Preparation method for improving strength of pure titanium bar

Abstract

The preparation method for improving the strength of the pure titanium bar comprises the following steps that firstly, zero-order large-particle sponge titanium and alloy element raw materials are mixed, pressed into an electrode block and welded, and a primary electrode is obtained; 2, performing vacuum consumable smelting for the third time to obtain a low-alloying titanium cast ingot; thirdly, cogging forging, upsetting and drawing deformation, remelting and drawing out are conducted, and a square blank is obtained; 4, heating and multi-pass rolling are conducted, and a bar billet is obtained; and 5, carrying out heat treatment, discharging and cooling to obtain the high-strength titanium bar. The low-alloying titanium cast ingot is obtained by properly increasing the content of Fe and O in the smelting process and adding not more than 0.5% of Al and not more than 1% of Zr, and the low-alloying titanium cast ingot is subjected to cogging forging, upsetting and drawing deformation, remelting, drawing, hot rolling and heat treatment in a matched mode, so that the effects that the structure is refined and uniform, and the strength is high are achieved. The tensile strength of the obtained high-strength titanium bar is about 50 MPa or above higher than that of conventional TA4, and batch production is easy to achieve.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of titanium and titanium alloy smelting, forging and rolling processing, and particularly relates to a preparation method for improving the strength of pure titanium bars. BACKGROUND

[0002] Titanium and titanium alloys are widely used in the fields of aviation, aerospace, shipbuilding, chemical industry, petroleum and biomedical science due to their high specific strength, excellent comprehensive mechanical properties, good corrosion resistance and excellent biocompatibility. Among all titanium alloy products, pure titanium products account for about 80%, and the product grades of pure titanium mainly include TA1, TA2, TA3 and TA4. Compared with the commonly used titanium alloys of these grades, the tensile strength is low, and after heat treatment of the existing pure titanium bars, the tensile strength is between 300 MPa and 650 MPa, and the yield strength is between 200 MPa and 550 MPa, which cannot meet the above requirements.

[0003] If some TC4 and TA5 with a large amount of added alloy are used, the production cost of TC4 titanium alloy is increased due to the high alloy content. In the material processing and preparation process, the material deformation is difficult due to the high degree of alloying, and the processing and preparation process is complex and difficult to produce, especially in some CNC environments requiring fine processing, the tool wear is large, and the yield is low. The whole process is complex, low in efficiency, and wasteful in materials, and poor in economy.

[0004] Therefore, there is an urgent need for a preparation method for improving the strength of pure titanium bars. SUMMARY

[0005] The technical problem to be solved by the application is to provide a preparation method for improving the strength of pure titanium bars to solve the above problems of the prior art. The method adds an appropriate amount of low alloying elements during smelting, and high-strength bars are prepared through vacuum consumable smelting, forging and hot rolling. The low alloying element method has the advantages of low production cost, easy deformation, easy processing and small material loss during forging and rolling, so that the tensile strength of the obtained high-strength titanium bar is higher than that of conventional TA4 by more than 50 MPa, and batch production can be easily realized.

[0006] To solve the above technical problems, the technical scheme adopted by the application is as follows: a preparation method for improving the strength of pure titanium bars, characterized in that the method comprises the following steps: Step one, mix the zero-level large-particle titanium sponge and alloy element raw materials uniformly in an automatic mixing machine to obtain a mixture, then prepare an electrode block by using an electrode press, and then weld the electrode block in a vacuum welding box to obtain a primary electrode; the mixture is composed of the following elements with mass fractions: Fe 0.29%~0.34%, O 0.29%~0.34%, Zr 0.40%~0.8%, Al 0.15%~0.45%, and the balance is Ti; Step two, perform three vacuum self-consumption smelting on the primary electrode obtained in step one in a vacuum self-consumption furnace to obtain a low-alloyed titanium ingot; Step three, after peeling and removing the head and tail of the titanium ingot obtained in step two, perform open-die forging, then perform upsetting and drawing deformation, then return to the furnace, then perform elongation, and then polish and remove the surface oxide skin to obtain a square billet; Step four, heat the square billet obtained in step three in an electric furnace, and then perform multi-pass rolling to obtain a rod blank; Step five, heat treat the rod blank obtained in step four in an electric furnace, and then cool it after being discharged from the furnace to obtain a high-strength titanium rod.

