A chain steel and a method of manufacturing the same

Abstract

The application discloses a chain steel, which comprises the following chemical elements in percentage by mass in addition to Fe and inevitable impurities: C: 0.18-0.30%, Si: 0.2-0.5%, Mn: 0.3-1.2%, Cr: 0.5-1.8%, Ni: 2.5-3.5%, Mo: 0.2-0.5%, Cu: 0.03-0.2%, Al: 0.01-0.05%, Nb: 0.008-0.025%, V: 0.03-0.25%, and N: 0.002-0.008%. The application also discloses a manufacturing method of the chain steel, which comprises the following steps: (1) smelting and casting; (2) heating and rolling; and (3) quenching + secondary tempering treatment, and the steel is water-cooled to room temperature after each tempering, wherein the quenching heating temperature is 850-950 DEG C, the holding time is 1-4h, the first tempering temperature is 350-550 DEG C, the holding time is 0.5-3h, and the second tempering temperature is 200-350 DEG C, and the holding time is 0.5-3h. The chain steel has good strength and toughness plastic matching, and has a very broad application prospect.

Description

Technical Field

[0001] This invention relates to metallic materials and their manufacturing methods, and more particularly to a chain steel and its manufacturing method. Background Technology

[0002] Mining circular link chains are an important component used in mechanized coal mining underground. They are mainly used as drive chains on scraper conveyors, scraper transfer machines, coal mining machines, and coal planers to perform transmission functions.

[0003] In practical applications, mining round link chains are required to possess high strength and toughness, fatigue resistance, and wear resistance to ensure normal operation. Since coal mines are often located underground in humid and corrosive environments, mining round link chains are also typically required to have good corrosion resistance.

[0004] In existing technologies, the steel commonly used for mining round link chains in the coal mining industry is usually the chain steel grade in "GB / T 10560-2017 Steel for Welded Round Link Chains in Mining". Among them, the high-strength mining round link chain steel is mainly 23MnNiMoCr54 steel (referred to as 54 steel) and other grades.

[0005] In response to the different downstream user needs in practical applications, major steel mills in China have developed a series of high-strength steels for mining chains.

[0006] For example, CN110714164B (“A high-quality Cr54 steel for coal mine chain links and its production method”, published on November 6, 2020) discloses a high-quality Cr54 steel for coal mine chain links, which improves the weldability of the chain steel and enhances its resistance to cold brittleness and hot brittleness by introducing carbon equivalent, cold crack sensitivity coefficient and hot crack sensitivity coefficient.

[0007] For example, CN104532143A (“A large-size, high-strength chain steel for mining and its preparation method”, published on April 22, 2015) discloses an improved large-size chain steel for mining with a diameter of 40 to 100 mm, a yield strength ≥980 MPa, a tensile strength ≥1180 MPa, an elongation ≥13%, a reduction of area ≥50%, and a room temperature Charpy impact energy >100 J.

[0008] In addition, existing technologies have optimized the composition of 54 steel. For example, CN111101078A (“A Nickel-Free High-Strength Mining Round Link Chain Steel and Its Production Method”, published on May 5, 2020) discloses a high-strength mining round link chain steel that does not contain Ni. By reducing the content of the precious metal element Ni alloy while increasing the content of C, Si, Cr, and Mo alloy elements, the production cost is significantly reduced while ensuring mechanical properties.

[0009] Currently, researchers in this field mainly focus on optimizing the design of components to prepare mining chain steel with higher strength, improve the wear resistance of chains, and achieve a longer service life.

[0010] However, it should be noted that in practical applications, underground coal mines are often humid working environments, and high-strength chains are inevitably subject to environmental corrosion during use. In addition, high-strength chains have high stress and are also more sensitive to stress corrosion corrosion, which can easily lead to corrosion fatigue fracture in the middle of the service life (frequent low-load brittle fractures can occur within a few months or even a few days), causing premature chain failure.

