A medium-low carbon high-phosphorus weather-resistant cold heading steel satisfying cold heading large deformation and a preparation method thereof

Abstract

The application provides a kind of low carbon high phosphorus weathering cold upsetting steel satisfying cold upsetting large deformation and preparation method, belongs to steel preparation field.The chemical composition of the cold upsetting steel includes:C:0.15%~0.25%, Si:0.20%~0.30%, Mn:0.30%~0.40%, Cu:0.20%~0.60%, P:0.08%~0.14%, S≤0.01%, Ni:0.10%~0.15%, Cr:0.20%~0.50%, Al T :0.025%~0.06%; wherein, C and P satisfy the following relationship: [P]*[C]≤0.035.Rationally design the chemical composition of cold upsetting steel, inhibit pitting by proper high phosphorus content and Cu, Ni element cooperation, form passivation film, satisfy the corrosion performance of the atmospheric environment characteristics of strong radiation, high SO2 concentration.At the same time, control C and P satisfy the relationship, avoid the problem of phosphorus segregation, grain boundary embrittlement, so as to satisfy the requirement of cold upsetting one-time forming limit quantity>80%.

Description

Technical Field

[0001] This application relates to the field of steel preparation technology, and in particular to a medium-low carbon high-phosphorus weather-resistant cold heading steel that meets the requirements of large deformation in cold heading and its preparation method. Background Technology

[0002] The paint-free application of atmospheric corrosion-resistant steel solves the problems of environmental pollution and high cost associated with painting, electroplating, or hot-dip galvanizing, and is therefore widely used in steel structures such as bridges, power transmission lines, photovoltaic systems, and stadiums. Fasteners play a crucial role in securing connections, and the load-bearing safety of bolted joints is of paramount importance.

[0003] In existing technologies, weathering cold heading steel uses a Cr-Ni-Cu composition, where Cr, Cu, and Ni are expensive, leading to high costs. Phosphorus, on the other hand, is inexpensive and exhibits excellent corrosion resistance in rural and industrial atmospheres. However, phosphorus is a harmful element in steel, causing problems such as dendrite segregation in cast billets, phosphorus segregation bands and grain boundary segregation in rolled products, cold brittleness, and poor cold deformation capacity. Currently, industrially used phosphorus-containing and high-phosphorus steels have a carbon content of ≤0.08% and a phosphorus content of ≤0.1%, primarily used in container plates. Fastener products, due to high strength requirements, must have a carbon content greater than 0.15%, and the processing must meet the "drawing + cold heading" forming process, with a primary deformation of 80-90% or more. Utilizing low-cost, high-corrosion-resistant, high-phosphorus weathering steel remains a challenge for the industry. Summary of the Invention

[0004] This application provides a medium-low carbon high phosphorus weather-resistant cold heading steel that meets the requirements of large deformation during cold heading and its preparation method, in order to solve the following technical problem: how to meet the requirement that the cold heading one-time forming limit of medium-low carbon high phosphorus weather-resistant cold heading steel is >80%.

[0005] In one aspect, this application provides a medium-low carbon, high-phosphorus weather-resistant cold heading steel that meets the requirements for large deformation in cold heading. The chemical composition of the cold heading steel, by mass fraction, includes: C: 0.15%–0.25%, Si: 0.20%–0.30%, Mn: 0.30%–0.40%, Cu: 0.20%–0.60%, P: 0.08%–0.14%, S≤0.01%, Ni: 0.10%–0.15%, Cr: 0.20%–0.50%, Al… T 0.025%–0.06%; balance being Fe and unavoidable impurities; wherein, C and P satisfy the following relationship:

[0006] [P]*[C]≤0.035

[0007] In the formula, [P] represents the value preceding the percentage of P content, and [C] represents the value preceding the percentage of C content.

[0008] Optionally, C and P satisfy the following relationship:

[0009] 0.02≤[P]*[C]≤0.035

[0010] In the formula, [P] represents the value preceding the percentage of P content, and [C] represents the value preceding the percentage of C content.

[0011] Optionally, Ni and P satisfy the following relationship:

[0012] 0.5 ≤ [Ni] / [P] ≤ 1.5

[0013] In the formula, [Ni] represents the content of Ni, and [P] represents the content of P.

[0014] Optionally, the diameter of the cold heading steel The thickness ranges from 6.5mm to 16mm.

