US20080302451A1 - Method of Manufacturing Semi-Finished Sheet Products From Titanium Alloy - Google Patents

Method of Manufacturing Semi-Finished Sheet Products From Titanium Alloy Download PDF

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US20080302451A1
US20080302451A1 US11/912,649 US91264907A US2008302451A1 US 20080302451 A1 US20080302451 A1 US 20080302451A1 US 91264907 A US91264907 A US 91264907A US 2008302451 A1 US2008302451 A1 US 2008302451A1
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Prior art keywords
rolling
temperature
billet
deformation
semi
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Vladimir Vasilievich Astanin
Oskar Akramovich Kaibyshev
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INSTITUT PROBLEM SVERKHPLASTICHNOSTI METALLOV RAN
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INSTITUT PROBLEM SVERKHPLASTICHNOSTI METALLOV RAN
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    • 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
    • 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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals

Definitions

  • Quality of semi-finished sheet products is defined by the following characteristics that are interrelated through rolling schedules and methods: surface condition, accuracy of geometrical dimensions and shape, mechanical properties of semi-finished product defined by its structure, including grain size, and anisotropy or isotropy of mechanical properties provided by the type of metallographic texture formed in the process of rolling.
  • the tolerance range becomes yet narrower as the sheet thickness reduces.
  • SMC and NC structure in a semi-finished sheet product is currently a pressing factor, as it will provide later on the fabrication of an intricately-shaped article by superplastic forming or by the combination of superplastic forming and diffusion welding (SPF/DW), using the low-temperature superplasticity effect.
  • SPF/DW superplastic forming and diffusion welding
  • Reduction in the forming and/or diffusion-welding temperature ensures improved stability of the tool set used in the processes, and makes the processes more economical as a whole. Bonding of titanium semi-finished sheet products can be improved owing to reduced gas saturation of the surfaces to be joined.
  • a method of manufacturing a semi-finished sheet product from a titanium alloy comprises pre-treating a billet to a structure with submicron grain size, followed by rolling [5].
  • the rolling is started at a temperature in the range by 150-500° C. below polymorphous transformation temperature dictated by the required submicron grain size in the semi-finished product to be produced.
  • the resulting semi-finished sheet product is suitable for further treatment in low-temperature superplasticity conditions.
  • the rolling as such provides for the use of the temperature range including, as a component, the temperature range typical for low-temperature superplasticity, it is not performed in superplasticity conditions.
  • Superplasticity conditions require strict correspondence of deformation parameters such as deformation temperature, strain rate and grain size in the billet being treated and observance of isothermal conditions in the deformation region.
  • the reduced temperature rolling to a desired thickness of the semi-finished product is conducted in several passes with partial reductions by 5-20%, and upon attaining the total strain amount of 40-65%, intermediate annealing is performed at a temperature below the polymorphous transformation temperature of the alloy by a value from 150 to 500° C.
  • a basic texture can be created to provide isotropy of mechanical properties in two directions in the sheet plane owing to the use of the longitudinal/transverse rolling step.
  • the step can be however generally employed only for square sheets.
  • the prior art method comprises heating the rolls.
  • the rolling is performed in isothermal conditions.
  • the step is however optional in the method.
  • the prior art rolling is started from a temperature lower than the polymorphic transformation temperature by 500° C., as the result of cooling-down at cold rolls, especially when thin semi-finished sheets are rolled, the rolling may become infeasible due to insufficient plasticity of the alloy.
  • the object of the present invention is to improve quality of semi-finished sheet products made from a titanium alloy adapted for further low-temperature superplastic deformation owing to stabilized grain size, more complete isotropy of properties, reduced variation in thickness of the semi-finished product and improved surface condition of said product, at reduced manufacturing costs of the semi-finished sheet product.
  • Another object of the present invention is to expand process capabilities of the method owing to production of especially thin semi-finished sheet products, including foil, with predetermined geometric dimensions, surface condition and grain size.
  • An object of the invention is to reduce potential variation in thickness of a semi-finished sheet product and improve its flatness.
  • a further object of the invention is to further reduce manufacturing costs of a semi-finished sheet product, including the step of preparing the structure in the original billet.
