A method for improving the strength of pure titanium bar

Abstract

The application discloses a preparation method for improving the strength of pure titanium rod, and comprises the following steps: 1, mixing zero-level large-particle sponge titanium and alloy element raw materials, pressing into electrode blocks and welding to obtain primary electrodes; 2, three-time vacuum self-consumption smelting to obtain low-alloyed titanium ingots; 3, blooming forging, upsetting deformation, re-melting and elongation to obtain square billet materials; 4, heating and multi-pass rolling to obtain rod blanks; 5, heat treatment and furnace-out cooling to obtain high-strength titanium rods. The application properly increases the content of Fe and O in the smelting process, and adds no more than 0.5% of Al and no more than 1% of Zr, so that a low-alloyed titanium ingot is obtained. In combination with blooming forging, upsetting deformation, re-melting, elongation, hot rolling and heat treatment of the low-alloyed titanium ingot, the structure is refined and uniform, the tensile strength of the obtained high-strength titanium rod is higher than that of conventional TA4 by more than 50 MPa, and batch production is easily realized.

Description

Technical Field

[0001] This invention belongs to the field of titanium and titanium alloy melting, forging, rolling and processing technology, and specifically relates to a method for preparing pure titanium bars to improve their strength. Background Technology

[0002] Titanium and titanium alloys are increasingly widely used in aerospace, shipbuilding, chemical, petroleum, and biomedical fields due to their high specific strength, excellent comprehensive mechanical properties, good corrosion resistance, and excellent biocompatibility. Pure titanium products account for approximately 80% of all titanium alloy products. The main grades of pure titanium include TA1, TA2, TA3, and TA4. Compared to commonly used titanium alloys, these grades have lower tensile strength. Existing pure titanium bars, after general heat treatment, typically have a tensile strength between 300 and 650 MPa and a yield strength between 200 and 550 MPa, which does not meet the aforementioned requirements.

[0003] If alloys with higher alloy content, such as TC4 and TA5, are used instead, the high alloy content of TC4 titanium alloys will first increase production costs. During material processing, the high degree of alloying makes material deformation during hot and cold working difficult, resulting in complex processing techniques and high production difficulty. This is especially true in CNC environments requiring precision machining, where tool wear is high and yield is low. The entire process is complex, inefficient, wasteful of materials, and uneconomical.

[0004] Therefore, there is an urgent need for a preparation method to improve the strength of pure titanium rods. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide a method for preparing pure titanium bars that improves their strength, addressing the shortcomings of the prior art. This method employs a strategy of adding appropriate amounts of low-alloying elements during the smelting process. High-strength bars are prepared through vacuum arc remelting, forging, and hot rolling. The low-alloying element method offers advantages such as low production cost, easy deformation and processing, and low material loss during forging and rolling. This results in high-strength titanium bars with tensile strength approximately 50 MPa higher than conventional TA4, facilitating mass production.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for preparing pure titanium rods with improved strength, characterized in that the method includes the following steps:

[0007] Step 1: Mix the zero-grade large-particle sponge titanium and alloy element raw materials evenly in an automatic mixing and spreading machine to obtain a mixture. Then, use an electrode press to prepare electrode blocks, and then weld the electrode blocks in a vacuum welding box to obtain a primary electrode. The mixture is composed of the following elements in mass fraction: Fe 0.29%~0.34%, O 0.29%~0.34%, Zr 0.40%~0.8%, Al 0.15%~0.45%, with the balance being Ti.

[0008] Step 2: The primary electrode obtained in Step 1 is subjected to three vacuum arc remelting processes in a vacuum arc remelting furnace to obtain a low-alloy titanium ingot.

[0009] Step 3: After peeling off the titanium ingot obtained in Step 2 and removing the head and tail, forge it into a billet, then upset and deform it, then return it to the furnace, and then draw it again, grind it and remove the surface oxide scale to obtain a square billet.

