CN110592425A - A kind of high impact toughness titanium alloy and the method for using titanium alloy to prepare seamless pipe - Google Patents

Abstract

The invention discloses a titanium alloy with high impact toughness, the chemical composition requirements of which are Al 4.0-9.0%, Mo 0.5-5.0%, Zr 1-5%, Nb 1-5%, Fe 0.2-2.0%, and the balance is Ti and impurities. The method of using this high impact toughness titanium alloy to prepare seamless pipes is as follows: weigh aluminum-niobium master alloy, molybdenum block, pure sponge zirconium, iron nails, and sponge titanium according to the chemical composition requirements and mix them, press them into electrode rods, and then put Put it into a vacuum consumable electric arc furnace for secondary melting to obtain titanium alloy ingots; open the titanium alloy ingots for forging at 1150 ° C, and re-forge at 970 ~ 1020 ° C to obtain billets; then heat the billets to 950 ~ 1200°C; cross-rolling and piercing the billet to obtain a tube billet; hot-rolling the billet by using the waste heat after cross-rolling and piercing, and then performing fixed diameter reduction to obtain a pipe; heat treatment, straightening, sawing, inspection, and storage of the pipe . The seamless pipe prepared by using the titanium alloy in the present invention has high strength, high plasticity, high low-temperature impact toughness and good corrosion resistance, and meets the application requirements of harsh working conditions of oil and gas wells.

Description

A kind of high impact toughness titanium alloy and the method for using titanium alloy to prepare seamless pipe

technical field

The invention relates to the field of manufacturing aluminum alloy materials and seamless pipes, in particular to a titanium alloy with high impact toughness and a method for preparing seamless pipes using the titanium alloy.

Background technique

Titanium and titanium alloys have low density, high specific strength, excellent corrosion resistance, good mechanical properties at medium and high temperatures, excellent fatigue and creep resistance, and have great application potential in the petrochemical industry. Titanium alloy pipes are widely used in the petrochemical industry due to their good corrosion resistance, especially resistance to seawater corrosion and biological corrosion. SY/T6896.3-2016 "Technical Specifications for Special Pipes in the Petroleum and Natural Gas Industry Part 3: Titanium Alloy Oil Pipes" requires the manufacturing process of titanium alloy oil pipes as follows: Titanium alloy oil pipes should be made of seamless titanium alloy pipes. The low-cost preparation technology of titanium alloy seamless pipes for petrochemical industry has always been a research hotspot all over the world.

The oil well pipe is subjected to various functions such as pulling, twisting, etc. in the downhole, and the internal pressure is tens of MPa, and the stress situation is complicated. Generally, the impact energy of P110 steel tubing reaches about 200J, while the impact energy of P110 steel grade titanium alloy is often 30-50J. In this case, oilfield users believe that titanium alloy has better corrosion resistance, but the impact toughness needs to be improved To improve the safety and reliability of the string. Domestic research units have improved commonly used titanium alloys such as TC4, but the impact toughness has not been improved. At present, the domestic titanium alloy tubing development method is basically based on the use of existing titanium alloys for performance assessment, and rarely develops new materials. Therefore, the application of titanium alloy tubing in China is slow, and due to the high deformation resistance of titanium alloy at room temperature, the processing of titanium alloy seamless pipes with a certain length and wall thickness and excellent mechanical properties is difficult.

Therefore, it is necessary to find a titanium alloy with high impact toughness and to explore the method of using this titanium alloy to prepare seamless pipes to meet the requirements of the petrochemical industry.

Contents of the invention

In order to solve the deficiencies in the prior art, the invention provides a titanium alloy with high impact toughness and a method for preparing a seamless pipe by using the titanium alloy.

In order to achieve the above object, the specific scheme adopted by the present invention is:

A titanium alloy with high impact toughness, its chemical composition is required to be Al4.0-9.0%, Mo0.5-5.0%, Zr 1-5%, Nb1-5%, Fe 0.2-2.0%, and the balance is Ti and not Impurities to avoid: the impurity content satisfies N≤0.05%, C≤0.1%, H≤0.015%, O≤0.15%.

