High-strength seawater-corrosion-resistant chain steel, chain and manufacturing method therefor

Abstract

The present disclosure provides a high-strength seawater-corrosion-resistant chain steel, a chain and manufacturing methods therefor. The chain steel comprises the following chemical elements in mass percentage: C: 0.25-0.35%, Si: 0.1-0.6%, Mn: 0.3-0.9%, Cr: 0.3-1.2%, Ni: 1.8-3.2%, Mo: 0.39-1.0%, Al: 0.02-0.05%, V: 0.08-0.30%, N: 0.009-0.02%, and the balance being Fe and inevitable impurities. The chain of the present disclosure has high strength, and also good toughness-plasticity matching as well as excellent seawater corrosion resistance, which can effectively solve the problem that the service life of existing chains is impaired due to the mismatch of strength, toughness and plasticity and corrosion resistance.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of chain steel and chain, specifically to a high-strength seawater-corrosion-resistant chain steel, a chain, and a manufacturing method therefor.BACKGROUND

[0002] Every year, approximately 1 / 6 of the world's annual production is lost due to corrosion. In China, the direct economic losses caused by steel corrosion exceed 10 billion CNY annually. Furthermore, steel corrosion reduces the service life of steel structures, causes casualties and economic losses, and results in environmental pollution due to emissions. Particularly in marine environments, chloride ions in seawater and sea surface air cause particularly severe corrosion to steel during service. To improve the corrosion resistance of steel, a coating treatment is usually applied to the steel surface. While this effectively slows down the corrosion process, during the service life of steel, once defects appear on the coating surface, corrosion will occur within the coating of the steel, causing the coating to fail rapidly. Although stainless steel possesses excellent corrosion resistance, the high cost due to the addition of a large amount of alloying elements limits its large-scale application. Therefore, low-alloy corrosion-resistant steel is attracting increasing attention due to its relatively low alloy content, excellent mechanical properties, and relatively good corrosion resistance. With the booming development of China's ocean shipping and marine engineering construction, increasingly higher requirements are being placed on the strength and corrosion resistance of steel, and the demand for high-strength chain steel with excellent seawater corrosion resistance is increasing.

[0003] Currently, numerous seawater-corrosion-resistant steels have been developed in China and other countries, mainly by optimizing alloying elements such as Cr, Ni, and Cu in the steels to improve their seawater corrosion resistance. For example, CN Patent Literature 1 (application number 201010266527.0) discloses an ultra-high-strength ship plate steel and a manufacturing method therefor. The slab has the following composition: C: 0.02-0.09%, Si: 0.1-0.4%, Mn: 0.5-1.6%, Alt: 0.01-0.04%, Nb: 0.02-0.05%, Ti 0.008-0.02%, Cr 0.3-0.7%, Mo 0.2-0.5%, Ni 0.5-1%, Cu 0.2-1%, P < 0.013%, S < 0.005%, O < 0.0012%, N < 0.0045%, H < 0.00015%. The ultra-high strength ship plate steel is manufactured by using controlled rolling and controlled cooling technology + subsequent heat treatment, and has a tensile strength of greater than 670 MPa and an impact energy at -60 °C of greater than 200 J. CN Patent Literature 2 (Application No. 201180066512.2) discloses an ultra-high strength structural steel with the following chemical composition: C: 0.07-0.12%, Si: 0.1-0.7%, Mn: 0.5-2.0%, Ni: 0.8-4.5%, Cu: 0.25-3.0%, Cr: 0.5-1.6%, Mo: <0.8%, and Ti: 0.04%, as well as Fe and inevitable impurities. This technology, with relatively low carbon content, through the addition of high amounts of alloying elements (Ni, Cu, Cr, and Mo) and the use of hot-rolling controlled-cooling process that directly quench to a temperature not exceeding 450 °C at a cooling rate of 20-150 °C / s after hot rolling, ultimately resulting in a steel with a yield strength of greater than 960 MPa and an impact energy of greater than 34J in the welding heat-affected zone at -40 °C. CN Patent Literature 3 (Application No. 201610993472.0) discloses a high-strength, high-toughness, and corrosion-resistant steel for chains with the following chemical composition: C: 0.06-0.11%, Si: 0.15-0.35%, Mn: 0.30-0.50%, Cr: 1.00-3.00%, Ni: 2.00-4.00%, Mo: 0.30-0.60%, Nb: 0.02-0.06%, V: 0.03-0.09%, P < 0.015%, S < 0.015%, with the balance being Fe and inevitable impurities. This technology adopts a double quenching heat treatment and a single tempering heat treatment process to obtain a lath martensite microstructure with a lath width of 0.3-5 µm, wherein granular cementite with a diameter of 0.2-0.8 µm and a volume fraction of 0.15%-0.35% and MC phase particles with a diameter of 5-15 nm and a volume fraction of 0.02%-0.08% are dispersed between and within the laths. The chain after heat treatment has a tensile strength of 1000 MPa grade and a KV2 (-60 °C) for both ring back and weld seam of 100 J and more, and has good resistance to seawater corrosion.

[0004] In addition, there are some weathering steel products specific to certain special service environments. For example, CN Patent Literature 4 (Application No. 201611102046.X) discloses a high-strength weathering steel for high-humidity and high-temperature marine atmospheric environments, with the following chemical composition (wt%): C: 0.01-0.03, Si: 0.30-0.50, Mn: 0.60-0.80, Cu: 0.90-1.10, Ni: 2.80-3.20, Mo: 0.20-0.40, Sn: 0.25-0.35, Sb: 0.05-0.10, Cr ≤ 0.03, Nb ≤ 0.02, P ≤ 0.01, S ≤ 0.01, RE: 0.03-0.05, with the balance being Fe. This technology significantly reduces the Cr content in the weathering steel by adding various microalloying elements such as Sn, Sb, Nb and RE based on the Cu-Ni-Mo alloy system, and achieves the formation of acicular ferrite and polygonal ferrite microstructures by controlling the cooling rate of the steel after hot rolling at 12-17 °C / s to cool to a temperature of 530-570 °C and hold at this temperature. The resulting steel has a yield strength of> 650 MPa, a tensile strength of> 750 MPa, and a half-size impact energy at 30 °C of> 65 J.

[0005] Referring to the aforementioned prior art, it can be seen that existing high-strength seawater-corrosion-resistant steel products mainly improve the seawater corrosion resistance of the steel substrate through alloy composition optimization, mostly have a yield strength of about 600 MPa to 900 MPa, and rarely have a yield strength exceeding 1000 MPa.

