Preparation method of titanium product

Abstract

The invention relates to a preparation method of a titanium product. The preparation method is characterized by comprising the following steps that S1, iron powder and titanium dioxide powder are evenly mixed and then smelted in a vacuum consumable electric arc furnace, and a square titanium plate blank is obtained; s2, the titanium plate blank is placed in an electric heating furnace to be heated, and then hot rolling is conducted; s3, the hot-rolled titanium material is placed in a continuous annealing furnace to be annealed and then subjected to acid pickling; s4, the titanium material is rolled through a twenty-roller single-rack reversible rolling mill; s5, the rolling oil attached to the surface of the titanium material is removed thoroughly through alkali liquor; s6, the titanium material is placed in a vacuum bell-type furnace, and annealing is conducted under argon protection; and S7, a stainless steel two-roller type temper mill is used for leveling the titanium material for two passes, a leveling working roller with the corresponding surface roughness and convexity is adopted for treatment in each pass, and finally a finished product plate is obtained. The stainless steel two-roller type temper mill is adopted for machining the titanium material, intermittent production can be achieved, the welding problem of the titanium material and stainless steel is avoided, meanwhile, various technical indexes of the titanium material product meet the requirements, and the quality is high.

Description

Technical Field

[0001] The present invention relates to the technical field of titanium material production and processing, and in particular to a method for preparing a titanium material product. Background Art

[0002] Titanium has been widely used in chemical, aviation and medical fields due to its advantages such as high specific strength, high toughness, high corrosion resistance and low elastic modulus. Usually, titanium is produced by hot rolling and cold rolling after vacuum casting. Plates above 3mm are produced by single plate hot rolling, while plates below 3mm are produced by coil cold rolling. Conventional titanium cold-rolled products mainly include pure titanium steel grades such as TA1. The thickness of the product is usually 0.3mm to 2.5mm. The usual production process is: titanium vacuum melting → slab hot rolling → hot rolled coil annealing and pickling → cold rolling → cold coil annealing → stretch bending and straightening machine → finished product delivery.

[0003] For example, a Chinese invention patent with patent number ZL201610381450.9 (publication number CN106011714B), "Method for producing thin TA4 titanium materials by coil cold rolling," discloses a titanium production method in which finished titanium coils with a thickness of less than 1 mm are annealed in a vacuum bell furnace, followed by flattening and straightening, and then slit into plates and strips. For finished titanium coils with a thickness of 1 to 3 mm, vacuum bell furnace annealing combined with flattening and straightening can be used to obtain titanium sheet strips. Alternatively, the finished product can be cold-rolled and then slit into suitable specifications for atmospheric annealing, followed by alkaline pickling or sandblasting pickling to obtain the finished product. Flattening and straightening of the titanium material requires the use of a stretch-bend straightening machine unit, which corrects the plate shape to achieve the desired effect. However, for stainless steel cold-rolled manufacturers, using a straightening machine to improve plate shape can only be done during continuous production. At this time, titanium and stainless steel must be welded together. However, the steel properties of titanium and stainless steel are very different, and the two cannot be directly welded, which cannot meet production requirements. At the same time, the straightening machine's performance control, plate shape correction, and surface roughness control effects on titanium are subject to many limitations.

[0004] Therefore, it is necessary to further improve the preparation method of titanium products. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing a titanium product that can avoid welding of titanium and stainless steel and can simultaneously achieve performance control, plate shape correction and surface roughness control in response to the above-mentioned existing technical status.

[0006] The technical solution adopted by the present invention to solve the above technical problems is: a method for preparing the titanium product, characterized in that it comprises the following steps:

[0007] S1. Vacuum melting: Iron powder and titanium dioxide powder with a purity of more than 99% are uniformly mixed and then pressed into electrodes, which are then vacuum welded. A vacuum consumable arc furnace is used for melting more than twice, and a square titanium slab is obtained after vacuum casting.

