Treatment method for eliminating TC4 wire rod rolling overheating structure

Abstract

The invention discloses a treatment method for eliminating a TC4 wire rod rolling overheating structure. The treatment method comprises the following steps that S1, a forged square billet of TC4 titanium alloy is preheated, heated and then subjected to heat preservation at the soaking temperature; s2, rolling to obtain a wire rod; s3, after high-speed spinning, quenching is conducted, an unconverted beta phase is reserved, a microstructure in a metastable state is obtained, after the wire rod with the microstructure in the metastable state is air-cooled, the wire rod is put into a heat insulation container, liquid nitrogen is sprayed, metastable state conversion is promoted, and microstress is implanted; and S4, the wire rod is opened to penetrate through an induction heating coil, rapid induction heating is conducted, high-temperature annealing is conducted on a surface fine grain area, recrystallization is achieved, air blowing cooling is conducted, and salt bath low-temperature annealing is conducted after the wire rod is wound into a coil. According to the method, the TC4 titanium alloy bar product with good surface quality, good roundness and uniform structure property is quickly and efficiently produced by optimizing key parameters such as heating temperature, rolling speed and hole pattern matching according to research on physical and chemical characteristics of titanium and titanium alloy materials.

Description

Technical Field

[0001] The invention relates to the technical field of hot-rolled titanium blanks, and in particular to a processing method for eliminating overheated structures of TC4 coil rolling. Background Art

[0002] TC4 titanium alloy is a metal that is difficult to deform and process due to its unique atomic structure and crystal structure. At present, the production methods of TC4 titanium alloy rods and coils mainly include plastic processing methods such as rolling and drawing. The most widely used two-roller and three-roller rolling methods require the rods to be repeatedly reheated during the rolling process. The process is not only complicated, but also greatly affects the performance of the rods. The Y-type rolling mill has poor stability and the equipment is relatively complex, and it is inconvenient to change rolls and maintain, so it is less used. The existing technology generally adopts segmented multi-fire heating and rolling of titanium and titanium alloy coils, but it is impossible to achieve a large coil weight (generally, the weight of a single coil of coil does not exceed 10Kg), and the rolling quality is poor, the cost is high, and the production efficiency is low. Moreover, the microstructure of the head and tail of the titanium alloy rod rolled by multiple fires is relatively different; hot drawing requires multiple tempering, the energy consumption is high, and the surface accuracy of the rod and coil is not easy to control.

[0003] The current development direction is to adopt hot rolling production. For example, the Chinese patent with application number 201410238311.1 proposes a hot rolling method. The initial rolling adopts 16 horizontal and vertical alternating tandem rolling mills for torsion-free rolling. The pre-finishing rolling adopts a group of collectively driven torsion-free cantilever roller mills to achieve short frame spacing torsion-free micro-tension rolling. The finishing rolling adopts Morgan high-speed torsion-free disc finishing mills. All rolling speeds are controlled at 50-100m / s. Due to the poor thermal conductivity of titanium and titanium alloys, the deformation heat generated by the deformation resistance during rolling is not easy to be transmitted. Especially when rolling high-strength and high-temperature titanium alloys, overheated structures are very likely to appear inside the metal, resulting in overheating and uneven structures in the rolled pieces. The internal structure and performance of the rolled pieces cannot be guaranteed, and it is difficult to obtain qualified discs.

[0004] In view of this, the existing technology should be improved. Summary of the invention

[0005] The main purpose of the present invention is to provide a treatment method for eliminating the overheating structure of TC4 coil rolling. According to the study of the physical and chemical properties of titanium and titanium alloy materials, by optimizing the key parameters such as heating temperature, rolling speed, and hole matching, TC4 titanium alloy bar products with good surface quality, good roundness, and uniform organizational properties are produced quickly and efficiently on a traditional steel hot rolling mill.

