Preparation method of high-strength titanium alloy bar for ocean engineering

Abstract

The invention discloses a high-strength titanium alloy bar for ocean engineering, which comprises the following components in percentage by mass: 4.0-5.5% of Al, 0.3-0.6% of Fe, 2.5-3.4% of V, 0.15-0.2% of O, less than or equal to 0.03% of C, less than or equal to 0.05% of N, less than or equal to 0.01% of H, less than or equal to 0.02% of B and the balance of Ti, sponge titanium, an intermediate alloy, an iron block, aluminum shots and titanium dioxide are mixed and then pressed to obtain an electrode block, the pressed electrode block is assembled and welded, and the high-strength titanium alloy bar for ocean engineering is obtained. The electrode is placed in a vacuum consumable electric arc furnace to be smelted twice or more to obtain an alloy ingot, the alloy ingot is subjected to cogging forging through free forging equipment, a primary forging stock is heated to the process temperature to be subjected to multi-heating-number upsetting and drawing forging, a refined forging stock is subjected to two-heating-number large deformation rolling, and a bar is obtained; the device is reasonable in structural design, beneficial for improving the productivity, capable of controlling the deformation amount to ensure that no crack occurs in the material rolling process, and suitable for machining and manufacturing of ocean engineering equipment.

Description

Technical Field

[0001] The invention relates to the technical field of titanium alloy bars, and more specifically, to a method for preparing a high-strength titanium alloy bar for marine engineering. Background Art

[0002] Marine engineering refers to new construction, reconstruction and expansion projects that are aimed at developing, utilizing, protecting and restoring marine resources, and the main body of the project is located on the seaward side of the coastline. Titanium alloys have become the preferred material for marine engineering equipment due to their high specific strength, good corrosion resistance and non-magnetic properties. Titanium alloys are also used in offshore oil and gas platforms, deep-sea drilling equipment, ships and marine structures in the field of marine engineering. Among them, offshore oil and gas platforms have the greatest demand for titanium metal, accounting for about 70% of the total amount of titanium used in marine engineering3. With the development of marine resources and the vigorous development of marine engineering, titanium and titanium alloys have become one of the preferred materials for marine engineering structures, equipment and components due to their excellent performance.

[0003] In actual use, due to the complexity of the marine environment, the stress conditions of equipment made of titanium alloy are complex during use. The alloy has insufficient impact performance and stress corrosion resistance, and cannot meet the requirements of complex working conditions for material performance. In order to improve the relevant performance, precious metal elements are often added to the alloy, but the cost of the material is also increased a lot. In addition, titanium alloy bars are forged by multiple fires during the forging process. The surface layer caused by high-temperature oxidation of titanium alloys is prone to surface cracks. Therefore, the machining allowance of titanium alloy bars is large, resulting in a low yield of bar materials. To this end, we proposed a method for preparing high-strength titanium alloy bars for marine engineering. Summary of the invention

[0004] The purpose of the present invention is to provide a high-strength titanium alloy bar for marine engineering and a preparation method thereof, so as to overcome the technical problems existing in the prior art.

[0005] In order to achieve the above technical objectives and the above technical effects, the present invention provides the following technical solutions:

[0006] A high-strength titanium alloy bar for marine engineering is composed of the following components in mass percentage: 4.0-5.5% Al, 0.3-0.6% Fe, 2.5-3.4% V, 0.15-0.2% O, C≤0.03%, N≤0.05%, H≤0.01%, B≤0.02%, and the balance is Ti.

[0007] A method for preparing a high-strength titanium alloy bar for marine engineering comprises the following steps:

[0008] Step 1: Mix titanium sponge, master alloy, iron block, aluminum bean and titanium dioxide, and then press them to obtain an electrode block;

[0009] Step 2: Weld the pressed electrode blocks to obtain long strip electrodes;

[0010] Step 3, placing the electrode in a vacuum consumable arc furnace and smelting it twice or more to obtain an alloy ingot;

[0011] Step 4: Forging the alloy ingot by using a free forging device to obtain a primary forging blank;

[0012] Step 5: heating the primary forging blank to the process temperature and performing multi-fire forging to obtain a refined forging blank;

[0013] Step 6: subjecting the refined forging blank to two rounds of large deformation rolling to obtain a bar;

[0014] Step 7: Straighten the bars, cut them to size and then perform stress annealing;

[0015] Step 8. The annealed bars are finely processed on a lathe and put into storage after passing the appearance inspection.