  • the objects of the invention are attained in a method of manufacturing a semi-finished sheet product from a titanium alloy adapted for low-temperature superplastic deformation, including rolling a billet with a prepared structure at a temperature below the polymorphous transformation temperature in isothermal or quasi-isothermal conditions provided by heating the rolls, wherein in accordance with the present invention said rolling is carried out in conditions of low-temperature superplastic deformation, the deformation being performed, predominantly in a first pass, to a strain amount of ⁇ min , where ⁇ min is the minimum amount at which a structural state required to provide cooperative grain boundary sliding (CGBS) in the deformation is formed in the alloy in selected rolling temperature/rate conditions; after each subsequent rolling pass the billet is cooled immediately when exiting the deformation region to maintain the structural state obtained in the deformation; a time period of heating the billet in a furnace for a subsequent rolling pass is restricted to prevent disturbance of the alloy structural state obtained in the previous rolling pass.
  • CGBS cooperative grain boundary sliding
  • said rolling is carried out at a temperature in the range from T pt -450° C. to T pt -350° C.;
  • said rolling is carried out with a strain rate in the range from 10 ⁇ 3 to 10 ⁇ 1 s ⁇ 1 ;
  • the billet prior to achieving a strain amount of 30-60%, the billet is rotated through 90 degrees after every three to five longitudinal passes and a transverse rolling pass is performed, the remaining strain amount being gained by rolling in single direction;
  • a billet with a prepared globular structure having a grain size less than 1 ⁇ m is used in said rolling;
  • a billet with a prepared lamellar structure having a cross-sectional grain size less than 1 ⁇ m is used in said rolling;
  • the billet structure is prepared for rolling by preliminarily rolling an original billet having a grain size not exceeding 10 ⁇ m at least in one section to a strain amount of at least 80%, said rolling being started at a temperature in the range from T pt -300° C. to T pt -200° C. and finished at a temperature not lower than the basic rolling temperature, wherein the strain rate is in the range from 10 ⁇ 2 to 10° s ⁇ 1 ;
  • the billet structure is prepared for rolling by preliminary two-stage rolling of an original billet having a grain size of from 10 to 80 ⁇ m, the first stage comprising rolling the original billet to a strain amount not exceeding 60%, the rolling being started at a temperature in the range from T pt -200° to T pt -50′ and finished at a temperature not lower than the basic rolling temperature, wherein the strain rate is in the range from 10 ⁇ 2 to 10 s ⁇ 1 ; the second stage comprising rolling the billet in isothermal conditions at the basic rolling temperature and strain rate to a strain amount of 20-30%;
  • said rolling is carried out at a rolling mill comprising two working rolls and at least four backup rolls;
  • deflection of the backup rolls directly contacting the working rolls is modified by changing the intensity of cooling bearings units of the backup rolls;
  • said working rolls are heated by electric resistance heating units mounted inside the rolls.
  • a principal distinctive feature of the invention is that the method is suitable not only for manufacturing semi-finished sheet products adapted for low-temperature superplastic deformation, but the rolling as such is carried out in conditions of low-temperature superplasticity. In this case the efforts directed at preparation of the billet structure for rolling are more strictly spent for intended purpose. But of more importance for attaining the objects of the invention is the change in the technical essence of the rolling method as compared to the prior art method.
  • GBS grain boundary slipping
  • CGBS development of CGBS does not begin at once when a deforming force is applied.
  • a shear band forms that unites a great number of series connected grain boundaries. This process proceeds on self-organization principle and is associated with increase in the angles in triple joints (rectification of boundaries).
  • the flow stress intensively grows, this leading to increased deforming force (FIGS. 7 , 8 ).
  • the flow stress becomes steady or decreases gradually.
  • a particular strain amount required to make the process steady depends on grain size in the billet being deformed; the less the grain size the smaller strain amount is required to form the desired structural state.
  • the steady flow stage corresponds to superplasticity conditions where CGBS is the main deformation mechanism.
  • Presence of formed shear bands i.e. CGBS
  • stress/strain flow stress versus strain chart
  • the structural state required to provide CGBS is achieved even after 5-7% strain.
  • the strain amount may be greater than in the previous case and reach 10-15%.
  • Another essential measure for rolling in superplasticity conditions is to cool the billet exiting the deformation region after the pass, this enabling the grain size and formed shear bands to be maintained. Holding the material between passes at a temperature close to the deformation temperature, which does not even leads to grain growth, gives rise to change in the grain boundary states and partial recovery of the original structure. All the more, annealing between passes leads to full recovery of equilibrium structure and coarsening the grains. In both cases, i.e. after holding and annealing, stresses increase as compared to stresses observed under continuous load for the same strains ( FIG. 7 ).