[0010] Step 4: Heat the square billet obtained in Step 3 in an electric furnace, and then roll it in multiple passes to obtain a bar billet;

[0011] Step 5: Heat treat the billet obtained in Step 4 in an electric furnace, then remove it from the furnace and cool it to obtain high-strength titanium rods.

[0012] This invention achieves low-alloying by controlling the composition of the mixture and quantitatively controlling the alloying elements. By appropriately increasing the Fe and O content in the mixture and adding no more than 0.5% Al and no more than 1% Zr, a metallurgical foundation is laid for improving the performance of titanium bars. The strengthening mechanism mainly manifests as follows: aluminum, as a typical α-stabilizing element, can form a continuous solid solution α phase with titanium. Due to the slight difference between the atomic radius of aluminum (0.143 nm) and titanium (0.147 nm), when aluminum atoms replace titanium atoms in the crystal lattice, it induces lattice distortion, hindering dislocation movement. This solid solution strengthening effect can significantly improve the room temperature and intermediate temperature strength of titanium bars and is one of the core mechanisms for achieving high strength in titanium bars. However, excessive aluminum cannot be added, as it will lead to subsequent difficulties. Processing; Oxygen atoms provided by oxygen can interstitially dissolve in the titanium lattice, forming a solid solution strengthening effect. When oxygen atoms enter the interstitial spaces of the titanium lattice, they cause lattice distortion, increasing the resistance to dislocation movement and thus improving the strength of the titanium rod. Zirconium enhances the strength of the titanium rod through solid solution strengthening. Unlike elements such as oxygen, zirconium has a smaller impact on the plasticity and toughness of the titanium rod while improving its strength, thus achieving a better balance between strength and plasticity. This allows zirconium-containing titanium rods to maintain good processing performance and toughness while possessing high strength. Iron enhances the strength of the titanium rod through both solid solution strengthening and precipitation strengthening. Compared with some other alloying elements, iron is relatively inexpensive. The synergistic effect of these four elements improves the performance of the titanium rod.

[0013] The above-mentioned method for preparing a pure titanium rod with improved strength is characterized in that the particle size of the zero-grade large-particle sponge titanium in step one is 0.83mm~25.4mm.

[0014] The above-mentioned method for preparing pure titanium rods with improved strength is characterized in that, in step two, the current for the first vacuum arc remelting is 10kA~14kA, the current for the second vacuum arc remelting is 20kA~24kA, and the current for the third vacuum arc remelting is 13kA~17kA. This invention achieves uniform low-alloy element composition in titanium ingots through three vacuum arc remelting processes, while simultaneously removing gaseous element impurities and improving material purity. The reason for setting the current range for the three processes is mainly that the first process uses a small ingot size, making a small current range suitable; the second process requires a larger current as the ingot size increases; and the third process appropriately reduces the current to achieve a more uniform composition and synergistic strengthening effect, which is beneficial for the uniform crystallization of alloy elements.

[0015] The above-mentioned method for preparing pure titanium bars with improved strength is characterized in that the forging temperature in step three is 1000℃~1050℃, and the holding time is 6h~9h. This invention, by controlling the forging parameters and adding low-content alloying elements, lowers the forging temperature, achieving sufficient fragmentation of coarse grains, resulting in a uniform material structure, thereby improving the material's strength, toughness, and plasticity, while reducing cracking and lowering production costs and losses.

[0016] The above-mentioned method for preparing pure titanium bars with improved strength is characterized in that the upsetting and drawing deformation in step three is carried out using a high-speed forging machine, and the deformation amount is 30%~50%. This invention, by controlling the parameters of the upsetting and drawing deformation and adding low-content alloying elements, further achieves the complete crushing of coarse grains, resulting in a uniform material structure and thus improving the strength, toughness, and plasticity of the material.

[0017] The above-mentioned method for preparing pure titanium rods with improved strength is characterized in that the remelting temperature in step three is 900℃~950℃, and the holding time is 2h~4h. This invention, by controlling the remelting parameters and adding low-content alloying elements, further achieves the thorough breaking down of coarse grains, resulting in a uniform material structure and thus improving the material's strength, toughness, and plasticity.

