Nb microalloyed high-carbon wire rod and production method thereof

Abstract

The invention particularly discloses a Nb microalloyed high-carbon wire rod and a production method thereof, and the Nb microalloyed high-carbon wire rod comprises the following components by mass percent: 0.90-1.10% of C; 1.20% to 1.60% of Si; 0.30% to 0.50% of Mn; 0.40% to 0.80% of Cr; 0.02 to 0.10 percent of V; nb: 0.002 to 0.009%; p is less than or equal to 0.03%; s is less than or equal to 0.03%, and the balance is Fe and inevitable impurities. According to the method, the number of TiN inclusions in the high-carbon wire rod is greatly reduced, and the residual Ti element in the wire rod is converted into a (Ti, Nb) (C, N) composite nanoscale precipitated phase with a certain precipitation strengthening effect; according to the high-carbon wire rod and the preparation method thereof, the reduction of area and the strength of the high-carbon wire rod are improved, the reduction of area can reach 35% or above, and the tensile strength can reach 1650 MPa.

Description

Technical Field

[0001] The present invention relates to the technical field of wire rod production, and in particular to a Nb micro-alloyed high-carbon wire rod and a production method thereof. Background Art

[0002] Prestressed steel strands and wires are essential, key, and basic materials for major projects such as bridges and large buildings, as well as for the manufacturing of high-end equipment such as automobiles and high-speed railways. Under the "dual carbon" backdrop, they are developing toward ultra-high strength, which is driving the development of raw wire rods toward ultra-high strengthening. There are two main ways to increase the strength of steel wire. One is to increase the wire rod specifications, thereby increasing the work hardening rate during the cold drawing process, thereby increasing the strength of the steel wire. However, this method is limited by the wire rod specifications. The other is to optimize the wire rod composition through microalloying. Increasing the C content in the wire rod is undoubtedly the most effective method, but the increase in C often aggravates the carbon content in the wire rod. Optimizing and innovating the existing wire rod alloy composition system is crucial.

[0003] However, as strength continues to increase, wire rod's cross-sectional reduction rate continues to decrease. Insufficient processing performance, such as cold deformation, and service performance, such as fatigue, have gradually become bottlenecks restricting further quality development. Residual Ti easily forms hard inclusions called TiN, and its adverse effects in steel wire have become increasingly prominent in recent years. Eliminating the adverse effects of residual Ti will effectively promote the development of improved steel wire quality. Summary of the Invention

[0004] The purpose of the present invention is to provide a Nb microalloyed high carbon wire rod and a production method thereof, so as to solve the problem in the current industry that high carbon steel wire rod has a large number of TiN hard inclusions, the strength is improved and the cross-sectional shrinkage rate is reduced.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A Nb-microalloyed high-carbon wire rod comprises the following components, by mass percentage: C: 0.90-1.10%; Si: 1.20-1.60%; Mn: 0.30-0.50%; Cr: 0.40-0.80%; V: 0.02-0.10%; Nb: 0.002-0.009%; P ≤ 0.03%; S ≤ 0.03%, with the remainder being Fe and unavoidable impurities. By adding 0.002-0.009% Nb during the steelmaking process, Nb refines the austenite grains, thereby improving the wire rod's reduction of area. Furthermore, considering that carbon content affects the precipitation of TiN inclusions, and Nb has a dragging effect on carbon atoms, adding 0.90-1.10% C further facilitates the precipitation of TiN inclusions, while also lowering the pearlite transformation temperature and refining the interlamellar spacing.

[0007] Carbon is the most important element in steel and the most effective element for increasing steel strength. Increasing the carbon content within a certain range can significantly improve steel strength: theoretically, every 0.1% increase in the mass fraction of carbon in high-carbon steel increases its tensile strength by approximately 30 to 40 MPa. However, increasing carbon undoubtedly promotes the precipitation of network cementite in high-carbon wire rod, affecting the wire rod's mechanical properties and service life. Because the wire rod in the present invention is produced using an online isothermal process, its carbon content can be appropriately higher, preferably between 0.90 and 1.10%.

[0008] Silicon exists primarily in the form of a solid solution in ferrite in steel, acting as a solid solution strengthening agent, improving the hardenability and strength properties of high-carbon steel. When the silicon content is less than 0.5%, the tensile strength of the wire rod increases by 8 MPa for every 0.1% increase in silicon content. However, excessive silicon content can negatively impact the torsional properties of the high-carbon steel wire, reduce its weldability, and increase crack sensitivity during wire rod welding. The preferred content is 1.20-1.60%.