[0016] Preferably, in a method for preparing a high-strength titanium alloy rod for marine engineering, the smelting current in step three is 5-12KA, and the smelting voltage is controlled at 26-45V.

[0017] Preferably, in a method for preparing a high-strength titanium alloy bar for marine engineering, the blank forging process temperature in step 4 is 1100°C.

[0018] Preferably, in a method for preparing high-strength titanium alloy bars for marine engineering, in step five, the primary forging blank is heated to a temperature of 1050-1100°C, and the holding time is 200-240 minutes, and then 2-3 fires of two upsetting and two drawing forging are performed, and then one fire of drawing process is performed, the heating temperature is 1000-1050°C, the final forging temperature is 900-950°C, and the holding time is 180 minutes.

[0019] Preferably, in a method for preparing high-strength titanium alloy bars for marine engineering, in step six, the refined forging blank is first heated to 860°C to 920°C and then hot rolled, and then cooled to 830°C to 880°C and then hot rolled, and the total deformation of the two hot rollings is 70% to 85%.

[0020] Preferably, in a method for preparing a high-strength titanium alloy rod for marine engineering, the annealing temperature in step seven is 700-750° C., the annealing time is 1-2 h, and the cooling method after annealing is air cooling.

[0021] Preferably, in a method for preparing a high-strength titanium alloy rod for marine engineering, the surface roughness during the appearance inspection in step eight is not greater than 6.3.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The present invention has a reasonable structural design. The blanking temperature is selected to be above or near the phase change point for forging, which can strive for a longer forging time, which is beneficial to improving productivity. The multi-fire forging process ensures that the forging process organization is improved, but does not affect the performance of the forging;

[0024] 2. The present invention adopts two-step rolling to obtain the rod material. The initial high-temperature rolling can ensure the plasticity of the alloy, and the subsequent low-temperature rolling can improve the strength of the material. Controlling the deformation can ensure that the material does not crack during the rolling process;

[0025] 3. The present invention performs stress annealing after straightening the rod, which can ensure the uniformity of the alloy composition, maintain the titanium alloy's good corrosion resistance, welding performance, good machinability and low-temperature mechanical properties, and is suitable for the processing and manufacturing of marine engineering equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solution of the present invention, the drawings required for use in the description of the specific implementation methods will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 It is a schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in 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 creative work are within the scope of protection of the present invention.

[0029] A high-strength titanium alloy bar for marine engineering is composed of the following components in mass percentage: 4.0-5.5% Al, 0.3-0.6% Fe, 2.5-3.4% V, 0.15-0.2% O, C≤0.03%, N≤0.05%, H≤0.01%, B≤0.02%, and the balance is Ti. Aluminum is a commonly used alloying element in titanium alloys, which can improve the strength and heat resistance of titanium alloys. Iron exists as an impurity element in titanium alloys, but the addition of Fe element can reduce the phase transition point, reduce the temperature during processing, and improve work efficiency. Vanadium is an important alloying element in titanium alloys, which can significantly improve the strength and toughness of titanium alloys. By accurately controlling the content of each element, especially strictly controlling the content of harmful impurities, and reasonably adding alloying elements, excellent mechanical properties and marine environment corrosion resistance are obtained.

[0030] A method for preparing a high-strength titanium alloy bar for marine engineering comprises the following steps:

[0031] Step 1: Mix titanium sponge, intermediate alloy, iron block, aluminum bean and titanium dioxide, and then press them to obtain electrode blocks. Put the mixed raw materials into a mold and press them. The purpose of pressing is to make the raw materials tightly combined to form an electrode block with a certain shape and density. The pressure and pressing time need to be controlled during the pressing process to ensure the quality of the electrode block.

[0032] Step 2: Weld the pressed electrode blocks together to obtain long strip electrodes. Before welding, clean the welding parts of the electrode blocks to remove impurities such as oil, oxides, etc. This helps to improve the welding quality and prevent welding defects. During the welding process, it is necessary to control parameters such as welding temperature, welding speed and welding pressure to ensure welding quality. At the same time, it is also necessary to pay attention to the alignment and gap control of the welding joint to avoid welding defects such as lack of fusion and pores. After welding, the welding joint needs to be post-processed, including removing welding spatter and grinding the welding joint to eliminate unevenness and burrs. In addition, heat treatment and other process treatments can also be performed to eliminate welding stress and improve the performance of the welding joint.

