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

Abstract

Disclosed in the present invention are a high-strength seawater-corrosion-resistant chain steel, a chain and a manufacturing method therefor. The chain steel comprises the following chemical components in percentage by mass: 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 iron and inevitable impurities. The chain of the present invention has high strength, and also good toughness-plasticity matching and good seawater corrosion resistance, and can effectively solve the problem of the service life of existing chains being affected by the mismatching of strength, toughness-plasticity and corrosion resistance.

Description

High-strength seawater corrosion-resistant chain steel, chain, and manufacturing method thereof Technical Field

[0001] The present invention relates to the technical field of chain steel and chains, and in particular to a high-strength seawater corrosion-resistant chain steel, a chain and a manufacturing method thereof. Background Art

[0002] Approximately one-sixth of the world's annual steel production is lost to corrosion. In my country, direct economic losses from steel corrosion exceed 10 billion yuan annually. Furthermore, steel corrosion reduces the service life of steel structures, causes casualties and economic losses, and contributes to environmental pollution. Chloride ions in seawater and surface air are particularly corrosive to steel during service. To improve the corrosion resistance of steel, coatings are often applied. While this effectively slows the corrosion process, surface defects in the coating can cause corrosion within the coating, leading to rapid failure. While stainless steel offers excellent corrosion resistance, the high cost associated with the addition of numerous alloying elements has limited its widespread application. Consequently, low-alloy corrosion-resistant steels, with their relatively low alloy content, excellent mechanical properties, and relatively good corrosion resistance, are attracting increasing attention. With the booming development of ocean shipping and marine engineering in my country, the demand for steel strength and corrosion resistance is increasing, leading to a growing demand for high-strength chain steel with excellent seawater corrosion resistance.

[0003] At present, many seawater corrosion-resistant steels have been developed both at home and abroad, mainly by optimizing the alloy elements such as Cr, Ni, and Cu in the steel to improve the seawater corrosion resistance of the steel. For example, Chinese Patent 1 (application number 201010266527.0) discloses an ultra-high-strength ship plate steel and a production method thereof. The slab composition is: 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 produced by controlled rolling and controlled cooling technology + subsequent heat treatment, with a tensile strength greater than 670 MPa and an impact energy greater than 200 J at -60°C. Chinese Patent 2 (application number 201180066512.2) discloses an ultra-high strength structural steel, the chemical composition of which is 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 iron and inevitable impurities; this technology adds a high content of Ni, Cu, Cr, and Mo alloying elements to a relatively low carbon content, adopts a hot rolling controlled cooling process, and directly quenches to a temperature not exceeding 450°C at a cooling rate of 20-150°C / s after hot rolling. The resulting steel has a yield strength greater than 960MPa and an impact energy of a -40°C welding heat-affected zone greater than 34J. Chinese Patent 3 (Application No. 201610993472.0) discloses a high-strength, high-toughness, corrosion-resistant chain steel, the chemical composition of which is 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%, the balance being Fe and inevitable Impurities; This technology adopts a process of two quenching heat treatments and one tempering heat treatment to obtain a lath martensite structure with a lath width of 0.3 to 5 μm. Granular cementite with a diameter of 0.2 to 0.8 μm and a volume fraction of 0.15% to 0.35% and MC phase particles with a diameter of 5 to 15 nm and a volume fraction of 0.02% to 0.08% are dispersed between and inside the laths; the tensile strength of the chain after heat treatment reaches 1000 MPa, the KV2 (-60°C) of the ring back and weld reaches more than 100 J, and the seawater corrosion resistance is good.

[0004] In addition, there are some weathering steel products for certain special service environments. For example, Chinese Patent 4 (application number 201611102046.X) discloses a high-strength weathering steel for high-humidity and high-heat marine atmospheric environment. Its chemical composition (wt%) is 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, and the rest is Fe; based on the Cu-Ni-Mo alloy system, this technology greatly reduces the Cr content in weathering steel by adding multiple microalloying elements such as Sn, Sb, Nb, RE, etc.; by controlling the cooling rate of the steel at 12~17℃ / s and cooling it to 530~570℃ for insulation after hot rolling, acicular ferrite and polygonal ferrite structures are formed, and the steel yield strength is greater than 650MPa and the tensile strength is greater than 750MPa, and the half-size impact energy at 30℃ is greater than 65J.

[0005] Referring to the above-mentioned prior art, it can be seen that existing seawater corrosion-resistant high-strength steel products mainly improve the seawater corrosion resistance of the base material by optimizing the alloy composition, and the yield strength is mostly around 600-900 MPa. There are very few high-strength seawater corrosion-resistant steel products with a yield strength exceeding 1000 MPa.

[0006] Based on this, the present invention aims to develop a new type of high-strength, seawater-corrosion-resistant chain steel. This chain steel combines chain heat treatment with coating processes, resulting in a finished chain with excellent overall performance. It not only exhibits high strength but also possesses an excellent balance between toughness and ductility. The chain also exhibits excellent corrosion resistance, effectively resolving the problem of existing chains that suffer from a mismatch between strength, toughness, ductility, and corrosion resistance, which limits their service life.

[0007] Summary of the Invention

[0008] To address the problem of existing chains' service life being impacted by a mismatch between strength, toughness, and ductility, as well as corrosion resistance, the present invention aims to provide a high-strength, seawater-corrosion-resistant chain steel, a chain, and a method for manufacturing the same. Specifically, by designing the components and optimizing the manufacturing process, the present invention achieves high strength, combined with a good toughness-ductility match and excellent seawater corrosion resistance. This makes the high-strength, seawater-corrosion-resistant chain steel particularly suitable for manufacturing high-strength, corrosion-resistant structural components, industrial products for mining, mooring, and other applications, and can be widely used in environments with a high concentration of corrosive media, such as engineering machinery, mining, shipbuilding, and marine engineering.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] A first aspect of the present invention provides a chain steel, which contains the following chemical components in percentage by mass: 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 is iron and unavoidable impurities.

