High strength seawater corrosion resistant chain steel and chain and method of making same

Abstract

The application discloses a high-strength seawater corrosion-resistant chain steel and a chain and a manufacturing method thereof. The high-strength seawater corrosion-resistant 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: 0.4-1.0%, Al: 0.02-0.05%, V: 0.08-0.30%, N: 0.009-0.02%, and the balance of iron and inevitable impurities. The high-strength seawater corrosion-resistant chain has high strength, good toughness and plasticity matching, and excellent seawater corrosion resistance, and can solve the problem that the service life is affected by the mismatching of strength, toughness and plasticity and corrosion resistance of the existing chain.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of chain steel and chain technology, and particularly relates to a high-strength seawater corrosion-resistant chain steel and chain and a manufacturing method thereof. BACKGROUND

[0002] About 1 / 6 of the world's annual steel production is lost due to corrosion, and the direct economic loss caused by steel corrosion in China is more than 10 billion yuan per year. Corrosion of steel reduces the service life of steel structures, causes personnel casualties and economic losses, and emits pollutants that pollute the environment. In particular, in the marine environment, the corrosion of steel during service is particularly serious due to the presence of chloride ions in seawater and sea air. In order to improve the corrosion resistance of steel, a coating treatment is usually performed on the surface of the steel. Although this can effectively delay the corrosion process, once a defect appears on the surface of the coating, corrosion will occur in the middle of the coating, leading to rapid failure of the coating. Although stainless steel has excellent corrosion resistance, the addition of a large amount of alloy elements leads to high cost, making it impossible to be widely used. Therefore, low-alloy corrosion-resistant steel has attracted more and more attention due to its relatively low alloy content, excellent mechanical properties and relatively good corrosion resistance. With the rapid development of China's ocean transportation and marine engineering construction, higher and higher requirements are put forward for the strength and corrosion resistance of steel, and the demand for high-strength chain steel with excellent seawater corrosion resistance is increasing.

[0003] Many seawater corrosion resistant steels have been developed at home and abroad, mainly by optimizing the Cr, Ni, Cu and other alloy elements in the steel to improve the seawater corrosion resistance of the steel. For example, Chinese patent CN201010266527.0 discloses an ultra-high strength ship plate steel and its production method, 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%, using controlled rolling and controlled cooling technology + subsequent heat treatment to produce ultra-high strength ship plate steel, the tensile strength is greater than 670 MPa, the impact energy at-60 ℃ is greater than 200 J. Chinese patent CN201180066512.2 discloses an ultra-high strength structural steel, its chemical composition 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%, and iron, inevitable impurities; the technology adds high content of Ni, Cu, Cr, Mo alloy elements in relatively low carbon content, adopts hot rolling controlled cooling process, directly quenches to a temperature not more than 450 ℃ at a cooling rate of 20-150 ℃ / s after hot rolling, and finally obtains a steel material with a yield strength greater than 960 MPa and an impact energy in the welded heat-affected zone at-40 ℃ greater than 34 J. Chinese patent CN201610993472.0 discloses a high-strength and high-toughness corrosion-resistant chain steel, its chemical composition 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; the technology adopts a process mode of twice quenching heat treatment and once tempering heat treatment, obtains a lath martensite structure with a lath block width of 0.3-5 μm, and the lath interstice and the lath interior are dispersedly distributed with 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%; the chain after heat treatment has a tensile strength of 1000 MPa level, a ring back and weld KV2(-60 ℃) of more than 100 J, and good seawater corrosion resistance.

[0004] In addition, there are some weathering steel products for some special service environment, such as Chinese patent CN201611102046.X discloses a kind of high-strength weathering steel for high humidity and heat marine atmosphere 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, the rest is Fe;The technology is based on Cu-Ni-Mo alloy system, by adding Sn, Sb, Nb, RE and other micro-alloy elements, the Cr content in weathering steel is greatly reduced;By controlling the cooling speed of steel after hot rolling to 12~17 ℃ / s and cooling to 530~570 ℃, acicular ferrite and polygonal ferrite structure is formed, and the yield strength of steel is greater than 650 MPa and the tensile strength is greater than 750 MPa, and the 30 ℃ half-size impact energy is greater than 65 J.

[0005] Referring to the prior art described above, it can be seen that the existing high-strength steel products resistant to seawater corrosion 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, and there are few high-strength seawater corrosion resistant steel products with yield strength exceeding 1000 MPa.

[0006] Based on this, the present application expects to obtain a new type of high-strength seawater corrosion resistant chain steel, which can combine chain heat treatment process with plating process, and the chain finished product has excellent comprehensive performance, which not only has high strength, but also has excellent toughness and plasticity matching, and excellent corrosion resistance of the chain, which can well solve the problem of the existing chain that the strength, toughness and plasticity and corrosion resistance do not match, thereby affecting the service life. SUMMARY

[0007] In view of the problem that the existing chain that the strength, toughness and plasticity and corrosion resistance do not match, thereby affecting the service life, the purpose of the present application is to provide a high-strength seawater corrosion resistant chain steel and chain and a manufacturing method thereof, by designing the composition and optimizing the manufacturing process, the high-strength seawater corrosion resistant chain steel has high strength, good toughness and plasticity matching and excellent seawater corrosion resistance, and is particularly suitable for manufacturing high-strength corrosion resistant structural parts, industrial products for mining, mooring and other purposes, and can be widely applied in environments with more corrosion media, such as engineering machinery, mines, ships and ocean engineering.

