Green and environment-friendly 2300MPa-grade steel strand wire rod and production method thereof

Abstract

The invention provides a green and environment-friendly steel wire rod for a 2300 MPa grade steel strand and a production method of the green and environment-friendly steel wire rod. The steel wire rod comprises, by weight, 0.95%-1.05% of C, 0.20%-0.40% of Si, 0.60%-0.90% of Mn, 0.10%-0.40% of Cr, smaller than or equal to 0.030% of V, smaller than or equal to 0.015% of P, smaller than or equal to 0.010% of S, 0.01%-0.04% of Al and the balance Fe. Through the special design of the components and through the processes of converter blowing, LF refining, RH refining, continuous casting, flaw detection and coping, high-speed wire rod rolling, online heat treatment and aging treatment, the strength of a steel strand finished product manufactured after an obtained wire rod is subjected to drawing, twisting and stabilizing treatment reaches 2300 MPa, and the tensile strength of the steel strand finished product reaches 2300 MPa. Meanwhile, the properties such as yield strength and elongation all meet the requirements, and the production method is efficient, green and energy-saving.

Description

Technical Field

[0001] The invention belongs to the technical field of metal wire manufacturing, and in particular relates to a green and environment-friendly 2300MPa grade wire rod for steel strands and a production method thereof. Background Art

[0002] With the rapid development of my country's economy, the construction of high-speed railways, bridges and other projects has entered a period of vigorous development. There are more and more railway planning projects in my country. According to statistics, the total mileage of railways put into use in China has exceeded 150,000 kilometers, of which high-speed railways have reached 40,000 kilometers. China has become the country with the most comprehensive technology, the strongest carrying capacity, the longest operating mileage, the fastest running speed, and the largest scale of use and construction of high-speed railway systems in the world. However, with the increasingly complex construction environment and geological conditions such as plateaus, as well as the requirements for project construction costs, the requirements for the load force, elongation, fatigue performance, etc. of prestressed steel strands for railways are getting higher and higher. The traditional 1860MPa grade prestressed steel strands can no longer meet the needs of future railway construction. In 2023, the national standard for prestressed concrete steel strands will be updated accordingly, and the strength levels will be increased to 2160MPa, 2230MPa, and 2360MPa, which will be widely used in the construction of newly started projects in the future. At the same time, with the development of the economy, the country has higher requirements for environmentally friendly production. Therefore, it is imperative to develop a production method for green and environmentally friendly high prestressed steel strands.

[0003] The wire rod for high-strength steel strand needs to have high strength, high toughness and fatigue resistance. At present, the composition system of high Si / high Mn / high Cr / high V is generally adopted, combined with the means of secondary heat treatment of hot-rolled wire rods to meet the use requirements. On the one hand, through microalloying, the Si element plays a good role in solid solution strengthening and cold working strengthening, the Mn element plays a role in solid solution strengthening and improving the stability of austenite, which helps to improve the strength and sorbitization rate. The Cr element mainly stabilizes the austenite and reduces its pearlite transformation temperature, plays a role in refining the pearlite lamellae, and also plays a role in improving the strength of the steel. The V element combines with the C element to form fine carbide particles and precipitates at a higher temperature, which plays a role in refining the austenite grains. At the same time, the fine carbides themselves also play a role in precipitation strengthening, thereby improving the strength of the steel. On the other hand, the hot-rolled wire rod is reheated offline and cooled in a salt bath, reheated to the austenite state, and then the cooling rate of the austenite-to-pearlite transformation process is increased by an offline salt bath, the interlamellar spacing is refined, and the sorbitization rate is increased, thereby increasing the strength of the wire rod to reach a tensile strength of more than 1450MPa for φ14mm wire rods. This method of secondary heat treatment reduces production efficiency and increases production costs, and the micro-alloying component system increases energy consumption, which does not conform to the green and environmentally friendly production concept. Summary of the invention

[0004] Aiming at the technical problems of high energy consumption and low production efficiency in the production method of wire rod for high prestressed steel strand, the present invention proposes a low-carbon and environmentally friendly production method for wire rod for steel strand that can produce 2300MPa-grade high-strength wire rod.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A green and environmentally friendly wire rod for 2300MPa grade steel strands, which comprises the following components in percentage by weight: C 0.95-1.05%, Si 0.20-0.40%, Mn 0.60-0.90%, Cr 0.10-0.40%, V≤0.030%, P≤0.015%, S≤0.010%, Al0.01-0.04%, and the remainder of Fe and unavoidable impurities.