[0009] Manganese is evenly distributed in the ferrite and cementite lamellae of high-carbon steel. For every 0.1% increase in manganese, the tensile strength of the wire rod increases by approximately 10 MPa. However, enriched Mn tends to segregate within the steel, leading to the formation of martensite, which affects the drawing properties of the wire rod and can cause breakage during drawing. The Mn content is preferably between 0.30% and 0.50%.

[0010] Chromium can replace the Fe element in high carbon steel, transforming the cementite into iron-chromium composite cementite (Fe, Cr)3C, greatly improving the strength of high carbon steel, and at the same time helping to improve the cross-sectional shrinkage rate of wire rod; however, when the Cr content is too high, the high carbon steel will cause delamination and fracture during the subsequent mechanical properties test, and its content is selected to be 0.40-0.80%.

[0011] Vanadium can react with carbon in high-carbon steel to form very fine carbides, such as vanadium carbide (VC). These carbides can precipitate in cementite lamellae, strengthening them and thus increasing the tensile strength of the wire rod. However, excessive addition of vanadium can significantly reduce the torsional properties of the wire rod after large deformation during cold working. Cold deformation causes fractures in the cementite Fe3C lamellae, reducing plasticity. The vanadium content is preferably between 0.02% and 0.10%.

[0012] As a microalloying element, niobium, when added to high-carbon wire rod, can increase undercooling and lower the pearlite transformation temperature curve. It also increases the eutectoid carbon content of the steel, which helps slow the precipitation of network cementite. Generally, considering consumption during the steelmaking process, niobium additions are generally not less than 0.010%. However, above 0.010%, niobium no longer further refines the pearlite lamellae, and higher Nb contents tend to increase segregation in the ingot. Considering cost factors, the Nb content is typically between 0.002% and 0.009%.

[0013] Preferably, the alloy comprises the following components by mass percentage: C: 0.95-1.00%; Si: 1.20-1.50%; Mn: 0.40-0.50%; Cr: 0.40-0.60%; V: 0.02-0.06%; Nb: 0.002-0.009%; P≤0.03%; S≤0.03%, and the rest is Fe and unavoidable impurities.

[0014] Furthermore, the diameter of the wire rod is greater than 13 mm.

[0015] Furthermore, the tensile strength of the wire rod reaches 1600-1650 MPa, and the cross-sectional shrinkage rate reaches more than 35%.

[0016] The present invention also provides a method for producing a Nb microalloyed high carbon wire rod, the method comprising the following steps in sequence:

[0017] (1) Smelting the raw materials and adding Nb element during smelting;

[0018] (2) Refining after smelting;

[0019] (3) After refining, continuous casting of billets is performed using a continuous casting machine;

[0020] (4) sending the billet into a heating furnace for heating;

[0021] (5) After the billet is heated, high-pressure water is used to remove phosphorus;

[0022] (6) After high-pressure water dephosphorization, high-speed wire rod rolling is performed using roughing, intermediate rolling, and finishing mills;

[0023] (7) After high-speed wire rolling, it is passed through a spinning machine for spinning;

[0024] (8) after spinning, an online isothermal salt bath treatment is performed;

[0025] (9) After spinning, the wire rod passes through a cleaning box to clean the salt particles on the surface of the wire rod;

[0026] (10) Finished products that have passed inspection are stacked in an insulated warehouse, waiting for delivery and transportation.

[0027] Preferably, in step (3), the continuous casting superheat is controlled to be ≤25°C, the casting speed is controlled to be 1.2-1.5m / min, the continuous casting water volume is 0.2-0.25L / kg, the end stirring current is 420-480A, and the end stirring frequency is 7-9Hz.

[0028] Preferably, in step (4), the preheating temperature of the heating furnace is controlled at 880°C to 940°C, the temperature of the heating section is controlled at 1120°C to 1200°C, and the temperature of the soaking section is controlled at 1150°C to 1250°C.

[0029] Preferably, in step (6), the temperature before rough rolling is controlled at 980°C to 1050°C, and the temperature before finish rolling is controlled at 880°C to 920°C.

[0030] Preferably, the spinning temperature in step (7) is 890°C to 950°C.

