Method for improving mechanical property of anchor rod steel

Abstract

The invention discloses a method for improving the mechanical property of anchor rod steel, and belongs to the technical field of steel and iron materials. The method comprises the following steps that (1) on the basis of traditional anchor rod steel components, the element content in steel is optimized through microalloying design; (2) the steel billet is heated to 1150 DEG C to 1250 DEG C; finish rolling is conducted at the temperature of 00-900 DEG C, and the deformation temperature and the accumulated deformation amount in the rolling process are strictly controlled; cooling is conducted after rolling, and the cooling rate is controlled to range from 15 DEG C / s to 25 DEG C / s; (3) after rolling, heating to 850-900 DEG C for quenching, keeping the temperature for 15-30 minutes, and then quickly cooling; and tempering at 200-250 DEG C, and preserving heat for 1-2 hours. The strength and toughness of the anchor rod steel can be remarkably improved, collaborative optimization of the strength and plasticity is achieved, meanwhile, by improving the technological process, the production cost is reduced, the production efficiency is improved, and the method is suitable for large-scale industrial production of the high-strength anchor rod steel.

Description

Technical Field

[0001] The invention belongs to the technical field of steel materials, and in particular relates to a method for improving the mechanical properties of anchor steel. Background Art

[0002] Anchor steel is a key material in support systems for coal mines, tunnels, and underground engineering. Its key performance attributes include high strength, high toughness, and excellent ductility, ensuring adequate load-bearing capacity and impact resistance under complex stress environments. However, existing anchor steel production processes typically rely on increasing carbon content or performing simple heat treatments to enhance strength, often at the expense of ductility and toughness. Furthermore, the uneven microstructural distribution in traditional processes leads to significant performance fluctuations, making them unable to meet the increasingly stringent requirements of modern engineering for anchor steel performance. In recent years, with the application of microalloying technology, while the addition of elements such as Nb, V, and Ti can improve the synergistic properties of strength and toughness to a certain extent, its strengthening mechanism is limited, and research on the optimization of controlled rolling, controlled cooling, and heat treatment parameters is insufficient. Furthermore, the high complexity and high cost of existing processes limit their widespread application in mass production. Therefore, developing a new method that can significantly improve the mechanical properties of anchor steel while simplifying the process and reducing production costs is of great theoretical and practical significance. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for improving the mechanical properties of anchor steel, which can significantly improve the strength and toughness of anchor steel, achieve coordinated optimization of strength and plasticity, and at the same time reduce production costs and improve production efficiency by improving the process flow, and is suitable for large-scale industrial production of high-strength anchor steel.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] The present invention provides a method for improving the mechanical properties of anchor steel, comprising the following steps:

[0006] (1) Based on the composition of traditional anchor steel, the element content in the steel is optimized through microalloying design. The mass percentage of its chemical composition includes: C 0.22-0.26%, Si 0.20-0.30%, Mn 1.10-1.40%, P≤0.015%, S≤0.010%, Nb 0.02-0.05%, V 0.05-0.10%, B 0.001-0.003%, and the rest is Fe and unavoidable impurities;

[0007] (2) The billet is heated to 1150-1250℃ to fully dissolve the alloy elements and ensure uniform structure; final rolling is carried out in the range of 800-900℃, and the deformation temperature and cumulative deformation during the rolling process are strictly controlled to refine the grains. The rolling temperature range is controlled between 1050℃ and the final rolling temperature of 850-880℃, wherein the single-pass deformation in the rough rolling stage is controlled at 10%-20%, and the single-pass deformation in the finishing rolling stage is controlled at 15%-25%, and the total cumulative deformation is not less than 70%; the interval between rolling passes is ≤10 seconds to prevent the recrystallization structure from being excessively coarsened. Maintaining a high deformation energy input throughout the rolling process is conducive to grain refinement and promotes the uniform precipitation of dispersed precipitates, thereby improving the subsequent structure stability; cooling after rolling, the cooling rate is controlled between 15-25℃ / s to obtain fine ferrite and dispersed precipitates;

[0008] (3) The rolled anchor steel is heated to 850-900°C for quenching, the holding time is 15-30 minutes, and then rapidly cooled; heated again to 200-250°C for tempering, the holding time is 1-2 hours, and finally a tempered bainite structure is obtained to ensure the coordination of strength and toughness.