[0008] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0009] The first aspect of the present application provides a high-strength seawater corrosion-resistant chain steel, comprising 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: 0.4-1.0%, Al: 0.02-0.05%, V: 0.08-0.30%, N: 0.009-0.02%, and the balance being iron and inevitable impurities.

[0010] Preferably, the components satisfy the following requirements: 1.3*Ni+2*Cr+7*Mo+0.5*Si+V≥8, wherein Ni, Cr, Mo, Si and V are the numerical values before the percentage symbol in the percentage by mass content of the corresponding elements.

[0011] Preferably, in the inevitable impurities, P≤0.015%, S≤0.01%, and O≤0.002%.

[0012] Preferably, the high-strength seawater corrosion-resistant chain steel has an austenite grain size≥7 levels; and after quenching heat treatment and thermal coating treatment, the microstructure of the high-strength seawater corrosion-resistant chain steel is needle-shaped tempered martensite and dispersedly distributed carbide.

[0013] Preferably, the performance satisfies: yield strength Rp 0.2 ≥1000MPa, tensile strength R m ≥1100MPa, elongation A≥14%, reduction of area Z≥50%, and Charpy impact energy A kv ≥60J at-20℃.

[0014] Preferably, after the surface of the high-strength seawater corrosion-resistant chain steel is treated by thermal coating, the corrosion rate is≤0.2g / m 2 .h after 5% NaCl neutral salt spray corrosion test for 120h.

[0015] The second aspect of the present application provides a high-strength seawater corrosion-resistant chain made of the high-strength seawater corrosion-resistant chain steel according to the first aspect of the present application, and the performance satisfies: yield strength Rp 0.2 ≥1000MPa, tensile strength R m ≥1100MPa, elongation A≥14%, reduction of area Z≥50%, and Charpy impact energy A kv ≥60J at-20℃; and the corrosion rate is≤0.2g / m 2 .h after 5% NaCl neutral salt spray corrosion test for 120h.

[0016] The third aspect of the present application provides a manufacturing method of the high-strength seawater corrosion-resistant chain according to the second aspect of the present application, comprising the following steps:

[0017] S1, smelting and casting;

[0018] S2, heating rolling, controlling the compression ratio of the material to be greater than or equal to 10;

[0019] S3, ring welding;

[0020] S4, quenching heat treatment, the heating temperature of the quenching heat treatment being 850-950℃, the holding time being 1-3h, and water quenching being used;

[0021] S5, acid pickling pretreatment;

[0022] S6, hot-dip galvanizing, the chain after the acid pickling pretreatment being preheated and then subjected to the hot-dip galvanizing to obtain a high-strength seawater corrosion-resistant chain, the preheating temperature of the preheating being controlled to be different from the temperature of the hot-dip galvanizing solution used in the hot-dip galvanizing by -30-30℃.

[0023] Preferably, in the step S1, the smelting includes electric furnace or converter smelting, LF refining, VD or RH vacuum treatment, and the casting uses continuous casting process.

[0024] Preferably, in the step S1, the vacuum treatment time of the VD or RH vacuum treatment is 10-20min, and in the casting process, the superheat of the molten steel in the tundish is controlled to be 15-40℃.

[0025] Preferably, in the step S2, in the heating rolling process, the heating temperature of the cast blank is controlled to be greater than or equal to 1150℃, the heating time is 3-6h, the finish rolling temperature is greater than or equal to 850℃, and air cooling or slow cooling is used after rolling.

[0026] Preferably, in the step S6, the preheating temperature is 400-550℃, and the preheating time is greater than or equal to 0.5h; the temperature of the hot-dip galvanizing solution used in the hot-dip galvanizing is 400-530℃.

[0027] Preferably, the thickness of the zinc layer on the surface of the high-strength seawater corrosion-resistant chain is 10-150μm.

[0028] Preferably, the microstructure of the high-strength seawater corrosion-resistant chain is needle-shaped tempered martensite and diffusely distributed carbide, and the size of the carbide is less than 300nm.

[0029] Preferably, the performance of the high-strength seawater corrosion-resistant chain satisfies: yield strength Rp 0.2 ≥1050MPa, tensile strength R m ≥1200MPa, elongation A≥14%, reduction of area Z≥50%, and Charpy impact energy A kv≥ 60 J; the corrosion rate is less than 0.2 g / m 2 .h.

[0030] In the high-strength seawater corrosion-resistant chain steel of the present application, the design principles of each chemical element are as follows:

[0031] C: In the high-strength seawater corrosion-resistant chain steel of the present application, C is an essential element to ensure the strength of the steel. Increasing the C content in the steel will increase the non-equilibrium structure transformation ability of the steel, thereby significantly improving the strength of the steel. In the present application, the diffusion of C element in the steel can be inhibited by quenching and tempering heat treatment process to form shear type martensite phase change, thereby significantly improving the strength of the steel. However, for the present application, the C content in the steel should not be too high. Too high C content will adversely affect the plasticity and toughness of the steel, and will significantly increase the carbon equivalent of the material, and deteriorate the welding performance of the steel. Based on this, in the high-strength seawater corrosion-resistant chain steel of the present application, the mass percentage of C element is controlled between 0.25-0.35%.

[0032] Si: In the high-strength seawater corrosion-resistant chain steel of the present application, Si element can be dissolved in the steel and play a role in solid solution strengthening, which can significantly improve the yield strength, fatigue strength and hardness of the steel. During corrosion, Si mainly exists in spinel-type oxides as divalent oxides, making the inner rust layer dense and preventing Cl - from penetrating, thereby improving the marine corrosion resistance of the steel. The solubility of Si in cementite is very low, and the Si content in the steel should not be too high. When the Si content in the steel is too high, not only will it form carbide-free bainite structure, but also will increase the brittleness of the steel. Based on this, in the high-strength seawater corrosion-resistant chain steel of the present application, the mass percentage of Si element is controlled between 0.1-0.6%.

