Method for producing high-strength and high-toughness PC steel bar by super-fast induction heating

Abstract

A method for producing high-strength, high-toughness PC steel bars using ultra-fast induction heating. This method employs an ultra-fast induction heating process, increasing the wire speed to 110-120 m / min to rapidly heat the 30MnSi base material to the austenitic phase region, followed by short-term holding and water quenching. Then, it is further ultra-fast induction heated to the tempering temperature, held for a short time, and then water quenched again. The 30MnSi PC steel bars of this invention maintain high strength while also possessing excellent toughness and plasticity, with a tensile strength of 1450-1480 MPa, a yield strength of 1270-1340 MPa, an elongation after fracture of 13%-15%, and a low-temperature (-20℃) impact energy of 48-52 J. Compared to conventional wire speed (70-85 m / min) production methods, the high-strength, high-toughness 30MnSi PC steel bars produced by this invention improve performance while increasing production efficiency by 30%-50%, significantly reducing costs.

Description

A method for producing high-strength and high-toughness PC steel bars using ultra-fast induction heating Technical Field

[0001] This invention relates to the field of materials heat treatment technology, specifically to high-strength and tough medium-carbon low-alloy PC steel bars and their ultra-fast induction heating production method. Background Technology

[0002] Steel has been the most widely used metallic material for the past few centuries. High-strength steel with good ductility has always been a goal pursued by scientists and a societal expectation, aiming to reduce the consumption of oil and resources by decreasing the amount of steel used in large buildings, thereby alleviating severe environmental pollution and energy shortages. However, in most metallic materials, increased strength comes at the cost of reduced ductility, demonstrating a trade-off between strength and ductility. This limits the widespread use of high-strength alloys. 30MnSi is a low-cost base material for producing PC steel bars. Many companies add alloying elements such as V, Ti, and Nb to further improve the strength and hydrogen embrittlement resistance of the steel bars, increasing the production cost of raw materials and reducing market competitiveness. In recent decades, ultra-rapid heating of steel has attracted considerable interest from researchers, and PC steel bars are heat-treated using high-speed induction heating production lines. Increasing the heating rate of induction heating can improve production efficiency and reduce costs, but ultra-rapid heating leading to an increase in the phase transformation point may introduce excessive residual ferrite, thereby reducing the strength of the steel bars. Therefore, it is necessary to study the optimal heat treatment parameters based on increasing the wire speed, so as to improve production efficiency and produce PC steel bars that meet national standards. This is the goal and aspiration of researchers and enterprises.

[0003] To improve productivity and enhance microstructure and material properties through grain refinement, rapid heat treatment has recently been widely recognized as an alternative to traditional heat treatment, which requires several hours of processing time. Rapid heat treatment technologies employ sustainable and energy-efficient manufacturing processes, such as induction heating or laser heating, and will facilitate numerous applications of quenched and tempered steels, particularly in the energy, defense, and transportation sectors. Overall, rapid heat treatment technologies offer significant advantages in improving production efficiency, reducing energy consumption, enhancing product quality, and enabling precise material control. This makes it an important process in many manufacturing and engineering fields. Due to their small diameter, PC steel bars allow for rapid heat transfer to the core. Therefore, combining rapid heat treatment technology with PC steel bars holds great promise for future applications.

[0004] In the prior art, Chinese patent CN103643135B discloses a PC steel bar with a tensile strength of 2000 MPa and above, and a heat treatment method. Its chemical composition by mass percentage is: 0.38-0.50% C, 1.50-2.0% Si, 0.30-0.50% Mn, 0.30-0.60% Cr, and 0.05-0.15% Mo, 0.05-0.3% V, 0.01-0.03% Nb, and 0.0005%-0.01% B. The main impurities P and S content are no more than 0.02%, Cu is less than 0.15%, and the balance is iron and other trace impurities unavoidable during the smelting process. This invention achieves a tensile strength of over 2000 MPa, uses a high-carbon alloy system in its composition design, and employs low-temperature tempering to improve strength, with an elongation after fracture only slightly exceeding 7%. The invention uses a large amount of alloys such as Si and Cr, which increases the cost. In addition, the austenitizing and tempering holding times are 5-10 seconds, and the production efficiency needs to be further improved.

