EP1945827B1 - Cold-workable ti alloy - Google Patents

Cold-workable ti alloy Download PDF

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Publication number
EP1945827B1
EP1945827B1 EP06806675A EP06806675A EP1945827B1 EP 1945827 B1 EP1945827 B1 EP 1945827B1 EP 06806675 A EP06806675 A EP 06806675A EP 06806675 A EP06806675 A EP 06806675A EP 1945827 B1 EP1945827 B1 EP 1945827B1
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Prior art keywords
titanium alloy
temperature
titanium
annealing temperature
annealing
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German (de)
French (fr)
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EP1945827A1 (en
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Svetlana Skvortsova
Alexander Ilin
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Hempel Robert P
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Hempel Robert P
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C14/00—Alloys based on titanium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/16—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of other metals or alloys based thereon
    • C22F1/18—High-melting or refractory metals or alloys based thereon
    • C22F1/183—High-melting or refractory metals or alloys based thereon of titanium or alloys based thereon

Definitions

  • the invention relates to a heat treatment process for producing cold-workable ( ⁇ + ⁇ ) titanium alloys.
  • the invention further relates to the use of heat-treated ( ⁇ + ⁇ ) titanium alloys for the production of components from the titanium alloy by means of cold forming.
  • titanium alloy components are becoming increasingly attractive in a wide variety of technical fields.
  • the reason for this attractiveness is in particular the low specific density of titanium alloys combined with high strength values and the low corrosion sensitivity of titanium alloys.
  • Titanium alloys can in principle be classified according to the phases present at room temperature into so-called ⁇ -, ⁇ + ⁇ - and ⁇ -titanium alloys. Pure titanium is present at room temperature in the ⁇ -phase (hexagonal structure) and transforms into a cubic-body-centered ⁇ -phase at about 890 ° C ( ⁇ -transus).
  • the transformation temperature of titanium alloys is influenced by the type and amount of alloying components and can also be influenced by a me chanical, chemical or thermal pretreatment of the titanium alloy.
  • the ⁇ -phase can be stabilized over a wider temperature range (increasing the ⁇ -transus temperature).
  • the addition of other alloying elements produces and stabilizes the ⁇ phase (lowering the ⁇ -transus temperature). It is therefore possible to subdivide the alloying elements into so-called ⁇ -stabilizers and ⁇ -stabilizers.
  • Technically used ⁇ -stabilizers are, for example, oxygen, nitrogen, carbon or aluminum.
  • Technically used ⁇ -stabilizers today are e.g. Hydrogen, vanadium, molybdenum, iron, chromium, copper, palladium or silicon.
  • Alloys with a high proportion of the ⁇ -phase regularly have lower strength values than alloys with a high proportion of the ⁇ -phase.
  • the specific gravity of high ⁇ -content titanium alloys is usually higher than the specific gravity of such high ⁇ -phase titanium alloys. Due to the greater number of slip planes of the ⁇ -titanium cubic lattice, the ⁇ -phase is better cold-formable than the ⁇ -phase.
  • Technically used alloys usually represent a compromise in which the proportion of the ⁇ -phase and ⁇ -phase is adjusted by alloying the corresponding ⁇ and ⁇ stabilizers as described e.g. require the desired manufacturing properties, strength values and corrosion properties of the component.
  • Titanium alloys are regularly weldable and thermoformable only with great effort.
  • technically customary titanium alloys are only cold-deformable to a very limited extent.
  • cold workability is meant the ability of a material to be deformed at room temperature without this deformation results in a considerable loss of strength or cracking.
  • Titanium alloy components are therefore currently used almost exclusively in high-priced products, e.g. in the field of aviation, in particular military aviation and medical technology.
  • a titanium alloy which comprises 1.5-3.0% by weight of aluminum (all% data are understood below as% by weight of information), 4.5-8.0% molybdenum, 1.0% 3.5% vanadium. Contains 1.5-3.8% iron.
  • This alloy which has been manufactured on the basis of relatively inexpensive alloying elements, can, after heat treatment, achieve a certain ratio of strength and ductile properties and be used for the manufacture of some types of fasteners and springs. The main drawback of this alloy is the costly heat treatment required to achieve these properties.
  • a titanium alloy comprising 1.2-3.8% aluminum, 5.1-6.5% molybdenum, 4.0-6.5% vanadium, 0.01-0.05% silicon, 0.005-0.015% is known. Contains hydrogen. Although this alloy has increased ductility during multi-stage deformation and is used to make rivets. However, this alloy does not have sufficiently high strength properties for highly stressed components.
  • titanium- ⁇ titanium alloy is known to be 5.05% Al, 1.98% Sn, 4.07% Zr, 4.03% Mo, 2.18% Cr, 1% Fe, and a titanium alloy of 4.9% Al, 2%. Sn, 4.37% Zr, 3.99% Mo, 2% Cr 0.93% Fe and small amounts of OC, H, N known.
  • the ⁇ -transus temperature is about 890 ° C.
  • the invention therefore an object of the invention to provide a method for processing a titanium alloy, which (s) allows more cost-effective processing.
  • a titanium alloy containing about 2-4.0 wt% aluminum, about 4-5.5 wt% vanadium, about 4.0-6.0 wt% molybdenum, about 0.5-1.5 % By weight of zirconium and about 0.5-1.5% by weight of tin On the one hand, it is suitable for direct processing by means of cold forming without a preceding separate heat treatment, ie immediately after the production of the semifinished product, for example by hot rolling.
  • the above-described cold-formable ⁇ + ⁇ -titanium alloy is also particularly suitable if higher cold working rates are to be achieved with simultaneously high strength of the cold-formed component, also for the application of the heat treatment process according to the invention described below.
  • the combination of the thus alloyed ⁇ + ⁇ -titanium alloy with the heat treatment process according to the invention achieves particularly good results in terms of cold workability and strength of the components produced.
  • the titanium alloy has about 0.1-0.4 wt .-% oxygen.
  • This alloying element has been found to be beneficial for the cold ductility and strength of the heat treated titanium alloy.
  • Oxygen is a strong ⁇ -stabilizing element.
  • An increase in the oxygen content in the alloy results in an increase of the ⁇ -phase content and a strong solidification due to the formation of solid interstitial solution.
  • the optimum oxygen content in the alloy is 0.1-0.4% of the mass. Such an oxygen content does not lead to a significant change in the ⁇ -phase content (about 3-5%), but allows to increase its strength and consequently the overall strength level practically without lowering the ductility.
  • the object underlying the invention is achieved by means of a heat treatment method according to claim 1.
  • the invention is based on the realization that the example of US 5,679,183 known alloy class achieved by their heat treatment no growth of existing ⁇ -particles, but creates new particles, which have a fine-lamellar morphology.
  • a bimodal structure formed in this way has an appreciable breaking strength, it does so at the expense of a considerable reduction in ductility.
  • the structure remains bimodal because it consists of a small amount of ⁇ -phase and ⁇ -phase particles of different morphology (geometrically uniform and lamellar). Such a structure can not provide a starting point for room temperature ductility.
  • the invention is based on the recognition that globular structures have a good combination of strength and ductility. They can be obtained in ( ⁇ + ⁇ ) titanium alloys after deformation in the two-phase region near the temperature of ⁇ -transus.
  • the balance of strength and ductility depends on the structural component size. The finer the ⁇ -phase precipitates are geometrically uniform, the higher the strength and the lower the ductility will be. A considerable decrease in strength and fracture resistance with little increase in ductility will occur with very large ⁇ -phase globular particles.
  • the heat treatment process according to the invention provides an ⁇ + ⁇ titanium alloy which, on the one hand, has a high ductility and, on the other hand, has a very low degree of solidification upon deformation.
  • the heating of the titanium alloy to the lower annealing temperature can be done with different heating rates. Preferably, a slow heating with a heating rate of less than 20 ° per minute is chosen to avoid the formation of stress cracks.
  • the annealing of the titanium alloy is preferably carried out in an inert atmosphere in order to avoid diffusion of embrittling elements (eg oxygen, nitrogen or carbon) into the titanium alloy.
  • embrittling elements eg oxygen, nitrogen or carbon
  • the cooling of the titanium alloy to ambient temperature is preferably also carried out in an inert atmosphere.
  • ⁇ + ⁇ titanium alloys are curable by quenching from an annealing temperature. However, this effect is undesirable if a good cold-workable titanium alloy material is to be produced.
  • the cooling rate is therefore preferably to be chosen so low that hardening of the titanium alloy is avoided.
  • the first stage of annealing is chosen at a temperature range of ⁇ -transus minus 50 ° C to ⁇ -transus minus 100 ° C.
  • the structure of the alloy is characterized by separate globular particles of the ⁇ -phase, which are arranged at this temperature in a ⁇ -matrix. Isothermal holding at this temperature not only provides a solution to the excess (secondary) ⁇ phase and approximation to the equilibrium state of the ⁇ and ⁇ phases, but also leads to a reduction in structural defects in the course of the realization of a polygonization process.
  • the alloy After completion of isothermal holding, the alloy is cooled to the temperature ⁇ -transus minus 160 ° C to ⁇ -transus minus 230 ° C at a cooling rate of 0.01-0.02 ° / sec. Such a cooling rate does not allow the formation of new ⁇ -phase particles from the ⁇ -matrix during cooling, but allows the growth of pre-existing, primary ⁇ -crystals in the structure. Isothermal holding for 3-6 hours at the second stage of annealing allows completion of the homogenization process. Subsequent cooling to room temperature is carried out at a cooling rate of 2.5-3.5 ° / s, which is sufficient to prevent precipitation of the secondary ⁇ -phase.
  • the phase composition to be achieved for good cold workability can hereby be further optimized.
  • the upstream annealing steps are again preferably carried out in an inert atmosphere. Again, as before, when cooling the titanium alloy to pay attention to a cooling rate, which avoids stress cracks.
  • the invention can be further optimized by the titanium alloy at the upper annealing temperature for more than one hour, in particular for about two hours, annealed.
  • the annealing time depends on the dimensions of the titanium alloy semifinished product. An annealing time of more than one hour, especially two hours, has proven to be reliable for the reproduction of the desired phase composition.
  • the titanium alloy is annealed at the lower annealing temperature more than three hours, preferably three to six, in particular about four hours. Due to the upstream annealing treatment at a higher temperature, the annealing time required for a reliable phase composition to the desired target can be reduced at the lower annealing temperature. More than three hours, in particular four hours, have been found in conventional dimensions, such as semi-finished in the form of round material in the diameter between 10 to 20mm sufficient.
  • the titanium alloy is cooled from the upper annealing temperature of air to the lower annealing temperature at a cooling rate of 0.01-0.02 ° C / min. At this cooling rate, the formation of undesirable phase fractions, internal stresses and the precipitation of alloying elements to an undesirable extent is avoided.
  • the upper annealing temperature is about 770-830 ° C, in particular 800 ° C. This temperature range has been found to be practicable for most of the commercially available ⁇ + ⁇ titanium alloys.
  • the process of the present invention can be further developed by cooling the titanium alloy from the lower annealing temperature of air to room temperature at a cooling rate of about 2.5 ° to 3.5 ° C / min. This cooling rate avoids unwanted precipitation of alloying elements as well as unwanted phase formations and achieves an optimum result in terms of the cold workability and the strength of the cold-formed component.
  • the method according to the invention can furthermore be advantageously used if the titanium alloy is processed by a hot rolling method before the heat treatment.
  • the hot rolling process is a process to produce, for example semi-finished profile products or semifinished titanium alloy products.
  • the hot rolling process influences the microstructure.
  • the structure influenced in this way is particularly suitable for the heat treatment steps according to the invention.
  • the lower annealing temperature is about 670-730 ° C, in particular 700 ° C. This annealing temperature has been found to be practicable for most of the technically common ⁇ + ⁇ titanium alloys.
  • the titanium alloy is alloyed with at least one ⁇ -stabilizer and at least one ⁇ -stabilizer.
  • a titanium alloy can be produced with a proportion of ⁇ -phase and ⁇ -phase optimized for the specific application.
  • the proportions of the stabilizing alloying elements are to be matched to the heat treatment process according to the invention in order to achieve the desired cold workability of the semifinished product and the desired strength of the cold-formed component.
  • the method according to the invention can be further developed by removing a surface layer of the titanium alloy mechanically, in particular by machining, after annealing at the lower annealing temperature and / or after annealing at the upper annealing temperature.
  • the annealing treatment often has some influence on the surface layer of the titanium alloy semi-finished product, even if it is performed in an inert atmosphere. This influence causes embrittlement and increased crack sensitivity of the semifinished product, which results in lower cold workability and lower strength of the cold-worked component.
  • This disadvantageous effect can be counteracted by removing the affected edge layer of the semifinished product before the cold deformation.
  • a machining production is suitable for this purpose.
  • Another aspect of the invention is the use of a heat treated ⁇ + ⁇ titanium alloy as described above to produce titanium components by cold working.
  • a heat treated ⁇ + ⁇ titanium alloy as described above to produce titanium components by cold working.
  • the cost-effective production of large-volume components made of a titanium alloy is possible. This is desirable, for example, for a variety of components in the automotive sector, especially for components that are installed as moving parts in the drive train.
  • the use according to the invention can serve in particular for the production of titanium screws by means of cold heading and / or thread rolling.
  • This use is suitable, for example, for the production of wheel bolts for the automotive sector.
  • the use of titanium alloy wheel bolts has the advantage that, on the one hand, the mass inertia forces of the wheel can be reduced and, as a result, the driving characteristics and the suspension comfort can be improved and the fuel consumption of the vehicle can be lowered.
  • the use of titanium screws has the further advantage that, especially when used in combination with alloy wheels made of aluminum alloys or magnesium alloys contact corrosion is avoided, as it often occurs, for example, when using steel screws.
  • titanium bolts achieve and exceed the strength values according to the DIN classification 8.8 and are thus suitable, for example, for use as wheel bolts.
  • the molybdenum equivalent is a value calculated from the type and amount of alloying components and is usually between 0 and 2.5 for ⁇ -titanium alloys, between 2.5 and 10 for ⁇ + ⁇ titanium alloys, and over 10 for ⁇ -titanium alloys.
  • the known alloy Ti - 3.0Al - 4.5V - 5.0Mo is used as the ⁇ + ⁇ -titanium alloy. After the alloy has been produced, a round material, for example 13 mm in diameter, is produced in a hot rolling process. This semi-finished is available in usual lengths.
  • the semifinished products treated in this way can then be processed further, for example by producing a screw head by means of a cold upsetting process and producing a thread by means of thread rolling at ambient temperature.
  • an edge layer of the semifinished product can be removed by mechanical processing prior to further processing.
  • the alloy was made by double vacuum reflow with sacrificial electrodes. Its chemical composition is as follows: Ti -3.0% Al - 5.0% Mo - 4.5% V - 1.0% Zr-1.0% Sn - 0.25% O (the temperature of ⁇ - Transus is 880 ° C).
  • the resulting bar of 8kg weight was isothermally forged at a temperature in the ⁇ -area to a square of 90x90mm and was then drop forged to a height of 45mm.
  • the billet was then cut into strips of rectangular cross section 45x45mm and forged at a temperature in the ( ⁇ + ⁇ ) region until rods with a diameter of 30mm were obtained.
  • the rods were machined using a lathe until a diameter of 25mm was obtained.
  • the blanks then obtained were rolled to a diameter of 16 mm at a temperature range of ⁇ -transus minus 50 ° C to ⁇ -transus minus 100 ° C.
  • the first heating to the predetermined temperature was carried out for 30 minutes. Subsequent heating between trains was for 4 minutes.
  • the total reduction rate was 65%.
  • the 16mm diameter rod was subjected to a heat treatment in the temperature range of 860-780 ° C for 2 hours followed by cooling at a cooling rate of 0.02K / s to a temperature of 700 ° C ( ⁇ -transus minus 190 ° C ) and isothermal hold for 4 hours. Cooling to room temperature was carried out at a cooling rate of 3K / s.
  • the rods were turned to 13mm diameter using a lathe.
  • a 16mm diameter rod was produced by the same method as in the second embodiment. After rolling, the 16mm diameter rod was heat treated at a temperature range of 860-780 ° C for 2 hours followed by air cooling to room temperature. Then the bar was heated to the temperature of 700 ° C ( ⁇ - Transus minus 190 ° C) and held for 4 hours. Cooling to room temperature was carried out in air.
  • the rods were turned to 13mm diameter using a lathe.