[0011] Preferably, the chemical composition of the chain steel satisfies the following formula: 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 are the values ​​before the percentage sign of the mass percentage content of the corresponding elements.

[0012] Preferably, among the unavoidable impurities, P≤0.015%, S≤0.01%, and O≤0.002%.

[0013] Preferably, the microstructure of the chain steel is acicular martensite.

[0014] Preferably, the chain steel has the following properties: yield strength Rp 0.2 ≥1050MPa, tensile strength R m ≥1100MPa, elongation A≥14%, section shrinkage Z≥50%, -20℃ Charpy impact energy A kv ≥60J.

[0015] A second aspect of the present invention provides a chain comprising: the above-mentioned chain steel and a galvanized layer coated on the chain steel.

[0016] Preferably, the thickness of the galvanized layer is 10-150 μm, preferably 40-150 μm; and / or the microstructure of the chain steel is acicular tempered martensite and dispersed carbides; preferably, the carbide size is less than 300 nm.

[0017] Preferably, the performance of the chain satisfies the following: Rp 0.2 ≥1050MPa, tensile strength R m ≥1100MPa, elongation A≥14%, section shrinkage Z≥50%, -20℃ Charpy impact energy A kv ≥60J; after 120h of 5% NaCl neutral salt spray corrosion test, the corrosion rate is ≤0.2g / m 2 .h.

[0018] A third aspect of the present invention provides a method for manufacturing a chain, the method comprising the following steps performed in sequence:

[0019] S1, smelting and casting molten steel to produce ingots;

[0020] S2, hot rolling the cast slab, wherein the compression ratio of the cast slab is ≥10;

[0021] S3, ring welding;

[0022] S4, quenching heat treatment, the heating temperature of the quenching heat treatment is 840-980°C, preferably 850-950°C, the holding time is 1-4 hours, preferably 1-3 hours, and water cooling quenching is adopted;

[0023] S5, pickling pretreatment to produce chain steel;

[0024] S6, hot-dip galvanizing, the chain steel after the pickling pretreatment is preheated and then hot-dip galvanized to obtain a chain including chain steel and a galvanized layer formed on the surface of the chain steel, and the temperature difference between the preheating temperature of the preheating treatment and the galvanizing liquid used for the hot-dip galvanizing is controlled to be -30 to 30°C.

[0025] Preferably, in the step S1, the smelting includes electric furnace or converter smelting, LF refining, VD or RH vacuum treatment; and the casting adopts a continuous casting process.

[0026] Preferably, in step S1, the vacuum treatment time of the VD or RH vacuum treatment is 10 to 20 minutes; and during the casting process, the superheat of the molten steel in the tundish is controlled to be 15 to 40°C.

[0027] Preferably, in step S2, during the heating and rolling process, the heating temperature of the ingot is ≥1150°C, the heating time is 3 to 6 hours, the final rolling temperature is ≥850°C, and air cooling or slow cooling is adopted after rolling.

[0028] Preferably, in step S6, the preheating temperature is 400-550°C, and the preheating time is ≥0.5h; and the temperature of the galvanizing solution used in the hot-dip galvanizing is 400-530°C.

[0029] Preferably, the thickness of the zinc plating layer is 10 to 150 μm, preferably 40 to 150 μm.

[0030] Preferably, the microstructure of the chain steel in the chain obtained in step S6 is needle-shaped tempered martensite and dispersed carbides; preferably, the carbide size is less than 300 nm.

[0031] Preferably, the performance of the chain meets the following requirements: yield strength Rp0.2 ≥1050MPa, tensile strength Rm ≥1100MPa, elongation A ≥14%, section shrinkage Z ≥50%, -20℃ Charpy impact energy Akv ≥60J; after 120h of 5% NaCl neutral salt spray corrosion test, the corrosion rate is less than 0.2g / m 2 .h.

[0032] In the high strength seawater corrosion resistant chain steel of the present invention, the design principle of each chemical element is as follows: In this article, unless otherwise explicitly stated, the element content is calculated in mass percentage.

[0033] C: C is an element necessary to ensure the strength of steel. Increasing the C content in steel will increase the steel's ability to undergo non-equilibrium structural transformations, thereby significantly improving the steel's strength. In the present invention, the diffusion of C in steel can be suppressed by a quenching heat treatment process to form a shear-type martensitic phase transformation, thereby significantly improving the steel's strength. However, for the present invention, the C content in the steel should not be too high. Excessive C content will have an adverse effect on the plasticity and toughness of the steel, and will significantly increase the carbon equivalent of the material, deteriorating the steel's welding performance. Based on this, in the high-strength seawater corrosion-resistant chain steel of the present invention, the mass percentage of C is controlled to be between 0.25% and 0.35%.

[0034] Si: Si element can be dissolved in steel and play a role of solid solution strengthening, which can significantly improve the yield strength, fatigue strength and hardness of steel. During the corrosion process, Si mainly exists in spinel oxides as divalent oxides, making the inner rust layer dense and hindering Cl - Infiltration improves the steel's marine corrosion resistance. Si has a very low solubility in cementite, so the Si content in the steel should not be too high. Excessive Si content in the steel not only forms a carbide-free bainite structure but also increases the steel's brittleness. Therefore, in the high-strength seawater corrosion-resistant chain steel of the present invention, the mass percentage of Si is controlled between 0.1% and 0.6%.

