A rolling method for MG500Wφ24 high-strength, high-toughness, small-pitch threaded rib anchor steel bar

Abstract

The present application provides a method for rolling MG500Wφ24 high-strength, high-toughness, small-pitch threaded rib anchor steel bars, wherein the composition of the steel billet is as follows: 0.23% to 0.28% C, 0.40% to 0.55% Si, 1.35% to 1.50% Mn, 0.080% to 0.100% V, S≤0.035%, P≤0.035%, and the balance is Fe; a process path of low-temperature rolling, controlled rolling and controlled cooling, and high-precision phase connection of the shaft and the cooling bed insulation cover is adopted. The line sets the starting rolling temperature at 920℃~960℃, the finishing rolling entrance temperature at 920℃~960℃, controlled cooling after rolling, the upper cooling bed temperature at 920℃-930℃, and the cooling bed insulation cover for insulation. The full-line micro-tension process, loop precision control process, and full-rolling guide process are adopted to achieve stable production of crescent rib anchor steel bars with full-length dimensional stability and excellent mechanical properties. At the same time, high-precision and high-efficiency phase connecting shafts are used to effectively ensure the rib dimensional accuracy and rib efficiency.

Description

Technical Field

[0001] The invention relates to the technical field of anchor rod steel bar rolling, in particular to a method for rolling MG500Wφ24 high-strength, high-toughness, small-pitch threaded rib anchor rod steel bars. Background Art

[0002] As mine tunnels deepen, the surrounding rock of coal seams becomes more complex and unstable, with numerous deep fault structures. Mine pressure manifests itself in high in-situ stress, large deformation, rapid deformation, a wide range of influence, and engineering soft rock characteristics, making tunnel support difficult. Consequently, major coal mines are placing increasingly stringent quality demands on anchor bolts, particularly in terms of high strength, high toughness, and high load-bearing coefficient. A minimum yield strength of 500 MPa is required, and after the anchor bolts are connected using connectors, they undergo tension testing, with a load-bearing coefficient (the ratio of the breaking tensile strength of the cap to the breaking tensile strength of the bolt body) exceeding 98% to further enhance mine safety.

[0003] Anchor rod products produced by conventional hot rolling process are very likely to produce harmful structures such as Widmanstätten structure + network cementite due to the high starting rolling temperature and controlled rolling and cooling temperature. The comprehensive mechanical properties and processing performance of the steel bars are poor, and they are prone to processing cracks and poor plasticity. In addition, the product dimensional accuracy requirements of anchor rods are very high. If the process equipment is not designed properly, large fluctuations in the dimensional properties of the rods are likely to occur, exceeding the standard range. At the same time, due to the small spacing between the transverse ribs, the use of ordinary phase connecting shafts cannot meet the rib requirements, and improved connecting shafts must be used to ensure product accuracy. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for rolling MG500Wφ24 high-strength, high-toughness, small-pitch threaded rib anchor steel bars.

[0005] In order to solve the above technical problems, the technical solution proposed by the present invention is:

[0006] A rolling method for MG500Wφ24 high-strength, high-toughness, small-pitch threaded rib anchor steel bar, the rolling method comprising the following steps in sequence: heating the steel billet in a heating furnace, rough rolling, intermediate rolling, pre-finishing rolling, primary controlled cooling, finishing rolling, secondary controlled cooling, shearing with a double-length flying shear, heat-insulating cooling on a cooling bed, and natural aging;

[0007] The steel slab comprises the following elements in percentage by mass: 0.23%-0.28% C, 0.40%-0.55% Si, 1.35%-1.50% Mn, 0.080%-0.100% V, S≤0.035%, P≤0.035%, and the balance Fe and unavoidable impurity elements;

[0008] The furnace gas temperature in the soaking section of the heating furnace is controlled at 1030℃-1080℃, the heating time is ≥1.5 hours, the start rolling temperature is set to 920℃-960℃, the finishing rolling inlet temperature is 920℃-960℃, the water pressure in the primary cooling is controlled to 0.5-0.7MPa, the upper cooling bed temperature is 920℃-930℃, and an insulation cover is set on the cooling bed for insulation. The spacing between the finished cross ribs is 6±0.15mm.