[0006] Therefore, the present disclosure aims to obtain a novel high-strength seawater-corrosion-resistant chain steel, which can be used to produce finished chains with excellent comprehensive properties by combining chain heat treatment and coating processes. The finished chain has not only high strength but also good toughness-plasticity matching, as well as excellent corrosion resistance, effectively solving the problem that the service life of existing chains is impaired due to the mismatch of strength, toughness, plasticity and corrosion resistance.SUMMARY

[0007] Aiming at the problem that the service life of existing chains is impaired due to the mismatch of strength, toughness, plasticity and corrosion resistance, the objective of the present disclosure is to provide a high-strength seawater-corrosion-resistant chain steel, a chain, and a manufacturing method therefor. Specifically, the present disclosure, through composition design and manufacturing process optimization, achieves a high-strength seawater-corrosion-resistant chain steel with not only high strength but also good toughness-plasticity matching and excellent seawater-corrosion-resistance, which is particularly suitable for manufacturing high-strength, corrosion-resistant structural components as well as mining, mooring, and other industrial products that can be widely applied in environments with a large amount of corrosive medium, such as engineering machinery, mines, ships, and marine engineering.

[0008] To achieve the above objective, the present disclosure provides the following technical solution: The first aspect of the present disclosure provides a chain steel, comprising the following chemical elements in mass percentage: C: 0.25-0.35%, Si: 0.1-0.6%, Mn: 0.3-0.9%, Cr: 0.3-1.2%, Ni: 1.8-3.2%, preferably 1.8-2.95%, Mo: 0.39-1.0%, preferably 0.4-1.0%, more preferably 0.4-0.88%, Al: 0.02-0.05%, V: 0.08-0.30%, N: 0.009-0.02%, and the balance being Fe and inevitable impurities.

[0009] Preferably, the chain steel has a chemical composition satisfying the following relational expression: 1.3*Ni+2*Cr+7*Mo+0.5*Si+V ≥ 8, preferably 8 ≤ 1.3*Ni+2*Cr+7*Mo+0.5*Si+V ≤ 10.22, where Ni, Cr, Mo, Si and V respectively represent the numerical values preceding the % symbol of the mass percentage contents of corresponding elements.

[0010] Preferably, the inevitable impurities comprise P ≤ 0.015%, S ≤ 0.01%, and O ≤ 0.002%.

[0011] Preferably, the chain steel has a microstructure of acicular martensite.

[0012] Preferably, the chain steel has the following properties: a yield strength Rp 0.2 of ≥ 1050 MPa, a tensile strength R m of ≥ 1100 MPa, an elongation A of ≥ 14%, a reduction of area Z of ≥ 50%, a Charpy impact energy Akv at -20 °C of ≥ 60 J.

[0013] The second aspect of the present disclosure provides a chain comprising: the chain steel as described above and a zinc coating coated on the chain steel.

[0014] Preferably, the zinc coating has a thickness of 10-150 µm, more preferably 40-150 µm; and / or, the chain steel has a microstructure of acicular tempered martensite and dispersed carbides, preferably, the carbides have a size of less than 300 nm.

[0015] Preferably, the chain has the following properties: a yield strength Rp 0.2 of ≥ 1050 MPa, a tensile strength R m of ≥ 1100 MPa, an elongation A of ≥ 14%, a reduction of area Z of ≥ 50%, a Charpy impact energy Akv at -20 °C of ≥ 60 J; and a corrosion rate of ≤ 0.2 g / m 2< ·h after 120 h of 5% NaCl neutral salt spray corrosion test.

[0016] The third aspect of the present disclosure provides a method for manufacturing the chain, comprising the following steps performed sequentially: S1, smelting and casting molten steel to obtain a cast slab; S2, heating and rolling the cast slab, wherein the reduction ratio of the cast slab is ≥ 10; S3, forming rings and welding; S4, performing quenching heat treatment, wherein for the quenching heat treatment, a heating temperature is 840-980 °C, preferably 850-950 °C, a holding time is 1-4 hours, preferably 1-3 hours, and water cooling is performed for quenching; S5, performing pickling pretreatment to obtain the chain steel; S6, hot-dip galvanizing, wherein the chain steel after pickling pretreatment is subjected to preheating treatment followed by hot-dip galvanizing to obtain the chain comprising the chain steel and a zinc coating formed on the surface of the chain steel; a temperature difference between a preheating temperature for the preheating treatment and a temperature of zinc bath used in the hot-dip galvanizing is controlled to -30 to 30 °C.

[0017] Preferably, in step S1, the smelting comprises electric furnace or converter smelting, LF refining, and VD or RH vacuum treatment; the casting adopts a continuous casting process.

[0018] Preferably, in step S1, the VD or RH vacuum treatment is performed for a time period of 10-20 min; during casting, the superheat degree of the molten steel in the tundish is controlled to 15-40 °C.

[0019] Preferably, in step S2, during heating and rolling, the cast slab is heated at a heating temperature of ≥ 1150 °C for a time period of 3-6 h, and the finishing rolling temperature is ≥850 °C; after rolling, air cooling or slow cooling is performed.

[0020] Preferably, in step S6, the preheating temperature is 400-550 °C, the preheating time is ≥ 0.5 h; the temperature of the zinc bath used in the hot-dip galvanizing is 400-530 °C.

[0021] Preferably, the zinc coating has a thickness of 10-150 µm, preferably 40-150 µm.

[0022] Preferably, the chain steel in the chain obtained in step S6 has a microstructure of acicular tempered martensite and dispersed carbides; preferably, the carbides have a size of less than 300 nm.

[0023] Preferably, the chain has the following properties: a yield strength Rp 0.2 of ≥ 1050 MPa, a tensile strength R m of ≥ 1100 MPa, an elongation A of ≥ 14%, a reduction of area Z of ≥ 50%, a Charpy impact energy Akv at -20 °C of ≥ 60 J; and a corrosion rate of less than 0.2 g / m 2< ·h after 120 h of 5% NaCl neutral salt spray corrosion test.

[0024] The design principles of chemical elements in the high-strength seawater-corrosion-resistant chain steel according to the present disclosure are as follows. In the present disclosure, unless otherwise explicitly stated, element contents are expressed as a mass percentage.

[0025] C: C is an essential element for ensuring the strength of the steel. Increasing the C content in the steel will enhance its non-equilibrium microstructure transformation capability, thereby significantly improving its strength. In the present disclosure, the diffusion of C in the steel can be inhibited by quenching heat treatment to induce a shear-type martensite phase transformation, thus significantly improving the strength of the steel. However, for the present disclosure, the C content in the steel should not be excessively high. An overly high C content will adversely affect the plasticity and toughness of the steel, and will significantly increase the carbon equivalent of the steel, deteriorating the weldability of the steel. Therefore, in the high-strength seawater-corrosion-resistant chain steel according to the present disclosure, the mass percentage content of C is controlled to 0.25% - 0.35%.