[0005] Chinese patent CN110747404B discloses a 1570MPa grade delayed fracture resistant steel bar and its manufacturing method. Its chemical composition (mass percentage) is: C: 0.34%-0.37%, Si: 1.95%-2.00%, Mn: 0.60%-0.90%, P≤0.020%, S≤0.020%, Ti: 0.06%-0.08%, with the balance being Fe and unavoidable impurities. The PC steel bar produced by this method has high strength, but the carbon content (0.34%-0.37%) and silicon content (1.80-2.00%) are higher than ordinary 30MnSi, resulting in higher costs. Furthermore, the quenching temperature is 920-950℃, leading to higher energy consumption. The elongation after fracture is 8-9%, potentially indicating a higher risk of brittle fracture. Additionally, the steel bars produced by this method can only be run at a speed of 30-45 m / min, resulting in low production efficiency. Summary of the Invention

[0006] Therefore, it is necessary to provide a high-strength and high-toughness medium-carbon low-alloy PC steel bar that combines high strength and high ductility, as well as an ultra-fast induction heating production method for this high-strength and high-toughness medium-carbon low-alloy PC steel bar. This invention produces 30MnSi PC steel bars by increasing the wire speed to 110-120 m / min, ensuring high strength while maintaining excellent toughness and ductility. The tensile strength is 1450-1480 MPa, the yield strength is 1270-1340 MPa, the elongation after fracture is 13%-15%, and the low-temperature (-20℃) impact energy is 48-52 J. Compared to the ordinary wire speed (70-85 m / min) production method, the high-strength and high-toughness 30MnSi PC steel bars produced by this invention improve performance while increasing production efficiency by 30%-50%, significantly reducing costs.

[0007] The technical solution of the present invention is as follows:

[0008] The high-strength and high-toughness medium-carbon low-alloy PC steel bar has the following chemical composition by mass percentage: C: 0.27%-0.32%, Si: 0.65%-0.90%, Mn: 0.85%-1.05%, Cr: 0.07%-0.11%, Cu: 0.05%-0.1%, Ni: 0.09%-0.11%; the balance being Fe and unavoidable impurities.

[0009] The high-strength and high-toughness medium-carbon low-alloy PC steel bar is produced by ultra-fast induction heating (110 m / min), including the following steps:

[0010] (1) The steel billet obtained by continuous casting is hot-rolled and then produced as hot-rolled wire rod;

[0011] (2) The hot-rolled wire obtained in step (1) is cold-drawn to obtain cold-drawn 30MnSi;

[0012] (3) The cold-drawn 30MnSi obtained in step (2) is first ultra-fast induction heated to 890-950℃ at a heating rate of 150℃ / s-300℃ / s, held for 1-3s, and then water-quenched to 40-60℃ for the first time; the steel bar after the first water quenching is then ultra-fast induction heated to 400-480℃ at a heating rate of 80-120℃ / s, held for 1-3s, and then water-quenched to 40-60℃ for the second time to obtain a high-strength and tough medium-carbon low-alloy PC steel bar.

[0013] The wire drawing speed during the cold drawing process described in this invention is 110-120 m / min.

[0014] Preferably, the chemical composition of the high-strength and tough medium-carbon low-alloy PC steel bar is as follows (by mass percentage): C: 0.300%, Si: 0.793%, Mn: 0.951%, Cr: 0.090%, Cu: 0.088%, Ni: 0.100%, with the balance being Fe and unavoidable impurities.

[0015] Preferably, the high-strength and toughness medium-carbon low-alloy PC steel bar contains martensite, a small amount of residual ferrite (less than 10 vol%), and dispersed fine carbides. The small amount of granular ferrite can absorb the residual stress of the martensite, improve the plasticity, toughness, and resistance to hydrogen embrittlement of the steel bar, enabling the medium-carbon low-alloy PC steel bar to possess both high strength and plasticity.

[0016] Preferably, the mass percentage of impurity chemical components is controlled as follows: P≤0.015%, S≤0.008%, O≤10ppm, H≤10ppm.