[0009] Preferably, a full-line micro-tension process is adopted: the rough and medium rolling tension is in a micro-pile state and cannot present an obvious concave or convex curve. The tension value is controlled at 0 to -1%, and 6 vertical loopers are used to ensure full-line micro-tension rolling.

[0010] Preferably, a precise looper control process is adopted: the looper height is controlled at 150-250mm, the looper is released instantly when the head bites in, the looper release time is within 200ms, the looper is dropped instantly after the tail leaves the rolling mill, the looper drop time is controlled within 300ms, and the height difference of the entire length looper is stable within ±2mm.

[0011] Preferably, the K1-K3 full rolling guide process is adopted: the K1-K3 inlet guides are rolling, among which the K1 and K2 inlets adopt front and rear double-row rolling guides, and the K3 inlet adopts a single-row rolling guide. The hole shape of the guide wheel is completely matched with the hole shape of the previous roller to clamp the incoming material and ensure the stable and reliable size of the finished product.

[0012] Preferably, the K1 roller phase connecting shaft adopts a crankshaft connecting shaft.

[0013] Preferably, a Φ40mm water penetration device is used, the water pressure in the secondary controlled cooling is controlled to 0.2-0.5MPa, the cooling time is 0.3-0.35s, and 0.8MPa back-blowing air is used to purge the steel surface to prevent red rust from appearing on the surface.

[0014] This application has achieved the following beneficial technical effects:

[0015] The present invention adopts the process route of low-temperature rolling + controlled rolling and controlled cooling + high-precision phase connecting shaft + cooling bed insulation cover, sets the rolling temperature to 920℃-960℃, the finishing rolling inlet temperature to 920℃-960℃, controls cooling after rolling, and the upper cooling bed temperature is 920℃-930℃. The cooling bed insulation cover is used for insulation. The whole-line micro-tension process, the loop precision control process and the full-rolling guide process are adopted to achieve the stable production of rib anchor steel bars with full-length dimensional stability and excellent mechanical properties. At the same time, the high-precision and high-efficiency phase connecting shaft is used to effectively ensure the rib dimensional accuracy and rib efficiency. DETAILED DESCRIPTION

[0016] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0017] The present application provides a rolling method for MG500Wφ24 high-strength, high-toughness, small-pitch threaded rib anchor steel bar, the rolling method comprising the following steps in sequence: heating the steel billet in a heating furnace, rough rolling, intermediate rolling, pre-finishing rolling, primary controlled cooling, finishing rolling, secondary controlled cooling, shearing with a multiple-length flying shear, heat preservation cooling on a cooling bed, and natural aging;

[0018] The steel slab comprises the following elements in percentage by mass: 0.23%-0.28% C, 0.40%-0.55% Si, 1.35%-1.50% Mn, 0.080%-0.100% V, S≤0.035%, P≤0.035%, and the balance Fe and unavoidable impurity elements;

[0019] The furnace gas temperature in the soaking section of the heating furnace is controlled at 1030℃-1080℃, the heating time is ≥1.5 hours, the start rolling temperature is set to 920℃-960℃, the finishing rolling inlet temperature is 920℃-960℃, the water pressure in the primary cooling is controlled to 0.5-0.7MPa, the upper cooling bed temperature is 920℃-930℃, and an insulation cover is set on the cooling bed for insulation. The spacing between the finished cross ribs is 6±0.15mm.

[0020] In one embodiment of the present application, a full-line micro-tension process is adopted: the rough and medium rolling tension is in a micro-pile state and cannot present an obvious concave or convex curve. The tension value is controlled at 0 to -1%, and 6 vertical loopers are used to ensure micro-tension rolling of the entire line.

[0021] In one embodiment of the present application, a precise loop control process is adopted: the loop height is controlled at 150-250mm, the loop is released instantly when the head bites in, the loop release time is within 200ms, the loop is dropped instantly after the tail leaves the rolling mill, the loop drop time is controlled within 300ms, and the height difference of the entire length of the loop is stable within ±2mm.