[0008] S2. Hot rolling: placing the titanium slab in an electric heating furnace and heating it to 850° C. to 900° C.;

[0009] S3, annealing and pickling: placing the hot-rolled titanium black hot coil in a continuous annealing furnace for annealing, and then pickling;

[0010] S4, rolling: rolling the titanium material using a 20-high single-stand reversing rolling mill until the titanium material is rolled to a thickness of 0.5 mm to 2 mm;

[0011] S5, degreasing: using alkali solution with a concentration of 3% to 10% to remove the rolling oil attached to the surface of the titanium material;

[0012] S6, annealing: placing the titanium material in a vacuum bell furnace at 500° C. to 700° C. for annealing, with argon gas as a protective gas in the vacuum bell furnace;

[0013] S7. Leveling: Using a stainless steel two-roller leveling machine, the titanium material is leveled in two passes, each pass being processed using leveling work rolls with different surface roughness and convexity, and finally a finished plate is obtained.

[0014] Furthermore, the chemical composition percentages of the titanium material in step S3 are: ≤0.1wt% C, ≤0.25wt% Fe, ≤0.03wt% N, ≤0.015wt% H, ≤0.20wt% O, and the remainder: Ti and impurities.

[0015] To meet process requirements, the thickness of the square titanium slab after vacuum casting in step S1 is preferably 180 mm to 250 mm. The titanium slab will subsequently undergo hot rolling and other processes, and processing it to 3 mm to 5 mm can meet the process requirements of post-annealing, pickling, cold rolling, and smoothing.

[0016] In order to remove the oxide layer on the surface of the titanium material, preferably, acid solution is used for pickling in step S3, and the acid solution includes nitric acid and hydrofluoric acid, the concentration of the nitric acid is 50g / L to 150g / L; the concentration of the hydrofluoric acid is 2g / L to 12g / L. Among them, a dense oxide layer will be formed on the surface of the titanium material during the hot rolling process, hydrofluoric acid can effectively dissolve titanium oxide and titanium matrix, and the oxidizing property of nitric acid can promote the passivation of the titanium surface, reducing the penetration of hydrogen atoms when hydrofluoric acid reacts with titanium, thereby reducing the risk of hydrogen embrittlement. When the concentration of nitric acid is lower than 50g / L, nitric acid cannot effectively inhibit the excessive corrosion of hydrofluoric acid on the titanium matrix, increasing the risk of hydrogen embrittlement; when the concentration of nitric acid is higher than 150g / L, the oxidizing property of nitric acid is too strong, and a too thick passivation film is generated on the titanium surface, hindering the subsequent pickling reaction; when the concentration of hydrofluoric acid is lower than 2g / L, it is difficult to effectively remove the oxide layer on the titanium surface, prolonging the pickling time and reducing production efficiency; when the concentration of hydrofluoric acid is higher than 12g / L, it will cause the titanium to dissolve too quickly, resulting in excessive corrosion of the titanium surface.

[0017] In order to remove the rolling oil and pollutants remaining on the surface of the titanium material, it is preferred that the concentration of the alkali solution in step S5 is 3% to 10%, and the alkali solution contains a small amount of potassium hydroxide. Among them, potassium hydroxide has a strong alkalinity and can emulsify stubborn grease and synthetic lubricants. When the concentration of the alkali solution is lower than 3%, the saponification reaction is incomplete and the emulsification ability of the alkali solution is weak. On the one hand, it is difficult to completely remove the synthetic lubricant or silicone oil on the surface of the titanium material, resulting in a decrease in subsequent rolling or coating adhesion; on the other hand, the residual mineral oil may form an oil film, which hinders the contact between the alkali solution and the oxide layer and increases the alkali washing time; when the concentration of the alkali solution is higher than 10%, the high concentration of potassium hydroxide will corrode the titanium matrix and cause surface micro-pits, and affect subsequent cold rolling. At the same time, the high concentration of potassium hydroxide increases the preparation cost. At this time, the alkali solution concentration of 3% to 10% is moderate and can effectively saponify grease and emulsify pollutants such as mineral oil and rolling oil.

