Hollow anchor rod body and forming process thereof

Abstract

The application provides a hollow anchor rod body and a forming process thereof, and belongs to the technical field of metal pipe forming. The forming process comprises the following steps: feeding a hollow pipe blank into a multi-zone independent temperature control electric annealing furnace for primary annealing, the primary annealing being performed in a protective atmosphere by using a staged gradient temperature control mode; directly feeding the hollow pipe blank after the primary annealing into a finishing mill unit for cold finishing without pickling; feeding the hollow rod body after the cold finishing into the multi-zone independent temperature control electric annealing furnace for secondary annealing, the secondary annealing being performed by using a staged gradient temperature control mode; feeding the hollow rod body after the secondary annealing into a composite straightening machine for straightening, and finally performing thread cold rolling thread processing to obtain the hollow anchor rod body. The application solves the problem of the mismatch between strength and plasticity of the traditional hollow anchor rod body through the synergistic effect of the primary annealing and the secondary annealing, and effectively improves the strength and plastic product of the hollow anchor rod body.

Description

Technical Field

[0001] This application belongs to the field of metal pipe forming technology, specifically hollow anchor rod body and its forming process. Background Technology

[0002] As the core component of the deep underground space support system, the hollow anchor rod body not only needs to have high yield strength, but also excellent elongation after fracture to meet the energy consumption requirements of large deformation when dealing with complex geological conditions such as high ground stress tunnels and sudden rock bursts.

[0003] Traditional hollow anchor rod forming processes typically employ conventional high-temperature hot rolling combined with quenching and tempering, or direct cold drawing and blind rolling after hot piercing. This forming process inherently suffers from physical defects in matching microstructure evolution with macroscopic mechanical properties. During conventional hot working and cooling, carbon atoms easily precipitate along the original grain boundaries, forming a continuous network of hard and brittle phases, significantly compressing the plastic reserves within the tube. When the hollow tube blank enters the cold deformation stage, these hard and brittle phases cannot slip cooperatively, easily inducing microcracks and introducing high-density dislocation entanglements and lattice distortion into the matrix during cold working. Due to the lack of multi-stage targeted annealing intervention, the enormous residual stress accumulated within the material cannot be effectively released. This directly leads to a severe mismatch between the yield strength and elongation after fracture of the hollow anchor rod, making it highly susceptible to brittle fracture under sudden high strain rate impacts from surrounding rock due to insufficient lattice buffer space. Furthermore, unresolved internal stresses can also cause long-wave torsional deformation of the hollow anchor rod during storage or the initial stages of service. Summary of the Invention

[0004] This application provides a hollow anchor rod body and its forming process, aiming to solve the problem that the mismatch between yield strength and elongation after fracture in the forming and processing of traditional hollow anchor rod bodies leads to brittle fracture under impact.

[0005] To achieve the above objectives, this application provides the following technical solution:

[0006] Firstly, this application provides a molding process for a hollow anchor rod body, the molding process comprising the following steps: The hollow tube blank is fed into a multi-zone independently temperature-controlled electric annealing furnace for primary annealing to obtain a primary annealed hollow tube blank. The atmosphere in the multi-zone independently temperature-controlled electric annealing furnace is a protective atmosphere, which is a nitrogen-hydrogen mixture, and the dew point temperature of the protective atmosphere is below -40℃. The specific steps of the primary annealing are as follows: first, heat to T1 at a heating rate of 8~12℃ / min (e.g., 8℃ / min, 8.5℃ / min, 9℃ / min, 9.5℃ / min, 10℃ / min, 10.5℃ / min, 11℃ / min, 11.5℃ / min, 12℃ / min, etc.) and hold at that temperature for 20~30min (e.g., 20min, 22min, 24min, 26min). The temperature is set at 830~850℃ (e.g., 830℃, 835℃, 840℃, 845℃, 850℃, etc.) for 28 min, 30 min, etc., and then cooled to T2 at a rate of 15~25℃ / h (e.g., 15℃ / h, 16℃ / h, 17℃ / h, 18℃ / h, 19℃ / h, 20℃ / h, 21℃ / h, 22℃ / h, 23℃ / h, 24℃ / h, 25℃ / h, etc.) and held at this temperature for 3~5 h (e.g., 3h, 3.5h, 4h, 4.5h, 5h, etc.). T2 is 0.80~0.85T1 (e.g., T2 is 0.80T1, 0.81T1, 0.82T1, 0.83T1, 0.84T1, 0.85T1, etc.), followed by cooling.

[0007] The hollow tube blank after the first annealing is directly fed into the finishing mill for cold finishing without pickling, to obtain the cold-finished hollow rod. The cold-rolled hollow bar is fed into the multi-zone independently temperature-controlled electric annealing furnace for secondary annealing to obtain a secondary annealed hollow bar. The specific steps of the secondary annealing are as follows: first, heating to T3 at a heating rate of 1~3℃ / min (e.g., 1℃ / min, 1.5℃ / min, 2℃ / min, 2.5℃ / min, 3℃ / min, etc.) and holding at that temperature for 1~1.5h (e.g., 1h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, etc.), with T3 being 0.53~0.60T1 (e.g., T3 being 0.53T1, 0.54T1, 0.55T1). 0.56T1, 0.57T1, 0.58T1, 0.59T1, 0.60T1, etc.; then continue heating to T4 at a heating rate of 100~150℃ / h (e.g., 100℃ / h, 110℃ / h, 120℃ / h, 130℃ / h, 140℃ / h, 150℃ / h, etc.) and hold at that temperature for 2~4h (e.g., 2h, 2.5h, 3h, 3.5h, 4h, etc.), with T4 being 0.70~0.75T1 (e.g., T4 being 0.70T1, 0.71T1, 0.72T1, 0.73T1, 0.74T1, 0.75T1, etc.), followed by cooling; The hollow rod body after secondary annealing is sent into a composite straightening machine for straightening to obtain a straightened hollow rod body. The straightened hollow rod body is subjected to cold thread rolling to obtain a hollow anchor rod body.

[0008] The advantages and technical effects of the hollow anchor rod molding process in this application are as follows: 1. This application induces a discrete eutectoid transformation in hollow tube blanks by subjecting them to a single annealing in a protective atmosphere, followed by a staged gradient temperature control method: rapid heating (8~12℃ / min), followed by a short high-temperature holding (T1=830~850℃, 20~30min), then slow cooling (15~25℃ / h), and finally a long low-temperature holding (T2=0.80~0.85T1, 3~5h). During the slow cooling zone from T1 to T2, carbon atoms possess sufficient diffusion kinetic energy, preventing the precipitation of a continuous network of hard and brittle phases along the original grain boundaries, and promoting the formation of dispersed spherical carbides within the hollow tube blank. This microstructural transformation eliminates rigid resistance points to dislocation slip during processing, providing ample lattice clearance space and the necessary basic plasticity for the hollow tube blank to withstand the high deformation reduction during subsequent cold finishing rolling.