A method for preparing a seamless pipe from a high-impact toughness titanium alloy mainly includes the following steps:

Step 1. Ingot preparation: Weigh aluminum-niobium master alloy, molybdenum block, pure sponge zirconium, iron nails, and sponge titanium according to the chemical composition requirements and mix them, press them into electrode rods, and then put them into a vacuum consumable electric arc furnace Perform secondary smelting to obtain titanium alloy ingots;

Step 2, billet preparation: the titanium alloy ingot obtained in step 1 is forged at 1150°C, and re-forged at 970-1020°C to obtain a billet;

Step 3. Cross-rolling and piercing: heat the billet obtained in step 2 to 950-1200°C in a heating furnace, and then keep it warm for the billet diameter × (0.5-1.1) min/mm; use molybdenum-based alloy Or high-alloy plug, the head is coated with lubricant, the lubricant is placed in the center hole of the heated billet, and the tube blank is made after piercing;

Step 4, hot rolling and fixed diameter reduction: hot rolling the tube blank obtained in step three, spraying borax inside the tube blank before hot rolling, controlling the deformation at 50-70%, and then performing fixed diameter reduction to obtain a pipe;

Step 5, heat treatment: place the pipe obtained in step 4 in a heat treatment furnace for heat treatment, and the heat treatment temperature is 800-980°C;

Step 6. Post-processing: Straighten, saw, inspect, and store the heat-treated pipes.

Preferably, the requirement for the tube blank prepared in step three is outer diameter/wall thickness=9-12.

Preferably, in step 3, in the billet heating process, the micro-oxidation atmosphere is kept in the heating furnace, the micro-oxidation atmosphere is a mixed atmosphere of air and natural gas, and the micro-oxidation atmosphere is realized by adjusting the ratio of air and natural gas (the ratio of air to natural gas can be Adjust as needed). Keeping the micro-oxidizing atmosphere in the furnace is beneficial to reduce the possibility of titanium alloy absorbing hydrogen.

Preferably, in step 4, the outer diameter reduction ratio in the diameter reduction process is 20-30%, and the wall thickness increase = wall thickness after hot rolling × (10%-15%).

Preferably, in step six, the pipe is heated to 600-700° C. for straightening treatment, and the straightened pipe bend is less than 1.5‰ of the full length of the pipe. The pipe prepared by this method has high strength, and the pipe needs to be heated to 600-700°C to be straightened.

Wherein, in the step 3, the lubricant used for cross-rolling perforation is glass powder lubricant.

Wherein, the hot rolling in the fourth step is carried out by using the waste heat after cross rolling and piercing, which can save resources on the basis of realizing hot rolling. Before hot rolling, borax is sprayed inside the tube billet, and borax is used to lubricate the inner wall of the tube to obtain a high-strength seamless tube.

In terms of process adaptability, the surface of titanium alloy is easy to crack during the heating process, which requires repeated grinding, resulting in low production efficiency. The addition of Fe element in the alloy greatly reduces the surface cracking of the alloy and improves the utilization rate of the material. This is because Fe can be solid-dissolved in α-Ti either by substitution or by interstitial solid-solution in α-Ti. When Fe is dissolved in the metal interstitial as a metal impurity atom with a small relative atomic radius, this fast-diffusing impurity will strongly accelerate the diffusion of the matrix material, especially when the temperature is in a certain range below the β-transus temperature. In this temperature range, there are Fe impurity atoms in the fast-moving impurity-vacancy pairs dissolved in the matrix from the gap, which will lead to a decrease in the matrix diffusion activation energy, promote the diffusion of the matrix material, and improve the effective diffusion capacity of the alloy. . When the temperature is close to the phase transition point, dislocation climbing needs to be realized by the diffusion of vacancies or interstitial atoms. The addition of Fe will generate impurity-vacancy pairs and strengthen the diffusion of interstitial atoms, which will promote the climbing movement of edge dislocations. , thereby greatly reducing the deformation resistance of titanium alloys.