[0017] Preferably, the high-strength and toughness medium-carbon low-alloy PC steel bar has a tensile strength of 1440-1480 MPa, a yield strength of 1286-1320 MPa, an elongation after fracture of 13%-15%, and a low-temperature impact toughness of 48-52 J.

[0018] Preferably, in step (1), the hot rolling specifically involves: an initial rolling temperature of 960-980℃ and a final rolling temperature of 880℃-890℃.

[0019] Preferably, in step (1), the steel billet is prepared by remelting scrap steel, refining it in an LF ladle, and then continuously casting it.

[0020] Preferably, in step (2), the total reduction rate of the cold drawing is 10-15%; the diameter of the cold-drawn 30MnSi is 10.7mm.

[0021] Preferably, in step (3), the temperature of the first ultra-fast induction heating is 890-950℃; and the temperature of the second ultra-fast induction heating is 400-480℃.

[0022] Preferably, in step (3), the cooling rate of the first water quench is 200-400℃ / s; and the cooling rate of the second water quench is 150-300℃ / s.

[0023] Preferably, in step (3), the heat preservation time is 1-3 seconds.

[0024] The above-mentioned ultra-fast induction heating production method for high-strength and high-toughness medium-carbon low-alloy PC steel bars includes the following steps:

[0025] (1) The steel billet obtained by continuous casting is hot-rolled and then produced as hot-rolled wire rod;

[0026] (2) The hot-rolled wire obtained in step (1) is cold-drawn to obtain cold-drawn 30MnSi;

[0027] (3) The cold-drawn 30MnSi obtained in step (2) is first ultra-fast induction heated to 890-950℃ at a heating rate of 150℃ / s-300℃ / s, held for 1-3s, and then water-quenched to 40-60℃ for the first time; the steel bar after the first water quenching is then ultra-fast induction heated to 400-480℃ at a heating rate of 80-120℃ / s, held for 1-3s, and then water-quenched to 40-60℃ for the second time to obtain a high-strength and tough medium-carbon low-alloy PC steel bar.

[0028] Preferably, the method for preparing the steel billet in step (1) is as follows: scrap steel is poured into an electric arc melting furnace to obtain molten steel; then, the molten steel is refined in a reducing atmosphere to obtain high-purity refined steel; finally, the refined steel is continuously cast to obtain a steel billet.

[0029] Preferably, the heating equipment described in step (3) consists of three induction heating furnaces: one 800KW GZP-800 / 8-HB (800KW-rated power, 8KHz frequency) solid-state medium-frequency induction heating furnace, and two solid-state ultra-high frequency induction heating furnaces GCYP-300 / 30-HB and GCYP-200 / 50-HB. Tempering is performed by a solid-state medium-frequency induction heating furnace GZP-350 / 8-HB.

[0030] Preferably, the water quenching in step (3) uses a spray quenching device with a water pressure set to 0.14-0.16 MPa.

[0031] In the composition design of the high-carbon low-alloy steel of this invention:

[0032] C: is the most common strengthening element in steel. 1. It forms a solid solution structure, increasing the strength of the steel. 2. It forms a carbide structure, which can increase the hardness and wear resistance of the steel.

[0033] Mn: Manganese provides solid solution strengthening and enables steel to obtain finer and stronger pearlite during the cooling process after hot rolling. The pearlite content increases with increasing manganese content. Manganese is also a carbide-forming element; manganese carbides can dissolve into cementite, thereby indirectly enhancing the strength of pearlite. Manganese can also improve the hardenability of steel, further increasing its strength.

[0034] Silicon (Si): Silicon forms a solid solution in ferrite or austenite, thereby enhancing the yield strength and tensile strength of steel. Furthermore, silicon increases the cold work hardening rate of steel, making it a beneficial element in alloy steels. Silicon can improve the strength, hardness, and wear resistance of steel without significantly reducing its plasticity within a certain range. Si can improve the tempering resistance of steel and inhibit the aggregation and growth of carbides.

[0035] Cr: Chromium primarily improves the hardenability of steel, giving it excellent overall mechanical properties. Chromium forms various carbides with carbon, exhibiting a greater affinity for carbon than iron and manganese. Chromium can also form intermetallic compounds with iron.