[0022] In one embodiment of the present application, a K1-K3 full rolling guide process is adopted: the K1-K3 inlet guides are rolling, wherein the K1 and K2 inlets adopt front and rear double-row rolling guides, and the K3 inlet adopts a single-row rolling guide. The hole shape of the guide wheel is completely matched with the hole shape of the previous roller to clamp the incoming material and ensure that the finished product size is stable and reliable.

[0023] In one embodiment of the present application, the K1 roller phase connecting shaft adopts a crankshaft connecting shaft.

[0024] In one embodiment of the present application, a Φ40mm water penetration device is used, the water pressure in the secondary controlled cooling is controlled to 0.2-0.5MPa, the cooling time is 0.3-0.35s, and 0.8MPa back-blowing air is used to purge the steel surface to prevent red rust from appearing on the surface.

[0025] In this application, the production process of the steel billet adopts converter smelting, LF furnace refining, strong deoxidation, furnace bottom argon blowing, and small square billet continuous casting to smelt the steel billet that meets the above MG500φ24 chemical composition.

[0026] In this application, the "W" in MG500W means exported from Mongolia, MG is the first letter of anchor steel bar, and 500 refers to the yield strength of 500 MPa.

[0027] In this application, K1 uses high-speed steel and pearlite II rollers with good wear resistance, which provides technical guarantee for the surface quality and size of the finished product.

[0028] The working principle of the rolling method of MG500Wφ24 high-strength, high-toughness, small-pitch threaded rib anchor steel bar provided in this application is as follows:

[0029] Low temperature rolling refers to the rolling temperature of 920℃-960℃, because the general rolling process, the rolling temperature is 1000-1050℃. The role of low temperature rolling is to refine the austenite grains and prevent them from coarsening. If they are coarse, the physical properties of the steel, such as elongation after fracture, will be poor.

[0030] Controlled rolling refers to the finishing rolling inlet temperature of 920℃-960℃. The main function of controlled rolling is to prevent the temperature from rising during the rolling process, which will cause the grains to become coarse and thus affect the mechanical properties.

[0031] Controlled cooling means that the upper cooling bed temperature is between 920℃ and 930℃. The function of controlled cooling is to control cooling after rolling and inhibit grain growth, thereby obtaining the desired metallographic structure and mechanical properties.

[0032] The functions and effects of the high-precision phase connecting shaft in this application are: to ensure the dimensional accuracy of the ribs, prevent the production of defective products due to misaligned ribs, and prevent the long process debugging time caused by misaligned ribs. The K1 roll phase connecting shaft adopts a new crankshaft connecting shaft. The functional design of this adjustable coupling realizes the relative rotation of the outer gear sleeve at the roll end and the inner gear ring of the reducer while controlling the two output shafts of the reducer matched with the inner gear ring of the reducer to remain stationary, thereby realizing the relative rotation of the phase of the circular holes of the threaded ribs of the two rolls, thereby meeting the requirements for rib dimensional accuracy;

[0033] The purpose of setting up a heat preservation cover on the cooling bed is to reduce the cooling rate of the steel and prevent abnormal bainite structure from being generated due to excessive cooling, thereby affecting the mechanical properties.

[0034] The contents (%) in this application are all mass percentages.

[0035] The methods and devices not fully described in the present invention are all prior art and will not be described in detail.

[0036] In order to further understand the present invention, the rolling method of a MG500Wφ24 high-strength, high-toughness, small-pitch threaded rib anchor steel bar provided by the present invention is described in detail below in conjunction with embodiments. The protection scope of the present invention is not limited by the following embodiments.

[0037] Example 1

[0038] A rolling method for MG500Wφ24 high-strength, high-toughness, small-pitch threaded rib anchor steel bar, the rolling method comprising the following steps in sequence: heating the steel billet in a heating furnace, rough rolling, intermediate rolling, pre-finishing rolling, primary controlled cooling, finishing rolling, secondary controlled cooling, shearing with a double-length flying shear, heat-insulating cooling on a cooling bed, and natural aging;

[0039] The steel slab includes the following elements in percentage by mass: 0.25% C, 0.45% Si, 1.37% Mn, 0.085% V, 0.030% S, 0.020% P, and the balance Fe and unavoidable impurity elements;