[0026] Si: Si can solid-dissolve in the steel and has a solid solution strengthening effect, significantly improving the yield strength, fatigue strength, and hardness of the steel. During corrosion, Si mainly exists as a divalent oxide in spinel-type oxides, densifying the inner rust layer to hinder Cl -< infiltration, thus improving the marine corrosion resistance of the steel. Si has very low solubility in cementite, thus the Si content in the steel should not be excessively high. An overly high Si content will not only lead to the formation of carbide-free bainite microstructure, but also increase the brittleness of the steel. Therefore, in the high-strength seawater-corrosion-resistant chain steel according to the present disclosure, the mass percentage content of Si is controlled to 0.1% - 0.6%.

[0027] Mn: Mn can improve the stability of austenite in the steel and also enhance the hardenability of the steel. Furthermore, Mn can also improve the strength of martensite in the steel through solid solution strengthening, thereby increasing the strength of the steel. However, it should be noted that the Mn content in the steel should not be excessively high. An overly high Mn content will cause austenite grains to tend to grow and promote the segregation of harmful elements at grain boundaries during quenching heating. Therefore, in the high-strength seawater-corrosion-resistant chain steel according to the present disclosure, the mass percentage content of Mn is controlled to 0.3% - 0.9%.

[0028] Cr: The addition of an appropriate amount of Cr can improve the hardenability of the steel and has a secondary hardening effect, which enables the formation of a hardened martensite microstructure and thereby is conducive to enhancing the strength of the steel. In addition, Cr carbides can slow down the grain growth in the heat-affected zone at the weld joint, which is very beneficial to the welding of the steel. The addition of appropriate amounts of Cr and Ni to the steel is beneficial for improving the corrosion resistance of the steel and promotes the formation of a passive film on the steel surface. A certain amount of Cr can significantly improve the corrosion resistance of the steel. However, the Cr content in the steel should not be excessively high. If the Cr content in the steel is excessively high, a large amount of carbides will be generated and accumulate at the grain boundaries, reducing the toughness of the steel and significantly increasing the carbon equivalent, thus deteriorating the weldability of the high-strength seawater-corrosion-resistant chain steel. Therefore, in the high-strength seawater-corrosion-resistant chain steel according to the present disclosure, the mass percentage content of Cr is controlled to 0.3% - 1.2%.

[0029] Ni: Ni is an austenite-forming element. Ni is one of the main strengthening elements and can be present in the steel in the form of solid solution and is infinitely soluble with iron, exhibiting resistance to both acids and alkalis, as well as resistance to atmospheric and salt corrosion. During corrosion, Ni replaces Fe ions in the form of divalent ions to form relatively stable spinel-type NiFe 2 O 4 compounds. When Ni is used in combination with Cr, the hardenability of the steel will be significantly improved. Furthermore, the addition of an appropriate amount of Ni to the steel can lower the C content at the eutectoid point, strengthen ferrite, and refine and increase pearlite, thereby improving the strength of the steel without significantly affecting its plasticity. Ni can improve the fatigue resistance of the steel, reduce its sensitivity to notch, lower its ductile-brittle transition temperature at low temperature, and improve its impact toughness. In addition, while improving the strength of the steel, Ni causes less damage to the toughness, plasticity, and other processing properties of the steel compared to other alloying elements. Therefore, in the high-strength seawater-corrosion-resistant chain steel according to the present disclosure, the mass percentage content of Ni element is controlled to 1.8% - 3.2%, preferably 1.8% - 2.95%.

[0030] Mo: Mo mainly exists in the steel in solid solution form and has a solid solution strengthening effect, which is beneficial to improving the hardenability of the steel, enabling the formation of martensite in the steel during quenching. At the same time, Mo can also improve the corrosion resistance of the steel to organic acids, sulfuric acid, and sulfates, and can passivate the steel surface in both reducing acid and strong oxidizing salt solutions, preventing pitting corrosion of the steel in chloride solutions. However, the Mo content in the steel should not be excessively high. When the Mo content in the steel is excessively high, the carbon equivalent of the steel will be significantly increased, which is detrimental to the weldability of the steel. In addition, Mo is also a precious alloying element, and the addition of a large amount of Mo will lead to an increase in alloy cost. Therefore, in the high-strength seawater-corrosion-resistant chain steel according to the present disclosure, the mass percentage content of Mo is controlled to 0.39% - 1.0%, preferably 0.4% - 1.0%, and more preferably 0.4% - 0.88%.

[0031] Al: Al element mainly functions for deoxidation and nitrogen fixation. AlN, formed by the combination of Al and N, can effectively refine the grains. However, it should be noted that the Al content in the steel should not be excessively high. An overly high Al content in the steel will affect the casting performance of the steel and impair its toughness. Therefore, in the high-strength seawater-corrosion-resistant chain steel according to the present disclosure, the mass percentage content of Al is controlled to 0.02% - 0.05%.

[0032] V: As a strong carbide-forming element, V can significantly improve the strength of the steel in the form of dispersed precipitates. V can also improve the pitting corrosion resistance of the steel. However, it should be noted that an excessively high addition of V in the steel will reduce the toughness and weldability of the steel. Therefore, in the high-strength seawater-corrosion-resistant chain steel according to the present disclosure, the mass percentage content of V is controlled to 0.08% - 0.30%.

[0033] N: N is an austenite-forming element and also an MX-type precipitate-forming element. To avoid N enrichment in the steel, an excessive amount of N should not be added to the steel. Therefore, the N content should be strictly controlled. In the high-strength seawater-corrosion-resistant chain steel according to the present disclosure, the mass percentage content of N is controlled to 0.009% - 0.02%.

[0034] The present disclosure, by virtue of the rational design of main alloying elements and taking full advantage of the effects of various alloying elements and their interactions on microstructure, mechanical properties, and corrosion resistance, precisely controls the microstructure of the chain steel according to the present disclosure to ensure that, when the chain steel is manufactured into chains via hot-dip galvanization, a mixed microstructure of acicular tempered martensite and dispersed carbides is formed in the chain steel, thereby improving the resistance of the chain steel to localized seawater corrosion. As a result, the chain according to the present disclosure has both high strength and good toughness-plasticity matching, along with excellent seawater-corrosion-resistance.

[0035] In a preferred embodiment, in the high-strength seawater-corrosion-resistant chain steel according to the present disclosure, the inevitable impurities comprise P ≤ 0.015%, S ≤ 0.01%, and O ≤ 0.002%.