[0006] According to one aspect of the present invention, a method for eliminating the overheating structure of TC4 coil rolling is provided, which comprises the following steps: S1. Heating: preheat the forged billet of TC4 titanium alloy to 920±10℃ and keep it at the absorptive temperature for 1~3h; S2, rolling: rolling the heated forged square billet to obtain a φ8~12mm round disc; S3, quenching and cryogenic treatment: after spinning at high speed, quenching is performed to retain the untransformed β phase to obtain a metastable microstructure. The disk with the metastable microstructure is air-cooled and then placed in an insulated container, sprayed with liquid nitrogen, and kept below -50°C for 20 to 40 minutes to promote metastable transformation and implant microscopic stress; S4. Surface high-frequency induction heating: The coil is opened and passed through the induction heating coil, and the surface layer temperature is quickly induction heated to 820~900℃, and the surface fine grain area is subjected to high-temperature annealing to achieve recrystallization, and then cooled by blowing air, and then annealed in a salt bath at low temperature after being wound into a coil.

[0007] According to one embodiment of the present invention, in step S1, preheating includes preheating at a temperature below 800° C. in a heating furnace for 1 to 2 hours.

[0008] According to an embodiment of the present invention, in step S1, the heating rate of the heating is ≤100°C / hour.

[0009] According to one embodiment of the present invention, the soaking temperature is 920±10°C.

[0010] According to one embodiment of the present invention, the cross section of the forged square billet is a square with a side length of 150-185 mm, and the length of the forged square billet is 6000 mm.

[0011] According to one embodiment of the present invention, in step S2, the rolling is performed for 28 to 32 passes, and the pass elongation coefficient is 1.1 to 1.3.

[0012] According to one embodiment of the present invention, in step S2, the rolling speed of the last stand is 18-24 m / s, and the final rolling temperature is 780-850°C.

[0013] According to an embodiment of the present invention, in step S4, the heating frequency of the induction heating coil is determined according to the depth of the surface grain inhomogeneity layer.

[0014] According to one embodiment of the present invention, the heating time of the rapid induction heating is ≤5s.

[0015] According to one embodiment of the present invention, the temperature range of the salt bath is 700-730°C.

[0016] In a processing method for eliminating the overheating structure of TC4 coil rolling according to an embodiment of the present invention, based on the study of the physical and chemical properties of titanium and titanium alloy materials, by optimizing key parameters such as heating temperature, rolling speed, and hole matching, TC4 titanium alloy bar products with good surface quality, good roundness, and uniform organizational properties are produced quickly and efficiently on a traditional steel hot rolling mill. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solution of the embodiment of the present invention, the drawings required for use in the embodiment will be briefly introduced below. Obviously, the drawings described below are only some implementation cases of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 A process flow chart showing a method for eliminating overheated structure of TC4 coil rolling according to an exemplary embodiment of the present invention is shown; Figure 2 A φ8.0 mm rolled TC4 edge portion according to an exemplary embodiment of the present invention is shown; Figure 3 Schematic diagram of a φ8.0 mm rolled TC4 core according to an exemplary embodiment of the present invention; Figure 4 The TC4 edge after homogenization of φ8.0 mm according to an exemplary embodiment of the present invention is shown; Figure 5 A TC4 core with a diameter of 8.0 mm after homogenization according to an exemplary embodiment of the present invention is shown. DETAILED DESCRIPTION

[0019] The detailed description of the following embodiments is used to exemplify the principles of the present invention, but cannot be used to limit the scope of the present invention. The present invention can be implemented in many different forms and is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

[0020] The present invention provides these embodiments to make this disclosure thorough and complete, and fully express the scope of the present invention to those skilled in the art. It should be noted that unless otherwise specifically stated, the relative arrangement of the parts and steps, the composition of materials, numerical expressions and numerical values ​​set forth in these embodiments should be interpreted as being merely exemplary, rather than as limiting.