[0009] Furthermore, the chemical composition includes, by weight percentage, C 0.24%, Si 0.25%, Mn 1.25%, P 0.012%, S 0.007%, Nb 0.03%, V 0.08%, B 0.002%, and the remainder is Fe and inevitable trace impurities, with a total weight fraction of 100%.

[0010] Furthermore, the steel billet is heated to 1200°C, kept warm for 1 hour and then rolled. The final rolling temperature is controlled at 880°C, and air cooling is adopted with a cooling rate of about 20°C / s; quenching: heating to 870°C, keeping warm for 20 minutes and then rapidly cooling; tempering: heating to 220°C, keeping warm for 1.5 hours and then air cooling; the yield strength of the steel reaches 720MPa, the tensile strength reaches 850MPa, the elongation is increased to 16.0%, the impact absorption energy at -20°C is 50J, and the structure is fine tempered bainite and dispersed precipitate phase, which meets the use requirements.

[0011] Furthermore, the mass percentage of its chemical composition includes: C 0.23%, Si 0.28%, Mn 1.30%, P 0.012%, S 0.007%, Nb 0.04%, V 0.06%, B 0.0015%, and the rest is Fe and inevitable trace impurities, with a total mass fraction of 100%.

[0012] Furthermore, the billet is heated to 1180°C, kept warm for 1 hour, and the final rolling temperature is 850°C. Spray cooling is adopted with a cooling rate of about 18°C / s; quenching: heating to 880°C, keeping warm for 25 minutes and then rapidly cooling; tempering: heating to 200°C, keeping warm for 2 hours and then air cooling; the yield strength of the steel reaches 740MPa, the tensile strength reaches 860MPa, the elongation is increased to 15.5%, the impact absorption energy at -20°C is 55J, and the structure is fine tempered bainite and dispersed precipitates, which meets the requirements of engineering applications.

[0013] Furthermore, the mass percentage of its chemical composition includes: C 0.25%, Si 0.22%, Mn 1.35%, P 0.011%, S 0.005%, Nb 0.02%, V 0.10%, B 0.0025%, and the rest is Fe and inevitable trace impurities, with a total mass fraction of 100%.

[0014] Furthermore, the billet is heated to 1220°C, kept warm for 1 hour, and the final rolling temperature is 870°C. Air cooling + water mist cooling is adopted, and the cooling rate is 22°C / s; quenching: heating to 860°C, keeping warm for 20 minutes and then rapidly cooling; tempering: heating to 250°C, keeping warm for 1 hour and then air cooling; the yield strength of the steel reaches 710MPa, the tensile strength reaches 840MPa, the elongation is increased to 17%, the impact absorption energy at -20°C is 60J, and the structure is fine tempered bainite and dispersed precipitate phase, which meets the support engineering requirements.

[0015] The rapid cooling is specifically: water cooling or mist cooling, with a cooling rate of 30 to 60° C. / s, cooling to room temperature.

[0016] The design ideas of chemical composition are as follows:

[0017] C: As a solid solution strengthening element, it improves the yield strength and tensile strength of steel. An appropriate carbon content can maintain good toughness and plasticity, while too high a carbon content will reduce forgeability and impact toughness. The C content of the present invention is controlled at 0.18% to 0.22%.

[0018] Si: It mainly plays a role in solid solution strengthening, improving the strength of steel; promoting the formation of ferrite, which helps to refine the grains; increasing the oxidation resistance of steel, enhancing the deoxidation effect, and helping to improve the purity of steel; too high Si content may reduce toughness. In the present invention, the Si content is controlled at 0.20-0.30%.

[0019] Mn: As a solid solution strengthening element, it improves the strength of steel; promotes the refinement of pearlite, which helps to improve toughness; excessive Mn may increase the brittleness of steel. In the present invention, the Mn content is controlled at 1.10-1.40%.

[0020] Nb: Refines grain size and increases the yield strength of the steel. It also forms dispersed precipitates such as NbC and NbN with C and N, enhancing the precipitation strengthening effect of the steel. It also inhibits austenite recrystallization, making the controlled rolling and controlled cooling process more stable and improving the structural uniformity of the anchor steel. The Nb content in this invention is controlled at 0.02-0.05%.