Abstract

The invention makes it possible to produce workpieces from titanium alloys in a low-cost cold-working process. This is achieved by means of a (α+β) titanium alloy with approximately 2 - 4.0% by weight of aluminium, approximately 4 - 5.5% by weight of vanadium, and approximately 4.5 - 6.0% by weight of molybdenum, which is made suitable for cold working while maintaining adequate strength of the workpiece produced by the additional alloying components of approximately 0.5 - 1.5% by weight of zirconium and approximately 0.5 - 1.5% by weight of tin. Furthermore, the cold workability is achieved according to the invention by means of a heat treatment process, comprising the steps of: annealing the titanium alloy at a lower annealing temperature that lies between 160° and 230° below the transformation temperature (β-transus) and cooling the titanium alloy to ambient temperature. The titanium alloy is preferably first annealed at an upper annealing temperature, which lies between 50° and 100° below the transformation temperature (β-transus).

Description

Die Erfindung betrifft ein Wärmebehandlungsverfahren zur Herstellung kaltverformbarer (α+β)-Titanlegierungen. Die Erfindung betrifft weiterhin die Verwendung wärmebehandelter (α+β)-Titanlegierungen zur Herstellung von Bauteilen aus der Titanlegierung mittels Kaltverformen.The invention relates to a heat treatment process for producing cold-workable (α + β) titanium alloys. The invention further relates to the use of heat-treated (α + β) titanium alloys for the production of components from the titanium alloy by means of cold forming.

Die Verwendung von Bauteilen aus Titanlegierungen wird in verschiedensten Technikbereichen zunehmend attraktiver. Grund für diese Attraktivität ist insbesondere die geringe spezifische Dichte von Titanlegierungen bei zugleich hohen Festigkeitswerten und die geringe Korrosionsempfindlichkeit von Titanlegierungen.The use of titanium alloy components is becoming increasingly attractive in a wide variety of technical fields. The reason for this attractiveness is in particular the low specific density of titanium alloys combined with high strength values and the low corrosion sensitivity of titanium alloys.

Titanlegierungen lassen sich grundsätzlich nach den bei Raumtemperatur vorliegenden Phasen in sogenannte α-, α+β- und β-Titanlegierungen einteilen. Reines Titan liegt bei Raumtemperatur in der α-Phase (hexagonale Struktur) vor und wandelt sich bei ca. 890°C (β-transus) in eine kubisch-raumzentrierte β-Phase um. Die Umwandlungstemperatur von Titanlegierungen wird durch Art und Menge der Legierungsanteile beeinflusst und kann darüber hinaus durch eine me chanische, chemische oder thermische Vorbehandlung der Titanlegierung beeinflusst werden.Titanium alloys can in principle be classified according to the phases present at room temperature into so-called α-, α + β- and β-titanium alloys. Pure titanium is present at room temperature in the α-phase (hexagonal structure) and transforms into a cubic-body-centered β-phase at about 890 ° C (β-transus). The transformation temperature of titanium alloys is influenced by the type and amount of alloying components and can also be influenced by a me chanical, chemical or thermal pretreatment of the titanium alloy.