[0035] Mn: The Mn element can improve the stability of austenite in steel and at the same time improve the hardenability of steel. In addition, Mn can also improve the strength of martensite in steel through solid solution strengthening, thereby improving the strength of steel. However, it should be noted that the Mn content in steel should not be too high. When the Mn content in steel is too high, it will make the austenite grains grow easily during quenching heating and promote the segregation of harmful elements at the grain boundaries. Based on this, in the high-strength seawater corrosion-resistant chain steel of the present invention, the mass percentage of the Mn element is controlled between 0.3 and 0.9%.

[0036] Cr: Adding an appropriate amount of Cr element can improve the hardenability of steel and has a secondary hardening effect. It can form a hardened martensite structure, which is beneficial to improving the strength of steel. In addition, Cr carbide can slow down the grain growth in the heat-affected zone at the weld joint, which is very beneficial for the welding of steel. Adding an appropriate amount of Cr and Ni elements to the steel is beneficial to improving the corrosion resistance of the steel and promoting the formation of a passivation film on the surface of the steel. When there is a certain content of Cr, the corrosion resistance of the steel is significantly improved. However, the Cr content in the steel should not be too high. When the Cr content in the steel is too high, a large amount of carbides will be generated and aggregated at the grain boundaries, reducing the toughness of the material and significantly increasing the carbon equivalent, deteriorating the welding performance of the high-strength seawater corrosion-resistant chain steel. Based on this, in the high-strength seawater corrosion-resistant chain steel of the present invention, the mass percentage of the Cr element is controlled between 0.3 and 1.2%.

[0037] Nickel: Nickel is an austenite-forming element and one of the primary strengthening elements. It can exist in steel as a solid solution and can dissolve infinitely with iron, providing resistance to acid, alkali, atmospheric air, and salt corrosion. During corrosion, nickel replaces iron ions with divalent ions to form the relatively stable spinel NiFe2O4 compound. When used in combination with Cr, nickel significantly improves the hardenability of the steel. Furthermore, adding an appropriate amount of nickel to steel can reduce the carbon content at the eutectoid point, strengthen ferrite, and refine and increase pearlite, thereby increasing the steel's strength without significantly affecting its ductility. Ni enhances steel's fatigue resistance, reduces its notch sensitivity, lowers its low-temperature brittle transition temperature, and improves its impact toughness. Furthermore, while nickel enhances steel's strength, it does so with less detriment to its toughness, ductility, and other processing properties than other alloying elements. Based on this, in the high-strength seawater corrosion-resistant chain steel of the present invention, the mass percentage of Ni element is controlled between 1.8 and 3.2%, preferably between 1.8 and 2.95%.

[0038] Mo: The Mo element mainly exists in the steel in the form of solid solution. It can play a solid solution strengthening effect, which is beneficial to improve the hardenability of the steel and form martensite in the quenching process. At the same time, the Mo element can also improve the corrosion resistance to organic acids, sulfuric acid and sulfates, etc., and can passivate the steel surface in 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 too high. When the Mo content in the steel is too high, it will significantly increase the carbon equivalent of the material, which is not conducive to the welding performance of the steel. In addition, Mo is also a precious alloying element. Adding excessive Mo will also lead to an increase in the cost of the alloy. Based on this, in the high-strength seawater corrosion-resistant chain steel of the present invention, the mass percentage of the Mo element is controlled between 0.39 and 1.0%, preferably 0.4 to 1.0%, and more preferably 0.4 to 0.88%.

[0039] Al: Al's primary function is deoxidation and nitrogen fixation. The AlN formed by Al combining with N effectively refines grains. However, it's important to note that the Al content in steel should not be too high. Excessive Al content can affect the steel's casting properties and compromise its toughness. Therefore, in the high-strength, seawater-corrosion-resistant chain steel of the present invention, the mass percentage of Al is controlled between 0.02% and 0.05%.

[0040] V: As a strong carbide-forming element, vanadium can significantly increase the strength of steel through dispersed precipitation. Vanadium can also improve the steel's resistance to pitting corrosion. However, it should be noted that excessive addition of vanadium to steel can reduce the steel's toughness and weldability. For this reason, the mass percentage of vanadium in the high-strength seawater-corrosion-resistant chain steel of the present invention is controlled between 0.08% and 0.30%.

[0041] N: N is an austenite-forming element and also a MX-type precipitate-forming element. To prevent N from accumulating in the steel, excessive N addition is not recommended. Therefore, the N content must be strictly controlled. In the high-strength, seawater-corrosion-resistant chain steel of the present invention, the N content is controlled to between 0.009% and 0.02% by weight.

[0042] The present invention rationally designs the main alloying elements and fully utilizes the effects of various alloying elements and the interactions therebetween on the microstructure, mechanical properties and corrosion resistance, thereby precisely controlling the microstructure of the steel of the present invention. This ensures that when the chain steel of the present invention is hot-dip galvanized to form a chain, a mixed microstructure of needle-shaped tempered martensite and dispersed carbides is formed in the chain steel, thereby improving the chain steel's resistance to localized seawater corrosion. This ensures that the chain of the present invention has both high strength and toughness-plasticity matching, as well as good seawater corrosion resistance.

[0043] In a preferred embodiment, in the high-strength seawater corrosion-resistant chain steel of the present invention, among the inevitable impurities, P≤0.015%, S≤0.01%, and O≤0.002%.