[0040] The qualified steel billets enter the steel rolling heating furnace for heating. The furnace gas temperature in the soaking section of the heating furnace is controlled at 1030℃-1080℃, the heating time is ≥1.5 hours, and the starting rolling temperature of the steel billets is 920℃-940℃;

[0041] The hot billet enters the roughing and intermediate rolling, pre-finishing and finishing rolling areas. The finishing rolling inlet temperature is 930℃-945℃. After rolling, the cooling is controlled. The water pressure in the primary controlled cooling is controlled at 0.5-0.7MPa. The upper cooling bed temperature is 925℃. The cooling bed is equipped with a heat preservation cover for heat preservation. The spacing between the finished transverse ribs is 6±0.15mm.

[0042] The entire line adopts micro-tension technology: the tension of roughing and intermediate rolling is in a micro-pile state, and no obvious concave or convex curve is presented. The tension value is controlled at -0.5%, and 6 vertical loopers are used;

[0043] Adopting precise looper control technology: the looper heights of 1-6# loopers are 225mm, 200mm, 215mm, 200mm, 205mm and 225mm respectively. The looper is started instantly when the head bites into the rolling mill, and the looper start time is 180ms. The looper is dropped instantly after the tail leaves the rolling mill, and the drop time is controlled within 200ms. The height difference of the full-length looper is stable within ±2mm.

[0044] Adopt K1-K3 full rolling guide technology: K1-K3 inlet guides are rolling type, of which K1 and K2 inlet adopt front and rear double-row rolling guides, and K3 inlet adopts single-row rolling guides. The hole shape of the guide wheel is completely matched with the hole shape of the previous roller, which can effectively clamp the incoming material;

[0045] The K1 roller connecting shaft adopts a new type of crankshaft phase connecting shaft;

[0046] A Φ40mm water penetration device is used, the water pressure in the secondary controlled cooling is controlled at 0.2-0.5MPa, the cooling time is 0.3-0.35s, and 0.8MPa back-blowing air is used to purge the steel surface to prevent red rust from appearing on the surface.

[0047] After testing, the performance test results of the MG500WΦ24 high-strength, high-toughness, small-pitch threaded rib anchor steel bar prepared in Example 1 are as follows: yield strength is 540 MPa, tensile strength is 695 MPa, elongation after fracture is 20%, metallographic structure is ferrite + pearlite, impact energy at 20°C is 50 J, and out-of-roundness is 0.3 mm.

[0048] Example 2

[0049] A rolling method for MG500Wφ24 high-strength, high-toughness, small-pitch threaded rib anchor steel bar, the rolling method comprising the following steps in sequence: heating the steel billet in a heating furnace, rough rolling, intermediate rolling, pre-finish rolling, primary controlled cooling, finish rolling, secondary controlled cooling, shearing with a double-length flying shear, holding cooling on a cooling bed, and natural aging;

[0050] The steel slab includes the following elements in percentage by mass: 0.26% C, 0.55% Si, 1.50% Mn, 0.100% V, 0.015% S, 0.020% P, and the balance Fe and unavoidable impurity elements;

[0051] The qualified steel billets enter the steel rolling heating furnace for heating. The furnace gas temperature in the soaking section of the heating furnace is controlled at 1030℃-1080℃, the heating time is ≥1.5 hours, and the starting rolling temperature of the steel billets is 945℃-955℃;

[0052] The hot billet enters the roughing and intermediate rolling, pre-finishing and finishing rolling areas. The finishing rolling inlet temperature is 940℃-950℃. After rolling, the cooling is controlled. The water pressure in the primary cooling is controlled at 0.5-0.7MPa. The upper cooling bed temperature is 930℃. The cooling bed is equipped with a heat preservation cover for heat preservation. The spacing of the finished transverse ribs is 6±0.15mm. Finally, MG500φ24 high-strength, high-toughness, small-pitch threaded rib anchor steel bars are rolled out.

