Hot rolling process of dense-pitch threaded rib anchor rod reinforcing steel bar

Abstract

The invention relates to the technical field of metallurgy, in particular to a hot rolling process of a dense-pitch threaded rib anchor rod reinforcing steel bar, which comprises the following steps: heating a steel billet, rolling, cooling after rolling, and naturally aging to obtain the dense-pitch threaded rib anchor rod reinforcing steel bar with the pitch of 4.0 + / -0.1 mm; rolling comprises rough rolling, intermediate rolling, pre-finish rolling and finish rolling, the accuracy of rough rolling and intermediate rolling is controlled to be + / -0.5 mm, and the accuracy of finish rolling is controlled to be + / -0.1 mm; the height of the loop device is set between 200 mm and 210 mm; roll gaps are controlled in place at one time, and the deviation is controlled to be + / -0.1 mm; a K1 roller connecting shaft is a crankshaft type phase connecting shaft, the bottom width of a transverse rib of the K1 roller is designed to be 2.8 mm, and the radius of a chamfer arc of the transverse rib is designed to be 1.5 mm. According to the method, high-quality production of the dense-pitch threaded rib anchor rod steel bar with the pitch of 4.0 + / -0.1 mm is realized by regulating and controlling various conditions of the hot rolling process.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, specifically to a hot rolling process for closely pitched threaded ribbed anchor bars. Background Technology

[0002] In underground coal seam operations, anchor bolts, as core support components ensuring mining safety, have stringent performance requirements. They need sufficient strength and toughness to resist the impact of in-situ stress under complex geological conditions and prevent breakage due to excessive stress. Their surface structure design must form a strong bond with the anchoring agent (such as cement grout) to ensure no slippage occurs during the transfer of loads from the soil and rock mass, thereby effectively maintaining the stability of the support system. Simultaneously, they must be compatible with nuts and other accessories to avoid performance degradation due to stress concentration during installation and use, providing a safe and stable guarantee for the entire coal seam mining operation. Currently, commonly used anchor bolt reinforcement bars in underground drilling have many shortcomings. Hot-rolled ribbed steel bars for anchor bolts require threading at the ends, weakening end strength and increasing processing costs and construction time. While hot-rolled ribbed steel bars for continuous equal-height threaded anchor bolts eliminate some machining steps and can connect fittings at any cross-section, they mostly use conventional pitches (e.g., ...). Figure 1 As shown in the figure, it performs poorly in terms of precision control.

[0003] With the increasing depth of coal seam mining, the ground stress and geological complexity have significantly increased, and existing conventional threaded anchor bars can no longer meet the support requirements with high safety factors. However, the production of closely spaced threaded anchor bars faces many problems: the smaller the thread pitch, the higher the precision requirements of the ribs; even a small error can lead to misalignment of the threaded ribs, and the bottom width of the threaded ribs will narrow as the thread pitch decreases. During the rolling process, the transverse ribs are prone to defects such as chipping and slotting due to stress concentration, affecting the quality of the steel bar forming. CN114505341A discloses a hot rolling process method for closely spaced threaded rib anchor bars, which uses a process route of "low-temperature initial rolling + controlled rolling" to prepare closely spaced threaded anchor bars, but its closely spaced thread pitch can only be controlled to 4.5±0.15mm, and there is still room for further improvement. Summary of the Invention

[0004] To address the technical problems of defects such as thread rib misalignment, transverse rib chipping, and groove bursting that easily occur during the production of closely pitched threaded rib anchor bars, this invention provides a hot rolling process for closely pitched threaded rib anchor bars. By controlling various conditions of the hot rolling process, high-quality production of closely pitched threaded rib anchor bars with a pitch of 4.0±0.1mm can be achieved.