[0031] Preferably, the salt bath temperature in step (8) is 480-580°C.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. The present invention significantly reduces the amount of TiN inclusions in high-carbon wire rods and converts the residual Ti element in the wire rods into a (Ti, Nb) (C, N) composite nano-scale precipitate phase with a certain precipitation strengthening effect.

[0034] 2. The present invention achieves an improvement in the cross-sectional shrinkage and strength of the high-carbon wire rod. The cross-sectional shrinkage can reach more than 35%, and the tensile strength can reach 1650 MPa.

[0035] 3. The high carbon wire rod produced according to the present invention can meet the requirements for the preparation of 2200MPa grade steel wire for bridge cables and 2400MPa prestressed steel strands. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a scanning electron microscope image of the wire rod structure of Example 1 of the present invention.

[0037] Figure 2 This is a scanning electron microscope image of the wire rod structure of Example 2 of the present invention.

[0038] Figure 3 This is a scanning electron microscope image of the wire rod structure of Example 3 of the present invention.

[0039] Figure 4 This is a scanning electron microscope image of the wire rod structure of Example 4 of the present invention.

[0040] Figure 5This is a scanning electron microscope image of the wire rod structure of Example 5 of the present invention.

[0041] Figure 6 This is a scanning electron microscope image of the wire rod structure of Example 6 of the present invention.

[0042] Figure 7 This is a scanning electron microscope image of the wire rod structure of Example 7 of the present invention.

[0043] Figure 8 This is a scanning electron microscope image of the wire rod structure of Example 8 of the present invention.

[0044] Figure 9 This is a scanning electron microscope image of the wire rod structure of Example 9 of the present invention.

[0045] Figure 10 This is a scanning electron microscope image of the wire rod structure of the comparative example of the present invention.

[0046] Figure 11 This is the room temperature tensile engineering stress-strain curve of Example 6 of the present invention.

[0047] Figure 12 This is a diagram showing the distribution of inclusions in the wire rod according to Example 6 of the present invention.

[0048] Figure 13 This is the inclusion distribution diagram of the wire rod in the comparative example of the present invention. DETAILED DESCRIPTION

[0049] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below through examples.

[0050] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0051] Secondly, the term "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive of other embodiments.

[0052] Example 1:

[0053] See also Figure 1This embodiment provides a Nb microalloyed high carbon wire rod, which includes the following components by mass percentage: C: 0.94%; Si: 1.21%; Mn: 0.44%; Cr: 0.44%; V: 0.035%; Nb: 0.002%; P: 0.007%; S: 0.001%, Ti: 0.0052%, and the rest is Fe and unavoidable impurities.

[0054] The production method of the wire rod comprises the following steps in sequence:

[0055] (1) Smelting the raw materials and adding Nb element during smelting;

[0056] (2) Refining after smelting;

[0057] (3) After refining, the billet was continuously cast using a continuous casting machine. The continuous casting superheat was controlled at 25°C, the casting speed was controlled at 1.3 m / min, the continuous casting water volume was 0.23 L / kg, the end stirring current was 450 A, and the end stirring frequency was 8 Hz.

[0058] (4) The billet is sent to a heating furnace for heating. The preheating temperature of the heating furnace is controlled at 900°C, the temperature of the heating section is controlled at 1150°C, and the temperature of the soaking section is controlled at 1200°C.

[0059] (5) After the billet is heated, high-pressure water is used to remove phosphorus;

[0060] (6) After high-pressure water dephosphorization, high-speed wire rod rolling is performed using rough rolling, intermediate rolling, and finishing rolling mills, wherein the temperature before rough rolling is controlled at 1000° C., and the temperature before finishing rolling is controlled at 900° C.;

[0061] (7) After high-speed wire rolling, the wire is passed through a spinning machine for spinning, and the spinning temperature is 920° C.

[0062] (8) After spinning, the silk was treated with an online isothermal salt bath at a temperature of 550°C;

[0063] (9) After spinning, the wire rod passes through a cleaning box to clean the salt particles on the surface of the wire rod;

[0064] (10) Finished products that have passed inspection are stacked in an insulated warehouse, waiting for delivery and transportation.

