RU2463376C2 - Method to produce cold-deformed pipes from double-phase alloys based on titanium - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method to manufacture cold-deformed pipes from double-phase alloys based on titanium includes ingot smelting, ingot forging in a β-area or β- and α+β-area with forging completion in the α+β-area into an intermediate blank with the specified forging reduction. The intermediate blank is produced with forging reduction of at least 1.35, a block is made from the intermediate blank, which is pressed into a billet and thermally treated at the temperature that is by 30°-40°C below the temperature of T_int, and them the billet is rolled with intermediate surface treatment, etching and thermal treatment. Drawing in process of rolling is defined using the following formula.

EFFECT: produced pipes are characterised by high physical-mechanical properties due to exclusion of formation of grain-to-grain microcracks.

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Description

The invention relates to pipe production, namely the production of high-strength pipes from two-phase alloys based on titanium, mainly from pseudo-α and (α + β) alloys. The invention can be used for the manufacture of critical products intended for use in various fields of the national economy, for example, guard shields of geophysical instruments, aircraft wing mechanization drives, aircraft fuselage frame, hydraulic systems, etc.

It is traditionally believed that two-phase alloys, due to their high strength, are technologically advanced only with hot or warm deformation.

The traditional method of pressure treatment of titanium alloys is known, in which the pre-treatment of the billet - ingot - is performed in the β- and (α + β) -regions, and the final - in the (α + β) -regions (see, for example, Production technology of titanium aircraft designs / A.G. Bratukhin, B.A. Kolachev, V.V. Sadkov and others - M .: Mechanical Engineering, 1995. - S.191-199).

A common drawback of such technologies is that when processing in the two-phase (α + β) region, even at low speeds and degrees of deformation, these alloys form intergrain boundary microcracks that are uncontrolled by ultrasonic testing and are detected only by microstructural analysis. They are the reason for the decrease in the physicomechanical properties of titanium alloys in which (α + β) phases are present (see, for example, E. Collings, Physical Metal Science of Titanium Alloys: Translated from English, edited by B. Verkin. , Moskalenko V.A. M.: Metallurgy, 1988 .-- P.165). Similar physical phenomena are also characteristic of other multiphase alloys, in particular, S.I. Gubkin warned of the possibility of the appearance of such defects back in 1947 - “in order to avoid uneven deformation and the appearance of significant additional stresses, it is not recommended to allow a change in the phase state during deformation. The temperature of the end of deformation should be taken 20-30 ° above the line of phase state change "(see S. I. Gubkin. Theory of metal forming. - M.: Metallurgizdat, 1947. - S. 470-471). Therefore, the processing of titanium alloys in the final deformation operations at high temperatures in the (α + β) region potentially reduces the physicomechanical properties of titanium alloys. Recommendations for the final operations of deformation of titanium alloys in the β-region can be applied with great assumptions due to the fact that there are prerequisites for coarsening the structure of the titanium alloy.

A known method for the production of hot rolled pipes from α and (α + β) -alloys based on titanium, including forging an ingot into a billet in the β-region or β- and (α + β) -regions with a given uk and subsequent machining, obtaining checkers, pipe deformation in the (α + β) region and heat treatment. The invention provides for the formation in the pipes of a fine-grained microstructure with a high degree of uniformity (RF Patent No. 2262401, IPC B21B 3/00, publ. 20.10.2005).

The method does not allow to fully realize the potential capabilities of pseudo-α and (α + β) alloys, since the final deformation is performed in the (α + β) region in roll calibers with outlets in which an unfavorable stress-strain state scheme is realized, and this leads to the formation of intergranular boundary microcracks that significantly reduce the physicomechanical properties of the alloys being processed and limit the permissible degrees of deformation during subsequent cold rolling of pipes.

A known method of manufacturing a hollow tube billet for the production of seamless pipes from pseudo-α and (α + β) -titanium alloys, including ingot smelting, ingot forging in the β-region or β- and α + β-region with the end of forging in α + β -regions in the intermediate billet with a given uk (RF Patent No. 2127160, IPC B21B 3/00, publ. 03/10/1999) - prototype.

The method does not take into account the physicomechanical properties of the alloys and does not guarantee the formation of secondary α-plates in the billet during the thermomechanical treatment, which impede the cold deformation of two-phase alloys.

