A vacuum heat treatment process for high-strength and high-toughness titanium alloy workpiece

Abstract

The present invention belongs to the field of material science and technology, and in particular, relates to a vacuum heat treatment process for a high-strength and tough titanium alloy workpiece. Compared with the prior art, the present invention performs solid solution at 30°C to 50°C below the phase transition point, at which time the primary α phase is precipitated inside the alloy, effectively increasing the strength performance, and then cools at an appropriate speed and keeps the temperature at a lower temperature, the alloy precipitates the secondary α phase, and by adjusting the heat treatment process parameters such as the cooling speed and the heating temperature to control the secondary α phase content, morphology and distribution, and size, etc., high strength is obtained while still retaining high plasticity, thereby obtaining a high-performance titanium alloy welded workpiece.

Description

Technical Field

[0001] The invention belongs to the field of material science and technology, and in particular relates to a vacuum heat treatment process for a high-strength and toughness titanium alloy workpiece. Background Art

[0002] Ti-55531 is a new type of high-strength and tough titanium alloy developed based on the optimization of TC18 titanium alloy. Its Mo equivalent is 14.3%, which is higher than the Mo equivalent of 12.51% of TC18 titanium alloy. Therefore, it has higher strength and is a typical representative of the current development of new high-strength and tough titanium alloys. This alloy is used to manufacture load-bearing components such as landing gear beams and suspension joints of Boeing, Airbus and other aircraft. At present, my country has set off a wave of research on this alloy. Many models have listed this alloy as an important material and carried out systematic research on it. Because this alloy also has good welding properties, the strength of the electron beam welding joint can reach more than 90% of the matrix, and the strength of the argon arc welding joint can reach more than 85% of the matrix.

[0003] However, there are few reports on heat treatment of Ti-55531 alloy welded parts at home and abroad. Different heat treatment schemes are given for Ti-55531 alloy according to the different performance requirements of the parts used. b ≥1240 MPa), solution aging or double annealing process is usually used. However, solution aging is mainly used for heat treatment of small-sized bars or forgings, and is not suitable for post-weld heat treatment of welded parts, which can easily cause serious deformation of parts. The double annealing process is too complicated and requires two vacuum heat treatments. At the same time, a large vacuum gas quenching heat treatment furnace must be available to achieve the required cooling rate. When the parts require Ti-55531 to have a higher fracture toughness (K IC ≥65 MPa·m 1 / 2 ) is used, at this time, the β annealing process is used to make the alloy obtain a lamellar structure of appropriate coarseness and fineness, and appropriately reduce its strength (σ b ≥1080 MPa) to make it have higher fracture toughness. However, this process requires heating above the phase transition point, which is likely to cause the coarse structure in the welding area to grow further. The structure is too coarse, reducing its strength and plasticity and other properties.

[0004] In order to achieve better weight reduction benefits, designers hope that the tensile strength of Ti-55531 titanium alloy welded parts can reach the level of forgings, that is, σ b ≥1080 MPa, δ≥6%, and it is not difficult to see that the existing heat treatment processes have shortcomings when used for post-weld heat treatment of welded parts. Summary of the invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a vacuum heat treatment process for high-strength and toughness titanium alloy workpieces. The heat treatment process is simple and has high production efficiency, and can expand the application of titanium alloys.

[0006] The present invention provides a vacuum heat treatment process for a high-strength and tough titanium alloy workpiece, comprising the following steps:

[0007] S1) The titanium alloy workpiece is heated stepwise to (T β -50)℃~(T β -30)℃ for the first insulation; β is the phase transition temperature;

[0008] S2) After the first heat preservation, cool to 650℃~680℃ and carry out the second heat preservation;

[0009] S3) After the second heat preservation, cool to below 300℃ and then air cool.

[0010] Preferably, the vacuum pressure of the vacuum condition is not greater than 6.7×10 -2 Pa.

[0011] Preferably, the step-wise heating includes a first stage heating, a second stage heating and a third stage heating; the first stage heating to 300°C-400°C; the first stage heating is followed by heat preservation for 10-40 min; the second stage heating to 600°C-700°C; the second stage heating is followed by heat preservation for 10-40 min; the third stage heating to (T β -50)℃~(T β -30)℃.

[0012] Preferably, the step-wise heating includes a first stage heating, a second stage heating and a third stage heating; the first stage heating to 350°C; the first stage heating is followed by 30 min of heat preservation; the second stage heating to 650°C; the second stage heating is followed by 30 min of heat preservation; the third stage heating to (T β -50)℃~(T β -30)℃.

[0013] Preferably, the temperature of the first insulation is (T β -50)℃~(T β -35)℃.

[0014] Preferably, the first insulation time is 1 to 2 h; the second insulation time is 1 to 4 h.

[0015] Preferably, the first insulation time is 1.5 to 2 h; the second insulation time is 2 h.