[0036] In the above technical solution, P, S, and O are all impurity elements in the steel. Where technical conditions permit, the content of impurity elements in the steel should be reduced as much as possible to obtain the high-strength seawater-corrosion-resistant chain steel with better performance and higher quality.

[0037] In the present disclosure, P and S are both inevitable harmful impurity elements in the steel, and both will deteriorate the properties of the steel. Although P can improve the weather resistance of the steel, its side effects are more significant overall. Therefore, in the present disclosure, P is controlled to ≤0.015%, S is controlled to ≤0.01%.

[0038] In the present disclosure, the impurity element O can form oxides and composite inclusions with deoxidizing elements such as Al in the steel, which is detrimental to the properties of the steel. Therefore, in the present disclosure, O is controlled to ≤0.002%.

[0039] Of course, in some other embodiments, other harmful elements such as As, Pb, Sn, Sb, Bi and the like may also be present in the steel. While in compliance with the requirements of national laws, regulations, and standards, the contents of these harmful elements should be reduced as much as possible.

[0040] During service, the coating of the chain may wear and peel off, locally exposing the steel substrate to the seawater environment and causing localized corrosion, which affects the safe operation of the chain. To improve the resistance of the steel substrate to localized seawater corrosion, the contents of Ni, Cr, Mo, Si, and V (the main alloying elements that improve the resistance to localized seawater corrosion) in the steel must further satisfy the following relational expression: 1.3*Ni+2*Cr+7*Mo+0.5*Si+V ≥ 8, preferably 8 ≤ 1.3*Ni+2*Cr+7*Mo+0.5*Si+V ≤ 10.22, where Ni, Cr, Mo, Si and V respectively represent the numerical values preceding the % symbol of the mass percentage contents of corresponding elements.

[0041] The inventors discovered through studies that, when the contents of Ni, Cr, Mo, Si, and V (alloying elements resistant to localized seawater corrosion) in the steel satisfy the relational expression 1.3*Ni+2*Cr+7*Mo+0.5*Si+V ≥ 8, the steel substrate has excellent resistance to localized seawater corrosion. The combination of the steel substrate and the coating on the steel surface can significantly reduce the corrosion rate of the steel in seawater environments. When the value of 1.3*Ni+2*Cr+7*Mo+0.5*Si+V (the relational expression of the contents of Ni, Cr, Mo, Si, and V in the steel) is less than 8, the resistance of the steel to localized corrosion decreases significantly, then if the coating of the chain experiences localized wear and fails, the exposed steel substrate will exhibit significant localized corrosion defects, leading to localized stress concentration in the chain and directly affecting the service life of the chain.

[0042] Compared with existing production technologies, the present disclosure has the following beneficial effects: 1. The present disclosure adopts a rational chemical composition design, fully considering the correlation between the content of alloying elements and the resistance of the chain steel to localized seawater corrosion, thereby improving the resistance of the chain steel to localized seawater corrosion. The present disclosure, by virtue of combining optimized manufacturing processes and taking full advantage of the effects of various alloying elements and chain processing procedures on the microstructure, precisely controls the microstructure of the chain steel. After quenching heat treatment, an acicular martensite microstructure forms in the chain steel. Preheating and hot-dip galvanizing to the chain steel allows for, on the one hand, the precipitation of fine dispersed carbides in the supersaturated solid solution formed in the chain steel after quenching, thus improving the properties of the chain steel; on the other hand, the formation of a zinc coating (or galvanized coating) with a certain thickness on the surface of the chain steel, and the coating of the chain can improve the seawater corrosion resistance of the chain. When the chain coating wears and fails, the localized corrosion resistance design of the chain steel substrate can reduce localized pitting corrosion of the steel, thereby improving the seawater corrosion resistance of the chain steel. 2. After the zinc coating is applied to the surface of the chain steel according to the present disclosure, it can isolate the corrosive medium of seawater from contacting the chain steel, thereby improving the corrosion resistance of the chain. When the coating on partial areas of the chain wears off, the localized corrosion resistance design of the steel substrate can prevent localized excessive corrosion of the chain during service, thus increasing the service life of the chain. 3. The chain steel according to the present disclosure has a reasonable chemical composition and process design, along with a wide process window, enabling mass commercial production. 4. The chain steel according to the present disclosure has excellent high strength and toughness as well as good resistance to localized seawater corrosion, and can be fabricated into high-strength and corrosion-resistant structural components, as well as various high-performance industrial chains such as mining and mooring chains, which are widely applied in engineering machinery, mines, marine engineering and other scenarios requiring steel with high strength, high toughness and high corrosion resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Other features, objectives, and advantages of the present disclosure will become more apparent by referring to the detailed description of a non-limiting example illustrated by the following accompanying drawings: FIG. 1 is a scanning electron microscope image of the chain steel manufactured in example 1 according to the present disclosure.DETAILED DESCRIPTION

[0044] To facilitate a better understanding of the aforementioned technical solutions according to the present disclosure, the technical solutions of the present disclosure are further described below with reference to the embodiments and FIG. 1.

[0045] The present disclosure provides a chain steel with high strength and high seawater corrosion resistance, which comprises, in addition to Fe and inevitable impurities, the following chemical elements in mass percentage: C: 0.25-0.35%, Si: 0.1-0.6%, Mn: 0.3-0.9%, Cr: 0.3-1.2%, Ni: 1.8-3.2%, preferably 1.8-2.95%, Mo: 0.39-1.0%, preferably 0.4-1.0%, more preferably 0.4-0.88%, Al: 0.02-0.05%, V: 0.08-0.30%, N: 0.009-0.02%.

[0046] The present disclosure, by virtue of the rational design of main alloying elements and taking full advantage of the effects of various alloying elements and their interactions on microstructure, mechanical properties, and corrosion resistance, improves the resistance of the chain steel to localized seawater corrosion. Meanwhile, the present disclosure adopts optimized quenching and coating processes to precisely control the microstructure of the steel according to the present disclosure, so as to ensure the formation of a mixed microstructure of acicular tempered martensite and dispersed carbides in the high-strength seawater-corrosion-resistant chain steel. The high-strength chain prepared therefrom has relatively high strength and toughness-plasticity matching, as well as good resistance to seawater corrosion.

[0047] In a specific embodiment, the high-strength seawater-corrosion-resistant chain steel has a chemical composition satisfying the following relational expression: 1.3*Ni+2*Cr+7*Mo+0.5*Si+V ≥ 8, where Ni, Cr, Mo, Si and V respectively represent the numerical values preceding the % symbol of the mass percentage contents of corresponding elements.