[0033] Mn: In the high-strength seawater corrosion-resistant chain steel of the present application, Mn element can improve the stability of austenite in the steel, and also can improve the hardenability of the steel. In addition, Mn can also improve the strength of martensite in the steel through solid solution strengthening, thereby improving the strength of the steel. However, it should be noted that the Mn content in the steel should not be too high. When the Mn content in the steel is too high, the austenite grains will easily grow during quenching heating, and the harmful elements will be segregated at the grain boundaries. Based on this, in the high-strength seawater corrosion-resistant chain steel of the present application, the mass percentage of Mn element is controlled between 0.3-0.9%.

[0034] Cr: In the high-strength seawater corrosion-resistant chain steel of the present application, the addition of an appropriate amount of Cr element can improve the hardenability of the steel and has the effect of secondary hardening, which can form hardened martensite structure, thus being beneficial to improving the strength of the steel. In addition, the carbide of Cr can slow down the grain growth of the heat-affected zone at the welding joint, which is very beneficial to the welding of the steel; the addition of appropriate amounts of Cr and Ni elements in 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 content of Cr element in the steel should not be too high. When the content of Cr element in the steel is too high, a large amount of carbide will be generated and will gather at the grain boundary, thus reducing the toughness of the material and significantly increasing the carbon equivalent, which will deteriorate the welding performance of the high-strength seawater corrosion-resistant chain steel. Therefore, in the high-strength seawater corrosion-resistant chain steel of the present application, the mass percentage content of Cr element is controlled to be between 0.3-1.2%.

[0035] Ni: In the high-strength seawater corrosion-resistant chain steel of the present application, Ni is an austenite-forming element, which is one of the main strengthening elements and can exist in the steel in the form of solid solution and can be infinitely dissolved with iron. It not only can resist acid, but also can resist alkali, and has corrosion resistance to atmosphere and salt. In the corrosion process, Ni replaces Fe ions in the form of divalent ions to form a relatively stable spinel NiFe2O4 compound. When Ni element is used in combination with Cr element, the hardenability of the steel can be significantly improved. In addition, the addition of an appropriate amount of Ni element in the steel can also reduce the C content at the eutectoid point, strengthen ferrite and refine and increase pearlite, which can improve the strength of the steel without significantly affecting the plasticity of the steel. Ni element can improve the fatigue resistance of the steel, reduce the sensitivity of the steel to notches, reduce the low-temperature embrittlement transition temperature of the steel, and improve the impact toughness of the steel. In addition, while improving the strength of the steel, the damage of Ni element to the toughness, plasticity and other process properties of the steel is smaller than that of other alloy elements. Therefore, in the high-strength seawater corrosion-resistant chain steel of the present application, the mass percentage content of Ni element is controlled to be between 1.8-3.2%.

[0036] Mo: In the high-strength seawater corrosion resistant chain steel of the present application, Mo element mainly exists in the form of solid solution in the steel, which can play a solid solution strengthening effect, and is beneficial to improve the hardenability of the steel, so that the steel forms martensite during quenching. At the same time, Mo element can also improve the corrosion resistance to organic acid, sulfuric acid and sulfate, and can passivate the steel surface in reducing acid and strong oxidizing salt solution, preventing pitting corrosion of the steel in chloride solution. However, the Mo content in the steel should not be too high, when the Mo content in the steel is too high, the carbon equivalent of the material will be significantly increased, which is not conducive to the welding performance of the steel; in addition, Mo is also a precious alloy element, and excessive Mo will also lead to the increase of alloy cost. Therefore, in the high-strength seawater corrosion resistant chain steel of the present application, the mass percentage of Mo element is controlled between 0.4-1.0%.

[0037] Al: In the high-strength seawater corrosion resistant chain steel of the present application, the main role of Al is deoxidization and nitrogen fixation, and A1N formed by the combination of A1 and N can effectively refine the grains. However, it should be noted that the Al content in the steel should not be too high, when the Al content in the steel is too high, it will affect the pouring performance of the steel, and will also damage the toughness of the steel. Therefore, in the high-strength seawater corrosion resistant chain steel of the present application, the mass percentage of Al element is controlled between 0.02-0.05%.

[0038] V: In the high-strength seawater corrosion resistant chain steel of the present application, V as a strong carbide forming element can significantly improve the strength of the steel in the form of dispersed precipitation, and vanadium can also improve the pitting corrosion resistance of the steel. However, it should be noted that when the addition amount of V element in the steel is too high, the toughness and welding performance of the steel will be reduced. Therefore, in the high-strength seawater corrosion resistant chain steel of the present application, the mass percentage of V element is controlled between 0.08-0.30%.

[0039] N: In the high-strength seawater corrosion resistant chain steel of the present application, N is an austenite forming element and also an MX precipitate forming element; in order to avoid the enrichment of N element in the steel, too much N should not be added to the steel. Therefore, the content of N element must be strictly controlled, and in the high-strength seawater corrosion resistant chain steel of the present application, the mass percentage of N element is controlled between 0.009-0.02%.

[0040] For the present application, by reasonable design of main alloying elements, full use of the influence of various alloying elements and their interaction on microstructure, mechanical properties and corrosion resistance, the microstructure of the present steel is precisely controlled to ensure that the high-strength seawater corrosion-resistant chain steel of the present application forms a mixed structure of acicular tempered martensite + dispersed carbides, improves the seawater local corrosion resistance of the chain steel, and makes the high-strength seawater corrosion-resistant chain steel of the present application have higher strength and toughness and plasticity matching, and good seawater corrosion resistance.