[0007] Preferably, the specification of the wire rod is Φ13.0~Φ14.0mm.

[0008] Preferably, the weight percentage of its components is: C 0.95-0.98%, Si 0.35-0.40%, Mn 0.70-0.80%, Cr 0.25-0.26%, V≤0.025%, P≤0.015%, S≤0.010%, Al 0.02-0.03%, and the balance Fe and inevitable impurities.

[0009] Preferably, the weight percentage of the components is: C 0.98%, Si 0.40%, Mn 0.75%, Cr 0.26%, V 0.025%, P 0.009%, S 0.001%, Al 0.01-0.04%, and the balance of Fe and unavoidable impurities.

[0010] A method for producing a green and environmentally friendly 2300MPa grade steel strand wire rod comprises the following steps:

[0011] (1) Converter blowing: The raw materials are smelted through blast furnace molten iron-KR desulfurization-100-ton top and bottom double-blowing converter. The converter steel is blown by double-blow method to reduce the content of impurity elements in the molten steel. The P content of the converter end point is ≤0.010%, and the S content is ≤0.005%;

[0012] (2) LF refining + RH refining: After the steel is tapped from the converter, it is refined in the LF furnace and the RH furnace. The LF furnace refining uses aluminum deoxidation, high basicity slag system and ultra-low oxygen production process to reduce the equilibrium oxygen content in the molten steel; the RH vacuum treatment time is ≥20 min, and the O content in the steel is controlled to be ≤12ppm and the N content is ≤50ppm;

[0013] (3) Continuous casting: Using dynamic soft reduction technology and the mathematical model of solidification heat transfer of the continuous casting machine, and using electromagnetic stirring of the crystallizer, electromagnetic stirring at the end of solidification, and automatic water distribution to control the segregation of the continuous casting billet composition, the segregation index of the continuous casting billet is below 1.05;

[0014] (4) Flaw detection and grinding: Shot blasting and flaw detection are performed on the continuous casting billet, surface defect inspection is performed, and the billet with defects is ground;

[0015] (5) High-speed wire rolling: select defect-free continuous casting billets, and sequentially go through step furnace heating - roughing mill - intermediate rolling mill - pre-finishing mill - pre-water cooling - finishing mill - water cooling - sizing mill - water cooling - laying head - super large fan air cooling line controlled cooling - coiling and collection;

[0016] (6) Online heat treatment: the rolled wire rod is sequentially subjected to wire rod spinning - roller conveying - constant temperature cooling toughening heat treatment - surface cleaning - collection and coiling, wherein the spinning temperature is 850-920°C; the constant temperature cooling toughening heat treatment step is to control the conveying speed of the roller to make the wire rod undergo isothermal transformation in a molten salt constant temperature cooling tank, the salt bath time is 1-3 minutes, and a mixed molten salt of potassium nitrate, sodium nitrate and sodium nitrite is used as the quenching medium, and the salt bath temperature is 520-570°C;

[0017] (7) Aging treatment: Place the wire rod in an aging warehouse at 50-80°C for 5-7 days to remove internal stress.

[0018] Preferably, in step (1), a slide plate is used to block slag during steel tapping from the converter, and the amount of slag is strictly controlled to prevent the slag from returning to P and contaminating the molten steel.

[0019] Preferably, in step (5), the heating temperature of the billet during the rolling process is 1100-1200° C., the rolling process and spinning temperature is 850-920° C., and the rolling speed is 20-35 m / s.

[0020] Preferably, in step (5), the step furnace heating adopts different temperature sections to heat the high temperature in sequence, the temperature of the preheating section and the heating section I is 950-1080°C, and the heating time is 30-50 minutes; the temperature of the high temperature section is 1100-1200°C, and the soaking time is 50-70 minutes.

[0021] Preferably, the mixed nitrate molten salt in step 6 comprises 10-20% potassium nitrate and 70-85% sodium nitrate, with the remainder being sodium nitrite.