Durch Zugabe von bestimmten Legierungselementen kann die α-Phase über einen weiteren Temperaturbereich stabilisiert werden (Erhöhung der β-transus Temperatur). Die Zugabe anderer Legierungselemente erzeugt und stabilisiert die β-Phase (Absenkung der β-transus Temperatur). Man kann die Legierungselemente daher in sogenannte α-Stabilisierer und β-Stabilisierer unterteilen. Technisch angewendete α-Stabilisierer sind zum Beispiel Sauerstoff, Stickstoff, Kohlenstoff oder Aluminium. Heutzutage technisch angewendete β-Stabilisierer sind z.B. Wasserstoff, Vanadium, Molybdän, Eisen, Chrom, Kupfer, Palladium oder Silizium.By adding certain alloying elements, the α-phase can be stabilized over a wider temperature range (increasing the β-transus temperature). The addition of other alloying elements produces and stabilizes the β phase (lowering the β-transus temperature). It is therefore possible to subdivide the alloying elements into so-called α-stabilizers and β-stabilizers. Technically used α-stabilizers are, for example, oxygen, nitrogen, carbon or aluminum. Technically used β-stabilizers today are e.g. Hydrogen, vanadium, molybdenum, iron, chromium, copper, palladium or silicon.

Legierungen mit einem hohen Anteil der α-Phase weisen regelmäßig geringere Festigkeitswerte auf als Legierungen mit einem hohen Anteil der β-Phase. Die spezifische Dichte von Titanlegierungen mit hohem β-Anteil ist regelmäßig höher als die spezifische Dichte solcher Titanlegierungen mit hohem Anteil der α-Phase. Aufgrund der größeren Anzahl an Gleitebenen des kubischen Gitters des β-Titans ist die β-Phase besser kaltverformbar als die α-Phase. Technisch verwendete Legierungen stellen in der Regel einen Kompromiss dar, bei dem der Anteil der α-Phase und β-Phase durch Zulegieren der entsprechenden α- und β-Stabilisierer so eingestellt wird, wie es z.B. die gewünschten Fertigungseigenschaften, Festigkeitswerte und Korrosionseigenschaften des Bauteils erfordern.Alloys with a high proportion of the α-phase regularly have lower strength values than alloys with a high proportion of the β-phase. The specific gravity of high β-content titanium alloys is usually higher than the specific gravity of such high α-phase titanium alloys. Due to the greater number of slip planes of the β-titanium cubic lattice, the β-phase is better cold-formable than the α-phase. Technically used alloys usually represent a compromise in which the proportion of the α-phase and β-phase is adjusted by alloying the corresponding α and β stabilizers as described e.g. require the desired manufacturing properties, strength values and corrosion properties of the component.

Ein noch ungelöstes Problem bei der Herstellung von Bauteilen aus Titanlegierungen ist die im Vergleich zu anderen metallischen Werkstoffen oder Kunststoffen geringe Vielfalt an zur Verfügung stehenden Fertigungsverfahren. Titanlegierungen sind regelmäßig nur mit großem Aufwand schweißbar und warmverformbar. Technisch gebräuchliche Titanlegierungen sind darüber hinaus nur in sehr geringem Umfang kaltverformbar. Unter Kaltverformbarkeit ist die Fähigkeit eines Materials zu verstehen, bei Raumtemperatur verformt zu werden, ohne daß
durch diese Verformung eine erhebliche Festigkeitseinbuße oder eine Rissbildung erfolgt.An unsolved problem in the manufacture of titanium alloy components is the limited variety of manufacturing techniques available compared to other metallic materials or plastics. Titanium alloys are regularly weldable and thermoformable only with great effort. In addition, technically customary titanium alloys are only cold-deformable to a very limited extent. By cold workability is meant the ability of a material to be deformed at room temperature without
this deformation results in a considerable loss of strength or cracking.

Schweißbearbeitung, Warmverformung und Kaltverformung beeinflussen darüber hinaus in beträchtlichem Maße die Festigkeitswerte der so hergestellten Bauteile, so dass hochbeanspruchte Bauteile oder Bauteile im sicherheitsrelevanten Bereich nur eingeschränkt auf solche Weise bearbeitet werden können. Bei der Fertigung von Titanbauteilen wird daher in großem Umfang auf die kostenintensive Fertigung mittels spanender Bearbeitung zurückgegriffen. Bauteile aus Titanlegierungen haben daher derzeit nahezu ausschließlich in hochpreisigen Produkten Anwendung gefunden, so z.B. im Bereich der Luftfahrt, insbesondere der militärischen Luftfahrt und im Bereich der Medizintechnik.In addition, welding, hot working and cold working have a considerable influence on the strength values of the components produced in this way, so that highly stressed components or components in the safety-relevant area can only be processed to a limited extent in such a way. In the production of titanium components is therefore resorted to on a large scale to the cost-intensive production by means of machining. Titanium alloy components are therefore currently used almost exclusively in high-priced products, e.g. in the field of aviation, in particular military aviation and medical technology.

Aus RU 2211873 ist eine Titanlegierung bekannt, die 1,5-3,0 Gew.-% Aluminium (alle %-Angaben sind im Folgenden als Gew.-%Angaben zu verstehen), 4,5-8,0 % Molybdän, 1,0-3,5 % Vanadium. 1,5-3,8 % Eisen enthält. Diese Legierung, welche auf der Basis von verhältnismäßig kostengünstigen Legierungselementen hergestellt worden ist, kann nach Wärmebehandlung ein bestimmtes Verhältnis von Festigkeit und duktilen Eigenschaften erreichen und für die Herstellung von einigen Arten von Befestigungselementen und Federn verwendet werden. Der Hauptnachteil dieser Legierung liegt in der aufwendigen Wärmebehandlung, die zum Erreichen dieser Eigenschaften erforderlich ist.Out RU 2211873 A titanium alloy is known which comprises 1.5-3.0% by weight of aluminum (all% data are understood below as% by weight of information), 4.5-8.0% molybdenum, 1.0% 3.5% vanadium. Contains 1.5-3.8% iron. This alloy, which has been manufactured on the basis of relatively inexpensive alloying elements, can, after heat treatment, achieve a certain ratio of strength and ductile properties and be used for the manufacture of some types of fasteners and springs. The main drawback of this alloy is the costly heat treatment required to achieve these properties.

Aus RU 1584408 ist eine Titanlegierung bekannt, die 1,2-3,8% Aluminium, 5,1-6,5 % Molybdän, 4,0-6,5 % Vanadium, 0,01-0,05 % Silizium, 0,005-0,015% Wasserstoff enthält. Diese Legierung hat zwar eine erhöhte Duktilität während mehrstufiger Verformung und wird zur Herstellung von Nieten verwendet. Jedoch hat diese Legierung keine ausreichend hohen Festigkeitseigenschaften für hochbeanspruchte Bauteile.Out RU 1584408 For example, a titanium alloy comprising 1.2-3.8% aluminum, 5.1-6.5% molybdenum, 4.0-6.5% vanadium, 0.01-0.05% silicon, 0.005-0.015% is known. Contains hydrogen. Although this alloy has increased ductility during multi-stage deformation and is used to make rivets. However, this alloy does not have sufficiently high strength properties for highly stressed components.

Aus US 4,842,652 ist ein Verfahren einer Wärmebehandlung von (α+β)-Titanlegierung (Ti-6426) bekannt, welches aus Warmschmieden bei einer Temperatur höher als β-Transus, Mischkristallbehandlung der Schmiedelegierung unterhalb β-Transus aber innerhalb β-Transus minus 50°C für eine bis vier Stunden, Wasserkühlen bei Raumtemperatur oder Transfer in ein Salzbad mit einer Temperatur von 100-1400°F (204-760°C) und Vergüten (Ausscheidungsbehandlung) bei einer Temperatur von 1100-1200°F (593-650°C) für zwei bis 16 Stunden besteht. Eine solche Wärmebehandlung erlaubt zwar die Erhöhung der Bruchfestigkeit und der niedrigen Schwingungsfestigkeit von (α+β)-Titanlegierungen, aber zugleich verliert die Legierung die plastische Verformbarkeit bei Raumtemperatur.Out US 4,842,652 a method of heat treatment of (α + β) titanium alloy (Ti-6426) is known which consists of hot forging at a temperature higher than β-transus, solid solution treatment of forging alloy below β-transus but within β-transus minus 50 ° C for a to four hours, water cooling at room temperature or transfer to a salt bath at a temperature of 100-1400 ° F (204-760 ° C) and quenching (excretion treatment) at a temperature of 1100-1200 ° F (593-650 ° C) for two to 16 hours. Although such a heat treatment allows the increase of the breaking strength and the low vibration resistance of (α + β ) titanium alloys, at the same time the alloy loses the plastic deformability at room temperature.

Aus dem Artikel L.X. Lee et al. "Flow stress behaviour and deformation characteristics of Ti-3AI-5V-5Mo compressed at elevated temperatures" materials and design, Bd. 23, 2002, S. 451-457 . XP002413477 ist eine Titanlegierung Ti-3AI-5V-5Mo bekannt. Die Legierung wird einem Drucktest in einem Temperaturbereich von 700 - 1000°C und einer Dehnungsrate von 0,05 - 15/s unterzogen. Die β-transus-Temperatur für die Legierung beträgt etwa 860°C. Aus der Legierung warden warmgewalzte Stangen hergestellt und auf 10 mm im Durchmesser abgedreht.From the Article LX Lee et al. "Flow stress behavior and deformation characteristics of Ti-3AI-5V-5Mo compressed at elevated temperatures" materials and design, Vol. 23, 2002, pp. 451-457 , XP002413477 is a titanium alloy Ti-3AI-5V-5Mo known. The alloy is subjected to a pressure test in a temperature range of 700-1000 ° C and a strain rate of 0.05-15 / s. The β-transus temperature for the alloy is about 860 ° C. Hot rolled rods were made from the alloy and turned to 10 mm in diameter.

Aus M.J. Donachie: "Titanium - technical guide" 2000, ASM International. Materials Park, Ohio, XP002413485 ist bekannt, 2 bis 6 Ges.-% Zinn als α-Stabilisierer und 2 bis 8 Gew.-% Zirkon als α- und β-Verfestiger in Titanlegierungen einzulegieren.From M.J. Donachie: "Titanium - technical guide" 2000, ASM International. Materials Park, Ohio, XP002413485 is known to alloy 2 to 6% by weight of tin as α-stabilizer and 2 to 8% by weight of zirconium as α- and β-stabilizer in titanium alloys.