Beneficial effect:

1. The present invention proposes to use Ti as the matrix, Al, Mo, Zr, Nb, and Fe as the main alloying elements, wherein the Al element is the main strengthening element, which can greatly improve the tensile strength and durability of the alloy; the Mo element is β Stable elements, while improving the room temperature and high temperature properties of the alloy, ensure the excellent process plasticity of the alloy. The addition of two elements at the same time is more conducive to the improvement of the overall performance than adding only one element; Zr is a neutral element, which can improve the alloy. The strength does not affect the thermal stability of the alloy and refines the grains. Nb element does not contribute much to the strength of titanium alloys, but it can greatly improve the thermal stability and corrosion resistance of titanium alloys. Fe is a β-stable element, which can greatly increase the room temperature strength of titanium alloys and reduce the high temperature strength without affecting the impact toughness and elongation, ensuring that the material has good processing properties.

2. The large-scale production of titanium alloy seamless pipes can be realized by adopting the preparation method of the present invention, with high efficiency and low cost. Moreover, the surface of the seamless pipe after heat treatment has a stable oxide layer, which can improve the hardness of the material surface while protecting the material, thereby enhancing the wear resistance of the pipe. In addition, the oxide layer is an insulating layer, which can well solve the problem of galvanic corrosion when in contact with dissimilar metals.

3. The titanium alloy pipe prepared by the present invention has high strength, high plasticity, high low-temperature impact toughness and good corrosion resistance, and meets the application requirements of harsh working conditions of oil and gas wells.

Detailed ways

The high impact toughness titanium alloy prepared by the present invention has a chemical composition range of: Al 4.0-9.0%, Mo 0.5-5.0%, Zr 1-5%, Nb 1-5%, Fe 0.2-2.0%, Ti quantity. Wherein the impurity content satisfies N≤0.05%, C≤0.1%, H≤0.015%, O≤0.15%.

A method for preparing a seamless pipe from a high-impact toughness titanium alloy mainly includes the following steps:

Step 1. Ingot preparation: According to the chemical composition requirements, mix aluminum-niobium master alloy, molybdenum block, pure zirconium sponge, iron nails, and sponge titanium, press them into electrode rods, and then put them into a vacuum consumable electric arc furnace for two secondary smelting to obtain titanium alloy ingots;

Step 2. Billet preparation: the titanium alloy ingot is forged at 1150°C, and re-forged at 970-1020°C to obtain a billet;

Step 3. Cross-rolling piercing: put the billet in a heating furnace and heat it to 950-1200°C, and keep it warm after reaching the temperature. The holding time is the diameter of the billet × (0.5-1.1) min/mm; use molybdenum-based alloy or high alloy The plug, the head is coated with lubricant, the lubricant is placed in the center hole of the billet, and the tube blank is made after piercing. The outer diameter/wall thickness of the tube blank is 9 to 12;

Step 4. Hot rolling and fixed diameter reduction: use the waste heat after cross rolling and piercing to carry out hot rolling of the tube billet, spray borax inside the tube billet as a lubricant before hot rolling, control the deformation at 50-70%, and then carry out fixed diameter reduction To obtain the pipe material, the outer diameter reduction ratio in the process of constant diameter reduction is 20-30%, and the wall thickness increase amount = wall thickness after hot rolling × (10%-15%);

Step 5, heat treatment: place the pipe in a heat treatment furnace for heat treatment, the heat treatment temperature is 800-980°C;

Step 6. Post-processing: Heating the heat-treated pipe to 600-700°C for straightening treatment. The bending degree of the straightened pipe is less than 1.5‰ of the total length of the pipe, and then sawing, inspection, and local defects on the surface Grinding is used for processing and storage.

