Hot rolled steel for 500MPa-grade high-ductility hollow anchor rod welded pipe as well as preparation method and application of hot rolled steel

Abstract

The invention discloses hot rolled steel for a 500MPa-grade high-ductility hollow anchor rod welded pipe as well as a preparation method and application of the hot rolled steel, and belongs to the technical field of hot continuous rolling plate strip production. The hot rolled steel for the 500MPa-grade high-ductility hollow anchor rod welded pipe is prepared through smelting, casting blank heating, rough rolling, coiling of a hot coiling box, finish rolling, laminar cooling and coiling. The yield strength is larger than or equal to 500 MPa, the tensile strength is larger than or equal to 600 MPa, the percentage elongation after fracture is larger than or equal to 26%, and the maximum force percentage elongation is larger than or equal to 14%. The hot rolled steel is subjected to the machining procedures of heating of a high-frequency electric heating device, three-roller spinning equal-diameter rolling, online heat treatment, saw cutting and slow cooling of a cooling bed, and a hollow anchor rod body is obtained; the yield force is larger than or equal to 150 kN, the tensile resistance is larger than or equal to 200 kN, and the maximum force elongation is larger than or equal to 6%. The method can effectively solve the problem that the ductility of the hollow anchor rod body prepared after heat treatment is poor due to the fact that existing anchor rod steel cannot have strength and ductility at the same time.

Description

Technical Field

[0001] The invention belongs to the technical field of hot-rolled plate and strip production, and specifically relates to a 500MPa-grade high-ductility hot-rolled steel for a hollow anchor rod welded pipe, and a preparation method and application thereof. Background Art

[0002] Anchor rods are the main supporting structures for roads, slopes, dams, tunnels, bridges and mine tunnels, playing a supporting and reinforcing role. With the promotion and development of technology, their application is becoming more and more extensive, and the demand is increasing. The working principle of anchor rods is to overcome the shortcoming that the tensile capacity of rock and soil is far lower than its compressive capacity through the longitudinal tension of the anchor rod body. On the surface, it limits the rock and soil from separating from the original body, and on a macroscopic level, it increases the cohesiveness of the rock and soil. It is a rod system structure for reinforcing rock and soil.

[0003] In the past, the brand of anchor steel products in my country was relatively single, almost all of which were MG335. Since 2019, after in-depth research on coal mining enterprises, engineering enterprises and other units, the state proposed to use high-strength anchor steel products to replace MG335 brand products, and then MG500, SMG600MPa and other brand products appeared, but these products are almost all produced by rolling rods and wires or drawing seamless steel pipes, with high costs, low yields, poor dimensional accuracy and surface quality. At present, foreign hollow anchor products are basically produced by hot-rolled steel strip welded pipes. Anchor products made of hot-rolled steel strips have the advantages of fine and uniform organization control, simple process, high yield, high dimensional accuracy and low cost. In addition, due to the characteristics of materials used in underground mine lanes and tunnels, the anchor rod body must have high ductility after heat treatment, and the existing mining steel cannot meet the high ductility requirements while ensuring strength.

[0004] CN116024494A discloses a corrosion-resistant hollow anchor rod welded pipe, hot-rolled steel strip and preparation method, wherein the weight percentage of the elements of the hot-rolled steel strip is as follows: C 0.18-0.23%, Si 0.15-0.30%, Mn 0.70-0.90%, P0.070-0.090%, S≤0.010%, Nb 0.03-0.04%, Cr 0.30-0.50%, Cu 0.30-0.50%, Ti0.01-0.03%, and the rest is Fe and inevitable impurities. The element composition of the method is matched with the corresponding steelmaking, continuous casting and hot rolling production processes to ensure that the material structure is fine and uniform, thereby obtaining a high-performance corrosion-resistant hollow anchor rod welded pipe hot-rolled steel strip, with a yield strength Rel≥460MPa, a tensile strength Rm≥650MPa, and an elongation≥23%. In this method, Nb element is used to refine the grains, and Cu element is used to ensure corrosion resistance, and the alloy cost is relatively high. In addition, this method does not mention the performance of the hollow anchor rod welded pipe, and its ductility is unclear.

