RU2355489C2 - Method of producing of hot-rolled pipes made of alpha- and semi- alpha-titanium alloys - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to pipe mill and can be used during the manufacturing of seamless pipes of α- and semi-α- titanium alloys. Ingot is forged into the blank for several passages with alternation β and (α+β)-area, with the last passage - in (α+β)-area. In blank it is formed central hole and blank is heated up to 650-800°C at a rate 50÷70°C/min, then at a rate 20÷30°C/min up to the pressing temperature. Compressing of tubular billet is implemented with rolling-out 2-7. Then tubular billet is heated up to the mandrel temperature at a rate 50÷70°C/min and it is implemented drawing with stretch 2-3.

EFFECT: method provides forming of microstructure, providing high technological and performance attributes of products.

2 dwg, 3 tbl, 2 ex

Description

The invention relates to pipe production and can be used in the manufacture of seamless pipes from α- and pseudo-α-titanium alloys. The invention can be used for the manufacture of products intended for use in various fields of industry, including aerospace.

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 hardening processes are combined 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 microstructure. If this metal structure is preserved, products made from it will have inherent low operational properties.

To improve the technological and operational properties, it is necessary to form a fine-grained (phase grain size of not more than 150-200 microns) microstructure in them. In addition, the achievement of a structurally uniform state in semi-finished products is especially important for evaluating the quality of pipes using ultrasonic testing methods, which are widely used in their control. With a highly homogeneous and fine-grained structure of a titanium alloy, the level of acoustic noise significantly decreases, the ultimate sensitivity of the method limited by these noise increases, 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 assemblies due to the operation of products with defects of an acceptable size.

A known method for the production of hot-rolled pipes from titanium α- and (α + β) -alloys, including forging an ingot into a bar for several transitions in the α- and (α + β) -regions, cutting blanks for cutting, making checkers for pressing, axial drilling holes and mechanical turning of the side surface, heating the billet above or below the polymorphic transformation temperature and pressing the hollow tube billet (RF patent No. 2127160, IPC V21B 23/00, B21B 3/00, publ. 1999.03.10.) - analogue.

This method is used for the manufacture of tube blanks.

A known method for the production of hot-rolled tubes from α- and (α + β) -alloys based on titanium, including forging an ingot into a billet with subsequent machining, obtaining a central hole, rolling on a pilgrim mill and machining, with forging at each transition begin to produce at a temperature in the β-region, or β- and (α + β) -regions, and as the workpiece cools, they finish in the (α + β) -regions with a yield of at least 20%. Through piercing of a continuous billet is carried out at a temperature of the β-region, and before rolling on a pilgrim mill, the stitched billet is cooled to a temperature of 30 ÷ 100 ° C below the TPP. Rolling is carried out at a strain rate

from 3 · 10 ^-3 s ^-1 to 10 ² s ^-1 (RF patent No. 2262401, IPC B21B 3/00, publ. 2005.10.20) - prototype. The invention provides for the formation in the pipes of a fine-grained microstructure with a high degree of uniformity.

The disadvantages of this method are the impossibility of obtaining a microstructure of a metal with a grain size of less than 150-200 microns, as well as the limited capabilities of pilgrim mills that do not allow the production of pipes with a diameter of less than 270 m

The aim of this invention is:

- creating a method for producing pipes from α- and pseudo-α-titanium alloys with a fine-grained (grain size not more than 50-100 microns) microstructure;

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

- expanding the technological capabilities of cross helical rolling mills.

The technical result achieved by the implementation of the invention is the creation of a technology in which the operations of forming the geometric dimensions of pipes from α- and pseudo-α-titanium alloys are combined, including with a diameter of less than 270 mm on transverse helical mills with processes of formation of a regulated microstructure that provides high technological and operational properties of products.

The specified technical result is achieved by the fact that in the proposed method for manufacturing hot-rolled pipes from α- and pseudo-α-titanium alloys, including forging an ingot into a billet in several transitions with alternating β, (α + β) -regions, the last transition being forged into ( α + β) -regions, obtaining a central hole in a workpiece, heating a workpiece with a central hole, pressing a pipe workpiece, heating a pipe workpiece for rolling, rolling on a mill and machining, heating a workpiece with a central hole is carried out to mperatury 650-800 ° C at a rate of 50 ÷ 70 ° C / min, then at 20 ÷ 30 ° C / min until the pressing temperature, determined by formula (1):

where T _pressing - pressing temperature;

T _PP - the temperature of the polymorphic transformation of the alloy, ° C;

σ _s - strain resistance taking into account the strain rate and strain temperature, MPa;

s is the specific heat of the alloy, kJ / kg · K;

ρ is the density of the alloy material, kg / m ³ ;

µ is the amount of hood

pressing of the pipe billet is carried out with a hood 2-7,

heating the tube billet for rolling is carried out with a heating rate of 50 ÷ 70 ° C / min to a temperature determined by the formula (2):

T _rolling - rolling temperature,

rolling is carried out with an extract of 2-3.

The essence of the claimed method is as follows.

Forging the ingot is carried out in several transitions with alternating forging in the β and (α + β) -regions. Forging in the β-region reduces the grain size. During subsequent forging with heating of the metal in the (α + β) -region, the grain is crushed.

Final forging in the (α + β) region allows the metal to be strengthened during deformation hardening due to an increase in the density of dislocations.

In the process of heating such a metal to a temperature of (α + β) -region (650-800 ° C) at a speed of 50 ÷ 70 ° C / min, and then slower heating at a speed of 20 ÷ 30 ° C / min to a pressing temperature T _pressing determined from formula (1), primary recrystallization from a large number of centers begins due to the increased internal energy accumulated by the metal during deformation. Regulated heating allows you to grind and even grain size over the cross section of the workpiece. When pressing with an extract of μ = 2 ÷ 7, the formation of crushed elongated grain occurs, while the onset of secondary recrystallization does not occur. With this, we prepare the structure before heating for rolling.