The objective of the invention is to provide a method for producing cold-deformed pipes from two-phase titanium alloys with enhanced physical and mechanical properties of the metal.

The technical result achieved by the implementation of the invention is the creation of technology that allows at the final stage of deformation to produce titanium pipes without the formation of intergranular boundary microcracks by the method of cold rolling, while rolling is carried out with the calculated value of the drawing, which ensures deformation without fracture.

The specified technical result is achieved by the fact that in the method of manufacturing cold-deformed pipes from two-phase alloys based on titanium, including ingot smelting, forging 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 billet with a given uk, the intermediate billet is obtained with a yoke of at least 1.35, a checker is made from the intermediate billet, which is pressed into a tube billet at a temperature not exceeding the temperature determined by the formula:

where T _n - the temperature of the heating of the pieces before pressing. ° C;

T _pp - the temperature of the polymorphic α↔β transformation, ° C;

σ _s (T _n ) is the deformation resistance of the metal at a heating temperature, MPa;

lnµ _i is the natural logarithm of the true stretch during pressing;

s - specific heat of metal, kJ / kg · ° C;

ρ is the density of the metal, g / cm ³ ,

after which the tube billet is heat treated at a temperature of 30-40 ° C below the temperature T _pp , and then the tube billet is rolled with intermediate surface treatment, etching and heat treatment, while the hood during rolling is determined by the formula:

where µ is the hood during cold rolling of pipes on HGT machines;

KCU - impact strength, kgf · m / cm ² ;

σ _0.2 - yield strength, MPa;

K is the plasticity safety factor K = 0.45-0.6.

The essence of the invention is as follows.

The first forging of the ingot into the intermediate billet at temperatures in the β, (α + β) -region destroys the cast structure and allows you to pre-prepare the microstructure (grind the grain), the final yarns of at least 1.35 and regulated heating form a microstructure with a globular α-phase in the checker for subsequent pressing it into a pipe billet at a temperature determined by the formula (1). The temperature is calculated taking into account the lowest possible temperature based on the physicomechanical properties of the alloy, at which the pressing process is ensured and the highest possible temperature, exceeding which will lead to the formation of secondary α-plates in the initial β-grain, which impedes the cold deformation of two-phase alloys. Subsequent heat treatment at a temperature of 30-40 ° C below the temperature T _PP contributes to the uniformity of the mechanical properties of the workpiece and the removal of internal stresses. Cold rolling of pipes is carried out with the hood, determined by the formula (2), which guarantees deformation without destruction. If necessary, the pipes are subjected to subsequent rolling with intermediate annealing.

The possibility of carrying out the invention is illustrated by an example of manufacturing a cold-rolled pipe размером48 × 5 mm in size from a titanium (α + β) alloy Gr23 (Ti-6Al-4V ELI) The chemical composition of the alloy Gr23 is shown in table 1.

Table 1 Selection area Ti The content of elements,% Al V Fe O ₂ FROM N H ₂ Every impurity Σ _pr AT main 5.98 4.0 0,064 0,075 0.008 0.008 <0.002 <0.1 0.128 N main 5.90 4.09 0,069 0,071 0.006 0.007 <0.002 <0.1 0.129 ASTM Requirement 861 main 5.5-6.5 3.5-4.5 No more 0.25 0.13 0.08 0,03 0.0125 0.1 0.4

Tpp = 948 ° C

The required level of mechanical properties according to ASTM B 861:

- tensile strength ≥828 MPa (120ksi),

- yield strength (0.2% offset) of at least 759 MPa (110ksi),

- elongation of 50 mm, not less than 10%.

The pipe was made as follows:

1. Forging the bar at ⌀140 × L mm according to the scheme: β, α + β, β, α + β (bats ≥3), the final bends are 1.35.

2. Machining, production of pieces of checkers ⌀132 × ⌀58 × 37 mm.

3. Heating to a temperature of 878 ° C, calculated by the formula (1):

4. Pressing the tube stock on a press of 660 tf. размер85 × ⌀57 × 14 mm.

5. Annealing: TPP - 30 ° holding for 60 minutes, cooling - air.

6. Editing.

7. Machining to a size of ⌀80 × ⌀60 × 10 mm.

8. Etching.

9. Oxidation annealing.

10. The first rolling at the KhPT 90 mill for a size of ⌀65 × ⌀52 × 6.5 mm, with a hood calculated according to formula (2).

