Heating-free direct rolling method for fastener steel bars and wires

Abstract

The invention belongs to the technical field of fastener rolling, and relates to a fastener steel bar and wire heating-free direct rolling method which comprises the following steps: controlling a casting blank speed parameter; casting blank temperature parameters are controlled; casting blank cooling parameters are controlled; casting blank sectional cooling parameters are controlled; and casting blank tissue parameters are controlled. According to the heating-free direct rolling method for the fastener steel bars and wires, the problems that in the prior art, fastener steel needs to be heated through a heating furnace, energy consumption of uniform rolling is high, and the production cost is high are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of fastener rolling, and in particular to a method for directly rolling fastener steel bars and wires without heating. Background Art

[0002] The steel industry accounts for approximately 15% of total industrial emissions and faces severe challenges, including overcapacity, energy, resource, and environmental issues. Energy conservation, emission reduction, and production cost reduction are urgent. Against this backdrop, the direct rolling process and control technology for bars and wire rods without heating have seen rapid development and application. With this direct rolling process, the ingots are rolled directly after cutting without passing through a heating furnace or requiring additional heating. This eliminates the fuel consumption of the heating furnace and the high-temperature heating losses of the ingots, significantly saving energy and reducing production costs.

[0003] Fasteners, core components of advanced manufacturing, are produced in large quantities and widely used, playing a vital supporting role in the manufacturing industry. Fastener steel is a key specialty steel material used in its production. The "drawing + upsetting" process and product characteristics dictate 100% inspection of raw materials, making it recognized in the industry as having the most demanding surface finish requirements.

[0004] Direct rolling without heating can significantly save energy, but it loses the uniform heating condition of the heating furnace. The head, middle, tail, cross-section and other positions of the continuous casting billet are in an uneven temperature-varying rolling state during the rolling process. The quality of the casting billet at high pulling speed and the product performance of the hot-rolled material fluctuate greatly, and the consistency of organization and performance and surface quality control become problems.

[0005] At present, only construction steel bar products are directly rolled in the industry, while industrial materials, especially fastener steel with high surface requirements, are not directly rolled without heating. Summary of the Invention

[0006] In view of this, the present invention provides a method for directly rolling fastener steel bars and wires without heating.

[0007] Specifically, the present invention is achieved through the following technical solutions:

[0008] According to a first aspect of the present invention, there is provided a method for direct rolling of fastener steel bars and wires without heating, the method comprising the steps of:

[0009] Control the casting speed parameters;

[0010] Control the temperature parameters of the casting billet;

[0011] Control the cooling parameters of the casting;

[0012] Control the segmented cooling parameters of the casting;

[0013] Control the microstructure parameters of the ingot.

[0014] Optionally, controlling the casting speed parameters comprises the steps of:

[0015] The casting speed is controlled to be 2.5-4.5m / min.

[0016] Optionally, controlling the temperature parameters of the casting blank comprises the steps of:

[0017] Control the surface temperature of the ingot to be higher than the critical temperature of complete recrystallization;

[0018] Control the core temperature of the ingot to be lower than the critical temperature of the first brittle zone.

[0019] Optionally, controlling the cooling parameters of the casting blank comprises the steps of:

[0020] Control the cooling water flow of the crystallizer;

[0021] Control the secondary cooling water ratio.

[0022] Optionally, the crystallizer cooling water flow rate is 120-160 m3 / h, and the secondary cooling water volume is 1.2-1.5 L / kg.

[0023] Optionally, controlling the segmented cooling parameters of the casting blank comprises the steps of:

[0024] Control cooling water flow;

[0025] Control cooling water pressure;

[0026] Control the temperature difference between the head and tail of the casting billet.

[0027] Optionally, the cooling water flow rate is 20-100m3 / h.

[0028] Optionally, the cooling water pressure is 0.3-0.6 MPa.

[0029] Optionally, the temperature difference between the head and tail of the casting billet is expressed as: Ttail-Thead≤30°C.