[0044] In the above technical solution, P, S and O are all impurity elements in steel. If technical conditions permit, in order to obtain high-strength seawater corrosion-resistant chain steel with better performance and higher quality, the content of impurity elements in the material should be reduced as much as possible.

[0045] In the present invention, both P and S are unavoidable harmful impurity elements in steel and both deteriorate the properties of the steel. Although P can improve the weather resistance of steel, its side effects are generally greater. Therefore, in the present invention, the P element is controlled to satisfy: P≤0.015%, and the S element is controlled to satisfy: S≤0.01%.

[0046] In the present invention, the impurity element O may form oxides and complex inclusions with deoxidizing elements such as Al in the steel, which is not conducive to the performance of the steel. Therefore, in the present invention, the O element is controlled to meet the following requirements: O≤0.002%.

[0047] Of course, in some other embodiments, other harmful elements may be present in the steel, such as As, Pb, Sn, Sb, Bi and the like. Under the requirements of national laws, regulations and standards, the content of these harmful elements should be reduced as much as possible.

[0048] During use, the chain's coating may wear and fall off, exposing the steel substrate to localized seawater corrosion, affecting the chain's safe use. To improve the steel's resistance to localized seawater corrosion, the contents of the alloying elements Ni, Cr, Mo, Si, and V, which are the main elements responsible for improving resistance to localized seawater corrosion, must satisfy the following formula: 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 are the values ​​preceding the percentage sign of the corresponding element's mass percentage content.

[0049] The study found that when the content of Ni, Cr, Mo, Si and V in the steel, which are alloying elements resistant to localized corrosion in seawater, meets 1.3*Ni+2*Cr+7*Mo+0.5*Si+V≥8, the steel matrix has excellent resistance to localized corrosion in seawater. Combined with the steel surface coating, it can greatly reduce the corrosion rate of the steel in seawater environments. When the content of Ni, Cr, Mo, Si and V in the steel is 1.3*Ni+2*Cr+7*Mo+0.5*Si+V and is lower than 8, the steel's resistance to localized corrosion is greatly reduced. When the chain coating fails due to localized wear, obvious localized corrosion defects will appear in the exposed steel matrix, causing localized stress concentration in the chain, which directly affects the chain's service life.

[0050] Compared with the existing production technology, the present invention has the following beneficial effects:

[0051] 1. The present invention adopts a reasonable chemical composition design, fully considering the interaction between the content of each alloy element and the chain steel's resistance to local corrosion in seawater, thereby improving the chain steel's resistance to local corrosion in seawater. The present invention fully utilizes the influence of various alloy elements and the chain's processing technology on the microstructure by coordinating and optimizing the manufacturing process, and accurately controls the microstructure of the chain steel of the present invention. After quenching heat treatment, the chain steel forms a needle-shaped martensite structure. Through preheating treatment and hot-dip galvanizing treatment of the chain, on the one hand, fine carbides can be dispersed and precipitated in the supersaturated solid solution formed by quenching the chain steel, thereby improving the performance of the chain steel; at the same time, a galvanized layer (or zinc layer) of a certain thickness can be formed on the surface of the chain steel, and the chain coating can improve the chain's resistance to seawater corrosion. When the chain coating fails due to wear, the chain steel matrix's anti-local corrosion design can reduce local pitting corrosion of the steel, thereby improving the chain steel's resistance to seawater corrosion.

[0052] 2. After the chain steel surface is coated with a galvanized layer, the present invention can isolate the seawater corrosive medium from contacting the chain steel, thereby improving the corrosion resistance of the chain. When the coating on some areas of the chain is worn, the anti-local corrosion design of the steel substrate can prevent local excessive corrosion during the use of the chain, thereby increasing the service life of the chain.

[0053] 3. The chemical composition and process design of the chain steel of the present invention are reasonable, and the process window is wide, which can realize batch commercial production;

[0054] 4. The chain steel of the present invention has excellent high strength and toughness and good resistance to local corrosion in seawater. It can be made into high-strength and corrosion-resistant structural parts and various high-performance industrial chains such as mining and mooring. It is widely used in engineering machinery, mining and marine engineering and other occasions that require high-strength, toughness and corrosion-resistant steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0056] FIG1 is a scanning electron microscope image of the chain steel manufactured in Example 1 of the present invention. DETAILED DESCRIPTION

[0057] In order to better understand the above technical solution of the present invention, the technical solution of the present invention is further described below in conjunction with Figure 1 and an embodiment.

[0058] The present invention provides a high-strength and high-seawater corrosion-resistant chain steel, which, in addition to containing Fe and inevitable impurities, also contains the following chemical components by 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%, and N: 0.009-0.02%.

[0059] The present invention improves the chain steel's resistance to localized seawater corrosion by rationally designing the main alloying elements and making full use of the effects of various alloying elements and their interactions on the microstructure, mechanical properties, and corrosion resistance. An optimized quenching and coating process is used to precisely control the steel's microstructure, ensuring that the high-strength seawater-corrosion-resistant chain steel forms a mixed structure of needle-shaped tempered martensite and dispersed carbides. The resulting high-strength chain has both high strength and toughness-plasticity matching, and good seawater corrosion resistance.

[0060] In a specific embodiment, the composition of the high-strength seawater corrosion-resistant chain steel meets the following requirements: 1.3*Ni+2*Cr+7*Mo+0.5*Si+V≥8, where Ni, Cr, Mo, Si, and V are the values ​​before the percentage sign of the mass percentage content of the corresponding elements.