  • FIG. 8 shows plots of continuous and fractionary process of applying a load to a specimen with partial cooling (by 100° C.) after removing the load, the plots noticeably approaching.
  • novel, non-obvious measure comprising effecting plastic properties of the rolled material in order to stabilize them by maintaining the grain boundary conditions in the process of fractionary, non-monotonic rolling deformation is efficient just in warm rolling. In hot rolling this effect will be lost against the background of intense temperature effect on the roll system stiffness. This necessitates another measure, rolling in the conditions of low-temperature superplasticity.
  • warm rolling enables the manufacture of semi-finished sheet products with improved accuracy and surface condition owing to substantially complete exclusion of forming of a gas-enriched layer and scale.
  • a wide range of semi-finished thin sheet products including foils of different thickness, can be produced without the use of vacuum or protective environment.
  • Reduced rolling forces, inherent in superplasticity, and elimination of further treatment of the semi-finished sheet product for removing the gas-enriched layer, as well as the absence of need to use vacuum substantially reduce the manufacturing costs of high-quality semi-finished sheet products despite the necessity to heat the rolls.
  • the individual temperature range inherent in low-temperature superplasticity is a constituent part of the conventional temperature range. But this step is used in combination with the other steps involved in the method.
  • the new combination provides numerous advantages. Thus, when considering the step of rolling in the temperature range which is a constituent part of the conventional range, as a component, it can be seen that the claimed technical solution provides a super-cumulative effect as compared to the prior art solutions.
  • the alloy should have a homogeneous, equiaxial fine-grain structure, and deformation should be carried out in isothermal conditions.
  • each particular temperature of deformation carried out in superplasticity conditions is associated with a specific grain size.
  • the grain size is less than 1 ⁇ m.
  • the billet structure is to be specially prepared.
  • isothermal conditions imply constant temperature in the deformation region.
  • the step of heating the rolls in the invented method is therefore essential for attaining the objects of the invention.
  • Mechanical heating caused by the deformation process occurring at a rate inherent in low-temperature superplastic deformation may be neglected.
  • mechanical heating of the billet can be fully compensated by the choice of a corresponding, lower roll temperature.
  • a similar step is used only to provide anisotropy of properties of the rolled sheet in respective directions on its plane.
  • a billet is heated immediately by contact with the working rolls.
  • the process can be considered as quasi-isothermal. Owing to small sheet thickness and low rate of rolling, the required temperature is sufficiently fast established in the deformation region, even at the initial rolling step. A billet of a greater thickness is heated slowly or even have no time to heat to a predetermined temperature for the rolling time, thus such a billet should be heated in a furnace immediately before the rolling. A through-type furnace is generally used in this case.
  • a billet with a prepared structure is used in the rolling process.
  • the structure must be a homogeneous structure with equiaxial (globular) grains of less than 1 ⁇ m size.
  • This structure may be provided in the original billet, i.e. using known methods [4,5]. In this case to make CGBS “work” it is sufficient to only form shear bands between the grains, this corresponding to about 5-10% strain as mentioned above.
  • the structure can be alternatively prepared so that to transform to the required structure in the rolling process, preferably in a first pass.
  • a lamellar structure with elongated grains having a cross-sectional size from 0.9 to 1.5 ⁇ m meets this requirement.
  • Low rolling temperature and strain rate provide dynamic recrystallization process with division of plates and formation of fine, about 0.2 ⁇ m, equiaxial grains. Isothermal conditions provide uniform behavior of the process and its smooth transformation to shear band formation process. This requires approximately 10-15% strain. In the following process, when CGBS is developing, i.e. in the absence of dynamic recrystallization, grains will retain their shape and size.
  • Such a lamellar structure can be provided by preliminarily rolling the original billet.
  • the billet is subjected to preliminary rolling started at a temperature below the polymorphous transformation temperature by 200-300° C. and finished at a temperature not less than the basic rolling temperature at a strain rate in the range from 10 ⁇ 2 to 10° s ⁇ 1 .
  • the strain rate in this range promotes active dynamic recrystallization process.
  • the strain amount exceeds the amount required to develop dynamic recrystallization, about 70%. The latter means that in the deformation process grains acquire equiaxial shape, and then lost it again, i.e. become elongated.