[0016] Preferably, the cooling rate in step S2) is 1.6-2.8°C / min;

[0017] The cooling in step S3) is furnace cooling.

[0018] Preferably, the titanium alloy workpiece is a Ti-55531 titanium alloy workpiece.

[0019] Preferably, the titanium alloy workpiece is a titanium alloy welded part.

[0020] The present invention provides a vacuum heat treatment process for a high-strength and tough titanium alloy workpiece, comprising the following steps: S1) heating the titanium alloy workpiece in a stepwise manner to (T β -50)℃~(T β -30)℃ for the first insulation; β is the phase transition temperature; S2) after the first heat preservation, cool to 650℃~680℃, and perform the second heat preservation; S3) after the second heat preservation, cool to below 300℃, and then air cool. Compared with the prior art, the present invention performs solid solution at 30℃~50℃ below the phase transition point, at which time the primary α phase precipitates inside the alloy, effectively increasing the strength performance, and then cools at an appropriate speed and keeps the temperature at a lower temperature, the alloy precipitates the secondary α phase, and the secondary α phase content, morphology, distribution and size are controlled by adjusting the heat treatment process parameters such as cooling speed and heating temperature, so as to obtain high strength while retaining high plasticity, thereby obtaining a high-performance titanium alloy welded workpiece.

[0021] Experimental results show that the vacuum heat treatment process provided by the present invention can stably achieve a strength of the titanium alloy workpiece of more than 1080 MPa and an elongation of more than 6%. DETAILED DESCRIPTION

[0022] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0023] The present invention provides a vacuum heat treatment process for a high-strength and tough titanium alloy workpiece, comprising the following steps: S1) heating the titanium alloy workpiece in a stepwise manner to (T β -50)℃~(T β -30)℃ for the first insulation; βis the phase change temperature; S2) after the first insulation, cool to 650℃~680℃ and carry out the second insulation; S3) after the second insulation, cool to below 300℃ and then air cool.

[0024] The present invention has no particular limitation on the sources of all raw materials, and any raw materials available on the market can be used.

[0025] In the present invention, the titanium alloy workpiece is preferably a Ti-55531 titanium alloy workpiece, that is, a Ti-5Al-5V-5Mo-3Cr-1Zr-0.4Fe titanium alloy workpiece; the titanium alloy workpiece is preferably a titanium alloy welded part, more preferably a Ti-55531 titanium alloy welded part.

[0026] The titanium alloy workpiece is heated stepwise to (T β -50)℃~(T β -30)℃ for the first insulation; the vacuum pressure of the vacuum condition is preferably not greater than 6.7×10 -2 Pa; the step-wise heating preferably includes a first stage heating, a second stage heating and a third stage heating; the first stage is preferably heated to 300°C-400°C, more preferably heated to 320°C-380°C, more preferably heated to 340°C-360°C, and most preferably heated to 350°C; after the first stage heating, it is preferably kept warm for 10-40 min, more preferably kept warm for 20-40 min, more preferably kept warm for 25-35 min, and most preferably kept warm for 30 min; the second stage is preferably heated to 600°C-700°C, more preferably heated to 620°C-680°C, more preferably heated to 640°C-660°C, and most preferably heated to 650°C; after the second stage heating, it is preferably kept warm for 10-40 min, more preferably kept warm for 20-40 min, more preferably kept warm for 25-35 min, and most preferably kept warm for 30 min; the third stage is heated to (T β -50)℃~(T β -30) ℃; the temperature of the first insulation is preferably (T β -50)℃~(T β In some embodiments provided by the present invention, the temperature of the first insulation is specifically (T β -50)℃、(T β -35)℃ or (T β The first insulation time is preferably 1 to 2 h, more preferably 1.5 to 2 h.

[0027] After the first insulation is completed, cool to 650℃~680℃ and perform a second insulation; the cooling rate is preferably 1.6~2.8℃ / min, more preferably 1.6~2.5℃ / min, and more preferably 1.8~2.5℃ / min; in some embodiments provided by the present invention, the cooling rate is specifically 1.8℃ / min, 2℃ / min or 2.5℃ / min; in some embodiments provided by the present invention, the temperature of the second insulation is specifically 680℃, 665℃ or 650℃; the time of the second insulation is preferably 1~4 h, more preferably 1~3 h, more preferably 1.5~2.5 h, and most preferably 2 h.

[0028] After the second heat preservation, the mixture is cooled to below 300°C and then air-cooled; the cooling is preferably furnace cooling.

[0029] In the present invention, the above vacuum heat treatment process is preferably carried out in a vacuum heat treatment furnace.

[0030] The present invention performs solid solution at 30°C to 50°C below the phase transformation point, at which time a primary α phase is precipitated inside the alloy, effectively increasing the strength performance. The alloy is then cooled at an appropriate speed and kept warm at a relatively low temperature, and a secondary α phase is precipitated in the alloy. The content, morphology, distribution and size of the secondary α phase are controlled by adjusting heat treatment process parameters such as cooling speed and heating temperature, so that high strength is obtained while still retaining high plasticity, thereby obtaining a high-performance titanium alloy welded workpiece.

