A process for improving the drawing formability of titanium / steel composite materials

Abstract

The present invention relates to the technical field of hot forming of sheet materials, and particularly relates to a process for improving the drawing forming performance of titanium / steel composite materials. The specific technical solution is as follows: a process for improving the drawing forming performance of titanium / steel composite materials, after connecting a titanium plate and a steel plate by explosive welding, annealing treatment is carried out to obtain a titanium-steel composite plate; a conductive coating and a high-temperature lubricating oil are sequentially coated on the surface of the titanium-steel composite plate; the titanium-steel composite plate is placed in a mold, and after pulse current-assisted drawing forming, pressure holding is carried out. The present invention solves the problems that the existing titanium / steel composite plate has limited forming ability at room temperature, and intermetallic compound layers will be generated at the interface at high temperature, resulting in a reduction in drawing forming performance and difficulty in forming complex parts.

Description

Technical Field

[0001] The present invention relates to the technical field of hot forming of plates, and particularly relates to a process for improving the drawing forming performance of titanium / steel composite materials. Background Art

[0002] Titanium / steel composite plates have both the corrosion resistance of titanium and the high strength of alloy steel, and at the same time have good comprehensive properties that can be directly welded to other offshore steel structures, becoming an indispensable structural material in modern chemical industry and bridge ships. Improving the forming ability of titanium / steel composite plates at medium temperature has extremely important practical significance for fields such as aerospace, petrochemical industry, and ship water conservancy.

[0003] For example, in the chemical industry, titanium has good stability in various acid, alkali, and salt media, except for four inorganic acids and highly corrosive aluminum chloride. Therefore, titanium is an excellent anti-corrosion material in the chemical industry and has been increasingly widely used in vacuum towers, distillation towers, heat exchangers in petroleum refining plants, various reaction towers, precipitation tanks, agitators, etc. in chemical plants. In salt-making equipment, titanium and its alloys have excellent properties of resisting seawater and chloride solution corrosion and fluid erosion.

[0004] In actual industrial production, it is often necessary to prepare titanium / steel composite plate structural parts with complex shapes. At room temperature, the forming ability of titanium / steel composite plates is limited. However, at high temperatures, both titanium and steel are very prone to severe oxidation, and it is difficult to maintain a vacuum environment during the stamping process at low cost. Moreover, the thermal physical properties of titanium and steel vary greatly, so intermetallic compound layers are easily generated at a certain high temperature. The existence of the compound layer will seriously affect the forming performance and mechanical properties of the titanium / steel composite plate, which severely restricts the development and application of the titanium / steel composite plate, resulting in the inability to achieve the forming ability required for forming complex components, that is, the forming ability of the titanium / steel composite plate during high-temperature forming is not directly proportional to the temperature increase. Therefore, the hot forming temperature should not be too high, so it is necessary to form these industrial parts at medium temperature.

[0005] Electroplastic-assisted forging and bending and other processes have been applied to some difficult-to-deform materials to a certain extent. At medium temperature, titanium / steel composite plates already have a certain forming ability. In order to further improve the forming ability of titanium / steel composite plates to achieve the forming ability required for forming titanium / steel composite plate components with complex shapes, electroplastic-assisted drawing forming is crucial for improving the forming ability.

[0006] A certain springback phenomenon will occur after the drawing process of the titanium / steel composite plate is completed. Reducing the springback phenomenon of the titanium / steel composite plate drawing formed parts and improving the quality of the formed parts is also crucial. Summary of the Invention

[0007] Aiming at the deficiencies of the existing technology, the present invention provides a process for improving the drawing formability of titanium / steel composite materials, which solves the problems that the existing titanium / steel composite plates have limited formability at room temperature and intermetallic compound layers are generated at the interface at high temperature, resulting in a reduction in drawing formability and difficulty in forming complex parts.

[0008] To achieve the above objectives, the present invention is realized through the following technical solutions:

[0009] The present invention discloses a process for improving the drawing formability of titanium / steel composite materials. After connecting a titanium plate and a steel plate by explosive welding, annealing treatment is carried out to obtain a titanium-steel composite plate; a conductive coating and a high-temperature lubricating oil are sequentially coated on the surface of the titanium-steel composite plate; the titanium-steel composite plate is placed in a mold, and after pulse current-assisted drawing forming, pressure holding is carried out.