[0022] Compared with the prior art, the advantages and positive effects of the present invention are:

[0023] The production method of the wire rod for 2300MPa grade steel strand of the present invention refines the original austenite grains through reasonable composition design, uses mixed nitrate molten salt as quenching medium, adopts online salt bath isothermal heat treatment equipment, and controls the temperature of the salt solution and the immersion time of the wire rod to maximize the phase change cooling rate and constant temperature transformation. The low alloying composition design has the advantages of energy saving and consumption reduction, and the continuous online salt bath heat treatment has the advantages of high production capacity, high yield rate and stable process.

[0024] The wire rod obtained by the production method of the present invention has a troostitization rate of more than 95%, the troostite lamellae are uniform and straight and as fine as 70nm, the pearlite spheroidal grain size is 9, the performance of the wire rod is uniform and stable, there is no abnormal structure that affects the use, and it has the characteristics of high strength, high toughness and fatigue resistance. After pickling, phosphating, drawing, stranding and stabilization, the 1*7 structure is produced. The final product strength of ultra-high-strength steel strand for railways is stabilized at 2330-2370MPa, while the yield strength, elongation, relaxation, fatigue and other properties all meet the requirements.

[0025] At the same time, the present invention does not require secondary heating or secondary billet rolling without adding precious alloy elements (and the content of alloy elements is lower than that of most similar products in the industry), and it achieves maximum strength and toughness of the product in an efficient, green and energy-saving manner. It is a low-cost, green and low-carbon production method. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the metallographic structure of the wire rod under a microscope (100 times magnification) in Example 1 of the present invention;

[0027] Figure 2 The figure is a schematic diagram of the metallographic structure of the wire rod in Example 1 of the present invention, taken by scanning electron microscope (10000 times);

[0028] Figure 3 Schematic diagram of the metallographic structure of the wire rod under a microscope (100 times magnification) in Example 2 of the present invention;

[0029] Figure 4 Schematic diagram of the metallographic structure of the wire rod in Example 2 of the present invention by scanning electron microscope (10000 times); DETAILED DESCRIPTION

[0030] In order to better understand the present invention, a detailed description is given below in conjunction with the accompanying drawings and embodiments.

[0031] Example:

[0032] Chemical composition is the basic condition that determines the microstructure of wire rod. It is not only related to the processing performance of wire rod, but also plays a key role in various performance indicators of wire rod. In the composition design of the present invention:

[0033] C: As a strong interstitial solid solution strengthening element, its solid solution strengthening is crucial to improving strength and is an effective element for improving wire rod strength. However, with the increase of carbon content, the plasticity and toughness of the wire rod will decrease, and the chemical composition will deviate too much from the eutectoid point of steel. During the cooling process, it is easy to form a pro-eutectoid carburized structure at the austenite grain boundary, which will reduce the performance of the wire rod. In order to control the carbon segregation of the continuous casting billet and the pro-eutectoid carburized structure, the carbon content should not be too high.

[0034] Si: It is a good deoxidizer and a non-carbide forming element. It is mainly dissolved in ferrite and exists in the form of solid solution in steel. It has a strong strengthening effect and improves local corrosion resistance. Si also has the effect of inhibiting the formation of proeutectoid cementite. Si needs to be used together with other strong carbide elements to avoid graphitization.

[0035] Mn: An appropriate amount of manganese has a great strengthening effect on steel. Manganese and iron form a solid body, which can refine pearlite and effectively improve the strength, hardness and wear resistance of steel. It can eliminate the hot brittleness of steel caused by sulfur and oxygen, improve the hot processing performance of steel, and improve the cold brittleness tendency of steel without significantly reducing the plasticity and impact toughness of steel. Manganese can also reduce the critical cooling rate of steel and improve the hardenability of steel. At the same time, manganese is prone to segregation, and too much manganese will increase the tendency of martensite formation.

[0036] Cr: It is a strong carbide-forming element, which reduces the critical cooling rate of steel, shifts the continuous transformation curve of steel to the right, improves the hardenability of steel, reduces the spacing between sorbite sheets, and improves the strength and plastic toughness of wire rod; it exists in the cementite lamellae to form alloy cementite, which can effectively reduce the carbon content of grain boundaries and thus inhibit the formation of proeutectoid cementite. However, too high Cr content will prolong the sorbite transformation time, easily form quenching structures such as martensite, and reduce the performance of wire rod.