[0030] Optionally, controlling the casting strand structure parameters comprises the steps of:

[0031] Control the normal grain size of medium carbon cold heading steel hot rolled coil or round steel to 20-30μm;

[0032] The percentage of abnormally thick tissue area at the edge or core should be controlled to be less than or equal to 1%.

[0033] The technical solution provided by the present invention brings at least the following beneficial effects:

[0034] The present application provides a method for direct rolling of fastener steel bars and wires without heating, which solves the problems in the prior art of fastener steel requiring heating in a heating furnace, high energy consumption during soaking rolling, and high production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or related technical descriptions. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0037] Figure 1 A schematic flow chart of a method for direct rolling fastener steel bars and wires without heating provided by an embodiment of the present invention;

[0038] Figure 2 This is a temperature control diagram of the low-carbon fastener steel casting process without heating direct rolling provided in an embodiment of the present application;

[0039] Figure 3 This is a simulated diagram of the temperature distribution at the surface, 1 / 4, and core of the low-carbon fastener steel ingot provided in Example 2 of the present application;

[0040] Figure 4 This is the abnormally coarse microstructure diagram of the edge of the 0.45% medium carbon steel direct-rolled bar and wire provided in Comparative Example 1 of this application;

[0041] Figure 5 This is the abnormally coarse microstructure diagram of the core of the 0.45% medium carbon steel direct-rolled bar and wire without heating provided in Comparative Example 1 of this application;

[0042] Figure 6 This is the metallographic structure diagram of the edge of the 0.45% medium carbon steel direct-rolled bar and wire provided in Example 1 of this application;

[0043] Figure 7 This is the metallographic structure diagram of the core of the 0.45% medium carbon steel direct-rolled bar and wire rod provided in Example 1 of the present application;

[0044] Figure 8 This is the metallographic structure diagram of the edge of the 0.20% low carbon steel direct rolled bar or wire rod provided in Application Example 3. DETAILED DESCRIPTION

[0045] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0046] Figure 1 The present invention schematically illustrates a flow chart of a method for direct rolling of fastener steel bars and wires without heating, which is applicable to an embodiment of the present invention.

[0047] See also Figure 1 The embodiment of the present invention provides a method for direct rolling of fastener steel bars and wires without heating, the method comprising the steps of:

[0048] S1: Control the casting speed parameters;

[0049] Exemplarily, the controlling of the casting speed parameters comprises the steps of:

[0050] The casting speed is controlled to be 2.5-4.5m / min.

[0051] In the embodiment of the present application, during the direct rolling of medium and low carbon fastener steel, the continuous casting billet pulling speed is 2.5-4.5m / min, and the billet starting rolling temperature is in the range of 970℃-1080℃. During the direct rolling of medium and low carbon fastener steel, the continuous casting billet pulling speed is 2.5-4.5m / min, and the billet starting rolling temperature is in the range of 970℃-1080℃. The advantage of this operation is that it can effectively improve production efficiency, reduce oxidation and decarburization of the billet at high temperature, and at the same time ensure the uniformity of the internal structure of the billet, providing a good foundation for the subsequent rolling process, thereby improving the quality and performance of the final product.

[0052] S2: Control the temperature parameters of the casting billet;

[0053] Exemplarily, controlling the temperature parameters of the casting strand comprises the steps of:

[0054] Control the surface temperature of the ingot to be higher than the critical temperature of complete recrystallization;

[0055] Control the core temperature of the ingot to be lower than the critical temperature of the first brittle zone.

[0056] In the embodiment of the present application, the higher the continuous casting billet pulling speed, the higher the billet temperature, but the billet defects such as depressions and cracks on the billet surface and shrinkage cavities and porosity in the core will be greatly increased. On the premise that the billet quality is good, the billet pulling speed matches the steel grade characteristics and rolling temperature, and the surface temperature is controlled to be greater than the critical temperature of complete recrystallization, and the core temperature is less than the critical temperature of the first brittle zone. In the embodiment of the present application, the higher the continuous casting billet pulling speed, the higher the billet temperature, but the billet defects such as depressions and cracks on the billet surface and shrinkage cavities and porosity in the core will be greatly increased. On the premise that the billet quality is good, the billet pulling speed matches the steel grade characteristics and rolling temperature, and the surface temperature is controlled to be greater than the critical temperature of complete recrystallization, and the core temperature is less than the critical temperature of the first brittle zone. The advantage of such operation is that it can ensure that the billet has good plasticity and toughness in the subsequent rolling process, avoid defects such as cracks and fractures caused by improper temperature, and improve the yield rate and product quality of the billet.

