eines vorgeformtes Stahlteils bereitgestellt. Wird eine bis dahin noch unverformte Stahlplatine als Vormaterial verarbeitet, wird der Gesamtprozess als "einstufiges" Verfahren bezeichnet. Wird dagegen ein vorgeformtes Stahlteil verarbeitet, spricht man von einem zweistufigen Prozess, wobej in der ersten Stufe eine bis dahin noch unverformte Platine so verformt wird, dass das dabei erhaltene Stahlbauteil seine Endform noch nicht erreicht hat.For this purpose, a starting material in the form of a steel plate or a preformed steel part is provided. If a hitherto undeformed steel plate is processed as a starting material, the entire process is referred to as a "one-step" process. If, on the other hand, a preformed steel part is processed, this is referred to as a two-stage process, whereby in the first stage a previously undeformed blank is deformed so that the steel component thus obtained has not yet reached its final shape.
Das jeweilige Vormaterial besteht erfindungsgemaß aus einem Stahl an sich bekannter Zusammensetzung, der neben Eisen und unvermeidbaren herstellungsbedingten Verunreinigungen (in Gew.-%) C: 0,02 - 0,6 %, Mn: 0,5 - 2,0 %, Al: 0,01 - 0,06 %, Si: bis zu 0,4 %, Cr: bis zu 1,2 %, P: bis zu 0,035 %, S: bis zu 0,035 % sowie optional eines oder mehrere Elemente aus der Gruppe "Ti, B, Mo, Ni, Cu, N" enthalt, wobei - sofern jeweils vorhanden - Ti in einem Gehalt von bis zu 0,05 %, Cu in einem Gehalt von bis zu 0,01 %, B in Gehalten von 0,0008 - 0,005 %, Mo in Gehalten von bis zu 0,3 %, Ni in Gehalten von bis zu 0,4 %, N m Gehalten von bis zu 0,01 %, enthalten sind. Besondere Bedeutung im Hinblick auf die Festigkeit erfindungsgemaß erzeugte Bauteile kommt dabei dem jeweiligen C-Gehalt zu, wogegen insbesondere die Gehalte an Si, Mn, Cr und B so eingestellt sind, dass die Bildung des Bainits gefordert und die Entstehung größerer Martensitmengen im Gefuge des Bauteils vermieden werden.According to the invention, the respective starting material consists of a steel of a known composition which, in addition to iron and unavoidable production-related impurities (in% by weight) C: 0.02-0.6%, Mn: 0.5-2.0%, Al : 0.01 - 0.06%, Si: up to 0.4%, Cr: up to 1.2%, P: up to 0.035%, S: up to 0.035% and optionally one or more elements from the group "Ti, B, Mo, Ni, Cu, N", wherein - if present - Ti in a content of up to 0.05%, Cu in a content of up to 0.01%, B in contents of 0 , 0008 - 0.005%, Mo in contents of up to 0.3%, Ni in contents of up to 0.4%, N m contents of up to 0.01%. Particular importance in terms of strength according to the invention produced components comes here to the respective C content, whereas in particular the contents of Si, Mn, Cr and B so are adjusted so that the formation of bainite required and the emergence of larger amounts of martensite in the Gefuge of the component are avoided.
Das derart zusammengesetzte Vormaterial (S tahlplatα ne bzw, vorgeformtes Stahlteil) wird bei einer zwischen der AcI- und der Ac3-Temperatur des Stahls liegenden Erwarmungstemperatur derart durcherwarmt , dass eine unvollständige Austenitisierung des Vormaterials eintritt. Am Ende der Austenitisierungsphase besteht das Gefuge des Vormaterials dementsprechend aus Ferrit und Austenit .The as-assembled starting material (steel plate or preformed steel part) is soaked through at a heating temperature lying between the AcI and the Ac3 temperature of the steel such that incomplete austenitisation of the starting material occurs. Accordingly, at the end of the austenitizing phase, the microstructure of the starting material consists of ferrite and austenite.
Anschließend wird das Vormateπal in ein Pressformwerkzeug eingelegt und darin zu dem Stahl formteil geformt. Das Pressharten erfolgt dabei in einem Temperaturbereich, in dem sich das Gefuge des Vormaterials im Zweiphasengebiet aus Ferrit und Austenit befindet .Subsequently, the Vormateπal is placed in a press mold and molded therein to the steel molding. Press-hardening takes place in a temperature range in which the microstructure of the primary material in the two-phase region is composed of ferrite and austenite.
Wesentlich für die Erfindung ist nun, dass das Stahlformteil auf eine Bainitbildungstemperatur gebracht wird, die oberhalb der Martensitstarttemperatur, jedoch unterhalb der Perlitumwandlungstemperatur des Stahls liegt, aus dem die Stahlplatine oder das vorgeformte Stahl teil jeweils hergestellt sind.Essential to the invention is now that the steel molding is brought to a bainite formation temperature, which is above the Martenitstarttemperatur, but below the Perlitumwandlungstemperatur the steel from which the steel plate or the preformed steel part are each made.
Ebenso wichtig ist, dass, sobald dieseEqually important is that once these
Bainitbildungstemperatur erreicht ist, das Stahlformteil erfindungsgemaß über eine Bainitisierungszeit im Wesentlichen isotherm auf der Bainitbildungstemperatur gehalten wird, bis sich in dem Stahlformteil ein Gefuge eingestellt hat, das zum überwiegenden Teil aus Ferrit und Bainit besteht. Die jeweils einzustellende Bainitisierungstemperatur richtet sich nach der Bainitumwandlungstemperatur , welche jeweils nach der chemischen Zusammensetzung des angereicherten Austenits durch die Martensitstarttemperatur nach unten und Perlitumwandlungstemperatur nach oben abgegrenzt ist.Bainitbildungstemperatur is achieved, the steel mold part according to the invention is kept substantially isothermally on the Bainitbildungstemperatur over a bainitization time until a Gefuge has set in the steel mold part, the majority of ferrite and bainite exists. The bainitization temperature to be set in each case depends on the bainite transformation temperature, which is differentiated upward in each case according to the chemical composition of the enriched austenite by the martensite start temperature and perlite transition temperature.