[0005] CN118854182A provides a 500MPa grade corrosion-resistant anchor rod and a production method. The anchor rod includes C: ≤0.06%, Si: 0.50-0.60%, Mn: 0.70-0.80%, P: ≤0.020%, S: ≤0.020%, Cr: 9.00-10.00%, Mo: 0.80-1.00%, V: 0.040-0.060%, and the balance is Fe and inevitable impurities. The production method specifically includes the following steps: electric furnace rough refining, LF refining, billet continuous casting, billet heating and rolling. The mechanical properties of the anchor rod steel bar meet the standards of 500MPa grade anchor rod steel bar, and at the same time have excellent chloride ion corrosion resistance. In this aspect, high content of Cr, Mn, and Mo elements are used in the alloy composition, and the alloy cost is high.

[0006] Therefore, it is necessary to study an anchor steel having both strength and ductility, and to provide a hollow anchor rod body with high ductility prepared by using the anchor steel. Summary of the invention

[0007] The technical problem to be solved by the present invention is that the existing anchor rod steel cannot have both strength and ductility, resulting in the problem that the hollow anchor rod body obtained after heat treatment has poor ductility.

[0008] The technical solution adopted by the present invention to solve its technical problem is:

[0009] In a first aspect, the present invention provides a method for preparing 500MPa grade hot-rolled steel for hollow anchor welded pipe with high ductility, the process flow of the preparation method comprising smelting, heating of ingot, rough rolling, hot coil box coiling, finishing rolling, laminar cooling, and coiling.

[0010] In the above preparation method, the smelting is to obtain a casting billet whose chemical composition meets the design requirements through molten iron desulfurization, converter smelting, LF refining and continuous casting.

[0011] Furthermore, the S of the molten iron is controlled to be ≤ 0.003% when the molten iron enters the converter through desulfurization of the molten iron.

[0012] Furthermore, the converter is cleaned before smelting, and the argon blowing time of the small platform process is controlled to be ≥8min during smelting.

[0013] Furthermore, argon is blown throughout the LF refining process, and the molten steel cannot be exposed. 70TiFe alloy is used for micro-titanium treatment before leaving the station.

[0014] Furthermore, the continuous casting is protected throughout the entire casting process, using low alloy protective slag.

[0015] Furthermore, the chemical composition of the ingot is C 0.19-0.22%, Si 0.20-0.30%, Mn1.55-1.60%, P≤0.020%, S≤0.010%, Cr 0.8-1.0%, Ti 0.02-0.035%, Als 0.01-0.04%, and the rest is Fe and unavoidable impurities.

[0016] Furthermore, the thickness of the ingot is 200 mm.

[0017] In the above preparation method, the heating temperature of the ingot is 1230°C to 1270°C, the heating time is 150 to 170 minutes, and the soaking time is ≥30 minutes.

[0018] In the above preparation method, the rough rolling is performed by 5 or 7 passes, and the odd-numbered passes are used for full descaling, and the intermediate billet is obtained and coiled in a hot coil box for heat preservation.

[0019] Furthermore, the thickness of the intermediate blank is 40-42 mm.

[0020] In the above preparation method, the finish rolling adopts 7 rolling passes, the reduction rates of the last three stands are ≥17%, ≥15% and ≥12% respectively, the starting rolling temperature is 1020℃~1080℃, and the final rolling temperature is 870℃~890℃.

[0021] In the above preparation method, the laminar cooling adopts a front-stage cooling mode, and the cooling rate is 60-70°C / s.

[0022] In the above preparation method, the coiling temperature is 600°C to 640°C.

[0023] In a second aspect, the present invention provides a 500MPa grade high ductility hot-rolled steel for hollow anchor welded pipe prepared by the above preparation method, wherein the yield strength is ≥500MPa, the tensile strength is ≥600MPa, the elongation after fracture is ≥26%, and the maximum force elongation is ≥14%.

[0024] The microstructure of the above-mentioned 500MPa grade hot-rolled steel for high ductility hollow anchor welded pipe is quasi-polygonal ferrite+pearlite, and the volume fraction thereof is 80% to 90% of ferrite and 10% to 20% of pearlite.

[0025] In the third aspect, the present invention provides an application of the above-mentioned 500MPa grade high ductility hot-rolled steel for hollow anchor rod welded pipe: the above-mentioned 500MPa grade high ductility hot-rolled steel for hollow anchor rod welded pipe is subjected to the processing steps of heating by a high-frequency electric heating device, three-roller spinning equal diameter rolling, online heat treatment, sawing and slow cooling on a cooling bed to obtain a hollow anchor rod body.