[0057] S3: Control the cooling parameters of the casting;

[0058] Exemplarily, controlling the cooling parameters of the casting strand comprises the steps of:

[0059] Control the cooling water flow of the crystallizer;

[0060] Control the secondary cooling water ratio.

[0061] In the embodiment of the present application, the temperature of the molten steel in the tundish is controlled at an overheat of 10 to 35°C, and the cooling water flow rate of the crystallizer and the water ratio of the secondary cooling are controlled. The parameter range of the electromagnetic stirring technology of the crystallizer is: frequency 3 to 6 Hz, current 200 to 400A. The surface, subcutaneous and middle cracks of the ingot are controlled to be 0, and the central porosity defect is less than level 1. In the embodiment of the present application, the temperature of the molten steel in the tundish is controlled to be an overheat of 10 to 35°C, and the cooling water flow rate of the crystallizer and the water ratio of the secondary cooling are controlled. The parameter range of the electromagnetic stirring technology of the crystallizer is: frequency 3 to 6 Hz, current 200 to 400A. The surface, subcutaneous and middle cracks of the ingot are controlled to be 0, and the central porosity defect is less than level 1. The advantage of such operation is that it can effectively improve the internal structure of the ingot, reduce the occurrence of defects, improve the quality and surface finish of the ingot, thereby creating favorable conditions for the subsequent rolling process, reducing the subsequent processing cost, and improving the performance and reliability of the final product.

[0062] Exemplarily, the crystallizer cooling water flow rate is 120-160 m3 / h, and the secondary cooling water volume is 1.2-1.5 L / kg.

[0063] In the embodiments of this application,

[0064] S4: Control the segmented cooling parameters of the slab;

[0065] Exemplarily, the controlling of the segmented cooling parameters of the casting strand comprises the steps of:

[0066] Control cooling water flow;

[0067] Control cooling water pressure;

[0068] Control the temperature difference between the head and tail of the casting billet.

[0069] In an embodiment of the present application, when a step-type segmented cooling process for the billet is adopted, the cooling water flow rate, cooling water pressure and temperature difference between the head and tail of the billet are controlled. In an embodiment of the present application, when a step-type segmented cooling process for the billet is adopted, the cooling water flow rate, cooling water pressure and temperature difference between the head and tail of the billet are controlled. The advantage of such operation is that the temperature difference between the head and tail of the billet and different positions of the cross section can be effectively controlled, and problems such as abnormal grain growth caused by uneven temperature can be avoided, and the billet can be ensured to have uniform structure and performance in the subsequent rolling process, thereby improving the dimensional accuracy and quality stability of the product and reducing the scrap rate. Exemplarily, the cooling water flow rate is 20-100m3 / h.

[0070] Exemplarily, the cooling water pressure is 0.3-0.6 MPa.

[0071] Exemplarily, the temperature difference between the head and tail of the ingot is expressed as: Ttail-Thead≤30°C.

[0072] In the embodiment of the present application, after adopting the direct rolling process without heating, the temperature of the head of the billet entering the rolling mill is lower than the temperature of the tail by more than 80-90°C, or even more than 100°C, resulting in large differences in recrystallization during the rolling process of the same billet. The head will be in the uncrystallized area and the tail will be in the fully recrystallized area, resulting in abnormally coarse grains in the cross section, more than 50-60μm, or even more than 100μm. After the billet is cut, cooling water is used to step-type cooling at different positions of the billet to control the temperature difference between the head and tail of the billet to within 30°C, so as to solve the grain abnormality caused by the temperature difference between the head and tail of the billet and different positions of the cross section.

[0073] S5: Control the microstructure parameters of the ingot.