Aus Y. Combres, J.-J. Blandin: "Comparison of the β-CEZ and Ti-64 superlastic properties", Titanium '95: Science and Technology, 1996, S. 864-871, XP002413478 Editors P.A. Blankinsop, W.J. Evans, H.M. Flower ist eine Titan-β-Titanlegierung mit 5,05% Al, 1.98% Sn, 4,07% Zr, 4,03% Mo, 2,18% Cr, 1 % Fe bekannt und eine Titanlegierung mit 4.9%Al, 2% Sn, 4,37% Zr, 3,99% Mo, 2% Cr 0,93% Fe und kleine Anteilen an O C, H, N bekannt. Die β-transus-Temperatur beträgt etwa 890°C.Out Y. Combres, J.-J. Blandin: "Comparison of the β-CEZ and Ti-64 superlastic properties", Titanium '95: Science and Technology, 1996, pp. 864-871, XP002413478 Editors PA Blankinsop, WJ Evans, HM Flower For example, titanium-β titanium alloy is known to be 5.05% Al, 1.98% Sn, 4.07% Zr, 4.03% Mo, 2.18% Cr, 1% Fe, and a titanium alloy of 4.9% Al, 2%. Sn, 4.37% Zr, 3.99% Mo, 2% Cr 0.93% Fe and small amounts of OC, H, N known. The β-transus temperature is about 890 ° C.

Schließlich ist aus US 5,697,183 ein Verfahren der Wäremebehandlung von (α+β)-Titanlegierung bekannt, umfassend eine Warmverarbeitung im (α+β)-Phasengebiet mit einer Verformungsrate von nicht weniger als 30%, darauf folgend Verarbeiten bei einem Temperaturbereich von β-Transus minus 55°C bis β-Transus minus10°C für 60 Minuten und Luftkühlen und folgende Wärmebehandlung der luftgekühlten Titanlegierung in einem Temperaturbereich von β-Transus minus 250°C bis β-Transus minus 120°C für 60 Minuten und Luftkühlen. Ein solches Verfahren einer Wärembehandlung erlaubt zwar wiederum das Erhöhen der Bruchfestigkeit ohne hierbei die Duktilität maßgeblich zu verschlechtem. Jedoch wird die Duktilität der Legierung nicht auf einen solchen Wert gebracht, dass die Legierung bei Raumtemperatur um einen für übliche Produktgeometrien ausreichenden Betrag verformen zu können.Finally is off US 5,697,183 a method of heat treatment of (α + β) titanium alloy comprising hot working in the ( α + β ) phase region at a strain rate of not less than 30%, subsequently processing at a temperature range of β-transus minus 55 ° C to β-transus minus 10 ° C for 60 minutes and air cooling and subsequent heat treatment of the air-cooled titanium alloy in a temperature range of β-transus minus 250 ° C to β-transus minus 120 ° C for 60 minutes and air cooling. Although such a method of heat treatment in turn allows increasing the breaking strength without significantly deteriorating the ductility. However, the ductility of the alloy is not brought to such a value that the alloy can be deformed at room temperature by an amount sufficient for common product geometries.

Aufgrund der eingangs genannten besonders vorteilhaften Eigenschaften von Titanlegierungen wäre aber der Einsatz von Bauteilen aus Titanlegierungen in einer Vielzahl anderer technischer Gebiete interessant, insbesondere in einigen Gebieten von Großserienprodukten, in denen eine günstige Fertigungstechnik erforderlich ist.Due to the above-mentioned particularly advantageous properties of titanium alloys but the use of components made of titanium alloys in a variety of other technical fields would be interesting, especially in some areas of mass production, where a favorable manufacturing technology is required.

Der Erfindung lag daher die Aufgabe zugrunde, ein Verfahren zur Verarbeitung einer Titanlegierung bereitzustellen, welche(s) eine kostengünstigere Verarbeitung erlaubt.The invention therefore an object of the invention to provide a method for processing a titanium alloy, which (s) allows more cost-effective processing.

Eine Titanlegierung, die etwa 2 - 4,0 Gew,-% Aluminium, etwa 4 - 5,5 Gew.-% Vanadium, etwa 4,0 - 6,0 Gew.- % Molybdän, etwa 0,5 - 1,5 Gew.-% Zirkon und etwa 0,5 - 1,5 Gew.-% Zinn aufweist,
eignet sich einerseits zur unmittelbaren Bearbeitung mittels Kaltverformung ohne vorangehende gesonderte Wärmebehandlung, also unmittelbar nach der Herstellung des Halbzeugs beispielsweise durch Warmwalzen. Die zuvor beschriebene kaltverformbare α+β-Titanlegierung eignet sich darüber hinaus jedoch insbesondere dann, wenn höhere Kaltverformungsraten bei gleichzeitig hoher Festigkeit des kaltverformten Bauteils erzielt werden sollen, auch für die Anwendung des nachfolgend beschriebenen, erfindungsgemäßen Wärmebehandlungsverfahrens. Die Kombination der solcherart legierten α+β-Titanlegierung mit dem erfindungsgemäßen Wärmebehandlungsverfahren erzielt besonders gute Ergebnisse hinsichtlich Kaltverformbarkeit und Festigkeit der hergestellten Bauteile.A titanium alloy containing about 2-4.0 wt% aluminum, about 4-5.5 wt% vanadium, about 4.0-6.0 wt% molybdenum, about 0.5-1.5 % By weight of zirconium and about 0.5-1.5% by weight of tin,
On the one hand, it is suitable for direct processing by means of cold forming without a preceding separate heat treatment, ie immediately after the production of the semifinished product, for example by hot rolling. However, the above-described cold-formable α + β-titanium alloy is also particularly suitable if higher cold working rates are to be achieved with simultaneously high strength of the cold-formed component, also for the application of the heat treatment process according to the invention described below. The combination of the thus alloyed α + β-titanium alloy with the heat treatment process according to the invention achieves particularly good results in terms of cold workability and strength of the components produced.

Durch die Zulegierung der genannten Legierungselemente in den genannten Massenanteilen wird eine für die Kaltverformbarkeit des Halbzeugs und die Festigkeit des Bauteils besonders vorteilhafte α+β-Mischphasenstruktur bei Raumtemperatur erzielt, insbesondere wenn die Legierung mit dem erfindungsgemäßen Wärmebehandlungsverfahren behandelt wird. Zinn und Zirkon sind neutrale Substitutionslegierungselemente und ihre Zugabe resultiert in einer wirksamen Mischkristallverfestigung. Der Gehalt von Zinn und Zirkon von weniger als 0,5 % resultiert nicht in einer Legierungsverfestigung. Der optimale Gehalt von Zinn und Zirkon in der Legierung ist 0,5-1,5% der Masse. Solche Konzentrationen führen zu einer Erhöhung der Legierungsfestigkeit aufgrund der Mischkristallverfestigung der α- und β-Phasen, aber wobei sich die Duktilität der Legierung praktisch nicht verändert. Eine Erhöhung des Gehalts von Zinn und Zirkon deutlich über 1,5% der Masse verschlechtert die Duktilität der Legierung.By alloying said alloying elements in said mass fractions is one for the cold workability of the semifinished product and the strength achieves the component particularly advantageous α + β mixed phase structure at room temperature, especially when the alloy is treated with the heat treatment process according to the invention. Tin and zirconium are neutral substitutional alloying elements and their addition results in efficient solid solution strengthening. The content of tin and zirconium of less than 0.5% does not result in alloy solidification. The optimum content of tin and zirconium in the alloy is 0.5-1.5% of the mass. Such concentrations lead to an increase in alloy strength due to solid solution strengthening of the α and β phases, but with virtually no change in the ductility of the alloy. Increasing the content of tin and zirconium well above 1.5% of the mass degrades the ductility of the alloy.

Weiterhin ist es vorteilhaft, wenn die Titanlegierung etwa 0,1-0,4 Gew.-% Sauerstoff aufweist. Die Zugabe dieses Legierungselements hat sich als vorteilhaft für die Kaltverformbarkeit und Festigkeit der wärmebehandelten Titanlegierung erwiesen. Sauerstoff ist ein stark α-stabilisierendes Element. Eine Erhöhung des Sauerstoffgehalts in der Legierung resultiert in einer Erhöhung des α-Phasenanteils und einer starken Verfestigung aufgrund der Ausbildung von fester Zwischengitterlösung. Der optimale Sauerstoffgehalt in der Legierung ist 0,1-0,4% der Masse. Ein solcher Sauerstoffgehalt führt nicht zu einer signifikanten Änderung des α-Phasenanteils (etwa 3-5%) aber erlaubt es, dessen Festigkeit und folglich den Gesamtfestigkeitslevel zu erhöhen praktisch ohne Absenkung der Duktilität.Furthermore, it is advantageous if the titanium alloy has about 0.1-0.4 wt .-% oxygen. The addition of this alloying element has been found to be beneficial for the cold ductility and strength of the heat treated titanium alloy. Oxygen is a strong α-stabilizing element. An increase in the oxygen content in the alloy results in an increase of the α-phase content and a strong solidification due to the formation of solid interstitial solution. The optimum oxygen content in the alloy is 0.1-0.4% of the mass. Such an oxygen content does not lead to a significant change in the α-phase content (about 3-5%), but allows to increase its strength and consequently the overall strength level practically without lowering the ductility.

Die der Erfindung zugrunde liegende Aufgabe wird erfindungsgemäß gelöst mittels eines Wärmebehandlungsverfahrens nach Anspruch 1.The object underlying the invention is achieved by means of a heat treatment method according to claim 1.