[0009] 2. The protective atmosphere for the first annealing is a nitrogen-hydrogen mixture, and the dew point temperature of the protective atmosphere is below -40℃. This can control the surface decarburization layer depth of the hollow tube blank after the first annealing to be less than 0.05mm, thereby effectively improving the surface strength, fatigue performance and impact toughness of the hollow tube blank after the first annealing, ensuring its comprehensive mechanical properties are uniform and stable, and improving the subsequent molding accuracy and product service reliability.

[0010] 3. This application further improves the comprehensive mechanical properties of hollow anchor rods by performing secondary annealing on the cold-rolled hollow rods and utilizing a staged gradient temperature control method of first holding at a low temperature (T3 is 0.53~0.60T1) and then holding at a high temperature (T4 is 0.70~0.75T1). Specifically, the cold-rolled hollow rods are first held at the T3 stress release platform to promote the mutual annihilation of internal vacancies and interstitial atoms to release residual distortion energy and prevent long-wave distortion of the hollow anchor rods during use and storage; then the temperature is further increased to the T4 final inspection holding zone, where the heated atoms become polygonal, transforming the deformed and fragmented grains into a distortion-free equiaxed subcrystalline structure. The equiaxed subcrystalline structure retains the high strength characteristics brought by cold precision rolling, while reducing local stress concentration. This allows the hollow anchor rod to have both high yield strength and excellent elongation after fracture, significantly improving the strength-ductility product and meeting the energy dissipation requirements of deep well support systems to cope with sudden high ground stress impacts.

[0011] 4. This application achieves precise control of the microstructure of hollow anchor rods from a thermodynamic and kinetic perspective through temperature-correlated synergistic control of primary and secondary annealing: Primary annealing promotes carbide dispersion and spheroidization through high-temperature short-time holding and low-temperature long-time holding, eliminating the brittle hard phase of the grain boundary network, and suppressing decarburization with a low dew point protective atmosphere, providing a tube blank with high plasticity, low stress, and uniform microstructure for cold finishing rolling; Cold finishing rolling introduces controllable work hardening on the basis of high plasticity, significantly improving strength; Secondary annealing adopts a two-stage temperature control related to the temperature of primary annealing, first eliminating internal stress and preventing deformation at a low temperature of T3, and then raising it to T4 to achieve equiaxed subgrain refinement, restoring plasticity while retaining the cold work strengthening effect. The temperature synergy of primary and secondary annealing allows the material to undergo a sequential transformation of microstructure, from spheroidization to strengthening, stabilization, and grain refinement. This results in hollow anchor rods possessing high yield strength, high tensile strength, high elongation after fracture, and ultra-high strength-ductility product, fundamentally solving the technical problems of strength-ductility mismatch, brittle fracture, easy deformation, and poor dimensional stability in traditional processes.

[0012] T3 is the stress-relief temperature, which must be within a fixed proportional range relative to T1 to ensure that only internal stress is relieved without recrystallization, to maintain the strengthening effect of cold rolling, and to prepare for subsequent recrystallization at T4. If T1 decreases while T3 remains unchanged, it will lead to a relatively high T3, resulting in premature recrystallization, grain coarsening, insufficient strength retention, limited improvement in plasticity, and a significant decrease in the strength-ductility product. Only by maintaining a dynamic proportional relationship of T3 = 0.53 to 0.60 T1 can the primary and secondary annealing achieve thermodynamic synergy, realizing the technical effects of sufficient stress relief, uniform recrystallization, ultra-fine grains, and high strength-ductility product.

[0013] In some embodiments, the hollow tube blank is a 40Cr hollow tube blank, which is obtained through the following specific preparation steps: 40Cr alloy structural steel solid round steel is selected as the base material, the base material is heated to 1050~1100℃ and held at that temperature to make the internal structure of the base material completely austenitized, thus obtaining an austenitized base material; the austenitized base material is continuously fed into a skew rolling mill for high-temperature hot deformation treatment and piercing to obtain the 40Cr hollow tube blank.

[0014] In some embodiments, based on the total weight of the 40Cr alloy structural steel solid round bars as 100%, the 40Cr alloy structural steel solid round bars comprise the following components: C 0.37~0.44%, Si 0.17~0.37%, Mn 0.50~0.80%, Cr 0.80~1.10%, S≤0.035%, P≤0.035%, with the balance being Fe and unavoidable impurities. Due to its excellent hardenability and mechanical properties, 40Cr alloy structural steel is preferably used as the base material for manufacturing hollow anchor bolts. Hollow anchor bolts prepared from the aforementioned 40Cr alloy structural steel solid round bars possess advantages such as high strength, good toughness, excellent hardenability, and an excellent strength-toughness ratio, perfectly meeting the engineering requirements of high load-bearing capacity, impact resistance, and long service life for hollow anchor bolts.

[0015] In some embodiments, T2 is 680~700℃, such as 680℃, 685℃, 690℃, 695℃, 700℃, etc. Meeting the above conditions is beneficial to further improve the strength-ductility product of the hollow anchor rod.

[0016] In some embodiments, the cooling method after the first annealing is to cool the furnace to 400~500°C and then remove it from the multi-zone independently temperature-controlled electric annealing furnace and air-cool it to room temperature.

[0017] In some embodiments, the process parameters of the cold finishing mill include: the operating speed of the finishing mill is set to 750~780 r / min, the single reduction rate is set to 10~15%, and the outer diameter of the hollow bar after cold finishing milling is set to 20~30 mm.

[0018] In some embodiments, T3 is 450~500℃, such as 450℃, 452℃, 455℃, 458℃, 500℃, etc.; T4 is 600~620℃, such as 600℃, 605℃, 610℃, 615℃, 620℃, etc. Meeting the above conditions is beneficial to further improve the strength-ductility product of the hollow anchor rod.

[0019] In some embodiments, the cooling method after the secondary annealing is to cool to room temperature at a cooling rate of 30~50℃ / h (e.g., 30℃ / h, 35℃ / h, 40℃ / h, 45℃ / h, 50℃ / h, etc.).