[0074] Exemplarily, the controlling of the casting strand structure parameters comprises the steps of:

[0075] Control the normal grain size of medium carbon cold heading steel hot rolled coil or round steel to 20-30μm;

[0076] The percentage of abnormally thick tissue area at the edge or core should be controlled to be less than or equal to 1%.

[0077] In the embodiment of the present application, the normal grain size of the hot-rolled coil or round steel of medium carbon cold heading steel is controlled to be 20-30μm, and the area percentage of abnormal coarse tissue at the edge or core is controlled to be less than or equal to 1%. In the embodiment of the present application, the advantage of controlling the normal grain size of the hot-rolled coil or round steel of medium carbon cold heading steel to be 20-30μm and the area percentage of abnormal coarse tissue at the edge or core is that it can ensure that the mechanical properties and processing performance of the product reach a high level. Smaller grain size can improve the strength and toughness of the material, while reducing the occurrence of abnormal coarse tissue can avoid the decline of local performance, so that the product has better plasticity and uniformity in subsequent cold heading, cold drawing and other processing processes, reduce the risk of cracking during processing, and improve the service life and reliability of the product.

[0078] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be understood as a hard limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numbers within the range. For example, the description of a range from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which applies regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0079] The manufacturing process of the fastener steel bar and wire of the patented invention is as follows: the molten iron undergoes pretreatment, converter or electric furnace smelting, refining, continuous casting and direct rolling without heating to obtain the fastener steel. The detailed parameters such as the chemical composition of the fastener steel, the matching of continuous casting and rolling processes, the quality of the ingot and the cross-sectional structure control of the bar and wire are shown in Table 1.

[0080] Table 1 Main chemical composition (wt%) of low carbon fastener steel and its continuous casting process, ingot quality, rolling process and structure

[0081]

[0082] From Table 1 we can see that:

[0083] 1. Demonstrating the synergistic effect of chemical composition and casting speed

[0084] Medium and low carbon steel (C≤0.35%)

[0085] Example 1-4 (C = 0.15-0.23%): The pulling speed is controlled at 3.5-4.5 m / min, and a higher rolling temperature (1080-1120°C) is used to achieve zero surface cracks, subcutaneous cracks, and middle cracks in the ingot, and center porosity <0.5.

[0086] Comparative Example 1-2 (C = 0.15-0.20%): The pulling speed was reduced to 2.8-3.0 m / min and the rolling temperature was insufficient (960-980° C.), resulting in cracks and central porosity (grade 2-2.5), and the proportion of coarse tissue was as high as 5-6%.

[0087] Medium and high carbon steel (C ≥ 0.35%) and alloy steel

[0088] Example 5-8 (C = 0.35-0.40%, containing Cr / Mo): pulling speed 3.0-3.2 m / min, starting rolling temperature 1030-1050°C, coarse structure ratio only 0.15-0.35%. The addition of Cr / Mo refines the grains.

[0089] Comparative Examples 3-5 (C = 0.35-0.45%): The pulling speed was too low (2.5-2.8 m / min) and the starting rolling temperature was insufficient (930-950° C.), resulting in grain coarsening (coarse structure 4.2-8.5%) and severe cracks (level 2-3.5).

[0090] 2. Prove the correlation between casting speed and slab defects

[0091] Optimization effect of high pulling speed (≥3.5m / min)

[0092] Example 1-4: When the pulling speed is 4.5-3.5 m / min, the surface / subcutaneous / middle cracks are all 0, and the center porosity is less than 0.5 level.

[0093] Negative effects of low pulling speed (≤3.0m / min)

[0094] Comparative Examples 1-5: At a pulling speed of 2.5-3.0 m / min, cracks and center porosity increased significantly. For example, in Comparative Example 5 (pulling speed 2.8 m / min), the head-to-tail temperature difference reached 80°C, and the coarse structure ratio was 8.5%, much higher than in the examples (≤1%).

[0095] 3. Demonstrating the key role of temperature parameters on tissue homogeneity

[0096] Rolling temperature and grain refinement

[0097] Example: The starting rolling temperature is 950-1120°C, combined with segmented cooling (temperature difference between the head and tail is ≤30°C), and the proportion of coarse structure is ≤1%.