[0065] Example 2:

[0066] See also Figure 2 This embodiment provides a Nb microalloyed high carbon wire rod, which includes the following components by mass percentage: C: 0.95%; Si: 1.22%; Mn: 0.33%; Cr: 0.52%; V: 0.044%; Nb: 0.008%; P: 0.007%; S: 0.001%, Ti: 0.0053%, and the rest is Fe and unavoidable impurities.

[0067] The production method of the wire rod comprises the following steps in sequence:

[0068] (1) Smelting the raw materials and adding Nb element during smelting;

[0069] (2) Refining after smelting;

[0070] (3) After refining, the billet was continuously cast using a continuous casting machine. The continuous casting superheat was controlled at 23°C, the casting speed was controlled at 1.2 m / min, the continuous casting water volume was 0.2 L / kg, the end stirring current was 420 A, and the end stirring frequency was 7 Hz.

[0071] (4) The billet is sent to a heating furnace for heating. The preheating temperature of the heating furnace is controlled at 880°C, the temperature of the heating section is controlled at 1120°C, and the temperature of the soaking section is controlled at 1150°C.

[0072] (5) After the billet is heated, high-pressure water is used to remove phosphorus;

[0073] (6) After high-pressure water dephosphorization, high-speed wire rod rolling is performed using rough rolling, intermediate rolling, and finishing rolling mills, wherein the temperature before rough rolling is controlled at 980° C., and the temperature before finishing rolling is controlled at 880° C.;

[0074] (7) After high-speed wire rolling, the wire is passed through a spinning machine for spinning, and the spinning temperature is 890° C.;

[0075] (8) After spinning, an online isothermal salt bath treatment is performed, and the salt bath temperature is 480°C;

[0076] (9) After spinning, the wire rod passes through a cleaning box to clean the salt particles on the surface of the wire rod;

[0077] (10) Finished products that have passed inspection are stacked in an insulated warehouse, waiting for delivery and transportation.

[0078] Example 3:

[0079] See also Figure 3 This embodiment provides a Nb microalloyed high carbon wire rod, which includes the following components by mass percentage: C: 0.95%; Si: 1.28%; Mn: 0.42%; Cr: 0.60%; V: 0.072%; Nb: 0.009%; P: 0.008%; S: 0.001%, Ti: 0.0048%, and the rest is Fe and unavoidable impurities.

[0080] The production method of the wire rod comprises the following steps in sequence:

[0081] (1) Smelting the raw materials and adding Nb element during smelting;

[0082] (2) Refining after smelting;

[0083] (3) After refining, the billet was continuously cast using a continuous casting machine. The continuous casting superheat was controlled at 25°C, the casting speed was controlled at 1.5m / min, the continuous casting water volume was 0.25L / kg, the end stirring current was 480A, and the end stirring frequency was 9Hz.

[0084] (4) The billet is sent to a heating furnace for heating. The preheating temperature of the heating furnace is controlled at 940°C, the temperature of the heating section is controlled at 1200°C, and the temperature of the soaking section is controlled at 1250°C.

[0085] (5) After the billet is heated, high-pressure water is used to remove phosphorus;

[0086] (6) After high-pressure water dephosphorization, high-speed wire rod rolling is performed using rough rolling, intermediate rolling, and finishing rolling mills, wherein the temperature before rough rolling is controlled at 1050° C., and the temperature before finishing rolling is controlled at 920° C.;

[0087] (7) After high-speed wire rolling, the wire is passed through a spinning machine for spinning, and the spinning temperature is 950° C.;

[0088] (8) After spinning, an online isothermal salt bath treatment is performed, and the salt bath temperature is 580°C;

[0089] (9) After spinning, the wire rod passes through a cleaning box to clean the salt particles on the surface of the wire rod;

[0090] (10) Finished products that have passed inspection are stacked in an insulated warehouse, waiting for delivery and transportation.

[0091] Example 4:

[0092] See also Figure 4 This embodiment provides a Nb microalloyed high carbon wire rod, which includes the following components by mass percentage: C: 0.94%; Si: 1.29%; Mn: 0.45%; Cr: 0.46%; V: 0.067%; Nb: 0.008%; P: 0.006%; S: 0.001%, Ti: 0.0043%, and the rest is Fe and unavoidable impurities.