  • the resulting billet acquires a lamellar structure with plates having a cross-sectional size of 0.9 to 1.5 ⁇ m.
  • the billet is subjected to two-stage preliminary rolling.
  • the original billet is rolled to a strain amount not exceeding 60%, the rolling being started in the temperature range from T pt -300° C. to T pt -200° C. and finished at a temperature not less than the rolling temperature at a strain rate in the range from 10 ⁇ 2 to 10 s ⁇ 1 .
  • the billet is rolled in isothermal conditions at the basic rolling temperature and strain rate until a strain amount of 20-30% is attained.
  • a feature of the two-stage rolling is that the strain amount at the first stage must be smaller than the strain amount causing formation of equiaxial (globular) grains in the billet owing to dynamic recrystallization. Deformation to a strain amount less than 60% causes only extension and thinning of the plates. If the grains become equiaxial and comparatively coarse, substantial deformation will be further required to render them plate-shaped. Thin plates may be obtained if development of dynamic recrystallization process is excluded. Then, by deforming thin plates at a lower temperature, precisely at the basic rolling temperature, finer plates can be obtained having a desired cross-sectional size.
  • the dynamic recrystallization process takes place with formation of equiaxial grains.
  • the formed grains are reasonably fine owing to a lower deformation temperature.
  • the grains become elongate again.
  • the billet acquires a lamellar structure with plates of less than 1 ⁇ m in cross section.
  • heating for the first pass may be accompanied by static recrystallization that promotes some conditioning of the structure and globularization of the grains.
  • the structure will be completely conditioned and grains will acquire equiaxial shape even in the basic rolling process.
  • the most precise dimensions of semi-finished sheet product can be obtained if the rolling is carried out at a rolling mill comprising two working rolls and at least four backup rolls, e.g. at a six roll mill ( FIG. 1 ).
  • Cooling of backup rolls that directly contact the working rolls enables, first, the roll system rigidity to be increased. Second, non-uniform cooling of the backup rolls directly contacting the working rolls provides a slight gradient along the working roll body that is sufficient to reduce lateral variation in the sheet thickness. Backup rolls can be most optimally cooled by cooling respective bearing units. Intensity of cooling the bearing units depends on the required roll body size.
  • FIG. 1 shows a schematic diagram of the method
  • FIG. 2 shows the microstructure (a) and electron diffraction pattern (b) of original billet
  • FIG. 3 shows the microstructure and electron diffraction pattern of a semi-finished sheet product obtained after rolling the original billet with a structure prepared by methods other than rolling;
  • FIG. 4 shows the microstructure of the original billet prepared by one stage rolling, ⁇ 500
  • FIG. 5 shows the microstructure of the original billet prepared by two-stage rolling, ⁇ 500
  • FIG. 6 shows the microstructure of semi-finished sheet product produced after rolling the original billet with a structure prepared by rolling
  • FIG. 7 shows the stress/strain plots for continuous and fractionary process with intermediate non-loaded annealing for 1 min
  • FIG. 8 shows stress/strain plots for continuous and fractionary process with partial cooling (by 100° at load removed
  • FIG. 9 shows the estimated deflection of a backup roll under experimentally found rolling force. Maximum deflection difference between the body center and end is 0.054 mm. It can be compensated by a temperature difference of 40° C. at TEC 18 ⁇ 10 ⁇ 6 and roll diameter of 150 mm.
  • FIG. 1 shows a billet 1 to be rolled, working rolls 2 with built-in heating units (not shown), backup rolls 3 (four), pre-heating through-type furnace 4 .
  • Examples describe methods of manufacturing a semi-finished sheet 0.3 mm thick and foil 0.05 mm thick from BT-6 and BT-22 titanium alloys.
  • Table 1 shows polymorphous transformation temperatures and chemical compositions, in percent by weight. In the Examples strips having a thickness of 0.1; 0.5 and 0.7 mm were manufactured.
  • a rolled sheet 0.5 mm thick was manufactured from a two-phase BT6 titanium alloy.
  • An original billet with a thickness of 14 mm and a size of 60 ⁇ 100 mm having the grain size of 0.4 ⁇ m was made by multiaxis swaging at a temperature reduced to 600° C. [5].
  • Rolling was performed at a temperature of 560° C., which is by 430° C. lower than polymorphous transformation temperature.