[0036] Microalloying elements Cu and Ni: Adding Cu to steel can refine the grains and improve its strength and toughness. Trace amounts of Ni can expand the austenite phase region and improve the low-temperature toughness of the steel bar. While microalloying elements are beneficial in this invention, excessive addition should be avoided considering cost and other factors.

[0037] The high-strength and high-toughness medium-carbon low-alloy PC steel bar obtained by this invention has a microstructure comprising martensite, a small amount of residual ferrite (less than 10 vol%), and dispersed fine carbides. The small amount of granular ferrite can absorb the residual stress of the martensite, improving the steel bar's plasticity, toughness, and resistance to hydrogen embrittlement, thus enabling the medium-carbon low-alloy PC steel bar to possess both high strength and plasticity.

[0038] In one embodiment, the structure is primarily a martensitic matrix and diffusely distributed fine carbides.

[0039] In one embodiment, the microstructure is primarily martensite, residual ferrite, and diffusely distributed fine carbides.

[0040] In one embodiment, the microstructure is primarily martensite, with a slightly higher proportion of granular residual ferrite and diffusely distributed fine carbides.

[0041] The high-strength and high-toughness medium-carbon low-alloy PC steel bar obtained by the above method through ultra-rapid heating has a microstructure consisting of martensite, a small amount of residual ferrite (less than 10 vol%), and dispersed fine carbides. The small amount of granular ferrite can absorb the residual stress of the martensite, improving the plasticity, toughness, and resistance to hydrogen embrittlement of the steel bar, enabling the medium-carbon low-alloy PC steel bar to possess both high strength and plasticity.

[0042] The advantages of this invention compared to tubular furnace heating production and slow line speed samples (70m / min or 85m / min) (hereinafter collectively referred to as conventional heat treatment methods) are as follows:

[0043] (1) The above-mentioned ultra-fast induction heating preparation method, with an average heating rate of 300℃ / s and a holding time of 1-3s, can improve production efficiency by 30%-50% compared to traditional heat treatment. The above-mentioned method for producing high-strength and high-toughness medium-carbon low-alloy PC steel bars by ultra-fast induction heating prepares the initial steel bar product from raw materials with appropriate proportions, and then performs rapid quenching and tempering treatment. In the rapid hot austenitization process, a large number of nucleated austenite primary phases do not have time to grow, which greatly refines the austenite grains, and a small amount of residual granular ferrite does not have time to austenitize, thus obtaining the final microstructure. Carbide precipitation and growth and martensite structure decomposition are the main changes that occur during the tempering process. In the rapid tempering process, the shorter treatment time reduces the annihilation of dislocations, resulting in more nucleation sites for cementite precipitation and a more uniform distribution of tempered precipitates. Ultimately, high-strength and high-toughness medium-carbon low-alloy PC steel bars can have both high strength and high plasticity. Compared to slow production line speeds and tube furnaces (or box furnaces) for producing PC steel bars, this method improves production efficiency while maintaining high mechanical properties and resistance to hydrogen embrittlement.

[0044] (2) Compared with traditional heat treatment processes, the high-strength and tough medium-carbon low-alloy PC steel bars obtained by ultra-fast induction heating heat treatment technology have reduced heating and homogenization time and shortened furnace length, resulting in reduced surface burn-off and significantly improved surface quality. Furthermore, due to the refinement of product grains and the reduction of material alloy content, the high-strength and tough medium-carbon low-alloy PC steel bars obtained by the technology of this invention also have improved forming performance and service performance.

[0045] (3) Compared to medium-carbon low-alloy PC steel bars obtained by traditional heat treatment methods, the high-strength and high-toughness medium-carbon low-alloy PC steel bars obtained by this invention have a tensile strength of 1440-1476 MPa, a yield strength of 1286-1308 MPa, an elongation after fracture of 13%-15%, and a low-temperature impact energy of 48-52 J. This material reduces the use of alloying elements while achieving high strength, and also maintains good plasticity and resistance to hydrogen embrittlement. Compared to slow production line speeds, it greatly improves production efficiency. It can be used in bridges, high-rise building concrete pipe piles, and some prestressed structural components to reduce the probability of brittle fracture and production costs. Attached Figure Description

[0046] Figure 1 shows the engineering stress-strain curves of the high-strength and high-toughness medium-carbon low-alloy PC steel bars produced in Examples 1-3 of the present invention.

