Medium-strength high-impact-toughness titanium alloy and preparation method thereof

Abstract

The invention belongs to the technical field of titanium alloys, and particularly relates to a moderate-strength high-impact-toughness titanium alloy and a preparation method thereof.The moderate-strength high-impact-toughness titanium alloy is composed of, by mass, 91.39-95% of Ti, 3.7-4.2% of Al, 1.7-2.3% of V, smaller than or equal to 0.3% of Zr, smaller than or equal to 0.25% of Fe, smaller than or equal to 0.1% of C, smaller than or equal to 0.12% of Si, smaller than or equal to 0.04% of N, smaller than or equal to 0.15% of O, smaller than or equal to 0.006% of H and smaller than or equal to 0.3% of the total content of other impurities. The titanium alloy material is simple in composition and processing technology and low in production cost, the strength and impact toughness of the alloy are greatly improved while good processing plasticity is kept, good mechanical performance can still be kept under the high-temperature condition (the environment temperature is higher than 400 DEG C), and the titanium alloy material has wide application prospects in the fields of aerospace, deep sea, open sea and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of titanium alloys, and in particular relates to a medium-strength and high-impact toughness titanium alloy and a preparation method thereof. Background Art

[0002] Titanium alloy has low density, high specific strength and excellent corrosion resistance. As an important structural metal material, titanium alloy can be processed into various semi-finished products such as bars, plates, foils, wires, rods, forgings, castings, etc., and is widely used in many fields such as aerospace, shipbuilding, chemical industry, medical equipment, etc.

[0003] At present, the commonly used low-medium-strength and high-toughness titanium alloys include TA2, TA16, TA17, and TA18, and their comprehensive performance of strength, impact toughness, and high-temperature performance is not ideal. Among them, the disadvantages of TA2 are low strength and low impact toughness. The σb of annealed TA2 forging rod is 490MPa, and it is mainly used for non-load-bearing components; TA16 alloy contains 2% Al and 2.5% Zr alloy elements by mass fraction, and the use temperature can reach 350-400℃, but the room temperature strength and room temperature impact toughness are low, σb≥470MPa, and the room temperature impact toughness is 100KJ / m2; when the Al mass fraction in TA16 alloy is increased to 3%, and the vanadium mass fraction is 2%, the TA18 alloy is obtained. The mechanical properties of TA18 are greatly improved compared with TA16, and its σ b≥620MPa, and the impact toughness of TA18 is ≥500KJ / m2, but the use temperature of TA18 is below 315℃. When the use temperature is 300℃, its σb is 503MPa. If TA18 is to reach high strength, it needs to be hardened. The processing technology is complicated and the cost is high. The internal stress generated by hardening will affect the performance. The mass fraction of aluminum in TA17 is 4%, and the mass fraction of vanadium is 2%. The room temperature mechanical properties are slightly different from those of TA18, and the impact toughness is higher than that of TA18. Its impact toughness is ≥690KJ / m2, and the use temperature is about 300℃ like TA18. It can be seen that increasing the aluminum and vanadium content of titanium alloy can improve the impact toughness of the alloy, but if the aluminum and vanadium content are increased blindly, good impact performance cannot be obtained. For example, the aluminum content of TC4 alloy is increased to 6% and the vanadium content is increased to 4%. Its strength is greatly improved, but the impact toughness is reduced to 400KJ / m2.

[0004] With the development of the industry and the continuous exploration of mankind in the fields of aerospace, deep sea and offshore, higher requirements are placed on the research and development of equipment in the above fields. The maximum operating temperature of the medium and high strength titanium alloys currently used is relatively low, and it is difficult to maintain good mechanical properties in a high temperature environment of 400°C, and it cannot meet the requirements for material performance in complex environments. Summary of the invention

[0005] At least in view of the technical problems mentioned in the background technology, the purpose of the present invention is to provide a medium-strength and high-impact toughness titanium alloy and a preparation method thereof.

[0006] The present invention adopts the following technical solutions:

[0007] A medium-strength and high-impact toughness titanium alloy, which is composed of the following components according to the mass percentage of alloy element components: Ti: 91.39-95%, Al: 3.7-4.2%, V: 1.7-2.3%, Zr: ≤0.3%, Fe≤0.25%, C≤0.1%, Si≤0.12%, N≤0.04%, O≤0.15%, H≤0.006%, and the total content of other impurities is ≤0.3%.