[0018] The above-described method for preparing pure titanium bars with improved strength is characterized in that the side length of the square billet in step three is 180mm~200mm. This invention controls the dimensions of the square billet by controlling its side length, and then obtains bars of suitable dimensions through rolling.

[0019] The above-mentioned method for preparing pure titanium bars with improved strength is characterized in that, in step four, the heating temperature is 800℃~850℃, the holding time is 4h~6h, the multi-pass rolling is 5~8 passes, and the diameter of the billet is 80mm~100mm. In this invention, the addition of low-content alloying elements gives the material a lower phase transformation point. Therefore, by controlling the parameters of the multi-pass rolling, the rolling temperature is reduced by 50℃, and the number of rolling passes is reduced by 1-2, resulting in a billet with excellent performance.

[0020] The above-mentioned method for preparing pure titanium rods with improved strength is characterized in that, in step five, the heat treatment refers to heating in an electric furnace at a temperature of 600-700℃ for a holding time of 2-3 hours. This invention, by setting the heat treatment parameters and cooling method, results in a fine and uniform microstructure in the titanium rods, thus obtaining high-strength rods.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] 1. This invention employs a strategy of adding appropriate amounts of low-alloying elements during the smelting process to produce high-strength titanium bars through vacuum arc remelting, forging, and hot rolling. The low-alloying element method has the advantages of low production cost and easy deformation, easy processing, and low material loss during forging and rolling. Vacuum arc remelting achieves uniform composition and removes impurities, while forging breaks down large grains. Hot rolling and heat treatment achieve a refined and uniform microstructure, resulting in high-strength titanium bars with a tensile strength approximately 50 MPa higher than conventional TA4, making mass production easily achievable.

[0023] 2. This invention improves strength by appropriately increasing Fe and O, and adding no more than 0.5% Al and no more than 1% Zr. Compared with other grades of titanium alloys, this invention has the advantage of low cost in terms of raw material input.

[0024] 3. The high-strength titanium rods prepared in this invention have a lower alloy element content compared to other grades of titanium alloys. During the forging and billet preparation process, the heating temperature of conventional grade titanium alloys is 1150℃, while the billet preparation temperature of this invention is 1050℃, which is 100℃ lower. This results in lower energy consumption and reduced production costs. In addition, the machined surface is less prone to cracking, and material loss is smaller.

[0025] 4. The high-strength titanium bars prepared by this invention have a heating temperature that is about 50°C lower than that of other grades of titanium alloys during hot rolling, and the rolling temperature and heat treatment temperature are reduced by 1 to 2 rolling passes, resulting in lower production costs.

[0026] The technical solution of the present invention will be further described in detail below through embodiments. Detailed Implementation

[0027] Example 1

[0028] This embodiment includes the following steps:

[0029] Step 1: Zero-grade large-particle sponge titanium with a particle size of 0.83mm~25.4mm and alloy element raw materials are mixed evenly in an automatic mixing and spreading machine to obtain a mixture. Then, electrode blocks are prepared using an electrode press, and the electrode blocks are welded in a vacuum welding box to obtain a primary electrode. The mixture is composed of the following elements by mass fraction: Fe 0.29%, O 0.29%, Zr 0.8%, Al 0.45%, with the balance being Ti.

[0030] Step 2: The primary electrode obtained in Step 1 is subjected to three vacuum arc remelting processes in a vacuum arc remelting furnace. The current for the first vacuum arc remelting is 10kA~14kA, the current for the second vacuum arc remelting is 20kA~24kA, and the current for the third vacuum arc remelting is 13kA~17kA, to obtain a low-alloy titanium ingot.