[0093] The production method of the wire rod comprises the following steps in sequence:

[0094] (1) Smelting the raw materials and adding Nb element during smelting;

[0095] (2) Refining after smelting;

[0096] (3) After refining, the billet was continuously cast using a continuous casting machine. The continuous casting superheat was controlled at 22°C, the casting speed was controlled at 1.4 m / min, the continuous casting water volume was 0.24 L / kg, the end stirring current was 460 A, and the end stirring frequency was 8 Hz.

[0097] (4) The billet is sent to a heating furnace for heating. The preheating temperature of the heating furnace is controlled at 920°C, the temperature of the heating section is controlled at 1140°C, and the temperature of the soaking section is controlled at 1210°C.

[0098] (5) After the billet is heated, high-pressure water is used to remove phosphorus;

[0099] (6) After high-pressure water dephosphorization, high-speed wire rod rolling is performed using rough rolling, intermediate rolling, and finishing rolling mills, wherein the temperature before rough rolling is controlled at 1020° C., and the temperature before finishing rolling is controlled at 910° C.;

[0100] (7) After high-speed wire rolling, the wire is passed through a spinning machine for spinning, and the spinning temperature is 940° C.

[0101] (8) After spinning, an online isothermal salt bath treatment is performed, and the salt bath temperature is 560°C;

[0102] (9) After spinning, the wire rod passes through a cleaning box to clean the salt particles on the surface of the wire rod;

[0103] (10) Finished products that have passed inspection are stacked in an insulated warehouse, waiting for delivery and transportation.

[0104] Example 5:

[0105] See also Figure 5 This embodiment provides a Nb microalloyed high carbon wire rod, which includes the following components by mass percentage: C: 0.96%; Si: 1.23%; Mn: 0.40%; Cr: 0.54%; V: 0.056%; Nb: 0.009%; P: 0.007%; S: 0.001%, Ti: 0.0051%, and the rest is Fe and unavoidable impurities.

[0106] The production method of the wire rod comprises the following steps in sequence:

[0107] (1) Smelting the raw materials and adding Nb element during smelting;

[0108] (2) Refining after smelting;

[0109] (3) After refining, the billet was continuously cast using a continuous casting machine. The continuous casting superheat was controlled at 23°C, the casting speed was controlled at 1.1 m / min, the continuous casting water content was 0.21 L / kg, the end stirring current was 430 A, and the end stirring frequency was 7 Hz.

[0110] (4) The billet is sent to a heating furnace for heating. The preheating temperature of the heating furnace is controlled at 890°C, the temperature of the heating section is controlled at 1130°C, and the temperature of the soaking section is controlled at 1160°C.

[0111] (5) After the billet is heated, high-pressure water is used to remove phosphorus;

[0112] (6) After high-pressure water dephosphorization, high-speed wire rod rolling is performed using rough rolling, intermediate rolling, and finishing rolling mills, wherein the temperature before rough rolling is controlled at 990° C., and the temperature before finishing rolling is controlled at 890° C.;

[0113] (7) After high-speed wire rolling, the wire is passed through a spinning machine for spinning, and the spinning temperature is 900° C.;

[0114] (8) After spinning, an online isothermal salt bath treatment is performed, and the salt bath temperature is 570°C;

[0115] (9) After spinning, the wire rod passes through a cleaning box to clean the salt particles on the surface of the wire rod;

[0116] (10) Finished products that have passed inspection are stacked in an insulated warehouse, waiting for delivery and transportation.

[0117] Example 6:

[0118] See also Figure 6 This embodiment provides a Nb microalloyed high carbon wire rod, which includes the following components by mass percentage: C: 0.93%; Si: 1.34%; Mn: 0.31%; Cr: 0.43%; V: 0.087%; Nb: 0.008%; P: 0.008%; S: 0.001%, Ti: 0.0052%, and the rest is Fe and unavoidable impurities.

[0119] The production method of the wire rod comprises the following steps in sequence:

[0120] (1) Smelting the raw materials and adding Nb element during smelting;

[0121] (2) Refining after smelting;

[0122] (3) After refining, the billet was continuously cast using a continuous casting machine. The continuous casting superheat was controlled at 21°C, the casting speed was controlled at 1.3 m / min, the continuous casting water content was 0.22 L / kg, the end stirring current was 470 A, and the end stirring frequency was 9 Hz.

[0123] (4) The billet is sent to a heating furnace for heating. The preheating temperature of the heating furnace is controlled at 910°C, the temperature of the heating section is controlled at 1180°C, and the temperature of the soaking section is controlled at 1240°C.

