RU2544333C1 - Manufacturing method of cold-rolled pipes from alpha- and pseudo-alpha-alloys based on titanium - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: manufacturing method cold-deformed pipes from α- and pseudo-α-alloys based on titanium involves melting of an ingot, forging of an ingot in β- and α+β-region with ending of forging in α+β-region into an intermediate shell with forging reduction of 2 to 3; piercing is performed at the temperature that is by 30-50°C higher than Tpp, by multiple-cone rolls and a mandrel with the specified geometry with water supply to a deformation zone, rolling of the shell is performed at the temperature that is by 10-90°C lower than Tpp; straightening of the pipe shell is performed at the temperature of 350-400°C, cold rolling is performed with drawing coefficient of 1.5-4.5 at several stages by alternation with intermediate annealing processes at the temperature equal to 600-750°C, and further heat treatment with the ready dimension at the temperature of 580÷650°C.

EFFECT: high mechanical properties of manufactured pipes, as well as high quality of pipe surface.

4 dwg, 3 tbl

Description

The invention relates to pipe production, namely to cold rolling of pipes from α- and pseudo-α-alloys based on titanium. The invention can be used for the manufacture of critical products intended for use in various fields of the national economy, for example, nuclear energy, shipbuilding, aviation, mechanical engineering, chemical industry, etc.

Cold rolling of pipes has a number of advantages compared to pressing and hot rolling, the most important of which are:

a) obtaining pipes with accurate geometric dimensions and especially with a small eccentricity of the outer diameter relative to the inner;

b) high surface finish of pipes;

c) high yield;

d) obtaining pipes with a ratio of diameter to wall thickness of 150: 1 or more;

e) a high degree of metal deformation per passage (up to 50-60%);

f) achieving significant hardening of the pipe metal during rolling due to compression both in diameter and in wall thickness, etc.

Billets for cold rolling of pipes are hot-deformed tube blanks.

From the set of properties of titanium alloys as structural materials for the manufacture of pipes of special technical and economic interest, it should be noted (Ostrenko V.Ya. et al. Pipes from titanium and its alloys. - M .: Ferrous metallurgy, 1987, 60 pp.): low density in comparison with steels, high level of mechanical characteristics, high level of special characteristics (heat resistance, creep, long strength, low-cycle fatigue, fracture toughness, erosion and cavitation resistance, low induced radiation, etc.), corrosion resistance, manufacturability.

The structure of titanium-based alloys determines the most important criteria for the quality of semi-finished products, has a significant variety and an extreme impact on mechanical properties. A feature of the production of pipes from titanium-based alloys is that the billets for their production are ingots obtained by the vacuum arc melting method, in which the melting, casting and solidification processes are connected together, and their separate regulation is practically impossible. A significant overheating of the melt occurs and a coarse-grained structure of the ingots is formed, which has a significant heterogeneity in the cross section and a coarse-grained lamellar microstructure. This leads to their reduced deformability and a low set of operational properties of the products.

To improve the technological and operational properties, it is necessary to form a fine-grained (phase grain size no more than 150–200 μm) microstructure in them. In addition, the achievement of a structurally uniform state in semi-finished products is important for assessing the quality of pipes by ultrasonic testing methods, which are widely used in their manufacture. In the case of a highly homogeneous and fine-grained structure of a titanium alloy, ultrasonic testing significantly reduces the level of acoustic noise, increases the maximum sensitivity of the method, limited by these noise, and the material becomes more "transparent", i.e. having a minimum level of structural interference, which makes it possible to detect defects of a minimum size. This implies an extension of the service life of the products, and, consequently, a decrease in the cost of machines and units due to the operation of products with defects of an acceptable size.

A known method of manufacturing cold-deformed pipes from two-phase alloys based on titanium (RF Patent No. 2463376, IPC C22F 1/18, B21B 3/00, publ. 12/20/2011), which includes ingot smelting, forging of the ingot in the β-region or β- and α + β-region with the end of forging in the α + β-region into the intermediate workpiece with a given yarn. An intermediate billet is obtained with a draft of at least 1.35, a block is made from an intermediate billet, which is pressed into a tube billet and heat treated at a temperature of 30-40 ° C below temperature T _pp , and then the tube billet is rolled with intermediate surface treatment, etching and heat treatment. The hood during rolling is determined by the given formula. The resulting pipes are characterized by high physical and mechanical properties due to the exclusion of the formation of intergranular microcracks.