The seamless pipe prepared by the preparation method can be used as a titanium alloy oil well pipe product.

In order to further understand the present invention, the embodiments of the present invention are described below in conjunction with the examples and attached tables, but it should be understood that these descriptions are only to further illustrate the features and advantages of the present invention, rather than limit the scope of the claims of the present invention.

Conventional instruments and equipment in the art are used in the following examples. For the experimental methods without specific conditions indicated in the following examples, the conventional conditions or the conditions suggested by the manufacturer are usually followed. Various starting materials were used in the following examples, and unless otherwise stated, conventional commercially available products were used.

Example 1

Step 1. Ingot preparation: Al-Nb master alloy, Mo block, pure sponge Zr, iron nails, and sponge Ti are smelted twice through mixing materials, pressing electrode rods, and vacuum self-consumption. The alloy ingot, the alloy transformation point is 973 ℃.

Step 2. Billet preparation: open billet forging at 1150°C, upsetting and drawing for 3-4 fires, and reforging twice at 960°C to prepare a Φ600 billet by machining.

Step 3, cross-rolling and piercing: heat the bar to 950° C. and keep it warm for 420 minutes, and then carry out cross-rolling and piercing to prepare a Φ630 tube blank.

Step 4, hot rolling and fixed diameter reduction: hot rolling the tube billet after cross rolling and piercing, spraying borax as lubricant inside the tube before hot rolling, and controlling the deformation at 50-70%. Then carry out fixed diameter reduction, the outer diameter decreases during the fixed diameter reduction process, the reduction ratio is 20-30%, the wall thickness is thickened by about 10% of the wall thickness after hot rolling, and the pipe material of Φ508×21 is prepared, and the maximum length of the pipe material Up to 10m.

Step 5. Heat treatment: Heat the pipe in an electric furnace to 820°C, keep it warm for 60 minutes, and then take it out of the furnace and cool it in air.

Step 6. Post-processing: heat the heat-treated pipe to 720°C, and straighten it on an automatic straightening machine. The bending degree of the pipe meets the technical requirements of ≤1.5‰, and then it is sawed, inspected, and put into storage.

Example 2

Step 1. Ingot preparation: Al-Nb master alloy, Mo block, pure sponge Zr, iron nails, and sponge Ti are smelted twice through mixing materials, pressing electrode rods, and vacuum self-consumption. The alloy ingot, the alloy transformation point is 988 ℃.

Step 2. Billet preparation: open billet forging at 1150°C, upsetting and drawing for 3-4 fires, and reforging twice at 960°C to prepare a Φ350 billet by machining.

Step 3, cross-rolling and piercing: heat the bar to 1000° C. and keep it warm for 200 minutes, and then carry out cross-rolling and piercing to prepare a Φ360 tube blank.

Step 4. Hot rolling and constant diameter reduction: Hot rolling the tube billet after cross rolling and piercing, spraying borax inside the tube as a lubricant before hot rolling, and controlling the deformation at 50-70%. Then carry out fixed diameter reduction, the outer diameter decreases during the fixed diameter reduction process, the reduction ratio is 20-30%, the wall thickness thickening is about 10% of the wall thickness after hot rolling, and the pipe material of Φ219×12.7 is prepared, and the length of the pipe material can be Up to 20m or more.

Step 5. Heat treatment: heat the pipe to 980° C. in a natural gas furnace with a slightly oxidizing atmosphere (mixed atmosphere of air and natural gas), keep it warm for 45 minutes, and then take it out of the furnace and cool it in air.

Step 6. Post-processing: heat the heat-treated pipe to 750°C, and straighten it on an automatic straightening machine. The bending degree of the pipe meets the technical requirements of ≤1.5‰, and then it is sawed, inspected, and put into storage.