Die Erfindung basiert auf der Erkenntnis, dass die beispielsweise aus US 5,679,183 bekannte Legierungsklasse durch ihre Wärmeberhandlung kein Wachstum existierender α-Partikel erreicht, sondern neue Partikel erzeugt, welche eine feinlamellare Morphologie aufweisen. Eine solcherart ausgebildete bimodale Struktur hat zwar eine nennenswerte Bruchfestigkeit, jedoch unter Inkaufnahme einer erheblichen Duktilitätsverringerung. Die folgende Erwärmung im Temperaturbereich von β-Transus minus 250°C bis β-Transus minus 120°C resultiert zwar in der Vergrößerung der verteilten Ausscheidungen und somit einer Erhöhung der Duktilität. Jedoch bleibt die Struktur bimodal, da sie aus einer kleinen Menge von β-Phase und Partikeln der α-Phase von unterschiedlicher Morphologie (geometrisch gleichmäßig und lamellar) besteht. Eine solche Struktur kann keinen Ausgangspunkt für eine Duktilität bei Raumtemperatur bereitstellen.The invention is based on the realization that the example of US 5,679,183 known alloy class achieved by their heat treatment no growth of existing α-particles, but creates new particles, which have a fine-lamellar morphology. Although a bimodal structure formed in this way has an appreciable breaking strength, it does so at the expense of a considerable reduction in ductility. The following heating in the temperature range of β-transus minus 250 ° C to β-transus minus 120 ° C. Although results in the increase in the distributed precipitates and thus an increase in ductility. However, the structure remains bimodal because it consists of a small amount of β-phase and α-phase particles of different morphology (geometrically uniform and lamellar). Such a structure can not provide a starting point for room temperature ductility.

Die Erfindung basiert auf der Erkenntnis, dass globulare Strukturen eine gute Kombination von Festigkeit und Duktilität aufweisen. Sie können erhalten werden in (α+β)-Titanlegierungen nach Verformung im Zweiphasengebiet nahe der Temperatur von β-Transus. Jedoch hängt die Ausgewogenheit von Festigkeit und Duktilität von der strukturellen Bauteilgröße ab. Je feiner die α-Phasenausscheidungen geometrisch gleichmäßig sind, desto höher wird die Festigkeit und desto geringer wird die Duktilität sein. Eine beachtliche Absenkung der Festigkeit und des Bruchwiderstands bei geringem Anstieg der Duktilität wird auftreten bei sehr großen globularen Partikeln der α-Phase.The invention is based on the recognition that globular structures have a good combination of strength and ductility. They can be obtained in (α + β) titanium alloys after deformation in the two-phase region near the temperature of β-transus. However, the balance of strength and ductility depends on the structural component size. The finer the α-phase precipitates are geometrically uniform, the higher the strength and the lower the ductility will be. A considerable decrease in strength and fracture resistance with little increase in ductility will occur with very large α-phase globular particles.

Folglich ist eine richtige Wahl der chemischen Legierungszusammensetzung und ein Verfahren der Wärmebehandlung für eine ausgewogene Duktilitätserhöhung ohne nennenswerte Festigkeitsverringerung erforderlich um eine Verformung bei Raumtemperatur um einen für typische Produktgeometrien ausreichenden Verformungsgrad, insbesondere einen Verformungsgrad von nicht weniger als 60% zu ermöglichen.Thus, a proper choice of chemical alloy composition and method of heat treatment for balanced ductility enhancement without significant strength reduction is required to allow for room temperature deformation to a degree sufficient for typical product geometries, particularly a degree of deformation of not less than 60%.

Durch das erfindungsgemäße Wärmebehandlungsverfahren wird eine α+β-Titanlegierung bereitgestellt, welche einerseits eine hohe Duktilität aufweist und andererseits eine sehr geringe Verfestigung bei Verformung aufweist. Die Erwärmung der Titanlegierung bis auf die untere Glühtemperatur kann mit unterschiedlichen Erwärmungsraten erfolgen. Vorzugsweise wird eine langsame Erwärmung mit einer Erwärmungsrate von weniger als 20° pro Minute gewählt, um die Ausbildung von Spannungsrissen zu vermeiden. Das Glühen der Titanlegierung erfolgt vorzugsweise in inerter Atmosphäre, um eine Diffusion versprödend wirkender Elemente (z.B. Sauerstoff, Stickstoff oder Kohlenstoff) in die Titanlegierung zu vermeiden.The heat treatment process according to the invention provides an α + β titanium alloy which, on the one hand, has a high ductility and, on the other hand, has a very low degree of solidification upon deformation. The heating of the titanium alloy to the lower annealing temperature can be done with different heating rates. Preferably, a slow heating with a heating rate of less than 20 ° per minute is chosen to avoid the formation of stress cracks. The annealing of the titanium alloy is preferably carried out in an inert atmosphere in order to avoid diffusion of embrittling elements (eg oxygen, nitrogen or carbon) into the titanium alloy.

Das Abkühlen der Titanlegierung auf Umgebungstemperatur erfolgt vorzugsweise ebenfalls in inerter Atmosphäre. α+β-Titanlegierungen sind, wie viele metallische Werkstoffe, durch Abschrecken von einer Glühtemperatur härtbar. Dieser Effekt ist jedoch unerwünscht, wenn ein gut kaltverformbarer Titanlegierungswerkstoff hergestellt werden soll. Die Abkühlrate ist daher vorzugsweise so gering zu wählen, dass eine Härtung der Titanlegierung vermieden wird.The cooling of the titanium alloy to ambient temperature is preferably also carried out in an inert atmosphere. Like many metallic materials, α + β titanium alloys are curable by quenching from an annealing temperature. However, this effect is undesirable if a good cold-workable titanium alloy material is to be produced. The cooling rate is therefore preferably to be chosen so low that hardening of the titanium alloy is avoided.

Das erfindungsgemäße Verfahren umfasst folgende Schritte vor dem Glühen bei der unteren Glühtemperatur:

  1. 1. Glühen der Titanlegierung bei einer oberen Glühtemperatur, welche 50° bis 100° unterhalb der Umwandlungstemperatur (β-transus), insbesondere 60° bis 100° unterhalb der Umwandlungstemperatur (β-transus) liegt,
  2. 2. Abkühlen der Titanlegierung auf die untere Glühtemperatur.
The method according to the invention comprises the following steps before annealing at the lower annealing temperature:
  1. 1. annealing the titanium alloy at an upper annealing temperature which is 50 ° to 100 ° below the transition temperature (β-transus), in particular 60 ° to 100 ° below the transition temperature (β-transus),
  2. 2. cooling the titanium alloy to the lower annealing temperature.

Die erste Stufe des Anlassens wir bei einem Temperaturbereich von β-Transus minus 50°C bis β-Transus minus 100°C gewählt. Die Struktur der Legierung ist durch separate globulare Partikel der α-Phase geprägt, welche bei dieser Temperatur in einer β-Matrix angeordnet sind. Isothermes Halten bei dieser Temperatur stellt nicht nur eine Lösung der überschüssigen (sekundären) α-Phase und eine Annäherung an den Gleichgewichtszustand der α- und der β-Phase bereit, sondern führt auch zu einer Verringerung der strukturellen Defekte im Zuge der Realisation eines Polygonisationsprozesses. Nach dem Beenden des isothermen Haltens wird die Legierung auf die Temperatur β-Transus minus 160°C bis β-Transus minus 230°C abgekühlt bei einer Kühlrate von 0.01-0.02 °/s. Eine solche Kühlrate erlaubt nicht die Ausbildung von neuen Partikeln der α-Phase aus der β-Matrix während des Abkühlens, sondern erlaubt das Wachstum bereits existierender, primärer α-Kristalle in der Struktur. Isothermes Halten für 3-6 Stunden bei der zweiten Stufe des Anlassens erlaubt das Vollenden des Homogenisationsprozesses. Nachfolgendes Kühlen auf Raumtemperatur wird ausgeführt bei einer Kühlrate von 2,5-3,5 °/s, was ausreichend ist, um Ausscheidung der sekundären α-Phase zu verhindern.The first stage of annealing is chosen at a temperature range of β-transus minus 50 ° C to β-transus minus 100 ° C. The structure of the alloy is characterized by separate globular particles of the α-phase, which are arranged at this temperature in a β-matrix. Isothermal holding at this temperature not only provides a solution to the excess (secondary) α phase and approximation to the equilibrium state of the α and β phases, but also leads to a reduction in structural defects in the course of the realization of a polygonization process. After completion of isothermal holding, the alloy is cooled to the temperature β-transus minus 160 ° C to β-transus minus 230 ° C at a cooling rate of 0.01-0.02 ° / sec. Such a cooling rate does not allow the formation of new α-phase particles from the β-matrix during cooling, but allows the growth of pre-existing, primary α-crystals in the structure. Isothermal holding for 3-6 hours at the second stage of annealing allows completion of the homogenization process. Subsequent cooling to room temperature is carried out at a cooling rate of 2.5-3.5 ° / s, which is sufficient to prevent precipitation of the secondary α-phase.

Das Ausführen des zweistufigen Anlassens erlaubt es, die Größe der α-Phasenpartikel von 1-2µm auf 5.7µm zu erhöhen und eine Zusammensetzung der β-Phase zu erhalten, welche einem [Mo]eq = 14-15 entspricht, und auch, die Fehlstellendichte in der α-Phase im Zuge der Realisation eines Polygonisationsprozesses bei der ersten Anlassstufe zu verringern. Die für eine gute Kaltverformbarkeit zu erzielende Phasenzusammensetzung kann hierdurch weiter optimiert werden. Die vorgeschalteten Glühbehandlungsschritte erfolgen wiederum vorzugsweise in inerter Atmosphäre. Wiederum ist, wie zuvor, beim Abkühlen der Titanlegierung auf eine Abkühlrate zu achten, die Spannungsrisse vermeidet.Performing the two-stage annealing makes it possible to increase the size of the α-phase particles from 1-2μm to 5.7μm and to obtain a β-phase composition corresponding to [Mo] eq = 14-15, and also the defect density in the α-phase in the course of the realization of a polygonisation process at the first tempering stage. The phase composition to be achieved for good cold workability can hereby be further optimized. The upstream annealing steps are again preferably carried out in an inert atmosphere. Again, as before, when cooling the titanium alloy to pay attention to a cooling rate, which avoids stress cracks.