[0026] Furthermore, the heating temperature of the high-frequency electric heating device is 920°C to 930°C, and the online heat treatment adopts annular constant temperature cooling water for online quenching heat treatment, the quenching temperature is 350°C to 360°C, and the residual heat of the anchor rod body is used for self-tempering treatment, and gradually cooled to room temperature.

[0027] Furthermore, the yield force of the hollow anchor rod body is ≥150 kN, the tensile strength is ≥200 kN, and the maximum force elongation is ≥6%.

[0028] The beneficial effects of the present invention are as follows: the present invention improves the material strength by controlling the solid solution strengthening of C, Si and Mn, and at the same time, in order to improve the hardenability of the material, a certain amount of Cr element is added to ensure the hardenability of the anchor rod body obtained after rolling, and obtain good online heat treatment performance. After that, the hollow anchor rod body is obtained through processing steps such as heating by a high-frequency electric heating device, three-roller spinning and equal-diameter rolling, online heat treatment, sawing, and slow cooling on a cooling bed, and the yield force is ≥150kN, the tensile strength is ≥200kN, and the maximum force elongation is ≥6%, which meets the technical requirements of the hollow anchor rod and reaches the user's use standards. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the metallographic structure of the hollow anchor rod body prepared in Example 1. DETAILED DESCRIPTION

[0030] The technical solution of the present invention can be specifically implemented in the following manner.

[0031] The chemical composition of 500MPa grade high ductility hot rolled steel for hollow anchor welded pipe is C 0.19-0.22%, Si 0.20-0.30%, Mn 1.55-1.60%, P≤0.020%, S≤0.010%, Cr 0.8-1.0%, Ti0.02-0.035%, Als0.01-0.04%, and the rest is Fe and unavoidable impurities.

[0032] The present invention controls the Si element content while ensuring the material strength and reducing the carbon equivalent by adding a relatively high C element, adds a trace Ti element to form precipitates during welding to inhibit the coarsening of the heat affected zone structure to improve the welding performance, adds a certain amount of Mn element to ensure the strength of the material, and adds a certain amount of Cr element to ensure the hardenability of the anchor rod body obtained after rolling, thereby obtaining good online heat treatment performance.

[0033] The preparation steps of the above-mentioned 500MPa grade high ductility hot-rolled steel for hollow anchor welded pipe are: molten iron desulfurization, converter, LF refining, continuous casting, heating furnace heating, rough rolling, hot coil box coiling, finishing rolling, laminar cooling, and coiling.

[0034] Preferably, slabs are smelted and continuously cast according to the components, S≤0.003% when the molten iron enters the converter, the converter needs to be "washed" before smelting, and the argon blowing time of the small platform process must be ≥8min to ensure low content of nitrogen, oxygen, and hydrogen in the molten steel and remove residual non-metallic inclusions in the molten steel; LF refining process must be argon blown throughout the process, and the molten steel must not be exposed, 70TiFe alloy is used for micro-titanium treatment before leaving the station, the continuous casting process is protected throughout the casting, low alloy protective slag is used, and "open casting" is not allowed, so as to obtain a continuous casting billet whose chemical composition meets the design requirements, and the billet thickness is 200mm.

[0035] Preferably, the heating temperature of the continuous casting steel billet is 1230℃~1270℃, the heating time is 150~170min, and the soaking time is ≥30min; the continuous casting steel billet is subjected to 5 or 7 passes of rough rolling, and the odd passes are fully descaled to obtain an intermediate billet with a thickness of 41±1mm, which is then coiled and kept warm in a hot coil box; the intermediate billet is subjected to 7 passes of finish rolling, the start temperature of the finish rolling is 1050±30℃, the reduction rates of the last three stands are ≥17%, ≥15% and ≥12% respectively, and the final rolling temperature is 870℃~890℃; the front-end cooling mode is adopted, the cooling rate is 65±5℃ / s, and the coiling temperature is 620±20℃.