[0041] In the preferred embodiment, in the high-strength seawater corrosion-resistant chain steel of the present application, among the unavoidable impurities, P≤0.015%, S≤0.01%, and O≤0.002%.

[0042] In the above technical solution, P element, S element and O element are all impurity elements in steel, and in the case of technical conditions, in order to obtain high-strength seawater corrosion-resistant chain steel with better performance and quality, the content of impurity elements in the material should be reduced as much as possible.

[0043] In the high-strength seawater corrosion-resistant chain steel of the present application, P element and S element are both harmful impurity elements in steel, and both will deteriorate the performance of the steel. Although P element can improve the weather resistance of the steel, its side effects are greater in general, so in the present application, P element is controlled to satisfy: P≤0.015%, and S element is controlled to satisfy: S≤0.01%.

[0044] Correspondingly, in the present application, impurity element O can form oxides and complex inclusions with deoxidizing elements such as Al in steel, which is not conducive to the performance of the steel, so in the present application, O element is controlled to satisfy: O≤0.002%.

[0045] Of course, in some other embodiments, other harmful elements such as As, Pb, Sn, Sb, Bi, etc. may also exist in the steel, and under the requirements of national laws, regulations and standards, the content of these harmful elements should be reduced as much as possible.

[0046] During use, the chain will have coating wear and fall off, exposing the steel substrate locally to seawater environment to produce local corrosion, affecting the safe use of the chain. In order to improve the seawater local corrosion resistance of the steel substrate, the content of main alloying elements Ni, Cr, Mo, Si and V in the steel for improving seawater local corrosion resistance also needs to satisfy:

[0047] 1.3*Ni+2*Cr+7*Mo+0.5*Si+V≥8

[0048] The research finds that when the content of the seawater corrosion resistance local corrosion alloy elements Ni, Cr, Mo, Si and V in the steel satisfies 1.3*Ni+2*Cr+7*Mo+0.5*Si+V >= 8, the steel substrate has excellent seawater corrosion resistance performance, and in combination with the steel surface coating, the corrosion speed of the steel in the seawater environment can be greatly reduced; when the content of the seawater corrosion resistance local corrosion alloy elements Ni, Cr, Mo, Si and V in the steel is less than 1.3*Ni+2*Cr+7*Mo+0.5*Si+V < 8, the local corrosion resistance of the steel is greatly reduced, when the coating of the chain is locally abraded and fails, the exposed steel substrate will have obvious local corrosion defects, so that the chain has local stress concentration, and the service life of the chain is directly affected.

[0049] Compared with the existing production technology, the high-strength seawater corrosion resistance chain steel has the following beneficial effects:

[0050] 1. The reasonable chemical composition design is adopted, the interaction between the content of each alloy element and the seawater corrosion resistance of the chain steel is fully considered, the seawater corrosion resistance of the chain steel is improved, the manufacturing process is optimized, the influence of various alloy elements and the processing process of the chain on the microstructure is fully utilized, and the microstructure of the high-strength seawater corrosion resistance chain steel is accurately controlled; after quenching heat treatment, the high-strength seawater corrosion resistance chain steel forms needle-shaped martensite structure, through preheating and hot dip galvanizing treatment of the chain, on one hand, fine carbides can be dispersedly precipitated in the supersaturated solid solution formed by quenching of the chain steel, so that the performance of the chain is improved; on the other hand, a certain thickness of zinc layer can be formed on the surface of the chain, so that the seawater corrosion resistance of the chain is improved through the coating of the chain, when the coating of the chain is abraded and fails, the local corrosion resistance design of the chain steel substrate can reduce the local pitting of the steel, so that the seawater corrosion resistance of the chain steel is improved.

[0051] 2. After the zinc layer is coated on the surface of the chain, the seawater corrosion medium can be isolated from the contact with the chain substrate, so that the corrosion resistance of the chain is improved; when the coating of the chain is abraded in part, the local corrosion resistance design of the steel substrate can prevent the local excessive corrosion phenomenon from occurring in the use process of the chain, so that the service life of the chain is improved.

[0052] 3. The chemical composition and process design of the high-strength seawater corrosion resistance chain steel are reasonable, and the process window is wide, so that batch commercial production can be realized.

[0053] 4. The high-strength seawater corrosion resistance chain steel has excellent high strength and toughness and good seawater local corrosion resistance, and can be made into high-strength corrosion resistance structural parts and various mining, mooring and other high-performance industrial chains, and is widely applied to occasions requiring high-strength and high-toughness and high-corrosion-resistance steel, such as engineering machinery, mines and ocean engineering. BRIEF DESCRIPTION OF DRAWINGS

[0054] Other features, objects, and advantages of the application will become more apparent from the following detailed description of non-limiting embodiments thereof, when read in conjunction with the accompanying drawings:

[0055] Figure 1 Scanning electron microscope image of high-strength high-seawater-corrosion-resistant chain steel manufactured for Example 1 of the application. DETAILED DESCRIPTION

[0056] In order to better understand the above technical solutions of the application, the technical solutions of the application are further described below in conjunction with examples.

[0057] The application provides a high-strength high-seawater-corrosion-resistant chain steel, which contains Fe and inevitable impurities, and further 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%, Mo: 0.4-1.0%, Al: 0.02-0.05%, V: 0.08-0.30%, and N: 0.009-0.02%.