[0007] The present application controls the composition of the mixture, quantitatively controls the alloy element raw materials, appropriately increases the content of Fe and O in the mixture, and adds not more than 0.5% Al and not more than 1% Zr, thereby realizing low alloying, laying a metallurgical foundation for improving the performance of the titanium rod, and strengthening the mechanism. Aluminum, as a typical alpha stabilizing element, can form a continuous solid solution alpha phase with titanium. Due to the slight difference between the atomic radius of aluminum (0.143 nm) and the atomic radius of titanium (0.147 nm), when aluminum atoms replace titanium atoms into the lattice, lattice distortion will be caused, which will hinder dislocation movement. This solid solution strengthening effect can significantly improve the room temperature and medium temperature strength of the titanium rod, which is one of the core mechanisms for realizing high strength of the titanium rod. However, excessive addition of aluminum will lead to subsequent difficult processing. Oxygen atoms can interstitially dissolve in the titanium lattice to form a solid solution strengthening effect. When oxygen atoms enter the interstitial space of the titanium lattice, the lattice will be distorted, increasing the resistance to dislocation movement and thus improving the strength of the titanium rod. Zirconium improves the strength of the titanium rod through solid solution strengthening. Unlike oxygen and other elements, zirconium has little effect on the plasticity and toughness of the titanium rod while improving the strength, which can better balance the strength and plasticity of the titanium rod. This makes the titanium rod containing zirconium have high strength while still maintaining good processing performance and toughness. Iron improves the strength of the titanium rod through solid solution strengthening and precipitation strengthening. Compared with other alloy elements, iron is relatively inexpensive. The four elements work together to improve the performance of the titanium rod.

[0008] The above-mentioned method for improving the strength of pure titanium rod, wherein the particle size of the zero-level large-particle titanium sponge in step one is 0.83mm~25.4mm.

[0009] The preparation method for improving the strength of pure titanium rod material has the characteristics that the current of the first vacuum self-consumption smelting in the third vacuum self-consumption smelting is 10kA-14kA, the current of the second vacuum self-consumption smelting is 20kA-24kA, and the current of the third vacuum self-consumption smelting is 13kA-17kA. The low alloy element composition of the titanium ingot is uniform through the three times of vacuum self-consumption smelting, and the gas element impurities are removed, so that the material purity is improved. The reason for setting the three current ranges is that the first ingot size is small, so a small current range is suitable; the second ingot size is increased, so the current is increased; and the third ingot size is further increased, so the current is appropriately reduced to make the composition more uniform and play a synergistic effect.

[0010] The preparation method for improving the strength of pure titanium rod material has the characteristics that the temperature of the open forging in the third step is 1000-1050℃, and the holding time is 6-9h. The coarse grains are fully broken through the control of the open forging parameters and the addition of the low-content alloying elements, so that the material organization is uniform, and the strength, toughness and plasticity of the material are improved, and the material is not easy to crack, so that the production and processing costs and the loss are reduced.

[0011] The preparation method for improving the strength of pure titanium rod material has the characteristics that the upsetting and drawing deformation is performed by a fast forging machine, and the deformation amount is 30%-50%. The coarse grains are fully broken through the control of the upsetting and drawing parameters and the addition of the low-content alloying elements, so that the material organization is uniform, and the strength, toughness and plasticity of the material are improved.

[0012] The preparation method for improving the strength of pure titanium rod material has the characteristics that the temperature of the open forging in the third step is 1000-1050℃, and the holding time is 6-9h. The coarse grains are fully broken through the control of the open forging parameters and the addition of the low-content alloying elements, so that the material organization is uniform, and the strength, toughness and plasticity of the material are improved, and the material is not easy to crack, so that the production and processing costs and the loss are reduced.

