CN112481568B - Ti6Al4V alloy forging beta annealing heat treatment method - Google Patents
Ti6Al4V alloy forging beta annealing heat treatment method Download PDFInfo
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- CN112481568B CN112481568B CN202011376544.XA CN202011376544A CN112481568B CN 112481568 B CN112481568 B CN 112481568B CN 202011376544 A CN202011376544 A CN 202011376544A CN 112481568 B CN112481568 B CN 112481568B
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
- C22F1/16—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of other metals or alloys based thereon
- C22F1/18—High-melting or refractory metals or alloys based thereon
- C22F1/183—High-melting or refractory metals or alloys based thereon of titanium or alloys based thereon
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
- C21D1/30—Stress-relieving
Abstract
The invention provides a beta annealing heat treatment method for a Ti6Al4V alloy forging, which comprises the following steps: the first step is as follows: beta annealing: heating the Ti6Al4V alloy forging to a temperature of 25-45 ℃ below the beta transformation point, keeping the temperature for a first heat preservation time, then heating to a temperature of 25-30 ℃ above the beta transformation point, keeping the temperature for a second heat preservation time, and after discharging, starting air cooling or air blowing cooling on the Ti6Al4V alloy forging within 2 min; the second step is that: and (5) stress relief annealing. The Ti6Al4V alloy forging beta annealing heat treatment method provided by the invention can obtain higher strength, plasticity and fracture toughness meeting the specification requirements, lower fatigue crack propagation rate, simple and stable process, convenient operation and suitability for industrial production.
Description
Technical Field
The invention belongs to the technical field of heat treatment of metal materials, and particularly relates to a beta annealing heat treatment method for a Ti6Al4V alloy forging.
Background
The Ti6Al4V is a typical two-phase titanium alloy, has low density, higher strength and fatigue strength, is widely applied to the fields of aviation, aerospace and the like, and in recent years, along with the requirements of an aviation aircraft on long service life and high reliability, an aviation structural material is changed from a design simply meeting the traditional static strength design to a damage tolerance design criterion, and the damage tolerance design is designed to ensure the safety of important components containing cracks or possibly containing cracks and provide requirements on fracture toughness, fatigue crack propagation resistance and the like.
Beta heat treatment of titanium alloys is one of the main technical approaches to obtaining high damage tolerance titanium alloys because the lamellar structure obtained after annealing the titanium alloy in the beta region has superior fracture toughness and fatigue crack propagation resistance compared to equiaxial or bimodal structures obtained by heat treatment in the conventional (alpha + beta) region. The standard requirements are that the yield strength and fracture toughness of the Ti6Al4V forgings subjected to common annealing are as follows: 830MPa and 55 MPa-m 1/2, and the yield strength and fracture toughness of the Ti6Al4V forgings subjected to beta annealing heat treatment are as follows: 830MPa and 80 MPa.m 1/2, the fracture toughness of the Ti6Al4V alloy forging subjected to beta annealing is obviously improved under the condition that the strength at room temperature is not reduced.
The beta annealing heat treatment parameters determined by the current specifications are as follows: heating temperature beta t +30 ℃ (± 15 ℃)/t ≥ 30min + destressing, the tissue requirement is: the single original beta crystal grain is transformed into a beta structure with a basket shape, the original beta crystal grain size is not more than 2mm, the tensile strength is not less than 900MPa, the yield strength is not less than 830MPa, the elongation is not less than 6%, the reduction of area is not less than 10%, and the fracture toughness requirement is not less than 80 MPa.m 1/2.
Tests and trial production find that the Ti6Al4V alloy forging is easy to have rapid growth of crystal grains after beta annealing, beta crystal grains larger than 2mm are generated, and the tissue is unqualified, the thin forging (the effective thickness is less than or equal to 50mm) is easy to have unqualified elongation, and the thick forging (the effective thickness is more than 50mm) is easy to have unqualified tensile strength.