[0036] The yield strength of the above-mentioned 500MPa grade high ductility hot-rolled steel for hollow anchor welded pipe is ≥500MPa, the tensile strength is ≥600MPa, the elongation after fracture is ≥26%, and the maximum force elongation is ≥14%; its microstructure is quasi-polygonal ferrite + pearlite, and its volume fraction is ferrite (F) 80% to 90%, and pearlite (P) 10% to 20%.

[0037] The rod body of the center control anchor is made of the above-mentioned 500MPa grade high ductility hot-rolled steel for hollow anchor welded pipe, and the preparation method includes heating with a high-frequency electric heating device, three-roller spinning and equal-diameter rolling, online heat treatment, sawing, and slow cooling on a cooling bed.

[0038] Preferably, the anchor steel is heated to 925±5°C by a high-frequency electric heating device, then three-roller spin-rolled into a hollow anchor rod body, and subjected to online quenching heat treatment using annular constant temperature cooling water at a quenching temperature of 355±5°C, and self-tempering treatment is performed using residual heat from the anchor rod body, and gradually cooled to room temperature.

[0039] The yield force of the above-mentioned center control anchor rod body is ≥150kN, the tensile strength is ≥200kN, and the maximum force elongation is ≥6%.

[0040] The technical solution and effects of the present invention are further illustrated below through practical examples.

[0041] Example

[0042] The present invention provides three groups of embodiments 1 to 3 for preparing 500MPa grade high ductility hot-rolled steel for hollow anchor welded pipe by the method of the present invention. The chemical composition of the hot-rolled steel is shown in Table 1, and the rest is Fe and unavoidable impurities.

[0043] Table 1 Chemical composition (by mass percentage, %)

[0044] C Si Mn P S Cr Ti Als Example 1 0.19 0.28 1.58 0.014 0.003 0.85 0.035 0.030 Example 2 0.20 0.26 1.60 0.010 0.001 0.90 0.035 0.037 Example 3 0.20 0.27 1.55 0.008 0.002 0.85 0.034 0.028

[0045] Example 1

[0046] The production method of the hot-rolled steel strip for the high-strength and high-uniform elongation hollow anchor welded pipe in this embodiment includes: molten iron desulfurization → converter → LF refining → continuous casting → hot rolling → laminar cooling → coiling; the key process steps are as follows: the continuous casting billet heating temperature is 1240°C, the heating time is 165min, and the soaking time is 35min; the continuous casting billet is subjected to 7 rough rolling passes, and the odd-numbered passes are fully descaled to obtain an intermediate billet with a thickness of 42mm, which is then coiled and kept warm in a hot coil box; the finishing rolling start temperature is 1060°C, the reduction rates of the last three stands are 18%, 17% and 13% respectively, and the final rolling temperature is 880°C; the front-end cooling mode is adopted, and the cooling rate is 68°C / s; the coiling temperature is 630°C.

[0047] The yield strength R of the hot-rolled steel for the prepared high ductility hollow anchor welded pipe eL The tensile strength is 516MPa, m The tensile strength is 663 MPa, the elongation after fracture is 29%, and the microstructure is quasi-polygonal ferrite + pearlite, of which ferrite is 83% and pearlite is 17%. The prepared high-ductility hollow anchor rod welded pipe is subjected to high-frequency resistance welding, high-frequency heating of the welded pipe to 920°C, and online quenching to 350°C to obtain a hollow anchor rod body with a yield strength of 180.2 kN, a tensile strength of 232.4 kN, and a maximum force elongation of 7.5%. The metallographic structure is as follows Figure 1 As shown by Figure 1 It can be seen that the metallographic structure of the hollow anchor rod body obtained by heat-treating the hot-rolled steel prepared in the present invention is tempered martensite and ferrite.

[0048] Example 2

[0049] The production method of the hot-rolled steel strip for the high-strength and high-uniform elongation hollow anchor welded pipe in this embodiment comprises: molten iron desulfurization → converter → LF refining → continuous casting → hot rolling → laminar cooling → coiling; the key process steps are as follows: the continuous casting billet heating temperature is 1245°C, the heating time is 160min, and the soaking time is 33min; the continuous casting billet is subjected to 7 rough rolling passes, and the odd-numbered passes are fully descaled to obtain an intermediate billet with a thickness of 41mm, which is then coiled and kept warm in a hot coil box; the finishing rolling start temperature is 1060°C, the reduction rates of the last three stands are 18%, 16% and 12% respectively, and the final rolling temperature is 885°C; the front-end cooling mode is adopted, and the cooling rate is 65°C / s; the coiling temperature is 636°C.

