Process for improving impact toughness of Ti80 titanium alloy

Abstract

The invention discloses a process for improving impact toughness of Ti80 titanium alloy, and belongs to the technical field of metal heat treatment. The method comprises the steps that S1, a Ti80 titanium alloy cast ingot is subjected to upsetting and drawing, and a blank is obtained; s2, the blank obtained in the step S1 is subjected to two-heating-number rolling, and a rolled sample is obtained; s3, performing first heat treatment on the rolled sample obtained in the step S2 to obtain a heat-treated sample; and S4, carrying out secondary heat treatment on the heat treatment sample obtained in the step S3. According to the method, the Ti80 titanium alloy with the tri-state structure is prepared, the alloy toughness is greatly improved under the condition that the alloy strength is guaranteed, the Ti80 titanium alloy has more excellent impact load bearing capacity, and the application scene range of the Ti80 titanium alloy is expanded.

Description

Technical Field

[0001] The invention belongs to the technical field of metal heat treatment, and in particular relates to a process for improving the impact toughness of Ti80 titanium alloy. Background Art

[0002] Ti80 titanium alloy is a new 800MPa near-α titanium alloy developed by my country for the ship field. Its nominal composition is Ti-6Al-3Nb-2Zr-1Mo. It has the comprehensive properties of high strength, weldability and good corrosion resistance. It has been used in my country's manned submersible pressure hulls, high-pressure vessels, ship welding structures, and load-bearing components of underwater weapons. Since Ti80 titanium alloy is very susceptible to impacts such as collisions and explosions during service, it needs to withstand huge impact loads during use. However, the impact toughness of Ti80 titanium alloy is generally low at present, and it is easy to be damaged when subjected to large impact loads, which leads to the loss of function of Ti80 titanium alloy and affects the normal use of products. Therefore, it is of great significance to improve the impact toughness of Ti80 titanium alloy.

[0003] The mechanical properties of titanium alloys mainly depend on their microstructures. The size and volume fraction of each component phase have an important influence on the mechanical properties. Titanium alloys can form five types of structures during heat treatment, including equiaxed structure, dual structure, tri-structure, basket structure and Widmanstatten structure. Among them, the tri-structure consists of the primary α phase (α p ), the layered α phase (α l ) and β-transformation organization (β t ) and has the performance advantages of dual-state organization and Widmanstatten organization. It can meet higher usage requirements and is often used as the target organization for structural parts.

[0004] At present, the improvement of the impact toughness of Ti80 titanium alloy is usually achieved by regulating the dual-state structure or equiaxed structure, and the effect of improving the impact toughness is relatively limited. For example, the patent with application number 202111060371.5 discloses a method for preparing a high impact toughness Ti80 titanium alloy bar, which comprehensively regulates the phase ratio and phase morphology in the Ti80 titanium alloy bar to make the α phase morphology and β grain size more uniform, thereby improving the impact toughness of the Ti80 titanium alloy. The impact toughness of the titanium alloy prepared by the method is as high as 94.6 J / cm 2 .

[0005] Therefore, it is necessary to provide a process for improving the impact toughness of Ti80 titanium alloy, so that the impact toughness of Ti80 titanium alloy can be further improved, so as to further improve the tolerance of Ti80 titanium alloy to impact load and reduce the probability of Ti80 titanium alloy being damaged by large impact load. Summary of the invention

[0006] In order to overcome the problems in the background technology, the present invention prepares a Ti80 titanium alloy with a tri-state structure, and greatly improves the impact toughness of the titanium alloy while ensuring the strength of the titanium alloy. The tensile strength of the Ti80 titanium alloy prepared by the present invention can reach 1137.45MPa, the yield strength can reach 1050.42MPa, and the impact toughness can reach 122.03J / cm 2 .

[0007] In order to achieve the above object, the present invention is implemented by the following technical solutions:

[0008] The process comprises the following steps:

[0009] S1: upsetting the Ti80 titanium alloy ingot to obtain a billet;

[0010] S2: performing two-time rolling on the billet obtained in step S1 to obtain a rolled sample;

[0011] S3: performing a first heat treatment on the rolled sample obtained in step S2 to obtain a heat-treated sample;

[0012] S4: performing a second heat treatment on the heat-treated sample obtained in step S3 to obtain a Ti80 titanium alloy with high impact toughness.

[0013] Preferably, in step S1, the specific process of upsetting the Ti80 titanium alloy ingot is: first, the titanium alloy ingot is upset and drawn twice in the single-phase region above the phase transformation point, and the temperature range is 1050-1150°C, and then the titanium alloy ingot is upset in the dual-phase region below the phase transformation point, and finally the Ti80 titanium alloy ingot is shaped and milled to obtain a billet.

[0014] Preferably, in step S2, the two-pass rolling is performed at a temperature of 30-80°C below the alloy phase transition point, and the rolling deformation is not greater than 60%. The alloy phase transition point can be measured by conventional synchronous thermal analyzer, continuous heating metallographic method, organization analysis calculation method, etc.