Die Abkühlgeschwind! gkeit beim Pressharten wird von der Austenitisierungs- und Werkzeugtemperatur maßgeblich beemflusst. Diese muss so schnell sein, dass die Platine umwandlungsfrei auf die Bainitumwandlungstemperatur abgekühlt und bei dieser Temperatur konstant gehalten wird. Durch diese Vorgehensweise wird erreicht, dass am Ende der Bamitisierungszeit in dem Stahlformteil ein Gefuge vorliegt, das neben den ferritischen und baimtischen Gefugeanteilen untergeordnete Mengen an Restaustenit und allenfalls unterhalb von 5 % liegende Gehalte an Martensit aufweist. Die vom im Wesentlichen vom Kohlenstoffgehalt bestimmten Restaustenitgehalte im erhaltenen Bauteil können bis zu 10 % betragen.The cooling rate! Press hardening is significantly influenced by the austenitizing and mold temperature. This must be so fast that the board is cooled without conversion to the Bainitumwandlungstemperatur and kept constant at this temperature. By this procedure it is achieved that at the end of Bamitisierungszeit in the steel mold part is a Gefuge, which has in addition to the ferritic and Bavarian constituent parts minor amounts of retained austenite and possibly below 5% levels of martensite. The residual austenite contents in the resulting component, which are essentially determined by the carbon content, can be up to 10%.
Nach dem Ende der Bamitisierungszeit wird das Stahlformteil auf Raumtemperatur abgekühlt.After the bamitization time has ended, the steel mold is cooled to room temperature.
Gemäß der Erfindung wird also die Temperaturfuhrung im Hinblick auf den Austenitisierungsprozess und das anschließende Pressharten so gesteuert, dass sich ein Mischgefuge aus Ferrit, Bainit und einem Anteil von Restaustenit im Bauteil einstellt . Das erfmdungsgemaße Verfahren liefert somit ein Stahlbauteil, dessen Gefuge durch eine ferπtisch-bainitische Mikrostruktur gekennzeichnet ist. Diese bainitische Mikrostruktur verleiht einem erfxndungsgemaß erzeugten Bauteil verbesserte Verformungsei genschaften, insbesondere eine verbesserte Restbruchdehnung. Damit einhergehend weisen erfindungsgemaß erzeugte Stahlformtei Ie ein verbessertes Crashverhalten auf, ohne dass es dazu einer gesonderten Anlassbehandlung bedarf, da Bainit als eine Art von angelassenem Martensit angesehen werden kann.According to the invention, therefore, the temperature control is controlled with respect to the austenitizing process and the subsequent press-hardening in such a way that a mixture of ferrite, bainite and a proportion of retained austenite in the component is established. The erfmdungsgemaße method thus provides a steel component whose Gefuge is characterized by a ferπtisch-bainitische microstructure. This bainitic microstructure gives a component produced erfxndungsgemaß improved Verformungsei properties, in particular an improved residual elongation at break. Along with this, steel moldings produced according to the invention have an improved crash behavior, without the need for separate tempering treatment, since bainite can be regarded as a type of tempered martensite.
Darüber hinaus erlaubt es das erfmdungsgemaße Verfahren, das Stahlbauteil langsamer abzukühlen als bei den konventionellen Verfahren, bei denen die Abkühlung im Werkzeug mit dem Ziel erfolgt, martensitisches Hartegefuge zu erzeugen. Daher ist bei einem erf i ndungsgemaßen Verfahren die Gefahr der Entstehung von Bauteilverzug minimiert und die erfindungsgemaß erzeugten Bauteile zeichnen sich durch eine besonders hohe Maßhaltigkeit aus . Um eine langsame Abkühlung des Stahlbauteils sicherzustellen, kann zur Durchfuhrung des erfi ndungsgemaßen Verfahrens das Presswerkzeug auch gezielt erwärmt werden.In addition, the erfmdungsgemaße method allows the steel component to cool more slowly than in the conventional method in which the cooling takes place in the tool with the aim to produce martensitic Hartegefuge. Therefore, in a erfI ndungsgemaßen process, the risk of the formation of component distortion is minimized and the components produced according to the invention are characterized by a particularly high dimensional stability. In order to ensure a slow cooling of the steel component, the pressing tool can also be specifically heated to carry out the method according to the invention.
Neben den voranstehend genannten Vorteilen bestehen weitere Vorteile der Erfindung in der durch die vergleichbar niedrigen Ofentemperatur bei der Austemtisierung möglichen Energieeinsparungen, in der reduzierten thermischen Belastung der gegebenenfalls vorhandenen Oberflachenbeschichtung, in dem durch die abgesenkte Ofentemperatur bei der Austemtisierung möglichen Einsatz von Zn-beschichtetem Vormaterial sowie darin, dass es bei erfmdungsgemaßer Vorgehensweise möglich ist, durch Variation der Austemtisierungs- und Werkzeugtemperatur die mechanischen Kennwerte nach der Baut ej Iforderung variabel einzustellen. Schließlich zeichnen sich erfindungsgemaß erzeugte Stahlformteile auch durch ein hohes Bake-Hardening Potenzial nach dem Pressharten aus.In addition to the above-mentioned advantages, there are further advantages of the invention in the energy savings possible by the comparatively low furnace temperature during austempering, in the reduced thermal load of the surface coating which may be present, in which the use of Zn-coated starting material, which may be due to the lowered furnace temperature during the austempering, and The fact that it is possible with erfmdungsgemaßer approach, by varying the Austemtisierungs- and tool temperature, the mechanical characteristics of the Builds a request variable. Finally, steel moldings produced according to the invention are also characterized by a high bake-hardening potential after press-hardening.