[0037] V: It can improve the hardenability of steel, refine grains, and form fine carbonitride particles with elements such as carbon and nitrogen, which prevents the growth of austenite grains during heating and plays a role in precipitation strengthening, thereby improving the strength of the wire rod; like Cr, it exists in the cementite layer to form alloy cementite, which can effectively reduce the carbon content at the grain boundary and thus inhibit the formation of proeutectoid cementite. However, if the vanadium content is too high, it will lead to an increase in carbonitride particles and the growth of particles, which will reduce the plasticity of the wire rod.

[0038] Al: It is a deoxidizer with much stronger deoxidation ability than silicon and manganese. It refines grains and is an effective element for adjusting the grain size of steel. During the solidification process, a large amount of finely dispersed aluminum oxide can promote the formation of fine-grained steel, thereby improving the strength of wire rod. However, coarse aluminum oxide will seriously affect wire rod drawing and reduce the fatigue performance of steel strands.

[0039] P, S: They are harmful elements in wire rods for steel strands, which significantly reduce the plasticity and toughness of steel and should be controlled.

[0040] Based on the effects of the above-mentioned elements, the chemical composition of the wire rod for the green and environmentally friendly 2300 MPa grade steel strand in Examples 1 to 2 of the present invention is shown in Table 1.

[0041] Table 1 Chemical composition of wire rod of Example 1-2 / %

[0042] serial number C Si Mn P S Cr V Al Example 1 0.95 0.35 0.75 0.009 0.002 0.25 0.025 0.026 Example 2 0.98 0.40 0.75 0.009 0.001 0.26 0.025 0.027

[0043] The production method of the green and environmentally friendly 2300 MPa grade steel strand wire rod described in Examples 1 to 2 is as follows:

[0044] (1) Converter blowing

[0045] The raw materials are smelted through blast furnace iron water-KR desulfurization-100-ton top and bottom double-blowing converter. The blast furnace iron water is treated with KR desulfurization to minimize the S content; the converter steel is blown by the double method to reduce the content of impurity elements in the molten steel. The P element content at the end of the converter is ≤0.010%, and the S element content is ≤0.005%. The LF furnace refining adopts aluminum deoxidation and high-basicity slag production process to reduce the O content of the molten steel. The continuous casting process adopts a control method combining protective pouring, electromagnetic stirring at the end of the crystallizer, and light pressure to distribute each roller and pull speed, strictly controlling the superheat to <25℃. In particular, the continuous casting machine solidification heat transfer mathematical model and nail shooting test are used to guide the continuous casting light pressure process parameters to solve the technical problems of center segregation and dendrite segregation of continuous casting billets with C content above 0.95%. By tracking large-sized inclusions and optimizing the flow field of the ladle and the tundish, the number and size of inclusions are reduced accordingly, which improves the cleanliness of the molten steel. The converter uses a slide plate to block the slag during steel tapping, strictly controlling the amount of slag to prevent the slag from returning to P and contaminating the molten steel.

[0046] (2) LF refining + RH refining

[0047] After the steel is tapped from the converter, it is refined in a 100-ton LF furnace and a 100-ton RH furnace. The LF furnace refining uses aluminum deoxidation, high-basicity slag system and ultra-low oxygen production process to reduce the equilibrium oxygen content in the molten steel; the molten steel after LF refining enters the RH furnace for vacuum degassing to further improve the purity of the molten steel. The RH vacuum treatment time is ≥20 minutes, and the O content in the steel is controlled to be ≤12ppm and the N content is ≤50ppm.

[0048] (3) Continuous casting

[0049] By utilizing dynamic soft reduction technology and the mathematical model of solidification heat transfer of the continuous casting machine, and adopting electromagnetic stirring of the crystallizer, electromagnetic stirring at the end of solidification, and automatic water distribution to control the composition segregation of the continuous casting billet, the segregation index of the continuous casting billet is below 1.05.

[0050] (4) Flaw detection and grinding

[0051] The continuous casting billets must be shot blasted, inspected for flaws, and tested for surface defects. The billets with defects must be repaired and ground accordingly to ensure that there are no defects on the surface of the continuous casting billets.