[0021] It should be noted that, in the description of the present invention, unless otherwise specified, the meaning of "multiple" is greater than or equal to two; the terms "upper", "lower", "left", "right", "inner", "outer", etc., indicating the orientation or positional relationship, are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0022] It should also be noted that in the description of the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected" and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances. When a specific device is described as being located between a first device and a second device, there may or may not be an intermediate device between the specific device and the first device or the second device.

[0023] All terms used in the present invention have the same meanings as those understood by those of ordinary skill in the art to which the present disclosure belongs, unless otherwise specifically defined. It should also be understood that terms defined in general dictionaries, for example, should be interpreted as having meanings consistent with their meanings in the context of the relevant technology, and should not be interpreted in an idealized or extremely formal sense, unless explicitly defined herein.

[0024] Technologies, methods, and apparatus known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, these technologies, methods, and apparatus should be considered part of the specification.

[0025] like Figure 1 As shown, the present invention provides a processing method for eliminating the overheating structure of TC4 coil rolling, which comprises the following steps: S1. Heating: preheat the forged billet of TC4 titanium alloy to 920±10℃ and keep it at the absorptive temperature for 1~3h; S2, rolling: rolling the heated forged square billet to obtain a φ8~12mm round disc; S3, quenching and cryogenic treatment: after spinning at high speed, quenching is performed to retain the untransformed β phase to obtain a metastable microstructure. The disk with the metastable microstructure is air-cooled and then placed in an insulated container, sprayed with liquid nitrogen, and kept below -50°C for 20 to 40 minutes to promote metastable transformation and implant microscopic stress; S4. Surface high-frequency induction heating: The coil is opened and passed through the induction heating coil, and the surface layer temperature is quickly induction heated to 820~900℃, and the surface fine grain area is subjected to high-temperature annealing to achieve recrystallization, and then cooled by blowing air, and then annealed in a salt bath at low temperature after being wound into a coil.

[0026] Specifically, the thermally insulated container includes one of a liquid oxygen container, a liquid nitrogen container, a liquid argon container, and a liquid helium container.

[0027] In the processing method for eliminating the overheating structure of TC4 coil rolling according to an embodiment of the present invention, based on the study of the physical and chemical properties of titanium and titanium alloy materials, by optimizing key parameters such as heating temperature, rolling speed, and hole matching, TC4 titanium alloy bar products with good surface quality, good roundness, and uniform organizational properties are produced quickly and efficiently on a traditional steel hot rolling mill.

[0028] In some specific embodiments, in step S1, preheating includes preheating in a heating furnace at a temperature below 800° C. for 1 to 2 hours. Preferably, the preheating time is 1 hour.

[0029] In some specific embodiments, in step S1, the heating rate of the heating is ≤100°C / hour.

[0030] Based on the above embodiment, the soaking temperature is 920±10°C. During the metal heat treatment process, soaking temperature can make the internal structure and composition of the material more uniform. Especially for castings or large forgings, soaking treatment helps to eliminate internal component segregation, grain unevenness and other problems.

[0031] In some specific embodiments, the cross section of the forged square billet is a square with a side length of 150-185 mm, and the length of the forged square billet is 6000 mm.

[0032] In some specific embodiments, in step S2, the rolling is performed for 28 to 32 passes, and the pass elongation coefficient is 1.1 to 1.3.

[0033] In some specific embodiments, in step S2, the rolling speed of the last stand is 18-24 m / s, and the final rolling temperature is 780-850°C.

[0034] Based on the above embodiment, in step S4, the heating frequency of the induction heating coil is determined according to the depth of the surface grain inhomogeneity layer. The heating frequency is negatively correlated with the depth of the surface grain inhomogeneity layer.

[0035] Specifically, the relationship between the induction heating frequency and the depth of the surface grain inhomogeneity layer is shown in the following table.