  • Peripheral roll speed was 1 mm/s, which corresponded to a strain rate of 5 ⁇ 10 ⁇ 3 s ⁇ 1 in the deformation region.
  • ⁇ min a minimum strain amount at which the alloy structural state required to provide CGBS in the deformation process is attained under the selected rolling temperature/rate conditions.
  • ⁇ min 9% was determined on the basis of the maximum flow stress value after which it gradually reduces ( FIG. 8 ).
  • the original billet was rolled at LIS-6/200 six-roll mill comprising heated working rolls of 65 mm in diameter ( FIG. 1 ).
  • the working rolls were heated to 560° C.
  • Built-in resistance heating units heated the rolls on the inside.
  • Backup rolls were heated by contact with the working rolls, the temperature attaining 120-180° C. in the roll body center.
  • the backup rolls were cooled a liquid lubricant circulating through bearing units. Intensity of the cooling was selected to provide a temperature difference of 40 ⁇ 5° C. between the center and ends of the backup roll bodies, this compensating deflection of the rolls and providing uniform thickness of sheet.
  • Temperature of the backup rolls was controlled by a temperature control unit.
  • a through-type furnace with a heating temperature of 560° C. was provided at the mill input ( FIG. 1 ). Strain amount in the first pass was 15%. As the final thickness approached, the one-pass strain amount was reduced. The total number of passes was 32.
  • the length of heated zone in the furnace was estimated as 1 ⁇ 54 ⁇ h, where ⁇ is the peripheral roll speed.
  • ⁇ is the peripheral roll speed.
  • the heated zone length should be at least 250 mm.
  • a long billet could not be fully heated since at a low rolling rate this would lead to holding at the rolling temperature.
  • the heated zone length in the furnace was 300 mm. This measure provided heating, but restricted the billet residence time under the rolling temperature, so the material structural state required to implement the basic superplasticity mechanism was maintained between passes.
  • the furnace temperature was set to 400-450° C. to avoid annealing before supplying to the rolls, and final heating was performed directly by the working rolls when the strip entered the contact zone.
  • An original billet of 15 mm in thickness and 60 ⁇ 80 mm in size was made from a two-phase BT22 titanium alloy with a grain size of 0.6 ⁇ m by multiaxis swaging at reduced temperature [5].
  • the billet was rolled to a thickness of 0.7 mm at LIS-6/200 six-roll mill comprising heated working rolls of 65 mm in diameter.
  • the roll heating temperature was 550° C., which was by 310° lower than polymorphous transformation temperature.
  • a through-type furnace at the mill input provided a heating temperature of 550° C.
  • Peripheral roll speed was 1 mm/s, which provided a strain rate of 6 ⁇ 10 ⁇ 3 s ⁇ 1 in the deformation region at 10% one-pass strain. This corresponded to the conditions of low-temperature superplasticity for given alloy. Usage of the through-type furnace eliminated cooling the billet at the so small supply speed. At output of the deformation region the billet was air cooled. The resulting strips were covered with a dark-blue, dense, thin, oxide film. Microstructural analysis and microhardness measurements did not reveal a gas-enriched surface layer at least at a depth of more than 1 ⁇ m. Variation in sheet thickness from the specified thickness of 0.7 mm did not exceed 0.01 mm.
  • the strip had a homogeneous microstructure in cross section with grains 0.3 ⁇ m in size, and the elongation factor not exceeding 1.4.
  • Example 2 The procedure was similar to that described in Example 1 except that the rolling temperature was 600° C., and the one-pass strain was 20% at the initial stage. At the same peripheral roll speed (1 mm/s) the strain rate in the deformation region was 1.1 ⁇ 10 ⁇ 2 s ⁇ 1 . This also corresponded to low-temperature superplasticity conditions for the alloy with given grain size at this temperature. As the result, the number of passes was reduced to 23 while geometry of the produced sheet was maintained. It this case the grain size of the original billet was maintained. This measure substantially improved the process efficiency. Temperature in the through-type furnace was 580° C., taking into account the initial deformation heating.