[0008] Technical principle of the present invention:

[0009] Aluminum, as an α-stabilizing element, plays a role in solid solution strengthening, improving the strength and heat resistance of the alloy. Since excessive aluminum content can easily cause the toughness of the material to deteriorate, the mass fraction of aluminum is controlled at 3.7-4.2%; vanadium is a β-stabilizing element and is one of the few alloying elements in titanium alloys that can both improve strength and improve plasticity. Vanadium can reduce the ratio of the c / a axis of the α-titanium lattice, thereby improving the plastic deformation ability of the α phase. In addition, vanadium can also inhibit the formation of the α2 superstructure phase and avoid alloy embrittlement during long-term use. Since the solubility of vanadium in the α phase is up to 2%, the mass fraction of vanadium is controlled at 1.7-2.3%; Zirconium has similar properties to titanium. As a neutral element, it can be infinitely dissolved in titanium and play a role in solid solution strengthening, especially strengthening high-temperature performance. A small amount of zirconium can also refine the crystal structure. It can purify grains and grain boundaries, form compounds with impurity elements, reduce the content of impurity elements near the grain boundaries, and improve the impact toughness of the alloy. The contribution of zirconium to impact toughness is greater than that of aluminum, but too high zirconium content will increase the density of the alloy and will not have much effect on improving the performance of the alloy. Therefore, it is best to control the mass fraction of zirconium to no more than 0.3% for the best overall effect. A small amount of impurity elements such as oxygen, nitrogen, carbon, iron, and silicon can increase the strength of titanium alloys, but will cause a large loss of plasticity, and have many adverse effects on some other important properties of titanium alloys, such as thermal stability, creep resistance, and notch sensitivity. Impurity elements near the grain boundaries can easily reduce the impact toughness of the alloy, so their content needs to be strictly controlled. Hydrogen will form a hydride phase with titanium, and as a harmful element, it must also be strictly limited.

[0010] In the present invention, Al: 4.1±0.02%, V: 2±0.05%, Zr: 0.25±0.05%, Fe: 0.2±0.02%, C: 0.06±0.02%, Si: 0.1±0.01%, N: 0.02±0.01%, O: 0.13±0.01%, and H: 0.002±0.001%.

[0011] In the present invention, a method for preparing a rod of the above-mentioned medium-strength and high-impact toughness titanium alloy comprises the following steps:

[0012] Step 1, subjecting the raw materials of the components to electrode pressing, and smelting in a vacuum consumable arc furnace to obtain a titanium alloy ingot;

[0013] Step 2, subjecting the obtained titanium alloy ingot to upsetting and free forging at 100-150° C. above the phase transition temperature to obtain a billet 1;

[0014] Step 3, forging and upsetting the obtained blank 1 at 30-50° C. below the phase transition temperature to obtain blank 2;

[0015] Step 4, forging the obtained billet 2 below the phase transition temperature to obtain a titanium alloy bar not larger than φ200 mm;

[0016] Step 5, annealing the obtained titanium alloy rod to obtain a near-α-type titanium alloy rod with high impact toughness.

[0017] In the present invention, the step 4 comprises subjecting the obtained billet 2 to upsetting and forging at 30-50° C. below the phase transition temperature to obtain a titanium alloy bar of φ200 mm.

[0018] In the present invention, the step 4 further comprises precision forging the obtained φ200 mm titanium alloy rod at 30-50° C. below the phase transition temperature to obtain a φ100 mm titanium alloy rod.

[0019] In the present invention, step 4 also includes cold forging the obtained φ100 mm titanium alloy rod to obtain a φ60 mm titanium alloy rod.

[0020] Beneficial effects of the present invention: The titanium alloy material provided by the present invention has simple composition and processing technology, low production cost, and greatly improves the strength and impact toughness of the alloy while maintaining good processing plasticity. It can still maintain good mechanical properties under high temperature conditions (ambient temperature greater than 400°C), and has excellent processing and welding properties. It can be applied to various welding methods. The strength and elongation of the fusion welded joint are roughly close to those of the base metal, and it has a wide range of application scenarios. DETAILED DESCRIPTION

[0021] The following is further described in detail through specific implementation methods:

[0022] Example 1

[0023] The medium strength and high impact toughness titanium alloy of this embodiment is composed of the following components according to the mass percentage of alloy element components: Al: 4.1±0.02%, V: 2±0.05%, Zr: 0.25±0.05%, Fe: 0.2±0.02%, C: 0.06±0.02%, Si: 0.1±0.01%, N: 0.02±0.01%, O: 0.13±0.01%, H: 0.002±0.001%, and the remainder is Ti and unavoidable impurities.