[0005] The technical solution of this invention is as follows: A hot rolling process for closely pitched threaded ribbed anchor bars involves heating, rolling, controlled cooling after rolling, and natural aging of steel billets to obtain closely pitched threaded ribbed anchor bars with a pitch of 4.0±0.1mm. The steel billet contains the following chemical composition by mass percentage: C 0.21%-0.28%, Si 0.40%-0.55%, Mn 1.4%-1.6%, S 0.02%-0.03%, P 0.02%-0.03%, V 0%-0.14%, N≤208ppm, O≤50ppm, with the balance being Fe and unavoidable impurities; Rolling includes roughing, intermediate rolling, pre-finishing, and finishing. The accuracy of roughing and intermediate rolling is controlled within ±0.5mm, and the accuracy of finishing rolling is controlled within ±0.1mm. The looper is set at a height between 200-210mm. The roll gap is controlled in one go, with a deviation controlled within ±0.1mm. The K1 roll connecting shaft adopts a crankshaft-type phase connecting shaft. The bottom width of the K1 roll cross rib is designed to be 2.8mm, and the radius of the cross rib chamfer arc is designed to be 1.5mm.

[0006] Furthermore, when preparing MG400 Φ22 close-pitch threaded ribbed anchor bars, the steel billet contains the following chemical composition by mass percentage: C 0.23%-0.28%, Si 0.40%-0.55%, Mn 1.4%-1.6%, S 0.02%-0.03%, P 0.02%-0.03%, O≤50ppm, with the balance being Fe and unavoidable impurities.

[0007] Furthermore, when preparing MG500 Φ22 closely threaded ribbed anchor bars, the steel billet contains the following chemical composition by mass percentage: C 0.22%-0.27%, Si 0.40%-0.55%, Mn 1.4%-1.6%, S 0.02%-0.03%, P 0.02%-0.03%, V 0.055%-0.075%, N 70.5ppm-97.5ppm, O≤50ppm, with the balance being Fe and unavoidable impurities.

[0008] Furthermore, when preparing MG600 Φ22 closely threaded ribbed anchor bars, the steel billet contains the following chemical composition by mass percentage: C 0.20%-0.24%, Si 0.40%-0.55%, Mn 1.4%-1.6%, S 0.02%-0.03%, P 0.02%-0.03%, V 0.14%-0.16%, N 182ppm-208ppm, O≤50ppm, with the balance being Fe and unavoidable impurities.

[0009] Furthermore, the nitrogen content is constrained based on the V content. The nitrogen content control requirement is: N content = V content × 1300; the unit of N is ppm, and the V content is the value without the percentage sign.

[0010] The mechanical strength requirements of closely pitched threaded ribbed anchor bars with specifications of MG500 and MG600 are high. Therefore, the mechanical properties of closely pitched threaded ribbed anchor bars can be improved by appropriately adding vitamin C and limiting the nitrogen content according to the vitamin C content.

[0011] Furthermore, during heating, the furnace gas temperature in the soaking zone of the hot furnace is controlled at 1080-1200℃, and the heating time is ≥1 hour.

[0012] Furthermore, during rolling, the initial rolling temperature is set to 950-985℃, and the finishing rolling inlet temperature is set to 945-970℃.

[0013] Furthermore, during rolling, the inlet guides of K1-K3 are all rolling guides, and the rolls are high-speed steel rolls.

[0014] Furthermore, the high-speed steel rolls comprise the following chemical composition by mass percentage: C 1.5%-2.0%, Si 0.3%-0.7%, Mn 0.3%-0.7%, P≤0.03%, S≤0.03%, Cr 4.0%-6.0%, Ni 0.7%-1.5%, Nb 0.5%-1.5%, Mo 3.0%-6.0%, V 3.0%-6.0%, W 5.0%-7.0%, Co 0%-2.0%, with the balance being Fe and unavoidable impurities.

[0015] A reduced pitch will increase the contact friction between the roll and the steel bar, accelerate the wear rate of the transverse ribs, and significantly shorten the life of the rolling groove. Using high-speed steel rolls with the above-mentioned chemical composition can improve the service life of the rolls.