[0047] Figure 2 shows scanning electron microscope (SEM) images of the high-strength and tough medium-carbon low-alloy PC steel bars produced in Examples 1-3 of the present invention. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of this invention clearer, a detailed description will be provided below in conjunction with various embodiments and accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the invention; however, the embodiments of the invention are not limited thereto. Those skilled in the art can make similar modifications without departing from the spirit of the invention; therefore, the invention is not limited to the specific embodiments described below.

[0049] Unless otherwise defined, the technical terms used below have the same meaning as commonly understood by those skilled in the art, and all raw materials, reagents, instruments and equipment used in this invention can be purchased on the market or prepared by existing methods.

[0050] The present invention provides a method for producing high-strength and tough medium-carbon low-alloy PC steel bars by ultra-fast induction heating, comprising: step one, composition design and hot rolling; step two, cold drawing; and step three, ultra-fast induction heating heat treatment.

[0051] In step one, the steel is refined according to the chemical composition ratio of high strength and toughness medium carbon low alloy PC steel bar, and the refined molten steel is continuously cast and rolled to obtain steel billet. The hot rolling is specifically as follows: the initial rolling temperature is 960-980℃, and the final rolling temperature is 880℃-890℃.

[0052] In step two, the hot-rolled wire obtained in step one is cold-drawn. The total area reduction rate of cold drawing is 10-15%, and the diameter of the cold-drawn steel bar is 10.7mm.

[0053] In step three, the cold-drawn 30MnSi obtained in step two is first ultra-fast induction heated to 890-950℃ at a heating rate of 150℃ / s-300℃ / s, held for 1-3s, and then first water-quenched to 40-60℃. The steel bar after the first water quenching is then second ultra-fast induction heated to 400-480℃ at a heating rate of 80-120℃ / s, held for 1-3s, and then water-quenched to 40-60℃ for the second time to obtain a high-strength and tough medium-carbon low-alloy PC steel bar.

[0054] Example 1

[0055] A method for producing medium-carbon low-alloy PC steel bars using a conventional tubular furnace includes the following steps:

[0056] Step 1: Refine the high-strength and tough medium-carbon low-alloy PC steel bars according to the chemical composition ratio in Table 1 below, and continuously cast and roll the refined molten steel to obtain steel billets.

[0057] Step 2: The hot-rolled wire obtained in Step 1 is cold-drawn. The total area reduction rate of cold drawing is 10-15%, and the diameter of the cold-drawn steel bar is 10.7mm.

[0058] Step 3: The cold-drawn 30MnSi obtained in Step 2 is heated to 920℃ in a tube furnace for the first time at a heating rate of 10℃ / s (drawing speed is 0m / min), heated and held for 15min, and then water-quenched to 50℃ for the first time; the steel bar after the first water quenching is heated to 400℃ in a tube furnace for the second time at a heating rate of 10℃ / s, heated and held for 15min, and then water-quenched to 50℃ for the second time to obtain ordinary medium carbon low alloy PC steel bar.

[0059] Example 2

[0060] A method for producing medium-carbon low-alloy PC steel bars by rapid induction heating includes the following steps:

[0061] Step 1: Refine the high-strength and tough medium-carbon low-alloy PC steel bars according to the chemical composition ratio in Table 1 below, and continuously cast and roll the refined molten steel to obtain steel billets.

[0062] Step 2: The hot-rolled wire obtained in Step 1 is cold-drawn. The total area reduction rate of cold drawing is 10-15%, and the diameter of the cold-drawn steel bar is 10.7mm.

[0063] Step 3: The cold-drawn 30MnSi obtained in Step 2 is first induction heated to 920℃ (please provide specific value) at a heating rate of 200℃ / s (drawing speed 85m / min), held for 3s, and then water-quenched to 50℃ for the first time. The steel bar after the first water quenching is then induction heated to 461℃ at a heating rate of 80℃ / s, held for 3s, and then water-quenched to 50℃ for the second time to obtain a medium carbon low alloy PC steel bar with high strength and toughness.