[0015] Optionally, the phosphorus segregation index of the cold heading steel is ≤1.25, wherein the segregation index = enriched element content / average element content in the steel.

[0016] Optionally, the cold heading steel meets at least one of the following properties: tensile strength of 520 MPa to 550 MPa, Z% ≥ 70%, allowable deformation ≥ 80%, and long-term corrosion rate ≤ 0.8 g / (m²) in high SO₂ concentration atmospheric environments. 2 ·h).

[0017] Secondly, this application provides a method for preparing cold heading steel according to any embodiment of the first aspect, the method comprising:

[0018] Molten steel with the aforementioned chemical composition is continuously cast, and the crystallizer water flow rate and secondary cooling dynamic water distribution mode of the continuous casting are optimized to obtain a cast billet; the continuous casting adopts an end electromagnetic stirring process.

[0019] The cast billet is heated and rolled into high-speed wire rod to obtain cold heading steel.

[0020] Optionally, the core / edge phosphorus segregation index ratio of the billet is ≤2, and the core phosphorus segregation index of the billet is ≤2.5, wherein the segregation index = enriched element content / average element content in steel.

[0021] Optionally, before continuously casting the molten steel having the aforementioned chemical composition, the method further includes:

[0022] Molten iron is subjected to RH vacuum degassing treatment to obtain a billet with a set chemical composition; the pure degassing time of the RH vacuum degassing treatment is ≥15min.

[0023] Thirdly, this application provides a fastener prepared by cold heading of cold heading steel as described in any embodiment of the first aspect and cold heading steel prepared by the method described in any embodiment of the second aspect.

[0024] The technical solutions provided in this application have the following advantages compared with the prior art:

[0025] This application provides a medium-low carbon, high-phosphorus weather-resistant cold heading steel that meets the requirements for large deformation in cold heading. The chemical composition of the cold heading steel, by mass fraction, includes: C: 0.15%–0.25%, Si: 0.20%–0.30%, Mn: 0.30%–0.40%, Cu: 0.20%–0.60%, P: 0.08%–0.14%, S≤0.01%, Ni: 0.10%–0.15%, Cr: 0.20%–0.50%, Al… T The content of phosphorus in cold heading steel is 0.025%–0.06%, with the balance being Fe and unavoidable impurities. The relationship between C and P is as follows: [P]*[C]≤0.035, where [P] represents the percentage of P content, and [C] represents the percentage of C content. A reasonable chemical composition of cold heading steel is designed, using an appropriate high phosphorus content in combination with Cu and Ni elements to suppress pitting corrosion and form a passivation film to hinder SO2 penetration from the atmosphere, thus meeting the corrosion performance requirements of atmospheric environments characterized by strong radiation and high SO2 concentration. Simultaneously, controlling the relationship between C and P avoids phosphorus segregation and grain boundary embrittlement, thereby meeting the requirement that the limit amount of phosphorus in a single cold heading process is >80%. Attached Figure Description

[0026] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0027] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 A schematic flowchart illustrating a method for preparing cold heading steel provided in this application embodiment;

[0029] Figure 2 This is a low-magnification photograph of the cross-section of the cast billet provided in Embodiment 2 of this application;

[0030] Figure 3 This is an electron probe phosphorus distribution map of the core of the cast billet provided in Embodiment 1 of this application;

[0031] Figure 4 This is an electron probe microanalysis diagram of phosphorus distribution in the core of cold-heading steel provided in Embodiment 2 of this application;

[0032] Figure 5 Metallographic diagram of the cold heading steel hot-rolled wire rod provided in Embodiment 2 of this application;

[0033] Figure 6 This is a longitudinal cross-sectional view of a fastener manufactured by cold heading according to Embodiment 2 of this application. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0035] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has 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., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0036] Furthermore, in the description of this application, the terms "comprising," "including," etc., mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" or "at least one of a, b, and c" can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be a single or multiple.

[0037] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0038] This application provides a medium-low carbon, high-phosphorus weather-resistant cold heading steel that meets the requirements for large deformation in cold heading. The chemical composition of the cold heading steel, by mass fraction, includes: C: 0.15%–0.25%, Si: 0.20%–0.30%, Mn: 0.30%–0.40%, Cu: 0.20%–0.60%, P: 0.08%–0.14%, S≤0.01%, Ni: 0.10%–0.15%, Cr: 0.20%–0.50%, Al… T 0.025%–0.06%; balance being Fe and unavoidable impurities; wherein, C and P satisfy the following relationship:

[0039] [P]*[C]≤0.035

[0040] In the formula, [P] represents the value preceding the percentage of P content, and [C] represents the value preceding the percentage of C content.