[0020] In some embodiments, the specific implementation method for feeding the hollow rod after secondary annealing into the composite straightening machine for straightening is as follows: the hollow rod after secondary annealing is fed into the composite straightening machine, and the depth of the reverse bending roller is dynamically adjusted by a laser online straightness monitoring instrument to control the straightness of the hollow rod after straightening to ≤1mm / m.

[0021] Secondly, this application provides a hollow anchor rod body, wherein the hollow anchor rod body is manufactured by the molding process described in the first aspect.

[0022] In some embodiments, the hollow anchor rod has a yield strength of 800 MPa or higher, a tensile strength of 1000 MPa or higher, an elongation at break of 20% or higher, and a strength-ductility product of 20000 MPa·% or higher. Preferably, the hollow anchor rod has a yield strength of 850 MPa or higher, a tensile strength of 1010 MPa or higher, an elongation at break of 21% or higher, and a strength-ductility product of 23000 MPa·% or higher. Attached Figure Description

[0023] Figure 1 This is a diagram showing the evolution of mechanical properties of the tube sample at each key process node in the molding process of Example 1. Detailed Implementation

[0024] The technical solutions of this application will be clearly and completely described below with reference to the preparation examples, embodiments, and test examples. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0025] Preparation Example 1: This preparation example provides a method for preparing a 40Cr hollow tube blank, including the following steps: (1) Material preparation: 40Cr alloy structural steel solid round steel is selected as the base material. The total weight of the 40Cr alloy structural steel solid round steel is 100%. The 40Cr alloy structural steel solid round steel includes the following components: C 0.40%, Si 0.27%, Mn 0.65%, Cr 0.95%, S≤0.035%, P≤0.035%, and the balance is Fe and unavoidable impurities. (2) High temperature heating: The above-mentioned substrate is placed in a heating furnace and heated to 1075℃ and held at this temperature for 1.2 min / mm diameter to make the internal structure of the substrate completely austenitized; (3) Piercing: The austenitized substrate is continuously fed into the skew rolling piercing mill for typical high-temperature hot deformation treatment, so that columnar austenite structure and deformation flow lines are formed inside the substrate, and finally piercing is used to obtain 40Cr hollow tube blank.

[0026] Preparation Example 2: This preparation example provides a method for preparing a 40Cr hollow tube blank, including the following steps: Material preparation: 40Cr alloy structural steel solid round bars are selected as the base material. Taking the total weight of the 40Cr alloy structural steel solid round bars as 100%, the 40Cr alloy structural steel solid round bars include the following components: C 0.40%, Si 0.27%, Mn 0.65%, Cr 0.95%, S≤0.035%, P≤0.035%, and the balance is Fe and unavoidable impurities; (2) High temperature heating: The above-mentioned substrate is placed in a heating furnace and heated to 1050℃ and held at this temperature for 1.2 min / mm diameter to make the internal structure of the substrate completely austenitized; (3) Piercing: The fully austenitized substrate is continuously fed into the skew rolling piercing mill for typical high-temperature hot deformation treatment, and finally pierced to obtain 40Cr hollow tube blank.

[0027] Preparation Example 3: This preparation example provides a method for preparing a 40Cr hollow tube blank, including the following steps: (1) Material preparation: 40Cr alloy structural steel solid round steel is selected as the base material. The total weight of the 40Cr alloy structural steel solid round steel is 100%. The 40Cr alloy structural steel solid round steel includes the following components: C 0.40%, Si 0.27%, Mn 0.65%, Cr 0.95%, S≤0.035%, P≤0.035%, and the balance is Fe and unavoidable impurities. (2) High temperature heating: The above-mentioned substrate is placed in a heating furnace, heated to 1100℃ and held at this temperature for 1.2 min / mm diameter, so that the internal structure of the substrate is completely austenitized; (3) Piercing: The fully austenitized substrate is continuously fed into the skew rolling piercing mill for typical high-temperature hot deformation treatment, and finally pierced to obtain 40Cr hollow tube blank.

[0028] Before proceeding with subsequent processes, to ensure the rigor of the parameter settings for primary annealing, cold finishing rolling, and secondary annealing, this application pre-calibrated the basic thermophysical characteristics and key process parameter boundaries of the 40Cr hollow tube blank obtained in Example 1, as shown in Table 1. The phase transformation critical point and mechanical safety threshold in this table constitute the underlying physical logic for the precise closed-loop of various process parameters in this application.

[0029] Table 1. Basic thermophysical and key process parameters of the 40Cr hollow tube blank obtained in Preparation Example 1

[0030] Example 1: This embodiment provides a refined forming process for 40Cr hollow anchor rods with high strength and high elongation after fracture, including the following steps: (1) Take the 40Cr hollow tube blank obtained in Preparation Example 1 and put it into a multi-zone independent temperature-controlled electric annealing furnace with a protective atmosphere (a mixture of 5% hydrogen and 95% nitrogen by volume, and a dew point temperature below -40℃) for a first annealing: first, heat it rapidly to 840℃ at a heating rate of 10℃ / min and hold it at this temperature for 25min; then, slowly cool it down to 690℃ at a rate of 20℃ / h and hold it at this temperature for 4h; during the constant temperature holding stage, high-precision PID regulation is used, and the temperature fluctuation range is strictly controlled within ±2℃; after power is cut off, slowly cool it down to 450℃ with the furnace and remove it from the furnace to air cool to room temperature.

[0031] The protective atmosphere is specifically a slightly reducing nitrogen-hydrogen mixture (a mixture of 5% hydrogen and 95% nitrogen by volume), and the dew point temperature is strictly controlled below -40℃ using an online dew point meter. This extremely low dew point slightly reducing nitrogen-hydrogen mixture effectively inhibits the oxidation reaction of carbon atoms on the surface of the hollow tube blank at high temperatures, ensuring that the depth of the decarburized layer on the surface of the hollow tube blank is strictly controlled within a safe range of less than 0.05mm.

[0032] Compared with traditional high-temperature tempering processes, the segmented and stepped temperature control logic described above significantly shortens the residence time in the absolute high-temperature zone, and the measured comprehensive energy consumption for heat treatment of a single ton of pipe is reduced by more than 30%.

[0033] (2) After the first annealing, the hollow tube blank is directly fed into the finishing mill for cold finishing without pickling: the running speed of the finishing mill is set to 765 r / min, the single reduction rate is set to 12.5%, and the outer diameter of the hollow rod after cold finishing is set to 25 mm.

[0034] (3) The hollow bar after cold precision rolling is annealed again: the bar is heated to 475°C at a heating rate of 120°C / h to establish a stress release platform and held for 1.2h; then it is heated to 610°C at a heating rate of 120°C / h for final inspection and held for 3h; finally, it is cooled to room temperature at a cooling rate of 40°C / h.