[0058] The application fully utilizes the influence of various alloy elements and the interaction therebetween on microstructure, mechanical properties and corrosion resistance by reasonable design of main alloy elements, improves the seawater local corrosion resistance of the chain steel, and precisely controls the microstructure of the steel by using an optimized quenching and plating process, so as to ensure that the high-strength seawater corrosion-resistant chain steel forms a mixed microstructure of acicular tempered martensite and dispersed carbides, and the manufactured high-strength chain has high strength and toughness and plasticity matching, and has good seawater corrosion resistance.

[0059] In specific examples, the composition of the high-strength seawater corrosion-resistant chain steel satisfies the following requirements: 1.3*Ni+2*Cr+7*Mo+0.5*Si+V≥8, wherein Ni, Cr, Mo, Si and V are the numerical values before the percentage symbol of the mass percentage content of the corresponding elements.

[0060] When the contents of the pitting corrosion-resistant alloy elements Ni, Cr, Mo, Si and V in the high-strength seawater corrosion-resistant chain steel satisfy 1.3*Ni+2*Cr+7*Mo+0.5*Si+V≥8, the steel has excellent seawater local corrosion resistance, and in combination with the surface coating, the corrosion speed of the steel in seawater environment can be greatly reduced; when the contents of the Ni, Cr, Mo, Si and V in the steel are lower than 1.3*Ni+2*Cr+7*Mo+0.5*Si+V<8, the seawater local corrosion resistance of the steel is greatly reduced, and when the coating of the chain is locally abraded and fails, the exposed steel substrate will be in contact with seawater and will have obvious local corrosion defects, so that the chain has local stress concentration, which directly affects the service life of the chain.

[0061] In the present application, the P element, the S element and the O element are all impurity elements in the steel, and the content of the impurity elements in the material should be reduced as much as possible to obtain high-strength steel with better performance and quality under the condition of technology.

[0062] In a specific embodiment, the high-strength seawater corrosion-resistant chain steel has an austenite grain size of ≥7 levels, and after quenching heat treatment and thermal coating treatment, the microstructure of the high-strength seawater corrosion-resistant chain steel is needle-shaped tempered martensite and dispersedly distributed carbide.

[0063] After heat treatment, the high-strength seawater corrosion-resistant chain steel has the following performance: yield strength Rp 0.2 ≥1000MPa, tensile strength R m ≥1100MPa, elongation A ≥14%, reduction of area Z ≥50%, Charpy impact energy A kv ≥60J at-20℃.

[0064] After thermal coating treatment, the high-strength seawater corrosion-resistant chain steel has a corrosion rate of less than 0.2g / m 2 .h after 120h of 5% NaCl neutral salt spray corrosion test.

[0065] The present application provides a high-strength seawater corrosion-resistant chain made of the high-strength seawater corrosion-resistant chain steel described above, which has the following performance: yield strength Rp 0.2 ≥1000MPa, tensile strength R m ≥1100MPa, elongation A ≥14%, reduction of area Z ≥50%, Charpy impact energy A kv ≥60J at-20℃; and a corrosion rate of less than 0.2g / m 2 .h after 120h of 5% NaCl neutral salt spray corrosion test.

[0066] The manufacturing method of the high-strength seawater corrosion-resistant chain of the present application is simple, and the obtained high-strength seawater corrosion-resistant chain has excellent high toughness and good seawater corrosion resistance, and the manufacturing method specifically comprises the following steps:

[0067] S1, smelting and casting;

[0068] Specifically, the smelting operation includes electric furnace or converter smelting, LF refining, VD or RH vacuum treatment; that is, smelting is carried out by using an electric furnace or a converter, and LF refining, VD or RH vacuum treatment is carried out, wherein the vacuum treatment time is 10-20 min, and after the chemical composition meets the requirements of the high-strength seawater corrosion-resistant chain steel designed in the application, the molten steel is tapped for casting; correspondingly, in the casting process, a continuous casting process is used to cast into a casting blank, the tundish molten steel superheat is controlled to be 15-40 ℃, and finally a casting blank with a chemical composition meeting the high-strength seawater corrosion-resistant chain steel is obtained.

[0069] S2, heating and rolling, controlling the compression ratio of the material to be ≥10;

[0070] Specifically, the casting blank is heated in a heating furnace, and then after high-pressure water dephosphorization, the rolling is started, and the casting blank is rolled into a round steel of finished size, that is, a high-strength seawater corrosion-resistant chain steel; the heating temperature of the casting blank is controlled to be ≥1150 ℃, the heating time is 3-6 h, and the finish rolling temperature is ≥850 ℃; after rolling, air cooling or slow cooling to room temperature is carried out; the compression ratio of the material is controlled to be ≥10; the finished size specification of the high-strength seawater corrosion-resistant chain steel is Φ30-150 mm.

[0071] S3, ring weaving welding: the rolled high-strength seawater corrosion-resistant chain steel is cut into a round steel of a fixed length, and after being woven into a single ring on a weaving machine, it is welded into a complete ring chain by using flash welding.

[0072] S4, quenching heat treatment, the heating temperature of the quenching heat treatment is 850-950 ℃, the holding time is 1-3 h, and water quenching is adopted;

[0073] Specifically, the ring-weaved and welded chain is subjected to quenching heat treatment, the heating temperature of the quenching heat treatment is 850-950 ℃, the holding time is 1-3 h, and then water quenching is carried out; when the ring-weaved and welded chain is heated at a high temperature, fine austenite grains are formed in the steel, and the austenite grain size is ≥7 levels; after quenching, the chain structure is transformed from the austenite structure at a high temperature into fine needle-shaped martensite structure.