[0013] The preparation method for improving the strength of pure titanium rod material has the characteristics that the temperature of the open forging in the third step is 1000-1050℃, and the holding time is 6-9h. The coarse grains are fully broken through the control of the open forging parameters and the addition of the low-content alloying elements, so that the material organization is uniform, and the strength, toughness and plasticity of the material are improved, and the material is not easy to crack, so that the production and processing costs and the loss are reduced.

[0014] The preparation method for improving the strength of pure titanium rod material has the characteristics that the heating temperature in the step four is 800-850 DEG C, the holding time is 4-6 hours, the multi-pass rolling is 5-8 passes, and the diameter of the rod blank is 80-100 mm. The low-content alloying element is added in the preparation method, so that the material has a low phase transition point. The parameters of the multi-pass rolling are controlled, so that the rolling temperature is reduced by 50 DEG C, the rolling passes are reduced by 1-2 passes, and the rod blank with excellent performance is obtained.

[0015] The preparation method for improving the strength of pure titanium rod material has the characteristics that the heating temperature in the step four is 800-850 DEG C, the holding time is 4-6 hours, the multi-pass rolling is 5-8 passes, and the diameter of the rod blank is 80-100 mm. The low-content alloying element is added in the preparation method, so that the material has a low phase transition point. The parameters of the multi-pass rolling are controlled, so that the rolling temperature is reduced by 50 DEG C, the rolling passes are reduced by 1-2 passes, and the rod blank with excellent performance is obtained.

[0016] Compared with the prior art, the preparation method for improving the strength of pure titanium rod material has the following advantages: 1. The low-alloying element is added in the smelting process, the high-strength titanium rod material is prepared through vacuum consumable smelting, forging and hot rolling, the low-alloying element has the advantages of low production cost, easy deformation, easy processing and small material loss in the forging and rolling process, the composition is uniform and impurities are removed through vacuum consumable smelting, large grains are broken through open-die forging, and the structure is refined and uniform through hot rolling and heat treatment, so that the tensile strength of the obtained high-strength titanium rod material is higher than that of conventional TA4 by more than 50 MPa, and batch production is easy to realize.

[0017] 2. The strength is improved by appropriately increasing Fe and O, and adding not more than 0.5% of Al and not more than 1% of Zr, and the raw material has the advantage of low cost compared with other titanium alloys.

[0018] 3. The high-strength titanium rod material prepared in the preparation method has low alloy element content compared with other titanium alloys, the open-die forging temperature is 1050 DEG C, which is 100 DEG C lower than the conventional titanium alloy, the energy consumption is low, the production cost is reduced, and the surface is not easy to crack and the material loss is small.

[0019] 4. The high-strength titanium rod material prepared in the preparation method has the advantages of low production cost, reduced rolling temperature and heat treatment temperature by about 50 DEG C, and reduced rolling passes by 1-2 passes compared with other titanium alloys.

[0020] The technical solutions of the present application will be further described in detail through the following examples. DETAILED DESCRIPTION

[0021] Example 1 The embodiment comprises the following steps: Step one, mix the zero-level large-particle titanium sponge with a particle size of 0.83mm~25.4mm and alloy element raw materials uniformly in an automatic mixing and distributing machine to obtain a mixed material, then prepare an electrode block by using an electrode press, and then weld the electrode block in a vacuum welding box to obtain a primary electrode; the mixed material is composed of the following elements with mass fractions: Fe 0.29%, O 0.29%, Zr 0.8%, Al 0.45%, and the balance being Ti; Step two, perform three times of vacuum self-consumption smelting on the primary electrode obtained in step one in a vacuum self-consumption furnace, wherein the current of the first time of vacuum self-consumption smelting is 10kA~14kA, the current of the second time of vacuum self-consumption smelting is 20kA~24kA, and the current of the third time of vacuum self-consumption smelting is 13kA~17kA, to obtain a low-alloyed titanium ingot; Step three, after peeling and removing the head and tail of the titanium ingot obtained in step two, perform open-die forging at a temperature of 1050℃ with a holding time of 6h, then perform upsetting and drawing deformation by using a fast forging machine with a deformation amount of 30%, and then perform re-melting at 950℃ for 2h, then perform elongation after discharging, and then polish and remove the surface oxide skin to obtain a square billet with a side length of 200mm; Step four, heat the square billet obtained in step three to 800℃ in an electric furnace and keep it for 4h, and then roll it for 5 times to obtain a rod blank with a diameter of 100mm; Step five, heat the rod blank obtained in step four to 600℃ in an electric furnace and perform heat treatment for 2h, and then cool it after discharging to obtain a high-strength titanium rod with a diameter of 100mm.