[0035] (4) The hollow rod after secondary annealing is fed into a 15-roll composite straightener. The depth of the reverse bending roller is dynamically adjusted by a laser online straightness monitor to control the straightness of the hollow rod to ≤1mm / m. (5) Finally, the straightened hollow anchor rod is subjected to cold thread rolling to obtain the hollow anchor rod body.

[0036] Example 2: This embodiment provides a refined forming process for 40Cr hollow anchor rods with high strength and high elongation after fracture, including the following steps: (1) Take the 40Cr hollow tube blank obtained in Preparation Example 2 and put it into a multi-zone independent temperature-controlled electric annealing furnace with a protective atmosphere (a mixture of 5% hydrogen and 95% nitrogen by volume, and a dew point temperature below -40℃) for a first annealing: first, heat it rapidly to 830℃ at a heating rate of 8℃ / min and hold it at this temperature for 20min; then, slowly cool it down to 680℃ at a rate of 20℃ / h and hold it at this temperature for 3h; during the constant temperature holding stage, high-precision PID regulation is used, and the temperature fluctuation range is strictly controlled within ±2℃; after power is cut off, slowly cool it down to 450℃ with the furnace and remove it from the furnace to air cool to room temperature.

[0037] (2) The hollow tube blank after one annealing is directly fed into the finishing mill for cold finishing without pickling: the running speed of the finishing mill is set to 750 r / min, the single reduction rate is set to 10%, and the outer diameter of the hollow rod after cold finishing is set to 25 mm.

[0038] (3) The hollow bar after cold precision rolling is annealed again: the bar is heated to 450°C at a heating rate of 60°C / h to establish a stress release platform and held for 1 hour; then it is heated to 610°C at a heating rate of 150°C / h for final inspection and held for 2 hours; finally, it is cooled to room temperature at a cooling rate of 50°C / h.

[0039] (4) The hollow rod after secondary annealing is fed into a 15-roll composite straightener for straightening. The depth of the reverse bending roller is dynamically adjusted by a laser online straightness monitor to control the straightness of the hollow rod to ≤1mm / m. (5) Finally, the straightened hollow anchor rod is subjected to cold thread rolling to obtain the hollow anchor rod body.

[0040] Example 3: This embodiment provides a refined forming process for 40Cr hollow anchor rods with high strength and high elongation after fracture, including the following steps: (1) Take the 40Cr hollow tube blank obtained in Preparation Example 3 and put it into a multi-zone independent temperature-controlled electric annealing furnace with a protective atmosphere (a mixture of 5% hydrogen and 95% nitrogen by volume, and a dew point temperature below -40℃) for a first annealing: first heat it to 850℃ at a heating rate of 12℃ / min and hold it at this temperature for 30min; then slowly cool it down to 700℃ at a rate of 20℃ / h and hold it at this temperature for 5h; high-precision PID regulation is used during the constant temperature holding stage, and the temperature fluctuation range is strictly controlled within ±2℃; after power is cut off, slowly cool it down to 450℃ with the furnace and remove it from the furnace to air cool to room temperature.

[0041] (2) The hollow tube blank after one annealing is directly fed into the finishing mill for cold finishing without pickling: the running speed of the finishing mill is set to 780 r / min, the single reduction rate is set to 15%, and the outer diameter of the hollow rod after cold finishing is set to 25 mm.

[0042] (3) The hollow bar after cold precision rolling is annealed again: the bar is heated to 500℃ at a heating rate of 180℃ / h to establish a stress relief platform and held for 1.5h; then it is heated to 610℃ at a heating rate of 100℃ / h for final inspection and held for 4h; finally, it is cooled to room temperature at a cooling rate of 30℃ / h.

[0043] (4) The hollow rod after secondary annealing is fed into a 15-roll composite straightener for straightening. The depth of the reverse bending roller is dynamically adjusted by a laser online straightness monitor to control the straightness of the hollow rod to ≤1mm / m. (5) Finally, the straightened hollow anchor rod is subjected to cold thread rolling to obtain the hollow anchor rod body.

[0044] Comparative Example 1: Compared with Example 1, the difference is that the traditional high-temperature hot rolling and quenching and tempering process in the industry is adopted. Instead of the first annealing, cold precision rolling and second annealing of Example 1, the straightening and cold thread rolling are performed directly. All other aspects are the same.

[0045] Comparative Example 2: Compared with Example 1, the difference is that the single annealing method of Example 1 is not used. The single annealing method of this comparative example is to directly heat to 800°C at a heating rate of 10°C / min and hold for 4 hours and 25 minutes. After power is cut off, it is slowly cooled to 450°C in the furnace and then removed from the furnace and air-cooled to room temperature. All other aspects are the same.

[0046] Comparative Example 3: Compared with Example 1, the difference is that the secondary annealing method of Example 1 is not used. The secondary annealing method of this comparative example is to directly heat to 610°C at a heating rate of 120°C / h for final inspection and hold for 4.2h. All other aspects are the same.

[0047] Comparative Example 4 Compared with Example 1, the difference is that: during the first annealing, the multi-zone independent temperature-controlled electric annealing furnace does not prepare a protective atmosphere (a mixture of 5% hydrogen and 95% nitrogen by volume, with a dew point temperature below -40°C); in addition, the hollow tube blank after the first annealing is pickled, and the pickled hollow tube blank is sent to the finishing mill for cold finishing rolling; everything else is the same.

[0048] Comparative Example 5 Compared with Example 1, the difference is that: during the second annealing, the temperature was raised to 610°C at a heating rate of 120°C / h and held for 1.2h; then the temperature was lowered to 475°C at a cooling rate of 20°C / h and held for 3h; finally, the temperature was cooled to room temperature at a cooling rate of 40°C / h; the rest were the same.

[0049] Comparative Example 6 Compared with Example 1, the difference is that: during the second annealing, the temperature was increased to 550°C at a heating rate of 120°C / h and held for 1.2h; then the temperature was increased to 610°C at a heating rate of 120°C / h and held for 3h; finally, the temperature was cooled to room temperature at a cooling rate of 40°C / h.

[0050] Test Example 1: Macroscopic Mechanical Property Evolution Test of Key Process Nodes Five 500mm long tube samples were randomly cut from the production line at three key nodes: after the first annealing process, after the cold finishing process, and after the second annealing process.

[0051] According to GB / T 228.1-2021 "Metallic materials, tensile testing, part 1: test at room temperature", the obtained tube samples from each key process node were processed into standard tensile specimens, and axial tensile tests were performed using a microcomputer-controlled electronic universal testing machine at a constant tensile rate of 2 mm / min. The elongation at fracture was recorded.