[0041] The control principle in the chemical composition design of this invention is as follows:

[0042] C: To meet the requirements of achieving a primary deformation of 85%–90% or more during cold heading and high strength of fasteners, the carbon content is controlled between 0.15% and 0.25%. A carbon content below 0.15% will result in low strength of the manufactured fasteners; however, increasing the carbon content will lead to a decrease in cold heading deformation capacity. Therefore, the carbon content is controlled below 0.25%. For example, the carbon content is 0.15%, 0.17%, 0.19%, 0.20%, 0.22%, 0.25%, etc.

[0043] Si: A commonly used deoxidizing element in steel. Solid solution strengthening of Si increases the work hardening rate of steel, but can significantly worsen the cold working properties of steel. At the same time, it promotes the segregation of P and S at grain boundaries. Its content should be controlled to not exceed 0.30%. For example, the Si content is 0.20%, 0.22%, 0.24%, 0.26%, 0.28%, 0.30%, etc.

[0044] Mn: A commonly used deoxidizing element in steel, it can improve the hardenability of steel. However, continuous casting carries the risk of center segregation and a strong tendency for grain boundary agglomeration during tempering, promoting temper brittleness. Therefore, the Mn content should be controlled between 0.30% and 0.40%. For example, the Mn content can be 0.30%, 0.32%, 0.34%, 0.36%, 0.38%, 0.40%, etc.

[0045] Phosphorus (P) tends to form central and micro-segregation during the solidification of molten steel, easily leading to billet cracks and phosphorus agglomeration at grain boundaries. Grain boundary embrittlement reduces cold heading ability. Simultaneously, P segregation significantly reduces atmospheric corrosion resistance. Considering the strength level required for fastener manufacturing, the carbon content is between 0.15% and 0.25%, therefore, the P content should be controlled between 0.08% and 0.14%. If the P content exceeds 0.14%, phosphorus segregation and grain boundary embrittlement will prevent cold heading from meeting the requirement of a single-piece forming limit greater than 80%. If the phosphorus content is less than 0.08%, the amount of corrosion-resistant elements Ni and Cr required to replace them increases. Therefore, controlling the P content between 0.08% and 0.14% allows for the maximum use of inexpensive P to replace expensive Ni, Cr, and Cu, achieving a low-cost, highly atmospheric corrosion-resistant new material. For example, the content of P is 0.08%, 0.09%, 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, etc.

[0046] Sulfur (S) reacts with manganese (Mn) in steel to form MnS inclusions and segregates at grain boundaries, causing hot brittleness and deteriorating the steel's machinability. Reducing the sulfur content in steel can improve its deformation properties, reduce non-metallic inclusions, and improve its machinability and toughness. Sulfur content should be controlled below 0.01%. For example, the sulfur content can be 0.002%, 0.004%, 0.006%, 0.008%, 0.01%, etc.

[0047] Cu, Ni, and Cr can significantly improve the weather resistance and acid resistance of steel. When the carbon content is 0.15%–0.25% and the limit amount of single cold heading deformation is greater than 80%, atmospheric corrosion resistance can be improved by combining Cu, Ni, and Cr with a phosphorus content of 0.08%–0.14%. For example, the Cu content is 0.20%, 0.30%, 0.40%, 0.50%, 0.60%, etc.; the Ni content is 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, etc.; and the Cr content is 0.20%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, etc.

[0048] In some implementations, C and P satisfy the following relationship:

[0049] 0.02≤[P]*[C]≤0.035

[0050] In the formula, [P] represents the value preceding the percentage of P content, and [C] represents the value preceding the percentage of C content.

[0051] In some implementations, Ni and P satisfy the following relationship:

[0052] 0.5 ≤ [Ni] / [P] ≤ 1.5

[0053] In the formula, [Ni] represents the content of Ni, and [P] represents the content of P.