[0022] After detection, the high-strength titanium rod prepared in the embodiment has a tensile strength of 750MPa and a yield strength of 630MPa, which is much higher than the required value of the national standard, and realizes the performance requirements of low alloying and high strength (the national standard requires that the tensile strength be not less than 580MPa and the yield strength be 485MPa~655MPa).

[0023] Embodiment 2 The embodiment comprises the following steps: Step one, mix the zero-level large-particle titanium sponge with a particle size of 0.83mm~25.4mm and alloy element raw materials uniformly in an automatic mixing and distributing machine to obtain a mixed material, then prepare an electrode block by using an electrode press, and then weld the electrode block in a vacuum welding box to obtain a primary electrode; the mixed material is composed of the following elements with mass fractions: Fe 0.29%, O 0.29%, Zr 0.8%, Al 0.45%, and the balance being Ti; Step 2: The primary electrode obtained in step 1 is subjected to three vacuum consumable melting in a vacuum consumable furnace, wherein the current of the first vacuum consumable melting is 10kA~14kA, the current of the second vacuum consumable melting is 20kA~24kA, and the current of the third vacuum consumable melting is 13kA~17kA, to obtain a low-alloyed titanium ingot; Step 3: The titanium ingot obtained in step 2 is peeled and the head and tail are removed, and then the billet is forged. The billet forging temperature is 1000°C, the holding time is 9 hours, and then a fast forging machine is used for upsetting deformation, and the deformation amount is 50%. After that, the billet is kept at 900°C for 4 hours and then returned to the furnace. After being taken out of the furnace, it is stretched and polished and the surface oxide scale is removed to obtain a square billet with a side length of 180 mm; Step 4: Heat the square billet obtained in step 3 to 850°C in an electric furnace and keep it at this temperature for 6 hours, then roll it 8 times to obtain a bar billet with a diameter of 80 mm; Step 5: Heat the rod blank obtained in step 4 to 700°C in an electric furnace and heat treat it for 3 hours, then take it out of the furnace and cool it to obtain a high-strength titanium rod with a diameter of 80 mm.

[0024] After testing, 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 much higher than the national standard requirements, and 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~655 MPa).

[0025] Example 3 This embodiment includes the following steps: Step 1: Mixing zero-grade large-particle titanium sponge with a particle size of 0.83 mm to 25.4 mm and alloy element raw materials in an automatic mixer to obtain a mixture, then preparing it into an electrode block using an electrode press, and then welding the electrode block in a vacuum welding box to obtain a primary electrode; the mixture consists of the following elements by mass fraction: Fe 0.32%, O 0.32%, Zr 0.55%, Al 0.35%, and the balance Ti; Step 2: The primary electrode obtained in step 1 is subjected to three vacuum consumable melting in a vacuum consumable furnace, wherein the current of the first vacuum consumable melting is 10kA~14kA, the current of the second vacuum consumable melting is 20kA~24kA, and the current of the third vacuum consumable melting is 13kA~17kA, to obtain a low-alloyed titanium ingot; Step 3: The titanium ingot obtained in step 2 is peeled and the head and tail are removed, and then the billet is forged. The billet forging temperature is 1050°C, the holding time is 8 hours, and then a fast forging machine is used for upsetting deformation, and the deformation amount is 40%. After that, it is kept at 950°C for 3 hours and then returned to the furnace. After being taken out of the furnace, it is stretched and polished and the surface oxide scale is removed to obtain a square billet with a side length of 190 mm; Step four, the billet obtained in step three is heated to 850 DEG C in an electric furnace and kept for 5h, and then rolled for 7 passes to obtain a rod with a diameter of 100mm; Step five, the rod obtained in step four is heated to 650 DEG C in an electric furnace and heat treated for 2.5h, and then discharged and cooled to obtain a high-strength titanium rod with a diameter of 100mm.