[0098] Head and tail temperature difference control

[0099] Example: The temperature difference between the head and tail is ≤30°C (such as the temperature difference of 25°C in Example 1) to avoid abnormal coarsening of grains.

[0100] Comparative Example: The temperature difference between the head and tail is ≥60°C (such as the temperature difference of 80°C in Comparative Example 5), which causes local grains to reach 50-100μm and is prone to cracking during cold heading.

[0101] 4. Prove the strengthening effect of alloying elements (Cr / Mo)

[0102] Example 5-8 (containing Cr / Mo):

[0103] The proportion of coarse structure is only 0.15-0.35%, which is better than similar carbon steel (such as the coarse proportion of 0.8-1.0% in Examples 9-10).

[0104] Comparative Example 3 (containing Cr / Mo but improper process): drawing speed 2.6 m / min, starting rolling temperature 940°C, coarse structure ratio 4.2%, indicating that alloying elements need to be combined with reasonable process to achieve their advantages.

[0105] 5. Prove economic benefits and process stability

[0106] Comprehensive benefits of the implementation examples

[0107] Energy saving: heating-free process reduces carbon emissions.

[0108] Quality: The defect rate approaches 0, meeting the high surface quality requirements of cold heading steel.

[0109] Comparative cost loss

[0110] High defect rates require additional annealing or scrapping, increasing costs by 20%-30%.

[0111] In summary, the embodiments of the present invention provide a method for direct rolling of fastener steel bars and wires without heating, which is significantly innovative in terms of process parameter optimization, temperature control strategy, and microstructure uniformity regulation:

[0112] 1. Collaborative Optimization of Process Parameters and Improvement of Energy Efficiency

[0113] Direct rolling without heating and matching the casting speed: The continuous casting speed is controlled at 2.5-4.5m / min (S1), combined with a starting rolling temperature of 970-1080°C. By dynamically adjusting the casting speed and temperature, the energy consumption caused by the heating furnace in traditional processes is reduced (saving fuel by over 90%). This method directly utilizes the waste heat of the casting, achieving complete heating-free operation and reducing equipment investment by over 30%.

[0114] Fine control of billet cooling parameters: mold cooling water flow (120-160m 3Optimizing cooling parameters (1.2-1.5 L / kg / h) and secondary cooling water volume (S3), combined with electromagnetic stirring (3-6 Hz, 200-400 A), eliminates cracks and center porosity in the slab (defect level < 1) and improves rolling stability. This method further enhances slab homogenization by synergizing cooling parameters with electromagnetic stirring.

[0115] 2. Temperature gradient control and tissue uniformity assurance

[0116] Differentiated temperature control between the surface and core: The surface temperature is controlled above the critical temperature for complete recrystallization (to promote dynamic recrystallization) and the core temperature is controlled below the critical temperature of the first brittle zone (to prevent shrinkage and cracking) (S2). This strategy avoids core defects caused by excessively high casting speeds (>4.5m / min) while also reducing the risk of grain coarsening. This method achieves precise temperature control by matching the steel grade's characteristics with a thermodynamic model.

[0117] Segmented cooling and head-to-tail temperature difference control: Adopt stepped segmented cooling (S4), cooling water flow rate 20-100m 3 / h and a pressure of 0.3-0.6MPa, limiting the temperature difference between the head and tail to ≤30°C, solving the problem of non-recrystallized head grains and overheating at the tail in the heating-free process. This method reduces the grain size fluctuation range from ±15μm in the traditional process to ±5μm through staged cooling.

[0118] 3. Organizational Performance Control and Quality Consistency Enhancement

[0119] Grain size and abnormal microstructure control: The hot-rolled grain size is controlled to 20-30μm (S5), with abnormal coarse microstructure at the edge / core ≤1%. By synergizing rolling force and speed, the strength-ductility match of cold-headed steel is improved (tensile strength ≥ 600MPa, elongation ≥ 15%). This method further refines the grain size by controlling microstructure parameters, reducing subsequent processing defects.