[0024] The method for preparing a rod of a medium-strength and high-impact toughness titanium alloy of this embodiment comprises the following steps:

[0025] Step 1, using 0-grade small-particle titanium sponge and master alloy to prepare materials according to the designed composition and mix them evenly, and then pressing them into electrodes through a pressing machine, and then melting the obtained electrodes through a vacuum consumable arc furnace three times, peeling and removing the riser to obtain a φ600mm titanium alloy ingot, and applying a high-temperature anti-oxidation coating on the surface of the titanium alloy ingot;

[0026] The composition of the obtained titanium alloy ingot is shown in Table 1:

[0027]

[0028] Table 1 Composition and proportion of titanium alloy ingot (by mass percentage)

[0029] Step 2, subjecting the obtained titanium alloy ingot to upsetting and free forging at 100-150° C. above the phase transition temperature to obtain a billet 1 of φ350 mm;

[0030] First fire: heating at 1100℃ for 7-8h

[0031] φ600×L→2 upsetting and 2 drawing→drawing to φ350×L, each upsetting ratio is 1.7, drawing ratio is 1.7, air cooling after forging, final forging temperature ≥850℃, grinding to eliminate surface defects, sawing and dividing, and switching to the second fire forging;

[0032] Step 3, forging and upsetting the obtained billet 1 at 30-50° C. below the phase transition temperature to obtain a billet 2 of φ360 mm;

[0033] Second fire: 930℃×4.5~5h

[0034] φ350×L→3 upsetting 3 drawing→ chamfering and rounding φ360×L, upsetting ratio of 1.7 each time, drawing ratio of 1.7, air cooling after forging, final forging temperature ≥700℃, grinding to eliminate surface defects, sawing and dividing, and switching to the third fire forging;

[0035] Step 4, forging the obtained billet 2 below the phase transition temperature to obtain a titanium alloy bar with a diameter of 200 mm;

[0036] Step 41, third fire: 930℃×2.5~3h

[0037] Φ360×L→2 upsetting 2 drawing→ chamfering and rounding φ200×L, upsetting ratio 1.8 each time, drawing ratio 1.8, air cooling after forging, final forging temperature ≥700℃;

[0038] Step 5, annealing the obtained φ200 mm titanium alloy rod at a temperature of 750° C. for 2 h to obtain a near-α-type titanium alloy rod with high impact toughness.

[0039] Example 2

[0040] The difference between this embodiment and embodiment 1 is that:

[0041] Step 4, forging the obtained billet 2 below the phase transition temperature to obtain a titanium alloy bar with a diameter of 200 mm;

[0042] Step 41, third fire: 930℃×2.5~3h

[0043] Φ360×L→2 upsetting 2 drawing→chamfering and rounding Each time the upsetting ratio is 1.8, the drawing ratio is 1.8, air cooling after forging, the final forging temperature is ≥700℃, sawing and dividing, grinding to eliminate surface defects, and then switching to the fourth fire forging;

[0044] Step 42, fourth fire: 920℃×2.5~3h

[0045] Φ200×L→Precision forging to Air cooling, forging ratio 4;

[0046] Step 5, annealing the obtained φ100 mm titanium alloy rod at a temperature of 750° C. for 2 h to obtain a near-α-type titanium alloy rod with high impact toughness.

[0047] Example 3

[0048] The difference between this embodiment and embodiment 1 is that:

[0049] Step 4, forging the obtained billet 2 below the phase transition temperature to obtain a titanium alloy bar with a diameter of 200 mm;

[0050] Step 41, third fire: 930℃×2.5~3h

[0051] Φ360×L→2 upsetting 2 drawing→chamfering and rounding Each time the upsetting ratio is 1.8, the drawing ratio is 1.8, air cooling after forging, the final forging temperature is ≥700℃, and after grinding to eliminate surface defects, it is turned to the fourth fire forging;

[0052] Step 42, fourth fire: 920℃×2.5~3h

[0053] Φ200×L→Precision forging to Air cooling, forging ratio 4, sawing and cutting, transfer to the next process;

[0054] Step 43, Φ100×L→cold forging to Forging ratio 2.78;

[0055] Step 5, annealing the obtained φ60 mm titanium alloy rod at a temperature of 750° C. for 2 h to obtain a near-α-type titanium alloy rod with high impact toughness.