Um die mit der Erfindung erzielten vorteilhaften Eigenschaften besonders sicher nutzen zu können, sollten die Ferrit- und Baimtanteile im Gefuge des Stahlformteils am Ende der Bainitisierungszeit Jn Summe mindestens 90 % betragen, wobei der Ferrit- und der Bainitanteil jeweils mindestens 30 % betragen sollten.In order to be able to use the advantageous properties achieved with the invention particularly safely, the ferrite and Baimtanteile should be in the Gefuge of the steel molding at the end of Bainitisierungszeit Jn sum at least 90%, the ferrite and bainite each should be at least 30%.
Da die Martcnsα tbildung erfindungsgemaß möglichst vollständig verhindert wird, ist es grundsätzlich vorteilhaft, wenn am Ende der Bainitisierungszeit der Martensitanteil des Stahlformteils weniger als 1 % betragt, insbesondere nur auf Spuren beschrankt ist.Since the curing according to the invention is prevented as completely as possible, it is fundamentally advantageous if, at the end of the bainitization time, the martensite portion of the steel molding is less than 1%, in particular limited to tracks.
Von der Legierung des Stahls, aus dem das erfindungsgemaß zu verarbeitende Vormaterial besteht, sind konventionelleThe alloy of the steel from which the starting material to be processed according to the invention is conventional
MnB-Stahle und Vergütungsstähle gleichermaßen umfasst. Eine für die Durchfuhrung des erfindungsgemaßen Verfahrens besonders geeigneter Vergütungsstahl weist neben Eisen und unvermeidbaren Verunreinigungen (in Gew.-%) C:MnB steels and tempered steels alike. A particularly suitable for the implementation of the inventive method tempered steel has in addition to iron and unavoidable impurities (in wt .-%) C:
0,25 - 0,6 %, Si: bis zu 0,4 %, Mn: 0,5 - 2,0 %, Cr: bis zu0.25 - 0.6%, Si: up to 0.4%, Mn: 0.5 - 2.0%, Cr: up to
0,6 %, P: bis zu 0,02 %, S: bis zu 0,01 %, Al:0.6%, P: up to 0.02%, S: up to 0.01%, Al:
0,01 - 0,06 %, Ti: bis zu 0,05 %, Cu: bis zu 0,1 % und0.01 - 0.06%, Ti: up to 0.05%, Cu: up to 0.1% and
B: 0,008 - 0,005 % auf. Für das erfindungsgemaße Verfahren in Frage kommende MnB-Stahle weisen dagegen C: 0,25 - 0,6B: 0.008 - 0.005%. In contrast, MnB steels which are suitable for the process according to the invention have C: 0.25-0.6
%, Si: bis zu 0,4 %, Mn: 0,5 - 2,0 %, Cr: bis zu 1,2 %, P: bis zu 0,035 %, S: bis zu 0,035 %, Mo: bis zu 0,3 %, Ni: bis zu 0,4 % und Al: 0,01 - 0,06 % auf. Typischerweise liegt die Austenitisierungstemperatur der Stahle, aus denen erfindungsgemaß verarbeitetes Vormaterial hergestellt ist, im Bereich von 750 - 810 0C. Die für das Durcherwarmen bei der Erwarmungstemperatur vorgesehene Erwärmungszeit liegt dabei üblicherweise im Bereich von 6 - 15 Minuten.%, Si: up to 0.4%, Mn: 0.5-2.0%, Cr: up to 1.2%, P: up to 0.035%, S: up to 0.035%, Mo: up to 0 , 3%, Ni: up to 0.4% and Al: 0.01-0.06%. Typically, the austenitizing temperature of the steels, which is made of processed accordance with the invention starting material, in the range 750-810 0 C. The intended for the Durcherwarmen at the warming temperature heating time is typically in the range 6 - 15 minutes.
Insbesondere bei der Herstellung von Stahlformteilen, die zum Bau von Karosserien für Fahrzeuge, insbesondere Automobile, bestimmt sind, ist es gunstig, wenn das Vormaterial mit einem vor Korrosion schutzenden metallischen Überzug versehen ist. Dieser Überzug schützt das jeweilige Vormaterial (Stahlplatine, vorgeformtes Stahlteil) auch beim Transport von dem Ofen, in dem es auf die Austenitisierungstemperatur vorerwarmt wird, zum Pressformwerkzeug. Die Korrosionsschutzbeschichtung kann dabei so ausgelegt werden, dass sie eine Oxidation des heißen Stahl Substrats mit dem Umgebungssauerstoff auch bei einem Transport an Luft schützt.In particular, in the production of steel moldings, which are intended for the construction of bodies for vehicles, especially automobiles, it is advantageous if the starting material is provided with a corrosion-protecting metallic coating. This coating also protects the respective starting material (steel plate, preformed steel part) from the press mold during transport from the oven, in which it is preheated to the austenitizing temperature. The corrosion protection coating can be designed so that it protects an oxidation of the hot steel substrate with the ambient oxygen even when transported in air.