[0052] (5) High-speed wire rolling

[0053] Use defect-free continuous casting billets, and the billets do not need to be opened again. The process flow is: continuous casting billet walking furnace heating - rough rolling unit - medium rolling unit - pre-finishing rolling unit - pre-water cooling - finishing rolling unit - water cooling - sizing unit - water cooling - laying head - super large fan air cooling line controlled cooling - coil collection.

[0054] The heating process of the walking furnace adopts a high-temperature heating process with different temperature sections in sequence, among which the temperature of the preheating section and the heating section I is 1080℃, the heating time is 50min, the temperature of the high-temperature section is 1120℃, and the soaking time is 60min. The heated continuous casting billet enters the high-speed wire rolling mill for rolling, and the wire laying temperature is 880±10℃. By controlling the conveying speed of the roller table, the isothermal transformation time of the wire rod in the salt bath is 1 to 3min, and the salt bath temperature is 530±10℃. After the austenite is fully transformed, the wire rod is rolled, the salt solution is rinsed with water, and the bundles are packaged.

[0055] (6) Online heat treatment

[0056] The process flow is: wire rod extrusion - roller conveying - constant temperature cooling toughening heat treatment - surface cleaning - collection into coils. After rolling, the extrusion temperature of the wire rod is controlled within the range of 880±10℃, and it is adjusted appropriately according to the specifications of the wire rod; by controlling the conveying speed of the roller, the isothermal transformation time of the wire rod in the molten salt constant temperature cooling tank is 1 to 3 minutes, and the salt bath temperature is 530±10℃, ensuring that the austenite structure is completely transformed into a fine and uniform sorbite structure, so that the wire rod has a high sorbite rate, good mechanical properties and drawing processing performance.

[0057] The constant temperature cooling toughening heat treatment step uses a mixed molten salt of potassium nitrate, sodium nitrate and sodium nitrite as the quenching medium, and the mixed nitrate molten salt includes 10-20% potassium nitrate and 70-85% sodium nitrate, and the balance is sodium nitrite. This formula is non-toxic and harmless, can be recycled repeatedly, and has the advantages of green, low-carbon and environmental protection. The relevant properties of the formula molten salt have been verified by the following experiments, proving that it has good thermal stability and cooling capacity, as follows:

[0058] In order to ensure the continuity of the phase change temperature range of the wire rod heat treatment, a high-temperature repeatability test was conducted: the temperature was 500-600℃ for 1200h, and the relevant thermophysical properties were monitored every 100h. It was shown that the mixed nitrate molten salt showed good thermal stability in the environment of 500-600℃. 120 quenching / heating cycle experiments and related thermophysical properties were tested in the molten salt thermal shock environment. The molten salt still showed good thermal stability, which provided a guarantee for the use of molten salt in large-scale industrial production. The cooling capacity of the molten salt was tested through the cooling characteristic test device. Under the standard test probe and heating temperature, the maximum cooling rate of the molten salt reached 55℃ / s. At the same time, the cooling capacity of the salt bath and the lead bath was compared using a standard probe, which verified that the cooling capacity and stability of the salt bath molten salt were equivalent to those of the lead bath.

[0059] The online heat treatment step utilizes the constant temperature cooling method of continuous online salt bath heat treatment after rolling and spinning to perform online "isothermal troostite toughening treatment" on the hot-rolled wire rod. Supercooling is the driving force for transformation, so the growth of troostite lamellae is closely related to the transformation temperature. Under the premise of not producing abnormal structures such as martensite and bainite, the relatively low and constant salt temperature allows the wire rod to quickly enter the salt tank in the austenite structure state for high cooling rate isothermal troostite phase transformation, so the smaller the interlamellar spacing obtained, the higher the troostitization rate, and therefore the strength and plasticity of the wire rod are better. Since the temperature of the solution in the salt tank is precisely controlled and fluctuates little, it can ensure that the obtained troostite structure is more stable and uniform, the troostite lamellae are straighter, and the performance of the rod is more uniform, meeting the performance requirements of ultra-high strength steel strands for strength, fatigue, relaxation, etc.

[0060] (7) Aging treatment

[0061] This process places the wire rod in an aging warehouse at a temperature of 50 to 80°C for 5 to 7 days, which can quickly remove internal stress and improve the plasticity of the wire rod.