[0015] Preferably, in step S3, the first heat treatment is performed at a heating temperature of 960-980° C., with a holding time of 0.5-1 h, and a cooling method of water cooling.

[0016] Preferably, in step S4, the second heat treatment heating temperature is 945-965° C., the holding time is 1-1.5 h, and the cooling method is air cooling.

[0017] Preferably, the Ti80 titanium alloy ingot comprises, by mass percentage, the following components: Al: 5.5-6.5%, Nb: 2.5-3.5%, Zr: 1.5-2.5%, Mo: 0.6-1.5%, Fe: ≤0.25%, Si: ≤0.15%, C: ≤0.10%, N: ≤0.05%, H: ≤0.015%, O: ≤0.15%, and the balance is Ti.

[0018] Preferably, the Ti80 titanium alloy ingot is obtained by melting a single metal three times under vacuum conditions.

[0019] Beneficial effects of the present invention:

[0020] 1. In the preparation process of the present invention, the volume fractions of the primary α phase and the secondary α phase are adjusted to finally obtain a Ti80 titanium alloy with a tri-state structure, which greatly improves the toughness of the alloy while ensuring the strength of the Ti alloy.

[0021] 2. The tensile strength of the Ti80 titanium alloy prepared by the present invention can reach 1137.45MPa, the yield strength can reach 1050.42MPa, and the impact toughness can reach 122.03J / cm 2 , with high strength and impact toughness.

[0022] 3. The process of the present invention is simple and feasible, easy to operate, and the product has excellent performance and uniform structure, and is suitable for industrial promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the microstructure diagram of the Ti80 titanium alloy plate sample prepared in Example 1.

[0024] Figure 2 This is the microstructure diagram of the Ti80 titanium alloy plate sample prepared in Comparative Example 1.

[0025] Figure 3 This is the microstructure diagram of the Ti80 titanium alloy plate sample prepared in Example 2.

[0026] Figure 4 This is the microstructure diagram of the Ti80 titanium alloy plate sample prepared in Example 3. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below in conjunction with specific embodiments.

[0028] All chemical reagents not specified in the examples and comparative examples of the present invention were commercially available analytically pure for experiments.

[0029] Example 1

[0030] In this embodiment, the composition of the Ti80 titanium alloy ingot is: Al: 6.2%, Nb: 2.8%, Zr: 2.1%, Mo: 1.2%, Fe: 0.03%, Si: 0.07%, C: 0.01%, N: <0.01%, H: 0.001%, O: 0.07%, and the balance is Ti.

[0031] In this embodiment, the single metal is weighed according to the above composition, and the single metal is placed in a vacuum consumable arc furnace for smelting three times to obtain a Ti80 titanium alloy ingot, and the diameter of the Ti80 titanium alloy ingot is 1020 mm.

[0032] In this embodiment, the Ti80 titanium alloy ingot is processed according to the following steps:

[0033] S1: First, the titanium alloy ingot is upset and drawn twice in the single-phase region above the phase transformation point at a temperature range of 1050-1150°C, and then the titanium alloy ingot is upset and drawn in the dual-phase region below the phase transformation point. Finally, the Ti80 titanium alloy ingot is shaped and milled to obtain a slab.

[0034] S2: In this embodiment, the alloy phase transformation point is 995°C. Under the temperature condition of 30-80°C below the alloy phase transformation point, the slab is subjected to two-pass rolling to control the rolling deformation amount to be no more than 60%, thereby obtaining a rolled plate.

[0035] S3: placing the rolled plate in a resistance furnace at 960°C for 0.5h, and water cooling after being taken out of the furnace;

[0036] S4: The Ti80 titanium alloy plate after water cooling in S3 is placed in a resistance furnace at a temperature of 945° C. and kept warm for 1 hour. After being taken out of the furnace, the plate is air-cooled to obtain a Ti80 titanium alloy plate.

[0037] The microstructure of the Ti80 titanium alloy sheet is shown in the figure below: Figure 1 As shown, through Figure 1 It can be seen that the Ti80 titanium alloy prepared in this embodiment contains a three-state structure consisting of 43% primary α phase, 31% lamellar secondary α phase and β transformation structure.

[0038] The Ti80 titanium alloy sheet was processed into a standard V-notch impact specimen and a standard tensile specimen, and the specimens were subjected to impact and tensile tests to measure the tensile strength, yield strength and impact toughness of the specimens. During the tensile test, the tensile rate was 1 mm / min. The results are shown in Table 1.

[0039] Comparative Example 1

[0040] This comparative example and Example 1 use the same Ti80 titanium alloy ingot for the experiment, the difference is that: this comparative example performs a heat treatment on the rolled plate, this comparative example is kept in a resistance furnace at a temperature of 960°C for 1 hour, and water-cooled after being taken out of the furnace.

[0041] The microstructure of the Ti80 titanium alloy sheet is shown in the figure below: Figure 2 As shown, through Figure 2 It can be seen that the Ti80 titanium alloy prepared in this embodiment has an equiaxed structure composed of a primary α phase and a β transformation structure.