[0018] To correct the shape of the titanium plate, the stainless steel two-roll skin-pass mill in step S7 preferably includes working rolls spaced apart from each other, with a gap between the working rolls for the titanium material to pass through. The working rolls have a diameter of 700 mm to 860 mm. A decoiler is provided at one end of the stainless steel two-roll skin-pass mill, and a coiler is provided at the other end. An entry guide roll is provided between the decoiler and the working rolls, and an exit guide roll is provided between the coiler and the working rolls. The working rolls on the stainless steel two-roll skin-pass mill apply rolling force to the titanium material, thereby correcting its flatness. When the working roll diameter is less than 700 mm, the contact area of ​​the rolls is small, and the rolls are prone to flattening due to insufficient rigidity. When the working roll diameter is greater than 860 mm, the excessive diameter increases the cost of the equipment, and the deformation penetration of the rolls is poor, making it difficult to effectively transmit the rolling force to the center layer of the titanium material.

[0019] In order to perform macroscopic correction on the plate shape of the titanium material, preferably, the stainless steel two-roller leveling machine in step S7 uses a working roll with a surface roughness Ra of ≤0.05μm and a convexity of 0.25-0.3mm in the first pass, the unwinding tension of the stainless steel two-roller leveling machine is ≤10 tons, the leveling speed is ≤100mpm, and the elongation of the titanium material is ≥0.2%. Among them, the surface roughness of the rolling roller Ra≤0.05μm, mainly to ensure that the titanium surface has a matte effect; due to the large fluctuations in the initial plate shape of the titanium material, the use of a rolling roller with a large convexity of 0.25mm~0.3mm can offset the flexural deformation of the rolling roller under high pressure, ensure that the rolling force is evenly distributed, and avoid local overpressure or underpressure; the first pass of the titanium material is annealed in a vacuum bell furnace, and the titanium layers are easy to adhere to each other, so the unwinding tension needs to be controlled at ≤10 tons to prevent tearing damage; the leveling speed of the stainless steel two-roller leveling mill is maintained at a low speed of ≤100mpm to ensure the stability of the plate shape correction; the elongation is ≥0.2% to activate plastic deformation.

[0020] In order to fine-tune the plate shape of the titanium material, preferably, the stainless steel two-roller leveling machine in step S7 uses a working roll with a surface roughness Ra of ≤0.05μm and a convexity of 0.1mm~0.15mm in the second pass, the unwinding tension of the stainless steel two-roller leveling machine is ≤15 tons, the leveling speed is ≤200mpm, and the elongation of the titanium material is ≥0.1%. Among them, the surface roughness of the rolling mill roller is Ra≤0.05μm, which is mainly to ensure that the titanium surface has a matte effect; after the first correction, the titanium material basically reaches the preset flatness. At this time, the use of a working roller with a small crown can finely adjust the residual stress distribution; in addition, the titanium plate shape of the second pass is relatively stable, so the unwinding tension is increased to ≤15 tons to improve the control accuracy; at the same time, the flattening speed of the equipment is increased to ≤200mpm, the purpose of which is to ensure a certain production efficiency through high speed; the elongation of the titanium material drops to ≥0.1%, mainly because: after the first pass, the titanium material has undergone partial work hardening, and maintaining a small elongation can avoid large deformation, thereby facilitating fine-tuning.

[0021] Compared with the prior art, the advantages of the present invention are:

[0022] 1. The preparation method of this application uses a stainless steel two-roller leveling mill to process titanium materials, which can achieve intermittent production and avoid the welding problem between titanium and stainless steel. It has strong production feasibility, reasonable process and easy operation.

[0023] 2. The use of a stainless steel two-roller leveling mill to process titanium materials can simultaneously meet the requirements of titanium material performance control, plate shape correction and surface roughness control. The technical indicators of the prepared titanium products meet the requirements and are of high quality. They can be used in high-end industries and fields such as marine engineering and heat exchangers. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the three-dimensional structure of a stainless steel two-roller skin-pass mill in an embodiment of the invention.