[0074] S5, pickling pretreatment: the chain after the quenching heat treatment is subjected to pickling pretreatment to remove the scale on the surface of the chain after quenching, and a layer of plating aid liquid is applied to the surface of the chain, so that the surface of the pickled chain can maintain a certain activity, avoid oxidation of the chain in the subsequent preheating process, and enhance the bonding force between the zinc plating layer and the substrate.

[0075] S6, hot-dip galvanizing, the chain after the pickling pretreatment is subjected to preheating and then hot-dip galvanizing to obtain a high-strength seawater corrosion-resistant chain, and the temperature difference between the preheating temperature and the temperature of the hot-dip galvanizing liquid used for hot-dip galvanizing is controlled to be -30-30 ℃.

[0076] Specifically, the chain after acid pickling pretreatment is hot-dip galvanized, in order to prevent problems such as zinc explosion in the subsequent hot-dip galvanizing process, the chain is preheated and then hot-dip galvanized to obtain a high-strength seawater corrosion-resistant chain; the temperature difference between the preheating temperature and the temperature of the hot-dip galvanizing solution used in the hot-dip galvanizing process is -30-30℃, wherein the preheating temperature is 400-550℃, and the preheating time is ≥0.5h; the temperature of the hot-dip galvanizing solution used in the hot-dip galvanizing process is 400-530℃, and the thickness of the zinc layer on the surface of the high-strength seawater corrosion-resistant chain is 10-150μm.

[0077] In the above hot-dip galvanizing process, the supersaturated martensite structure formed after quenching of the chain begins to precipitate fine carbides, the strength of the chain decreases, but the elongation and impact toughness begin to increase. Fine needle-shaped martensite is beneficial to the precipitation of fine and dispersed carbides from the steel during hot-dip galvanizing, the size of the carbides is less than 300nm, and a high-strength seawater corrosion-resistant chain with excellent strength and toughness is obtained.

[0078] The microstructure of the high-strength seawater corrosion-resistant chain manufactured above is needle-shaped tempered martensite and dispersed carbides; the size of the carbides is less than 300nm.

[0079] The performance of the high-strength seawater corrosion-resistant chain above meets: yield strength Rp0 .2 ≥1050MPa, tensile strength R m ≥1200MPa, elongation A ≥14%, reduction of area Z ≥50%, Charpy impact energy A kv ≥60J at -20℃; after 120h of neutral salt spray corrosion test in 5% NaCl, the corrosion rate is less than 0.2g / m 2 .h.

[0080] The present application fully utilizes the influence of various alloying elements and manufacturing processes on microstructure and corrosion resistance by reasonable design of alloying elements and optimization of manufacturing process, precisely controls the microstructure of high-strength seawater corrosion-resistant chain steel, and improves the seawater local corrosion resistance of the chain steel matrix. After quenching heat treatment, the high-strength seawater corrosion-resistant chain steel forms needle-shaped martensite structure, and through hot-dip galvanizing treatment of the chain after quenching, fine and dispersed carbides can be precipitated from the chain steel during hot-dip galvanizing, and the strength and toughness of the chain are improved; a certain thickness of zinc coating is formed on the surface of the chain, and the seawater corrosion resistance of the chain is improved through the design of the pitting corrosion resistance of the steel matrix and the chain coating; when the chain coating is worn out, the seawater local corrosion resistance design of the chain steel matrix can reduce the local corrosion of the steel, thereby improving the seawater corrosion resistance of the chain steel.

[0081] In the manufacturing method of the high-strength seawater corrosion-resistant chain of the present application, the quenching and tempering process of the conventional chain is combined with the hot galvanizing process, the tempering process of the chain is saved, the precipitation of carbides in the steel is realized in the hot dip galvanizing process, and the efficient production of the high-strength seawater corrosion-resistant chain is realized, so that the high-strength seawater corrosion-resistant chain steel and the chain of the present application have high strength and toughness and plasticity matching, and good corrosion resistance.

[0082] The high-strength seawater corrosion-resistant chain steel and chain and the manufacturing method thereof of the present application will be further described below in combination with specific examples.

[0083] Examples

[0084] As shown in Table 1, Table 2-1 and Table 2-2, the high-strength seawater corrosion-resistant chain steel and chain of Examples 1-6 are obtained by the following steps:

[0085] (1) The chemical composition shown in Table 1 is used for smelting and continuous casting to obtain a casting blank. The smelting can be carried out by an electric furnace or a converter, and the composition is refined by LF and VD or RH vacuum treatment for 10-20 min, and the molten steel is tapped after the composition meets the requirements, and then the continuous casting is carried out to cast the casting blank, and the molten steel overheat degree in the tundish is controlled to be 15-40℃.

[0086] (2) Heating and rolling: the casting blank is heated in a heating furnace, and then the phosphorus is removed by high-pressure water to process a round steel with a finished size, i.e. the high-strength seawater corrosion-resistant chain steel, and the rolling finished size specification range is Φ30-150mm, and the material compression ratio is controlled to be ≥10. In the rolling process, the casting blank heating temperature is controlled to be ≥1150℃, the heating time is 3-6h, and the finish rolling temperature is ≥850℃; and the round steel is air-cooled or slowly cooled to room temperature after rolling.

[0087] (3) Ring weaving and welding: the high-strength seawater corrosion-resistant chain steel is cut into a round steel with a fixed length, and then is woven into a single ring on a weaving machine, and then is welded into a complete circular chain by flash welding.

[0088] (4) Quenching heat treatment: the chain after ring weaving and welding is subjected to quenching heat treatment, the heating temperature of the quenching heat treatment is controlled to be 850-950℃, the holding time is 1-3h, and then water quenching is carried out.