[0021] V: forms dispersed V(C,N) precipitates, improves precipitation strengthening effect, and enhances steel strength; promotes fine grain strengthening, and enhances steel plasticity and toughness; during tempering, effectively prevents grain growth, improves tempering stability, and enhances high-temperature strength; the V content of the present invention is controlled at 0.05-0.10%.

[0022] B: By inhibiting the precipitation of ferrite and pearlite, it helps to obtain fine martensite or bainite structure and improve toughness. Excessive boron can easily lead to hot brittleness. In the present invention, the B content is controlled at 0.001-0.003%.

[0023] P and S: Strictly control P≤0.015% and S≤0.010%. As impurity elements, their content is controlled to reduce the adverse effect on the toughness of steel.

[0024] Compared with the prior art, the present invention has the following beneficial technical effects:

[0025] This method, developed by the present invention, improves the mechanical properties of anchor steel. By optimizing chemical composition, controlled rolling and cooling, and heat treatment, it successfully increases the yield strength and tensile strength of the steel, achieving a good balance between strength and toughness. This method is simple, cost-effective, and suitable for large-scale industrial production, providing an innovative technical solution for improving the performance of anchor steel.

[0026] The beneficial effects of the present invention are:

[0027] (1) By optimizing the chemical composition, controlled rolling and cooling, and heat treatment processes, the yield strength of the anchor steel reaches 700-800 MPa, and the tensile strength reaches 800-900 MPa. At the same time, the elongation is increased to 14-18%, and the impact energy is increased to 40-60 J, which significantly improves the coordinated matching of strength and toughness, and improves the service life and safety performance of the anchor steel.

[0028] (2) By adding microalloying elements Nb, V, and B and combining them with controlled rolling and controlled cooling processes, the grain growth is effectively inhibited, forming a fine and uniform ferrite + bainite or tempered bainite structure, reducing performance fluctuations, and improving the stability and reliability of anchor steel under complex stress environments.

[0029] (3) Compared with the traditional process, the high-temperature tempering and secondary heat treatment steps are reduced, the microstructure is optimized by means of controlled rolling and controlled cooling process, the production process is simplified, the energy consumption and production cost are reduced, and the production efficiency is improved, so that it is more suitable for large-scale industrial production. DETAILED DESCRIPTION

[0030] The method for improving the mechanical properties of anchor rod steel according to the present application is further described in detail below.

[0031] Embodiment: The present embodiment is one of the preferred embodiments of the various embodiments of the present application.

[0032] The method for improving the mechanical properties of anchor rod steel according to the present embodiment has a chemical composition with a mass percentage of: C 0.22-0.26%, Si 0.20-0.30%, Mn 1.10-1.40%, P≤0.015%, S≤0.010%, Nb 0.02-0.05%, V 0.05-0.10%, B 0.001-0.003%, and the rest being Fe and inevitable trace impurities, with a total mass percentage of 100%.

[0033] The method for improving the mechanical properties of anchor rod steel according to the present embodiment has the following key steps: chemical composition design, controlled rolling and controlled cooling process, and heat treatment process.

[0034] Further, on the basis of the traditional anchor rod steel composition, the element content in the steel is optimized through micro-alloying design, and the method for improving the mechanical properties of anchor rod steel according to the present application has a chemical composition with a mass percentage of: C 0.22-0.26%, Si 0.20-0.30%, Mn 1.10-1.40%, P≤0.015%, S≤0.010%, Nb 0.02-0.05%, V 0.05-0.10%, B 0.001-0.003%, thereby improving the strength and toughness of the steel;

[0035] Further, the billet is heated to 1150-1250℃ to fully dissolve the alloying elements and ensure uniform organization; final rolling is performed in the range of 800-900℃, and the deformation temperature and cumulative deformation during rolling are strictly controlled to refine the grains; after rolling, spray cooling is adopted with a cooling rate controlled between 15-25℃ / s to obtain fine ferrite and dispersed distribution of precipitated phases;

[0036] Further, the anchor rod steel after rolling is heated to 850-900℃ for quenching with a holding time of 15-30 minutes, and then rapidly cooled; it is heated again to 200-250℃ for tempering treatment with a holding time of 1-2 hours, and finally a tempered sorbite structure is obtained to ensure the coordination of strength and toughness.