Eine besonders praxisgerechte Variante des erfmdungsgemaßen Verfahrens ist dadurch gekennzeichnet, dass die Pressformgebung und die Bainitisierung des im Zuge der Pressformgebung erzeugten Stahlbauteils im Pressformwerkzeug erfolgt. Dementsprechend sieht eine besonders vorteilhafte Variante der Erfindung vor, dass nach dem Pressformen des Vormaterials das dann erhaltene Stahlformteil in dem Pressformwerkzeug verbleibt und dort auf die Bamitbildungstemperatur gebracht und für die Bamitisierungszeit gehalten wird. Dabei ist das Pressformwerkzeug bevorzugt so temperiert, dass das Vormaterial ausgehend von einer über der Bainitisi erungstemperatur liegenden Temperatur berexts wahrend ihrer Pressverformung zu dem Stahlbauteil auf die Ba Lnitisierungstemperatur abgekühlt werden. Die Werkzeugschließzeit des Presswerkzeugs, innerhalb der die Formgebung, Abkluhlung und Bainitisierung des Stahlformteils erfolgt, betragt in diesem Fall üblicherweise 5 - 60 Sekunden, insbesondere 20 - 60 Sekunden.A particularly practical variant of the method according to the invention is characterized in that the press forming and the bainitization of the steel component produced in the course of the press forming takes place in the press forming tool. Accordingly, a particularly advantageous variant of the invention provides that after the compression molding of the starting material, the steel mold part then obtained remains in the compression mold and brought there to the Bamitbildungstemperatur and kept for the Bamitisierungszeit. In this case, the press mold is preferably tempered so that the starting material, starting from one above the Bainitisi tion temperature lying temperature during their compression deformation to the steel component to the Ba Lnitisierungstemperatur be cooled. The tool closing time of the pressing tool, within which the shaping, Abkluhlung and Bainitisierung of the steel molding takes place in this case is usually 5 - 60 seconds, especially 20 - 60 seconds.
Im Fall , dass die Abkühlung auf dieIn the event that the cooling on the
Bainitisierungstemperatur und die Bainitisierung in einem Werkzeug absolviert werden, ist die Bainitisierungszeit jeweils um die Zeitdauer kurzer als dieBainitisierungstemperatur and bainitization are completed in a tool, the bainitization time is shorter in each case by the time duration
Werkzeugschließzeit, die benotigt wird, um das jeweilige Vormaterial auf die Bainitisierungstemperatur zu bringen.Tool closing time, which is required to bring the respective starting material to the Bainitisierungstemperatur.
Alternativ zu einer Bainitisierung im Pressformwerkzeug ist es auch denkbar, nach dem Pressformen das aus dem Vormaterial pressgeformte Stahlformteil aus der Pressform zu entnehmen und in einem separaten Arbeitsgang auf die Bainitbildungstemperatur zu bringen und auf dieser über die Bainitj SD erungszeit zu halten. Eine solche Vorgehenswei se kann angezeigt sein, wenn eine entsprechende Anlagentechnik zur Verfugung steht. So lasst sich eine solche Vorgehensweise beispielsweise dann anwenden, wenn zum Erwarmen auf und Halten bei der Bainitisierungstemperatur ein SaI z- oder ein Bleibad zur Verfugung stehen, in die das Stahlbauteil nach der Pressformgebung verbracht werden kann.As an alternative to bainitization in the press-forming tool, it is also conceivable to remove the press-formed from the starting material steel molding from the mold after pressing and to bring in a separate operation on the Bainitbildungstemperatur and keep on this over the Bainitj SD erungszeit. Such a procedure may be indicated if appropriate system technology is available. Thus, such an approach can be used, for example, when a SaI z- or a lead bath are available for heating and holding at the Bainitisierungstemperatur in which the steel component can be spent after the press molding.
Der typische Bereich der Bainitisierungstemperatur, bei der die erfindungsgemaße Baintisierung mit dem Ziel der Ausbildung eines ferritisch/bainitischen Gefuges bevorzugt durchgeführt wird, ist nach unten typischerweise durch Martensitstarttemperatur der [jeweiligen Stahlzusammensetzung des Vormaterials begrenzt, wahrend sie nach oben hin jeweils niedriger als 500 0C eingestellt werden kann, um die Perlitbildung zu vermeiden .The typical range of the bainitization temperature at which the baintization according to the invention with the aim of Formation of a ferritic / bainitic Gefuges is preferably carried out, is typically bounded below by the martensite [respective steel composition of the raw material, while it may be adjusted upwardly in each case lower than 500 0 C in order to avoid the formation of pearlite.
Der mit der Durchfuhrung des erfindungsgemaßen Verfahrens verbundene verfahrenstechnische Aufwand kann auch dadurch auf ein Minimum reduziert werden, dass nach dem Ende der Bainiti sierungszeit die Abkühlung des erhaltenen Stahlformteils auf einfache Weise an Luft durchgeführt wird.The procedural expense associated with the implementation of the inventive method can also be reduced to a minimum, that after the end of the Bainiti sierungszeit the cooling of the resulting steel molding is carried out in a simple manner in air.
Für die Durchfuhrung des erfindungsgemaßen Verfahrens eignen sich Stahlplatinen, die von einem warmgewalzten oder kaltgewalzten Flachprodukt, wie Band oder Blech, abgeteilt worden sind. Ebenso ist es möglich, das erfindungsgemaße Verfahren auf ein Stahlteil anzuwenden, das in einem vorangegangenen Arbeitsschritt vorgeformt worden ist. Letzteres bietet sich beispielsweise dann an, wenn die Formgebung des herzustellenden Stahlbauteils so komplex ist, dass für ihre Herstellung mehrere Formgebungsschritte erforderlich sind.For carrying out the process according to the invention, steel blanks which have been divided off from a hot-rolled or cold-rolled flat product, such as strip or sheet, are suitable. It is likewise possible to apply the method according to the invention to a steel part which has been preformed in a previous work step. The latter is useful, for example, when the shape of the steel component to be produced is so complex that several shaping steps are required for its production.