[0054] Through extensive comparison of elemental matching relationships using laboratory cyclic immersion corrosion results and verification using actual service environment corrosion results, the study found that Ni, C, and P elements require appropriate composite addition in suitable proportions, with the following content requirements: 0.02 ≤ [P]*[C] ≤ 0.035, 0.5 ≤ [Ni] / [P] ≤ 1.5. When [P]*[C] is greater than 0.035, the probability of cold heading cracking increases significantly, failing to meet the requirement of a single-step cold heading limit of over 80%. When [P]*[C] is less than 0.035, the content of high-priced corrosion-resistant elements, such as phosphorus, is low, increasing the manufacturing cost of the steel. When [Ni] / [P] is greater than 1.5, corrosion resistance can achieve a low corrosion rate, but this significantly increases the manufacturing cost of the steel. When [Ni] / [P] is less than 0.5, the number of manufacturing defects and cracks in the material increases significantly, making subsequent deep processing impossible. For example, the value of [P]*[C] can be 0.02, 0.022, 0.025, 0.028, 0.03, 0.032, 0.035, etc.; the value of [Ni] / [P] can be 0.5, 0.7, 0.9, 1.0, 1.2, 1.4, 1.5, etc.

[0055] In some embodiments, the diameter of the cold heading steel The diameter ranges from 6.5mm to 16mm. For example, the diameter of cold-heading steel... It can be 6.5mm, 7mm, 9mm, 10mm, 12mm, 14mm, 16mm, etc.

[0056] In some embodiments, the phosphorus segregation index of the cold heading steel is ≤1.25, where segregation index = enriched element content / average element content in the steel. For example, the phosphorus segregation index of the cold heading steel can be 1.10, 1.15, 1.18, 1.20, 1.22, 1.25, etc.

[0057] In some embodiments, the cold heading steel satisfies at least one of the following properties: tensile strength of 520 MPa to 550 MPa, Z% ≥ 70%, allowable deformation ≥ 80%, and long-term corrosion rate ≤ 0.8 g / (m²) in high SO₂ concentration atmospheric environments. 2 ·h). Z represents the range of tensile forces that cold heading steel can withstand in the thickness direction.

[0058] This application rationally designs the chemical composition of cold heading steel, using an appropriate high phosphorus content in combination with Cu and Ni elements to suppress pitting corrosion and form a passivation film to hinder SO2 penetration from the atmospheric environment, thus meeting the corrosion performance requirements of atmospheric environments characterized by strong radiation and high SO2 concentration. Simultaneously, it avoids problems such as phosphorus segregation and grain boundary embrittlement, thereby meeting the requirement that the limit amount of phosphorus in a single cold heading process is greater than 80%.

[0059] Please see Figure 1 This application provides a method for preparing cold heading steel according to any embodiment of the first aspect, the method comprising:

[0060] S1. The molten steel with the aforementioned chemical composition is continuously cast, and the crystallizer water flow rate and the dynamic water distribution mode of the secondary cooling system are optimized to obtain a cast billet; the continuous casting adopts an end electromagnetic stirring process.

[0061] In some embodiments, the core / edge phosphorus segregation index ratio of the billet is ≤2, and the core phosphorus segregation index of the billet is ≤2.5, wherein the segregation index = enriched element content / average element content in steel.

[0062] By optimizing the water flow rate in the continuous casting crystallizer, the dynamic water distribution mode in the secondary cooling system, and the end-stage electromagnetic stirring process, the uniformity of phosphorus segregation distribution across the billet cross-section can be controlled. For example, the core / edge phosphorus segregation index ratio of the billet can be 1.45, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, etc., and the core phosphorus segregation index of the billet can be 2.1, 2.15, 2.2, 2.25, 2.3, 2.4, 2.5, etc.

[0063] In some embodiments, the method further includes, prior to continuous casting of molten steel having the said chemical composition:

[0064] Molten iron is subjected to RH vacuum degassing treatment to obtain a billet with a set chemical composition; the pure degassing time of the RH vacuum degassing treatment is ≥15min.

[0065] During RH vacuum degassing, the pure degassing time is ≥15 min to ensure that the [H] content meets the requirements after vacuum treatment. For example, the pure degassing time can be 15 min, 16 min, 17 min, 18 min, 19 min, 20 min, etc.

[0066] In some embodiments, the billet continuous casting includes: controlling the target temperature of the molten steel at 10-40°C above the liquidus temperature, and the thickness of the billet is 150mm or 200mm.

[0067] S2. The billet is heated and rolled into high-speed wire to obtain cold heading steel.