Example 3

Step 1. Ingot preparation: Al-Nb master alloy, Mo block, pure sponge Zr, iron nails, and sponge Ti are smelted twice through mixing materials, pressing electrode rods, and vacuum self-consumption. The alloy ingot, the alloy phase transition point is 983 ℃.

Step 2. Billet preparation: open billet forging at 1150°C, upsetting and drawing for 3-4 fires, and reforging twice at 950°C to prepare a Φ350 billet by machining.

Step 3, cross-rolling and piercing: heat the bar to 1250°C and keep it warm for 90 minutes, then cross-roll and perforate it to prepare a Φ159 tube blank.

Step 4, hot rolling and fixed diameter reduction: hot rolling the tube billet after cross rolling and piercing, spraying borax as lubricant inside the tube before hot rolling, and controlling the deformation at 50-70%. Then carry out fixed diameter reduction, the outer diameter decreases during the fixed diameter reduction process, the reduction ratio is 20-30%, the wall thickness is thickened by about 10% of the wall thickness after hot rolling, and the pipe material of Φ42×4.85 is prepared, and the maximum length of the pipe material Up to 20m.

Step 5. Heat treatment: heat the pipe in a protective atmosphere furnace to 850°C, keep it warm for 45 minutes, and then take it out of the furnace and cool it in air.

Step 6. Post-processing: heat the heat-treated pipe to 610°C, and straighten it on an automatic straightening machine. The bending degree of the pipe meets the technical requirements of ≤1.5‰, and then perform sawing, inspection, and storage.

Effect Example

(1), the composition of the titanium alloy ingot prepared in embodiment 1-3 by mass percentage

The composition (/wt%) of the titanium alloy ingot prepared by the embodiment 1-3 of table 1 by mass percentage

(2), the mechanical property detection of the titanium alloy seamless pipe material that embodiment 1-3 prepares

The titanium alloy seamless pipe prepared in Examples 1-3, a domestic P110 steel grade G3 alloy oil pipe, a foreign Q125 steel grade G3 pipe and the mechanical property requirements of API related standards were compared, as shown in Table 2.

Table 2 Comparison of titanium alloy seamless pipes prepared in Examples 1-3 with oil pipes in the prior art and API-related standards

It can be seen from Table 2 that the tensile strength, elongation and impact energy of titanium alloy seamless pipes all meet the mechanical properties of API SPEC 5CT for P110 steel grade. And the impact energy of the titanium alloy seamless pipe prepared in Examples 1-3 is significantly greater than that of the domestic G3 pipe of the same level.

(3), the corrosion resistance detection of the titanium alloy seamless pipe material prepared in embodiment 1-3

Select a relatively serious corrosion site working condition, and conduct a corrosion evaluation test of simulated working conditions on titanium alloy seamless pipes to evaluate the uniform corrosion performance of titanium alloy seamless pipes under specific working conditions. The corrosion performance detection mainly includes two aspects: On the one hand, the evaluation test is carried out according to NACE-MR0175. The test temperature is 160°C, the H2S partial pressure is 5MPa, the _CO2 partial pressure is _11MPa , the NaCl concentration is 100000ppmCl, the elemental sulfur is 3g/L, and the SSCB test period is 720h. The test period of the corrosion coupon is 168h, and the test results obtained according to the above test conditions (including the test results of method A, the test results of the four-point bending method and the 7-day corrosion condition of the corrosion coupon) are shown in Table 3. On the other hand, the annual corrosion rate of seamless pipes is tested, and the test results are shown in Table 3.

The corrosion resistance test result of the titanium alloy seamless pipe prepared by the embodiment 1-3 of table 3

It can be seen from Table 3 that the corrosion resistance test results of the titanium alloy seamless pipe prepared in Examples 1-3 meet the requirements of NACE-MR0175 on the degree of corrosion, and no obvious corrosion or pitting was found on the surface of the seamless pipe. The annual corrosion rate of the seamless pipe is low, so the titanium alloy seamless pipe in the present invention has excellent corrosion resistance.