[0037] Embodiment 1:

[0038] The chemical composition in mass percent is C 0.24%, Si 0.25%, Mn 1.25%, P 0.012%, S 0.007%, Nb 0.03%, V 0.08%, B 0.002%, and the balance of Fe and inevitable trace impurities, with the total being 100%. The steel billet is heated to 1200°C, and held for 1 hour before rolling, with the finish rolling temperature controlled at 880°C. The cooling rate is about 20°C / s by air cooling. Quenching: heated to 870°C, held for 20 minutes, and then rapidly cooled (water cooling, cooling rate of 45°C / s, and cooled to room temperature). Tempering: heated to 220°C, held for 1.5 hours, and then air cooled. The yield strength of the steel reaches 720 MPa, the tensile strength reaches 850 MPa, the elongation is increased to 16.0%, the impact energy at -20°C is 50 J, the microstructure is fine tempered sorbite and dispersed distribution of precipitates, and the steel satisfies the use requirements.

[0039] Example 2:

[0040] The chemical composition in mass percent is C 0.23%, Si 0.28%, Mn 1.30%, P 0.012%, S 0.007%, Nb 0.04%, V 0.06%, B 0.0015%, and the balance of Fe and inevitable trace impurities, with the total being 100%. The steel billet is heated to 1180°C, and held for 1 hour, with the finish rolling temperature controlled at 850°C. The cooling rate is about 18°C / s by spray cooling. Quenching: heated to 880°C, held for 25 minutes, and then rapidly cooled (fog cooling, cooling rate of 40°C / s, and cooled to room temperature). Tempering: heated to 200°C, held for 2 hours, and then air cooled. The yield strength of the steel reaches 740 MPa, the tensile strength reaches 860 MPa, the elongation is increased to 15.5%, the impact energy at -20°C is 55 J, the microstructure is fine tempered sorbite and dispersed distribution of precipitates, and the steel satisfies the engineering application requirements.

[0041] Example 3:

[0042] The chemical composition by mass percentage is C 0.25%, Si 0.22%, Mn 1.35%, P 0.011%, S 0.005%, Nb 0.02%, V 0.10%, B 0.0025%, with the remainder being Fe and unavoidable trace impurities, totaling 100%. The billet is heated to 1220°C, held for 1 hour, and then rolled to a final temperature of 870°C using air cooling and water mist at a cooling rate of 22°C / s. Quenching: Heating to 860°C, holding for 20 minutes, followed by rapid cooling (water cooling at a cooling rate of 50°C / s to room temperature). Tempering: Heating to 250°C, holding for 1 hour, then air cooling. The yield strength of the steel reaches 710MPa, the tensile strength reaches 840MPa, the elongation is increased to 17%, the impact absorption energy at -20℃ is 60J, and the structure is fine tempered bainite and dispersed precipitation phase, which meets the requirements of support engineering.

[0043] Comparative Example 1:

[0044] In Comparative Example 1, the chemical composition by mass percentage is C 0.24%, Si 0.25%, Mn 1.20%, P 0.011%, S 0.005%, and the rest is Fe and unavoidable trace impurities, with a total mass fraction of 100%. The steel billet is heated to 1200°C, the final rolling temperature is 890°C, and air cooling is adopted with a cooling rate of about 15°C / s. Quenching: heating to 870°C, holding for 20 minutes, and then rapid cooling (water cooling, cooling rate of 45°C / s, cooling to room temperature). Tempering: heating to 220°C, holding for 1.5 hours, and then air cooling. The yield strength of the steel reaches 650MPa, the tensile strength reaches 780MPa, the elongation is increased to 14%, and the impact absorption energy at -20°C is 25J. This comparative example does not add microalloying elements such as Nb, V, and B, resulting in coarse grains and a lack of precipitation strengthening and fine grain strengthening mechanisms, making the strength and toughness lower than the embodiments of the present invention, especially the impact energy is significantly reduced, making it difficult to meet the requirements of high-strength anchor steel.