[0062] Comparative Example:

[0063] The chemical composition of the wire rod for comparative steel strand is: C 0.92%, Si 0.30, Mn 0.80,

[0064] P 0.008, S 0.002, Cr 0.20, V 0.020, Al 0.020.

[0065] The wire rod is prepared by a traditional production method, which specifically includes the following steps:

[0066] (1) Converter blowing

[0067] The raw materials are smelted through blast furnace iron water-KR desulfurization-100-ton top and bottom double-blowing converter. The blast furnace iron water is treated with KR desulfurization to minimize the S content; the converter steel is blown by double-joint method to reduce the content of impurity elements in the molten steel. The P element content at the converter end is ≤0.010%, and the S element content is ≤0.005%.

[0068] (2) LF refining + RH refining

[0069] After the steel is tapped from the converter, it is refined in a 100-ton LF furnace and a 100-ton RH furnace. The LF furnace refining uses aluminum deoxidation, high-basicity slag system and ultra-low oxygen production process to reduce the equilibrium oxygen content in the molten steel; the molten steel after LF refining enters the RH furnace for vacuum degassing to further improve the purity of the molten steel. The RH vacuum treatment time is ≥20 minutes, and the O content in the steel is controlled to be ≤12ppm and the N content is ≤50ppm.

[0070] (3) Continuous casting

[0071] By utilizing dynamic soft reduction technology and the mathematical model of solidification heat transfer of the continuous casting machine, and adopting electromagnetic stirring of the crystallizer, electromagnetic stirring at the end of solidification, and automatic water distribution to control the composition segregation of the continuous casting billet, the segregation index of the continuous casting billet is below 1.05.

[0072] (4) Flaw detection and grinding

[0073] The continuous casting billets must be shot blasted, flaw detected, and inspected for surface defects. The billets with defects must be repaired and ground accordingly to ensure that there are no defects on the surface of the continuous casting billets.

[0074] (5) High-speed wire rolling

[0075] Use defect-free continuous casting billets, and the billets do not need to be opened again. The process flow is: continuous casting billet walking furnace heating - rough rolling unit - medium rolling unit - pre-finishing rolling unit - pre-water cooling - finishing rolling unit - water cooling - sizing unit - water cooling - laying head - super large fan air cooling line controlled cooling - coil collection.

[0076] The heating process of the stepping furnace adopts a high-temperature heating process with different temperature sections in sequence, among which the temperature of the preheating section and the heating section I is 1080℃, the heating time is 50min, the temperature of the high-temperature section is 1120℃, and the soaking time is 60min. The heated continuous casting billet enters the high-speed wire rolling mill for rolling, and the wire laying temperature is 880±10℃. By controlling the conveying speed of the roller table, the isothermal transformation time of the wire rod in the salt bath is 1 to 3min. The salt bath temperature is determined according to the wire rod specifications and the wire laying temperature, and the temperature range is 530±10℃. After the austenite is fully transformed, the wire rod is rolled, the salt solution is rinsed with water, and the bundles are packaged.

[0077] (6) Online heat treatment

[0078] The process flow is: wire rod spinning - roller conveying - salt bath treatment - surface cleaning - collection into coils. After rolling, the spinning temperature of the wire rod is controlled within the range of 880±10℃, and it is adjusted appropriately according to the specifications of the wire rod; by controlling the conveying speed of the roller, the isothermal transformation time of the wire rod in the molten salt constant temperature cooling tank is 1 to 3 minutes, the salt bath medium is 20% potassium nitrate and 80% sodium nitrate, and the salt bath temperature is determined according to the wire rod specifications and spinning temperature, and the temperature range is 530±10℃.

[0079] (7) Aging treatment

[0080] This process places the wire rod in an aging warehouse at a temperature of 50 to 80°C for 5 to 7 days, which can quickly remove internal stress and improve the plasticity of the wire rod.

[0081] The specifications and mechanical properties of the steel strand wire rods obtained in Examples 1-2 and the comparative example are shown in Table 2. The structure, specifications and mechanical properties of the railway steel strand wire rods obtained by drawing, stranding and stabilization of the steel strand wire rods in Examples 1-2 and the comparative example are shown in Table 3.