[0036]

[0037] Based on the above embodiments, the heating time of rapid induction heating is ≤5s. The induction heating coil can efficiently convert electrical energy into thermal energy, and the heating efficiency is usually as high as 96% or more. This efficient energy conversion reduces energy waste and makes the heating process faster.

[0038] Based on the above examples, the temperature range of the salt bath is 700-730° C. Salt bath low temperature annealing helps the material obtain good hardness and wear resistance at low temperature by precisely controlling the heating and cooling temperatures.

[0039] Slow quenching rates can reduce quenching stresses, reduce the risk of workpiece deformation and cracking, while maintaining the material's fine grain size. Fine-grained materials generally have higher strength and toughness, thereby improving overall material properties.

[0040] The present application is described below with reference to specific embodiments.

[0041] Example 1 S1. Heating: preheating the forged square billet of TC4 titanium alloy in a heating furnace at a temperature below 800° C. for 1 hour, then heating to 920° C. at a heating rate of 100° C. / hour, and keeping at the soaking temperature for 2 hours. The soaking temperature of the forged square billet of TC4 titanium alloy is 920° C., and the size of the forged square billet is 160 mm square section×6000 mm; S2, rolling: rolling the heated forged square billet for 32 passes to obtain a φ8 mm coil, with a pass elongation coefficient of 1.1 to 1.3; the final stand rolling speed is 22 m / s, and the final rolling temperature of the TC4 titanium alloy rolled piece is 780 to 850°C; S3, quenching: after high-speed spinning, quenching retains the untransformed β phase and obtains a metastable microstructure; S4, cryogenic treatment: After air cooling the disk with metastable microstructure, put it into an insulated container, spray liquid nitrogen, and keep it below -50℃ for 30 minutes to promote metastable transformation and implant micro stress; S5, surface high-frequency induction heating: the coil is opened and passed through the induction heating coil, the heating frequency is 200kHz, the surface layer temperature is quickly induction heated to 850℃, the heating time is 3s, the surface fine grain area is subjected to high temperature annealing to achieve recrystallization, and then the coil is cooled by blowing and wound into a coil; S6. Salt bath low temperature annealing: The salt bath temperature is 730℃ to achieve the purpose of stabilizing the organization and achieving organizational homogenization.

[0042] Figure 2 The S2 step shows the microstructure of the edge after rolling. It can be seen that the microstructure type is the strip α phase transformed from the equiaxed α phase and the superheated high-temperature β phase.

[0043] Figure 3The center structure after rolling obtained in step S2 is shown in FIG. 1 , and it can be seen that the structure type is a strip-shaped α phase transformed from the superheated high-temperature β phase, and a grain boundary network α phase.

[0044] Figure 4 The edge structure obtained in step S6 is shown in the figure. It can be seen that the structure type is equiaxed α phase and very little grain boundary β phase, and there is no coarse strip α phase.

[0045] Figure 5 The edge structure obtained in step S6 is shown in the figure. It can be seen that the structure type is equiaxed α phase and very little grain boundary β phase, without coarse strip α phase and harmful grain boundary network α phase.

[0046] like Figures 2~5 As shown, the present invention is based on in-depth research and careful analysis of the physical and chemical properties of titanium and titanium alloy materials, and has successfully optimized a series of key production process parameters such as heating temperature, rolling speed, and hole matching through calculation and experimental verification. Thereby, the rapid and efficient production of TC4 titanium alloy bar products is achieved on the traditional steel hot rolling mill. The produced TC4 titanium alloy bar products not only have extremely high surface quality standards, showing the characteristics of smoothness and flawlessness without obvious defects, but also have excellent roundness, dimensional accuracy and shape stability. In addition, its internal organizational structure is uniform and its mechanical properties are stable, which fully meets the high standards and strict requirements for titanium alloy materials in high-end application fields.

[0047] The successful implementation of this invention not only expands the application scope of traditional hot rolling mills, but also provides new ideas and solutions for the efficient and low-cost production of titanium alloy materials. It has important practical value and broad market application prospects.