[0016] Furthermore, during the air cooling after rolling, the temperature of the upper cooling bed is 825-850℃, and an insulation cover is installed on the inlet side of the cooling bed for insulation.

[0017] The beneficial effects of this invention are as follows: This invention provides a hot rolling process for closely spaced threaded ribbed anchor bars. This process effectively avoids rib misalignment by precisely controlling the material shape, tension, and roll gap throughout the entire process, achieving precise rib alignment. Simultaneously, through optimization of the guide system, transmission structure, and roll pass parameters, it further improves rolling accuracy and roll life while ensuring precise rib alignment. It successfully solves the problem of material loss and groove bursting of transverse ribs due to stress concentration during rolling, providing a reliable guarantee for the stable production of closely spaced threaded anchor bars. The closely spaced threaded ribbed anchor bars obtained using the hot rolling process of this invention have a small pitch and a small thread root width, with the pitch controllable to 4.0±0.1mm and the thread root width controllable to 2.6mm. Compared to the situation before the adoption of the process of this invention, where the minimum pitch of the anchor rod rebar could only be controlled to 4.5±0.15mm and the minimum thread width could only be controlled to 3.2mm, the matching degree between the nut and the anchor rod body is higher, the connection is tighter, and the contact area is larger, thereby effectively improving the efficiency bearing coefficient between the rod body and the nut, and further improving the intrinsic safety factor of the mine. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 It is a hot-rolled ribbed steel bar for continuous equal-height threaded anchor rods with conventional pitch, which is a technology currently in use.

[0020] Figure 2 This is the closely pitched threaded ribbed anchor bar of Embodiment 1 of the present invention.

[0021] Figure 3 The present invention is a closely spaced threaded rib anchor bar with defects such as thread rib misalignment, transverse rib chipping, and groove bursting, as described in Comparative Example 1 of the present invention.

[0022] In the diagram, 1-misaligned thread rib, 2-bursting groove, 3-chipped material. Detailed Implementation

[0023] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0024] Example 1 A hot rolling process for MG400 Φ22 closely spaced threaded ribbed anchor bars includes the following steps: (1) Steel billet heating: The furnace gas temperature in the soaking section of the heating furnace is controlled at 1080℃, and the heating time is ≥1 hour; the steel billet includes the following chemical composition by mass percentage: C 0.23%, Si 0.45%, Mn 1.4%, S 0.02%, P 0.022%, O 45ppm, with the balance being Fe and unavoidable impurities; (2) Rolling: including roughing, intermediate rolling, pre-finishing rolling and finishing rolling, with the initial rolling temperature set at 985℃ and the finishing rolling inlet temperature at 945℃; Precise rib alignment is achieved through precise control of material shape, tension, and roll gap throughout the entire process, including: The accuracy of roughing and intermediate rolling is controlled within ±0.5mm, and the accuracy of finishing rolling is controlled within ±0.1mm to ensure accurate material shape control throughout the entire line; the looper device is set at a height between 200-210mm and is used in a fixed position to prevent excessive adjustment of the looper; the roll gap is controlled in one go with a deviation of ±0.1mm to prevent misalignment caused by roll movement. By optimizing the guide system, transmission structure, and roll pass parameters, the rolling accuracy and roll life after precise rib alignment are improved, and the problem of transverse rib breakage is solved, including: All imported guides for K1-K3 rolls are rolling guides. The original semi-steel rolls have been upgraded to high-speed steel rolls (special type), solving the problem of low roll groove life. The high-speed steel rolls (special type) have the following chemical composition by mass percentage: C 1.5%, Si 0.3%, Mn 0.3%, P 0.03%, S 0.03%, Cr 4.0%, Ni 0.7%, Nb 0.5%, Mo 3.0%, V 3.0%, W 5.0%, with the balance being Fe and unavoidable impurities. The K1 roll connecting shaft adopts a crankshaft-type phase connecting shaft, improving transmission accuracy. The K1 roll pass is precisely designed, with a bottom width of 2.8mm for the K1 roll transverse ribs and a radius of 1.5mm for the transverse rib chamfer radius, solving the problem of transverse rib breakage. (3) Air cooling after rolling: The temperature of the upper cooling bed is 825℃. An insulation cover is installed on the inlet side of the cooling bed (the insulation cover is the same length as the cooling bed, which is 108m and the width of the insulation cover is 2m). The cooling bed insulation cover is used for insulation. After natural aging, MG400 Φ22 dense pitch threaded rib anchor rod steel bars are obtained.