[0061] In this high-strength seawater corrosion-resistant chain steel, when the pitting-resistant alloying elements Ni, Cr, Mo, Si, and V content in the steel meet 1.3*Ni+2*Cr+7*Mo+0.5*Si+V≥8, the steel exhibits excellent resistance to localized seawater corrosion. Combined with its surface coating, it can significantly reduce its corrosion rate in seawater environments. When the Ni, Cr, Mo, Si, and V content in the steel (1.3*Ni+2*Cr+7*Mo+0.5*Si+V) is less than 8, the steel's resistance to localized seawater corrosion is significantly reduced. When the chain coating exhibits localized wear and failure, the exposed steel substrate will develop obvious localized corrosion defects upon contact with seawater, causing localized stress concentration in the chain, directly affecting the chain's service life.

[0062] In the present invention, P, S, and O are all impurity elements in steel. To obtain high-strength steel with better performance and quality, the content of these impurity elements in the material should be reduced as much as possible, provided that technical conditions permit. P and S are both unavoidable harmful impurity elements in steel, and both deteriorate the properties of the steel. Although P can improve the weather resistance of steel, its side effects are generally greater. O can form oxides and complex inclusions with deoxidizing elements such as Al in steel, which are detrimental to the performance of the steel. Therefore, among the unavoidable impurities, P ≤ 0.015%, S ≤ 0.01%, and O ≤ 0.002%.

[0063] In a specific embodiment, the microstructure of the high-strength seawater corrosion-resistant chain steel is acicular martensite.

[0064] The performance of the high strength seawater corrosion resistant chain steel meets the following requirements: Yield strength Rp 0.2 ≥1050MPa, tensile strength R m ≥1100MPa, preferably ≥1150MPa, more preferably ≥1183MPa, most preferably ≥1200MPa, elongation A ≥14%, section shrinkage Z ≥50%, -20℃ Charpy impact energy A kv ≥60J, preferably ≥79J.

[0065] The present invention provides a chain made of the above-mentioned high-strength seawater corrosion-resistant chain steel, whose performance meets the following requirements: Rp 0.2 ≥1050MPa, tensile strength R m ≥1100MPa, preferably ≥1150MPa, more preferably ≥1183MPa, most preferably ≥1200MPa, elongation A ≥14%, section shrinkage Z ≥50%, -20℃ Charpy impact energy A kv ≥60J, preferably ≥79J; after 120h of 5% NaCl neutral salt spray corrosion test, the corrosion rate is ≤0.2g / m 2 .h.

[0066] The chain manufacturing method of the present invention is simple to produce, and the obtained high-strength seawater corrosion-resistant chain has excellent high strength and toughness and good seawater corrosion resistance. The manufacturing method specifically includes the following steps.

[0067] S1, smelting and casting. Specifically, the smelting operation includes electric furnace or converter smelting, LF refining, VD or RH vacuum treatment; that is, smelting is carried out in an electric furnace or converter, and undergoes LF refining, VD or RH vacuum treatment. Among them, the vacuum treatment time is 10 to 20 minutes, and the steel is tapped for casting after the chemical composition meets the requirements of the high-strength seawater corrosion-resistant chain steel designed by the present invention. Accordingly, in the casting process, a continuous casting process is adopted to cast the ingot, and the superheat of the molten steel in the tundish is controlled at 15 to 40°C, and finally the ingot whose chemical composition meets the requirements of the high-strength seawater corrosion-resistant chain steel is obtained.

[0068] S2, hot rolling, wherein the compression ratio of the ingot is ≥10. Specifically, the ingot is first heated in a heating furnace, then removed from the furnace, and then dephosphorized with high-pressure water. Finally, rolling begins, and the ingot is finally rolled into round steel of finished size. The heating temperature of the ingot is controlled to be ≥1150°C, the heating time is 3 to 6 hours, and the final rolling temperature is ≥850°C. After rolling, the ingot is air-cooled or slowly cooled to room temperature. The compression ratio of the ingot is ≥10. The finished size of the round steel obtained is Φ26 to 150 mm, preferably Φ30 to 150 mm.

[0069] S3, ring welding: The rolled round steel is cut into fixed lengths, then braided into single rings on a braiding machine, and finally flash welded into complete rings to obtain a chain-like matrix.

[0070] S4, quenching heat treatment. The quenching heat treatment can be performed at a temperature of 840-980°C, with a holding time of 1-4 hours, using water-cooling quenching. Specifically, the chain-shaped substrate of the ring-welded chain is quenched at a temperature of 850-950°C, with a holding time of 1-3 hours, followed by water-cooling quenching. When the ring-welded chain-shaped substrate is heated at high temperature, fine austenite grains are formed in the steel, with an austenite grain size of ≥7. After water-cooling quenching, the chain steel structure transforms from the high-temperature austenite structure to a fine, acicular martensite structure.

[0071] S5, Pickling Pretreatment: The chain-shaped substrate after quenching heat treatment is pickled to remove the oxide scale on the chain surface after quenching, thereby obtaining chain steel. Preferably, a layer of flux is applied to the surface of the chain steel to maintain a certain degree of activity on the chain surface after pickling, prevent oxidation of the chain steel during subsequent preheating, and enhance the bonding strength between the zinc coating and the chain steel. It should be noted that the flux in the present invention is a commonly used additive for zinc plating in the art and is commercially available.

[0072] S6, hot-dip galvanizing. After pickling, the chain steel is preheated and then hot-dip galvanized to produce a high-strength chain resistant to seawater corrosion. The difference between the preheating temperature and the galvanizing bath temperature is controlled to be -30 to 30°C.