[0050] The yield strength R of the hot-rolled steel for the prepared high ductility hollow anchor welded pipe eL The tensile strength is 510MPa and the m The tensile strength is 665MPa, the elongation after fracture is 30%, and the microstructure is quasi-polygonal ferrite + pearlite, of which ferrite is 81% and pearlite is 19%. The prepared high-ductility hollow anchor rod welded pipe hot-rolled steel is subjected to high-frequency resistance welding, high-frequency heating of the welded pipe to 930°C, and online quenching to 355°C to obtain a hollow anchor rod body with a yield strength of 180.2kN, a tensile strength of 232.4kN, and a maximum force elongation of 7%.

[0051] Example 3

[0052] The production method of the hot-rolled steel strip for the high-strength and high-uniform elongation hollow anchor welded pipe in this embodiment includes: molten iron desulfurization → converter → LF refining → continuous casting → hot rolling → laminar cooling → coiling; the key process steps are as follows: the continuous casting billet heating temperature is 1260°C, the heating time is 162min, and the soaking time is 30min; the continuous casting billet is subjected to 7 rough rolling passes, and the odd-numbered passes are fully descaled to obtain an intermediate billet with a thickness of 40mm, which is then coiled and kept warm in a hot coil box; the finishing rolling start temperature is 1065°C, the reduction rates of the last three stands are 17%, 15% and 12% respectively, and the final rolling temperature is 880°C; the front-end cooling mode is adopted, and the cooling rate is 67°C / s; the coiling temperature is 630°C.

[0053] The yield strength R of the hot-rolled steel for the prepared high ductility hollow anchor welded pipe eL The tensile strength is 525MPa, m The tensile strength is 679MPa, the elongation after fracture is 29%, and the microstructure is quasi-polygonal ferrite + pearlite, of which ferrite is 85% and pearlite is 15%. The prepared high-ductility hollow anchor rod welded pipe hot-rolled steel is subjected to high-frequency resistance welding, high-frequency heating of the welded pipe to 923°C, and online quenching to 355°C to obtain a hollow anchor rod body with a yield strength of 186.7kN, a tensile strength of 241.3kN, and a maximum force elongation of 6.5%.

[0054] Comparative Example

[0055] Comparative Example According to the chemical composition of Example 3 in Table 1, a hot-rolled steel strip for hollow anchor welded pipe with high strength and high uniform elongation is smelted, and its production method includes: molten iron desulfurization → converter → LF refining → continuous casting → hot rolling → laminar cooling → coiling; the key process steps are as follows: the continuous casting billet is heated to 1260°C, the heating time is 162min, and the soaking time is 30min; the continuous casting billet is subjected to 7 rough rolling passes, and the odd number of passes are descaled throughout the process to obtain an intermediate billet with a thickness of 40mm, which is then coiled and kept warm in a hot coil box; the finishing rolling start temperature is 1060°C, the reduction rates of the last three stands are 17%, 15% and 12% respectively, and the final rolling temperature is 850°C; the front-end cooling mode is adopted, and the cooling rate is 70°C / s; the coiling temperature is 580°C.

[0056] The yield strength R of the hot-rolled steel for the prepared high ductility hollow anchor welded pipe eL The tensile strength is 549MPa, m The tensile strength is 713MPa, the elongation after fracture is 21%, and the microstructure is quasi-polygonal ferrite + pearlite, of which ferrite is 85% and pearlite is 15%. The prepared high-ductility hollow anchor rod welded pipe hot-rolled steel is subjected to high-frequency resistance welding, high-frequency heating of the welded pipe to 923°C, and online quenching to 355°C to obtain a hollow anchor rod body with a yield strength of 189.2kN, a tensile strength of 254.4kN, and a maximum force elongation of 4.5%.

[0057] By comparing the comparative example with Example 3, it can be seen that the finishing rolling temperature in the comparative example is lower, resulting in a lower coiling temperature. Although hot-rolled steel with higher yield strength and tensile strength is obtained, the elongation after fracture is poor. After the obtained hot-rolled steel is treated with the same heat treatment process as Example 3, the strength of the hollow anchor rod body reaches the standard, but its maximum elongation is low and cannot meet the technical requirements of the hollow anchor rod.