[0124] (5) After the billet is heated, high-pressure water is used to remove phosphorus;

[0125] (6) After high-pressure water dephosphorization, high-speed wire rod rolling is performed using rough rolling, intermediate rolling, and finishing rolling mills, wherein the temperature before rough rolling is controlled at 1040° C., and the temperature before finishing rolling is controlled at 900° C.;

[0126] (7) After high-speed wire rolling, the wire is passed through a spinning machine for spinning, and the spinning temperature is 910° C.;

[0127] (8) After spinning, an online isothermal salt bath treatment is performed, and the salt bath temperature is 490°C;

[0128] (9) After spinning, the wire rod passes through a cleaning box to clean the salt particles on the surface of the wire rod;

[0129] (10) Finished products that have passed inspection are stacked in an insulated warehouse, waiting for delivery and transportation.

[0130] Example 7:

[0131] See also Figure 7 This embodiment provides a Nb microalloyed high carbon wire rod, which includes the following components by mass percentage: C: 0.94%; Si: 1.26%; Mn: 0.44%; Cr: 0.65%; V: 0.068%; Nb: 0.006%; P: 0.009%; S: 0.001%, Ti: 0.0054%, and the rest is Fe and unavoidable impurities.

[0132] The production method of the wire rod comprises the following steps in sequence:

[0133] (1) Smelting the raw materials and adding Nb element during smelting;

[0134] (2) Refining after smelting;

[0135] (3) After refining, the billet was continuously cast using a continuous casting machine. The continuous casting superheat was controlled at 23.5°C, the casting speed was controlled at 1.45 m / min, the continuous casting water volume was 0.22 L / kg, the end stirring current was 440 A, and the end stirring frequency was 8 Hz.

[0136] (4) The billet is sent to a heating furnace for heating. The preheating temperature of the heating furnace is controlled at 930°C, the temperature of the heating section is controlled at 1160°C, and the temperature of the soaking section is controlled at 1180°C.

[0137] (5) After the billet is heated, high-pressure water is used to remove phosphorus;

[0138] (6) After high-pressure water dephosphorization, high-speed wire rod rolling is performed using rough rolling, intermediate rolling, and finishing rolling mills, wherein the temperature before rough rolling is controlled at 1010° C., and the temperature before finishing rolling is controlled at 915° C.;

[0139] (7) After high-speed wire rolling, the wire is passed through a spinning machine for spinning, and the spinning temperature is 930° C.;

[0140] (8) After spinning, the silk is treated with an online isothermal salt bath at a temperature of 500°C;

[0141] (9) After spinning, the wire rod passes through a cleaning box to clean the salt particles on the surface of the wire rod;

[0142] (10) Finished products that have passed inspection are stacked in an insulated warehouse, waiting for delivery and transportation.

[0143] Example 8:

[0144] See also Figure 8 This embodiment provides a Nb microalloyed high carbon wire rod, which includes the following components by mass percentage: C: 0.95%; Si: 1.36%; Mn: 0.33%; Cr: 0.72%; V: 0.047%; Nb: 0.009%; P: 0.006%; S: 0.001%, Ti: 0.0052%, and the rest is Fe and unavoidable impurities.

[0145] The production method of the wire rod comprises the following steps in sequence:

[0146] (1) Smelting the raw materials and adding Nb element during smelting;

[0147] (2) Refining after smelting;

[0148] (3) After refining, the billet was continuously cast using a continuous casting machine. The continuous casting superheat was controlled at 22°C, the casting speed was controlled at 1.4 m / min, the continuous casting water volume was 0.20 L / kg, the end stirring current was 460 A, and the end stirring frequency was 7 Hz.

[0149] (4) The billet is sent to a heating furnace for heating. The preheating temperature of the heating furnace is controlled at 915°C, the temperature of the heating section is controlled at 1170°C, and the temperature of the soaking section is controlled at 1190°C.

[0150] (5) After the billet is heated, high-pressure water is used to remove phosphorus;

[0151] (6) After high-pressure water dephosphorization, high-speed wire rod rolling is performed using rough rolling, intermediate rolling, and finishing rolling mills, wherein the temperature before rough rolling is controlled at 1030° C., and the temperature before finishing rolling is controlled at 910° C.;

[0152] (7) After high-speed wire rolling, the wire is passed through a spinning machine for spinning, and the spinning temperature is 920° C.