[0073] Specifically, the chain steel after pickling pretreatment is hot-dip galvanized. In order to prevent problems such as zinc explosion during the subsequent hot-dip galvanizing process, it is preferred to preheat the chain steel before hot-dip galvanizing to obtain a high-strength seawater corrosion-resistant chain. The temperature difference between the preheating temperature and the galvanizing solution used for hot-dip galvanizing is controlled to be -30 to 30°C. For example, the preheating temperature may be 400 to 550°C, and the preheating time may be ≥0.5h. The temperature of the galvanizing solution used for hot-dip galvanizing may be 400 to 530°C. The thickness of the galvanized layer on the surface of the high-strength seawater corrosion-resistant chain may be 10 to 150 μm, preferably 40 to 150 μm.

[0074] During the hot-dip galvanizing process, fine carbides begin to precipitate from the chain steel's supersaturated acicular martensite, causing a slight decrease in strength but an increase in elongation and impact toughness. The fine acicular martensite facilitates the precipitation of fine, dispersed carbides from the steel during hot-dip galvanizing. These carbides are less than 300nm in size, resulting in a high-strength, seawater-corrosion-resistant chain with excellent toughness.

[0075] The microstructure of the chain manufactured above is needle-shaped tempered martensite and dispersed carbides; wherein the size of the carbides is less than 300nm.

[0076] The performance of the above chain meets the following requirements: Yield strength Rp 0.2 ≥1050MPa, tensile strength Rm ≥1100MPa, preferably ≥1150MPa, more preferably ≥1183MPa, most preferably ≥1200MPa, elongation A ≥14%, cross-sectional shrinkage Z ≥50%, -20℃ Charpy impact energy Akv ≥60J, preferably ≥79J; after 120h of 5% NaCl neutral salt spray corrosion test, its corrosion rate is less than 0.2g / m 2 .h.

[0077] The present invention makes full use of the influence of various alloying elements and manufacturing processes on microstructure and corrosion resistance through the rational design of alloying elements and the optimization of manufacturing processes, accurately controls the microstructure of high-strength seawater corrosion-resistant chain steel, and improves the local corrosion resistance of the chain steel matrix in seawater. The chain steel has a needle-shaped martensite structure. By hot-dip galvanizing the chain steel, on the one hand, fine and dispersed carbides can be precipitated from the chain steel during hot-dip galvanizing, thereby improving the strength and toughness of the chain; on the other hand, a zinc layer of a certain thickness can be formed on the surface of the chain steel. Combined with the anti-pitting corrosion component design of the steel matrix, the seawater corrosion resistance of the chain is improved by the zinc layer. When the zinc layer in the chain fails due to wear, the seawater local corrosion resistance design of the chain steel can reduce local corrosion of the steel, thereby improving the seawater corrosion resistance of the chain.

[0078] In the chain manufacturing method of the present invention, the quenching and tempering process of the traditional chain is combined with the hot-dip galvanizing process, which saves the tempering process of the chain and fully utilizes the precipitation of carbides in the chain steel during the hot-dip galvanizing process, thereby achieving efficient production of high-strength seawater corrosion-resistant chains, so that the high-strength seawater corrosion-resistant chain steel and the chain of the present invention have higher strength and toughness-plasticity matching, and have good corrosion resistance.

[0079] The following is a further description of the high-strength seawater corrosion-resistant chain steel and chain and its manufacturing method of the present invention with reference to specific examples. It should be understood that the following examples are only used to describe the specific embodiments of the present disclosure and are not intended to limit the scope of protection of the present disclosure.

[0080] Example

[0081] Examples 1-6

[0082] With reference to Table 1, Table 2-1 and Table 2-2, the manufacturing method of the chain steel and chain of Examples 1-6 sequentially adopts the following steps:

[0083] (1) Smelting and continuous casting are performed according to the chemical composition shown in Table 1 below to obtain ingots. The smelting can be performed in an electric furnace or a converter, followed by LF refining and VD or RH vacuum treatment. The VD or RH vacuum treatment lasts for 10 to 20 minutes. Steel is then tapped after the composition meets the requirements. Continuous casting can then be used to form ingots. During the continuous casting process, the superheat of the molten steel in the tundish is controlled at 15 to 40°C.

[0084] (2) Hot rolling: The ingot is first heated in a heating furnace, dephosphorized with high-pressure water, and finally rolled into finished round steel. The finished product size ranges from Φ30 to 150 mm, and the compression ratio of the ingot is ≥10. During the rolling process, the ingot heating temperature is controlled to be ≥1150°C, the heating time is 3 to 6 hours, and the final rolling temperature is ≥850°C. After rolling, the ingot is air-cooled or slowly cooled to room temperature.

[0085] (3) Ring welding: The obtained round steel is cut into fixed lengths, then braided into single rings on a braiding machine, and finally flash welded into a chain-like matrix of complete rings.

[0086] (4) Quenching heat treatment: The chain-shaped base after ring welding is subjected to quenching heat treatment, and the heating temperature of the quenching heat treatment is controlled to be 840-980°C, and the holding time is 1-4 hours; followed by water cooling quenching.

[0087] (5) Pickling pretreatment: The chain-like substrate after quenching heat treatment is pickled and pretreated to remove the oxide scale on the chain surface. The chain-like substrate after pickling pretreatment is then preheated to prevent problems such as zinc explosion during the subsequent hot-dip galvanizing process. The preheating temperature of the chain is 400-550°C, and the preheating time is ≥0.5h. The temperature difference between the preheating temperature of the preheating treatment and the galvanizing solution used in the subsequent hot-dip galvanizing is controlled at -30°C to 30°C.