[0056] The medium-strength and high-impact-toughness titanium alloy bars prepared in each embodiment were sampled and tested for room temperature mechanical properties. The test results are shown in Table 2 below:

[0057] Example Sample No. Rm / MPa Rp0.2 / MPa A / ％ Z / ％ aKU / (KJ / m2) Φ200 1# 685 612 20.5 34 921 2# 692 621 18 32 909 Φ100 1# 735 652 16 30 886 2# 726 648 15.5 30 894 Φ60 1# 802 684 13 28 725 2# 796 678 13.5 29 736

[0058] Table 2 Room temperature mechanical properties of samples after annealing at 750℃ / 2h

[0059] The φ60 mm medium strength and high impact toughness titanium alloy bar obtained in Example 3 was tested for high and low temperature mechanical properties. The test results are shown in Table 3 below:

[0060] Detection temperature / ℃ Rm / MPa Rp0.2 / MPa A / ％ 100 705 623 18 200 593 492 21 300 556 472 20 400 515 426 24 500 436 322 32

[0061] Table 3 High and low temperature mechanical properties test data of φ60 bar

[0062] From the background technology, embodiments and the results of the above-mentioned performance tests, it can be seen that the medium-strength and high impact toughness titanium alloy of the present invention has a strength much higher than TA2, and its room temperature strength and room temperature impact toughness are higher than TA16, and its room temperature impact toughness is higher than TA18. In addition, its operating temperature is higher than TA18 and TA17, and it can still maintain good strength (greater than 500MPa) in a high temperature environment above 400°C.

[0063] In summary, this medium-strength and high impact toughness titanium alloy effectively improves the alloy plasticity and impact toughness by adding 0.2-0.3% zirconium by mass. Whether at room temperature or at high temperature, this titanium alloy can maintain good mechanical properties and has excellent comprehensive mechanical properties. It has broad application prospects in aerospace, deep sea and other fields.

[0064] The medium-strength high-impact titanium alloy provided by the present invention has simple composition and processing technology. Compared with TA18, it can achieve high-strength performance without work hardening, reduces the processing steps, effectively saves processing costs, avoids internal stress caused by work hardening, and has excellent performance.

[0065] The above is only an embodiment of the present invention, and the common knowledge such as the known specific technical solutions and / or characteristics in the solution is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several modifications and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A medium-strength and high-impact toughness titanium alloy, characterized in that: According to the mass percentage of alloying elements, it is composed of the following components, Ti: 91.39-95%, Al: 3.7-4.2%, V: 1.7-2.3%, Zr: ≤0.3%, Fe≤0.25%, C≤0.1%, Si≤0.12%, N≤0.04%, O≤0.15%, H≤0.006%, the total content of other impurities ≤0.3%.

2. The medium-strength and high-impact-toughness titanium alloy according to claim 1, characterized in that: Al: 4.1±0.02%, V: 2±0.05%, Zr: 0.25±0.05%, Fe: 0.2±0.02%, C: 0.06±0.02%, Si: 0.1±0.01%, N: 0.02±0.01%, O: 0.13±0.01%, H: 0.002±0.001%.

3. A method for preparing a rod of a medium-strength and high-impact-toughness titanium alloy as claimed in claim 1 or 2, characterized in that: The following steps are involved: Step 1, subjecting the raw materials of the components to electrode pressing, and smelting in a vacuum consumable arc furnace to obtain a titanium alloy ingot; Step 2, subjecting the obtained titanium alloy ingot to upsetting and free forging at 100-150° C. above the phase transition temperature to obtain a billet 1; Step 3, forging and upsetting the obtained blank 1 at 30-50° C. below the phase transition temperature to obtain blank 2; Step 4, forging the obtained billet 2 below the phase transition temperature to obtain a titanium alloy bar not larger than φ200 mm; Step 5, annealing the obtained titanium alloy rod to obtain a near-α-type titanium alloy rod with high impact toughness.

4. The method for preparing a rod of a medium-strength and high-impact-toughness titanium alloy according to claim 3, characterized in that: The step 4 comprises subjecting the obtained billet 2 to upsetting and forging at 30-50° C. below the phase transition temperature to obtain a titanium alloy bar of φ200 mm.

5. The method for preparing a rod of a medium-strength and high-impact-toughness titanium alloy according to claim 4, characterized in that: The step 4 also includes precision forging the obtained φ200 mm titanium alloy rod at 30-50° C. below the phase transition temperature to obtain a φ100 mm titanium alloy rod.

6. The method for preparing a rod of a medium-strength and high-impact-toughness titanium alloy according to claim 5, characterized in that: Step 4 also includes cold forging the obtained φ100 mm titanium alloy rod to obtain a φ60 mm titanium alloy rod.

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