Aufgrund ihres Eigenschaftsprofils eignen sich erfmdungsgemaß erzeugte Stahlbauteile besonders für eine Verwendung als crashrelevante Teile einer Automobilkarosserie. Das erfindungsgemaße Verfahren eignet sich dabei insbesondere für die Herstellung von Längs- und Bodenquertragern, die in der Praxis exn besonders gutes Energieaufnahmevermogen aufweisen sollen.Because of their property profile, steel components produced according to the invention are particularly suitable for use as crash-relevant parts of an automobile body. The inventive method is particularly suitable for the production of Longitudinal and bottom crossbeams, which in practice should have a particularly good energy absorption capacity.
Nachfolgend wird die Erfindung anhand von Äusfuhrungsbeispielen naher erläutert.Hereinafter, the invention will be explained in more detail with reference to Äusfuhrungsbeispielen.
In Fig. 1 ist ein typischer bei der Durchfuhrung eines erfindungsgemaßen Verfahrens eingehaltener Verlauf der Temperatur T über die Zeit t aufgezeichnet. Demnach wird als Vormaterial eine jeweils zu einem Stahlbauteil zu verformende, beispielsweise mit einer vor Korrosion schutztenden AlSi-Beschichtung versehene Stahlplatine zunächst auf eine Austenitisierungstemperatur TA erwärmt, die unterhalb der Ac3-Temperatur jedoch oberhalb der AcI Temperatur des Stahls liegt, aus dem die Stahlplatine jeweils hergestellt ist. Bei der dieserFIG. 1 shows a typical course of the temperature T over the time t, which is maintained during the execution of a method according to the invention. Accordingly, as a starting material to be deformed in each case to a steel component, for example, provided with a corrosion-protective AlSi coating steel plate first heated to an austenitizing TA, which is below the Ac3 temperature but above the AcI temperature of the steel, from which the steel plate respectively is made. In the case of this
Austenitisierungstemperatur TA wird die Stahlplatme für eine Zeit tA gehalten, bis die Stahlplatine vollständig durcherwarmt ist, so dass in ihr ein aus Austenit und Ferrit bestehendes Mischgefuge vorliegt. Der Bereich, in dem der Stahl ein Gefuge aufweist, ist in Fig. 1 mit A gekennzeichnet, wahrend der Bereich des Mischgefuges aus Ferrit und Austenit mit "A+F" gekennzeichnet ist.Austenitizing temperature TA, the Stahlplatme is held for a time tA until the steel plate is completely soaked through, so that there is an existing austenite and ferrite Mischgefuge. The area where the steel has a groove is indicated by A in Fig. 1, while the area of the mixed ferrite and austenite core is indicated by "A + F".
Nach Ende der Austenitisierungszeit tA wird die Stahlplatine zu einem Pressformwerkzeug transportiert. Die bis zum Schließen des Pressformwerkzeugs benotigte Transferzeit ist in Fig. 1 mit tT bezeichnet. Die Temperatur TW, mit der die Stahlplatine in das Pressformwerkzeug gelangt, liegt immer noch innerhalb des Temperaturbandes Ac3 - AcI. Das Pressformwerkzeug ist mit einer Temperiereinrichtung ausgestattet, die es auf einer konstanten Temperatur halt, die der Ba mitisierungstemperatur TB entspricht. Das aus der Stahlplatine geformte, mit dem Pressformwerkzeug unmittelbar in Kontakt kommende Stahlformteil wird dementsprechend über eine Abkuhlzeit tK auf die Bainitisierungstemperatur TB gekühlt. Die Bainitisierungstemperatur TB liegt dabei oberhalb der Martensitstarttemperatur Ms, jedoch unterhalb der Perlitumwandlungstemperatur . Das Gebiet, in dem es zur Bildung von Perlit kommt, ist m Fig. 1 mit P gekennzeichnet. Zusätzlich ist in Fig. 1 mit F das Gebiet, in dem reiner Ferrit vorhanden ist, und mit M das Gebiet gekennzeichnet, in dem Martensit vorliegt.After the end of the austenitizing time tA, the steel plate is transported to a press forming tool. The transfer time required until the mold is closed is designated tT in FIG. The temperature TW at which the steel plate enters the die is still within the temperature range Ac3 - AcI. The press mold is equipped with a tempering device, which keeps it at a constant temperature, which corresponds to the Ba mitisierungsstemperatur TB. The shaped steel part formed from the steel plate and coming into direct contact with the press mold is accordingly cooled to the bainitizing temperature TB over a cooling time tK. The bainitization temperature TB is above the martensite start temperature Ms but below the pearlite transformation temperature. The region in which it comes to the formation of perlite, M m Fig. 1 marked with P. In addition, in Fig. 1, F indicates the area where pure ferrite is present and M denotes the area in which martensite is present.
Sobald die Bainitisierungstemperatur TB erreicht ist, wird das nach wie vor in dem Pressformwerkzeug sitzende Stahlbauteil über eine Baimtisierungszeit tB isotherm auf der Bainitisierungstemperatur TB gehalten. Die Baimtisierungszeit tB ist dabei so bemessen, dass an ihrem Ende das Gefuge des Stahlbauteils im Wesentlichen vollständig baimtisch ist.Once the bainitizing temperature TB is reached, the steel component still sitting in the die is kept isothermal at the bainitizing temperature TB for a period of time tB. The Baimtisierungszeit tB is dimensioned so that at its end the Gefuge of the steel component is substantially completely baimtisch.
Die ΛbkuhLung der Stahlplatine im temperierten Presswerkzeug erfolgt dabei innerhalb der Abkuhlzeit tK so schnell, dass der Stahl das Zweiphasenmischgebiet A+F durchlauft und eine Umwandlung im Martensitbereich M und Perlitbereich P verhindert wird, wobei die Martensitbildung möglichst vollständig vermieden wird.The cooling of the steel plate in the tempered pressing tool takes place within the cooling time tK so fast that the steel passes through the two-phase mixing area A + F and conversion in the martensite area M and perlite area P is prevented, wherein the martensite formation is avoided as completely as possible.