[0042] The Ti80 titanium alloy sheet was processed into a standard V-notch impact specimen and a standard tensile specimen, and the specimens were subjected to impact and tensile tests to measure the tensile strength, yield strength and impact toughness of the specimens. During the tensile test, the tensile rate was 1 mm / min. The results are shown in Table 1.

[0043] Example 2

[0044] This embodiment and embodiment 1 use the same Ti80 titanium alloy ingot for experimentation and have the same treatment process, except that: in this embodiment, the first heat treatment temperature is 970°C and kept warm for 1 hour, and the second heat treatment temperature is 955°C and kept warm for 1.3 hours.

[0045] The microstructure of the Ti80 titanium alloy sheet is shown in the figure below: Figure 3 As shown, through Figure 3 It can be seen that the Ti80 titanium alloy prepared in this example contains a three-state structure consisting of 38% primary α phase, 34% lamellar secondary α phase and β transformation structure.

[0046] The Ti80 titanium alloy sheet was processed into a standard V-notch impact specimen and a standard tensile specimen, and the specimens were subjected to impact and tensile tests to measure the tensile strength, yield strength and impact toughness of the specimens. During the tensile test, the tensile rate was 1 mm / min. The results are shown in Table 1.

[0047] Example 3

[0048] This embodiment and embodiment 1 use the same Ti80 titanium alloy ingot for experimentation and have the same treatment process, except that: the first heat treatment temperature in this embodiment is 980°C, and the temperature is kept for 0.7h, and the second heat treatment temperature is 965°C, and the temperature is kept for 1.5h.

[0049] The microstructure of the Ti80 titanium alloy sheet is shown in the figure below: Figure 4 As shown, through Figure 4 It can be seen that the Ti80 titanium alloy prepared in this embodiment contains a three-state structure consisting of 23% primary α phase, 47% lamellar secondary α phase and β transformation structure.

[0050] The Ti80 titanium alloy sheet was processed into a standard V-notch impact specimen and a standard tensile specimen, and the specimens were subjected to impact and tensile tests to measure the tensile strength, yield strength and impact toughness of the specimens. During the tensile test, the tensile rate was 1 mm / min. The results are shown in Table 1.

[0051] Table 1

[0052]

[0053] It can be seen from Table 1 that the tensile strength, yield strength and impact toughness of the Ti80 titanium alloy (Examples 1-3) prepared by the method of the present invention are improved relative to those of Comparative Example 1, among which the performance improvement effect of the Ti80 titanium alloy of Example 1 is the most significant. At the same time, the impact toughness in Example 1 is improved by more than 110% relative to that of Comparative Example 1.

[0054] In summary, the Ti80 titanium alloy prepared by the present invention contains three structures, namely, primary α phase (α p ), the layered α phase (α l ) and β-transformation organization (β t ), the Ti80 titanium alloy prepared by the present invention can significantly improve the impact toughness of the alloy while ensuring the strength of the Ti80 titanium alloy, so that the Ti80 titanium alloy has a higher ability to withstand impact loads during use, thereby expanding its scope of application.

[0055] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A process for improving the impact toughness of Ti80 titanium alloy, characterized in that: The process comprises the following steps: S1: upsetting the Ti80 titanium alloy ingot to obtain a billet; S2: performing two-time rolling on the billet obtained in step S1 to obtain a rolled sample; S3: performing a first heat treatment on the rolled sample obtained in step S2 to obtain a heat-treated sample; S4: performing a second heat treatment on the heat-treated sample obtained in step S3 to obtain a Ti80 titanium alloy with high impact toughness.

2. The process according to claim 1, characterized in that: In the step S1, the specific process of upsetting the Ti80 titanium alloy ingot is: first, the titanium alloy ingot is upset and drawn twice in the single-phase region above the phase transformation point, and the temperature range is 1050-1150°C, and then the titanium alloy ingot is upset in the dual-phase region below the phase transformation point, and finally the Ti80 titanium alloy ingot is shaped and milled to obtain a blank.

3. The process according to claim 1, characterized in that: In the step S2, the two-pass rolling is performed at a temperature of 30 to 80° C. below the alloy phase transformation point, and the rolling deformation is not greater than 60%.

4. The process according to claim 1, characterized in that: In step S3, the first heat treatment is performed at a heating temperature of 960-980° C., a heat preservation time of 0.5-1 h, and a cooling method of water cooling.

5. The process according to claim 1, characterized in that: In step S4, the second heat treatment is performed at a heating temperature of 945-965° C., a heat preservation time of 1-1.5 h, and an air cooling method.

6. The process according to any one of claims 1 to 5, characterized in that: The Ti80 titanium alloy ingot comprises, by mass percentage, Al: 5.5-6.5%, Nb: 2.5-3.5%, Zr: 1.5-2.5%, Mo: 0.6-1.5%, Fe: ≤0.25%, Si: ≤0.15%, C: ≤0.10%, N: ≤0.05%, H: ≤0.015%, O: ≤0.15%, and the balance is Ti.

7. The process according to claim 6, characterized in that: The Ti80 titanium alloy ingot is prepared by melting a single metal three times under vacuum conditions.

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