Dabei kann die Erfindung weiter optimiert werden, indem die Titanlegierung bei der oberen Glühtemperatur mehr als eine Stunde lang, insbesondere etwa zwei Stunden lang, geglüht wird. Wiederum hängt die Glühdauer von den Abmessungen des Titanlegierungshalbzeugs ab. Eine Glühdauer von mehr als einer Stunde, insbesondere von zwei Stunden, hat sich als zuverlässig für die Reproduktion der gewünschten Phasenzusammensetzung erwiesen.In this case, the invention can be further optimized by the titanium alloy at the upper annealing temperature for more than one hour, in particular for about two hours, annealed. Again, the annealing time depends on the dimensions of the titanium alloy semifinished product. An annealing time of more than one hour, especially two hours, has proven to be reliable for the reproduction of the desired phase composition.

Weiterhin ist es bei dieser Verfahrensfortbildung vorteilhaft, wenn die Titanlegierung bei der unteren Glühtemperatur mehr als drei Stunden, vorzugsweise drei bis sechs, insbesondere etwa vier Stunden lang geglüht wird. Aufgrund der vorgeschalteten Glühbehandlung bei höherer Temperatur kann die für eine zuverlässige Phasenzusammensetzung nach dem gewünschten Ziel erforderliche Glühdauer bei der unteren Glühtemperatur verringert werden. Mehr als drei Stunden, insbesondere vier Stunden, haben sich bei üblichen Abmessungen, wie beispielsweise Halbzeug in Form von Rundmaterial im Durchmesser zwischen 10 bis 20mm als ausreichend erwiesen.Furthermore, it is advantageous in this process development, if the titanium alloy is annealed at the lower annealing temperature more than three hours, preferably three to six, in particular about four hours. Due to the upstream annealing treatment at a higher temperature, the annealing time required for a reliable phase composition to the desired target can be reduced at the lower annealing temperature. More than three hours, in particular four hours, have been found in conventional dimensions, such as semi-finished in the form of round material in the diameter between 10 to 20mm sufficient.

Es ist besonders vorteilhaft, wenn die Titanlegierung von der oberen Glühtemperatur an Luft bei einer Kühlrate von 0,01 - 0.02°C/min auf die untere Glühtemperatur abgekühlt wird. Bei dieser Kühlrate wird die Bildung von unerwünschten Phasenanteilen, inneren Spannungen und die Ausscheidung von Legierungselementen in ungewünschtem Umfang vermieden.It is particularly advantageous if the titanium alloy is cooled from the upper annealing temperature of air to the lower annealing temperature at a cooling rate of 0.01-0.02 ° C / min. At this cooling rate, the formation of undesirable phase fractions, internal stresses and the precipitation of alloying elements to an undesirable extent is avoided.

Es ist besonders vorteilhaft, wenn die obere Glühtemperatur etwa 770-830°C, insbesondere 800°C beträgt. Dieser Temperaturbereich hat sich für die meisten technisch gebräuchlichen α+β-Titanlegierungen als praktikabel erwiesen.It is particularly advantageous if the upper annealing temperature is about 770-830 ° C, in particular 800 ° C. This temperature range has been found to be practicable for most of the commercially available α + β titanium alloys.

Das erfindungsgemäße Verfahren kann weiter fortgebildet werden, indem die Titanlegierung von der unteren Glühtemperatur an Luft bei einer Kühlrate von etwa 2,5° bis 3,5°C/min auf Raumtemperatur abgekühlt wird. Durch diese Abkühlrate werden unerwünschte Ausscheidungen von Legierungselementen sowie unerwünschte Phasenbildungen vermieden und ein optimales Ergebnis hinsichtlich der Kaltverformbarkeit und der Festigkeit des kaltverformten Bauteils erreicht.The process of the present invention can be further developed by cooling the titanium alloy from the lower annealing temperature of air to room temperature at a cooling rate of about 2.5 ° to 3.5 ° C / min. This cooling rate avoids unwanted precipitation of alloying elements as well as unwanted phase formations and achieves an optimum result in terms of the cold workability and the strength of the cold-formed component.

Das erfindungsgemäße Verfahren kann weiterhin vorteilhaft eingesetzt werden, wenn die Titanlegierung vor der Wärmebehandlung durch ein Warmwalzverfahren bearbeitet wird. Das Warmwalzverfahren ist ein Verfahren, um beispielsweise Profilhalbzeuge oder Blechhalbzeuge aus Titanlegierungen herzustellen. Durch das Warmwalzverfahren wird das Gefüge beeinflusst. Das solcher Art beeinflusste Gefüge eignet sich für die erfindungsgemäßen Wärmebehandlungsschritte besonders gut.The method according to the invention can furthermore be advantageously used if the titanium alloy is processed by a hot rolling method before the heat treatment. The hot rolling process is a process to produce, for example semi-finished profile products or semifinished titanium alloy products. The hot rolling process influences the microstructure. The structure influenced in this way is particularly suitable for the heat treatment steps according to the invention.

Es ist weiterhin vorteilhaft, wenn die untere Glühtemperatur etwa 670-730°C, insbesondere 700°C beträgt. Diese Glühtemperatur hat sich für die meisten technisch gebräuchlichen α+β-Titanlegierungen als praktikabel erwiesen.It is also advantageous if the lower annealing temperature is about 670-730 ° C, in particular 700 ° C. This annealing temperature has been found to be practicable for most of the technically common α + β titanium alloys.

Es ist weiterhin vorteilhaft für das erfindungsgemäße Verfahren, wenn die Titanlegierung mit mindestens einem α-Stabilisierer und mindestens einem β-Stabilisierer legiert ist. Durch Zugabe solcher Legierungselemente kann eine Titanlegierung mit einem auf die spezifische Anwendung optimierten Anteil an α-Phasen und β-Phasen hergestellt werden. Die Anteile der stabilisierenden Legierungselemente sind dabei auf das erfindungsgemäße Wärmebehandlungsverfahren abzustimmen, um die gewünschte Kaltverformbarkeit des Halbzeugs und die gewünschte Festigkeit des kaltverformten Bauteils zu erreichen.It is furthermore advantageous for the method according to the invention if the titanium alloy is alloyed with at least one α-stabilizer and at least one β-stabilizer. By adding such alloying elements, a titanium alloy can be produced with a proportion of α-phase and β-phase optimized for the specific application. The proportions of the stabilizing alloying elements are to be matched to the heat treatment process according to the invention in order to achieve the desired cold workability of the semifinished product and the desired strength of the cold-formed component.

Das erfindungsgemäße Verfahren kann weiter fortgebildet werden, indem nach dem Glühen bei der unteren Glühtemperatur und/oder nach dem Glühen bei der oberen Glühtemperatur eine Oberflächenschicht von der Titanlegierung mechanisch, insbesondere spanend, entfernt wird. Die Glühbehandlung hat oftmals, selbst wenn sie bei inerter Atmosphäre durchgeführt wird, einen gewissen Einfluss auf die Oberflächenschicht des Titanlegierungshalbzeugs. Dieser Einfluss bewirkt eine Versprödung und erhöhte Rissempfindlichkeit des Halbzeugs, was sich in einer geringeren Kaltverformbarkeit und niedrigeren Festigkeit des kaltverformten Bauteils auswirkt. Diesem nachteiligen Effekt kann entgegengewirkt werden, indem die beeinflusste Randschicht des Halbzeugs vor der Kaltverformung entfernt wird. Hierzu eignet sich insbesondere eine spanende Fertigung.The method according to the invention can be further developed by removing a surface layer of the titanium alloy mechanically, in particular by machining, after annealing at the lower annealing temperature and / or after annealing at the upper annealing temperature. The annealing treatment often has some influence on the surface layer of the titanium alloy semi-finished product, even if it is performed in an inert atmosphere. This influence causes embrittlement and increased crack sensitivity of the semifinished product, which results in lower cold workability and lower strength of the cold-worked component. This disadvantageous effect can be counteracted by removing the affected edge layer of the semifinished product before the cold deformation. In particular, a machining production is suitable for this purpose.

Ein weiterer Aspekt der Erfindung ist die Verwendung einer gemäß der vorangehenden Beschreibung wärmebehandelten α+β-Titanlegierung zur Herstellung von Titanbauteilen mittels Kaltverformung. Hierdurch ist die kostengünstige Fertigung von Großserienbauteilen aus einer Titanlegierung möglich. Dies ist beispielsweise für eine Vielzahl von Bauteilen im Automobilbereich erstrebenswert, insbesondere für Bauteile, die als bewegte Teile im Antriebsstrang verbaut sind.Another aspect of the invention is the use of a heat treated α + β titanium alloy as described above to produce titanium components by cold working. As a result, the cost-effective production of large-volume components made of a titanium alloy is possible. This is desirable, for example, for a variety of components in the automotive sector, especially for components that are installed as moving parts in the drive train.

Dabei kann die erfindungsgemäße Verwendung insbesondere zur Herstellung von Titanschrauben mittels Kaltstauchen und/oder Gewinderollen dienen. Diese Verwendung ist beispielsweise zur Herstellung von Radschrauben für den Automobilbereich geeignet. Die Verwendung von Radschrauben aus einer Titanlegierung hat den Vorteil, dass einerseits die Massenträgheitskräfte des Rades verringert werden können und hierdurch die Fahreigenschaften und der Federungskomfort verbessert und der Verbrauch des Fahrzeugs gesenkt werden können. Die Verwendung von Titanschrauben hat den weiteren Vorteil, dass insbesondere bei der Verwendung in Kombination mit Leichtmetallfelgen aus Aluminiumlegierungen oder Magnesiumlegierungen eine Kontaktkorrosion vermieden wird, wie sie beispielsweise bei der Verwendung von Stahlschrauben häufig auftritt.In this case, the use according to the invention can serve in particular for the production of titanium screws by means of cold heading and / or thread rolling. This use is suitable, for example, for the production of wheel bolts for the automotive sector. The use of titanium alloy wheel bolts has the advantage that, on the one hand, the mass inertia forces of the wheel can be reduced and, as a result, the driving characteristics and the suspension comfort can be improved and the fuel consumption of the vehicle can be lowered. The use of titanium screws has the further advantage that, especially when used in combination with alloy wheels made of aluminum alloys or magnesium alloys contact corrosion is avoided, as it often occurs, for example, when using steel screws.