The disadvantages of this method is that the action of this method is narrowly specialized and is limited to the field of manufacture of pipes from two-phase titanium alloys. In addition, cold-formed pipes are rolled from a pressed tube billet, which is characterized by an increased specific metal consumption (by 15-30% compared to rolling) due to the drilling of a central hole before the pressing operation and the presence of a press residue, insufficient dimensional accuracy, in particular the presence of deep scoring on the surface. A limiting factor in the production of a hot-pressed billet is the limited length of the initial billet during pressing.

A known method of manufacturing pipes from non-ferrous metals and alloys (RF Patent No. 2048219, IPC V21V 23/00, V21V 3/00, V21V 19/02, publ. 11/20/1995) - a prototype that provides hot screw firmware and rolling on mandrels, in three-roll calibers formed by multicone rolls having an angle of inclination of the conical generatrix to the rolling axis at the entrance to the gauge by 7–25 ° more than in front of the mandrel toe, with a compression at the inlet portion of 0.3–0.8 from the compression in front of the toe mandrels. The method also provides for rolling the stitched sleeve in rolls having two crimp sections (ridges), separated by intermediate calibration and rolling sections, the angle of inclination of the generatrix to the rolling axis of one of them being 1.5-5.0 ° less and the other more than the angle of inclination of the generatrix of the input section of the piercing rolls to the rolling axis. The method allows to increase the yield and to improve the stability of the process when processing expanding metals.

The disadvantage of this method is the unstable primary and secondary capture of the workpiece during firmware, due to the large angle of the input cone 4-8 °. The geometric shape of the mandrel is not optimal, because the large tendency of titanium alloys to stick and tear and their low thermal conductivity is not fully taken into account. As a result, large friction forces arise on the surface of the mandrel, under the influence of which intense heating of the metal occurs, which does not allow it to withstand the technological temperature range when piercing workpieces made of titanium alloys, and intense wear of the surface of the mandrel also occurs. The consequence of this is the adhesion of the pressed (stitched) metal on the surface of the mandrel, causing instability of the firmware process, the formation of defects on the surface of the workpiece and distortion of its geometric dimensions, these defects are further inherited in subsequent operations and can lead to marriage. The method does not regulate the thermal deformation parameters of the manufacturing process of pipes from non-ferrous metals, in particular from alloys based on titanium, which does not guarantee a microstructure with the required quality indicators.

The objective of the invention is:

- creation of a method for processing α- and pseudo-α-alloys based on titanium, which allows to obtain a fine-grained (grain size not more than 100 microns) microstructure in pipes;

- achieving a structurally homogeneous state in the finished product, providing "transparency" for ultrasonic quality control of semi-finished products and products;

- improving surface quality and accuracy of the geometric dimensions of manufactured pipes;

- improving the stability of the process;

- quick transition from one size to another;

- increase tool life.

The technical result achieved by the implementation of the invention is the creation of a cost-effective technology for the manufacture of pipes from α- and pseudo-α-titanium alloys, which combines the operations of forming the geometric dimensions and high-quality surface of the products with the processes of forming a regulated microstructure that provides high technological and operational properties products.

The specified technical result is achieved by the fact that in the method of manufacturing cold-rolled pipes from α- and pseudo-α-alloys based on titanium, including ingot smelting, forging the ingot into a cylindrical billet in several transitions with alternating deformation in β- and (α + β) - areas, and the last forging transition is carried out in the (α + β) region, machining, obtaining a tube billet by deformation, dressing, annealing, surface treatment of the tube billet, cold rolling with intermediate finishing operations and finishing dressing, to the taste of the ingot in a cylindrical billet is finished with a draft of 2 to 3 after heating in the (α + β) region, the flashing and rolling are carried out from one installation, the flashing is carried out at a temperature of 30-90 ° C above the temperature of polymorphic transformation (TPP) with multi-cone rolls wherein the angle of inclination of the generatrix of the input cone is 5 _-1 °, of the calibrating portion 3 _-1 °, of the vanishing portion 2 _-1 °, on a water-cooled mandrel with a crimp cone consisting of a conical and spherical sections, with a radius R of the spherical portion of the mandrel, calculated by the formula :