[0089] (5) Pickling pretreatment: the chain after quenching is pickled to remove the oxide skin on the surface of the chain. Then the chain is subjected to preheating treatment to prevent problems such as zinc explosion in the subsequent hot dip galvanizing process, the chain preheating temperature is 400-550℃, the preheating time is ≥0.5h, and the preheating temperature of the preheating treatment and the temperature of the galvanizing liquid used in the subsequent hot dip galvanizing process differ by -30℃-30℃.

[0090] (6) Hot-dip galvanizing: hot-dip galvanizing is performed on the chain after preheating treatment, the temperature of the zinc liquid is 400-530°C, and the thickness of the zinc layer on the surface of the chain is controlled to be 10-150 μm.

[0091] As shown in Tables 1, 2-1 and 2-2, the chemical composition design and the related process parameters of the high-strength seawater corrosion-resistant chain steel prepared in Examples 1-6 all meet the design specification requirements of the present application. The comparative steel material of Comparative Example 1-2 is a finished steel material from a different manufacturer, the chemical composition design of which can be seen from Table 1, and the manufacturing process thereof is different from that of Examples 1-6. The parameters of the heat treatment process used in Comparative Example 1-2 are shown in Tables 2-1 and 2-2.

[0092] Table 1 Chemical composition of chain steel (wt.%, balance being Fe and other impurities except P and S)

[0093]

[0094] Table 2-1 Process parameters in the preparation process of examples and comparative examples

[0095]

[0096] Table 2-2 Process parameters in the preparation process of examples and comparative examples

[0097]

[0098] The finished chain of Examples 1-6 and the comparative chain of Comparative Example 1-2 after coating treatment were collected and respectively subjected to performance detection to obtain the performance of the finished steel of each example and comparative example.

[0099] The finished chain of Examples 1-6 and the comparative chain of Comparative Example 1-2 were respectively subjected to neutral salt spray corrosion test, tensile test and impact performance test, and the test results are shown in Table 3.

[0100] The specific detection means of the related neutral salt spray corrosion test, tensile test and impact test are as follows:

[0101] (1) Neutral salt spray corrosion test is carried out by the following steps: taking 100 mm long round steel of the finished chain of Example 1-6 after plating treatment and the chain of Comparative Example 1-2 as a salt spray corrosion sample, the two end faces are closed with silicone rubber, and 5wt% NaCl salt spray corrosion test is carried out according to GB / T 10125 standard (laboratory temperature 35℃, saturated barrel temperature 47℃, corrosion medium is 5wt.% NaCl aqueous solution, pH=6.5, the test sample is at an angle of 20° in the longitudinal direction, the test time is 120h, the continuous spraying mode is used, and the salt spray deposition amount is 1.5mL / (h·80cm2)). After the 120h neutral salt spray test, the test sample is taken out, the silicone rubber at both ends is peeled off, the surface corrosion product is removed, the sample is dried and weighed as M', and then the salt spray corrosion rate R of each example and comparative example sample is calculated:

[0102] R=(M-M') / (S·T)

[0103] Wherein, M is the initial mass of the sample, with the dimension of g; M' is the mass of the sample after removing the corrosion product and drying, 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, with the dimension of h; the salt spray corrosion rate R has the dimension of g / m 2 .h.

[0104] Tensile test: the finished chain of Example 1-6 after plating treatment and the comparative chain of Comparative Example 1-2 are sampled according to the national standard GB / T 2975 to form tensile samples, and the tensile property test is carried out according to the national standard GB / T 228.1 to measure the yield strength Rp 0.2 , tensile strength R m , elongation A and reduction of area Z of the high-strength seawater corrosion-resistant chain of Example 1-6 and the comparative chain of Comparative Example 1-2.

[0105] Impact test: the finished chain of Example 1-6 after plating treatment and the comparative chain of Comparative Example 1-2 are sampled according to the national standard GB / T 2975 to form impact samples, and the impact property test is carried out according to the national standard GB / T 229 to measure the Charpy impact energy A kv of the high-strength chain of Example 1-6 and the comparative chain of Comparative Example 1-2 at-20℃.

[0106] Table 3 Performance of the chain of examples and comparative examples

[0107]

[0108] In combination with Table 3, the high-strength seawater corrosion-resistant chain in the examples has excellent comprehensive performance, and the yield strength Rp 0.2 of the chain is between 1066MPa and 1185MPa, the tensile strength Rm Between 1183-1285 MPa, elongation A≥14%, cross-sectional shrinkage rate Z≥50%, Charpy impact energy A kv ≥60J at -20℃.

[0109] In combination with Table 1, Table 3, the content of alloying elements Ni, Cr, Mo, Si, V in the steel of Comparative Example 1-2 cannot satisfy 1.3Ni+2Cr+7Mo+0.5Si+V≥8, and cannot achieve the seawater corrosion resistance of the present technology.

[0110] In combination with Table 3, the neutral salt spray corrosion rate of the high-strength seawater corrosion-resistant chain of the present application Example 1-6 is ≤0.19g / m 2 .h, which is much lower than the neutral salt spray corrosion rate of the comparative chain in Comparative Example 1-2. It can be seen that the corrosion resistance of the high-strength seawater corrosion-resistant chain steel of the present application after heat treatment and hot-dip galvanizing is significantly better than that of the existing comparative chain selected in Comparative Example 1-2.

[0111] Figure 1 The electron microscope scanning image of the microstructure of the chain steel in Example 1. In combination with Figure 1 Table 3, the microstructure of the chain steel after quenching + plating treatment in Example 1 is needle-shaped tempered martensite, and fine dispersed nanoscale carbides are precipitated on the martensite matrix, with a carbide size of less than 300um. The fine nanoscale carbides can greatly improve the strength and toughness of the steel, thereby obtaining a high-strength high-toughness chain steel with excellent performance.