[0010] Preferably, the thickness ratio of the steel plate to the titanium plate is 5-20:1.

[0011] Preferably, the temperature of the annealing treatment is 540±25°C, and the annealing time is 1-4 h.

[0012] Preferably, the coating thickness of the conductive coating is 50 nm-20 μm, and the coating thickness of the high-temperature lubricating oil is 50 nm-20 μm.

[0013] Preferably, after the titanium / steel composite plate coated with the conductive coating and the high-temperature lubricating oil is heat-insulated, electroplasticity-assisted medium-temperature drawing forming is carried out.

[0014] Preferably, the temperature of the heat insulation is 200-500°C, and the heat insulation time is 5-10 min.

[0015] Preferably, a pulse current-assisted forming device is arranged in the mold, and the pulse current density range is 300-350 A / mm 2 .

[0016] Preferably, the pressure holding time is 10-15 min, the punch force is maintained at 5-10 Mpa during pressure holding, and after the pulse power supply is closed for 180-300 s during the pressure holding process, the power switch is disconnected.

[0017] Preferably, the density of the explosive used in the explosive welding is 0.92 g / cm 3 , the explosive detonation velocity is 2200 m / s, and the distance between the titanium plate and the steel plate is set to 10 mm.

[0018] The present invention has the following beneficial effects:

[0019] The limiting drawing ratio of the electroplastic-assisted hot drawing forming of the titanium / steel composite plate of the present invention can reach 5.17, and complex-shaped parts can be formed. Moreover, the pulsed current-assisted forming can not only improve the forming ability of the titanium / steel composite plate, but also has a certain auxiliary shape correction effect on the drawn parts during the pressure holding process, and can be used for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a process implementation process diagram of the present invention;

[0021] Figure 2 It is a schematic diagram of the mold structure;

[0022] Figure 3 It is a schematic diagram of the structure after the punch extends into the groove;

[0023] In the figure: punch 1, insulation area 2, brush device 3, pulsed power supply 4, blank holder device 5, blank 6, die 7, base 8, insulation layer 9. DETAILED DESCRIPTION OF THE INVENTION

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0025] Unless otherwise specified, the technical means used in the implementation examples are conventional means well known to those skilled in the art.

[0026] The present invention discloses a process for improving the drawing forming performance of a titanium / steel composite material, including the following steps:

[0027] (1) After connecting a titanium plate and a steel plate by explosive welding, annealing treatment is carried out to obtain a titanium-steel composite plate (a titanium / steel composite plate with internal stress can also be obtained by hot rolling); wherein, the layer thickness ratio of the base plate and the clad plate of the composite plate is 5-20:1. The base plate is made of low-carbon steel, including but not limited to Q235, Q345, 45 steel, and the clad plate is made of pure titanium plate or titanium alloy plate, including but not limited to TA1, TA2, TC4. The stress-relieving annealing treatment is carried out on the titanium / steel composite plate after explosive welding, and the annealing treatment temperature is 540±25°C, and the annealing treatment time is 1-4h, so as to obtain a stress-relieved titanium / steel composite plate. The density of the explosive used in explosive welding is 0.92 g / cm 3 , the explosive detonation velocity is 2200 m / s, and the distance between the titanium plate and the steel plate is set to 10 mm.

[0028] (2) Surface treatment: Cut the stress-relieved annealed titanium / steel composite plate into the required shape and size. To ensure good electrical conductivity, apply a conductive coating, such as a graphite coating, with a thickness of 50 nm to 20 μm, on the surface of the cut titanium / steel composite plate that contacts the punch. To reduce the friction between the punch and the titanium / steel composite plate during deep drawing, apply a high-temperature deep drawing lubricant or MoS 2 , with a thickness of 50 nm to 20 μm.

[0029] (3) Electro-plasticity-assisted hot deep drawing: Keep the titanium / steel composite plate coated with a conductive coating and high-temperature lubricating oil in a vacuum state for heat preservation. The heat preservation temperature is 200 - 500 °C, and the heat preservation time is 5 - 10 min to ensure uniform temperature distribution. Then quickly transfer it onto the die within 1 - 3 s to prevent excessive heat loss during deep drawing, and perform rapid deep drawing at medium temperature. The medium-temperature deep drawing forming temperature is 200 - 500 °C. A pulsed current-assisted forming device is set inside the die. The positive and negative electrodes of the pulsed power supply are directly in contact with the punch of the die and the titanium / steel composite plate respectively through a brush device. After the titanium / steel composite plate is transferred to the die, close the pulsed power supply switch. The pulsed current density range is 300 - 350 A / mm 2 , and complete the deep drawing forming of complex parts within 2 - 3 s.