[0082] Table 2 Specifications and mechanical properties of Example 1-2 and Comparative Example wire rod

[0083] serial number Specification tensile strength Sectional shrinkage Comparative Example Φ14.0mm 1466MPa 42％ Example 1 Φ14.0mm 1510MPa 40％ Example 2 Φ15.0mm 1525MPa 38％

[0084] Table 3 Structure, specification and mechanical properties of steel strands of Examples 1-2 and Comparative Examples

[0085] serial number structure Specification tensile strength Comparative Example 1*7 Φ15.2mm 2275MPa Example 1 1*7 Φ15.2mm 2330MPa Example 2 1*7 Φ15.2mm 2370MPa

[0086] The schematic diagram of the metallographic structure of the wire rod under a microscope (100 times) in Example 1 is as follows: Figure 1 As shown, the schematic diagram of the metallographic structure of the scanning electron microscope (10000 times) is as follows Figure 2 The schematic diagram of the metallographic structure of the wire rod under the microscope (100 times) in Example 2 is shown as follows: Figure 1 As shown, the schematic diagram of the metallographic structure of the scanning electron microscope (10000 times) is as follows Figure 2 As shown; it can be seen from the figure that the wire rods obtained in Examples 1 and 2 have a pearlite spheroid grain size of 9.0, a troostitization rate of 96%, an average troostite lamellar spacing of 60nm, a uniform and stable structure, and no abnormal structure that affects use.

[0087] Combining the experimental results in Table 2 and Table 3, it can be seen that the wire rod obtained by the production method described in this embodiment has a uniform structure without abnormal structures such as network carbides and martensite that affect the use while increasing the wire rod diameter and greatly improving the high strength of the wire rod. After the wire rod is drawn, twisted, and stabilized, the strength of the finished product of the Φ15.2mm large-section steel strand reaches 2330-2370MPa, and the quality meets the requirements.

[0088] The production method of the wire rod for 2300MPa grade steel strand of the present invention refines the original austenite grains through reasonable composition design, and adopts online salt bath isothermal heat treatment equipment with mixed nitrate molten salt as quenching medium, and controls the temperature of the salt solution and the immersion time of the wire rod to maximize the phase change cooling rate and constant temperature transformation. The low alloying composition design has the advantages of energy saving and consumption reduction, and the continuous online salt bath heat treatment has the advantages of high production capacity, high yield rate and stable process.

[0089] The wire rod obtained by the production method of the present invention has a troostitization rate of more than 95%, the troostite lamellae are uniform and straight and as fine as 70nm, the pearlite spheroid grain size is 9 levels, the performance of the wire rod is uniform and stable, there is no abnormal structure that affects the use, and it has the characteristics of high strength, high toughness and fatigue resistance.

[0090] Income The tensile strength of standard wire rod reaches more than 1500MPa, and the cross-sectional shrinkage rate reaches 40%. The tensile strength of the standard wire rod reaches more than 1520MPa, and the cross-sectional shrinkage rate reaches 38%. After pickling, phosphating, drawing, twisting and stabilization, the 1*7 structure is produced. The final product strength of ultra-high-strength steel strand for railway is stable at 2330-2370MPa, and the yield strength, elongation, relaxation, fatigue and other properties all meet the requirements. At the same time, the present invention does not need to perform secondary heating and secondary blanking and rolling without adding precious alloy elements (and the alloy element content is lower than most similar products in the industry), and achieves the maximum strength and toughness of the product in an efficient, green and energy-saving manner. It is a low-cost, green and low-carbon production method.

[0091] The above description is only a preferred embodiment of the present invention and does not limit the present invention in other forms. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes and apply it to other fields. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A green and environmentally friendly 2300MPa grade steel strand wire rod, characterized in that: The weight percentage of its components is: C 0.95-1.05%, Si 0.20-0.40%, Mn 0.60-0.90%, Cr 0.10-0.40%, V≤0.030%, P≤0.015%, S≤0.010%, Al 0.01-0.04%, and the balance of Fe and inevitable impurities.

2. The green and environmentally friendly 2300MPa grade steel strand wire rod according to claim 1, characterized in that: The specification of the wire rod is Φ13.0~Φ14.0mm.