[0052] Annular specimens were cut from the non-deformation zone or the remaining tube at the end of the tensile specimen. After being sanded and mechanically polished with sandpaper, the Vickers hardness (HV10) was measured at 5 equidistant points along the tube wall thickness direction using a fully automatic Vickers hardness tester under a load of 10 kgf and a holding time of 15 s. The maximum and minimum values ​​were removed, and the average value was recorded in the test file.

[0053] Table 2. Test data on the evolution of mechanical properties of pipe samples at key process nodes in Example 1

[0054] Note: In Table 2, S-1A to S-1E represent 5 parallel tube samples taken after "first annealing", S-2A to S-2E represent 5 parallel tube samples taken after "cold finishing rolling", and S-3A to S-3E represent 5 parallel tube samples taken after "second annealing".

[0055] according to Figure 1 Compared with the data in Table 2, the tube samples at each key process node showed a clear and regular evolution trajectory of macroscopic mechanical properties at each molding stage. Figure 1 The combination with Table 2 visually confirms the actual response of the staged gradient temperature control method used in the primary and secondary annealing processes of this application in actual mass production.

[0056] Based on the minimal data dispersion in groups S-1A to S-1E in Table 2, Figure 1 The short error bars attached to this node clearly reflect the high homogeneity of the internal structure of a single batch of material. Based on the applicant's previous observations on the solid-state phase transformation behavior of 40Cr hollow tube blanks near the critical point of 800℃, this excellent softening state indicates that the discrete eutectoid transformation induced by the first annealing in this application effectively promotes the uniform precipitation of carbides, thereby providing ample lattice slip space and plasticity reserve for subsequent handling of the high deformation reduction of 12.5%.

[0057] As the production process progresses to the cold finishing rolling stage... Figure 1 The two physical quantity monitoring curves in the table showed a sharp crossover and reversal. Reading along the left axis, the solid line representing hardness rose sharply, with its value generally jumping to around 250 HV10 (extreme values ​​distributed in the range of 248.5~258.4 HV10). Referring to the right axis, the dashed line representing elongation after fracture experienced a precipitous drop, falling below the 10% baseline across the board. High-strength cold-rolling induced severe lattice distortion and dislocation entanglement within the material, leading to the full manifestation of typical work hardening characteristics. The extreme elongation after fracture of groups S-2A to S-2E in Table 2, ranging from 7.9% to 9.3%, aptly explains why, if the hollow bar after cold-rolling is directly used without the secondary annealing described in this application, it is highly susceptible to delayed fracture under strong residual stress.

[0058] After entering the second annealing, Figure 1The final curve trend exhibits an asymmetric recovery behavior highly consistent with engineering expectations. While the solid line indicating hardness changes dips somewhat, it remains strongly within the high-strength effective range around 226HV10. In stark contrast, the dashed line corresponding to elongation after fracture experiences a dramatic rebound, ultimately converging steadily towards the safe operating range of around 23%. A deeper analysis of this multi-directional data evolution reveals that the dual thermal control strategy of the 475℃ stress release platform and the 610℃ sub-temperature recrystallization zone clearly endows the atoms within the substrate with sufficient diffusion kinetic energy. While targeting and removing the large amount of microscopic distortion energy introduced by cold finishing rolling, the system successfully induces the natural transformation of grains elongated and fragmented due to deformation into equiaxed subgrains. This is achieved through… Figure 1 The systematic observation of the discrete characteristics of multiple sets of parallel samples by biaxial interlaced curves and Table 2 quantitatively confirms that the molding process of this application can achieve precise recovery of the plasticity of materials under large deformation while retaining the high standard structural strength required for the hollow anchor rod body. This also provides a solid material science demonstration for preventing the failure of deep underground space due to impact pressure.

[0059] Test Example 2: Comprehensive Macroscopic Mechanical Properties and Strength-Plasticity Matching Test of Hollow Anchor Bolt Body Hollow anchor bolts produced through a complete and refined molding process in Examples 1 to 3, and corresponding specifications of hollow anchor bolts from the production lines of Comparative Examples 1 to 6 were selected as test objects. Hollow anchor bolts with a length of 600 mm were randomly cut from each of the corresponding batches as test samples.

[0060] To prevent the hydraulic chuck of the testing machine from introducing non-axial radial compressive stress during clamping, which could lead to premature deformation or breakage of the specimen ends, high-hardness solid alloy steel mandrels with interference fit to the inner hole are pressed into both ends of the hollow anchor rod sample. Then, in accordance with the specifications for room temperature tensile testing of metallic materials, the sample is assembled onto a microcomputer-controlled electro-hydraulic servo universal testing machine, and a high-precision strain measurement module equipped with double-sided extensometers is installed in the gauge section in the middle of the hollow anchor rod sample.

[0061] The testing machine was set to apply a constant stress rate during the elastic phase, and after yielding, the load was switched to a constant displacement beam movement rate of 2 mm / min until the specimen broke. The testing system automatically recorded the load and displacement curves, and calculated the yield strength (Ryield) of the empty anchor rod samples in each embodiment and comparative example. p0.2 ), tensile strength (R) m The tensile strength and elongation after fracture (A) were calculated. The product of tensile strength and elongation after fracture was extracted to construct and record a strength-ductility product parameter (MPa·%) that comprehensively reflects the energy absorption and tensile properties of the material. The comprehensive macroscopic mechanical property test data of the hollow anchor rod samples of each embodiment and each comparative example are shown in Table 3.

[0062] Table 3. Comprehensive macroscopic mechanical performance test data of hollow anchor rod samples from each embodiment and comparative example.

[0063] According to the data in Table 3, the hollow anchor rod samples from each embodiment and comparative example exhibit significant dispersion in their final mechanical properties, spanning multiple orders of magnitude, after undergoing different thermal processing and deformation paths. It is important to understand that in conventional failure analysis cases of deep underground space support components, the mismatch between yield strength and elongation after fracture is often the physical root cause of sudden rockburst failure.

[0064] Referring to the mechanical properties of the hollow anchor rod sample in Comparative Example 1 in Table 3, its yield strength is only 754.3 MPa, its elongation after fracture is as low as 14.3%, and its strength-ductility product barely remains in the low range of 13178.9 MPa·%. This is because the forming process using traditional high-temperature hot rolling and quenching and tempering involves an excessively long residence time in the high-temperature austenitic region, inevitably inducing abnormal grain growth. The coarse original structure not only leads to an inherent deficiency in the material's macroscopic load-bearing capacity, but the thermal stress accumulated during its internal cooling stage also directly cuts off the material's plastic elongation space.