where d ₀ - rolling diameter of the mandrel, mm,

the diameter of the mandrel nose is 20 ± 10 mm, the nozzle has a hole from which water is supplied to the deformation zone under a pressure of 1.0-2.0 MPa, and a steam “shirt” is formed between the surfaces of the wrought metal and the mandrel, followed by rolling of the tube stock they are carried out after being cooled in air to a temperature of 10-90 ° C below the temperature range, the tube billet is straightened at a temperature of 350-400 ° C, subsequent oxidative annealing at a temperature of 600 ± 20 ° C, cold rolling is carried out with a drawing coefficient of 1.5-4 , 5 in several stages, alternating with intermediate annealing at a temperature of 600-750 ° C, and heat treatment at the finished size in a vacuum resistance furnace at a temperature of 580 ÷ 650 ° C.

The invention is illustrated by drawings, in which Fig. 1 shows a multiconus roll, Fig. 2 - a water-cooled mandrel used for flashing, Fig. 3 - the microstructure of a cold-rolled pipe ⌀50 × 5 mm from a pseudo-α-alloy PT7M, Fig. 4 - microstructure of a cold-rolled tube made of α-alloy VT1-0 with a size of Ø 51 × 4.5 mm.

The essence of the invention is based on the fact that under the thermomechanical conditions of the proposed treatment, the formation of the product geometry is consistent with the regulated processes of recrystallization and phase transformations in workpieces from α- and pseudo-α-alloys based on titanium, in which a fine-grained microstructure with a high degree of uniformity is formed.

Forging an ingot into a bar at the temperature of the β-region in the first passes destroys the cast structure. Subsequent forging in the (α + β) region with a total yield of 2 to 3 destroys the high-angle grain boundaries of the so-called “Half-hot hardening”, during which the metal receives enough energy to facilitate the recrystallization process during subsequent heating of the slab to β-region temperatures.

The resulting cylindrical billet is heated at temperatures above TPP by 30-90 ° C (β-region) and the through hole is flashed, and the following positive factors are realized:

1. Deformation in the β-region at a temperature above the TPP by 30-50 ° C after the previous forging operations is accompanied by a recrystallization of the structure with grain refinement.

2. The deformational change in shape occurs under favorable temperature conditions, because the metal in the β region has a good ductility margin.

It is known that titanium alloys have a low coefficient of friction at the piercing temperature, lower inertial forces due to lower specific gravity and are prone to broadening, and therefore, there are prerequisites for the emergence of an unstable process.

To ensure a stable firmware process, the pulling forces are provided by multicone rolls (Fig. 1), in which the angle of inclination of the generatrix of the input cone 1 is 5 _-1 °, the calibrating section 2 is 3 _-1 °, the vanishing section 3 is 2 _-1 °. This geometry is selected empirically and provides sufficient pulling forces on the contact surface of the rolls to overcome the resistance of the metal, as well as the descent of the rear end of the sleeve on the calibrating portion of the mandrel.

The main deformation of the metal is carried out in the area of the crimp cone of the mandrel. The profile of the crimping cone of the mandrel determines the nature of the change in the wall thickness of the workpiece along the length of the deformation zone. For the optimal distribution of deformation along the length of the deformation zone, a water-cooled mandrel was designed, in which the crimp cone consists of two zones: spherical 4 and conical 5 (figure 2). The mandrel section with a conical profile of the mandrel provides a private compression of the wall, which increases along the rolling. With an increase in the partial compression of the wall, the increment in the diameter of the pipe as a result of transverse rolling increases. Therefore, by the end of the deformation zone, the metal significantly departs from the mandrel, which ensures the sleeve to exit. The forming radius of the spherical portion 4 of the mandrel is calculated by the formula:

where d ₀ is the rolling diameter of the mandrel.

Experimentally, the optimal diameter of the nose of the mandrel 5 was determined, at which a relatively small axial resistance and a sufficiently high resistance are achieved. This diameter was 20 mm. Also in the nose of the mandrel there are openings 6 for supplying water, which flows under pressure of 1.0-2.0 MPa into the cavity between the deformable metal and the surface of the mandrel. This water pressure serves to maintain optimal temperature conditions. In this case, a steam “shirt” is formed, which not only protects the metal from overheating, but also protects the surface of the mandrel from metal buildup, thereby contributing to improving the quality of the inner surface of the pipes. In the process of reinforcing the stitched billet before rolling to a temperature of 10-90 ° C below the TPP, the polymorphic β → α transformation occurs in the alloys, the α phase is released in the form of plates. During rolling, the α-plates undergo deformation. In this case, their shape changes from rectilinear to curved. The curvature of the α-plates, as well as the presence in the structure of a large number of twins and shear bands, the beginning of dynamic or metadynamic recrystallization processes ensures a favorable state of the metal for subsequent annealing of the pipes.

