Method of thermo-mechanical treatment of titanium blanks

FIELD: mechanical engineering; aircraft engine manufacture and medicine.

SUBSTANCE: proposed method is accompanied by change in physico-mechanical properties of metal. Proposed method of production of ultra-fine-grain titanium blanks includes intensive plastic deformation of blanks in crossing vertical and horizontal channels at temperature of 500-250°C and thermo-mechanical treatment. Thermo-mechanical treatment including annealing and deformation is performed before intensive plastic deformation at stored logarithmic degree of deformation no less than 4.5; annealing is carried out at temperature not above temperature of polymorphous transformation minus 200°C; thermo-mechanical treatment is started at annealing temperature which is reduced in stepwise manner to temperature of intensive plastic deformation. Ultra-fine-grain structure is formed at lesser number of technological passes.

EFFECT: improved strength characteristics; reduced labor consumption; enhanced efficiency.

2 cl, 1 tbl, 1 ex

 

The invention can be used in mechanical engineering, aircraft engine industry and medicine in the manufacture of semi-finished titanium by deformation-heat treatment, accompanied by the change of physico-mechanical properties of the metal.

Known methods of treatment of metals to improve their properties, in particular to obtain ultrafine-grained (UMP) structures for the improvement of physical-mechanical characteristics. These methods can be combined with the plastic deformation and thermomechanical processing.

A method of obtaining ultrafine-grained structure of commercially pure titanium by repeated forging a comprehensive flat strikers at temperatures of 400-700° ("Formation of submicrocrystalline structure in titanium alloys by severe plastic deformation". Stallions SV, Galeev P.M., O.R. Valiakhmetov, Malyshev, S. p., Saliev GA, Myshlyaev MM-Forging production, No. 7, 1999, p.17-22).

A method of obtaining ultrafine-grained titanium billets, including severe plastic deformation of the blank in overlapping vertical and horizontal channels ("the Impact of routes pressing on microstructure and properties of pure titanium". Stolyarov V.V., Zhu YT, Alexandrov I.V., low FORCE, Valiev R.Z. Material science Andes engineering A (2001) p.59-6).

The known method combined intensive plastic deformation of workpieces, including deformation by torsion in the screw channel, then equal-channel angular pressing (RF patent No. 2240197, IPC B 21 J 5/00, C 22 F 1/18, 21 25/00, publ. 20.11.04).

However, the known processing methods do not allow to provide the required physical and mechanical characteristics and the uniformity of their distribution in cross sections of the workpiece.

Closest to the proposed method is a method of processing workpieces, comprising the plastic deformation of the workpiece in intersecting vertical and horizontal channels, with subsequent thermomechanical processing (patent RF №2175685, MKI 22 F 1/18, 21 J 5/00, publ. 10.11.01).

This method allows you to get through severe plastic deformation of ultrafine-grained structure of the processed material and to increase the level of physical and mechanical properties. However, the disadvantage of this method is the high complexity of the process of obtaining blanks associated with the need for a large number of passages severe plastic deformation (SPD) in intersecting vertical and horizontal channels (4 or more passes), high utilization rate of the metal, as well as the heterogeneity of the structure of the resulting workpiece, leading to anisotropy of mechanical properties.

p> The objective of the invention is to reduce the complexity of the production process semi-finished products, the improvement of the mechanical properties of the processed material (tensile strength, yield strength, fatigue limit) while maintaining good ductility, as well as the achievement of their uniformity along the length of the workpiece.

This object is achieved by a method of obtaining ultrafine-grained billets, including severe plastic deformation of the blank in overlapping vertical and horizontal channels at a temperature of 500-250°and thermomechanical processing. Unlike the prototype thermo-mechanical processing, including annealing and deformation, are exposed to severe plastic deformation and annealing is carried out at a temperature not higher than the temperature of polymorphic transformation minus 200°and the deformation starts to conduct when the annealing temperature and speed to reduce temperature severe plastic deformation in intersecting vertical and horizontal channels, reaching a cumulative logarithmic degree of deformation of at least 4.5.

Conducting deformation-heat treatment before severe plastic deformation in these modes allows you to pre-chop the structure and thus provide conditions for the formation of further processing, one is native ultrafine-grained structure. This increases the strength characteristics and the uniformity of their distribution in cross sections of the workpiece. This can be reduced the number of passes SDI. Forming in the workpiece homogeneous UMP patterns with fewer passes in industrial applications is promising to reduce the complexity of the process, increasing the efficiency of use of metal.

The method is as follows.

Titanium workpiece in the form of a rod subjected to annealing at a temperature not higher than the temperature of polymorphic transformation minus 200°C. This temperature heat treatment provides the best combination of mechanical properties, and also provides for the formation of equiaxial globular structure (Kolachev B.A., Yelagin V., Livanov VA Metallography and heat treatment of nonferrous metals and alloys: the Textbook for high schools. - M.: MISA, 2001, 416 S.). The deformation is carried out, since the annealing temperature, which speed to reduce temperature severe plastic deformation in intersecting vertical and horizontal channels, reaching a cumulative logarithmic degree of deformation of at least 4.5.

After the deformation conduct intensive plastic deformation in intersecting vertical and horizontal channels at a temperature 00-250° C. Then, the workpiece is removed, cooled to room temperature and subjected to the edit processing on a lathe to remove the defective layer, followed by the control micro-hardness, mechanical properties of tensile strength and microstructure.

An example of a specific implementation.

Took the rod of alloy CP-Ti Grade 2 diameter of 24.5 mm and a length of 120 mm

The rod was subjected to annealing at a temperature of 680°C for 2 hours and strain isothermal forging. The number of consecutive passes isothermal forging n=3, resulting in the degree of deformation e≈4,5. Temperature treatment, respectively, was $ 680, 570 and 450°C.

In the next step, the workpiece was subjected to 2 passages of intense plastic deformation in intersecting vertical and horizontal channels at a temperature of 450°C. the resulting deformation was achieved degree of deformation e≈2. After cooling the preform to room temperature, it was subjected to straightening and machining. Metallographic analysis revealed a high homogeneity of the structure section of the workpiece.

The control of mechanical properties in tension at room temperature showed:

Table
After 2 passes SDIAfter the seat reservation processing and SDI
Tensile strength, MPa568740
Yield strength, MPa515684
Elongation, %1715

The results of the control of mechanical properties presented in the table show that the introduction of pre-treatment not only provides increased strength properties, but also maintaining the ductility of titanium. In addition, reducing the number of passes SDI up to 2, due to the introduction of pre-processing, which allows to obtain homogeneous UMP structure, allows to significantly reduce the complexity of the process.

Thus, the proposed method of producing ultrafine-grained titanium billets significantly improves the mechanical properties of the processed material, the uniformity of the cross-sections of the workpiece.

1. The way to obtain ultrafine-grained titanium billets, including severe plastic deformation of the blank in overlapping vertical and horizontal channels at a temperature of 500-250°and thermomechanical processing, characterized in that thermo-mechanical processing, including annealing and deformation, are exposed to severe plastic deformation, while achieving an accumulated logarithmic degree of deformation is not IU is its 4.5, moreover, the annealing is carried out at a temperature not higher than the temperature of polymorphic transformation minus 200°, thermomechanical processing begin to conduct when the annealing temperature, which speed to reduce temperature severe plastic deformation.

2. The method according to claim 1, characterized in that the severe plastic deformation spend several passes with the change of deformation axis.



 

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