[0031] Step 3: After peeling off the titanium ingot obtained in Step 2 and removing the head and tail, forge the billet at a temperature of 1050℃ for 6 hours. Then, use a high-speed forging machine to upset and deform it by 30%. After that, hold it at 950℃ for 2 hours and then remelt it. After taking it out of the furnace, draw it again, grind it and remove the surface oxide scale to obtain a square billet with a side length of 200mm.

[0032] Step 4: Heat the square billet obtained in Step 3 to 800℃ in an electric furnace and hold for 4 hours. Then roll it 5 times to obtain a bar billet with a diameter of 100mm.

[0033] Step 5: Heat the billet obtained in Step 4 to 600℃ in an electric furnace and heat treat for 2 hours. Then remove it from the furnace and cool it to obtain a high-strength titanium rod with a diameter of 100mm.

[0034] Testing revealed that the high-strength titanium rod prepared in this embodiment has a tensile strength of 750 MPa and a yield strength of 630 MPa, which are far higher than the national standard requirements. This achieves the performance requirements of low alloying and high strength (the national standard requires a tensile strength of not less than 580 MPa and a yield strength of 485 MPa to 655 MPa).

[0035] Example 2

[0036] This embodiment includes the following steps:

[0037] Step 1: Zero-grade large-particle sponge titanium with a particle size of 0.83mm~25.4mm and alloy element raw materials are mixed evenly in an automatic mixing and spreading machine to obtain a mixture. Then, electrode blocks are prepared using an electrode press, and the electrode blocks are welded in a vacuum welding box to obtain a primary electrode. The mixture is composed of the following elements by mass fraction: Fe 0.34%, O 0.34%, Zr 0.40%, Al 0.15%, with the balance being Ti.

[0038] Step 2: The primary electrode obtained in Step 1 is subjected to three vacuum arc remelting processes in a vacuum arc remelting furnace. The current for the first vacuum arc remelting is 10kA~14kA, the current for the second vacuum arc remelting is 20kA~24kA, and the current for the third vacuum arc remelting is 13kA~17kA, to obtain a low-alloy titanium ingot.

[0039] Step 3: After peeling off the titanium ingot obtained in Step 2 and removing the head and tail, forge the billet at a temperature of 1000℃ and a holding time of 9h. Then, use a high-speed forging machine to perform upsetting and drawing deformation with a deformation amount of 50%. After that, hold at 900℃ for 4h and remelt. After taking it out of the furnace, draw it again, grind it and remove the surface oxide scale to obtain a square billet with a side length of 180mm.

[0040] Step 4: Heat the square billet obtained in Step 3 to 850℃ in an electric furnace and hold for 6 hours. Then roll it 8 times to obtain a bar billet with a diameter of 80mm.

[0041] Step 5: Heat the billet obtained in Step 4 to 700℃ in an electric furnace and heat treat it for 3 hours. Then remove it from the furnace and cool it to obtain a high-strength titanium rod with a diameter of 80mm.

[0042] Testing revealed that the high-strength titanium rod prepared in this embodiment has a tensile strength of 700 MPa and a yield strength of 590 MPa, which are far higher than the national standard requirements. This achieves the performance requirements of low alloying and high strength (the national standard requires a tensile strength of not less than 580 MPa and a yield strength of 485 MPa to 655 MPa).

[0043] Example 3

[0044] This embodiment includes the following steps:

[0045] Step 1: Zero-grade large-particle sponge titanium with a particle size of 0.83mm~25.4mm and alloy element raw materials are mixed evenly in an automatic mixing and spreading machine to obtain a mixture. Then, electrode blocks are prepared using an electrode press, and the electrode blocks are welded in a vacuum welding box to obtain a primary electrode. The mixture is composed of the following elements by mass fraction: Fe 0.32%, O 0.32%, Zr 0.55%, Al 0.35%, with the balance being Ti.

[0046] Step 2: The primary electrode obtained in Step 1 is subjected to three vacuum arc remelting processes in a vacuum arc remelting furnace. The current for the first vacuum arc remelting is 10kA~14kA, the current for the second vacuum arc remelting is 20kA~24kA, and the current for the third vacuum arc remelting is 13kA~17kA, to obtain a low-alloy titanium ingot.

