RU2205891C2 - Method for producing article from titanium alloy and method for thermal processing of article from titanium alloy - Google Patents

Abstract

FIELD: mechanical engineering. SUBSTANCE: method involves deforming article at deformation extent ε, satisfying the requirement ε≤K₁•(18,5-1,8•10^-5σ $\genfrac{}{}{0ex}{}{\text{2}}{\text{t}}$ ), where K₁=0.4-1 coefficient, σ_t is temporary resistance, Mpa; subjecting article to annealing for removing deposit and improving mechanical properties by heating article to temperature (T_h) selected from formula T_h = K₂•(σ_t-190)+360, where K₂=0.2-0.3 C/MPa is coefficient, σ_t is temporary resistance, MPa. Method may be used for manufacture of sheet constructions from titanium alloys with the use of forming processes, for example cold stamping, with following thermal processing. Method allows cyclic strength of article to be increased by eliminating or reducing number of intermediate annealing operations in the process of deformation. EFFECT: improved mechanical characteristics of article, increased efficiency by selecting optimal temperature modes, reduced labor intensity and manufacture cycle time, increased operation time of articles from expensive titanium alloys and reduced production costs. 3 cl, 1 tbl

Description

 The invention relates to mechanical engineering and can be used in the manufacture of sheet structures of titanium alloys with the use of shaping, for example cold stamping, and subsequent heat treatment.

A known method of manufacturing stamped products from titanium alloys, mainly from sheet blanks, including stamping, welding and heating, in which the blank before stamping is heated to 900-1000 ^o C for 10-60 minutes, and the product after welding is heated to 1000-1050 ^o C, kept in a heated state for 10-60 minutes and cooled at a speed of 10 ^o C per minute to 900-600 ^o C (description to the USSR AS 333998, 21 D 35/00).

 The known method requires significant energy consumption for heat treatment. Moreover, the choice of temperature conditions is not regulated depending on the material being processed. This leads to cost overruns, the complexity of the process and, in some cases, to reduced mechanical properties.

 A known method of manufacturing a product from titanium alloys by pressure treatment of a sheet stock, in which the workpiece is deformed in a cold state, and in the process of stamping it is subjected to intermediate annealing (prototype, see Production technology of titanium aircraft structures. / A. G. Bratukhin, B.A. Kolachev, V.V. Sadkov and others. M .: Mechanical Engineering, 1995. S.181-183).

 In the known method, intermediate annealing is necessary to increase the plasticity characteristics of the workpiece, which are reduced due to fretting during cold plastic deformation.

 However, intermediate annealing complicates the technological process of shaping and increases the complexity, energy consumption, increase the duration of the manufacturing cycle.

A known method of heat treatment of caked sheet parts of titanium and titanium alloys, including heating, holding at a temperature T _an , selected by the formula
T _OTL = T _n.R -K (σ _at +20)
where T _n.r. - the temperature of the onset of recrystallization of the alloy, ^o C;
σ _in - temporary tensile strength of the alloy, MPa;
k = 0.4-0.5 ^o C / MPa (description of the patent of the Russian Federation 2100473, C 22 F 1/18).

 The known method allows to improve the mechanical characteristics of the cured metal.

 However, for alloys of medium and especially high strength, the annealing temperature by the known method is insufficient to increase the plastic properties of the metal after cold deformation and this does not allow to fully restore the product's performance under cyclic loading. Therefore, the method is not effective enough in relation to cold-deformed sheet structures made of titanium alloys.

A known method of heat treatment of products made of titanium alloys, including low-temperature annealing at 450-510 ^o C for 5-10 hours, cooling and polishing of products (description to the AS of the USSR 411154, C 22 F 1/18, prototype).

 The known method allows to increase the endurance of products.

 However, the choice of temperature is not regulated depending on the particular alloy and its strength level, which can lead to underestimated fatigue characteristics. In addition, a significant heating time leads to significant energy costs and increases the cost of production.

 The technical result from the use of the invention is to reduce the level of energy consumption and cost of production while increasing the cyclic strength of the product by eliminating or reducing the number of intermediate annealing of the workpiece during deformation, which is regulated by the degree of deformation, as well as by choosing the optimal temperature regime for annealing the product during heat treatment .

The technical result is achieved by the fact that in the method of manufacturing a product from titanium alloys, including forming a sheet preform by cold plastic deformation and heating, deformation of the preform is carried out with a degree of deformation ε satisfying the condition:
ε≤K ₁ • (18.5-1.8 • 10 ^-5 • σ $\genfrac{}{}{0ex}{}{\text{2}}{\text{in}}$ ),
where K ₁ = 0.4 ... 1 is the coefficient,
σ _in - temporary tensile strength of the alloy, MPa,
and the product after forming is subjected to heat treatment, including low-temperature annealing.

In the method of heat treatment of a product from titanium alloys, including low-temperature annealing, the products are annealed by heating to a temperature T _n selected by the formula
T _n = K ₂ • (σ _in -190) +360,
where K ₂ = 0.2 ... 0.3 ^o C / MPa - coefficient;
σ _in - temporary tensile strength of the alloy, MPa.