[0120] Dynamic recrystallization and defect suppression: The synergy between the start rolling temperature (970-1080°C) and the rolling speed, combined with the secondary cooling process, promotes complete dynamic recrystallization and inhibits the precipitation of brittle phases at grain boundaries (such as carbide segregation). Traditional high-speed wire rolling typically starts at 850-900°C. This method achieves full softening of medium-carbon steel in a higher temperature range, reducing rolling forces by over 20%.

[0121] 4. Economic and Environmental Benefits

[0122] Energy saving and consumption reduction: The completely heating-free process reduces CO2 emissions by approximately 1.2 tons per ton of steel (compared to the traditional heating furnace process), while shortening the production process (reducing the heating furnace section) and increasing production capacity by 15-20%.

[0123] Cost optimization: Equipment modification costs are reduced (no tunnel furnace or supplementary heating device is required), and operation and maintenance costs are reduced by 25%.

[0124] The present application provides a method for direct rolling of fastener steel bars and wires without heating, which solves the problems in the prior art of fastener steel requiring heating in a heating furnace, high energy consumption during soaking rolling, and high production costs.

[0125] It should be understood that the above-described specific embodiments of the present invention are merely illustrative or illustrative of the principles of the present invention and do not constitute limitations of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made without departing from the spirit and scope of the present invention should be included within the scope of protection of the present invention. In addition, the appended claims are intended to cover all variations and modifications that fall within the scope and metes and bounds of the appended claims, or equivalents thereof.

[0126] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or device comprising the element.

[0127] The foregoing description is intended only to provide specific embodiments of the present invention, which will enable those skilled in the art to understand and implement the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not intended to be limited to the embodiments shown herein, but is intended to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for direct rolling of fastener steel bars and wires without heating, characterized in that: The method comprises the steps of: Control the casting speed parameters; Control the temperature parameters of the casting billet; Control the cooling parameters of the casting; Control the segmented cooling parameters of the casting; Control the microstructure parameters of the ingot.

2. The method for directly rolling fastener steel bars and wires without heating according to claim 1, characterized in that: The control of the casting speed parameters comprises the steps of: The casting speed is controlled to be 2.5-4.5m / min.

3. The method for directly rolling fastener steel bars and wires without heating according to claim 1, characterized in that: The control of the temperature parameters of the casting blank comprises the steps of: Control the surface temperature of the ingot to be higher than the critical temperature of complete recrystallization; Control the core temperature of the ingot to be lower than the critical temperature of the first brittle zone.

4. The method for directly rolling fastener steel bars and wires without heating according to claim 1, characterized in that: The control of the cooling parameters of the casting blank comprises the steps of: Control the cooling water flow of the crystallizer; Control the secondary cooling water ratio.

5. The method for directly rolling fastener steel bars and wires without heating according to claim 4, characterized in that: The crystallizer cooling water flow rate is 120-160 m3 / h, and the secondary cooling water volume is 1.2-1.5 L / kg.

6. The method for directly rolling fastener steel bars and wires without heating according to claim 1, characterized in that: The control of the segmented cooling parameters of the casting blank comprises the following steps: Control cooling water flow; Control cooling water pressure; Control the temperature difference between the head and tail of the casting billet.

7. The method for directly rolling fastener steel bars and wires without heating according to claim 6, characterized in that: The cooling water flow rate is 20-100m3 / h.

8. The method for directly rolling fastener steel bars and wires without heating according to claim 6, characterized in that: The cooling water pressure is 0.3-0.6 MPa.

9. The method for directly rolling fastener steel bars and wires without heating according to claim 6, characterized in that: The expression for the temperature difference between the head and tail of the casting billet is: Ttail-Thead≤30°C.

10. The method for directly rolling fastener steel bars and wires without heating according to claim 1, characterized in that: The control of the casting strand structure parameters comprises the following steps: Control the normal grain size of medium carbon cold heading steel hot rolled coil or round steel to 20-30μm; The percentage of abnormally thick tissue area at the edge or core should be controlled to be less than or equal to 1%.

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