[0025] In the figure: 1. Working roller; 2. Entry guide roller; 3. Exit guide roller; 4. Uncoiler; 5. Coiler. DETAILED DESCRIPTION

[0026] The present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

[0027] Example 1:

[0028] like Figure 1 The method for preparing the titanium product is characterized by comprising the following steps:

[0029] S1. Vacuum melting: Iron powder and titanium dioxide powder with a purity of more than 99% are uniformly mixed and then pressed into electrodes, which are then vacuum welded. A vacuum consumable arc furnace is used for melting more than twice, and a square titanium slab is obtained after vacuum casting.

[0030] S2. Hot rolling: The titanium slab is placed in an electric heating furnace and heated to 850℃~900℃, usually rolled to 3.0mm~5.0mm;

[0031] S3, annealing and pickling: placing the hot-rolled titanium black hot coil in a continuous annealing furnace for annealing, followed by pickling;

[0032] S4. Rolling: Rolling the titanium material using a 20-high single-stand reversing rolling mill until the thickness of the titanium material is rolled to 0.5 mm to 2 mm;

[0033] S5. Degreasing: Use 3% to 10% alkali solution to remove the rolling oil attached to the surface of the titanium material;

[0034] S6. Annealing: annealing the titanium material in a vacuum bell furnace at 500°C to 700°C, with argon gas introduced into the vacuum bell furnace as a protective gas;

[0035] S7. Leveling: Use a stainless steel two-roller leveling machine to level the titanium material in two passes. Each pass is processed using a leveling work roll 1 with different surface roughness and convexity, and finally a finished plate is obtained.

[0036] The chemical composition of the titanium material in this embodiment is shown in Table 1:

[0037] Table 1: Chemical composition of titanium materials (wt%)

[0038]

[0039] The titanium slab will subsequently undergo multiple processes such as hot rolling, rolling and cold rolling. In order to meet the process requirements, this embodiment hot rolls the titanium slab to 4 mm. At this time, the thickness of the titanium slab is moderate, and the difficulty of controlling the plate shape is moderate. At the same time, the rolling force requirements of the rolling mill are also within a reasonable range.

[0040] During the hot rolling process, a dense oxide layer will form on the surface of the titanium material. The acid solution in this embodiment includes nitric acid and hydrofluoric acid. Hydrofluoric acid can effectively dissolve titanium oxide and titanium matrix. The oxidizing property of nitric acid can promote the passivation of the titanium surface and reduce the penetration of hydrogen atoms when hydrofluoric acid reacts with titanium, thereby reducing the risk of hydrogen embrittlement. The concentration of nitric acid is preferably 100 g / L, and the concentration of hydrofluoric acid is preferably 7 g / L. Nitric acid and hydrofluoric acid under this mixing ratio can effectively clean the oxide layer.

[0041] After rolling, contaminants such as rolling oil remain on the surface of titanium materials. If not cleaned promptly, hydrogen atoms in the rolling oil may penetrate the titanium grain boundaries during vacuum bell furnace annealing, causing delayed hydrogen embrittlement fracture. In this embodiment, the preferred alkali solution concentration is 6%, and the alkali solution contains potassium hydroxide. This moderate alkali solution concentration effectively saponifies grease and emulsifies contaminants such as rolling oil. This avoids the difficulty of completely removing rolling oil from the titanium surface due to low concentrations, which could lead to quality defects on the titanium surface during subsequent vacuum bell furnace annealing. It also prevents corrosion of the titanium substrate due to high concentrations, which could cause surface micropitting and affect subsequent surface quality control.

[0042] refer to Figure 1 In step S7 of this embodiment, a stainless steel two-roller skin-pass mill is used to correct the shape of the titanium plate. The stainless steel two-roller skin-pass mill includes working rolls 1 spaced apart in an upper and lower manner. A gap is provided between the working rolls 1 for the titanium material to pass through. The roll diameter of the working roll 1 is preferably 780 mm. At this time, the working roll 1 is relatively rigid and not easily flattened. At the same time, the rolling force can be effectively transmitted to the center layer of the titanium material. In addition, an uncoiler 4 is provided at one end of the stainless steel two-roller skin-pass mill, and a coiler 5 is provided at the other end. An entrance guide roll 2 is provided between the uncoiler 4 and the working roll 1, and an exit guide roll 3 is provided between the coiler 5 and the working roll 1.