[0045] Comparative Example 2:

[0046] In Comparative Example 2, the chemical composition by mass percentage is C 0.23%, Si 0.28%, Mn 1.30%, P 0.013%, S 0.006%, Nb 0.03%, V 0.06%, B 0.0015%, with the remainder being Fe and unavoidable trace impurities, totaling 100% by mass. The steel was heated to 1180°C, finished at 950°C, and spray-cooled at a cooling rate of approximately 18°C / s. Quenching: Heating to 880°C, holding for 25 minutes, then rapidly cooling (mist cooling at a cooling rate of 40°C / s to room temperature). Tempering: Heating to 200°C, holding for 2 hours, then air-cooling. The steel achieved a yield strength of 670 MPa, a tensile strength of 800 MPa, an elongation of 15%, and an impact energy absorption of 32 J at -20°C. The finishing rolling temperature of this comparative example is too high, resulting in insufficient recrystallization, grain growth, and microstructure coarsening, which significantly reduces the yield strength and impact toughness and fails to achieve the optimal mechanical properties of the present invention.

[0047] Comparative Example 3:

[0048] In Comparative Example 3, the chemical composition by mass percentage is C 0.25%, Si 0.22%, Mn 1.35%, P 0.014%, S 0.008%, Nb 0.02%, V 0.10%, B 0.0025%, with the remainder being Fe and unavoidable trace impurities, totaling 100% by mass. The billet was heated to 1220°C, finished at 870°C, and cooled using air and water mist at a cooling rate of approximately 22°C / s. Quenching: Heating to 860°C, holding for 20 minutes, then rapidly cooling (water cooling at a cooling rate of 50°C / s to room temperature). Tempering: Heating to 350°C, holding for 1 hour, then air cooling. The steel achieved a yield strength of 680 MPa, a tensile strength of 820 MPa, an elongation of 16.5%, and an impact energy absorption of 28 J at -20°C. The tempering temperature of this comparative example is too high, resulting in a weakening of the precipitation strengthening effect and a deeper tempering degree of martensite, which leads to a decrease in strength. Although the plasticity is slightly improved, the strength and toughness are lower than those of the examples of the present invention.

[0049] The optimization scheme of the present invention achieves synergistic optimization of the strength, ductility, and toughness of anchor steel through rational composition design, controlled rolling and cooling processes, and heat treatment, making it more suitable for high-strength support projects. In contrast, the three comparative examples exhibited reduced mechanical properties due to a lack of microalloying, excessively high final rolling temperatures leading to grain coarsening, and excessively high tempering temperatures leading to reduced precipitation strengthening.

[0050] It can be seen from the above embodiments and comparative examples that the embodiments of the present invention have obvious advantages over the comparative examples: (1) Improvement of comprehensive mechanical properties: By optimizing the contents of C, Si, and Mn, and introducing microalloying elements such as Nb, V, and B, and combining with the controlled rolling and controlled cooling process, the yield strength of the anchor steel is increased by 50-90 MPa, the tensile strength is increased by 50-80 MPa, and the plasticity and impact toughness are significantly improved. Compared with the case without microalloying treatment (Comparative Example 1), the present invention has a better match between strength and toughness. (2) Better structural uniformity, avoiding performance fluctuations: By adopting an appropriate final rolling temperature (850-880°C), the grain size is effectively controlled, making the steel structure more uniform, avoiding the grain coarsening problem caused by excessively high final rolling temperature (Comparative Example 2), thereby improving the stability of the anchor steel and ensuring reliable mechanical properties under complex working conditions. (3) Optimize the heat treatment process to ensure a balance between high strength and toughness: By controlling the appropriate tempering temperature (200-250°C), the precipitation strengthening phase is ensured to fully play its role, which not only ensures that the strength meets the requirements but also improves the low-temperature impact toughness. Compared with the strength drop caused by the tempering temperature being too high (Comparative Example 3), the embodiment of the present invention achieves a better balance between strength, plasticity and toughness, making the anchor steel more suitable for support projects with high stress and high impact loads.