11. Sandblasting, etching.

12. Annealing.

13. Editing, trimming the ends.

14. The second rolling at the HPT 3 ½ mill for a size of ⌀48.2 × ⌀38 × 5.1 mm, with a hood calculated by the formula (2).

15. Sandblasting, etching.

16. Annealing.

17. Editing, etching, trimming, control.

⌀48 × 5 mm cold-rolled pipes made of Gr23 alloy are delivered according to the results of tensile tests.

The results of mechanical tests of hot-pressed heat-treated pipes ⌀85 × 14 mm, after heat treatment (heating 918 ° C (T _pp - 30 ° C), holding time 60 minutes, cooling - air) are shown in table 2.

table 2 Sample No. Yield strength Tensile strength Relates. elongation Relates. narrowing Impact Strength (KCU) ksi MPa ksi MPa % % kgf · m / cm ² one 117.3 809 129.9 896 16.8 46.5 8.1 2 115.6 797 129.3 892 16,4 46.2 8.3 3 115.9 799 129.1 890 16,4 41.5 7.8 max 117.3 809 129.9 896 16.8 46.5 8.3 min 115.6 797 129.1 890 16,4 41.5 7.8 average arithm. 116.2 801.7 129.4 892.7 16.5 44.7 8.1 ASTM B 861 ≥110 ≥759 ≥120 ≥828 > 10

The results of mechanical testing of finished pipe samples (delivery values) at a size of ⌀48 × 5 mm from Gr23 alloy are shown in Table 3 and 4.

Table 3 shows the mechanical properties of a cold-rolled pipe with a size of ⌀48 × 5 mm, and the condition after heat treatment. Heat treatment according to the mode: heating 700 ° C, holding for 60 minutes, cooling - air (heat treatment in a vacuum oven).

Table 3 Sample No. Yield strength Tensile strength Relates. elongation ksi MPa ksi MPa % one 126.9 875 146.6 1011 11.6 ASTM B 861 ≥110 ≥759 ≥120 ≥828 > 10

Table 4 - mechanical properties of cold-rolled pipe size

⌀48 × 5 mm, condition - after heat treatment. Heat treatment according to the mode: heating 700 ° C, holding for 60 minutes, cooling - air (selection of the mode in the STC laboratory).

Table 4 Sample No. Yield strength Tensile strength Relates. elongation ksi MPa ksi MPa % one 122.1 842 140.9 972 10.3 2 122,2 843 142.8 985 10,2 max 122,2 843 142.8 985 10.3 min 122.1 842 140.9 972 10,2 average arithm. 122,2 842.5 141.9 978.5 10.25 ASTM B 861 ≥110 ≥759 ≥120 ≥828 > 10

The practical application of the manufacture of cold-deformed pipes from two-phase alloys based on titanium, in particular the manufacture of pipes from Gr23 alloy, has shown the possibility of obtaining products with desired strength properties. The technological process is stable, out of 10 launched pipe billets, there were no waste losses. The technology used standard equipment.

Claims (1)

A method of manufacturing cold-deformed pipes from titanium-based two-phase alloys, including ingot smelting, ingot forging in the β region or β and α + β regions with the end of forging in the α + β region into an intermediate billet with a predetermined yield, characterized in that an intermediate billet is obtained with a draft of at least 1.35, a checker is made from an intermediate billet, which is pressed into a tube billet at a temperature not exceeding the temperature determined by the formula:

where T _n - the temperature of the heating of the pieces before pressing, ° C;
T _pp - the temperature of the polymorphic α↔β transformation, ° C;
σ _s (T _n ) is the deformation resistance of the metal at a heating temperature, MPa;
lnµ _i is the natural logarithm of the true stretch during pressing;
c - specific heat of metal, kJ / (kg · ° C);
ρ is the density of the metal, g / cm ³ ,
then the tube billet is heat treated at a temperature of 30-40 ° C below the temperature T _pp , and then the tube billet is rolled with intermediate surface treatment, etching and heat treatment, while the hood during rolling is determined by the formula:

where µ is the hood during cold rolling of pipes on HGT machines;
KCU - impact strength, kgf · m / cm ² ;
σ _0.2 - yield strength, MPa;
K is the plasticity safety factor, K = 0.45-0.6.