[0043] Refer to Table 2, which shows the performance comparison between the conventional bending leveler and the stainless steel two-roller skin-pass mill in this embodiment:

[0044] Table 2: Equipment comparison between the tension and bending leveling unit and the stainless steel two-roller skin-pass mill

[0045]

[0046] The stainless steel two-roller leveler in this embodiment uses two passes to correct the titanium material, wherein the main purpose of the first pass is to make macro corrections to the plate, and the main purpose of the second pass is to fine-tune the shape of the titanium plate. Specifically, the stainless steel two-roller leveler in step S7 uses a working roll 1 with a surface roughness Ra of ≤0.05μm and a convexity of 0.25-0.3mm in the first pass. The unwinding tension of the stainless steel two-roller leveler is 8 tons, the leveling speed is ≤80mpm, the titanium material elongation is 0.35%, and the surface roughness Ra of the roll is ≤0.0 5μm, mainly to ensure that the titanium surface has a matte effect; due to the large fluctuations in the initial plate shape of titanium, the use of a roller with a large crown of 0.25 to 0.3mm can offset the flexural deformation of the roller under high pressure, ensure that the rolling force is evenly distributed, and avoid local overpressure or underpressure; the first pass of titanium material has high surface activity and the titanium layers are easy to adhere to each other, so the unwinding tension needs to be controlled at 8 tons to prevent tearing damage; the leveling speed of the stainless steel two-roller leveling mill is maintained at a low speed of ≤80mpm to ensure the stability of the plate shape correction; the elongation is 0.35% to activate plastic deformation.

[0047] The stainless steel two-roller leveling mill in step S7 uses a working roll 1 with a surface roughness Ra of ≤0.05μm and a crown of 0.1~0.15mm in the second pass. The uncoiling tension of the stainless steel two-roller leveling mill is 15 tons, the leveling speed is ≤150mpm, and the elongation of the titanium material is 0.2%. The surface roughness Ra of the rolling roll is ≤0.05μm, which is mainly to ensure that the titanium surface has a matte effect; after the correction of the first pass, the titanium material basically reaches the preset flatness. At this time, the use of a working roll 1 with a small crown can finely adjust the residual stress distribution; in addition, the titanium plate shape of the second pass is relatively stable, so the uncoiling tension is increased to 15 tons to improve the control accuracy; at the same time, the leveling speed of the equipment is increased to ≤150mpm, the purpose of which is to ensure a certain production efficiency through high speed; the elongation of the titanium material drops to 0.2%, mainly considering that after the first pass, the titanium material has undergone partial work hardening, and maintaining a small elongation can avoid large deformation, thereby facilitating fine-tuning.

[0048] The key process parameters in this embodiment are shown in Table 3:

[0049] Table 3: Key process parameters of the stainless steel two-roller skin-pass mill in Example 1

[0050]

[0051] Example 2:

[0052] The steps of the preparation method of this embodiment are the same as those of Example 1. The only difference is the key process parameters of the stainless steel two-roller skin pass mill and the titanium product. The specific key process parameters are shown in Table 4:

[0053] Table 4: Key process parameters of the stainless steel two-roller skin pass mill in Example 2

[0054]

[0055] Comparative Example 1:

[0056] The titanium material composition used in this comparative example is the same as that in the embodiment, the product thickness is 2 mm, and the annealing and previous processes are the same as those in Example 1. The only difference is that this comparative example uses a bending and straightening unit to correct the plate shape and finally obtain a titanium cold-rolled product. The key process parameters of the bending and straightening unit in this comparative example are shown in Table 5:

[0057] Table 5: Key process parameters of the tension-bend leveling unit in comparative example 1

[0058]

[0059] The performance of the titanium products prepared in Example 1, Example 2 and Comparative Example 1 was tested and compared. The test results are shown in Table 6:

[0060] Table 6: Performance parameters of titanium products in the embodiments of the present invention and the comparative examples

[0061]

[0062] It can be seen from Table 6 that although the titanium cold-rolled products prepared in the embodiments of the present invention and the comparative examples all meet the roughness Ra=0.2~0.5μm, the yield strength is 140~310Mpa, the tensile strength is ≥240Mpa, and the elongation is ≥30%, the roughness of the titanium cold-rolled products prepared in the embodiments of the present invention is significantly lower than that of the comparative example, achieving a more matte effect, and the tensile strength and yield strength are significantly improved. The performance strength requirements, plate flatness requirements and surface roughness requirements of the titanium cold-rolled products are of high quality, meeting the use requirements of high-end industries and fields such as marine engineering and heat exchangers.