Ein weiterer Aspekt der Erfindung ist ein Verfahren zur Herstellung von Titanschrauben mit den Schritten

  • Herstellung eines Rundmaterials mittels Warmwalzen,
  • Wärmebehandeln des Rundmaterials nach einem Verfahren gemäß dem zuvor beschriebenen Wärmebehandlungsverfahren,
  • Ausformen des Schraubenkopfes durch Kaltstauchen und
  • Ausformen des Gewindes durch Gewinderollen.
Another aspect of the invention is a method of making titanium screws with the steps
  • Production of a round material by means of hot rolling,
  • Heat treating the round material by a method according to the above-described heat treatment method,
  • Forming the screw head by cold heading and
  • Forming the thread by thread rolling.

Mittels dieses Verfahrens ist eine fertigungstechnisch besonders kostengünstige Herstellung von Titanschrauben als Großserienbauteil möglich. Die Titanschrauben erzielen und übertreffen dabei die Festigkeitswerte gemäß der DIN-Klassifizierung 8.8 und sind somit beispielsweise für den Einsatz als Radschrauben geeignet.By means of this method, a manufacturing technology particularly cost-effective production of titanium screws as a mass-produced component is possible. The titanium bolts achieve and exceed the strength values according to the DIN classification 8.8 and are thus suitable, for example, for use as wheel bolts.

Die erfindungsgemäße Titanlegierung mit α- und β-Phasenanteil, zeichnet sich insbesondere dadurch aus, dass die Größe der α-Phasenpartikel etwa 5-7µm beträgt. Dabei kann sie vorzugsweise Legierungselemente enthalten , die einen Molybdän-Äquivalent von [Mo]eq =14-15 ergeben. Der Molybdän-Equivalent ist ein aus der Art und Menge der Legierungsanteile errechneter Wert und liegt für α-Titanlegierungen üblicherweise zwischen 0 und 2,5, für α+β- Titanlegierungen zwischen 2,5 und 10 und für β-Titaniegierungen über 10.The titanium alloy according to the invention with α- and β-phase content, is characterized in particular by the fact that the size of the α-phase particles is about 5-7μm. In doing so, it may preferably contain alloying elements giving a molybdenum equivalent of [Mo] eq = 14-15. The molybdenum equivalent is a value calculated from the type and amount of alloying components and is usually between 0 and 2.5 for α-titanium alloys, between 2.5 and 10 for α + β titanium alloys, and over 10 for β-titanium alloys.

Besonders bevorzugte Ausbildungen der Erfindung werden im Folgenden in Form von beispielhaften Verfahrensabläufen und Legierungszusammensetzungen beschrieben.Particularly preferred embodiments of the invention are described below in the form of exemplary process sequences and alloy compositions.

I. Erstes Ausführungsbeispiel I. First embodiment

Als α+β-Titanlegierung wird die bekannte Legierung Ti - 3,0Al - 4,5V - 5,0Mo verwendet. Nach der Herstellung der Legierung wird in einem Warmwalzverfahren ein Rundmaterial mit beispielsweise 13mm Durchmesser hergestellt. Dieses Halbzeug ist in üblichen Längen beziehbar.As the α + β-titanium alloy, the known alloy Ti - 3.0Al - 4.5V - 5.0Mo is used. After the alloy has been produced, a round material, for example 13 mm in diameter, is produced in a hot rolling process. This semi-finished is available in usual lengths.

Das Halbzeug wird in einem Glühofen der folgenden Wärmebehandlung unterzogen:

  • Aufwärmen auf 800°C,
  • Glühbehandlung bei 800°C für eine Dauer von zwei Stunden,
  • Abkühlen mit einer Rate von 0,02°C pro Sekunde auf 770°C,
  • Glühen bei 770°C für eine Dauer von 30 Minuten,
  • Abkühlen mit einer Rate von 0,02°C pro Sekunde auf 740°C,
  • Glühbehandlung bei 740°C für eine Dauer von 30 Minuten,
  • Abkühlen mit einer Rate von 0,02°C pro Sekunde auf 700°C,
  • Glühen bei 700°C für eine Dauer von vier Stunden, und
  • Entnahme der Halbzeuge aus dem Glühofen und Abkühlen der Halbzeuge an Umgebungsluft.
The semi-finished product is subjected to the following heat treatment in an annealing furnace:
  • Warm up to 800 ° C,
  • Annealing at 800 ° C for a period of two hours,
  • Cooling at a rate of 0.02 ° C per second to 770 ° C,
  • Annealing at 770 ° C for 30 minutes,
  • Cooling at a rate of 0.02 ° C per second to 740 ° C,
  • Annealing at 740 ° C for 30 minutes,
  • Cooling at a rate of 0.02 ° C per second to 700 ° C,
  • Annealing at 700 ° C for a period of four hours, and
  • Removing the semi-finished products from the annealing furnace and cooling the semi-finished products to ambient air.

Die so behandelten Halbzeuge können hierauf folgend weiterverarbeitet werden, beispielsweise durch Herstellen eines Schraubenkopfes mittels eines Kaltstauchverfahrens und Herstellen eines Gewindes mittels Gewinderollen bei Umgebungstemperatur. Optional kann vor der Weiterverarbeitung eine Randschicht des Halbzeugs durch mechanische Bearbeitung abgetragen werden.The semifinished products treated in this way can then be processed further, for example by producing a screw head by means of a cold upsetting process and producing a thread by means of thread rolling at ambient temperature. Optionally, an edge layer of the semifinished product can be removed by mechanical processing prior to further processing.

II. Zweites AusführungsbeispielII. Second embodiment

Die Legierung wurde hergestellt durch zweifache Vakuumrückschmelzung mit Opferelektroden. Ihre chemische Zusammensetzung ist wie folgt: Ti -3,0%Al - 5,0%Mo - 4,5%V - 1,0%Zr-1,0%Sn - 0,25%O (die Temperatur von β-Transus ist 880°C).The alloy was made by double vacuum reflow with sacrificial electrodes. Its chemical composition is as follows: Ti -3.0% Al - 5.0% Mo - 4.5% V - 1.0% Zr-1.0% Sn - 0.25% O (the temperature of β- Transus is 880 ° C).

Der erhaltene Barren mit 8kg Gewicht wurde isotherm geschmiedet bei einer Temperatur im β-Gebiet auf ein Quader von 90x90mm und wurde dann auf eine Höhe von 45mm gesenkgeschmiedet. Dann wurde der Barren in Streifen mit einem rechteckigen Querschnitt von 45x45mm geschnitten und bei einer Temperatur im (α+β)-Gebiet geschmiedet, bis man Stäbe mit einem Durchmesser von 30mm erhält. Die Stäbe wurden unter Verwendung einer Drehbank zerspant, bis ein Durchmesser von 25mm erhalten wurde. Die dann erhaltenen Rohlinge wurden auf einen Durchmesser von 16mm bei einem Temperaturbereich von β-Transus minus 50°C bis β-Transus minus 100°C gewalzt. Die erste Erwärmung auf die vorgegebene Temperatur wurde für 30 Minuten ausgeführt. Nachfolgendes Erwärmen zwischen den Zügen erfolgte für 4 Minuten. Die gesamte Reduktionsrate war 65%.The resulting bar of 8kg weight was isothermally forged at a temperature in the β-area to a square of 90x90mm and was then drop forged to a height of 45mm. The billet was then cut into strips of rectangular cross section 45x45mm and forged at a temperature in the (α + β) region until rods with a diameter of 30mm were obtained. The rods were machined using a lathe until a diameter of 25mm was obtained. The blanks then obtained were rolled to a diameter of 16 mm at a temperature range of β-transus minus 50 ° C to β-transus minus 100 ° C. The first heating to the predetermined temperature was carried out for 30 minutes. Subsequent heating between trains was for 4 minutes. The total reduction rate was 65%.

Nach dem Walzen wurde der 16mm-Durchmesser-Stab einer Wärmebehandlung im Temperaturbereich von 860-780°C für 2 Stunden mit nachfolgendem Kühlen bei einer Kühlrate von 0,02K/s auf eine Temperatur von 700°C (β-Transus minus 190°C) und isothermem Halten für 4 Stunden unterzogen. Das Kühlen auf Raumtemperatur wurde bei einer Kühlrate von 3K/s ausgeführt.After rolling, the 16mm diameter rod was subjected to a heat treatment in the temperature range of 860-780 ° C for 2 hours followed by cooling at a cooling rate of 0.02K / s to a temperature of 700 ° C (β-transus minus 190 ° C ) and isothermal hold for 4 hours. Cooling to room temperature was carried out at a cooling rate of 3K / s.

Die Stäbe wurden unter Verwendung einer Drehbank auf einen Durchmesser von 13mm abgedreht.The rods were turned to 13mm diameter using a lathe.

II. Drittes Ausführungsbeispiel II. Third Embodiment

Es wurde ein 16mm-Durchmesser-Stab mit dem gleichen Verfahren wie im zweiten Ausführungsbeispiel erzeugt. Nach dem Walzen wurde der 16mm-Durchmesser-Stab wärmebehandelt bei einem Temperaturbereich von 860-780°C für 2 Stunden mit nachfolgendem Luftkühlen auf Raumtemperatur. Dann wurde der Stab auf die Temperatur von 700°C (β-Transus minus 190°C) erwärmt und für 4 Stunden gehalten. Das Kühlen auf Raumtemperatur wurde in Luft ausgeführt.A 16mm diameter rod was produced by the same method as in the second embodiment. After rolling, the 16mm diameter rod was heat treated at a temperature range of 860-780 ° C for 2 hours followed by air cooling to room temperature. Then the bar was heated to the temperature of 700 ° C (β - Transus minus 190 ° C) and held for 4 hours. Cooling to room temperature was carried out in air.