After the rolling operation, the tube billet is straightened at a temperature of 400-450 ° C. At a given temperature, α- and pseudo-α-alloys have a creep sufficient to effectively correct geometric shape errors.

The hot-rolled tubular billet is machined on the outer and inner surfaces to remove defects and the gas-saturated layer after hot deformation. Next, the workpieces are subjected to etching and oxidative annealing at a temperature of 600 ± 20 ° C to ensure a sufficient level of metal ductility, as well as the formation of an oxide layer on the surface of the workpiece, which, when cold rolled, acts as a “lubricant” layer, which ensures that the metal does not adhere to the surface of the gauges during cold rolling and mandrels. Cold rolling is carried out with a draw ratio from 1.5 to 4.5 in several transitions. This range of extraction is due to the receipt of the specified geometric dimensions of the product when performing technological recommendations for the cold deformation of titanium alloys without fracture. In the intervals between cold rolling, the pipes are etched, if necessary, by sandblasting (possibly grinding) to remove defects from the pipe surface that could have formed during cold rolling, and annealed at a temperature of 740-760 ° C. Annealing between cold rolling and at a final size is necessary to eliminate internal stresses, reduce hardness and increase the ductility of the metal. At the finished size, the final annealing is carried out in a vacuum oven at a temperature of 700-780 ° C. Annealing is carried out in a vacuum furnace in order to avoid hydrogen pickup of the metal and to provide the required level of hydrogen content.

The possibility of carrying out the invention is illustrated by specific examples of the manufacture of cold rolled pipes.

Example 1. A cold-rolled pipe размером50 × 5 mm in size was made of titanium pseudo-α-alloy PT7M for compliance with the requirements of TU 14-3-820-79, TPP = 935 ° C.

The pipe is made according to the technological scheme:

Ingot → forging in the β-region for several transitions → forging in the (α + β) -region, Ukov = 2 ÷ 3, T = TPP-30 ° C → mech. processing at ⌀130 mm → centering the workpieces → heating T = TPP + 30-50 ° C → firmware on PVP ⌀100 × ⌀64 × 18 mm → rolling at T = TPP-10-90 ° C to the size ⌀88 × ⌀54 × 17 mm → dressing at a temperature of 400-450 ° C → fur. processing (turning, boring) ⌀85 × ⌀56 × 14.5 mm → etching → annealing Т = 600 ° C, 60 min → cold rolling ⌀65 × ⌀48 × 8.5 mm (hood 2.13) → etching → annealing Т = 760 ° C, 60 min → cold rolling ⌀50 × ⌀40 × 5 mm (hood 2.09), straightening.

The mechanical properties are shown in Table 1. Also, the pipes passed the flattening test until a gap between the flattening surfaces H = 35.405 mm was obtained.

Table 1 Sample No. σ _0.2 MPa, kgf / mm ² σ _in MPa, kgf / mm ² δ,% σ _0.2 MPa, kgf / mm ² σ _in MPa, kgf / mm ² Test temperature 350 ° C one 452 575 27.5 232 315 (46.1) (58.6) (23.6) (32.1) 2 448 575 25,2 241 317 (45.1) (58.7) (24.5) (32.3) 3 441 572 25,2 232 315 (44.9) (58.3) (23.7) (32.1) four 445 572 23.8 228 313 (45.4) (58.4) (23.2) (31.9) Specification Requirements TU 14-3-820-79 382 480-667 twenty 176 245 (39) (49-68) (eighteen) (25)

The pipe geometry requirements are shown in table 2.

table 2 Pipe diameter mm Limit deviations in the outer diameter of the pipes. Increased manufacturing accuracy Wall thickness mm Limit deviations in pipe wall thickness. Increased manufacturing accuracy Tolerance field, mm according to TU 14-3-820 Actual tolerance field, mm Tolerance field, mm according to TU 14-3-820 Actual tolerance field, mm fifty 5 49.5-50.5 49.8-50.3 4,5-5,5 4.7-5.2 Compliance with TU 14-3-820 Acc. Compliance with TU 14-3-820 Acc.