Fast (high-speed) heating at a speed of 50 ÷ 70 ° C / min to the rolling temperature T of the _rolling , calculated by the formula (2), and subsequent rolling with a hood of at least 2 to ensure the required degree of deformation, but not more than 3, in order to avoid deformation overheating and “bloating” the pipe, provides a small, recrystallized grain formed from elongated grains. As a result, macrograins are formed with a size of no more than 2 points. Heating of the pipe billet with a speed of less than υ = 50 ÷ 70 ° C / min leads to the formation of sections of large grain. At a higher heating rate, the uniformity of the temperature field is not ensured, and special technological equipment is required.

Examples of specific performance.

Example 1 (α-titanium alloy). A ⌀740 mm ingot from the Gr2 alloy was forged into a ⌀285 mm bar in several transitions with alternating β and (α + β) regions, and the last transition was carried out in the (α + β) region. A piece with dimensions of 75275 mm × ⌀50 mm × 112.5 mm was made from a forged, machined bar ⌀280 mm for further pressing on a press of 3150 t.p. The heating temperature for pressing T _{pressing was} determined by the formula (1):

The billet was heated at a speed of 50-60 ° C / min to a temperature of T = 700 ° C, then at a speed of 20-30 ° C / min to T _pressing and holding for 30 minutes at this temperature. The tube billet was pressed with a hood equal to 4.51.

The resulting tube billet ⌀133 × ⌀45 × 44 mm was heated under rolling to a temperature determined by the formula (2):

at a speed of 70 ° C / min, then holding for 10 minutes at a given temperature, then the pipe was rolled out on a cross-helical mill with a degree of drawing equal to 4.51.

Further, the pipes were machined to a finished size of ⌀125 mm × ⌀101 mm × 12 mm and subjected to ultrasonic testing.

Pipes from the Gr2 alloy with a size of ⌀125 mm × ⌀101 mm × 12 mm manufactured by the proposed method have the mechanical properties shown in Tables 1 and 2. The macrostructure is shown in FIG. 1.

Table 1 Sample No. Mechanical properties of pipes размером125 × ⌀101 × 12 mm in size, Gr2 alloy σ _V , MPa σ _0.2 , MPa δ,% ψ,% one 493 370 33.3 64.6 2 489 387 32.1 61.3 3 490 381 34.6 65.7 four 488 375 35.8 64.6 ASTM B861 Requirement ≥345 275-450 twenty -

table 2 Sample No. The results of the tests for impact strength, KCU, kgf · m / cm ² one 15.7 2 17.5 3 17.0 four 16.6

Example 2

An example for pseudo-α-titanium alloys (alloy OT4).

An ⌀740 mm ingot is forged into a ⌀280 mm bar with the end of forging in the (α + β) -region, machined by ⌀275 mm. A checker is made for pressing ⌀275 × ⌀50 × 225 mm.

For this ingot, the temperature of the polymorphic transformation T _PP = 950 ° C.

The billet with a central hole is heated in the inductor to a temperature of 750-850 ° C with a speed equal to 20-30 ° C / min to a pressing temperature:

where σ _s = 95 MPa, µ = 4.68, s = 0.73 kJ / (kg · K), ρ = 4.55 g / cm ³ .

Before rolling, the workpiece is heated at a speed of 50-70 ° C / min to a temperature:

The mechanical properties of pipes размером107 × ⌀87 × 10 mm in size from OT4 alloy are given in Table 3. The macrostructure is shown in figure 2.

Table 3 Sample No. Mechanical properties σ _in , MPa (kgf / mm ² ) δ,% ψ,% one 753.62 (76.9) 17.6 44.3 2 753.62 (76.9) 17.6 49.2 3 752.64 (76.8) 21.6 50,4 four 761.46 (77.7) 16.8 47.0 5 774.2 (79.0) 18,4 50,2 6 774.2 (79.0) 18.8 51.6 Requirement TU 1-5-107 617.8-833.6 (63-85) Not less than 8 -

An analysis of the microstructure of the pipes showed that its structure is equiaxial, close to globular with a grain size of 65-90 microns.

The claimed method allows one to obtain from α- and pseudo-α-titanium alloys by rolling on transverse helical mills pipes with a diameter of less than 270 mm with a fine-grained (grain size of not more than 50-100 μm) microstructure, which determines the high technological and operational properties of the products, in t .h. reduction of structural noise during ultrasonic testing.

Claims (1)

A method of manufacturing hot rolled pipes from α- or pseudo-α-titanium alloys, including forging an ingot into a billet in several transitions with alternating β and (α + β) regions, the last transition being forged in the (α + β) region, producing the central hole in the billet, heating the billet with the central hole, pressing the tube billet, heating the tube billet for rolling, rolling in the mill and machining, characterized in that the billet with the central hole is heated to a temperature of 650-800 ° C at a speed of 50 ÷ 70 ° C / min, yes it at 20 ÷ 30 ° C / min until the pressing temperature, determined by the formula

where T _pressing - pressing temperature;
T _PP - the temperature of the polymorphic transformation of the alloy, ° C;
σ _s - strain resistance taking into account the strain rate and strain temperature, MPa;
s is the specific heat of the alloy, kJ / (kg · K);
ρ is the density of the alloy material, kg / m ³ ;
µ is the amount of hood
pressing of the tube stock is carried out with a hood 2-7, heating of the tube stock for rolling is carried out at a heating rate of 50 ÷ 70 ° C / min to a temperature determined by the formula

T _rolling - rolling temperature,
and rolling is carried out with an extract of 2-3.

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