[0030] (4) Pressure holding and auxiliary shape correction: Since the titanium / steel composite plate will have a certain degree of springback phenomenon after deep drawing forming, pressure is held for 10 - 15 min after deep drawing forming. During pressure holding, the pressure of the punch of the die is maintained within the range of 5 - 10 MPa. During the pressure holding process, after the pulsed power supply is closed for 180 - 300 s (the current density range is 300 - 350 A / mm 2 ), disconnect the power switch. This process makes the temperature of the part dissipate slowly due to the Joule heat, and has the effect of electro-pulse-assisted shape correction, making the produced parts more accurate. After the pressure holding process is completed, take out the stamping parts.

[0031] The present invention will be further elaborated below in conjunction with specific embodiments.

[0032] Example 1

[0033] A process for improving the deep drawing forming performance of titanium / steel composites, and the implementation process is referred to Figure 1 as shown. The specific steps are as follows:

[0034] (1) The pure titanium plate TA1 (with dimensions of 1000 mm × 1000 mm × 1 mm) and the steel plate Q235 (1000 mm × 1000 mm × 5 mm) are surface-treated, that is, impurities on the plate surface are removed. Then explosive welding is carried out, and the layer thickness ratio of the pure titanium plate to the steel plate is 1:5. The explosive used for explosive welding is ammonium nitrate fuel oil (ANFO) mixture, with a density of 0.92 g / cm 3 , and the detonation velocity of the explosive is 2200 m / s. The thickness of the explosive layer is set to 60 mm, and the distance between the pure titanium plate and the steel plate is set to 10 mm. After explosive welding, the titanium / steel composite plate is straightened and pickled. The titanium / steel composite plate after explosive welding is stress-relieved annealed at 540 °C for 2 h.

[0035] (2) A circular blank with a diameter of 145 mm is cut out. First, a conductive coating - graphite coating with a thickness of about 1 μm is applied to the surface in contact with the punch. To prevent excessive friction between the punch and the blank from reducing the forming ability, a high-temperature lubricant with a thickness of about 500 nm is then applied to this surface. It is quickly heated to 300 °C in a heating furnace and vacuum-insulated for 10 min (argon gas is introduced into the heating furnace for protection).

[0036] (3) After the insulation is completed, the blank is quickly transferred to the die equipped with pulsed current, and the transfer time is controlled within about 2 s. After the blank is placed on the die, the power supply is turned on, and the pulsed current density is maintained at 300 A / mm 2 , and rapid deep drawing forming is completed within 2 s (the diameter of the drawing punch is 30 mm, and during the entire drawing process, it is ensured that the punch contacts the steel side and the die contacts the titanium side). The blank is successfully drawn into a complete formed part.

[0037] Among them, the die is as Figures 2 - 3 shown, including a punch 1 and a die 7. The edges of the punch 1 and the die 7 are rounded. The radius of the punch fillet is 6 mm, and the radius of the die fillet is 10 mm. There is a central hole in the die 7 to ensure the normal passage of the power supply line. An insulating area 2 is provided on the punch 1, which can block the energization of the entire stamping device (referring to the power device connected to the punch, and this power device is a prior art, such as a cylinder, etc.), making the stamping process safer. The blank 6 is placed on the die 7, and a blank holder device 5 is placed on the blank 6. The pressure exerted by the blank holder device 5 on the blank 6 is 10 KN, and the blank holder device 5 is an existing device, such as a cylinder, etc.

[0038] The brush device 3 is connected to the pulsed power supply 4 through a wire and is connected to the blank 6 through the brush device 3. Specifically: the positive pole of the pulsed current electrode is connected to the side of the punch 1, while the negative pole is connected to the blank 6 through the brush device 3. The brush device 3 and the contact parts of the punch 1 and the die 7 it contacts (i.e., a groove is opened at the bottom of the die) are respectively opened with a groove, which can just hold the brush and make a flat contact (the part of the bottom of the drawn part in contact with the die hardly deforms during the drawing process). After being polished smoothly, an insulating layer 9 is placed between the die 7 and the base 8 to prevent electric shock caused by the energization of the entire device, that is, the die is fixed on the base through the insulating layer. The punch 1 in contact with the brush device 3 is long enough to avoid the circuit entering the gap between the punch 1 and the die 7 as much as possible to avoid accidents.