Disclosure of Invention
The invention aims to provide a Ti6Al4V alloy forging beta annealing heat treatment method, the Ti6Al4V alloy forging processed by the method has a microstructure meeting requirements, high strength, a plasticity index meeting the requirements, high fracture toughness and a low fatigue crack propagation rate, and the problem that the microstructure and the performance cannot meet the standard requirements in the prior art is solved.
The invention relates to a beta annealing heat treatment method for a Ti6Al4V alloy forging, which comprises the following steps:
the first step is as follows: beta annealing:
heating the Ti6Al4V alloy forging to a temperature of 25-45 ℃ below the beta transformation point, keeping the temperature for a first heat preservation time, then heating to a temperature of 25-30 ℃ above the beta transformation point, keeping the temperature for a second heat preservation time, and after discharging, starting air cooling or air blowing cooling on the Ti6Al4V alloy forging within 2 min;
the second step is that: and (5) stress relief annealing.
Optionally, the first heat preservation time is within 60min to 120 min.
Optionally, the second heat preservation time is within 40min to 60 min.
Optionally, the larger the effective thickness of the Ti6Al4V alloy forging, the longer the first or second holding time period.
Optionally, the volume fraction of the equiaxed alpha phase in the microstructure of the Ti6Al4V alloy forging is 30-45%.
Optionally, the heating to a temperature 25-30 ℃ above the phase transition point comprises:
the temperature is raised to be 25-30 ℃ above the phase transformation point within 35-45 min.
Optionally, the air cooling or air blowing cooling of the Ti6Al4V alloy forging includes:
when the effective thickness of the Ti6Al4V alloy forging is less than or equal to 50mm, air cooling is adopted;
and when the effective thickness of the Ti6Al4V alloy forging is larger than 50mm, adopting air blowing and cooling.
Optionally, the stress relief annealing includes:
heating the Ti6Al4V alloy forging cooled to room temperature by air cooling or air blowing cooling to 720-740 ℃, preserving heat for 2-5 h, and air cooling to room temperature; the room temperature is less than or equal to 40 ℃.
The invention provides a beta annealing heat treatment method for a Ti6Al4V alloy forging, which has the following advantages:
in the first step, before the temperature is raised to the temperature above the phase transformation point, the temperature is preserved in the upper part of the alpha + beta region, and then the temperature is raised to the beta phase region, so that the heating and heat preservation time in the beta phase region can be greatly shortened, the possibility of the growth of beta crystal grains is reduced, the obtained tissue is uniform, the crystal grains reach the standard, the loss of plasticity index is small, and the specification requirement is easily met.
The cooling mode after the first step keeps warm carries out the cooling of different modes for the forging of different thickness, guarantees that the whole cooling rate of forging satisfies the performance requirement, in the cooling process, when the temperature is cooled to (alpha + beta) phase region certain temperature by the beta phase region, appear beta → alpha transition, because the grain boundary has higher energy, alpha crystal nucleus is preferred to be formed at the grain boundary department, grow along certain direction in to the crystalline grain by the grain boundary, the continuous longitudinal growth of the alpha piece of different directions, until meeting with other alpha piece, form different alpha and restraint promptly. The larger the cooling speed, the more nucleation positions are, the finer the alpha sheet layer is, the more complex the growth direction of the alpha sheet layer is, the smaller the cluster size formed by the alpha sheet layers in different directions is, and the higher the strength is. The method can ensure that forgings with different thicknesses can generate small alpha sheet layer thickness and alpha bundling size so as to obtain higher tensile strength.
And the stress relief annealing temperature in the second step is selected to be 720-740 ℃, and the stress relief annealing is carried out for the purpose of continuously decomposing metastable beta obtained in the beta annealing process in sequence, stabilizing the structure performance and eliminating stress. The stress relief annealing temperature is positioned at the middle upper part of the two-phase region, the stress relief annealing temperature is too low to completely relieve stress, the temperature is too high, and although the improvement of plasticity and fracture toughness is facilitated, the tensile strength is obviously reduced. Which can affect the alloy properties by adjusting the microstructure.