[0068] The product prepared by the method of preparing cold heading steel is the aforementioned cold heading steel. The chemical composition and microstructure of the cold heading steel prepared by the method of preparing cold heading steel can be referred to the above embodiments. Since the method of preparing cold heading steel adopts some or all of the technical solutions of the cold heading steel embodiments, it has at least all the beneficial effects brought about by the technical solutions of the cold heading steel embodiments, which will not be elaborated here.

[0069] This application provides a fastener prepared by cold heading steel.

[0070] The raw material of the fastener is the aforementioned cold heading steel, which is prepared based on the aforementioned method. Since the raw material cold heading steel of the fastener adopts some or all of the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the cold heading steel embodiments, which will not be elaborated here.

[0071] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to industry standards. If there is no corresponding industry standard, then common international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0072] The molten iron is pretreated, smelted in a converter or electric furnace, refined, and continuously cast to obtain the chemical composition of cold heading steel, as shown in Table 1.

[0073] Table 1. Chemical composition (wt%) of cold heading steel, balance being Fe and unavoidable impurities.

[0074] Group C Si Mn P S Cr Ni Cu [C]*[P] [Ni] / [P] Example 1 0.15 0.20 0.35 0.140 0.008 0.45 0.10 0.35 0.0210 0.7 Example 2 0.25 0.25 0.40 0.140 0.005 0.50 0.15 0.60 0.0350 1.1 Example 3 0.17 0.27 0.32 0.120 0.004 0.48 0.11 0.22 0.0204 0.9 Example 4 0.18 0.30 0.38 0.130 0.006 0.48 0.10 0.45 0.0234 0.8 Example 5 0.24 0.21 0.34 0.100 0.007 0.30 0.12 0.35 0.0238 1.2 Example 6 0.23 0.23 0.35 0.090 0.006 0.25 0.12 0.40 0.0207 1.3 Example 7 0.25 0.28 0.34 0.080 0.006 0.50 0.10 0.25 0.0200 1.3 Example 8 0.18 0.29 0.32 0.120 0.008 0.30 0.10 0.20 0.0216 0.8 Example 9 0.19 0.22 0.34 0.135 0.007 0.28 0.12 0.45 0.0257 0.9 Example 10 0.21 0.20 0.32 0.125 0.009 0.32 0.13 0.40 0.0263 1.0 Comparative Example 1 0.15 0.30 0.40 0.015 0.007 0.35 0.25 0.3 0.0023 16.7 Comparative Example 2 0.20 0.30 0.45 0.025 0.008 0.55 0.40 0.25 0.0050 16.0 Comparative Example 3 0.18 0.30 0.50 0.010 0.004 0.40 0.35 0.35 0.0018 35.0

[0075] Based on the chemical composition of cold heading steel in the embodiments and comparative examples, this embodiment also provides a method for preparing cold heading steel, including the following steps:

[0076] S1. The molten steel with the aforementioned chemical composition is continuously cast, and the crystallizer water flow rate and the dynamic water distribution mode of the secondary cooling system are optimized to obtain a cast billet; the continuous casting adopts an end electromagnetic stirring process.

[0077] S2. The billet is heated and rolled into high-speed wire rod to obtain cold heading steel wire rod.

[0078] The phosphorus segregation index of the cast billets and cold heading steel obtained in Examples 1-10 and Comparative Examples 1-3 was tested; the mechanical properties of the cold heading steel wire rod were tested, and the long-term corrosion rate test of the cold heading steel wire rod in a high SO2 concentration atmospheric environment was conducted using the periodic immersion corrosion method, with a period of 320 hours. The performance results of the cast billets and cold heading steel are shown in Table 2.

[0079] Table 2. Properties of cast billets and cold heading steels from Examples 1-10 and Comparative Examples 1-3

[0080]

[0081] Figure 2 This is a low-magnification photograph of the cross-section of the cast billet provided in Embodiment 2 of this application;

[0082] Depend on Figure 2 It can be seen that there are no cracks on the surface of the cast billet.

[0083] Figure 3 This is an electron probe phosphorus distribution map of the core of the cast billet provided in Embodiment 1 of this application;

[0084] Depend on Figure 3 It can be seen that the phosphorus segregation index in the core of the billet is ≤2.5.

[0085] Figure 4 This is an electron probe phosphorus distribution map of the core of a hot-rolled cold-heading steel wire rod provided in Embodiment 2 of this application;

[0086] Depend on Figure 4 It can be seen that the phosphorus segregation index of 0.14% P steel can be ≤1.25 through this patented technology.

