RU2285737C1 - Method of thermo-mechanical treatment of titanium blanks - Google Patents

Abstract

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

Description

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

Known methods of processing metals in order to increase their properties, in particular to obtain ultrafine-grained (UFG) structure, providing improved physical and mechanical characteristics. These methods can combine plastic deformation and thermomechanical processing.

A known method for producing ultrafine-grained structure of technically pure titanium by repeated comprehensive forging by flat dies at temperatures of 400-700 ° C ("Formation of a submicrocrystalline structure in titanium alloys by intense plastic deformation". Zherebtsov SV, Galeev PM, Valiakhmetov OR, Malysheva S.P., Salishchev G.A., Myshlyaev M.M. Forging and stamping, No. 7, 1999, pp. 17-22).

A known method for producing ultrafine-grained titanium billets, including intense plastic deformation of the billet in intersecting vertical and horizontal channels ("The influence of ECAP routes on the microstructure and properties of pure titanium." Stolyarov VV, Zhu Yu.T., Alexandrov IV, Low T.S., Valiev R.Z. Material Science and Engineering A299 (2001) p. 59-67).

A known method of combined intensive plastic deformation of workpieces, including torsion deformation in a helical channel, then equal-channel angular pressing (RF patent No. 2240197, IPC B 21 J 5/00, C 22 F 1/18, B 21 C 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 over the sections of the workpiece.

Closest to the proposed method is a method of processing workpieces, including plastic deformation of the workpiece in intersecting vertical and horizontal channels, followed by thermomechanical processing (RF patent No. 2175685, MKI C 22 F 1/18, 21 J 5/00, publ. 10.11. 01).

This method allows to obtain due to intense plastic deformation of the 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 passes of intense plastic deformation (SPD) in intersecting vertical and horizontal channels (4 or more passes), a high utilization of metal, as well as the heterogeneity of the structure of the resulting workpiece, resulting to anisotropy of mechanical properties.

The objective of the invention is to reduce the complexity of the process of obtaining semi-finished products, improve the mechanical properties of the processed material (tensile strength, yield strength, endurance) while maintaining good ductility, as well as achieving their uniformity along the length of the workpiece.

The problem is achieved by the method of producing ultrafine-grained billets, including intense plastic deformation of the billet in intersecting vertical and horizontal channels at a temperature of 500-250 ° C and thermomechanical processing. In contrast to the prototype, thermomechanical treatment, including annealing and deformation, is carried out before intense plastic deformation, and annealing is carried out at a temperature not higher than the polymorphic transformation temperature minus 200 ° C, and the deformation is carried out at the annealing temperature and is gradually reduced to the temperature of intense plastic deformation in intersecting vertical and horizontal channels, reaching an accumulated logarithmic degree of deformation of at least 4.5.

Deformation-heat treatment before intense plastic deformation in these modes allows you to pre-grind the structure and thereby provide conditions for the formation of further processing of a homogeneous ultrafine-grained structure. This leads to an increase in strength characteristics and uniformity of their distribution over the sections of the workpiece. In this case, the number of IPD passes can be reduced. The formation of a homogeneous UFG structure in a workpiece with a smaller number of passes in an industrial application is promising for reducing the complexity of the process, increasing the efficiency of the metal.

The method is as follows.

The titanium billet in the form of a bar is annealed at a temperature not higher than the temperature of the polymorphic transformation minus 200 ° C. This temperature regime of heat treatment provides the best combination of mechanical properties, and also provides the formation of equiaxial globular structure (Kolachev B.A., Elagin V.I., Livanov V.A. Metallurgy and heat treatment of non-ferrous metals and alloys: Textbook for universities. - M .: MISIS, 2001, 416 p.). The deformation is carried out starting from the annealing temperature, which is gradually reduced to the temperature of intense plastic deformation in the intersecting vertical and horizontal channels, reaching an accumulated logarithmic degree of deformation of at least 4.5.

After the stage of deformation, an intensive plastic deformation is carried out in intersecting vertical and horizontal channels at a temperature of 500-250 ° C. Then the preform is removed, cooled to room temperature and subjected to dressing and processing on a lathe to remove the defective layer, after which the microhardness, tensile properties and microstructure are checked.

An example of a specific implementation.

We took a bar from CP-Ti Grade 2 alloy with a diameter of 24.5 mm and a length of 120 mm.

The bar was annealed at a temperature of 680 ° C for 2 hours and deformed by isothermal forging. The number of successive passes of isothermal forging is n = 3, as a result of which a degree of deformation of e≈4.5 is achieved. The processing temperature, respectively, was 680, 570 and 450 ° C.

At the next stage, the billet was subjected to 2 passes of intense plastic deformation in intersecting vertical and horizontal channels at a temperature of 450 ° C. As a result of the deformation, the degree of deformation e≈2 was achieved. After cooling the workpiece to room temperature, it was subjected to dressing and turning. Metallographic analysis revealed a high uniformity of the structure over the sections of the workpiece.

The control of tensile mechanical properties at room temperature showed:

Table After 2 passes IPD After pretreatment and IPD Tensile strength, MPa 568 740 Yield Strength, MPa 515 684 Relative extension, % 17 fifteen

The results of the control of mechanical properties presented in the table show that the introduction of pre-treatment provides not only an increase in strength properties, but also the preservation of the ductility of titanium. In addition, reducing the number of IPD passes to 2, due to the introduction of pre-treatment, which allows to obtain a uniform UFG structure, can significantly reduce the complexity of the process.

Thus, the proposed method for producing titanium ultrafine-grained billets significantly improves the mechanical properties of the processed material, their uniformity over the sections of the billet.

Claims (2)

1. A method of producing ultrafine-grained titanium billets, comprising intensive plastic deformation of the billet in intersecting vertical and horizontal channels at a temperature of 500-250 ° C and thermomechanical processing, characterized in that the thermomechanical treatment, including annealing and deformation, is carried out before intense plastic deformation, reaching at this accumulated logarithmic degree of deformation of at least 4.5, and annealing is carried out at a temperature not higher than the temperature of the polymorphic transformation minus 2 00 ° C, thermomechanical treatment begins to be carried out at the annealing temperature, which is gradually reduced to the temperature of intense plastic deformation. 2. The method according to claim 1, characterized in that the intense plastic deformation is carried out in several passes with a change in the axis of deformation.