In conclusion, the invention defines the technological parameters of the beta annealing heat treatment of the Ti6Al4V alloy forging by comprehensively considering the influence of parameters such as the heat treatment temperature rise mode, the heating temperature, the heat preservation time, the cooling mode and the like on the alloy structure and the performance, can ensure that the alloy obtains a microstructure with the original beta grain size of 1.2-2.0 mm, the alpha cluster size in the beta grain of 0.3-0.8 mm and the thickness of the alpha phase of the secondary lamella of 2-4 mu m through parameter control, and obtains higher strength, plasticity and fracture toughness meeting the specification requirements, lower fatigue crack propagation rate, simple and stable process and convenient operation, and is suitable for industrial production.
Drawings
FIG. 1 is a schematic flow chart of a heat treatment method for beta annealing of a Ti6Al4V alloy forging according to an embodiment of the invention;
FIG. 2 is a schematic microstructure of a heat treated Ti6Al4V alloy forging according to an embodiment of the present invention;
FIG. 3 is a schematic microstructure of a heat treated Ti6Al4V alloy forging according to another embodiment of the present invention.
Detailed Description
Fig. 1 is a schematic flow chart of a β annealing heat treatment method for a Ti6Al4V alloy forging according to an embodiment of the present invention, and as shown in fig. 1, the β annealing heat treatment method for a Ti6Al4V alloy forging includes:
the first step is as follows: beta annealing
Heating the forged Ti6Al4V alloy to a temperature of 25-45 ℃ below the beta transformation point, preserving heat for 60-120 min, then heating to a temperature of 25-30 ℃ above the transformation point for 35-45 min, preserving heat for 40-60 min, discharging, completing transfer and dispersion of the forge piece within 2min, and performing air cooling or air blowing cooling.
The second step is that: and (5) stress relief annealing.
FIG. 2 is a schematic microstructure diagram of a heat-treated Ti6Al4V alloy forging according to an embodiment of the present invention, in this embodiment, a Ti6Al4V alloy forging with an external dimension of 768.3 × 575 × 172.5 is used, the effective thickness of the forging is 45mm, the forging microstructure is composed of a β phase and an equiaxed α phase; the volume fraction of the equiaxial alpha phase is 35 percent, the transformation point is 998 ℃, the alloy is heated to 35 ℃ (963 ℃) below the transformation point in the first step, the temperature is kept for 90min, the temperature is raised to 30 ℃ (1028 ℃) above the transformation point for 40min, the temperature is kept for 45min, the forging is cooled in a scattered mode, the forging is heated to 730 ℃, the temperature is kept for 120min, and the forging is cooled in an air cooling mode.
The room-temperature mechanical property parameters of the treated Ti6Al4V alloy forging of the embodiment are shown in the following table 1, and the microstructure is shown in FIG. 2. The left 500 μm in FIG. 2 represents a magnification of 20 times, and the right 50 μm represents a magnification of 200 times.
TABLE 1
FIG. 3 is a schematic microstructure diagram of a heat-treated Ti6Al4V alloy forging according to another embodiment of the present invention, in this embodiment, a Ti6Al4V alloy forging with overall dimensions of 437.2 × 357.8 × 140 is used, the effective thickness is 111mm, the forging microstructure is a β -phase and equiaxed α -phase composition; the volume fraction of the equiaxial alpha phase is 40 percent, the transformation point is 1003 ℃, the alloy is heated to 35 ℃ (968 ℃) below the transformation point in the first step, the temperature is preserved for 90min, then the temperature is raised to 30 ℃ (1033 ℃) above the transformation point in 40min, the temperature is preserved for 60min, due to the thick size, the forge piece is heated to 730 ℃ in the second step, the temperature is preserved for 120min, and air cooling is carried out.
The room-temperature mechanical property parameters of the treated Ti6Al4V alloy forging of the embodiment are shown in the following table 2, and the microstructure is shown in FIG. 3. The left 500 μm in FIG. 3 represents a magnification of 20 times, and the right 50 μm represents a magnification of 200 times.