Nach Erreichen des Endes der Baimtisierungszeit tB wird das Werkzeug geöffnet und das Stahlbauteil an ruhender Luft auf Raumtemperatur abgekühlt. Die die Abkuhlzeit tK und die Bainitisi erungszeit tB umfassende Werkzeugschließzeit tW betragt abhangig von der Komplexität der Formgebung des herzustellenden Stahlbauteils und der Blechdicke der jeweils verarbeiteten Stahlplatine 5 - 60 Sekunden.After reaching the end of the Baimtisierungszeit tB the tool is opened and the steel component in still air cooled to room temperature. The tool closing time tW, which comprises the cooling time tK and the bainitization time tB, is 5 to 60 seconds, depending on the complexity of the shape of the steel component to be produced and the sheet thickness of the respectively processed steel plate.
Für zwei Versuche sind aus einem Warmband von 3 - 4 mm Dicke durch Kaltwalzen zwei 1,5 - 2 mm dicke Stahlplatme SPl, SP2 erzeugt worden, die aus einem 27MnCrB5-2 Stahl mit der in Tabelle 1 in Gew.-% angegebenen Zusammensetzung bestanden.For two tests, two 1,5 - 2 mm thick steel plates SP1, SP2 were produced from a hot strip of 3 - 4 mm thickness by cold rolling, which consisted of a 27MnCrB5-2 steel with the composition given in% by weight in Table 1 ,
Die erste Stahlplatine SPl ist dann auf eine Austenitisierungstemperatur TA von 780 0C erwärmt und auf dieser Temperatur TA für eine Austenitisierungszeit tA von 6 min gehalten worden.The first steel plate SPl has been heated to an austenitizing temperature TA of 780 0 C and maintained at this temperature TA for a Austenitisierungszeit tA of 6 min.
C Si Mn P S o, 294 0 ,24 1,13 o, 01 7 o, 002C Si Mn P S o, 294 0, 24 1.13 o, 01 7 o, 002
Al N Cr Ti BAl N Cr Ti B
0 ,035 o, 0038 0,43 0 , 033 0, 00100, 035 o, 0038 0.43 0, 033 0, 0010
Rest Ei sen und unvermeidbare VerunreinigungenRemainder eggs and unavoidable impurities
Tabelle 1Table 1
Anschließend ist die Stahlplatine SPl in einer 6 bis 12 s betragenden Transferzeit tT an Luft in ein Pressformwerkzeug transportiert worden, das auf eine Bainitisierungstemperatur TB von 400 0C aufgeheizt und bei dieser Temperatur TB konstant gehalten worden ist. In dem Presswerkzeug ist da e Stahlplatme SPl dann über e me Werkzeugschließzeit tW von 40 s pressverformt worden. Die Gesamtpresszea t umfasste die Abkuhizeit IK, m der die Stahlplatme SPl von der Werkzeugeintrittstemperatur TW auf die Bamitis Lerungstemperatur TB abgekühlt worden ist, und die Bamitisierungszeit tB, in der sich das Bamitgefuge in dem im Pressformwerkzeug warmpressgeforrnten Stahlbauteil gebildet hat. Anschließend ist das Presswerkzeug geöffnet worden und das Stahlbauteil an ruhender Luft auf Raumtemperatur abgekühlt worden.Subsequently, the steel plate SPI has been transported in a 6 to 12 s transfer time tT in air in a press mold, which has been heated to a bainitization temperature TB of 400 0 C and kept constant at this temperature TB. By doing Pressing tool has been press-formed over a tool closing time tW of 40 s. The total press temperature t comprised the cooling time IK in which the steel plates SPl had been cooled from the tool inlet temperature TW to the Bamitis release temperature TB, and the bittitization time tB in which the bamit fusion was formed in the steel component hot-press-forged in the press forming tool. Subsequently, the pressing tool has been opened and the steel component has been cooled to room temperature in still air.
Das Gefuge des so erhaltenen Stahlformteils wies einen Ferπtantei] von 50 %, einen Baimtanteil von 40 %, einen Restaustemtanteil von 6 % und einen Martensitanteil von 4 % auf.The Gefuge of the thus obtained steel molding had a Ferπtantei] of 50%, a Baimtanteil of 40%, a Restauustemtanteil of 6% and a Martensitanteil of 4%.
In dem zweiten Versuch ist die zweite Stahlplatme SP2 bei einer Aus! enitisierungstemperatur TA von 800 0C so durcherwarmt worden, dass auch sie nur unvollständig austenα tisiert war. Nach dieser Teilaustenα tisierung hat die zweite Stahlplatme SP2 dieselben Prozessschritte durchlaufen wie die erste Stahlplatme SPl .In the second attempt the second steel plate SP2 is at an off! enitisierungstemperatur TA was 800 0 C durcherwarmt so that she too was incomplete austenα tisiert. After this partial Austenα tisierung the second Stahlplatme SP2 has undergone the same process steps as the first Stahlplatme SPl.
Die Eigenschaften der aus den Stahlplatanen SPl, SP2 in der voranstehend beschriebenen Weise erzeugten Stahlformteile sind in Tabelle 2 angegeben.The properties of the steel moldings produced from the steel platelets SP1, SP2 in the manner described above are given in Table 2.