[0088] (6) Hot-dip galvanizing: The chain-shaped substrate after preheat treatment and pickling is hot-dip galvanized, the zinc liquid temperature is 400-530°C, and the thickness of the zinc coating on the surface of the chain is controlled to be 10-150 μm, thereby obtaining a chain including chain steel and the zinc coating on the surface of the chain steel.

[0089] As shown in Table 1, Table 2-1, and Table 2-2, the chemical composition design and related process parameters of the chain steel prepared in Examples 1-6 all meet the design specification requirements of the present invention.

[0090] Comparative Example 1-2

[0091] The comparative steels used in Comparative Examples 1-2 are finished steel products from different manufacturers. Their chemical compositions are shown in Table 1. Their manufacturing processes differ from those of Examples 1-6. The heat treatment parameters used in Comparative Examples 1-2 are shown in Tables 2-1 and 2-2. The tempering temperatures and times in Table 2-2 refer to the tempering process used in Comparative Examples 1-2.

[0092] Table 1 shows the chemical compositions of the chain steels of Examples 1-6 and the comparative steels of Comparative Examples 1-2.

[0093] Table 1 (wt.%, the balance is Fe and other impurities except P and S)

[0094] Table 2-1 and Table 2-2 show the process parameters of the finished chains of Examples 1-6 and the comparative chains of Comparative Examples 1-2 during the preparation process.

[0095] Table 2-1

[0096] Table 2-2

[0097] The finished chains of Examples 1-6 and the comparative chains of Comparative Examples 1-2 were collected and performance tests were performed on each of them to obtain the performance of the finished steel of each Example and Comparative Example;

[0098] The finished chains of Examples 1-6 and the comparative chains of Comparative Examples 1-2 were subjected to a neutral salt spray corrosion test, a tensile test, and an impact performance test, respectively, and the test results are listed in Table 3.

[0099] The specific detection methods for relevant neutral salt spray corrosion test, tensile test and impact test are as follows:

[0100] (1) The neutral salt spray corrosion test was carried out by the following steps: 100 mm long round steel was taken from the finished chains of Examples 1-6 and the comparative chains of Comparative Examples 1-2 as salt spray corrosion specimens, both end faces were sealed with silicone rubber, and a 5 wt% NaCl salt spray corrosion test was carried out in accordance with GB / T 10125 (laboratory temperature 35°C, saturated barrel temperature 47°C, corrosive medium 5 wt.% NaCl aqueous solution, pH = 6.5, the test sample was longitudinally at an angle of 20°, the test time was 120 h, continuous spraying was adopted, and the salt spray deposition rate was 1.5 mL / (h·80 cm 2 )). After the 120h neutral salt spray test, the test sample was taken out, the silicone rubber at both ends was peeled off, the surface corrosion products were removed, and the sample was weighed after drying, and the mass was recorded as M'. The salt spray corrosion rate R of each embodiment and comparative example sample was then calculated: R = (M-M') / (S·T); wherein M is the initial mass of the sample, with the dimension of g; M' is the mass of the sample after the corrosion products are removed and dried, with the dimension of g; S is the corrosion test area of ​​the sample, with the dimension of m 2 ; T is the corrosion time, the dimension is h; the salt spray corrosion rate R is g / m 2 .h.

[0101] Tensile test: The finished chains of Examples 1-6 and the comparative chains of Comparative Examples 1-2 were sampled and made into tensile specimens according to the national standard GB / T 2975. The tensile performance test was carried out according to the national standard GB / T 228.1 to measure the yield strength Rp of the finished chains of Examples 1-6 and the comparative chains of Comparative Examples 1-2. 0.2 , tensile strength R m , elongation A and cross-sectional shrinkage Z.

[0102] Impact test: The finished chains of Examples 1-6 and the comparative chains of Examples 1-2 were sampled and made into impact specimens according to the national standard GB / T2975. The impact performance test was carried out according to the national standard GB / T 229 to measure the Charpy impact energy A of the finished chains of Examples 1-6 and the comparative chains of Comparative Examples 1-2 at -20°C. kv .

[0103] Table 3 shows the performance parameters of the finished chains of Examples 1-6 and the comparative chains of Comparative Examples 1-2.

[0104] Table 3

[0105] As shown in Table 3, the comprehensive performance of the finished chain in the embodiment of the present invention is excellent, and its yield strength Rp 0.2 Between 1066 and 1185 MPa, the tensile strength R m Between 1183 and 1285 MPa, elongation A≥14%, section shrinkage Z≥50%, -20℃ Charpy impact energy A kv ≥60J.

[0106] As shown in Table 1 and Table 3, the contents of alloying elements Ni, Cr, Mo, Si, and V in the chemical composition of the comparative steel in Comparative Examples 1-2 cannot meet 1.3Ni+2Cr+7Mo+0.5Si+V≥8, and the seawater corrosion resistance of the present technology cannot be achieved.

[0107] As shown in Table 3, the neutral salt spray corrosion rate of the finished chains of Examples 1-6 of the present invention is ≤0.19g / m 2 h, which is much lower than the neutral salt spray corrosion rate of the comparative chain in Comparative Examples 1-2. Therefore, it can be seen that the corrosion resistance of the finished chain obtained by preheating and hot-dip galvanizing the chain steel of the present invention is significantly better than that of the existing comparative chain selected in Comparative Examples 1-2.