[0031] In order to further illustrate the present invention, a vacuum heat treatment process for a high-strength and toughness titanium alloy workpiece provided by the present invention is described in detail below in conjunction with embodiments.

[0032] The reagents used in the following examples are all commercially available.

[0033] A vacuum heat treatment process for a high-strength and tough titanium alloy welded part comprises the following steps:

[0034] 1) Place the cleaned titanium alloy welded parts and the furnace samples into the vacuum heat treatment furnace. The vacuum working pressure in the vacuum chamber should not exceed 6.7×10 -2 Pa;

[0035] 2) The vacuum heat treatment furnace adopts a step-by-step heating method to heat up to T1= (T β -50)℃~(T β -30)℃, keep warm for 1h ~2h;

[0036] 3) Cool in the furnace to T2 = 650 ° C ~ 680 ° C at a cooling rate of 1.6 ~ 2.8 ° C / min, and keep warm for 1h ~ 4h;

[0037] 4) Cool the titanium alloy welded parts and the furnace samples to below 300°C and air-cool them after they are taken out of the furnace.

[0038] Example 1

[0039] According to the above heat treatment process, the heat treatment process steps and parameters for the Ti-55531 titanium alloy welded parts and welding samples in this embodiment are shown in Table 1, and the performance is shown in Table 2.

[0040] Table 1 Process steps and process parameters of Example 1 (T β =851℃)

[0041]

[0042] Table 2 Room temperature tensile properties of the furnace samples of Example 1

[0043]

[0044] Example 2

[0045] According to the above heat treatment process, the heat treatment process steps and parameters for the Ti-55531 titanium alloy welded parts and welding samples in this embodiment are shown in Table 3, and the performance is shown in Table 4.

[0046] Table 3 Process steps and process parameters of Example 2 (T β =848℃)

[0047]

[0048] Table 4 Room temperature tensile properties of the furnace samples of Example 2

[0049]

[0050] Example 3

[0051] According to the above heat treatment process, the heat treatment process steps and parameters for the Ti-55531 titanium alloy welded parts and welding samples in this embodiment are shown in Table 5, and the performance is shown in Table 6.

[0052] Table 5 Process steps and process parameters of Example 3 (T β =852℃)

[0053]

[0054] Table 6 Room temperature tensile properties of the furnace samples of Example 3

[0055]

[0056] It can be seen from the performance indicators of Examples 1, 2, and 3 that for Ti-55531 welded parts of different furnace numbers and batches, by adopting the heat treatment process of the present invention, the strength of the welded parts is maintained at a strength level of more than 1080 MPa, and the elongation is ≥6%, so that the Ti-55531 welded parts have excellent performance.

[0057] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A vacuum heat treatment process for a high-strength and tough titanium alloy workpiece, characterized in that: The following steps are involved: S1) The titanium alloy workpiece is heated stepwise to (T β -50)℃~(T β -30)℃ for the first insulation; β is the phase transition temperature; the titanium alloy workpiece is a Ti-55531 titanium alloy welded part; S2) After the first heat preservation, cool to 650℃~680℃ and carry out the second heat preservation; S3) After the second heat preservation, cool to below 300℃ and then air cool.

2. The vacuum heat treatment process according to claim 1, characterized in that: The vacuum pressure of the vacuum condition is not greater than 6.7×10 -2 Pa.

3. The vacuum heat treatment process according to claim 1, characterized in that: The step-by-step heating includes a first stage heating, a second stage heating and a third stage heating; the first stage heating to 300°C-400°C; the first stage heating is followed by a 10-40 min heat preservation; the second stage heating to 600°C-700°C; the second stage heating is followed by a 10-40 min heat preservation; the third stage heating to (T β -50)℃~(T β -30)℃.

4. The vacuum heat treatment process according to claim 1, characterized in that: The step-by-step heating includes the first stage heating, the second stage heating and the third stage heating; the first stage heating to 350°C; the first stage heating is followed by 30 minutes of heat preservation; the second stage heating to 650°C; the second stage heating is followed by 30 minutes of heat preservation; the third stage heating to (T β -50)℃~(T β -30)℃.

5. The vacuum heat treatment process according to claim 1, characterized in that: The temperature of the first insulation is (T β -50)℃~(T β -35)℃.

6. The vacuum heat treatment process according to claim 1, characterized in that: The first insulation time is 1 to 2 hours; the second insulation time is 1 to 4 hours.

7. The vacuum heat treatment process according to claim 1, characterized in that: The first insulation time is 1.5 to 2 h; the second insulation time is 2 h.

8. The vacuum heat treatment process according to claim 1, characterized in that: The cooling rate in step S2) is 1.6-2.8°C / min; The cooling in step S3) is furnace cooling.

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