[0053] The entire line adopts micro-tension technology: the tension of roughing and intermediate rolling is in a micro-pile state, and no obvious concave or convex curve is presented. The tension value is controlled at -0.8%, and 6 vertical loopers are used;

[0054] Adopting precise looper control technology: the looper heights of 1-6# loopers are 210mm, 205mm, 205m, 200mm, 200mm, and 210mm respectively. The looper is started the moment the head bites into the rolling mill, and the looper start time is 150ms. The looper is dropped the moment the tail leaves the rolling mill, and the drop time is controlled within 180ms. The height difference of the full-length looper is stable within ±2mm.

[0055] Adopt K1-K3 full rolling guide technology: K1-K3 inlet guides are rolling type, of which K1 and K2 inlet adopt front and rear double-row rolling guides, and K3 inlet adopts single-row rolling guides. The hole shape of the guide wheel is completely matched with the hole shape of the previous roller, which can effectively clamp the incoming material;

[0056] The K1 roller connecting shaft adopts a new type of crankshaft phase connecting shaft;

[0057] A Φ40mm water penetration device is used, the water pressure in the secondary controlled cooling is controlled at 0.2-0.5MPa, the cooling time is 0.3-0.35s, and 0.8MPa back-blowing air is used to purge the steel surface to prevent red rust from appearing on the surface.

[0058] After testing, the performance test results of the MG500WΦ24 high-strength, high-toughness, small-pitch threaded rib anchor steel bar prepared in Example 2 are as follows: yield strength is 580 MPa, tensile strength is 735 MPa, elongation after fracture is 20%, metallographic structure is ferrite + pearlite, impact energy at 20°C is 50 J, and out-of-roundness is 0.2 mm.

[0059] The above embodiments are only intended to help understand the method and core concept of the present invention. It should be noted that, without departing from the principles of the present invention, a number of improvements and modifications may be made to the present invention by those skilled in the art, and such improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for rolling MG500Wφ24 high-strength, high-toughness, small-pitch threaded rib anchor steel bars, characterized in that: The rolling method comprises the following steps in sequence: heating the steel billet in a heating furnace, rough rolling, intermediate rolling, pre-finishing rolling, primary controlled cooling, finishing rolling, secondary controlled cooling, shearing by a double-length flying shear, holding cooling on a cooling bed, and natural aging; The steel slab comprises the following elements in percentage by mass: 0.23%-0.28% C, 0.40%-0.55% Si, 1.35%-1.50% Mn, 0.080%-0.100% V, S≤0.035%, P≤0.035%, and the balance Fe and unavoidable impurity elements; The furnace gas temperature of the soaking section of the heating furnace is controlled at 1030℃-1080℃, the heating time is ≥1.5 hours, the starting rolling temperature is set at 920℃-960℃, the finishing rolling inlet temperature is 920℃-960℃, the water pressure in the primary controlled cooling is controlled at 0.5-0.7MPa, the upper cooling bed temperature is 920℃-930℃, and an insulation cover is installed on the cooling bed for insulation. The spacing between the finished transverse ribs is 6±0.15mm; The entire line adopts a micro-tension process: the tension of roughing and intermediate rolling is in a micro-pile state, and no obvious concave or convex curve is presented. The tension value is controlled between 0 and -1%. Six vertical loopers are used to ensure micro-tension rolling throughout the line. Adopting precise looper control technology: the looper height is controlled at 150-250mm, the looper is started instantly when the head bites into the rolling mill, and the looper start time is within 200ms. The looper is dropped instantly after the tail leaves the rolling mill, and the drop time is controlled within 300ms. The looper height difference is stable within ±2mm throughout the whole process. Adopting K1-K3 full rolling guide technology: K1-K3 inlet guides are rolling type, of which K1 and K2 inlet adopt front and rear double-row rolling guides, and K3 inlet adopts single-row rolling guides. The hole shape of the guide wheel is completely matched with the hole shape of the previous roller to clamp the incoming material and ensure the stable and reliable size of the finished product; The K1 roller phase connecting shaft adopts a crankshaft type connecting shaft; A Φ40mm water penetration device is used, the water pressure in the secondary controlled cooling is controlled at 0.2-0.5MPa, the cooling time is 0.3-0.35s, and 0.8MPa back-blowing air is used to purge the steel surface to prevent red rust from appearing on the surface.