Tabelle 2 Schließlich ist zum Vergleich eine ebenfalls aus dem 27MnCrB5-2 - Stahl bestehende Stahlplatine in konventioneller Weise martensitisch zu einem Stahlformteil pressformgehartet worden. Die Restbruchdehnung A80 betrug bei dem so erhaltenen Bauteil nur ca. 6%. Nach dem erfundenen Verfahren liegt die Restbruchdehnung A80 der gleichen Gute dagegen ca. 19%.Table 2 Finally, for comparison, a steel plate, also made of 27MnCrB5-2 steel, was conventionally martensitic to form a steel formed part. The residual breaking strain A80 was only about 6% in the component thus obtained. By contrast, the residual strength at break A80 of the same good is about 19% according to the invented method.
Beim erfindungsgemaßen baini tischen Pressharten handelt es sich somit um ein Verfahren zum Warmpressharten, bei dem anstelle des üblicherweise erzeugten Martensitgefuges ein überwiegend aus Ferrit und Bainit bestehendes Gefuge durch eine isothermische Umwandlung beim Pressharten am jeweils pressgeformten Stahlbauteil eingestellt wird. Das erhaltene ferritisch/bainitische Gefuge weist im Vergleich zu Martensit eine verbesserte Restbruchdehnung bei hoher Festigkeit auf. The inventive baini tables press hardening is thus a process for hot pressing, in which instead of the usually produced Martensitgefuges a predominantly consisting of ferrite and bainite Gefuge is set by an isothermal conversion during press-hardening on each press-formed steel component. The resulting ferritic / bainitic structure has improved residual elongation at high strength compared to martensite.

Claims

24. April 2009P A T E N T A N S P R Ü C H E April 24, 2009P ATENTANSPR Ü CHE
1. Verfahren zum Herstellen eines Stahlformteils mit einem überwiegend ferπtisch-bainitischen Gefuge,1. A process for producing a steel molding having a predominantly ferritic-bainitic structure,
- bei dem ein Vormateπal in Form einer Stahlplatine oder eines vorgeformten Stahltei] s bereitgestellt wird, das jeweils aus einem Stahl hergestellt ist, der (in Gew.-%)in which a material is provided in the form of a steel plate or a preformed steel part, each made of a steel containing (in% by weight)
C: 0, 02 - 0, 6 %,C: 0, 02 - 0, 6%,
Mn: 0,5 - 2,0 %,Mn: 0.5-2.0%,
Al: 0, 01 - 0,06 %,Al: 0, 01 - 0.06%,
Si : Max. 0, 4 %,Si: max. 0, 4%,
Cr: Max. 1,2 %,Cr: Max. 1.2%,
P: Max. 0,035 %,P: Max. 0.035%,
S: Max. 0,035 %, sowie optional eines oder mehrere der Elemente aus der Gruppe "Ti, Cu, B, Mo, Ni, N" mit der MaßgabeS: Max. 0.035%, and optionally one or more of the elements from the group "Ti, Cu, B, Mo, Ni, N" with the proviso
Ti : Max. 0,05 %,Ti: Max. 0.05%,
Cu: Max. 0,01 %,Cu: max. 0.01%,
B: 0,0008 - 0,005 %,B: 0.0008 - 0.005%,
Mo: Max. 0,3 %,Mo: Max. 0.3%,
Ni: Max. 0,4 %,Ni: Max. 0.4%,
N: max. 0,01 %, und als Rest Eisen und unvermeidbare Verunreinigungen enthalt,N: max. 0.01%, and the balance contains iron and unavoidable impurities,
bei dem das Vormaterial bei einer zwischen der Äcl- und der Ac3-Temperatur des Stahls liegenden Erwarmungsterrtperatur (TA) durcherwarmt wird, so dass eine allenfalls unvollständige Austeniti sierung des Vormaterials eintritt,in which the starting material is subjected to a heating at a heating temperature (TA) between the Äcl- and the Ac3 temperature of the steel, so that at most incomplete Austeniti sation of the starting material occurs,
bei dem das Vormaterial in ein Pressformwerkzeug eingelegt und darin zu dem Stahlformteil geformt wird,in which the starting material is inserted into a press-forming tool and formed therein into the steel molding,
bei dem das Stahlformteil auf eine Bainitbil dungstemperatur (TB) gebracht wird, die oberhalb der Martensitstarttemperatur (Ms), jedoch unterhalb der Perlitumwandlungstemperatur des Stahls liegt, aus dem das Vormaterial jeweils hergestellt ist,in which the steel molding is brought to a bainite formation temperature (TB) which is above the martensite start temperature (Ms) but below the pearlite transformation temperature of the steel from which the starting material is produced,
bei dem das Stahlformteil nach der Abkühlung über eine Bainitisierungszeit (tB) im Wesentlichen isotherm auf der Bainitbildungstemperatur (TB) gehalten wird, bis in dem Stahlformteil ein zum überwiegenden Teil aus Ferrit und Bainit bestehendes Gefuge entstanden ist, dessen Martensitgehalt weniger als 5 % betragt, woben Restaustenitgehalte von bis zu 10 % vorhanden sein können, und - bei dem das Stahl formteil nach dem Ende der Bainitisierungszeit (tB) auf Raumtemperatur gebracht wird.in which the steel shaped part after cooling is kept substantially isothermally at the bainite formation temperature (TB) for a bainitization time (tB), until in the steel molded part a predominantly ferrite and bainite core having a martensite content of less than 5% is formed, where retained austenite levels of up to 10% may be present, and - In which the steel molding is brought to room temperature after the end of the bainitization time (tB).
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 Stahl2. The method of claim 1, wherein said steel is the steel
(in Gew.-%)(in% by weight)
C: 0,25 - 0,6 % ,C: 0.25-0.6%,
Si: max. 0,4 %,Si: max. 0.4%,
Mn : 0,5 - 2,0 % ,Mn: 0.5-2.0%,
Cr : max . 0,6 % ,Cr: max. 0.6%,
P: max. 0,02 %,P: max. 0.02%,
S: max. 0,01 %,S: max. 0.01%,
Al: 0,01 - 0,06 %,Al: 0.01-0.06%,
Ti: max. 0,05 %,Ti: max. 0.05%,
Cu : max . 0,1 % ,Cu: max. 0.1%,
B: 0,008 - 0,005 % und als Rest Eisen und unvermeidbare Verunreinigungen enthält.B: 0.008 - 0.005% and the balance iron and unavoidable impurities.