[0108] 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, the microstructure of the chain steel in the finished chain manufactured in Example 1 after quenching and hot-dip galvanizing is characterized by needle-shaped tempered martensite, with fine, dispersed nano-sized carbides precipitated within the martensite matrix. The carbides are less than 300 μm in size. These fine nano-sized carbides significantly enhance the strength and toughness of the steel, resulting in a chain with excellent performance.

[0109] In summary, the present invention improves the ability of the steel matrix to resist local corrosion in seawater by a reasonable chemical composition design, and combines the chain heat treatment and the subsequent galvanizing process to form an optimized quenching and hot-dip galvanizing process, thereby obtaining a chain with excellent performance. The chain of the present invention has excellent comprehensive performance. It not only has high strength, but also has excellent toughness and plasticity matching. It is made into a chain with excellent corrosion resistance, which can well solve the problem of the existing chain that the service life is affected by the mismatch of strength, toughness, plasticity and corrosion resistance. The chain steel of the present invention can be made into various high-performance industrial chains such as mooring and mining, and is widely used in marine engineering, engineering machinery, mines and other occasions that require high-strength, high-toughness and high-corrosion-resistant chains.

[0110] It should be noted that all technical features described in this application can be freely combined or combined in any way unless there is a contradiction between them. Various modifications and variations can be made to the present invention without departing from the scope of the present invention, which will be apparent to those skilled in the art. For example, a feature shown or described as part of one embodiment can be used together with another embodiment to produce another embodiment. Therefore, the present invention is intended to encompass these modifications and variations that fall within the scope of the appended claims and their equivalents.

Claims

1. A chain steel, characterized in that: The chain steel contains the following chemical components 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 is iron and unavoidable impurities.

2. The chain steel according to claim 1, characterized in that: The chemical composition of the chain steel satisfies the following formula: 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 are the values ​​before the percentage sign of the mass percentage content of the corresponding elements.

3. The chain steel according to claim 1, characterized in that: Among the unavoidable impurities, P≤0.015%, S≤0.01%, and O≤0.002%.

4. The chain steel according to claim 1, characterized in that: The microstructure of the chain steel is acicular martensite.

5. The chain steel according to claim 1, characterized in that: The properties of the chain steel meet the following requirements: yield strength Rp 0.2 ≥1050MPa, tensile strength R m ≥1100MPa, elongation A≥14%, section shrinkage Z≥50%, -20℃ Charpy impact energy A kv ≥60J.

6. A chain comprising: The chain steel according to any one of claims 1 to 5 and a galvanized layer coated on the chain steel.

7. The chain according to claim 6, characterized in that The thickness of the galvanized layer is 10-150 μm, preferably 40-150 μm; and / or the microstructure of the chain steel is needle-shaped tempered martensite and dispersed carbides; preferably, the size of the carbides is less than 300 nm.

8. The chain according to claim 6 or 7, characterized in that: The performance of the chain meets the following requirements: Rp 0.2 ≥1050MPa, tensile strength R m ≥1100MPa, elongation A≥14%, section shrinkage Z≥50%, -20℃ Charpy impact energy A kv ≥60J; After 120h of 5% NaCl neutral salt spray corrosion test, the corrosion rate is ≤ 0.2g / m 2 .h.

9. A method for manufacturing a chain as claimed in any one of claims 6 to 8, characterized in that: The manufacturing method comprises the following steps performed in sequence: S1, smelting and casting molten steel to obtain ingots; S2, heating and rolling the ingot, wherein the compression ratio of the ingot is ≥10; S3, ring welding; S4, quenching heat treatment, the heating temperature of the quenching heat treatment is 840-980°C, preferably 850-950°C, the holding time is 1-4 hours, preferably 1-3 hours, and water cooling quenching is adopted; S5, pickling pretreatment to obtain chain steel; S6, hot dip galvanizing, the chain steel after pickling pretreatment is subjected to preheating treatment and then hot dip galvanizing to obtain a chain including chain steel and a galvanized layer formed on the surface of the chain steel, and the temperature difference between the preheating temperature of the preheating treatment and the galvanizing liquid used for the hot dip galvanizing is controlled to be -30 to 30°C.

10. The manufacturing method according to claim 9, characterized in that: In the step S1, the smelting includes electric furnace or converter smelting, LF refining, VD or RH vacuum treatment; the casting adopts a continuous casting process; preferably, the vacuum treatment time of the VD or RH vacuum treatment is 10 to 20 minutes; during the casting process, the superheat of the molten steel in the tundish is controlled to be 15 to 40°C; In the step S2, during the heating and rolling process, the heating temperature of the ingot is ≥1150°C, the heating time is 3-6h, the final rolling temperature is ≥850°C, and air cooling or slow cooling is adopted after rolling; In the step S6, the preheating temperature is 400-550°C, and the preheating time is ≥0.5h; the temperature of the galvanizing solution used in the hot-dip galvanizing is 400-530°C.

11. The manufacturing method according to claim 9, characterized in that: The thickness of the zinc layer on the surface of the chain is 10 to 150 μm, preferably 40 to 150 μm.

12. The manufacturing method according to claim 9, characterized in that: The microstructure of the chain steel in the chain obtained in step S6 is needle-shaped tempered martensite and dispersed carbides; preferably, the carbide size is less than 300nm.

13. The manufacturing method according to claim 9, characterized in that: The performance of the chain meets the following requirements: Yield strength Rp 0.2 ≥1050MPa, tensile strength R m ≥1100MPa, elongation A≥14%, section shrinkage Z≥50%, -20℃ Charpy impact energy A kv ≥60J; After 120h of 5% NaCl neutral salt spray corrosion test, the corrosion rate is less than 0.2g / m 2 .h.

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