The way to obtain ultrafine-grained titanium billets

 

(57) Abstract:

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. The essence of the method consists in the following: hold the plastic deformation of the workpiece in intersecting vertical and horizontal channels with decreasing temperature in the range 500-250oC accumulated logarithmic degree of deformation e 4, followed by thermomechanical processing alternation of cold deformation with the degree of 30-90% with intermediate and final annealing in the temperature range 250-500oC for 0.5-2 hours Technical result of the invention is the improvement of the mechanical properties of the processed material by increasing the strength and fatigue characteristics while maintaining ductility. The combination of severe plastic deformation and subsequent thermomechanical processing in these modes allows to form in the material of thermally stable ultra fine-grained structure with a grain size not more than 0.1 μm, it increases the level the political process changes the physical-mechanical properties of the metal and can be used in mechanical engineering, the aircraft engine industry and medicine in the manufacture of semi-finished titanium.

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

For example, the mode of deformation of the workpieces in overlapping vertical and horizontal channels (see C. M. Sehgal, V. I. Kopylov, V. I. Reznikov "a plastic structure formation metals", Minsk: Nauka and Technica, 1994, S. 26) allows to solidify the metal in the process due to the high intensity of the accumulated shear strain.

A method of processing titanium workpieces along.with. USSR N 1737920, IPC C 22 F 1/18, publ. 15.12.94, consists in the deformation of the material at the temperature change of the mechanism of homogeneous primary deformation twinning on the mechanism of heterogeneous deformation layered over.

The known method of heat treatment of parts made of titanium alloys, including heating to 150-200oC, the shutter speed for 2-3 h, the cooling and subsequent heating up to 500-750ooC (and.with. USSR N 1613505, IPC C 22 F 1/18, publ. 15.12.90 year).

Known processing methods do not allow to obtain the required physical and mechanical characteristics, including endurance and low cycle fatigue of the material.

The closest to the invention is a method of processing workpieces, including severe plastic deformation of the blank in overlapping vertical and horizontal channels pressurized in the past, which is carried out at the initial and final stages of the deformation process (patent RF N 2139164, the IPC 21 J 5/00, publ. 10.10.99 year).

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 generated structure and the resulting mechanical properties (strength) is insufficient for use in critical structures.

Invented starostik characteristics while maintaining ductility.

This object is achieved by a method of obtaining ultrafine-grained titanium billets, including plastic deformation of the workpiece in intersecting vertical and horizontal channels pressurized in the past. Unlike the prototype, the plastic deformation is carried out at lower temperatures in the range of 500-250oC accumulated logarithmic degree of deformation e 4, followed by thermomechanical processing alternation of cold deformation with the degree of 30-90% with intermediate and final annealing in the temperature range 250-500oC for 0.5-2 hours

The combination of severe plastic deformation and subsequent thermomechanical processing in these modes allows to form in the material of thermally stable ultra fine-grained structure with a grain size not more than 0.1 μm, it increases the level of tensile strength and fatigue strength.

The method is as follows.

Titanium workpiece in the form of a rod is subjected to plastic deformation in intersecting vertical and horizontal channels pressurized in the past, which is provided by the difference in cross section of the channels and SUP>C in several successive passes, between which the rod rotate around the longitudinal axis at an angle of 90ofor a uniform structure processing. The number of passes is determined by the accumulated achievement of the logarithmic strain e 4.

After the plastic deformation of the workpiece is removed from the tooling and cooled to room temperature. Then it is 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.

In the next step, called thermomechanical treatment (TMT), the workpiece is subjected to multi-step rolling on 4 roller mill with intermediate and final anneals. The temperature of annealing at an intermediate stage is 500-350oC, time of 0.5-2 hours At the final temperature annealing is 350-250oC, time of 0.5-2 hours total degree of deformation of the workpiece is 30-90%. After the TMO again they control the microstructure, microhardness and mechanical properties.

An example of a specific implementation.

Take the original gorjachekatanuju procurement of technically th with an average grain size of 10 μm.

The rod was subjected to plastic deformation by the above method. The angle of intersection of channels = 90o. The temperature of the beginning and end of the deformation was 450 and 400oC, respectively. The number of consecutive passes n=8, resulting in the degree of deformation e=9,2. After cooling the preform to room temperature, it was subjected to straightening and turning to a diameter of 22 mm Control parameters and mechanical properties showed:

the grain size is d = 0.3 ám

tensile strength -in= 710 MPa

yield strength -02= 640 MPa

fatigue strength --1= 400 MPa on the basis of 2-107cycles

microhardness - Hv= 3000 MPa

elongation - = 14%

relative narrowing - = 60%

In the next step, the rod was subjected to thermomechanical processing, namely multi-pass rolling on 4 roller mill with intermediate and final annealing scheme:

rolling with the degree of deformation of 43%;

intermediate annealing at t=350oC for 1 h;

rolling with the degree of deformation of 61%;

the final annealing at t=300oC for 1 h

The total degree of deformation from the initial cross section 22 mm to the final 15 mm was 78%. the ROM 14 mm and a length of ~ 200 mm

The control parameters and mechanical properties showed:

the grain size is d = 0.1 ám

tensile strength -in= 1115 MPa

yield strength -02= 1050 MPa

fatigue strength --1= 500 MPa

microhardness - Hv= 3200 MPa

elongation - = 10%

relative narrowing - = 60%

Thus, the proposed method of producing ultrafine-grained titanium billets significantly improves the mechanical properties of the processed material that can be used in critical structures.

The way to obtain ultrafine-grained titanium billets, including plastic deformation of the workpiece in intersecting vertical and horizontal channels pressurized in the latter, characterized in that the plastic deformation is carried out at lower temperatures in the range of 500-250°C, with accumulated logarithmic degree of deformation E4, followed by thermomechanical processing alternation of cold deformation with the degree of 30-90% with intermediate and final annealing in the temperature range 250-500°C for 0.5-2 hours

 

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FIELD: metal working.

SUBSTANCE: hard alloy matrix has casing, bushing pressed in the case and hard alloy insertion. Bushing has multifaced hole. Hard alloy insertion is composed by several sections made in form of trapezoidal-section prisms which have cut angles at their non-working edges. Number of sections corresponds to number of faces of item to be headed. Cuts of angles are made symmetrically to faces of working edge. Slits are made in several places of multifaced hole bushing at the ponts where faces cross each other.

EFFECT: improved resistance of matrix; simplified assembly.

3 cl, 1 dwg

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