[0047] Step 3: After peeling off the titanium ingot obtained in Step 2 and removing the head and tail, forge the billet at a temperature of 1050℃ and a holding time of 8h. Then, use a high-speed forging machine for upsetting and deformation with a deformation amount of 40%. After that, hold at 950℃ for 3h and remelt. After taking it out of the furnace, draw it again, grind it and remove the surface oxide scale to obtain a square billet with a side length of 190mm.

[0048] Step 4: Heat the square billet obtained in Step 3 to 850℃ in an electric furnace and hold for 5 hours. Then roll it 7 times to obtain a bar billet with a diameter of 100mm.

[0049] Step 5: Heat the billet obtained in Step 4 to 650℃ in an electric furnace and heat treat it for 2.5 hours. Then remove it from the furnace and cool it to obtain a high-strength titanium rod with a diameter of 100mm.

[0050] Testing revealed that the high-strength titanium rod prepared in this embodiment has a tensile strength of 730 MPa and a yield strength of 620 MPa, which are far higher than the national standard requirements. This achieves the performance requirements of low alloying and high strength (the national standard requires a tensile strength of not less than 580 MPa and a yield strength of 485 MPa to 655 MPa).

[0051] Example 4

[0052] This embodiment includes the following steps:

[0053] Step 1: Zero-grade large-particle sponge titanium with a particle size of 0.83mm~25.4mm and alloy element raw materials are mixed evenly in an automatic mixing and spreading machine to obtain a mixture. Then, electrode blocks are prepared using an electrode press, and the electrode blocks are welded in a vacuum welding box to obtain a primary electrode. The mixture is composed of the following elements by mass fraction: Fe 0.31%, O 0.31%, Zr 0.65%, Al 0.35%, with the balance being Ti.

[0054] Step 2: The primary electrode obtained in Step 1 is subjected to three vacuum arc remelting processes in a vacuum arc remelting furnace. The current for the first vacuum arc remelting is 10kA~14kA, the current for the second vacuum arc remelting is 20kA~24kA, and the current for the third vacuum arc remelting is 13kA~17kA, to obtain a low-alloy titanium ingot.

[0055] Step 3: After peeling off the titanium ingot obtained in Step 2 and removing the head and tail, forge the billet at a temperature of 1050℃ for 6 hours. Then, use a high-speed forging machine to upset and deform it by 45%. After that, hold it at 950℃ for 3.5 hours and then remelt it. After taking it out of the furnace, draw it again, grind it and remove the surface oxide scale to obtain a square billet with a side length of 200mm.

[0056] Step 4: Heat the square billet obtained in Step 3 to 850℃ in an electric furnace and hold for 6 hours. Then roll it 8 times to obtain a bar billet with a diameter of 100mm.

[0057] Step 5: Heat the billet obtained in Step 4 to 680℃ in an electric furnace and heat treat for 2 hours. Then remove it from the furnace and cool it to obtain a high-strength titanium rod with a diameter of 100mm.

[0058] Testing revealed that the high-strength titanium rod prepared in this embodiment has a tensile strength of 710 MPa and a yield strength of 595 MPa, which are far higher than the national standard requirements. This achieves the performance requirements of low alloying and high strength (the national standard requires a tensile strength of not less than 580 MPa and a yield strength of 485 MPa to 655 MPa).

[0059] Example 5

[0060] This embodiment includes the following steps:

[0061] Step 1: Zero-grade large-particle sponge titanium with a particle size of 0.83mm~25.4mm and alloy element raw materials are mixed evenly in an automatic mixing and spreading machine to obtain a mixture. Then, electrode blocks are prepared using an electrode press, and the electrode blocks are welded in a vacuum welding box to obtain a primary electrode. The mixture is composed of the following elements by mass fraction: Fe 0.31%, O 0.30%, Zr 0.60%, Al 0.40%, with the balance being Ti.