The seamless pipe prepared by the invention can reduce the weight of the pipe string by 40%, thereby improving the tensile safety factor of the pipe string; at the same time, it can well solve the problem of low safety caused by the existing P110 grade pipe string, It provides a reliable guarantee for the improvement of my country's oil and natural gas mining capacity.

Above, a kind of high impact toughness titanium alloy provided by the present invention and the method for preparing seamless pipe by using titanium alloy have been introduced in detail. In this paper, specific examples have been used to illustrate the principle and specific implementation of the present invention. The above-mentioned examples It is only used to help understand the method and core idea of the present invention. It should be pointed out that for those skilled in the art, any simple modifications, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention fall within the protection scope of the present invention.

Claims (6)

1. The titanium alloy with high impact toughness is characterized by comprising the following chemical components in percentage by weight: 4.0 to 9.0 percent of Al, 0.5 to 5.0 percent of Mo, 1 to 5 percent of Zr, 1 to 5 percent of Nb, 0.2 to 2.0 percent of Fe, and the balance of Ti and inevitable impurities; wherein the content of impurities satisfies N is less than or equal to 0.05%, C is less than or equal to 0.1%, H is less than or equal to 0.015%, and O is less than or equal to 0.15%.

2. A method for producing a seamless pipe using the high impact toughness titanium alloy of claim 1, which essentially comprises the steps of:

step one, ingot preparation: respectively weighing the aluminum-niobium intermediate alloy, the molybdenum block, the pure sponge zirconium, the iron nail and the sponge titanium according to the chemical composition requirements in claim 1, mixing, pressing into an electrode rod, and then putting into a vacuum consumable arc furnace for secondary smelting to obtain a titanium alloy ingot;

step two, preparing a bar blank, namely cogging and forging the titanium alloy ingot obtained in the step one at 1150 ℃, and performing forge change at 970 ~ 1020 ℃ to obtain the bar blank;

step three, oblique piercing, namely placing the bar blank obtained in the step two in a heating furnace to heat to 950 ~ 1200 ℃ and preserving heat for the time of the diameter x (0.5 ~ 1.1.1) min/mm of the bar blank, then adopting a molybdenum-based alloy or high alloy top head, coating a lubricant on the head, placing the lubricant in a central hole of the bar blank after heat preservation, and piercing to obtain a tube blank;

step four, hot rolling and fixed reducing, namely hot rolling the tube blank obtained in the step three, spraying borax into the tube blank before hot rolling, controlling the deformation to be 50 ~ 70%, and then performing fixed reducing to obtain a tube;

step five, heat treatment, namely placing the pipe obtained in the step four into a heat treatment furnace for heat treatment, wherein the heat treatment temperature is 800 ~ 980 ℃;

step six, post-treatment: and (4) straightening, sawing, inspecting and warehousing the heat-treated pipe.

3. The method for preparing seamless pipe material with high impact toughness titanium alloy as claimed in claim 2, wherein in step three, the requirement of the prepared pipe blank is that the outer diameter/wall thickness is =9 ~ 12.

4. The method for preparing the seamless pipe by using the high impact toughness titanium alloy according to the claim 2, wherein in the third step, the micro-oxidation atmosphere in the heating furnace is kept during the heating process of the bar billet, and the micro-oxidation atmosphere is a mixed atmosphere of air and natural gas.

5. The method for producing a seamless pipe using the high impact toughness titanium alloy as claimed in claim 2, wherein in the fourth step, the outside diameter reduction ratio in the sizing and reducing process is 20 ~ 30%, and the wall thickness thickening = wall thickness x after hot rolling (10% ~ 15%).

6. The method for preparing the seamless pipe by using the high-impact-toughness titanium alloy as claimed in claim 2, wherein in the sixth step, the pipe is heated to 600 ~ 700 ℃ for straightening treatment, and the bending degree of the straightened pipe is less than 1.5 per mill of the full length of the pipe.