3. 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 Stahl3. The method of claim 1, wherein said steel is the steel
(in Gew. -%)(in% by weight)
C: 0, 25 - 0, 6 %, Si: max. 0, 4 %, Mn: 0, 5 - 2, 0 %, Cr : max . 1, 2 % , P: max. 0, 035 %, S: max. 0, 035 %,C: 0, 25 - 0, 6%, Si: max. 0, 4%, Mn: 0, 5 - 2, 0%, Cr: max. 1, 2%, P: max. 0, 035%, S: max. 0, 035%,
Mo: max. 0, 3 %,Mo: max. 0, 3%,
Ni: max. 0, 4 %,Ni: max. 0, 4%,
Al: 0, 01 - 0, 06 %, und als Rest Eisen und unvermeidbare Verunreini gungen enthalt .Al: 0, 01-0.0%, and the remainder contains iron and unavoidable impurities.
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 Summe der Ferrit- und Bainitanteile im Gefuge des Stahlformteils am Ende der Bainitisierungszeit (tB) mindestens 90 % betragt.4. Method according to one of the preceding claims, wherein the sum of the ferrite and bainite portions in the joint of the steel molding at the end of the bainitization time (tB) amounts to at least 90%.
5. 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 am Ende der Bainitisierungszeit (tB) der Bainitisierungszeit der Martensitanteil des5. Method according to one of the preceding claims, characterized in that at the end of the bainitization time (tB) of the bainitization period the martensite fraction of the
Stahlformteα Is weniger als 1 % betragt, insbesondere auf Spuren beschrankt ist.Stahlformteα Is less than 1% amounts, especially on tracks is limited.
6. 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 Austenitisierungstemperatur (TA) 750 - 810 0C betragt .6. The method according to any one of the preceding claims, characterized in that the Austenitisierungstemperatur (TA) 750 - 810 0 C amounts.
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 die für das Durcherwarmen bei der7. The method according to any one of the preceding claims, characterized in that the for the warmth at the
Erwarmungstemperatur (TA) vorgesehene Erwärmungszeit (tA) 6 - 15 Minuten betragt.Heating temperature (TA) provided heating time (tA) is 6 - 15 minutes.
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 das Vormaterial mit einem vor Korrosion schutzenden metallischen Überzug versehen ist.8. Method according to one of the preceding claims, characterized in that the starting material is provided with a metallic coating which protects against corrosion.
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 nach dem Pressformen des Vormaterials das erhaltene Stahlformteil in dem Pressformwerkzeug auf die Bainitbildungstemperatur (TB) gebracht und für die Bainitisierungszeit (tB) gehalten wird.9. Method according to one of the preceding claims, characterized in that, after the primary material has been press-formed, the obtained steel molded part is brought to the bainite formation temperature (TB) in the press mold and held for the bainitization time (tB).
10. Verfahren nach Anspruch 9, 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 Werkzeugschließzeit (tW) des Presswerkzeugs 5 - 60 Sekunden, insbesondere 20 - 60 Sekunden, betragt.10. The method according to claim 9, wherein the tool closing time (tW) of the pressing tool is 5-60 seconds, in particular 20-60 seconds.
11. Verfahren nach Anspruch _0, 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 Bainitisierungszeit (tB) kurzer als die Werkzeugschließzeit (tW) ist. 11. The method according to claim _0, characterized in that the bainitization time (tB) is shorter than the tool closing time (tW).
12. 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 nach dem Pressformen das aus dem Vormaterial pressgeformte Stahlformteil aus der Pressform entnommen und in einem separaten ArbeLtsgang auf die Bainitbildungstemperatur (TB) gebracht und über die Bainitisierungszeit (tB) gehalten wird.12. Method according to one of claims 1 to 8, wherein, after the press molding, the steel shaped part press-molded from the starting material is removed from the press mold and brought to the bainite formation temperature (TB) in a separate working step and held for the bainitization time (tB).
13. 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 Ba i m tα sierungs temperatur (TB) hoher als die Martens i tstarttemperatur der jeweiligen Zusammensetzung des Vormaterials kleiner als 500 0C ist .13. The method according to any one of the preceding claims, characterized in that the Ba in tα sierungstemperatur (TB) higher than the Martens i tstarttemperatur the respective composition of the starting material is less than 500 0 C.
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 die Abkühlung des erhaltenen Stahlformteils nach dem Ende der Bainitisierungszeit (tB) an Luft durchgeführt wird.14. Method according to one of the preceding claims, characterized in that the cooling of the resulting steel molding after the end of the bainitization time (tB) is carried out in air.
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 es sich bei dem Stahlformteil um einen Teil einer Λutomobi] karosseri e handelt. 15. Method according to one of the preceding claims, characterized in that the steel shaped part is a part of a Λutomobi] body.
EP09741994.9A 2008-05-06 2009-04-24 Method for producing a formed steel part having a predominantly ferritic-bainitic structure Active EP2297367B9 (en)

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DE102008022399A DE102008022399A1 (en) 2008-05-06 2008-05-06 Process for producing a steel molding having a predominantly ferritic-bainitic structure
PCT/EP2009/054961 WO2009135776A1 (en) 2008-05-06 2009-04-24 Method for producing a formed steel part having a predominantly ferritic-bainitic structure

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CA2725210A1 (en) 2009-11-12
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