3. The green and environmentally friendly 2300MPa grade steel strand wire rod according to claim 1, characterized in that: The weight percentage of its components is: C 0.95-0.98%, Si 0.35-0.40%, Mn 0.70-0.80%, Cr 0.25-0.26%, V≤0.025%, P≤0.015%, S≤0.010%, Al 0.02-0.03%, and the balance of Fe and inevitable impurities.

4. The green and environmentally friendly 2300MPa grade steel strand wire rod according to claim 1, characterized in that: The weight percentage of its components is: C 0.98%, Si 0.40%, Mn 0.75%, Cr 0.26%, V 0.025%, P 0.009%, S 0.001%, Al 0.01-0.04%, and the balance of Fe and inevitable impurities.

5. A method for producing green and environmentally friendly 2300MPa grade steel strand wire rod, characterized in that: The following steps are involved: (1) Converter blowing: The raw materials are smelted through blast furnace molten iron-KR desulfurization-100-ton top and bottom double-blowing converter. The converter steel is blown by double-blow method to reduce the content of impurity elements in the molten steel. The P content of the converter end point is ≤0.010%, and the S content is ≤0.005%; (2) LF refining + RH refining: After the steel is tapped from the converter, it is refined in the LF furnace and the RH furnace. The LF furnace refining uses aluminum deoxidation, high basicity slag system and ultra-low oxygen production process to reduce the equilibrium oxygen content in the molten steel; the RH vacuum treatment time is ≥20 min, and the O content in the steel is controlled to be ≤12ppm and the N content is ≤50ppm; (3) Continuous casting: Using dynamic soft reduction technology and the mathematical model of solidification heat transfer of the continuous casting machine, and using electromagnetic stirring of the crystallizer, electromagnetic stirring at the end of solidification, and automatic water distribution to control the segregation of the continuous casting billet composition, the segregation index of the continuous casting billet is below 1.05; (4) Flaw detection and grinding: Shot blasting and flaw detection are performed on the continuous casting billet, surface defect inspection is performed, and the billet with defects is ground; (5) High-speed wire rolling: select defect-free continuous casting billets, and sequentially go through step furnace heating - roughing mill - intermediate rolling mill - pre-finishing mill - pre-water cooling - finishing mill - water cooling - sizing mill - water cooling - laying head - super large fan air cooling line controlled cooling - coiling and collection; (6) Online heat treatment: the rolled wire rod is sequentially subjected to wire rod spinning - roller conveying - constant temperature cooling toughening heat treatment - surface cleaning - collection and coiling, wherein the spinning temperature is 850-920°C; the constant temperature cooling toughening heat treatment step is to control the conveying speed of the roller to make the wire rod undergo isothermal transformation in a molten salt constant temperature cooling tank, the salt bath time is 1-3 minutes, and a mixed molten salt of potassium nitrate, sodium nitrate and sodium nitrite is used as the quenching medium, and the salt bath temperature is 520-570°C; (7) Aging treatment: Place the wire rod in an aging warehouse at 50-80°C for 5-7 days to remove internal stress.

6. The method for producing green and environmentally friendly 2300MPa grade steel strand wire rod according to claim 1, characterized in that: In step (1), a slide plate is used to block slag during steel tapping from the converter, and the amount of slag discharged is controlled.

7. The method for producing green and environmentally friendly 2300 MPa grade steel strand wire rod according to claim 1, characterized in that: In step (5), the heating temperature of the billet during the rolling process is 1100-1200° C., the rolling process and the spinning temperature are 850-920° C., and the rolling speed is 20-35 m / s.

8. The method for producing green and environmentally friendly 2300 MPa grade steel strand wire rod according to claim 1, characterized in that: Step (5) of the step beam furnace heating is carried out by heating in different temperature sections in sequence with increasing high temperature. The temperature of the preheating section and the heating section I is 950-1080°C, and the heating time is 30-50 min; the temperature of the high temperature section is 1100-1200°C, and the soaking time is 50-70 min.

9. The method for producing green and environmentally friendly 2300 MPa grade steel strand wire rod according to claim 1, characterized in that: The mixed nitrate molten salt in step 6 includes 10-20% potassium nitrate and 70-85% sodium nitrate, and the remainder is sodium nitrite.

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