[0048] In the high-strength seawater-corrosion-resistant chain steel, when the contents of the pitting corrosion-resistant alloying elements Ni, Cr, Mo, Si and V in the steel satisfy the relational expression of 1.3*Ni+2*Cr+7*Mo+0.5*Si+V ≥ 8, the steel has excellent localized seawater corrosion resistance, and its combination with the coating on the steel surface enables to significantly reduce the corrosion rate of the steel in the seawater environment. When the value of 1.3*Ni+2*Cr+7*Mo+0.5*Si+V (the relational expression of the contents of Ni, Cr, Mo, Si, and V in the steel) is less than 8, the resistance of the steel to localized seawater corrosion decreases significantly, then if the coating of the chain experiences localized wear and fails, the exposed steel substrate will exhibit significant localized corrosion defects, leading to localized stress concentration in the chain and directly affecting the service life of the chain.

[0049] In the present disclosure, P, S, and O are all impurity elements in the steel. Where technical conditions permit, the content of impurity elements in the steel should be reduced as much as possible to obtain the high-strength steel with better performance and higher quality. P and S are both inevitable harmful impurities in the steel, and both will deteriorate the properties of the steel. Although P can improve the weather resistance of the steel, its side effects are more significant overall. O can form oxides and composite inclusions with deoxidizing elements such as Al in the steel, which is detrimental to the properties of the steel. Therefore, the inevitable impurities comprise P ≤ 0.015%, S ≤ 0.01%, and O ≤ 0.002%.

[0050] In a specific embodiment, the high-strength seawater-corrosion-resistant chain steel has a microstructure of acicular martensite.

[0051] The high-strength seawater-corrosion-resistant chain steel has the following properties: a yield strength Rp 0.2 of ≥ 1050 MPa, a tensile strength R m of ≥ 1100 MPa, preferably ≥ 1150 MPa, more preferably ≥ 1183 MPa, most preferably ≥ 1200 MPa, an elongation A of ≥ 14%, a reduction of area Z of ≥ 50%, a Charpy impact energy Akv at -20 °Cof≥ 60 J, preferably ≥ 79 J.

[0052] The present disclosure provides a chain manufactured from the aforementioned high-strength seawater-corrosion-resistant chain steel, and the chain has the following properties: a yield strength Rp 0.2 of ≥ 1050 MPa, a tensile strength R m of ≥ 1100 Mpa, preferably ≥ 1150 MPa, more preferably ≥ 1183 MPa, most preferably ≥ 1200 MPa, an elongation A of ≥ 14%, a reduction of area Z of ≥ 50%, a Charpy impact energy Akv at -20 °C of ≥ 60 J, preferably ≥ 79 J; a corrosion rate of ≤ 0.2 g / m 2< ·h after 120 h of 5% NaCl neutral salt spray corrosion test.

[0053] The method for manufacturing the chain according to the present disclosure has a simple production process, and the obtained high-strength, seawater-corrosion-resistant chain has excellent high strength and toughness as well as good seawater corrosion resistance. The manufacturing method specifically comprises the following steps: S1, Smelting and casting. Specifically, the smelting operation comprises electric furnace or converter smelting, LF refining, and VD or RH vacuum treatment. That is to say, smelting is performed using an electric furnace or converter, followed by LF refining and VD or RH vacuum treatment, wherein the vacuum treatment is performed for 10-20 minutes, and the molten steel is tapped for casting after the chemical composition meets the design requirements of the high-strength, seawater-corrosion-resistant chain steel according to the present disclosure. Then, during casting, the molten steel is cast into a slab using continuous casting, controlling the superheat degree of the molten steel in the tundish to 15-40 °C, and a cast slab with a chemical composition that meets the requirements of the high-strength, seawater-corrosion-resistant chain steel is ultimately obtained. S2, Heating and rolling, wherein the reduction ratio of the cast slab is ≥ 10. Specifically, the cast slab is first heated in a heating furnace, then tapped, and subsequently subjected to high-pressure water descaling, and finally subjected to rolling to roll the cast slab into round steel of finished size; wherein the cast slab is controlled to be heated at a heating temperature of ≥ 1150 °C for 3-6 h, and the finishing rolling temperature is ≥850 °C. After rolling, air cooling or slow cooling is performed to room temperature. The reduction ratio of the cast slab is ≥ 10. The resulting round steel has a finished size specification of Φ 26 to 150 mm, preferably Φ 30 to 150 mm. S3, Forming rings and welding. The round steel obtained by rolling is cut to fixed length, then formed into individual rings on a chain making machine, and finally weld them into complete rings by flash welding to obtain a chain-like substrate. S4, performing quenching heat treatment. For the quenching heat treatment, a heating temperature can be 840-980 °C, a holding time can be for 1-4 hours, and water cooling is performed for quenching. Specifically, the chain-like substrate obtained by forming rings and welding is subjected to quenching heat treatment, wherein for the quenching heat treatment, a heating temperature is 850-950 °C, a holding time is 1-3 hours, followed by water cooling for quenching. During the high-temperature heating of the chain-like substrate obtained by forming rings and welding, fine austenite grains are formed in the steel, with an austenite grain size of ≥ Grade 7. After water cooling for quenching, the microstructure of the chain steel transforms from the austenite microstructure under high-temperature heating to fine acicular martensite microstructure. S5, Pickling pretreatment. The chain-like substrate after quenching heat treatment is subjected to pickling pretreatment to remove the oxide scale on the surface of the chain after quenching, obtaining the chain steel. Preferably, a layer of flux is applied to the surface of the chain steel to maintain a certain level of activity on the pickled chain surface, preventing oxidation of the chain steel during subsequent preheating treatment and enhancing the bonding force between the zinc coating and the chain steel. It should be noted that the flux used in the present disclosure is a commonly used additive in galvanizing in the art, which are commercially available. S6, Hot-dip galvanizing. The chain steel after pickling pretreatment is subjected to preheating treatment followed by hot-dip galvanizing to obtain a high-strength seawater-corrosion-resistant chain. The temperature difference between the preheating temperature and the temperature of the zinc bath used in the hot-dip galvanizing is controlled to -30 to 30 °C.

[0054] Specifically, after pickling pretreatment, the chain steel is subjected to hot-dip galvanizing. Preferably, the chain steel is subjected to preheating treatment before hot-dip galvanizing to prevent problems such as zinc explosion (or zinc spattering) during the subsequent hot-dip galvanizing process, thereby obtaining a high-strength, seawater-corrosion-resistant chain. The temperature difference between the preheating temperature and the temperature of the zinc bath used in the hot-dip galvanizing is controlled to -30 to 30 °C. For example, the preheating temperature may be 400 - 550 °C, and the preheating time may be ≥ 0.5 h. The temperature of the zinc bath used in the hot-dip galvanizing may be 400 - 530 °C. The thickness of the zinc coating on the surface of the high-strength, seawater-corrosion-resistant chain may be 10 -150 µm, preferably 40 - 150 µm.