TABLE 2
Claims (5)
1. The beta annealing heat treatment method for the Ti6Al4V alloy forging is characterized by comprising the following steps of:
the first step is as follows: beta annealing:
heating the Ti6Al4V alloy forging to a temperature of 25-45 ℃ below the beta transformation point, keeping the temperature for a first heat preservation time, then heating to a temperature of 25-30 ℃ above the beta transformation point, keeping the temperature for a second heat preservation time, and after discharging, starting air cooling or air blowing cooling on the Ti6Al4V alloy forging within 2 min;
the second step is that: stress relief annealing;
the first heat preservation time is within 60-120 min;
the second heat preservation time is within 40-60 min;
the stress relief annealing comprises:
heating the Ti6Al4V alloy forging cooled to room temperature by air cooling or air blowing cooling to 720-740 ℃, preserving heat for 2-5 h, and air cooling to room temperature; the room temperature is less than or equal to 40 ℃.
2. The method of claim 1, wherein the greater the effective thickness of the Ti6Al4V alloy forging, the longer the first or second soak period.
3. The method of claim 1, wherein the microstructure of the Ti6Al4V alloy forging has a volume fraction of equiaxed alpha phase of 30% to 45%.
4. The method of claim 1, wherein raising the temperature to 25 ℃ to 30 ℃ above the transformation point comprises:
the temperature is raised to be 25-30 ℃ above the phase transformation point within 35-45 min.
5. The method of claim 1, wherein the initiating air or air cooling of the Ti6Al4V alloy forging comprises:
when the effective thickness of the Ti6Al4V alloy forging is less than or equal to 50mm, air cooling is adopted;
and when the effective thickness of the Ti6Al4V alloy forging is larger than 50mm, adopting air blowing and cooling.
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| CN115807201A (en) * | 2022-12-09 | 2023-03-17 | 陕西宏远航空锻造有限责任公司 | Heat treatment method of Ti-6Al-4V alloy forging |
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| CN105154786A (en) * | 2015-10-23 | 2015-12-16 | 何鹏 | Wear-resistant vanadium-titanium gear and preparation method thereof |
| CN109207892A (en) * | 2018-11-05 | 2019-01-15 | 贵州大学 | A kind of organizational controls technique deforming biphase titanium alloy |
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| JPH04301044A (en) * | 1991-03-28 | 1992-10-23 | Sumitomo Metal Ind Ltd | High toughness titanium alloy capable of cold working |
| GB0906850D0 (en) * | 2009-04-22 | 2009-06-03 | Rolls Royce Plc | Method of manufacturing an aerofoil |
| CN104451213B (en) * | 2013-09-24 | 2017-05-17 | 宝钛集团有限公司 | Preparation method for titanium alloy with high dynamic bearing performance and low cost |
| CN107779801A (en) * | 2017-11-02 | 2018-03-09 | 中国兵器科学研究院宁波分院 | The heat treatment method of armoring titanium alloy TC 4 |
| CN107760925B (en) * | 2017-11-10 | 2018-12-18 | 西北有色金属研究院 | A kind of preparation method of high-strength modified Ti-6Al-4V titanium alloy large size bar |
| JP7119840B2 (en) * | 2018-03-23 | 2022-08-17 | 日本製鉄株式会社 | α＋β type titanium alloy extruded shape |
| CN109554649A (en) * | 2018-12-11 | 2019-04-02 | 陕西宏远航空锻造有限责任公司 | A kind of method and device of titanium alloy fatigue crack growth rate |
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| CN105154786A (en) * | 2015-10-23 | 2015-12-16 | 何鹏 | Wear-resistant vanadium-titanium gear and preparation method thereof |
| CN109207892A (en) * | 2018-11-05 | 2019-01-15 | 贵州大学 | A kind of organizational controls technique deforming biphase titanium alloy |
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