Claims

1. A method for preparing a titanium product, characterized in that: The steps include: S1. Vacuum melting: Iron powder and titanium dioxide powder with a purity of more than 99% are uniformly mixed and then pressed into electrodes, which are then vacuum welded. A vacuum consumable arc furnace is used for melting more than twice, and a square titanium slab is obtained after vacuum casting. S2. Hot rolling: placing the titanium slab in an electric heating furnace and heating it to 850°C to 900°C, and rolling it to a thickness of 3mm to 5mm; S3, annealing and pickling: placing the hot-rolled titanium black hot coil in a continuous annealing furnace for annealing, and then pickling; S4, rolling: rolling the titanium material using a 20-high single-stand reversing rolling mill until the titanium material is rolled to a thickness of 0.5 mm to 2 mm; S5, degreasing: using alkali solution with a concentration of 3% to 10% to remove the rolling oil attached to the surface of the titanium material; S6, annealing: placing the titanium material in a vacuum bell furnace at 500° C. to 700° C. for annealing, with argon gas as a protective gas in the vacuum bell furnace; S7. Leveling: Using a stainless steel two-roller leveling machine, the titanium material is leveled in two passes, each pass being processed using a leveling work roll (1) with corresponding surface roughness and convexity, and finally a finished plate is obtained.

2. The method for preparing a titanium product according to claim 1, characterized in that: The thickness of the square titanium slab after forging in step S1 is 3 mm to 5 mm.

3. The method for preparing a titanium product according to claim 1, wherein: The chemical components of the titanium material in step S3 are as follows: ≤0.1wt% C, ≤0.25wt% Fe, ≤0.03wt% N, ≤0.015wt% H, ≤0.20wt% O, and the remainder is Ti and impurities.

4. The method for preparing a titanium product according to claim 1, wherein: In step S3, acid washing is performed using an acid solution, wherein the acid solution includes nitric acid and hydrofluoric acid, wherein the concentration of the nitric acid is 50 g / L to 150 g / L; and the concentration of the hydrofluoric acid is 2 g / L to 12 g / L.

5. The method for preparing a titanium product according to claim 1, wherein: The concentration of the alkali solution in step S5 is 3% to 10%.

6. The method for preparing a titanium product according to claim 1, wherein: The stainless steel two-roller leveling mill in step S7 includes working rolls (1) spaced apart from each other, a gap for titanium material to pass through is provided between the working rolls (1), the roller diameter of the working rolls (1) is 700 mm to 860 mm, an uncoiler (4) is provided at one end of the stainless steel two-roller leveling mill, and a coiler (5) is provided at the other end, an inlet guide roll (2) is provided between the uncoiler (4) and the working rolls (1), and an outlet guide roll (3) is provided between the coiler (5) and the working rolls (1).

7. The method for preparing a titanium product according to claim 6, characterized in that: The stainless steel two-roller leveling machine in step S7 uses a working roll (1) with a surface roughness Ra of ≤0.05 μm and a convexity of 0.25-0.3 mm in the first pass, the unwinding tension of the stainless steel two-roller leveling machine is ≤10 tons, the leveling speed is ≤100 mpm, and the elongation of the titanium material is ≥0.2%.

8. The method for preparing a titanium product according to claim 7, characterized in that: The stainless steel two-roller leveling machine in step S7 uses a working roll (1) with a surface roughness Ra of ≤0.05 μm and a convexity of 0.1 to 0.15 mm in the second pass, the unwinding tension of the stainless steel two-roller leveling machine is ≤15 tons, the leveling speed is ≤200 mpm, and the elongation of the titanium material is ≥0.1%.

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