[0025] The performance test results of MG400 Φ22 closely threaded ribbed anchor bars are as follows: yield strength 455MPa, tensile strength 605MPa, and elongation after fracture 18%. The dimensional parameters of MG400 Φ22 closely threaded ribbed anchor bars are: pitch 4.0±0.1mm, thread root width 2.6mm (e.g., ...). Figure 2 (As shown).

[0026] Example 2 A hot rolling process for MG500 Φ22 closely spaced threaded ribbed anchor rod steel bars includes the following steps: (1) Steel billet heating: The furnace gas temperature in the soaking section of the heating furnace is controlled at 1080℃, and the heating time is ≥1 hour; the steel billet includes the following chemical composition by mass percentage: C 0.27%, Si 0.40%, Mn 1.4%, S 0.02%, P 0.022%, V 0.055%, N 71.5ppm, O 50ppm, with the balance being Fe and unavoidable impurities; The nitrogen content is constrained based on the v content. The nitrogen content control requirement is: N content (ppm) = v content × 1300. The v content is a value without a percentage sign. For example, when v = 0.05%, N = 0.055 × 1300 = 71.5 ppm. The source of N is to select alloy materials with higher nitrogen content to ensure that the nitrogen content of the added alloy meets the nitrogen content control requirements, or / and during the converter or electric furnace smelting process, N can be appropriately blown to increase the N content and prepare steel billets with the required N content. (2) Rolling: including roughing, intermediate rolling, pre-finishing rolling and finishing rolling, with the initial rolling temperature set at 985℃ and the finishing rolling inlet temperature at 945℃; Precise rib alignment is achieved through precise control of material shape, tension, and roll gap throughout the entire process, including: The accuracy of roughing and intermediate rolling is controlled within ±0.5mm, and the accuracy of finishing rolling is controlled within ±0.1mm to ensure accurate material shape control throughout the entire line; the looper device is set at a height between 200-210mm and is used in a fixed position to prevent excessive adjustment of the looper; the roll gap is controlled in one go with a deviation of ±0.1mm to prevent misalignment caused by roll movement. By optimizing the guide system, transmission structure, and roll pass parameters, the rolling accuracy and roll life after precise rib alignment are improved, and the problem of transverse rib breakage is solved, including: All imported guides for K1-K3 rolls are rolling guides. The original semi-steel rolls have been upgraded to high-speed steel rolls (special type), solving the problem of low roll groove life. The high-speed steel rolls (special type) have the following chemical composition by mass percentage: C 2.0%, Si 0.7%, Mn 0.7%, P 0.03%, S 0.03%, Cr 6.0%, Ni 1.5%, Nb 1.5%, Mo 6.0%, V 6.0%, W 7.0%, Co 2.0%, with the balance being Fe and unavoidable impurities. The K1 roll connecting shaft adopts a crankshaft-type phase connecting shaft, improving transmission accuracy. The K1 roll pass is precisely designed, with a cross rib bottom width of 2.8mm and a cross rib chamfer radius of 1.5mm, solving the problem of cross rib breakage. (3) Air cooling after rolling: The temperature of the upper cooling bed is 825℃. An insulation cover is set on the inlet side of the cooling bed (the insulation cover is the same length as the cooling bed, which is 108m and the width of the insulation cover is 2m). The cooling bed insulation cover is used for insulation (to avoid the formation of Widmanstätten structure). After natural aging, MG500Φ22 dense pitch threaded rib anchor rod steel bars are obtained.