[0153] (8) After spinning, an online isothermal salt bath treatment is performed, and the salt bath temperature is 510°C;

[0154] (9) After spinning, the wire rod passes through a cleaning box to clean the salt particles on the surface of the wire rod;

[0155] (10) Finished products that have passed inspection are stacked in an insulated warehouse, waiting for delivery and transportation.

[0156] Example 9:

[0157] See also Figure 9This embodiment provides a Nb microalloyed high carbon wire rod, which includes the following components by mass percentage: C: 0.95%; Si: 1.44%; Mn: 0.36%; Cr: 0.43%; V: 0.059%; Nb: 0.007%; P: 0.007%; S: 0.001%, Ti: 0.0053%, and the rest is Fe and unavoidable impurities.

[0158] The production method of the wire rod comprises the following steps in sequence:

[0159] (1) Smelting the raw materials and adding Nb element during smelting;

[0160] (2) Refining after smelting;

[0161] (3) After refining, the billet was continuously cast using a continuous casting machine. The continuous casting superheat was controlled at 24°C, the casting speed was controlled at 1.4 m / min, the continuous casting water volume was 0.24 L / kg, the end stirring current was 450 A, and the end stirring frequency was 9 Hz.

[0162] (4) The billet is sent to a heating furnace for heating. The preheating temperature of the heating furnace is controlled at 940°C, the temperature of the heating section is controlled at 1190°C, and the temperature of the soaking section is controlled at 1240°C.

[0163] (5) After the billet is heated, high-pressure water is used to remove phosphorus;

[0164] (6) After high-pressure water dephosphorization, high-speed wire rod rolling is performed using rough rolling, intermediate rolling, and finishing rolling mills, wherein the temperature before rough rolling is controlled at 1000° C., and the temperature before finishing rolling is controlled at 900° C.;

[0165] (7) After high-speed wire rolling, the wire is passed through a spinning machine for spinning, and the spinning temperature is 920° C.

[0166] (8) After spinning, an online isothermal salt bath treatment is performed, and the salt bath temperature is 530°C;

[0167] (9) After spinning, the wire rod passes through a cleaning box to clean the salt particles on the surface of the wire rod;

[0168] (10) Finished products that have passed inspection are stacked in an insulated warehouse, waiting for delivery and transportation.

[0169] Comparative Example:

[0170] See also Figure 10 This embodiment provides a Nb microalloyed high carbon wire rod, which includes the following components by mass percentage: C: 0.95%; Si: 1.00%; Mn: 0.65%; Cr: 0.35%; V: 0.038%; P: 0.007%; S: 0.001%, Ti: 0.0050%, and the rest is Fe and unavoidable impurities.

[0171] Wire rod microstructure

[0172] Test Method: 10 mm high metallographic specimens were prepared from the finished wire rods of Examples 1-9 and the comparative example using wire cutting. The specimens were then ground, mechanically polished, and vibratory polished, and then etched with 4% nital. Scanning electron microscopy was used to analyze the interlamellar spacing and pellet size, as shown in Table 1.

[0173] Table 1 Wire rod microstructure measurement results

[0174] Examples Pearlite average pellet size (μm) Pearlite average lamellar spacing (nm) Example 1 2.4 103 Example 2 2.3 85 Example 3 2.2 89 Example 4 2.4 98 Example 5 2.5 94 Example 6 2.1 83 Example 7 2.6 89 Example 8 2.7 104 Example 9 2.6 104 Comparative Example 3.4 110

[0175] As can be seen from Table 1, the wire rod pellets obtained by the production method of the present invention are finer in size. Compared with the comparative example, the wire rod pellets produced by the present invention are 20-38% finer in size and 5-24% finer in interlamellar spacing.

[0176] Mechanical properties of wire rod

[0177] Test method: Use a hydraulic universal testing machine to conduct a tensile test on the finished wire rod, and record the tensile strength, yield strength and cross-sectional shrinkage of the wire rod as shown in Table 2.