[0065] Referring to the test results of Comparative Example 2, its strength-ductility product data further deteriorated and fell below the threshold of 11000 MPa·%, while the elongation after fracture was severely compressed to the edge of engineering failure at 10.8%. This is because, without the intervention of a staged gradient temperature control method, carbon atoms spontaneously precipitate along the original grain boundaries during the first annealing process and form a continuous network of carbide skeletons. This hard and brittle phase cannot generate cooperative slip when subjected to the high-intensity cold deformation of the finishing mill, and is very likely to induce the nucleation and expansion of micropores at the grain boundaries, resulting in the complete depletion of the remaining plastic reserves of the tube.

[0066] Referring to the test results of Comparative Example 3, Comparative Example 3 used a constant-temperature secondary annealing method, lacking a low-temperature stress release stage. This resulted in the residual internal stress introduced by cold-rolling not being fully eliminated, easily causing subsequent deformation and dimensional instability. The deformed grains could not gradually complete the polygonization and equiaxed subgrain transformation, and the microstructure still retained a large number of elongated and broken grains and dislocation entanglements. Therefore, although Comparative Example 3 retained some strength, its plasticity recovery was insufficient, the elongation after fracture decreased significantly, and the strength-ductility product was greatly reduced. Therefore, Comparative Example 3 could not achieve the synergistic effect of "retaining strength and restoring plasticity", and its mechanical properties were significantly inferior to those of Example 1 of this application.

[0067] Referring to the test results of Comparative Example 4, since no protective atmosphere was configured during the first annealing of Comparative Example 4, severe oxidation and decarburization occurred on the surface of the tube blank at high temperature, the depth of the surface decarburized layer increased significantly, and the surface strength, fatigue performance and impact toughness decreased significantly. Although pickling can help remove the surface oxide layer, it further damages the surface quality, resulting in uneven surface structure and increased defects. Subsequent cold finishing rolling and secondary annealing cannot repair the surface defects and decarburized layer, ultimately leading to insufficient overall strength of the hollow anchor rod, large plasticity fluctuations, low strength-plasticity product, and comprehensive performance far lower than that of Example 1.

[0068] Comparative Example 5 reversed the heating sequence of the two stages of secondary annealing, starting with high temperature and then low temperature, which violates the law of microstructure evolution: direct heating at the high temperature stage will cause the cold-worked microstructure to undergo rapid excessive recrystallization or even grain coarsening, resulting in a significant loss of strength; the subsequent low-temperature holding cannot reverse the coarsened grains, nor can it achieve orderly stress release; ultimately, the result is a decrease in strength, no effective improvement in plasticity, and a significant deterioration in the strength-plasticity product, which completely fails to achieve the synergistic effect of "high strength + high plasticity" of this application.

[0069] The strength of Comparative Example 6 was similar to that of Example 1, but its plasticity decreased significantly: the elongation after fracture decreased from 23.4% to 17.8%; the strength-ductility product decreased significantly from 24506.8 MPa·% to 18380.3 MPa·%. The reason is that the temperature of the second return to the first stage in Comparative Example 6 was too high, resulting in insufficient release of internal stress, premature grain coarsening, and disruption of the strength-ductility balance.

[0070] The test results of Examples 1 to 3 of this application show an evolutionary trend of simultaneous leap in tensile strength and large deformation capacity. This is essentially a macroscopic quantitative manifestation of the coupling effect of primary annealing, cold precision rolling, and secondary annealing. Table 3 records in detail that Examples 1 to 3 all exceeded the yield strength benchmark of 850 MPa, and the elongation after fracture was greater than 21%. This characteristic enabled the hollow anchor rods of Examples 1 to 3 to firmly stand at the extremely high strength-ductility accumulation level of over 23000 MPa. This atypical mechanical characteristic, simultaneously possessing high strength and large deformation capacity, stems from the discrete eutectoid transformation induced by the primary annealing process in this application. The highly dispersed spherical carbides provide ample space for dislocation multiplication and entanglement during the subsequent 10-15% cold rolling reduction, thus locking in a high-strength substrate. Simultaneously, the 475℃ stress release platform and 610℃ final inspection holding mechanism set in the secondary annealing process precisely intervene in this microstructural evolution. Thermally activated atoms, without destroying the existing high-density dislocation cell structure, promote the transformation of elongated grains into a distortion-free equiaxed subcrystalline structure through polygonization. Penetrating the discrete appearance of surface data, this thermodynamic grain boundary reconstruction mechanism fundamentally eliminates the large-scale internal stress associated with work hardening, endowing the material with the necessary microscopic yielding and elongation kinetic energy to withstand sudden large deformation impacts from the surrounding rock.

[0071] Test Example 3: Dynamic Impact Response and Energy Dissipation Characteristics Test of High-Energy Drop Hammer Hollow anchor bolts from the production lines of Examples 1 to 3, and corresponding specifications of hollow anchor bolts from Comparative Examples 1 to 5 were selected as test objects. Hollow anchor bolts with an effective working section length of 1200 mm were randomly selected from each consecutive batch as samples.

[0072] Hollow anchor rod samples were installed one by one into the special surrounding rock simulation fixture of the DIT-3000 instrumented drop hammer impact testing machine. The two ends of the hollow anchor rod samples were kept in a fixed constraint state, and an axial static load of 120kN was applied by the bottom hydraulic servo cylinder to restore the real initial pre-tightening service conditions of deep underground support.

[0073] The counterweight hammer of the testing machine was set to a mass of 2000 kg and released freely from the fixed guide rail at high altitude, forming a high-energy dynamic impact with an initial contact velocity of approximately 6.8 m / s. Using a 100 kHz high-frequency piezoelectric force sensor and a synchronously triggered dynamic laser displacement gauge arranged at the bearing end of the fixture, transient data of impact load and axial elongation of the hollow anchor rod sample during the short-term violent deformation process were continuously collected. By performing time integration calculation on the load-displacement transient data stream, the total energy dissipation of a single tube until fracture failure was obtained.

[0074] Table 4. Test data on dynamic impact mechanical response and energy dissipation of hollow anchor rods in each embodiment and comparative example using a falling hammer.