Claims

A method for preparing hot-rolled steel for 1.500MPa grade high ductility hollow anchor welded pipe, characterized in that: The process flow of the preparation method is smelting, heating of ingot, rough rolling, hot coil box coiling, finishing rolling, laminar cooling and coiling; The smelting process includes hot metal desulfurization, converter smelting, LF refining and continuous casting to obtain a casting billet with chemical composition meeting the design requirements; The chemical composition of the ingot is C 0.19-0.22%, Si 0.20-0.30%, Mn 1.55-1.60%, P≤0.020%, S≤0.010%, Cr 0.8-1.0%, Ti 0.02-0.035%, Als 0.01-0.04%, and the rest is Fe and unavoidable impurities; The heating temperature of the ingot is 1230℃~1270℃, the heating time is 150~170min, and the soaking time is ≥30min; Finish rolling adopts 7-pass rolling, with the reduction rates of the last three stands being ≥17%, ≥15% and ≥12% respectively, the starting rolling temperature being 1020℃~1080℃, and the final rolling temperature being 870℃~890℃; The coiling temperature is 600°C to 640°C.

2. The method for preparing the 500MPa grade high ductility hot rolled steel for hollow anchor welded pipe according to claim 1, characterized in that: The smelting process shall meet at least one of the following requirements: Through hot metal desulfurization, the S content of hot metal entering the converter is controlled to be ≤0.003%; Wash the converter before smelting, and control the argon blowing time of the small platform process to ≥8min during smelting; Argon is blown throughout the LF refining process, and the molten steel must not be exposed. 70TiFe alloy is used for micro-titanium treatment before leaving the station; The continuous casting process is protected by pouring and low alloy protective slag is used.

3. The method for preparing the 500MPa grade high ductility hot rolled steel for hollow anchor welded pipe according to claim 1, characterized in that: The thickness of the ingot is 200 mm.

4. The method for preparing the 500MPa grade high ductility hot rolled steel for hollow anchor welded pipe according to claim 1, characterized in that: The rough rolling is performed in 5 or 7 passes, and the odd-numbered passes are used for full descaling, and the intermediate billet is coiled and kept warm in a hot coil box.

5. The method for preparing the 500MPa grade high ductility hot rolled steel for hollow anchor welded pipe according to claim 4, characterized in that: The thickness of the intermediate blank is 40-42 mm.

6. The method for preparing the 500MPa grade high ductility hot rolled steel for hollow anchor welded pipe according to claim 1, characterized in that: The laminar cooling adopts a front-stage cooling mode, and the cooling speed is 60-70°C / s. 7.500MPa grade high ductility hot rolled steel for hollow anchor welded pipe, characterized by: Prepared by the preparation method according to any one of claims 1 to 6; Its yield strength is ≥500MPa, tensile strength is ≥600MPa, elongation after fracture is ≥26%, and elongation at maximum force is ≥14%.

8. The 500MPa grade high ductility hot rolled steel for hollow anchor welded pipe according to claim 7, characterized in that: The microstructure is quasi-polygonal ferrite + pearlite, with the volume fractions of ferrite being 80% to 90% and pearlite being 10% to 20%.

9. Application of 500MPa grade high ductility hot rolled steel for hollow anchor welded pipe, characterized by: The 500MPa grade high ductility hot-rolled steel for hollow anchor rod welded pipe according to any one of claims 7 to 8 is subjected to the processing steps of heating by a high-frequency electric heating device, three-roller spinning equal diameter rolling, online heat treatment, sawing and slow cooling on a cooling bed to obtain a hollow anchor rod body; The yield force of the hollow anchor rod body is ≥150kN, the tensile strength is ≥200kN, and the maximum force elongation is ≥6%.

10. The use of the 500MPa grade high ductility hot rolled steel for hollow anchor welded pipe according to claim 9, characterized in that: The heating temperature of the high-frequency electric heating device is 920°C to 930°C. The online heat treatment adopts annular constant temperature cooling water for online quenching heat treatment. The quenching temperature is 350°C to 360°C. The residual heat of the anchor rod body is used for self-tempering treatment and gradually cooled to room temperature.

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