[0062] Step 2: The primary electrode obtained in Step 1 is subjected to three vacuum arc remelting processes in a vacuum arc remelting furnace. The current for the first vacuum arc remelting is 10kA~14kA, the current for the second vacuum arc remelting is 20kA~24kA, and the current for the third vacuum arc remelting is 13kA~17kA, to obtain a low-alloy titanium ingot.

[0063] Step 3: After peeling off the titanium ingot obtained in Step 2 and removing the head and tail, forge the billet at a temperature of 1050℃ and a holding time of 6.5h. Then, use a high-speed forging machine for upsetting and deformation with a deformation amount of 35%. After that, hold at 950℃ for 2h and remelt. After taking it out of the furnace, draw it again, grind it and remove the surface oxide scale to obtain a square billet with a side length of 200mm.

[0064] Step 4: Heat the square billet obtained in Step 3 to 800℃ in an electric furnace and hold for 4.5 hours. Then roll it 6 times to obtain a bar billet with a diameter of 100mm.

[0065] Step 5: Heat the billet obtained in Step 4 to 600℃ in an electric furnace and heat treat for 3 hours. Then remove it from the furnace and cool it to obtain a high-strength titanium rod with a diameter of 100mm.

[0066] Testing revealed that the high-strength titanium rod prepared in this embodiment has a tensile strength of 735 MPa and a yield strength of 625 MPa, which are far higher than the national standard requirements. This achieves the performance requirements of low alloying and high strength (the national standard requires a tensile strength of not less than 580 MPa and a yield strength of 485 MPa to 655 MPa).

[0067] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A production method for improving the strength of a pure titanium bar, characterized by, The method includes the following steps: Step 1: Mix the zero-grade large-particle sponge titanium and alloy element raw materials evenly in an automatic mixing and spreading machine to obtain a mixture. Then, use an electrode press to prepare electrode blocks, and then weld the electrode blocks in a vacuum welding box to obtain a primary electrode. The mixture is composed of the following elements in mass fraction: Fe 0.29%~0.34%, O 0.29%~0.34%, Zr 0.40%~0.8%, Al 0.15%~0.45%, with the balance being Ti. Step 2: The primary electrode obtained in Step 1 is subjected to three vacuum arc remelting processes in a vacuum arc remelting furnace to obtain a low-alloy titanium ingot; the current for the first vacuum arc remelting process is 10kA~14kA, the current for the second vacuum arc remelting process is 20kA~24kA, and the current for the third vacuum arc remelting process is 13kA~17kA. Step 3: After peeling and removing the head and tail of the titanium ingot obtained in Step 2, forge it into a billet, then upset it, and then remelt it for further drawing, grinding, and removal of surface oxide scale to obtain a square billet. The forging temperature is 1000℃~1050℃, and the holding time is 6h~9h. The upsetting deformation is carried out using a high-speed forging machine, and the deformation amount is 30%~50%. The remelting temperature is 900℃~950℃, and the holding time is 2h~4h. Step 4: Heat the square billet obtained in Step 3 in an electric furnace, and then roll it in multiple passes to obtain a bar billet; the heating temperature is 800℃~850℃, the holding time is 4h~6h, the multiple rolling is 5 passes~8 passes, and the diameter of the bar billet is 80mm~100mm. Step 5: Heat-treat the billet obtained in Step 4 in an electric furnace, then remove it from the furnace and cool it to obtain a high-strength titanium rod; the heat treatment temperature is 600℃~700℃, and the holding time is 2h~3h.

2. The method for improving the strength of a pure titanium bar according to claim 1, wherein The particle size of the zero-grade large-particle sponge titanium mentioned in step one is 0.83mm~25.4mm.

3. The method for preparing a pure titanium rod with improved strength according to claim 1, characterized in that, The side length of the square billet mentioned in step three is 180mm~200mm.