[0027] The performance test results of MG500 Φ22 closely threaded ribbed anchor bars are as follows: yield strength 550MPa, tensile strength 700MPa, and elongation after fracture 19%. The dimensional parameters of MG500 Φ22 closely threaded ribbed anchor bars are: pitch 4.0±0.1mm, thread root width 2.6mm.

[0028] Example 3 A hot rolling process for MG600 Φ22 closely spaced threaded ribbed anchor bars includes the following steps: (1) Steel billet heating: The furnace gas temperature in the soaking section of the heating furnace is controlled at 1080℃, and the heating time is ≥1 hour; the steel billet includes the following chemical composition by mass percentage: C 0.24%, Si 0.40%, Mn 1.6%, S 0.03%, P 0.02%, V 0.14%, N 182ppm, O 38ppm, with the balance being Fe and unavoidable impurities; The nitrogen content is constrained based on the v content. The nitrogen content control requirement is: N content (ppm) = v content × 1300. The v content is a value without a percentage sign. For example, when v = 0.14%, N = 0.14 × 1300 = 182 ppm. The source of N is to select alloy materials with higher nitrogen content to ensure that the nitrogen content of the added alloy meets the nitrogen content control requirements, or / and during the converter or electric furnace smelting process, N can be appropriately blown to increase the N content and prepare steel billets with the required N content. (2) Rolling: including roughing, intermediate rolling, pre-finishing rolling and finishing rolling, with the initial rolling temperature set at 985℃ and the finishing rolling inlet temperature at 940℃; Precise rib alignment is achieved through precise control of material shape, tension, and roll gap throughout the entire process, including: The accuracy of roughing and intermediate rolling is controlled within ±0.5mm, and the accuracy of finishing rolling is controlled within ±0.1mm to ensure accurate material shape control throughout the entire line; the looper device is set at a height between 200-210mm and is used in a fixed position to prevent excessive adjustment of the looper; the roll gap is controlled in one go with a deviation of ±0.1mm to prevent misalignment caused by roll movement. By optimizing the guide system, transmission structure, and roll pass parameters, the rolling accuracy and roll life after precise rib alignment are improved, and the problem of transverse rib breakage is solved, including: All imported guides for K1-K3 rolls are rolling guides. The original semi-steel rolls have been upgraded to high-speed steel rolls (special type), solving the problem of low groove life. The high-speed steel rolls (special type) have the following chemical composition by mass percentage: C 1.5%, Si 0.7%, Mn 0.7%, P 0.02%, S 0.02%, Cr 6.0%, Ni 0.7%, Nb 0.5%, Mo 6.0%, V 6.0%, W 5.0%, with the balance being Fe and unavoidable impurities. The K1 roll connecting shaft adopts a crankshaft-type phase connecting shaft, improving transmission accuracy. The K1 roll pass is precisely designed, with a bottom width of 2.8mm for the K1 roll transverse ribs and a radius of 1.5mm for the transverse rib chamfer radius, solving the problem of transverse rib breakage. (3) Air cooling after rolling: The temperature of the upper cooling bed is 825℃. An insulation cover is set on the inlet side of the cooling bed (the insulation cover is the same length as the cooling bed, which is 108m and the width of the insulation cover is 2m). The cooling bed insulation cover is used for insulation. After natural aging, MG600 Φ22 dense pitch threaded rib anchor rod steel bars are obtained.

[0029] The performance test results of MG600 Φ22 closely threaded ribbed anchor bars are as follows: yield strength 631MPa, tensile strength 785MPa, and elongation after fracture 20%. The dimensional parameters of MG600 Φ22 closely threaded ribbed anchor bars are: pitch 4.0±0.1mm, thread root width 2.6mm.