[0048] The above are exemplary embodiments disclosed in the present invention. The order disclosed in the above embodiments of the present invention is for description only and does not represent the advantages and disadvantages of the embodiments. However, it should be noted that the discussion of any of the above embodiments is only exemplary and is not intended to imply that the scope disclosed in the embodiments of the present invention (including the claims) is limited to these examples. Various changes and modifications may be made without departing from the scope defined in the claims. The functions, steps and / or actions of the method claims according to the disclosed embodiments described herein do not need to be performed in any particular order. In addition, although the elements disclosed in the embodiments of the present invention may be described or required in individual form, they may also be understood as multiple unless explicitly limited to the singular.

[0049] A person skilled in the art should understand that the discussion of any of the above embodiments is only exemplary and is not intended to imply that the scope of the disclosure of the embodiments of the present invention (including the claims) is limited to these examples; under the concept of the embodiments of the present invention, the technical features in the above embodiments or different embodiments can also be combined, and there are many other changes in different aspects of the embodiments of the present invention as described above, which are not provided in detail for the sake of simplicity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the embodiments of the present invention should be included in the protection scope of the embodiments of the present invention.

Claims

1. A method for eliminating the overheating structure of TC4 coil rolling, characterized in that: The following steps are involved: S1. Heating: preheat the forged billet of TC4 titanium alloy to 920±10℃ and keep it at the absorptive temperature for 1~3h; S2, rolling: rolling the heated forged square billet to obtain a φ8~12mm round disc; S3, quenching and cryogenic treatment: after spinning at high speed, quenching is performed to retain the untransformed β phase to obtain a metastable microstructure. The disk with the metastable microstructure is air-cooled and then placed in an insulated container, sprayed with liquid nitrogen, and kept below -50°C for 20 to 40 minutes to promote metastable transformation and implant microscopic stress; S4. Surface high-frequency induction heating: The coil is opened and passed through the induction heating coil, and the surface layer temperature is quickly induction heated to 820~900℃, and the surface fine grain area is subjected to high-temperature annealing to achieve recrystallization, and then cooled by blowing air, and then annealed in a salt bath at low temperature after being wound into a coil.

2. The method for eliminating the overheated structure of TC4 coil rolling according to claim 1 is characterized in that: In step S1, the preheating includes preheating at a temperature below 800° C. in a heating furnace for 1 to 2 hours.

3. The method for eliminating the overheated structure of TC4 coil rolling according to claim 1 is characterized in that: In step S1, the heating rate of the heating is ≤100°C / hour.

4. The method for eliminating the overheating structure of TC4 coil rolling according to claim 1 is characterized in that: The soaking temperature is 920±10°C.

5. The method for eliminating the overheated structure of TC4 coil rolling according to claim 1 is characterized in that: The cross section of the forged square billet is a square with a side length of 150-185 mm, and the length of the forged square billet is 6000 mm.

6. The method for eliminating the overheated structure of TC4 coil rolling according to claim 1 is characterized in that: In step S2, rolling is performed for 28 to 32 passes, and the pass elongation coefficient is 1.1 to 1.

3.

7. The method for eliminating the overheated structure of TC4 coil rolling according to claim 1 is characterized in that: In step S2, the final rolling speed is 18-24 m / s, and the final rolling temperature is 780-850°C.

8. The method for eliminating the overheated structure of TC4 coil rolling according to claim 1 is characterized in that: In step S4, the heating frequency of the induction heating coil is determined according to the depth of the surface grain inhomogeneity layer.

9. The method for eliminating the overheated structure of TC4 coil rolling according to claim 1 is characterized in that: The heating time of the rapid induction heating is ≤5s.

10. The method for eliminating the overheated structure of TC4 coil rolling according to claim 1, characterized in that: The temperature range of the salt bath is 700-730°C.

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