[0033] Step 3: Place the electrode in a vacuum consumable arc furnace and smelt it more than twice to obtain an alloy ingot. The smelting current is 5-12KA, and the smelting voltage is controlled at 26-45V. Under vacuum or inert gas protection, arc heat is used to melt the consumable electrode and refine it into an alloy ingot. This equipment can effectively remove impurities in the raw materials and improve the purity and performance of the alloy. According to requirements, the molten alloy is smelted multiple times. Each smelting will further remove impurities and improve the purity and uniformity of the alloy. Multiple smelting can also make the composition of the alloy more uniform, reduce the occurrence of segregation, and provide high-quality raw materials for subsequent material processing and application.

[0034] Step 4: Use free forging equipment to forge the alloy ingot to obtain the primary forging blank. The forging process temperature is 1100℃. Titanium alloy has high plasticity and low deformation resistance in the β phase region. Therefore, the forging temperature is selected to be above or near the phase change point for forging, which can strive for a longer forging time and is conducive to improving productivity. The heated ingot is placed on the anvil of the free forging equipment for preliminary forging. The purpose of the preliminary forging is to remove defects such as scale, cracks and shrinkage cavities on the surface of the ingot and to preliminarily change the shape of the ingot. During the preliminary forging process, the forging force and speed need to be controlled to avoid new cracks or defects. During the entire forging process, the heating temperature and forging temperature of the ingot need to be strictly controlled. Too high or too low temperature will affect the forging effect and quality. Free forging equipment usually has a large impact and vibration, so the operator needs to strictly abide by the safety operating procedures and wear protective equipment to ensure personal safety.

[0035] Step 5, heating the primary forging billet to the process temperature for multi-fire upsetting and drawing forging to obtain a refined forging billet, heating the primary forging billet to a temperature of 1050-1100°C, holding time of 200-240min, performing 2-3 fires of two upsetting and two drawing forging, and then performing one fire of drawing process, heating temperature of 1000-1050°C, final forging temperature of 900-950°C, holding time of 180min, which is lower than but close to the phase transformation point, can ensure that the forging process organization is improved, but does not affect the performance of the forging, During the forging process, the metal material is heated and stretched multiple times. This process uses repeated heating and forging to gradually refine the grains, eliminate internal defects, and improve density and mechanical properties of the metal material during multiple plastic deformations. After each heating and forging, the internal structure and mechanical properties of the material will be improved to a certain extent. By repeating this process multiple times, the required material properties can be gradually achieved. Roughening and stretching operations help eliminate defects such as pores and cracks inside the material and improve the density of the material.

[0036] Step 6: The refined forging blank is subjected to two large deformation rollings to obtain a bar. The refined forging blank is first heated to 860°C-920°C and then hot rolled. Then the temperature is lowered to 830°C-880°C and then hot rolled. The total deformation of the two hot rollings is 70%-85%. Through the two-step rolling, in the first step of rolling, the initial high-temperature rolling can ensure the plasticity of the alloy. In the second step of rolling, the subsequent low-temperature rolling can improve the strength of the material. At the same time, controlling the deformation can ensure that the material does not crack during the rolling process. The high and low temperature hot rolling and controlled deformation The shaping process can ensure that the plasticity and strength of the material match; the heated raw material is sent to the rolling mill for the first rolling. During the rolling process, the raw material is continuously pressed down by multiple rollers, gradually undergoing plastic deformation, reducing the cross-sectional area and increasing the length to form a preliminary bar shape. The first rolling is usually a large deformation to quickly change the shape and size of the raw material. After the first rolling is completed, the bar may need to be intermediately cooled. The cooling method can be natural cooling or water spray cooling, etc., depending on the type of material and the required performance. The purpose of intermediate cooling is to control the temperature and organizational structure of the material and prepare for the next rolling. The bar that has been rolled and cooled for the first time is put into the heating furnace again and heated to the rolling temperature. The heated bar is sent to the rolling mill again for the second rolling. The second rolling is usually to further adjust the shape and size of the bar after the first rolling to meet the final specification requirements. The second rolling can also be a large deformation, but the specific deformation depends on the shape of the bar after the first rolling and the required final product specifications.