[0075] According to the data in Table 4, when the hollow anchor rod samples of each embodiment and comparative example faced a high-strain-rate transient impact boundary constructed by a large-mass drop hammer, the resistance to cleavage fracture of their internal structure underwent a fundamental physical differentiation. In the initial stage, the hollow anchor rods of each embodiment and comparative example rapidly increased from a pre-tightened baseline of 120 kN, but their response trajectories after entering the plastic yielding stage differed significantly from their survival periods. Referring to the test results of Comparative Example 1 in Table 4, its peak impact load only climbed to 345.6 kN before instability occurred, and the maximum axial extension stopped abruptly at 32.1 mm. The hollow anchor rod underwent penetrating brittle fracture within 4.8 ms after impact, with a total energy dissipation of an extremely low level of 8.5 kJ. This is because the coarse grain boundaries left over from the traditional high-temperature hot working system cannot activate enough slip systems to dissipate the locally concentrated strain energy under the high-frequency compression of the shock wave front. Microcracks rapidly nucleate at the coarse austenite grain boundaries and propagate along the grain at an extremely high rate, resulting in the material exhibiting extremely scarce buffer space on a macroscopic scale.

[0076] In Comparative Example 2, due to the absence of a phase transition environment induced by a staged gradient temperature control method during annealing, the continuously precipitated carbide phase essentially served as a physical channel for rapid crack penetration. Although its dissipation of 12.3 kJ was slightly increased, it still falls within the typical engineering failure category in the face of the dynamic load equivalent of deep well rock bursts.

[0077] Comparative Example 3 did not employ the two-stage stepped heating secondary annealing process of this application, lacking a low-temperature stress release stage. This resulted in the inability to fully eliminate residual stress after cold finishing rolling, uncontrollable recrystallization, insufficient grain refinement, decreased microstructure uniformity and stability, and an imbalance between strength and plasticity. Consequently, under dynamic impact, its peak load, maximum elongation, total energy dissipation, and fracture delay were significantly lower than those of Example 1, indicating significantly poorer impact resistance and energy dissipation capacity.

[0078] Comparative Example 4 suffered from a lack of protective atmosphere during primary annealing, pickling damage, and decarburization embrittlement, resulting in comprehensive deterioration of both the surface and core structures. Its impact performance was even lower than that of Comparative Example 1, which used a traditional process.

[0079] Comparative Example 5, due to the reversed order of the secondary annealing, resulted in grain coarsening and residual internal stress, which was significantly inferior to the high strength, high toughness, and high impact resistance technical effect of Example 1 of this application.

[0080] Comparative Example 6 showed significantly lower elongation, energy dissipation, and fracture delay compared to Example 1. This is because it lacked plasticity and had coarse grains, making it unable to form effective plastic deformation and dissipate energy under high strain rate impact, thus significantly reducing its impact resistance.

[0081] Under the same dynamic load input conditions, the test results of Examples 1-3 exhibit an overwhelming reserve of impact toughness. Table 4 clearly shows that the total energy dissipation of Examples 1 to 3 all exceeded the high threshold of 27.0 kJ, the failure delay of Examples 1-3 was significantly extended to over 13 ms, and the maximum axial elongation reached over 85 mm. Referring to the transient response index of Example 1, after the material crossed an extremely high peak load of 412.5 kN, it did not experience the proportional instantaneous unloading collapse, but maintained an extremely long plastic tensile plateau accompanied by a huge energy dissipation of 28.4 kJ. Delving into the material science mechanism behind this macroscopic phenomenon, the sub-temperature recrystallization and stress-targeted exfoliation strategy constructed a strong and tough coupled network composed of fine equiaxed subgrains and nanoscale spheroidized carbides within the material matrix. When the high strain rate impact wavelength penetrates directly, the extremely high density of grain boundaries and phase interfaces forces dislocations to frequently undergo cross-slip and bypass mechanisms during the movement, and a large amount of kinetic energy is efficiently converted into plastic work heat energy within the crystal lattice. The micron-level geometric dimensional consistency ensured by the cold-rolling process completely eliminates weak points of stress concentration from the geometric morphology perspective, enabling a single hollow anchor rod to uniformly participate in deformation energy dissipation along its entire length. This deep synergy between microstructure and macrostructure effectively hinders the convergence and unstable propagation of impact microcracks, providing a crucial engineering redundancy to prevent sudden disintegration of the support system in deep, high-stress roadways caused by rockburst.

[0082] Test Example 4: Inspection of Grain Size and Depth of Surface Decarburized Layer Hollow anchor rods from the production lines of Examples 1 to 3, and hollow anchor rods of corresponding specifications obtained from Comparative Examples 1 to 6 were selected as samples. Meanwhile, to verify the microstructure evolution after a single annealing, hollow tube blanks after a single annealing were randomly selected as samples before cold finishing rolling in each example and comparative example.

[0083] According to GB / T 13298-2015 "Methods for Examination of Metal Microstructure", the hollow tube blank samples and hollow anchor rod samples after one annealing of each example and comparative example were transversely cut and prepared into standard metallographic specimens. After mechanical polishing and etching with 4% nitric acid alcohol solution, the microstructure was observed using an optical metallographic microscope and a scanning electron microscope.

[0084] Using metallographic image analysis software, the final average grain size level of the hollow anchor rods in each embodiment and comparative example was evaluated according to GB / T 6394-2017 "Method for Determination of Average Grain Size of Metals"; the total decarburization layer depth (mm) on the surface of the hollow anchor rod samples in each embodiment and comparative example was measured according to GB / T 224-2019 "Method for Determination of Decarburization Layer Depth of Steel"; and the pearlite spheroidization level inside the matrix of the hollow tube blank after one annealing was evaluated.

[0085] Table 5. Comparison of microstructure and decarburized layer depth of hollow anchor rods in each embodiment and comparative example.

[0086] Based on the microstructure and decarburization layer depth test results in Table 5, this application obtained intuitive metallographic confirmation through the underlying material science intervention introduced by refined temperature control and protective atmosphere. Observing the test results of Examples 1 to 3, the hollow tube blanks successfully obtained an excellent spheroidization level of 5 to 6 after one annealing. This confirms that the process combination of short-term holding at 800℃ followed by extremely slow cooling to 690℃ precisely triggered the discrete eutectoid transformation, providing extremely uniformly distributed dispersed phase support for subsequent high-strength cold deformation. In terms of the grain size performance of the hollow anchor rod body, the data of each example stably converged to an ultrafine grain level of 10.5 to 11.5. This secondary grain refinement is due to the Zener pinning effect on grain boundaries generated by high-standard spheroidized carbides during the finishing rolling process, and the perfect control of the sub-temperature recrystallization process during the secondary annealing stage, which completely blocked the growth channel of coarse grains.