[0064] Example 3

[0065] The production of high-strength and high-toughness medium-carbon low-alloy PC steel bars by ultra-fast induction heating includes the following steps:

[0066] Step 1: Refine the high-strength and tough medium-carbon low-alloy PC steel bars according to the chemical composition ratio in Table 1 below, and continuously cast and roll the refined molten steel to obtain steel billets.

[0067] Step 2: The hot-rolled wire obtained in Step 1 is cold-drawn. The total area reduction rate of cold drawing is 10-15%, and the diameter of the cold-drawn steel bar is 10.7mm.

[0068] Step 3: The cold-drawn 30MnSi obtained in Step 2 is first ultra-fast induction heated to 920℃ at a heating rate of 300℃ / s (drawing speed 110m / min), held for 2s, and then first water-quenched to 50℃; the steel bar after the first water quenching is then ultra-fast induction heated to 465℃ at a heating rate of 110℃ / s, held for 2s, and then water-quenched to 50℃ for the second time to obtain a high-strength and tough medium-carbon low-alloy PC steel bar.

[0069] Table 1 is a list of the chemical components of the above embodiments of the present invention;

[0070] Table 1. Chemical composition (mass percentage) of each embodiment.

[0071]

[0072] Table 2 shows the cold drawing and rapid heat treatment process parameters of the above embodiments of the present invention;

[0073] Table 2. Process parameters for cold drawing and rapid heat treatment in each embodiment.

[0074]

[0075] The medium-carbon low-alloy steel bars prepared in the above embodiments were subjected to mechanical property tests, and the test results are shown in Table 3.

[0076] Table 3. Mechanical properties of medium-carbon low-alloy steel bars prepared in each example.

[0077]

[0078] As can be seen from Tables 1 to 3, the method of this invention can produce high-strength and high-toughness medium-carbon low-alloy PC steel bars with excellent mechanical properties. These bars exhibit tensile strength exceeding 1476 MPa, yield strength exceeding 1308 MPa, elongation after fracture exceeding 14%, and low-temperature impact toughness exceeding 48 J. Furthermore, the significantly refined microstructure and dispersed carbides ensure a high strength-ductility product for the medium-carbon low-alloy steel. In particular, Example 3, with its faster heating rate (faster wire speed), retains some residual ferrite and absorbs some residual stress from martensite, further improving toughness and ductility. The tensile strength reaches 1476 MPa, and the ductility reaches 14.0%. The strength-ductility product and low-temperature impact toughness are higher than those of PC steel bars produced by traditional processes and samples with a wire speed of 85 m / min.

[0079] Figure 1 shows the engineering stress-strain curves of the high-strength and high-toughness medium-carbon low-alloy PC steel bars prepared in Examples 1-3 of this invention. It can be seen that the sample of Example 1, prepared by the traditional heating method, has the highest strength but the worst plasticity. The sample prepared by the fast-running line speed (85 m / min) has a tensile strength that is 25 MPa higher than that prepared by the slow-running line speed, and the elongation after fracture decreases by one percentage point, while still maintaining high plasticity.

[0080] Figure 2 shows SEM images of the high-strength and high-toughness medium-carbon low-alloy PC steel bars prepared in Examples 1-3. (a) represents Example 1, (b) represents Example 2, and (c) represents Example 3. It can be seen that the original austenite diameter in Examples 2-3 in Figure 2 is relatively small. This is because the ultra-rapid heating prevents the austenite from growing quickly enough, thus refining the grain size. Furthermore, the rapid heating rate pushes the austenitization temperature to a higher level, further accelerating the nucleation rate and refining the microstructure, ultimately improving the material's ductility and toughness. In Examples 1 to 3, as the heating rate increases, A... C3The increased phase transformation point and ferrite content lead to a decrease in steel bar strength and an increase in plasticity. However, due to the faster tempering heating rate in Example 3, the strength is actually higher. In particular, Example 3, due to its rapid heating rate, retains a small amount of granular ferrite, which absorbs the residual stress of martensite, improving overall plasticity and toughness. Furthermore, the higher boundary density of martensite in Example 3 further resists crack propagation. In summary, high-strength and high-toughness medium-carbon low-alloy PC steel bars produced using ultra-fast induction heating wires maintain high strength while possessing excellent plasticity and toughness. With reasonable parameter adjustments, a tensile strength of 1476 MPa, a yield strength of 1308 MPa, an elongation after fracture of 14%, and a low-temperature impact energy of 52 J can be obtained.