Die Stäbe wurden unter Verwendung einer Drehbank auf einen Durchmesser von 13mm abgedreht.The rods were turned to 13mm diameter using a lathe.

Weiter vorteilhafte Abläufe der erfindungsgemäßen Wärmebehandlung zeigt Tabelle 1: Wärmebehandlungsschritte Temperatur, °C Glühbehandlungsdauer (Stunden) Abkühlverfahren mechanische Bearbeitung Glühen nach der mechanischen Behandlungen 700 2,5 Umgebungsluft + - 700 7 Umgebungsluft + - 700 7 Umgebungsluft + 700°C, 1 Stunde 700 2,5 in Glühofen + - 700 7 in Glühofen + - 700 7 in Glühofen + 700°C, 1 Stunde 800°C, abkühlen auf 700°C 4 Umgebungsluft + - 800°C, abkühlen auf 700°C 7 Umgebungsluft + - 800°C, abkühlen auf 700°C 4 Umgebungsluft + 700°C, 1 Stunde 800°C, abkühlen auf 700°C 4 in Glühofen + - 800°C, abkühlen auf 700°C 7 in Glühofen + - 800°C, abkühlen auf 700°C 4 in Glühofen + 700°C, 1 Stunde Further advantageous processes of the heat treatment according to the invention are shown in Table 1: Heat treatment steps Temperature, ° C Annealing time (hours) cooling process mechanical machining Annealing after the mechanical treatments 700 2.5 ambient air + - 700 7 ambient air + - 700 7 ambient air + 700 ° C, 1 hour 700 2.5 in annealing furnace + - 700 7 in annealing furnace + - 700 7 in annealing furnace + 700 ° C, 1 hour 800 ° C, cool to 700 ° C 4 ambient air + - 800 ° C, cool to 700 ° C 7 ambient air + - 800 ° C, cool to 700 ° C 4 ambient air + 700 ° C, 1 hour 800 ° C, cool to 700 ° C 4 in annealing furnace + - 800 ° C, cool to 700 ° C 7 in annealing furnace + - 800 ° C, cool to 700 ° C 4 in annealing furnace + 700 ° C, 1 hour

Die nachfolgenden Tabellen zeigen die vorteilhaften Eigenschaften der Erfindung im Vergelich zur gebräuchlichen Legierung Ti - 3,8% - 6,5%V - 5,1 %Mo - 0,01%H - 0,05%Si. Legierung Temperatur der ersten Stufe, °C* Temperatur der zweiten Stufe, °C** Mechanische Eigenschaften Φ, % Maximaler Verformungsgrad bei Druck, % σ0,2, MPa σs, MPa δ, % Ti -
3,0%Al -
5,0%Mo -
4,5%V -
1,0%Zr
-1,0%Sn
-0,25%O 860 (Ac3 -30°) 700 (Ac3 - 190°) 940 1010 15 60 60 840 (Ac3 -50°) 930 990 18 68 70 820 (Ac3 - 70°) 915 970 20 70 72 800 (Ac3 - 90°) 910 960 22 71 73 780 (Ac3 - 920 990 16 65 65 Ti -
3,8%Al
-6,5%V
-5,1%Mo-
0,01%OH
-0,05 %Si, 860 700 720 940 17 60 65 840 685 920 20 68 74 820 670 900 25 70 75 800 660 880 27 70 76 780 700 930 22 65 70 * Kühlen auf die zweite Stufe wurde bei einer Kühlrate von 0,02Grad./s ausgeführt.
** Kühlen nach Beenden der Wärmebehandlung wurde ausgeführt bei einer Kühlrate von 3Grad/s. Legierung Temperatur der ersten Stufe, °C* Temperatur der zweiten Stufe, °C** Mechanische Eigenschaften Φ, % Maximaler Verformungsgrad bei Druck, % σ0,2MPa σs, MPa δ, % /o Ti -
3,0%Al -
5,0%Mo -
4,5%V -
1,0%Zr -
1,0%Sn -
0,25%O 860 1010 1150 8 20 25 840 1000 1130 8 23 25 820 700 990 1080 9,5 27 29 800 975 1040 10 29 31 780 950 1000 12 34 34 *Kühlen nach der ersten Stufe auf Raumtemperatur wurde in Luft ausgeführt.
**Kühlen nach Beenden der Wärmebehandlung wurde in Luft ausgeführt. The following tables show the advantageous properties of the invention in comparison to the conventional alloy Ti - 3.8% - 6.5% V - 5.1% Mo - 0.01% H - 0.05% Si. alloy Temperature of the first stage, ° C * Temperature of the second stage, ° C ** Mechanical properties Φ,% Maximum degree of deformation at pressure,% σ 0.2 , MPa σ s , MPa δ,% Ti -
3.0% Al -
5.0% Mo -
4.5% V -
1.0% Zr
1.0% Sn
0.25% O 860 (Ac 3 -30 °) 700 (Ac 3 - 190 °) 940 1010 15 60 60 840 (Ac 3 -50 °) 930 990 18 68 70 820 (Ac 3 - 70 °) 915 970 20 70 72 800 (Ac 3 - 90 °) 910 960 22 71 73 780 (Ac3 - 920 990 16 65 65 Ti -
3.8% Al
-6.5% V
-5.1% Mo
0.01% OH
-0.05% Si, 860 700 720 940 17 60 65 840 685 920 20 68 74 820 670 900 25 70 75 800 660 880 27 70 76 780 700 930 22 65 70 * Cooling to the second stage was performed at a cooling rate of 0.02 degrees / s.
** Cooling after completion of the heat treatment was carried out at a cooling rate of 3Grad / s. alloy Temperature of the first stage, ° C * Temperature of the second stage, ° C ** Mechanical properties Φ,% Maximum degree of deformation at pressure,% σ 0.2 MPa σ s , MPa δ,% / o Ti -
3.0% Al -
5.0% Mo -
4.5% V -
1.0% Zr -
1.0% Sn
0.25% O 860 1010 1150 8th 20 25 840 1000 1130 8th 23 25 820 700 990 1080 9.5 27 29 800 975 1040 10 29 31 780 950 1000 12 34 34 * Cooling after the first stage to room temperature was carried out in air.
** Cooling after completion of the heat treatment was carried out in air.

Man erkennt, dass die Zulegierung von Zinn und Zirkon eine Erhöhung der Festigkeit erlaubt, während die plastischen Eigenschaften auf einem hohen Level verbleiben (Tabelle 1). Neben den beanspruchten Bedingungen der Warmverformung und der Wärmebehandlung im Vergleich zum Stand der Technik (Tabelle 2) wird die Realisierung einer Verformung durch Druck bei Raumtemperatur zu einem Betrag von nicht weniger als 60% ermöglicht (Tabelle 1).It can be seen that the addition of tin and zirconium allows an increase in strength, while the plastic properties remain at a high level (Table 1). Besides the stressed conditions of hot working and heat treatment in comparison with the prior art (Table 2), it is possible to realize deformation by pressure at room temperature to an amount of not less than 60% (Table 1).

Claims (16)

  1. Heat treatment method for producing cold-workable (α+β) titanium alloys, comprising the steps:
    - annealing the titanium alloy at a lower annealing temperature which is between 160° to 230° below the transformation temperature (β transus),
    - cooling the titanium alloy to ambient temperature,
    characterised by the following steps prior to the annealing at the lower annealing temperature:
    - annealing the titanium alloy at an upper annealing temperature which is 50° to 100° below the transformation temperature (β transus),
    - cooling the titanium alloy to the lower annealing temperature.
  2. Method according to claim 1, characterised in that the upper annealing temperature is 60° to 100° below the transformation temperature (β transus).
  3. Method according to claim 2, characterised in that the titanium alloy is annealed at the upper annealing temperature for more than one hour, in particular for two hours.
  4. Method according to claim 2 or 3, characterised in that the titanium alloy is annealed at the lower annealing temperature for more than three hours, in particular for three to six hours, preferably for four hours.
  5. Method according to one of claims 2 to 4, characterised in that the titanium alloy is cooled from the upper annealing temperature to the lower annealing temperature in air at a cooling rate of 0.01 - 0.02°C/min.
  6. Method according to one of claims 2 to 5, characterised in that the upper annealing temperature is 770-830°C, in particular 800°C.
  7. Method according to one of the preceding claims, characterised in that the titanium alloy is cooled from the lower annealing temperature to room temperature in air at a cooling rate of 2.5° to 3.5°C/min ["air cooling"].
  8. Method according to one of the preceding claims, characterised in that the titanium alloy is processed by a hot rolling process prior to the heat treatment.
  9. Method according to one of the preceding claims, characterised in that the lower annealing temperature is 670-730°C, in particular 700°C.
  10. Method according to one of the preceding claims, characterised in that the titanium alloy is alloyed with at least one α stabiliser and at least one β stabiliser.
  11. Method according to claim 10, characterised in that the titanium alloy comprises
    - 2 - 4.0% by weight of aluminium,
    - 4 - 5.5% by weight of vanadium,
    - 4.5 - 6.0% by weight of molybdenum,
    - 0.5 - 1.5% by weight of zirconium and
    - 0.5 - 1.5% by weight of tin,
    - the remainder being titanium and impurities.
  12. Method according to one of the preceding claims, characterised in that, after the annealing at the lower annealing temperature and/or after the annealing at the upper annealing temperature, a surface layer is mechanically removed from the titanium alloy, in particular by machining.
  13. Use of an (α+β) titanium alloy heat-treated according to one of claims 1-12 to produce titanium components by means of cold working.
  14. Use according to claim 13 to produce titanium bolts by means of cold heading and/or thread rolling.
  15. Method for producing titanium bolts, which comprises:
    - producing a round material by means of hot rolling,
    - heat-treating the round material by a method according to one of claims 1-12,
    - forming the bolt head by cold heading, and
    - forming the thread by thread rolling.
  16. Method according to claim 15, which comprises:
    - forming the thread by thread rolling.
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EP1945827A1 (en) 2008-07-23
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ES2387684T3 (en) 2012-09-28
JP2009515047A (en) 2009-04-09
JP5210874B2 (en) 2013-06-12

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