[0051] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for improving the mechanical properties of anchor steel, characterized in that: The steps include: (1) Based on the composition of traditional anchor steel, the element content in the steel is optimized through microalloying design. The mass percentage of its chemical composition includes: C 0.22-0.26%, Si 0.20-0.30%, Mn 1.10-1.40%, P≤0.015%, S≤0.010%, Nb 0.02-0.05%, V 0.05-0.10%, B 0.001-0.003%, and the rest is Fe and unavoidable impurities; (2) The billet is heated to 1150-1250℃ to fully dissolve the alloy elements and ensure uniform microstructure; final rolling is carried out in the range of 800-900℃, and the deformation temperature and cumulative deformation during the rolling process are strictly controlled to refine the grains; cooling is carried out after rolling, and the cooling rate is controlled between 15-25℃ / s to obtain fine ferrite and dispersed precipitates; (3) The rolled anchor steel is heated to 850-900°C for quenching, the holding time is 15-30 minutes, and then rapidly cooled; heated again to 200-250°C for tempering, the holding time is 1-2 hours, and finally a tempered bainite structure is obtained to ensure the coordination of strength and toughness.

2. The method for improving the mechanical properties of anchor steel according to claim 1, characterized in that: The mass percentages of its chemical components include: C 0.24%, Si 0.25%, Mn 1.25%, P 0.012%, S 0.007%, Nb 0.03%, V 0.08%, B 0.002%, and the rest are Fe and inevitable trace impurities, with a total mass fraction of 100%.

3. The method for improving the mechanical properties of anchor steel according to claim 2, characterized in that: The billet is heated to 1200℃, kept at this temperature for 1 hour and then rolled. The final rolling temperature is controlled at 880℃, and air cooling is adopted with a cooling rate of about 20℃ / s. Quenching: heating to 870℃, keeping at this temperature for 20 minutes and then rapidly cooling. Tempering: Heat to 220℃, keep warm for 1.5 hours and then air cool; the yield strength of the steel reaches 720MPa, the tensile strength reaches 850MPa, the elongation increases to 16.0%, the impact absorption energy at -20℃ is 50J, and the structure is fine tempered bainite and dispersed precipitates, which meets the use requirements.

4. The method for improving the mechanical properties of anchor steel according to claim 1, characterized in that: The mass percentages of its chemical components include: C 0.23%, Si 0.28%, Mn 1.30%, P 0.012%, S 0.007%, Nb 0.04%, V 0.06%, B 0.0015%, and the rest are Fe and inevitable trace impurities, with a total mass fraction of 100%.

5. The method for improving the mechanical properties of anchor steel according to claim 4, characterized in that: The billet is heated to 1180°C, held for 1 hour, and the final rolling temperature is 850°C. Spray cooling is used with a cooling rate of about 18°C / s. Quenching: heated to 880°C, held for 25 minutes, and then rapidly cooled. Tempering: Heat to 200℃, keep warm for 2 hours, and then air cool; the yield strength of the steel reaches 740MPa, the tensile strength reaches 860MPa, the elongation increases to 15.5%, the impact absorption energy at -20℃ is 55J, and the structure is fine tempered bainite and dispersed precipitates, meeting the requirements of engineering applications.

6. The method for improving the mechanical properties of anchor steel according to claim 1, characterized in that: The mass percentages of its chemical components include: C 0.25%, Si 0.22%, Mn 1.35%, P 0.011%, S 0.005%, Nb 0.02%, V 0.10%, B 0.0025%, and the rest are Fe and inevitable trace impurities, with a total mass fraction of 100%.

7. The method for improving the mechanical properties of anchor steel according to claim 6, characterized in that: The steel billet is heated to 1220℃, kept warm for 1 hour, and the final rolling temperature is 870℃. Air cooling + water mist cooling is adopted with a cooling rate of 22℃ / s; quenching: heated to 860℃, kept warm for 20 minutes and then quickly cooled; tempering: heated to 250℃, kept warm for 1 hour and then air cooled; the yield strength of the steel reaches 710MPa, the tensile strength reaches 840MPa, the elongation is increased to 17%, the impact absorption energy at -20℃ is 60J, and the structure is fine tempered bainite and dispersed precipitate phase, which meets the support engineering requirements.

8. The method for improving the mechanical properties of anchor steel according to any one of claims 1 to 7, characterized in that: The rapid cooling is specifically: water cooling or mist cooling, with a cooling rate of 30 to 60° C. / s, cooling to room temperature.