[0081] In summary, the high-strength and high-toughness medium-carbon low-alloy PC steel bars produced by ultra-fast induction heating in this invention achieve refined microstructure, retaining a small amount of granular ferrite and finely dispersed carbides, and possessing high dislocation density and boundary density, thus obtaining excellent mechanical properties. Simply increasing the wire speed, without adding many expensive rare metals, can improve plasticity, toughness, and production efficiency, while rapid heat treatment has enormous development and application value. The combination of these two factors will undoubtedly provide greater scope for the development and production of medium-carbon low-alloy steel!

[0082] The embodiments described above merely illustrate concentrated implementations of the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still make various modifications and improvements to the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features, without departing from the concept of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A method for producing high-strength and high-toughness medium-carbon low-alloy PC steel bars using ultra-fast induction heating, characterized in that, Its chemical composition by mass percentage is as follows: C: 0.27% - 0.32%, Si: 0.65% - 0.90%, Mn: 0.85% - 1.05%, Cr: 0.07% - 0.11%, Cu: 0.05% - 0.1%, Ni: 0.09% - 0.11%, S ≤ 0.008%, P ≤ 0.015%, balance being Fe; the high-strength and tough medium-carbon low-alloy PC steel bar is produced by ultra-fast induction heating, including the following steps: (1) hot-rolling the continuously cast steel billet and drawing it into hot-rolled wire; (2) cold-drawing the hot-rolled wire obtained in step (1) to obtain cold-drawn 30MnSi; (3) first ultra-fast induction heating the cold-drawn 30MnSi obtained in step (2) to 890-950℃ at a heating rate of 150℃ / s-300℃ / s, holding it at that temperature, and then first water quenching it to 40-60℃; the steel bar after the first water quenching is second ultra-fast induction heating to 400-480℃ at a heating rate of 80-120℃ / s, holding it at that temperature, and then second water quenching it to 40-60℃ to obtain a high-strength and tough medium-carbon low-alloy PC steel bar; the holding time is 1-3s; the wire speed during the cold drawing process is 110-120 m / min; control impurity chemical composition by mass percentage: O≤10ppm, H≤10ppm; the high-strength and tough medium-carbon low-alloy PC steel bar has a tensile strength of 1450-1490MPa, a yield strength of 1270-1340MPa, an elongation after fracture of 13%-15.0%, and an impact energy of 48-52J at -20℃; the high-strength and tough medium-carbon low-alloy PC steel bar includes martensite, less than 10 vol% residual ferrite, and dispersed fine carbides.

2. The method according to claim 1, characterized in that, The chemical composition of the high-strength and tough medium-carbon low-alloy PC steel bar by mass percentage is as follows: C: 0.300%, Si: 0.793%, Mn: 0.951%, Cr: 0.090%, Cu: 0.088%, Ni: 0.100%, with the balance being Fe.

3. The method according to claim 1, characterized in that, In step (1), the hot rolling specifically refers to the initial rolling temperature being 960-980℃ and the final rolling temperature being 880℃-890℃.

4. The method according to claim 1, characterized in that, In step (2), the total reduction rate of the cold drawing is 10-15%.

5. The method according to claim 1, characterized in that, In step (2), the diameter of the cold-drawn 30MnSi is 10.7mm.

6. The method according to claim 1, characterized in that, The cooling rate of the first water quench in step (3) is 200-400℃ / s; the cooling rate of the second water quench is 150-300℃ / s.

7. The method according to claim 1, characterized in that, In step (1), the billet is prepared by remelting scrap steel, refining it in an LF ladle, and then continuously casting it.

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