[0112] In summary, the present application improves the seawater local corrosion resistance of the steel base by reasonable chemical composition design, and combines the chain heat treatment and subsequent galvanizing process to form an optimized quenching and hot-dip galvanizing process, so as to obtain a high-strength seawater corrosion-resistant chain with excellent performance. The high-strength seawater corrosion-resistant chain of the present application has excellent comprehensive performance, not only has high strength, but also has excellent toughness and plasticity matching, and can be made into a high-strength seawater corrosion-resistant chain with excellent corrosion resistance, which can well solve the problem of mismatching of strength, toughness and plasticity and corrosion resistance of the existing chain, thereby affecting the service life. The high-strength seawater corrosion-resistant chain steel of the present application can be made into various high-performance industrial chains such as mooring and mining, and is widely used in marine engineering, engineering machinery and mining, and other occasions requiring high-strength, high-toughness and high-corrosion-resistant chains.

[0113] It should be noted that those skilled in the art should recognize that the above examples are only used to illustrate the present application, and are not used as a limitation of the present application. Any changes and modifications of the above examples within the spirit and scope of the present application will fall within the scope of the claims of the present application.

Claims

1. A high-strength, seawater-corrosion-resistant chain steel, characterized in that, The composition includes 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%, Mo: 0.4–1.0%, Al: 0.02–0.05%, V: 0.08–0.30%, N: 0.009–0.02%, with the balance being iron and unavoidable impurities. The austenitic grain size of the high-strength seawater corrosion resistant chain steel is ≥7 grade; after quenching heat treatment and hot coating treatment, the microstructure of the high-strength seawater corrosion resistant chain steel is acicular tempered martensite and dispersed carbides. After quenching heat treatment, its properties meet the following requirements: yield strength Rp 0.2 ≥1000MPa, tensile strength R m ≥1100MPa, elongation A≥14%, reduction of area Z≥50%, Charpy impact energy A at -20℃ kv ≥60J; After the high-strength, seawater-corrosion-resistant chain steel surface is treated with hot-dip galvanizing, its corrosion rate is ≤0.2 g / m after 120 hours of neutral salt spray corrosion testing in 5% NaCl. 2 ·h.

2. The high-strength, seawater-corrosion-resistant chain steel according to claim 1, characterized in that, Its composition 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.

3. The high-strength, seawater-corrosion-resistant chain steel according to claim 1, characterized in that, Of the unavoidable impurities, P ≤ 0.015%, S ≤ 0.01%, and O ≤ 0.002%.

4. A high-strength, seawater-corrosion-resistant chain manufactured using the high-strength, seawater-corrosion-resistant chain steel as described in any one of claims 1-3, characterized in that, Its properties satisfy: yield strength Rp 0.2 ≥1000MPa, tensile strength R m ≥1100MPa, elongation A≥14%, reduction of area Z≥50%, Charpy impact energy A at -20℃ kv ≥60J; after 120h of neutral salt spray corrosion test in 5% NaCl, its corrosion rate is ≤0.2g / m³. 2 ·.h.

5. A method for manufacturing a high-strength, seawater-corrosion-resistant chain as described in claim 4, characterized in that, Includes the following steps: S1, smelting and casting; S2, heated rolling, controlling the material's compression ratio ≥10; S3, braided ring welding; S4, quenching heat treatment, the heating temperature of quenching heat treatment is 850~950℃, the holding time is 1~3h, and water quenching is used; S5, pickling pretreatment; S6, hot-dip galvanizing: the chain after pickling pretreatment is preheated and then hot-dip galvanized to obtain a high-strength chain resistant to seawater corrosion. The temperature difference between the preheating temperature of the preheating treatment and the temperature of the galvanizing solution used for hot-dip galvanizing is controlled to be -30 to 30°C.

6. The method for manufacturing a high-strength, seawater-corrosion-resistant chain according to claim 5, characterized in that, In step S1, the smelting includes electric furnace or converter smelting, LF refining, and VD or RH vacuum treatment; the casting adopts continuous casting process, wherein 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 step S2, during the heating and rolling process, the heating temperature of the billet is controlled to be ≥1150℃, the heating time is 3~6h, the final rolling temperature is ≥850℃, and air cooling is used after rolling. In step S6, the preheating temperature is 400-550℃ and the preheating time is ≥0.5h; the temperature of the galvanizing solution used in hot-dip galvanizing is 400-530℃.

7. The method for manufacturing a high-strength, seawater-corrosion-resistant chain according to claim 5, characterized in that, The thickness of the zinc layer on the surface of the high-strength, seawater-resistant chain is 10–150 μm.

8. The method for manufacturing a high-strength, seawater-corrosion-resistant chain according to claim 5, characterized in that, The microstructure of the high-strength, seawater-resistant chain consists of acicular tempered martensite and diffusely distributed carbides; the carbide size is less than 300 nm.

9. The method for manufacturing a high-strength, seawater-corrosion-resistant chain according to claim 5, characterized in that, The high-strength, seawater-corrosion-resistant chain meets the following performance requirements: yield strength Rp 0.2 ≥1050MPa, tensile strength R m ≥1200MPa, elongation A≥14%, reduction of area Z≥50%, Charpy impact energy A at -20℃ kv ≥60J; after 120h of neutral salt spray corrosion test in 5% NaCl, its corrosion rate is less than 0.2g / m³. 2 ·h.

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