[0030] Comparative Example 1 A hot rolling process for MG400 Φ22 closely spaced threaded ribbed anchor bars includes the following steps: (1) Steel billet heating: The furnace gas temperature in the soaking section of the heating furnace is controlled at 1080℃, and the heating time is ≥1 hour; the chemical composition of the steel billet is the same as in Example 1; (2) Rolling: including roughing, intermediate rolling, pre-finishing rolling and finishing rolling, with the initial rolling temperature set at 985℃ and the finishing rolling inlet temperature at 945℃; The accuracy of roughing, intermediate rolling and finishing rolling is controlled within ±0.5mm; the looper setting height is between 200-210mm; the roll gap is controlled in one go, with the deviation controlled within ±0.5mm; All K1-K3 imported guides are rolling guides, using high-speed steel rolls (ordinary type). The high-speed steel rolls (ordinary type) have the following chemical composition by mass percentage: C 1.5%, Si 0.7%, Mn 0.3%, P 0.03%, S 0.03%, Cr 4.0%, Ni 1.5%, Mo 3.5%, V 4.5%, W 1.8%, with the balance being Fe and unavoidable impurities. The K1 roll connecting shaft adopts a crankshaft-type phase connecting shaft. The bottom width of the K1 roll transverse rib is 2.6mm, and the radius of the chamfered arc of the transverse rib is 0.5mm. (3) Air cooling after rolling: The temperature of the upper cooling bed is 825℃. An insulation cover is installed on the inlet side of the cooling bed (the insulation cover is the same length as the cooling bed, which is 108m and the width of the insulation cover is 2m). The cooling bed insulation cover is used for insulation. After natural aging, MG400 Φ22 dense pitch threaded rib anchor rod steel bars are obtained.

[0031] The performance test results of MG400 Φ22 closely threaded ribbed anchor bars are as follows: yield strength 420MPa, tensile strength 597MPa, and elongation after fracture 16%. The dimensional parameters of MG400 Φ22 closely threaded ribbed anchor bars are as follows: the minimum thread pitch can only be controlled to 4.5±0.1mm, the minimum thread root width can only be controlled to 3.2mm, and when the thread pitch reaches 4.0±0.1mm, if... Figure 3 As shown, defects such as thread rib misalignment, transverse rib chipping, and groove bursting may occur.

[0032] Comparative Example 2 A hot rolling process for MG500 Φ22 closely spaced threaded ribbed anchor rod steel bars includes the following steps: (1) Steel billet heating: The furnace gas temperature in the soaking section of the heating furnace is controlled at 1080℃, and the heating time is ≥1 hour; the steel billet includes the following chemical composition by mass percentage: C 0.27%, Si 0.40%, Mn 1.4%, S 0.02%, P 0.022%, O 50ppm, with the balance being Fe and unavoidable impurities; (2) Rolling: including roughing, intermediate rolling, pre-finishing rolling and finishing rolling, with the initial rolling temperature set at 985℃ and the finishing rolling inlet temperature at 945℃; The accuracy of roughing, intermediate rolling and finishing rolling is controlled within ±0.5mm; the looper setting height is between 200-210mm; the roll gap is controlled in one go, with the deviation controlled within ±0.5mm; All K1-K3 imported guides are rolling guides, using high-speed steel rolls (ordinary type). The high-speed steel rolls (ordinary type) have the following chemical composition by mass percentage: C 1.5%, Si 0.7%, Mn 0.3%, P 0.03%, S 0.03%, Cr 4.0%, Ni 1.5%, Mo 3.5%, V 4.5%, W 1.8%, with the balance being Fe and unavoidable impurities. The K1 roll connecting shaft adopts a crankshaft-type phase connecting shaft. The bottom width of the K1 roll transverse rib is 2.6mm, and the radius of the chamfered arc of the transverse rib is 0.5mm. (3) Air cooling after rolling: The temperature of the upper cooling bed is 825℃. An insulation cover is set on the inlet side of the cooling bed (the insulation cover is the same length as the cooling bed, which is 108m and the width of the insulation cover is 2m). The cooling bed insulation cover is used for insulation (to avoid the formation of Widmanstätten structure). After natural aging, MG500Φ22 dense pitch threaded rib anchor rod steel bars are obtained.