[0055] During hot-dip galvanizing as described above, fine carbides precipitate from the supersaturated acicular martensite microstructure of the chain steel, resulting in a slight decrease in strength but an increase in elongation and impact toughness. The fine acicular martensite facilitates the precipitation of fine, dispersed carbides (less than 300 nm in size) in the steel during hot-dip galvanizing, thereby obtaining a high-strength, seawater-corrosion-resistant chain with excellent strength and toughness.

[0056] The chain manufactured as described above has a microstructure of acicular tempered martensite and dispersed carbides; wherein the carbides have a size of less than 300 nm.

[0057] The above-mentioned chain has the following properties: a yield strength Rp 0.2 of ≥ 1050 MPa; a tensile strength R m of ≥ 1100 MPa, preferably ≥ 1150 MPa, more preferably ≥ 1183 MPa, most preferably ≥ 1200 MPa; an elongation A of ≥ 14%; a reduction of area Z of ≥ 50%; a Charpy impact energy Akv at -20 °C of ≥ 60 J, preferably ≥ 79 J; a corrosion rate of less than 0.2 g / m 2< ·h after 120 h of 5% NaCl neutral salt spray corrosion test.

[0058] The present disclosure, by virtue of rational design of alloying elements combined with optimized manufacturing process and taking full advantage of the effects of various alloying elements and the manufacturing process on the microstructure and corrosion resistance, precisely controls the microstructure of high-strength seawater-corrosion-resistant chain steel, thereby improving the localized seawater corrosion resistance of the chain steel substrate. The chain steel has an acicular martensite microstructure. Hot-dip galvanizing treatment of the chain steel allows for, on the one hand, the precipitation of fine, dispersed carbides in the chain steel during the hot-dip galvanizing, thus improving the strength and toughness of the chain; on the other hand, it allows for the formation of a zinc coating with a certain thickness on the surface of the chain steel. In addition to the pitting corrosion-resistant composition design of the steel substrate, the seawater corrosion resistance of the chain is also enhanced by the zinc coating. When the zinc coating of the chain wears and fails, the localized seawater corrosion-resistant design of the chain steel can reduce the localized corrosion of the steel, thereby improving the seawater corrosion resistance of the chain.

[0059] In the manufacturing method of the chain according to the present disclosure, the conventional quenching process of chain is combined with the hot-dip galvanizing process, and the tempering process of the chain is omitted. By fully utilizing the precipitation of carbides in the steel during the hot-dip galvanizing process, the efficient production of the high-strength seawater-corrosion-resistant chain is achieved. As a result, the high-strength seawater-corrosion-resistant chain steel and chain according to the present disclosure have high strength and toughness-plasticity matching, as well as good corrosion resistance.

[0060] The high-strength seawater-corrosion-resistant chain steel, chain and manufacturing method therefor according to the present disclosure are further described below reference to the specific examples. It should be clearly stated that the following examples are only used to describe the specific embodiments of the present disclosure and do not constitute any limitation on the protection scope of the present disclosure.EXAMPLES Examples 1-6

[0061] As shown in Tables 1, 2-1, and 2-2, the chain steels and chains of Examples 1-6 were manufactured by method with the following steps performed in sequence: (1) Smelting and continuous casting were performed in accordance with the chemical composition shown in Table 1 below to obtain cast slabs. Smelting could be performed in an electric furnace or converter, followed by LF refining and VD or RH vacuum treatment. The VD or RH vacuum treatment were performed for 10-20 min, and the molten steel was tapped after the chemical composition met the requirements. Then, the molten steel could be cast into cast slabs using continuous casting. The superheat degree of the molten steel in the tundish was controlled to 15-40 °C during continuous casting. (2) Heating and rolling: The cast slabs were first heated in a heating furnace, then subjected to high-pressure water descaling, and finally rolled into round steels of finished size. The rolled round steels had a finished size specification of Φ 30 to 150 mm, and the reduction ratio of the cast slabs was ≥ 10. During rolling, the cast slabs were controlled to be heated at the heating temperature of ≥ 1150 °C for 3-6 h, and the finishing rolling temperature was ≥850 °C. After the rolling was completed, air cooling or slow cooling was performed to room temperature. (3) Forming rings and welding: The obtained round steels were cut to fixed length, then made into individual rings on a chain making machine, and finally welded them into chain-like substrates of complete rings by flash welding. (4) Quenching heat treatment: the chain-like substrates obtained after forming rings and welding were subjected to quenching heat treatment. For the quenching heat treatment, the heating temperature was controlled to 840-980 °C, and the holding time was 1-4 hours, followed by water cooling for quenching. (5) Pickling pretreatment: The chain-like substrates after quenching heat treatment were subjected to pickling pretreatment to remove the oxide scale on the chain surfaces. Then, the chain-like substrates after pickling pretreatment were subjected to preheating treatment to prevent problems such as zinc explosion (or zinc spattering) during subsequent hot-dip galvanizing. The chain-like substrates were subjected to preheating treatment at a temperature of 400-550 °C for ≥ 0.5h. The temperature difference between the preheating temperature of the preheating treatment and the temperature of the zinc bath used in the subsequent hot-dip galvanizing was controlled to -30 to 30 °C. (6) Hot-dip galvanizing: The chain-like substrates after pickling pretreatment and preheating treatment were hot-dip galvanized at a zinc bath temperature of 400-530 °C, and the thickness of the zinc coating on the chain surface was controlled to 10-150 µm, chains comprising chain steel and a zinc coating on the chain steel surface were obtained.

[0062] As shown in Tables 1, 2-1, and 2-2, the chemical composition designs and related process parameters of the chain steels prepared in Examples 1-6 all meet the design requirements of the present disclosure.Comparative Examples 1-2

[0063] The comparative steels of Comparative Examples 1-2 were finished steels from different manufacturers, and their chemical compositions are shown in Table 1. The manufacturing processes of the comparative steels differed from those of Examples 1-6, the parameters of the heat treatment adopted in Comparative Examples 1-2 are shown in Tables 2-1 and 2-2. The tempering temperature and tempering time in Table 2-2 all represent the tempering process of Comparative Examples 1-2.