[0087] Figure 5 Metallographic diagram of cold heading steel provided in Embodiment 2 of this application;

[0088] Depend on Figure 5 It can be seen that the microstructure of hot-rolled wire rod is ferrite + pearlite, with uniform grain size.

[0089] Figure 6 This is a longitudinal cross-sectional view of a fastener manufactured by cold heading steel forming according to Embodiment 2 of this application.

[0090] Depend on Figure 6 It can be seen that the fastener is a hexagonal head bolt. After longitudinal sectioning, it was observed that there were no defects in the areas of the nut and threads with large cold deformation.

[0091] Furthermore, one or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0092] In this embodiment of the invention, The phosphorus segregation index of the specified cold-heading steel wire rod is ≤1.25, the tensile strength is 520~550MPa, Z% ≥70%, the allowable deformation is ≥80%, and the long-term corrosion rate in high SO2 concentration atmospheric environments is ≤0.8g / (m²). 2 ·h).

[0093] In this embodiment of the invention, the content and relationship of carbon and phosphorus elements in the steel are controlled, the distribution of phosphorus element segregation in the cross section of the billet is consistent, and the phosphorus segregation index after rolling is controlled, so as to achieve a limit of ≥80% for the primary deformation of high phosphorus content steel (i.e., the allowable degree of deformation).

[0094] In this embodiment of the invention, the amount of expensive corrosion-resistant elements Cr, Cu and Ni added is reduced, thereby saving costs.

[0095] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. 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 this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A medium-low carbon, high-phosphorus weather-resistant cold-heading steel that meets the requirements for large deformation in cold heading, characterized in that, The chemical composition of the cold heading steel, by mass fraction, is as follows: C: 0.15%~0.25%, Si: 0.20%~0.30%, Mn: 0.30%~0.40%, Cu: 0.20%~0.60%, P: 0.08%~0.14%, S≤0.01%, Ni: 0.10%~0.15%, Cr: 0.20%~0.50%, Al T 0.025%~0.06%; the balance is Fe and unavoidable impurities; wherein, C and P satisfy the following relationship: [P]*[C]≤0.035 In the formula, [P] represents the value before the percentage of P content, and [C] represents the value before the percentage of C content; The relationship between Ni and P is: 0.5 ≤ Ni content / P content ≤ 1.

5.

2. The cold heading steel according to claim 1, characterized in that, C and P satisfy the following relationship: 0.02≤[P]*[C]≤0.035 In the formula, [P] represents the value preceding the percentage of P content, and [C] represents the value preceding the percentage of C content.

3. The cold heading steel according to claim 1, characterized in that, The diameter φ of the cold heading steel is 6.5mm~16mm.

4. The cold heading steel according to claim 3, characterized in that, The phosphorus segregation index of the cold heading steel is ≤1.25, where segregation index = enriched element content / average element content in steel.

5. The cold heading steel according to claim 4, characterized in that, The cold heading steel must meet at least one of the following properties: tensile strength of 520 MPa to 550 MPa, Z% ≥ 70%, allowable deformation ≥ 80%, and long-term corrosion rate ≤ 0.8 g / (m²) in high SO₂ concentration atmospheric environments. 2 ·h), where Z represents the range of tensile forces that cold heading steel can withstand in the thickness direction.

6. A method for preparing cold heading steel according to any one of claims 1 to 5, characterized in that, The method includes: Molten steel with the aforementioned chemical composition is continuously cast, and the crystallizer water flow rate and secondary cooling dynamic water distribution mode of the continuous casting are optimized to obtain a cast billet; the continuous casting adopts an end electromagnetic stirring process. The cast billet is heated and rolled into high-speed wire rod to obtain cold heading steel.

7. The preparation method according to claim 6, characterized in that, The ratio of phosphorus segregation index in the core to the edge of the billet is ≤2, and the phosphorus segregation index in the core of the billet is ≤2.5, wherein the segregation index = enriched element content / average element content in steel.

8. The preparation method according to claim 6, characterized in that, Before continuously casting the molten steel having the aforementioned chemical composition, the method further includes: Molten iron is subjected to RH vacuum degassing treatment to obtain a billet with a set chemical composition; the pure degassing time of the RH vacuum degassing treatment is ≥15min.

9. A fastener, characterized in that, The fastener is prepared by cold heading of cold heading steel as described in any one of claims 1 to 5 and cold heading steel prepared by the preparation method as described in any one of claims 6 to 8.

Images