[0026] It is detected that the high-strength titanium rod prepared in the embodiment has a tensile strength of 730MPa and a yield strength of 620MPa, which is much higher than the required value of the national standard, and the performance requirements of low alloying and high strength are achieved (the national standard requires that the tensile strength is not less than 580MPa and the yield strength is 485MPa~655MPa).

[0027] Example 4 The embodiment includes the following steps: Step one, the zero-level large-particle sponge titanium with a particle size of 0.83mm~25.4mm and alloying element raw materials are uniformly mixed in an automatic mixing and batching machine to obtain a mixed material, and then an electrode block is prepared by using an electrode press, and the electrode block is welded in a vacuum welding box to obtain a primary electrode; the mixed material is composed of the following elements with mass fractions: Fe 0.31%, O 0.31%, Zr 0.65%, Al 0.35%, and the balance is Ti; Step two, the primary electrode obtained in step one is subjected to three times of vacuum consumable smelting in a vacuum consumable furnace, wherein the current of the first vacuum consumable smelting is 10kA~14kA, the current of the second vacuum consumable smelting is 20kA~24kA, and the current of the third vacuum consumable smelting is 13kA~17kA, to obtain a low-alloyed titanium ingot; Step three, the titanium ingot obtained in step two is peeled and the head and tail are removed, and then is subjected to cogging forging at a temperature of 1050 DEG C and a holding time of 6h, and then is subjected to upsetting and drawing deformation by using a fast forging machine, and the deformation amount is 45%, and then is subjected to re-melting at 950 DEG C for 3.5h, and then is subjected to lengthening, polishing and removing the surface oxide skin after discharging, to obtain a square billet with a side length of 200mm; Step four, the square billet obtained in step three is heated to 850 DEG C in an electric furnace and kept for 6h, and then rolled for 8 passes to obtain a rod with a diameter of 100mm; Step five, the rod obtained in step four is heated to 680 DEG C in an electric furnace and heat treated for 2h, and then discharged and cooled to obtain a high-strength titanium rod with a diameter of 100mm.

[0028] The high-strength titanium rod prepared in the embodiment is detected to have a tensile strength of 710 MPa and a yield strength of 595 MPa, which are much higher than the required values in the national standard, and the performance requirements of low alloying and high strength are achieved (the national standard requires that the tensile strength is not less than 580 MPa and the yield strength is 485 MPa to 655 MPa).

[0029] Embodiment 5 The embodiment comprises the following steps: Step one, uniformly mix zero-level large-particle sponge titanium with a particle size of 0.83 mm to 25.4 mm and alloy element raw materials in an automatic mixing and distributing machine to obtain a mixed material, then prepare an electrode block by using an electrode press, and then weld the electrode block in a vacuum welding box to obtain a primary electrode; the mixed material is composed of the following elements in mass fraction: Fe 0.31%, O 0.30%, Zr 0.60%, Al 0.40%, and the balance is Ti; Step two, perform three times of vacuum self-consumption smelting on the primary electrode obtained in step one in a vacuum self-consumption furnace, wherein the current of the first time of vacuum self-consumption smelting is 10 kA to 14 kA, the current of the second time of vacuum self-consumption smelting is 20 kA to 24 kA, and the current of the third time of vacuum self-consumption smelting is 13 kA to 17 kA, to obtain a low-alloyed titanium ingot; Step three, after peeling and removing the head and tail of the titanium ingot obtained in step two, perform open-die forging at a temperature of 1050°C for 6.5 h, then perform upsetting and drawing deformation by using a fast forging machine, and the deformation amount is 35%, then perform re-melting at 950°C for 2 h, then perform elongation after discharging, and then polish and remove the surface oxide skin to obtain a square billet with a side length of 200 mm; Step four, heat the square billet obtained in step three to 800°C in an electric furnace and keep the temperature for 4.5 h, then perform rolling for 6 passes to obtain a rod blank with a diameter of 100 mm; Step five, heat the rod blank obtained in step four to 600°C in an electric furnace and perform heat treatment for 3 h, then discharge and cool to obtain a high-strength titanium rod with a diameter of 100 mm.