Figure 3 shows the microstructure of a cold-rolled pipe ⌀50 × 5 mm from a pseudo-α-alloy PT7M in the longitudinal direction with an increase of × 200. Grain size d = 0.95-2.36 μm.

Example 2. The manufacture of pipes from VT1-0 alloy with a size of ⌀51 × 4.5 mm for compliance with the requirements of GOST 22897-86. TPP = 920 ° C.

The pipe is made according to the technological scheme:

⌀740 mm ingot → forging of the rod by ⌀140 mm in the β-region → machining by ⌀130 mm → centering the workpiece → heating T = 990-1010 ° C → flashing and rolling on the PVP mill 40-80 ⌀88 × ⌀54 × 17 mm → dressing → machining (turning, boring) ⌀85.5 × ⌀56 × 14.75 mm. → etching → annealing Т = 700 ° C → cold rolling to a size of ⌀ 65 × ⌀48 × 8.50 mm → etching → annealing T = 700 ° C → cold rolling to a size of ⌀51 × ⌀42 × 4.5 mm → etching → annealing in a vacuum oven T = 650 ° C → editing.

The mechanical properties are shown in table 3.

Table 3 Sample No. σ _0.2 MPa, kgf / mm ² σ _in MPa, kgf / mm ² δ,% one 343 491 24.6 (49.73) (71.2) 2 350 488 28.6 (50.75) (70.76) Specification Requirements GOST 22897-86 216 343-568 24 (22) (35-58)

The pipes also passed flattening tests until a gap between the flattening surfaces was H = 35.45 mm.

Figure 4 shows the microstructure of a cold-rolled α1 VT1-0 α-alloy pipe with a size of ⌀51 × 4.5 mm in the longitudinal direction with an increase of × 200. Grain size d = 7.5-8.0 microns.

The resulting pipes in their mechanical properties and geometric parameters significantly exceed the requirements of the current regulatory and technical documentation, the technology based on the use of standard technological equipment provides stability and quick reconfiguration of the manufacturing process of a product of one standard size to another, creates favorable working conditions for the tool, and the finished the highly homogeneous and fine-grained structure of the titanium alloy allows you to limit the level of ukturnyh noise during ultrasonic inspection.

Claims (1)

A method of manufacturing cold-rolled pipes from α- and pseudo-α-alloys based on titanium, including smelting an ingot, forging an ingot into a cylindrical billet in several transitions with alternating deformation in β- and (α + β) regions, the last forging transition being carried out in (α + β) -regions, machining, obtaining a tube stock by deformation, dressing, annealing, surface treatment of the tube stock, cold rolling with intermediate finishing operations and finishing dressing, characterized in that the forging of the ingot into a cylindrical stock the taste ends with a draft of 2 to 3 after heating in the (α + β) region, the tube billet is produced by flashing and rolling from one installation, flashing is carried out at a temperature of 30-50 ° C above the polymorphic transformation temperature (CCI) with multicone rolls, the inclination angle of the generatrix of the input cone is 5 _-1 °, the calibrating section is 3 _-1 °, the vanishing section is 2 _-1 °, on a water-cooled mandrel with a crimp cone, consisting of a conical and spherical sections, with a radius R forming the spherical section of the mandrel, calculated according to Ole:
$$R=\frac{\sqrt{4900+{(d_0-23,669)}^2}}{2\sin (arctg\frac{d_0-23,669}{140}-3^{\circ })}$$

where d ₀ - rolling diameter of the mandrel, mm,
the diameter of the mandrel nose is 20 ± 10 mm, and water is supplied from the hole in the nozzle to the deformation zone under a pressure of 1.0-2.0 MPa to ensure the formation of a steam jacket between the surfaces of the deformable metal and the mandrel, the subsequent rolling of the tube stock is carried out after air to a temperature of 10-90 ° C below the TPP, dressing of the pipe billet is carried out at a temperature of 350-400 ° C, subsequent oxidative annealing is carried out at a temperature of 600 ± 20 ° C, cold rolling is performed with a draw ratio of 1.5-4.5 per several stages , Alternating with an intermediate annealing at a temperature of 600-750 ° C, and final heat treatment to the finished size is performed in a vacuum furnace at a temperature resistance of 580 ÷ 650 ° C.

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