[0064] Table 1 shows the chemical compositions of the chain steels of Examples 1-6 and the comparative steels of Comparative Examples 1-2. Table 1 (wt.%, the balance being Fe and other impurities in addition to P and S)CSiMnPSCrNiMoAlVNO1.3Ni+2Cr+7Mo +0.5 Si+VExample 10.250.340.550.010.0070.552.480.510.0210.130.00910.00188.19Example 20.350.470.890.0150.0080.311.570.880.0310.210.01070.00139.27Example 30.320.130.820.0060.010.892.310.410.0480.290.01920.00098.01Example 40.30.570.690.0130.0091.151.860.720.0250.180.01250.002010.22Example 50.260.250.320.010.0021.062.950.390.0320.250.01450.00129.06Example 60.280.20.440.0120.0020.722.020.620.0350.090.01760.00158.6Comparative Example 10.230.151.30.0080.0060.550.980.560.0270.0050.00860.00126.37Comparative Example 20.210.251.250.0130.0061.51.00.350.030.0030.010.00196.88

[0065] Tables 2-1 and 2-2 show the process parameters for the preparation of the finished chains of Examples 1-6 and the comparative chains of Comparative Examples 1-2. Table 2-1Step (1)Step (2)Round steel specification (mm)Reduction ratioSmelting and castingVacuum treatment time (min)Superheat degree of molten steel (°C)Heating temperature (°C)Heating time (h)Finishing rolling temperature (°C)Example 1Electric furnace + LF + VD + Continuous casting152312204960Φ12511Example 2Electric furnace + LF + VD + Continuous casting121812005880Φ2691Example 3Electric furnace + LF + VD + Continuous casting183511503920Φ4875Example 4Electric furnace + LF + RH + Continuous casting202512404900Φ6070Example 5Electric furnace + LF + RH + Continuous casting143011806850Φ10025Example 6Electric furnace + LF + RH + Continuous casting133912204980Φ15011Comparative Example 1Electric furnace + LF + VD + Continuous castingΦ48Comparative Example 2Electric furnace + LF + RH + Continuous castingΦ38 Table 2-2 Step (4)Step (5)Step (6)Quenching temperature (°C)Holding time (h)Preheating / Tempering temperature (°C)Preheating / Tempering time (h)Zinc bath temperature (°C)Zinc coating thickness (µm)Example 198035101.5500125Example 288014300.541015Example 393024150.843580Example 491024601.245040Example 584034901.5470105Example 695045402530145Comparative Example 188014101Comparative Example 288014301

[0066] Finished chains of Examples 1-6 and comparative chains of Comparative Examples 1-2 were collected, and property tests were conducted on them respectively to obtain the properties of the finished steels of each Example and Comparative Example.

[0067] Neutral salt spray corrosion test, tensile test and impact property test were conducted on the finished chains of Examples 1-6 and the comparative chains of Comparative Examples 1-2 as mentioned above, and the test results are listed in Table 3.

[0068] The specific testing methods for the aforementioned neutral salt spray corrosion test, tensile test and impact test are as follows: Neutral salt spray corrosion test was conducted through the following steps: 100 mm-long round steels were taken from the finished chains of Examples 1-6 and the comparative chains of Comparative Examples 1-2 as salt spray corrosion test specimens, with both end surfaces sealed with silicone rubber. 5 wt% NaCl salt spray corrosion tests were performed in accordance with the standard GB / T 10125 (test chamber temperature: 35°C, saturation barrel temperature: 47°C, corrosive medium: 5 wt% NaCl aqueous solution, pH=6.5, the test specimens were positioned at a 20° angle to the vertical direction, the test was performed for a test duration of 120 h with a continuous spraying mode, and the salt spray deposition rate was 1.5 mL / (h·80 cm 2< )). After 120 h of neutral salt spray test, the test specimens were taken out, the silicone rubber at both ends was stripped off, surface corrosion products were removed, and the specimens were blow-dried and weighed to record the mass as M'. The salt spray corrosion rate R of the test specimens of each Example and Comparative Example was then calculated: R=(M-M') / (S·T), wherein Mis the initial mass of the specimen in the unit of grams (g); M' is the mass of the specimen after removing corrosion products and blow-drying in the unit of grams (g); S is the corrosion test area of the specimen in the unit of square meters (m 2< ); T is the corrosion time in the unit of hours (h); the salt spray corrosion rate R is in the unit of g / m 2< ·h.

[0069] Tensile test: The finished chains of Examples 1-6 and the comparative chains of Examples 1-2 were sampled and prepared into tensile test specimens in accordance with the national standard GB / T 2975, and tensile property tests were conducted in accordance with the national standard GB / T 228.1 to determine the yield strength Rp 0.2 , tensile strength R m , elongation A and reduction of area Z of the finished chains of Examples 1-6 and the comparative chains of Comparative Examples 1-2.

[0070] Impact test: The finished chains of Examples 1-6 and the comparative chains of Examples 1-2 were sampled and prepared into impact test specimens according to national standard GB / T 2975, and impact property tests were conducted in accordance with the national standard GB / T 229 to determine the Charpy impact energy Akv at -20 °C of the finished chains of Examples 1-6 and the comparative chains of Comparative Examples 1-2.

[0071] Table 3 shows the property parameters of the finished chains of Examples 1-6 and the comparative chains of Comparative Examples 1-2. Table 3Yield strength R p0.2 (MPa)Tensile strength R m (MPa)Elongation A (%)Reduction of area Z (%)Charpy impact energy A kv at -20 °C (J)Salt spray corrosion rate (g / m 2< ·h)Example 11160127814.555670.11Example 21185128515521020.14Example 31076120118.565990.19Example 4108511921758850.15Example 51105125618.568790.13Example 6106611831862960.14Comparative Example 1110412891358512.61Comparative Example 297511531757771.79

[0072] As shown in Table 3, the finished chains of the Examples of the present disclosure exhibited excellent comprehensive properties, with a yield strength Rp 0.2 of 1066 - 1185 MPa, a tensile strength R m of 1183 - 1285 MPa, an elongation A of ≥ 14%, a reduction of area Z of ≥ 50%, and a Charpy impact energy Akv at -20 °C of ≥ 60 J.

[0073] As shown in Table 1 combined with Table 3, the contents of the alloying elements Ni, Cr, Mo, Si and V in the chemical composition of the comparative steels of Comparative Examples 1-2 failed to satisfy the requirement of 1.3Ni+2Cr+7Mo+0.5Si+V ≥ 8, thus failing to achieve the seawater corrosion resistance of the present disclosure.

[0074] As shown in Table 3, the neutral salt spray corrosion rate of the finished chains of Examples 1-6 of the present disclosure was ≤ 0.19 g / m 2< ·h, which was much lower than that of the comparative chains of Comparative Examples 1-2. It can be seen that the finished chains prepared from the chain steel of the present disclosure through preheating treatment and hot-dip galvanizing exhibited significantly better corrosion resistance than that of the existing comparative chains selected in Comparative Examples 1-2.