  • Example 2 The procedure was similar to that described in Example 1 except that at the initial rolling stage the billet was rotated through 90° after every three passes and rolled in transverse direction. This step was performed until 60% strain was attained, in this case the billet width reached the width of the roll body (200 mm). To provide a desired combination of strain amount and billet width, the original billet size was 16 ⁇ 60 ⁇ 80 mm in contrast to that in Example 1. This measure provided the following results:
  • width of the rolled billet was increased if the original billet had restricted dimensions, e.g. a conventional rod shape
  • the procedure was similar to that described in Example 1, but the aim was to manufacture sheets less then 0.5 mm thick. Once this value was attained, the strip was fed to hot rolls without pre-heating, or the temperature of input device was set to a value not exceeding half of the rolling temperature. This step restricted to the limit the billet residence time at the rolling temperature, ensuring thereby maintenance of the material superplasticity state between passes and providing more precise width of the resulting rolled product. To this end, the heating power of the working rolls should be raised to some extent to compensate heat loss for heating the billet. If the roll heating units have a heating power margin and comprise a feedback heat controller, the heating power will be automatically compensated. Automatic operation of the heating units requires about 30% power margin in excess of the rated value. The resulting foil specimens had a thickness of 0.1 ⁇ 0.01 mm.
  • a commercial rod of 60 mm in diameter from BT22 alloy with lamellar structure comprising plates having the average size of 80 ⁇ 6 ⁇ m was used as an original billet.
  • the billet was heated to a temperature of 850° C., which was by 30° C. lower than polymorphic transformation temperature and by 300° C. higher than the basic rolling temperature.
  • the billet was rolled at DUO 300 rolling mill using cold rolls with a rate of 200 mm/s. At 20% one-pass strain this corresponded to the strain rate of 1.2 s ⁇ 1 in the deformation region. Rolling was performed in several passes to a thickness of 10 mm, which corresponded to 83% reduction. After first three passes the billet was rotated and rolled transversely in one pass.
  • the billet temperature was decreased by 10-15° C. in each pass until it reached 700° C. With the temperature decrease the one-pass strain amount was reduced, such that the strain rate gradually reduced to values below 10 s ⁇ 1 in the deformation region. Then scale and gas-enriched layer 0.12 mm thick were removed from each side of the billet.
  • the resulting lamellar structure had thin grains elongated in the rolling direction with the mean size of 1.3 ⁇ m in lateral direction ( FIG. 4 ).
  • Final rolling was performed in the way similar to that described in Example 2. However, the rolling stand pressure force had to be increased at the first pass. The lamellar structure was then gradually transforming to globular submicrocrystalline structure, and the process changed to the low-temperature superplasticity regime.
  • the resulting sheet had a less homogenous structure than the submicrocrystalline billet, although the structure was still submicrocrystalline with grains of 0.4-0.5 ⁇ m in size and the elongation factor of 1.4 in the strip longitudinal section. Crystallographic texture was feebly marked.
  • An original billet was a billet of 1000 ⁇ 60 ⁇ 60 mm in size made from BT22 alloy with the average grain size of 50 ⁇ m.
  • the billet was heated to 820° C.
  • the billet was rolled at DUO 300 rolling mill using cold rolls with a rate of 100 mm/s. At 20% one-pass strain this corresponded to a strain rate of 0.7 s ⁇ 1 in the deformation region.
  • Rolling was performed in two stages, each stage including several passes. The first stage included rolling to a thickness of 27 mm which corresponded to 55% reduction.
  • the billet temperature was decreased by 10-15° C. in each pass until the temperature of 650° was reached.

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RU2006125691 2006-07-06
RU2006125691/02A RU2320771C1 (ru) 2006-07-06 2006-07-06 Способ изготовления листового полуфабриката из титанового сплава
PCT/RU2007/000123 WO2008004906A1 (fr) 2006-07-06 2007-03-14 Procédé de fabrication d'un blanc en feuille à partir d'un alliage de titane

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CN109750185A (zh) * 2019-03-20 2019-05-14 中国科学院金属研究所 一种超塑性成形用650℃高温钛合金薄板的制备方法
CN114309116A (zh) * 2021-11-18 2022-04-12 洛阳双瑞精铸钛业有限公司 一种宽幅超薄钛箔带材的制备方法

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CN102921731B (zh) * 2012-11-13 2014-12-31 西部钛业有限责任公司 一种钛合金薄板的温轧加工方法
RU2639744C1 (ru) * 2016-11-14 2017-12-22 Дмитрий Вадимович Гадеев Способ термомеханической обработки листов из двухфазных титановых сплавов для получения низких значений термического коэффициента линейного расширения в плоскости листа
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