[0033] The performance test results of MG500 Φ22 closely threaded ribbed anchor bars are as follows: yield strength 506MPa, tensile strength 620MPa, and elongation after fracture 18%. The dimensional parameters of MG500 Φ22 closely threaded ribbed anchor bars are as follows: the minimum thread pitch can only be controlled to 4.5±0.1mm, and the minimum thread root width can only be controlled to 3.2mm. When the thread pitch reaches 4.0±0.1mm, defects such as thread rib misalignment, transverse rib chipping, and groove bursting occur.

[0034] Comparative Example 3 A hot rolling process for MG600 Φ22 closely spaced threaded ribbed anchor bars includes the following steps: (1) Steel billet heating: The furnace gas temperature in the soaking section of the heating furnace is controlled at 1080℃, and the heating time is ≥1 hour; the steel billet includes the following chemical composition by mass percentage as in Example 3; (2) Rolling: including roughing, intermediate rolling, pre-finishing rolling and finishing rolling, with the initial rolling temperature set at 1000℃ and the finishing rolling inlet temperature at 940℃; The accuracy of roughing, intermediate rolling and finishing rolling is controlled within ±0.5mm; the looper setting height is between 200-210mm; the roll gap is controlled in one go, with the deviation controlled within ±0.5mm; All K1-K3 imported guides are rolling guides, using high-speed steel rolls (ordinary type). The high-speed steel rolls (ordinary type) have the following chemical composition by mass percentage: C 1.5%, Si 0.7%, Mn 0.3%, P 0.03%, S 0.03%, Cr 4.0%, Ni 1.5%, Mo 3.5%, V 4.5%, W 1.8%, with the balance being Fe and unavoidable impurities. The K1 roll connecting shaft adopts a crankshaft-type phase connecting shaft. The bottom width of the K1 roll transverse rib is 2.6mm, and the radius of the chamfered arc of the transverse rib is 0.5mm. (3) Air cooling after rolling: The temperature of the upper cooling bed is 825℃. An insulation cover is set on the inlet side of the cooling bed (the insulation cover is the same length as the cooling bed, which is 108m and the width of the insulation cover is 2m). The cooling bed insulation cover is used for insulation. After natural aging, MG600 Φ22 dense pitch threaded rib anchor rod steel bars are obtained.

[0035] The performance test results of MG600 Φ22 closely threaded ribbed anchor bars are as follows: yield strength 615MPa, tensile strength 737MPa, and elongation after fracture 19%. The dimensional parameters of MG600 Φ22 closely threaded ribbed anchor bars are as follows: the minimum thread pitch can only be controlled to 4.5±0.1mm, and the minimum thread root width can only be controlled to 3.2mm. When the thread pitch reaches 4.0±0.1mm, defects such as thread rib misalignment, transverse rib chipping, and groove bursting occur.

[0036] Although the present invention has been described in detail with reference to the accompanying drawings and preferred embodiments, the present invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should also be covered within the protection scope of the present invention.

Claims

1. A hot rolling process for closely pitched threaded ribbed anchor bars, characterized in that, Steel billets are heated, rolled, cooled under controlled conditions after rolling, and naturally aged to obtain closely spaced threaded ribbed anchor bars with a pitch of 4.0±0.1mm; The steel billet contains the following chemical composition by mass percentage: C 0.21%-0.28%, Si 0.40%-0.55%, Mn 1.4%-1.6%, S 0.02%-0.03%, P 0.02%-0.03%, V 0%-0.14%, N≤208ppm, O≤50ppm, with the balance being Fe and unavoidable impurities; Rolling includes roughing, intermediate rolling, pre-finishing, and finishing. The accuracy of roughing and intermediate rolling is controlled within ±0.5mm, and the accuracy of finishing rolling is controlled within ±0.1mm. The looper is set at a height between 200-210mm. The roll gap is controlled in one go, with a deviation controlled within ±0.1mm. The K1 roll connecting shaft adopts a crankshaft-type phase connecting shaft. The bottom width of the K1 roll cross rib is designed to be 2.8mm, and the radius of the cross rib chamfer arc is designed to be 1.5mm.