[0039] (4) After the mold is closed, the obtained part is held under pressure for 10 min, and the holding pressure is about 5 MPa. During the holding pressure process, the power supply is closed for 300 s and then disconnected (the current density is 300 A / mm 2 , which is consistent with the previous step (3)) to achieve the effect of pulsed current assisted shape correction and make the precision of the drawn part higher. After the holding pressure is completed, the drawn part is taken out.

[0040] (5) Cut circular blanks with a diameter of 150 mm, repeat steps 2, 3, and 4, and a complete formed part can be drawn. Cut circular blanks with a diameter of 155 mm, repeat steps 2, 3, and 4, and a complete formed part can be drawn. Cut circular blanks with a diameter of 160 mm, repeat steps 2, 3, and 4, and at this time the drawing fails and a complete formed part cannot be drawn, indicating that under the condition of pulsed current assisted forming, the limiting drawing ratio of the titanium / steel composite plate at high temperature can reach 5.17, and more complex drawn parts can be produced. The limiting drawing ratio is the ratio of the maximum blank diameter that can successfully draw a formed part to the punch diameter.

[0041] Comparative example

[0042] Cut circular blanks with a diameter of 115 mm, repeat the above steps 2, 3, and 4. At the same time, without pulsed current assisted forming, a complete formed part can be drawn. Cut circular blanks with a diameter of 120 mm, repeat steps 2, 3, and 4. At the same time, without pulsed current assisted forming, the drawing fails at this time and a complete formed part cannot be drawn, indicating that under the condition of no pulsed current assisted forming, the limiting drawing ratio of the titanium / steel composite plate at high temperature is 3.83.

[0043] In the description of the present invention, it should be understood that the orientation or positional relationships indicated by the terms "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. are based on the orientation or positional relationships shown in the drawings, and are only for the convenience of describing the present invention, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0044] The embodiments described above are only for describing the preferred embodiments of the present invention, rather than limiting the scope of the present invention. Without departing from the spirit of the design of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A process for improving the drawing formability of titanium / steel composite materials, characterized in that: After connecting the titanium plate and the steel plate by explosive welding, annealing treatment is carried out to obtain a titanium-steel composite plate; a conductive coating and high-temperature lubricating oil are sequentially coated on the surface of the titanium-steel composite plate; at 200-500 °C, after heat preservation for 5-10 min, the titanium-steel composite plate is placed in a mold, and after drawing forming assisted by pulsed current, pressure holding is carried out, the pressure holding time is 10-15 min, the punch force during pressure holding is maintained at 5-10 Mpa, and after the pulsed power supply is closed for 180-300 s during the pressure holding process, the power switch is disconnected; The thickness ratio of the steel plate to the titanium plate is 5-20:1; The temperature of the annealing treatment is 540±25 °C, and the annealing time is 1-4 h; A pulse current assisted forming device is arranged in the mold. The positive and negative electrodes of the pulse power supply are directly in contact with the punch of the mold and the titanium steel composite plate respectively through the brush device, and the pulse current density ranges from 300 to 350 A / mm 2 , and the drawing forming is completed within 2 to 3 s.

2. The process for improving the drawing formability of titanium / steel composite materials according to claim 1, characterized in that: The coating thickness of the conductive coating is 50 nm-20 μm, and the coating thickness of the high-temperature lubricating oil is 50 nm-20 μm.

3. The process for improving the drawing formability of titanium / steel composite materials according to claim 1, characterized in that: After heat preservation of the titanium / steel composite plate coated with a conductive coating and high-temperature lubricating oil, warm drawing forming assisted by electroplasticity is carried out.

4. The process for improving the drawing formability of titanium / steel composite materials according to claim 1, characterized in that: The density of the explosive used in the explosive welding is 0.92 g / cm 3 , the detonation velocity of the explosive is 2200 m / s, and the distance between the titanium plate and the steel plate is set at 10 mm.

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