[0030] The high-strength titanium rod prepared in the embodiment is detected to have a tensile strength of 735 MPa and a yield strength of 625 MPa, which are much higher than the required values in the national standard, and the performance requirements of low alloying and high strength are achieved (the national standard requires that the tensile strength is not less than 580 MPa and the yield strength is 485 MPa to 655 MPa).

[0031] The above is only a preferred embodiment of the present application, and does not limit the present application in any way. Any simple modification, change and equivalent change made according to the technical essence of the present application to the above embodiment are still within the protection scope of the technical solution of the present application.

Claims

1. A method for improving the strength of pure titanium rods, characterized in that: The method comprises the following steps: Step 1: Mix the zero-grade large-particle titanium sponge and the alloy element raw materials in an automatic mixing machine to obtain a mixture, then use an electrode press to prepare an electrode block, and then weld the electrode block in a vacuum welding box to obtain a primary electrode; the mixture is composed of the following elements by mass fraction: Fe 0.29%~0.34%, O 0.29%~0.34%, Zr 0.40%~0.8%, Al0.15%~0.45%, and the balance is Ti; Step 2: The primary electrode obtained in step 1 is subjected to vacuum consumable melting three times in a vacuum consumable furnace to obtain a low-alloyed titanium ingot; Step 3: The titanium ingot obtained in step 2 is peeled and the head and tail are removed, and then the billet is forged, and then upsetting and deforming is performed, and then the billet is returned to the furnace, and then the billet is stretched, polished and the surface oxide scale is removed to obtain a square billet; Step 4: heating the square billet obtained in step 3 in an electric furnace, and then rolling it through multiple passes to obtain a bar billet; Step 5: heat-treat the rod blank obtained in step 4 in an electric furnace, then take it out of the furnace and cool it to obtain a high-strength titanium rod.

2. A preparation method for improving the strength of pure titanium rod according to claim 1, characterized in that: The particle size of the zero-grade large-particle titanium sponge described in step 1 is 0.83 mm to 25.4 mm.

3. The method for preparing a pure titanium rod for improving strength according to claim 1, characterized in that: In the three vacuum consumable melting processes in step 2, the current of the first vacuum consumable melting process is 10kA-14kA, the current of the second vacuum consumable melting process is 20kA-24kA, and the current of the third vacuum consumable melting process is 13kA-17kA.

4. The method for preparing a pure titanium rod for improving its strength according to claim 1, characterized in that: The temperature of the blank forging in step 3 is 1000° C. to 1050° C., and the holding time is 6 h to 9 h.

5. The method for preparing a pure titanium rod for improving its strength according to claim 1, characterized in that: The upsetting deformation in step 3 is performed using a fast forging machine, and the deformation amount is 30% to 50%.

6. The method for improving the strength of pure titanium rod according to claim 1, characterized in that: The temperature of the furnace in step 3 is 900° C. to 950° C., and the holding time is 2 h to 4 h.

7. The method for preparing a pure titanium rod for improving its strength according to claim 1, characterized in that: The side length of the square billet in step 3 is 180mm~200mm.

8. The method for improving the strength of pure titanium rod according to claim 1, characterized in that: The heating temperature in step 4 is 800° C. to 850° C., the holding time is 4 h to 6 h, the multi-pass rolling is 5 to 8 passes, and the diameter of the rod blank is 80 mm to 100 mm.

9. The method for preparing a pure titanium rod for improving its strength according to claim 1, characterized in that: The heat treatment temperature in step 5 is 600° C. to 700° C., and the holding time is 2 h to 3 h.