[0178] Table 2 Test results of mechanical properties of wire rod

[0179] Examples Tensile strength (MPa) Yield strength (MPa) Sectional shrinkage (%) Example 1 1604 1120 36 Example 2 1647 1150 35 Example 3 1643 1147 37 Example 4 1632 1152 38 Example 5 1624 1148 36 Example 6 1651 1153 35 Example 7 1642 1150 35 Example 8 1610 1143 36 Example 9 1609 1157 37 Comparative Example 1600 1175 30

[0180] As shown in Table 2, the cross-sectional shrinkage of the wire rod obtained by the production method of the present invention can reach 38%, and the tensile strength can reach 1650 MPa. The room temperature tensile stress-strain curve of Example 6 is as follows: Figure 11 shown.

[0181] Inclusion analysis

[0182] Taking Example 6 as an example, the inclusions in Example 6 and the comparative example were counted by an automatic inclusion scanner, and the specific statistical results are shown in Table 3. The distribution of inclusions in Example 6 is as follows: Figure 12 As shown, the inclusion distribution in the comparative example is as follows Figure 13 The addition of Nb element greatly reduces the number of TiCN inclusions in the steel.

[0183] Table 3 Comparison of the number of inclusions in the wire rod produced in Example 6 of the present invention and the wire rod of the comparative example

[0184]

[0185] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A Nb microalloyed high carbon wire rod, characterized in that: In terms of mass percentage, it includes the following ingredients: C: 0.90~1.10%; Si: 1.20~1.60%; Mn: 0.30~0.50%; Cr: 0.40~0.80%; V: 0.02~0.10%; Nb: 0.002~0.009%; P≤0.03%; S≤0.03%, and the rest are Fe and unavoidable impurities.

2. The Nb microalloyed high carbon wire rod according to claim 1, characterized in that In terms of mass percentage, it includes the following components: C: 0.95-1.00%; Si: 1.20-1.50%; Mn: 0.40-0.50%; Cr: 0.40-0.60%; V: 0.02~0.06%; Nb: 0.002~0.009%; P≤0.03%; S≤0.03%, and the rest are Fe and unavoidable impurities.

3. The Nb microalloyed high carbon wire rod according to claim 1 or 2, characterized in that: The tensile strength of the wire rod reaches 1600-1650 MPa, and the cross-sectional shrinkage rate reaches more than 35%.

4. The Nb microalloyed high carbon wire rod according to claim 1 or 2, characterized in that: The diameter of the wire rod is greater than 13 mm.

5. A method for producing Nb microalloyed high carbon wire rod, characterized in that: The production method comprises the following steps in sequence: (1) Smelting the raw materials and adding Nb element during smelting; (2) Refining after smelting; (3) After refining, continuous casting of billets is performed using a continuous casting machine; (4) sending the billet into a heating furnace for heating; (5) After the billet is heated, high-pressure water is used to remove phosphorus; (6) After high-pressure water dephosphorization, high-speed wire rod rolling is performed using roughing, intermediate rolling, and finishing mills; (7) After high-speed wire rolling, it is passed through a spinning machine for spinning; (8) after spinning, an online isothermal salt bath treatment is performed; (9) After spinning, the wire rod passes through a cleaning box to clean the salt particles on the surface of the wire rod; (10) Finished products that have passed inspection are stacked in an insulated warehouse and await delivery and transportation.

6. The method for producing hot-rolled wire rod for ultra-high-strength bridge cables according to claim 5, characterized in that: In step (3), the continuous casting superheat is controlled to be ≤25°C, the casting speed is controlled to be 1.2-1.5m / min, the continuous casting water volume is 0.2-0.25L / kg, the end stirring current is 420-480A, and the end stirring frequency is 7-9Hz.

7. The method for producing hot-rolled wire rod for ultra-high-strength bridge cables according to claim 5, characterized in that: In step (4), the preheating temperature of the heating furnace is controlled at 880°C to 940°C, the temperature of the heating section is controlled at 1120°C to 1200°C, and the temperature of the soaking section is controlled at 1150°C to 1250°C.

8. The method for producing hot-rolled wire rod for ultra-high-strength bridge cables according to claim 5, characterized in that: In step (6), the temperature before rough rolling is controlled at 980°C to 1050°C, and the temperature before finish rolling is controlled at 880°C to 920°C.

9. The method for evaluating center segregation of medium and low carbon steel wire rod according to claim 5, characterized in that: The spinning temperature in step (7) is 890°C to 950°C.

10. The method for evaluating center segregation of medium and low carbon steel wire rod according to claim 5, characterized in that: The salt bath temperature in step (8) is 480-580°C.

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