2. The hot rolling process for a closely pitched threaded ribbed anchor bar as described in claim 1, characterized in that, When preparing MG400 Φ22 closely pitched threaded ribbed anchor bars, the steel billet contains the following chemical composition by mass percentage: C 0.23%-0.28%, Si 0.40%-0.55%, Mn 1.4%-1.6%, S 0.02%-0.03%, P 0.02%-0.03%, O≤50ppm, with the balance being Fe and unavoidable impurities.

3. The hot rolling process for a closely pitched threaded ribbed anchor bar as described in claim 1, characterized in that, When preparing MG500 Φ22 closely threaded ribbed anchor bars, the steel billet contains the following chemical composition by mass percentage: C 0.22%-0.27%, Si 0.40%-0.55%, Mn 1.4%-1.6%, S 0.02%-0.03%, P 0.02%-0.03%, V 0.055%-0.075%, N 70.5ppm-97.5ppm, O≤50ppm, with the balance being Fe and unavoidable impurities.

4. The hot rolling process for a closely pitched threaded ribbed anchor bar as described in claim 1, characterized in that, When preparing MG600 Φ22 closely threaded ribbed anchor bars, the steel billet contains the following chemical composition by mass percentage: C 0.20%-0.24%, Si 0.40%-0.55%, Mn 1.4%-1.6%, S 0.02%-0.03%, P 0.02%-0.03%, V 0.14%-0.16%, N 182ppm-208ppm, O≤50ppm, with the balance being Fe and unavoidable impurities.

5. The hot rolling process for a closely pitched threaded ribbed anchor bar as described in claim 3 or claim 4, characterized in that, The nitrogen content is constrained based on the V content. The nitrogen content control requirement is: N content = V content × 1300; the unit of N is ppm, and the V content is the value without the percentage sign.

6. The hot rolling process for a closely pitched threaded ribbed anchor bar as described in claim 1, characterized in that, During heating, the furnace gas temperature in the soaking zone of the hot furnace is controlled at 1080-1200℃, and the heating time is ≥1 hour.

7. The hot rolling process for a closely pitched threaded ribbed anchor bar as described in claim 1, characterized in that, During rolling, the initial rolling temperature is set to 950-985℃, and the finishing rolling inlet temperature is set to 945-970℃.

8. The hot rolling process for a closely pitched threaded ribbed anchor bar as described in claim 1, characterized in that, During rolling, the inlet guides of K1-K3 are all rolling guides, and the rolls are high-speed steel rolls.

9. The hot rolling process for a closely pitched threaded ribbed anchor bar as described in claim 8, characterized in that, High-speed steel rolls contain the following chemical composition by mass percentage: C 1.5%-2.0%, Si 0.3%-0.7%, Mn 0.3%-0.7%, P≤0.03%, S≤0.03%, Cr 4.0%-6.0%, Ni 0.7%-1.5%, Nb 0.5%-1.5%, Mo 3.0%-6.0%, V 3.0%-6.0%, W 5.0%-7.0%, Co 0%-2.0%, with the balance being Fe and unavoidable impurities.

10. The hot rolling process for a closely pitched threaded ribbed anchor bar as described in claim 1, characterized in that, When air cooling is performed after rolling, the temperature of the upper cooling bed is 825-850℃. An insulation cover is installed on the inlet side of the cooling bed for insulation.

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