[0075] Figure 1 is a scanning electron microscope image of the microstructure of the chain steel in the chain manufactured in Example 1. As shown in Figure 1, in Example 1, the microstructure of the chain steel in the finished chain after quenching + hot-dip galvanizing treatment was acicular tempered martensite, with fine dispersed nanoscale carbides precipitated in the martensite matrix. The carbides had a size of less than 300 µm. The fine nanoscale carbides can significantly improve the strength and toughness of the steel, thereby obtaining chains with excellent properties.

[0076] In summary, the present disclosure improves the localized seawater corrosion resistance of the steel substrate through rational chemical composition design; meanwhile, the present disclosure combines the chain heat treatment with the subsequent galvanizing process to form an optimized quenching and hot-dip galvanizing process, thereby obtaining the chain with excellent properties. The chain according to the present disclosure has excellent comprehensive properties. The chain has not only high strength but also good toughness-plasticity matching, as well as excellent corrosion resistance, effectively solving the problem that the service life of existing chains is impaired due to the mismatch of strength, toughness, plasticity and corrosion resistance. The chain steel of the present disclosure can be fabricated into various high-performance industrial chains such as mining and mooring chains, which are widely applied in marine engineering, engineering machinery, mines and other scenarios requiring chains with high strength, high toughness and high corrosion resistance.

[0077] It should be noted that all the technical features described in the present disclosure can be freely combined in any ways unless contradicted with each other. Various modifications or variations may be made to the present disclosure without departing from the scope thereof. Such modifications or variations will be apparent to those skilled in the art. For example, a feature shown or described as part of one embodiment may be used with another embodiment to produce yet another embodiment. Therefore, the present disclosure is intended to cover such modifications and variations that fall within the scope of the appended claims and their equivalents.

Claims

1. A chain steel, comprising the following chemical elements in mass percentage: C: 0.25-0.35%, Si: 0.1-0.6%, Mn: 0.3-0.9%, Cr: 0.3-1.2%, Ni: 1.8-3.2%, preferably 1.8-2.95%, Mo: 0.39-1.0%, preferably 0.4-1.0%, more preferably 0.4-0.88%, Al: 0.02-0.05%, V: 0.08-0.30%, N: 0.009-0.02%, and the balance being Fe and inevitable impurities.

2. The chain steel according to claim 1, wherein the chain steel has a chemical composition satisfying the following relational expression: 1.3*Ni+2*Cr+7*Mo+0.5*Si+V ≥ 8, preferably 8 ≤ 1.3*Ni+2*Cr+7*Mo+0.5*Si+V ≤ 10.22, wherein Ni, Cr, Mo, Si and V respectively represent the numerical values preceding the % symbol of the mass percentage contents of corresponding elements.

3. The chain steel according to claim 1, wherein the inevitable impurities comprise P, S, and O, wherein P ≤ 0.015%, S ≤ 0.01%, and O ≤ 0.002%.

4. The chain steel according to claim 1, wherein the chain steel has a microstructure of acicular martensite.

5. The chain steel according to claim 1, wherein the chain steel has the following properties: a yield strength Rp0.2 of ≥ 1050 MPa, a tensile strength Rm of ≥ 1100 MPa, an elongation A of ≥ 14%, a reduction of area Z of ≥ 50%, a Charpy impact energy Akv at -20 °C of ≥ 60 J.

6. A chain comprising: the chain steel according to any one of claims 1 to 5, and a zinc coating coated on the chain steel.

7. The chain according to claim 6, wherein the zinc coating has a thickness of 10-150 µm, preferably 40-150 µm; and / or the chain steel has a microstructure of acicular tempered martensite and dispersed carbides; preferably, the carbides have a size of less than 300 nm.

8. The chain according to claim 6 or 7, wherein the chain has the following properties: a yield strength Rp0.2 of ≥ 1050 MPa, a tensile strength Rm of ≥ 1100 MPa, an elongation A of ≥ 14%, a reduction of area Z of ≥ 50%, a Charpy impact energy Akv at -20 °C of ≥ 60 J, a corrosion rate of ≤ 0.2 g / m2·h after 120 h of 5% NaCl neutral salt spray corrosion test.

9. A manufacturing method for the chain according to any one of claims 6 to 8, wherein the manufacturing method comprises the following steps performed in sequence: S1, smelting and casting molten steel to obtain a cast slab; S2, heating and rolling the cast slab, wherein a reduction ratio of the cast slab is ≥ 10; S3, forming rings and welding; S4, performing quenching heat treatment, wherein for the quenching heat treatment, a heating temperature is 840-980 °C, preferably 850-950 °C, a holding time is 1-4 hours, preferably 1-3 hours, and water cooling is performed for quenching; S5, performing pickling pretreatment to obtain a chain steel; S6, hot-dip galvanizing, wherein the chain steel after the pickling pretreatment is subjected to preheating treatment followed by hot-dip galvanizing to obtain the chain comprising the chain steel and a zinc coating formed on the surface of the chain steel; a temperature difference between a preheating temperature for the preheating treatment and a temperature of zinc bath used in the hot-dip galvanizing is controlled to -30 to 30 °C.

10. The manufacturing method according to claim 9, wherein in step S1, the smelting comprises electric furnace or converter smelting, LF refining, and VD or RH vacuum treatment; the casting is performed using a continuous casting process; preferably, the VD or RH vacuum treatment is performed for a time period of 10-20 min; during casting, a superheat degree of molten steel in tundish is controlled to 15-40 °C; in step S2, during heating and rolling, the cast slab is heated at a temperature of ≥ 1150 °C for a time period of 3-6 h, a finishing rolling temperature is ≥ 850 °C, and after rolling, air cooling or slow cooling is performed; in step S6, the preheating temperature is 400-550 °C, and a preheating time is ≥ 0.5 h; the temperature of zinc bath used in the hot-dip galvanizing is 400-530 °C.

11. The manufacturing method according to claim 9, wherein the zinc coating on the surface of the chain has a thickness of 10-150 µm, preferably 40-150 µm.

12. The manufacturing method according to claim 9, wherein the chain steel in the chain obtained in step S6 has a microstructure of acicular tempered martensite and dispersed carbides; preferably, the carbides have a size of less than 300 nm.

13. The manufacturing method according to claim 9, wherein the chain has the following properties: a yield strength Rp0.2 of ≥ 1050 MPa, a tensile strength Rm of ≥ 1100 MPa, an elongation A of ≥ 14%, a reduction of area Z of ≥ 50%, a Charpy impact energy Akv at -20 °C of ≥ 60 J; a corrosion rate of lower than 0.2 g / m2·h after 120 h of 5% NaCl neutral salt spray corrosion test.

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