[0037] Step 7: Straighten the rod, cut it to size and then perform stress annealing. The annealing temperature is 700-750℃, the annealing time is 1-2h, and the cooling method after annealing is air cooling. The annealing temperature and annealing time can ensure the uniformity of the alloy composition, and the internal structure of the alloy is based on α-Ti, maintaining the good corrosion resistance, welding performance, good machinability and low-temperature mechanical properties of the titanium alloy, and ensuring the application of the titanium alloy under service conditions. During the processing of titanium alloy bars, due to hot rolling, forging or cold drawing, certain shape deviations, internal stress and structural inhomogeneity are often produced. In order to improve these problems, the straightness and dimensional precision of titanium alloy bars are improved. In order to improve the degree and mechanical properties, straightening, cutting and stress annealing are usually carried out. Straightening is to apply external force to the titanium alloy bar to correct the bent or twisted part and restore or approach its original straight state. The straightening method can be mechanical straightening, hydraulic straightening or roller straightening. The straightened titanium alloy bar is cut into the required length. The cutting method can be mechanical cutting or laser cutting. Stress annealing treatment is to eliminate the internal stress and tissue heterogeneity generated by the titanium alloy bar during the processing. By heating to an appropriate temperature and keeping it warm for a period of time, and then slowly cooling it, the stress inside the material can be released and the tissue is more uniform, thereby improving the mechanical properties and stability of the material.

[0038] Step 8. The annealed bars are finished on a lathe and put into storage after passing the appearance inspection. The surface roughness is not more than 6.3. After the titanium alloy bars are annealed, in order to further improve their dimensional accuracy and surface quality, they are usually finished on a lathe. Finishing is an important process in metal processing, which aims to remove tiny unevenness and excess on the surface of the material to achieve the required dimensional accuracy and surface roughness requirements, providing reliable quality assurance for subsequent use.

[0039] The titanium alloy prepared by the invention has low production cost, good impact resistance, high corrosion resistance, good surface elongation, and no cracks during the rolling process, and is suitable for the processing and production of marine engineering equipment.

[0040] The embodiments described in the present invention are merely descriptions of the preferred implementation modes of the present invention, and are not intended to limit the concept and scope of the present invention. Without departing from the design concept of the present invention, various modifications and improvements made to the technical solutions of the present invention by engineers and technicians in this field should fall within the protection scope of the present invention. The technical contents for which protection is sought in the present invention have all been recorded in the claims.

Claims

1. A high-strength titanium alloy bar for marine engineering, characterized in that: It is composed of the following components in mass percentage: 4.0-5.5% Al, 0.3-0.6% Fe, 2.5-3.4% V, 0.15-0.2% O, C≤0.03%, N≤0.05%, H≤0.01%, B≤0.02%, and the balance is Ti.

2. A method for preparing high-strength titanium alloy bars for marine engineering, characterized in that: The following steps are involved: Step 1: Mix titanium sponge, master alloy, iron block, aluminum bean and titanium dioxide, and then press them to obtain an electrode block; Step 2: Weld the pressed electrode blocks to obtain long strip electrodes; Step 3, placing the electrode in a vacuum consumable arc furnace and smelting it twice or more to obtain an alloy ingot; Step 4: Forging the alloy ingot by using a free forging device to obtain a primary forging blank; Step 5: heating the primary forging blank to the process temperature and performing multi-fire forging to obtain a refined forging blank; Step 6: subjecting the refined forging blank to two rounds of large deformation rolling to obtain a bar; Step 7: Straighten the bars, cut them to size and then perform stress annealing; Step 8. The annealed bars are finely processed on a lathe and put into storage after passing the appearance inspection.

3. The method for preparing a high-strength titanium alloy bar for marine engineering according to claim 2, characterized in that: In step 3, the smelting current is 5-12KA, and the smelting voltage is controlled at 26-45V.

4. The method for preparing a high-strength titanium alloy bar for marine engineering according to claim 2, characterized in that: In step 4, the forging process temperature is 1100°C.

5. The method for preparing a high-strength titanium alloy bar for marine engineering according to claim 2, characterized in that: Step 5: Heat the primary forging billet to 1050-1100°C, keep it warm for 200-240min, then perform 2-3 rounds of two upsetting and two drawing forging, and then perform one round of drawing process, with a heating temperature of 1000-1050°C, a final forging temperature of 900-950°C, and a holding time of 180min.

6. The method for preparing a high-strength titanium alloy bar for marine engineering according to claim 2, characterized in that: In step six, the refined forging blank is first heated to 860°C to 920°C and then hot rolled, and then cooled to 830°C to 880°C and then hot rolled. The total deformation of the two hot rollings is 70% to 85%.

7. The method for preparing a high-strength titanium alloy bar for marine engineering according to claim 2, characterized in that: In step seven, the annealing temperature is 700-750° C., the annealing time is 1-2 hours, and the cooling method after annealing is air cooling.

8. The method for preparing a high-strength titanium alloy bar for marine engineering according to claim 2, characterized in that: The surface roughness during the appearance inspection in step 8 shall not exceed 6.3.

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