[0087] In contrast, Comparative Examples 1 and 2, lacking the primary annealing method of this application, had average grain sizes of 7.5 to 8.0, which are conventional coarse grains. Comparative Example 1 has a continuous network carbide skeleton without spheroidized carbides. Although the carbides in Comparative Example 2 were spheroidized, the degree of spheroidization was only 3 and there were residual network carbides. This directly explains the root cause of the severe deterioration in plasticity and impact toughness in the previous Test Examples 2 and 3.

[0088] Comparative Example 3 did not employ the two-stage stepped heating secondary annealing process of this application. Direct high-temperature annealing led to grain coarsening during recrystallization, resulting in a final grain size of only 9.5 grade, significantly coarser than the 11.5 grade ultrafine grain structure of Example 1. Grain coarsening reduces grain boundary density, weakens the inhibition of dislocation movement, incompletely eliminates internal stress, and decreases microstructural stability. Consequently, Comparative Example 3 exhibits significantly inferior elongation after fracture, strength-ductility product, and dynamic impact resistance compared to Example 1.

[0089] Comparative Example 4 suffered from low spheroidization level, coarse grain size, and excessive decarburization layer due to the lack of a protective atmosphere during the first annealing and the subsequent acid pickling. This resulted in a comprehensive deterioration of the microstructure and surface properties.

[0090] Comparative Example 5 suffered from an abnormally coarsened recrystallized grain due to the reversed heating sequence during the secondary annealing. Although spheroidization and decarburization were normal, the grain refinement strengthening effect was lost, and the mechanical properties and impact resistance were significantly reduced.

[0091] In Comparative Example 6, the temperature of the first stage of secondary annealing was 550℃, which exceeded the suitable range for low-temperature recovery and stress relief, and entered the partial recrystallization temperature range. Holding at this temperature would cause premature local recrystallization of the microstructure after cold finishing rolling, resulting in insufficient recovery and incomplete elimination of residual internal stress. The recrystallization started too early and was uneven, and when the temperature was raised to 610℃, the grains were prone to coarsening. The final grain size was only grade 10.0, which was significantly coarser than grade 11.5 in Example 1.

[0092] Furthermore, the depth of the decarburized layer in the hollow anchor rods of each embodiment in Table 5 was strictly locked between 0.02 and 0.03 mm, while in Comparative Example 1, due to the use of traditional high-temperature long-term heating and the lack of protective atmosphere monitoring, the surface decarburized layer reached as high as 0.18 mm. This test example fully closed the technical verification chain from grain boundary evolution and surface decarburization control to the leap in macroscopic impact resistance mechanical properties.

[0093] In this application, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0094] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. The forming process of a hollow anchor rod body, characterized in that, The molding process includes the following steps: The hollow tube blank is fed into a multi-zone independently temperature-controlled electric annealing furnace for primary annealing to obtain a primary annealed hollow tube blank. The atmosphere in the multi-zone independently temperature-controlled electric annealing furnace is a protective atmosphere, which is a nitrogen-hydrogen mixture, and the dew point temperature of the protective atmosphere is below -40℃. The specific steps of the primary annealing are as follows: first, heating to T1 at a heating rate of 8~12℃ / min and holding at that temperature for 20~30min, where T1 is 830~850℃; then cooling to T2 at a cooling rate of 15~25℃ / h and holding at that temperature for 3~5h, where T2 is 0.80~0.85T1; followed by cooling. The hollow tube blank after the first annealing is directly fed into the finishing mill for cold finishing without pickling, to obtain the cold-finished hollow rod. The cold-rolled hollow bar is fed into the multi-zone independent temperature-controlled electric annealing furnace for secondary annealing to obtain a secondary annealed hollow bar. The specific steps of the secondary annealing are as follows: first, heating to T3 at a heating rate of 1~3℃ / min and holding at that temperature for 1~1.5h, where T3 is 0.53~0.60T1; then heating to T4 at a heating rate of 100~150℃ / h and holding at that temperature for 2~4h, where T4 is 0.70~0.75T1, followed by cooling. The hollow rod body after secondary annealing is sent into a composite straightening machine for straightening to obtain a straightened hollow rod body. The straightened hollow rod body is subjected to cold thread rolling to obtain a hollow anchor rod body.

2. The forming process of the hollow anchor rod body according to claim 1, characterized in that, The hollow tube blank is a 40Cr hollow tube blank, which is obtained through the following specific preparation steps: 40Cr alloy structural steel solid round steel is selected as the base material. The base material is heated to 1050~1100℃ and held at that temperature to obtain an austenitized base material. The austenitized substrate is continuously fed into a skew rolling mill for high-temperature hot deformation treatment and piercing to obtain the 40Cr hollow tube blank.

3. The forming process of the hollow anchor rod body according to claim 2, characterized in that, Based on the total weight of the 40Cr alloy structural steel solid round steel as 100%, the 40Cr alloy structural steel solid round steel comprises the following components: C 0.37~0.44%, Si 0.17~0.37%, Mn 0.50~0.80%, Cr 0.80~1.10%, S≤0.035%, P≤0.035%, with the balance being Fe and unavoidable impurities.

4. The forming process of the hollow anchor rod body according to any one of claims 1 to 3, characterized in that, T2 is 680~700℃.

5. The forming process of the hollow anchor rod body according to any one of claims 1 to 3, characterized in that, The process parameters for cold finishing rolling include: the operating speed of the finishing mill is set to 750~780 r / min, the single reduction rate is set to 10~15%, and the outer diameter of the hollow bar after cold finishing rolling is set to 20~30 mm.

6. The forming process of the hollow anchor rod body according to any one of claims 1 to 3, characterized in that, T3 is 450~500℃, and T4 is 600~620℃.

7. The forming process of the hollow anchor rod body according to any one of claims 1 to 3, characterized in that, The specific implementation method of feeding the hollow rod after secondary annealing into the composite straightening machine for straightening is as follows: the hollow rod after secondary annealing is fed into the composite straightening machine, and the depth of the reverse bending roller is dynamically adjusted by the laser online straightness monitoring instrument to control the straightness of the hollow rod after straightening to ≤1mm / m.

8. A hollow anchor rod body, characterized in that, The hollow anchor rod body is manufactured by the molding process described in any one of claims 1 to 7.

9. The hollow anchor rod body according to claim 8, characterized in that, The hollow anchor rod has a yield strength of over 800 MPa, a tensile strength of over 1000 MPa, an elongation after fracture of over 20%, and a strength-ductility product of over 20000 MPa·%.

10. The hollow anchor rod body according to claim 9, characterized in that, The hollow anchor rod has a yield strength of over 850 MPa, a tensile strength of over 1010 MPa, an elongation after fracture of over 21%, and a strength-ductility product of over 23000 MPa·%.

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