The maximum degree of deformation calculated by the formula ε = K ₁ • (18.5-1.8 • 10 ^-5 • σ $\genfrac{}{}{0ex}{}{\text{2}}{\text{in}}$ ), where K ₁ = 0.4 ... 1, taking into account the level of strength of the metal, allows it to provide, in combination with subsequent heat treatment, the maximum indicators of cyclic strength. The proposed empirical formula is derived experimentally and allows one to determine the ultimate degrees of deformation ε at which the critical dislocation density is achieved and the likelihood of crack formation for a particular alloy increases, taking into account its strength properties. The coefficient K ₁ takes into account the pattern of deformation of the workpiece during shaping (drawing, bending) and the features of the workpiece - the presence or absence of welds in the deformation zone (i.e. the type of microstructure of the metal, as well as the presence of geometric concentrators characteristic of the weld, - undercuts, reinforcements etc.).

Low-temperature annealing is carried out to partially remove the fretting and improve the mechanical characteristics of the product. The heating temperature is calculated by the formula T _n = K ₂ • (σ _in -190) +360, obtained experimentally from the conditions for optimizing the cyclic durability of products taking into account the strength characteristics of the metal. Low-temperature annealing provides a certain decrease in the dislocation density, ordering of the structure due to the onset of the polygonization process, and dispersion hardening during the decomposition of metastable phases recorded during previous operations (for example, argon-arc welding). As a result, an increase in the cyclic strength of the metal is achieved. The value of the coefficient K ₂ is selected depending on various technological factors (the presence of welds in the product, the presence or absence of a previous shaping operation and deformation scheme) and taking into account the nature of operational loads (static and re-static or fatigue.

 Known solutions containing distinctive features were not found.

Concrete example
A piece of a cup type was made by drawing using a VT1-0 sheet of technical titanium sheet with a thickness of 1.2 mm, a diameter of 180 mm, and a depth of 18 mm (maximum tensile ratio 20%). Temporary tensile strength of titanium VT1-0 σ _in = 450 MPa.
Before drawing, the billet is subjected to complete annealing in a vacuum furnace type UVN-1500 in the mode of 550 ^o C, 2 hours

According to the proposed method, the limiting value of the degree of deformation ε for the selected coefficient K ₁ = 1 is ε = 14.86%. Thus, the drawing process according to the proposed method is carried out in two transitions with degrees of deformation of 10% with 1 intermediate complete vacuum annealing according to the mode of 550 ^o C, 2 hours

According to the prototype, the degree of stretching in one transition is limited for titanium VT1-0 to a value of 7% (see, for example, the book: Technology for the production of titanium aircraft structures. / A.G. Bratukhin, B.A. Kolachev, V.V. Sadkov and Dr. M.: Mechanical Engineering, 1995. P.182). After this, an intermediate complete vacuum annealing is required at a temperature of 550 ^° C for 2 hours, i.e., a 20% deformation by the method taken as a prototype is ensured in three transitions with two intermediate vacuum annealing according to the 550 ^° C mode, 2 hours .

The cost of electricity for 1 charge in a vacuum furnace type UVN-1500 at a mode of 550 ^o C, 2 hours is ≈3680 kWh.

After shaping operations, the product is subjected to final low-temperature air annealing in an ETA-4 type furnace at a mode of 465 ^o С, 1 h (see, for example, incomplete annealing modes in the book: Production technology of titanium aircraft structures. / A.G. Bratukhin, B. A. Kolachev, V.V. Sadkov, and others. M .: Engineering, 1995. S. 79). The cost of electricity for 1 charge in the furnace type ETA-4 at a mode of 465 ^o C, 1 h is ≈1850 kWh. According to the proposed method of heat treatment, the heating temperature is T _n = K ₂ • (450-190) +360, where K ₂ in this case is 0.2. T _n = 0.2 • 260 + 360 = 412 ^o C. The exposure time (taking into account the recovery time of the furnace) is 1 hour. The cost of electricity for 1 charge in the furnace type ETA-4 mode 412 ^o C, 1 h is ≈1680 kWh

According to the prototype, a regime of 450 ^o C was selected, 8 hours. Electricity consumption for 1 charge in an ETA-4 type furnace under a regime of 450 ^o C, 8 hours was ≈3890 kWh.

The finished products were subjected to comparative cyclic tests with pulsating internal pressure at a frequency f = 0.2 Hz, the cycle asymmetry coefficient R = + 0.1. The maximum stress of the cycle σ _max was 350 MPa.

 Comparative data on the proposed method and prototype are summarized in table.

 The economic effect consists in saving, reducing the complexity and duration of the product manufacturing cycle, as well as increasing the life of products from expensive titanium alloys.

Claims (2)

1. A method of manufacturing a product from a titanium alloy, comprising forming a preform by cold plastic deformation and heat treatment, characterized in that the deformation of the preform is carried out with a degree of deformation
ε≤K ₁ • (18.5-1.8 • 10 ^-5 σ $\genfrac{}{}{0ex}{}{\text{2}}{\text{in}}$ ),
where K ₁ = 0.4 ... 1 is the coefficient;
σ _in - temporary resistance, MPa,
and heat treatment is carried out using low temperature annealing. 2. A method of heat treatment of a titanium alloy product, including low-temperature annealing, characterized in that the low-temperature annealing is carried out at a heating temperature
T _n = K ₂ • (σ _in -190) +360,
where K ₂ = 0.2 ... 0.3 ^o C / MPa - coefficient;
σ _in - temporary resistance, MPa.

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