[0011] Based on this, the inventors intend to provide a novel chain steel with excellent comprehensive performance, which not only has high strength but also excellent toughness and plasticity matching, thereby effectively solving the problem of service life affected by the mismatch between strength, toughness and plasticity, weldability and corrosion resistance of existing chains. Summary of the Invention

[0012] In order to solve the above-mentioned problems in the prior art, the purpose of this invention is to provide a high-strength and high-toughness chain steel and its manufacturing method.

[0013] On one hand, the present invention relates to a chain steel, which, in addition to containing more than 90% Fe and unavoidable impurities, also contains the following chemical elements in mass percentage:

[0014] C: 0.18-0.30%, Si: 0.2-0.5%, Mn: 0.3-1.2%, Cr: 0.5-1.8%, Ni: 2.5-3.5%, Mo: 0.2-0.5% , Cu: 0.03-0.2%, Al: 0.01-0.05%, Nb: 0.008-0.025%, V: 0.03-0.25%, N: 0.002-0.008%.

[0015] Preferably, the chain steel contains the following chemical elements by mass percentage:

[0016] C: 0.18-0.30%, Si: 0.2-0.5%, Mn: 0.3-1.2%, Cr: 0.5-1.8%, Ni: 2.5-3.5%, Mo: 0.2-0.5%, Cu: 0.03-0.2%, Al: 0.01-0.05%, Nb: 0.008-0.025%, V: 0.03-0.25%, N: 0.002-0.008%; balance Fe and unavoidable impurities.

[0017] Through extensive research, the inventors unexpectedly discovered that when chain steel is composed of the above-mentioned chemical elements and the content of each chemical element meets the above-mentioned range, the chain steel exhibits excellent performance. Specifically, the design principles of the above-mentioned chemical elements are as follows. In this document, unless otherwise explicitly stated, element content is expressed as a percentage by mass.

[0018] Carbon (C): Carbon is an essential element for ensuring the strength of steel. Increasing the C content in steel will enhance its ability to undergo non-equilibrium structural transformations, thereby significantly improving its strength. In this invention, a quenching and tempering heat treatment process is used to suppress the diffusion of C in the steel, forming a shear-type martensitic phase transformation, thus significantly improving the steel's strength. However, the C content in the steel should not be too high. Excessive C content will adversely affect the plasticity and toughness of the steel and will significantly increase the carbon equivalent of the material, thus deteriorating the weldability of the steel. Based on this, the C content is controlled at 0.18-0.30%.

[0019] Si (Si): Adding an appropriate amount of Si to steel can improve the stability of austenite during cooling and prevent the formation of coarse carbides. However, it is important to note that the Si content in steel should not be too high. Excessive Si content increases the brittleness of the steel. Therefore, the Si content is controlled at 0.2-0.5%.

[0020] Mn: Adding an appropriate amount of Mn can not only improve the stability of austenite in steel, but also improve the hardenability of the steel. Furthermore, in this invention, Mn can also enhance the strength of martensite in steel through solid solution strengthening, thereby increasing the strength of the steel. However, it should be noted that the Mn content in the steel should not be too high. When the Mn content in the steel is too high, it will make the austenite grains grow more easily during quenching and will also promote the segregation of harmful elements at grain boundaries. Based on this, the Mn content is controlled at 0.3-1.2%.

[0021] Cr: Cr can improve the hardenability of steel and form a hardened martensitic structure, which is beneficial to improving the strength of the steel. In addition, Cr carbides can slow down grain growth in the heat-affected zone at weld joints, which is very beneficial to the weld structure of mining chains. Adding appropriate amounts of Cr and Ni to steel is beneficial to improving its corrosion resistance. However, it is important to note that the Cr content in steel should not be too high. When the Cr content in steel is too high, the formation of carbides during heat treatment will consume a large amount of C in the steel, and a large amount of carbides will accumulate at grain boundaries, reducing the toughness of the material and significantly increasing the carbon equivalent, thereby reducing the flash weldability of the chain steel. Based on this, the Cr content is controlled at 0.5-1.8%.

[0022] Ni: Ni can exist in steel in solid solution form. Ni can be used in combination with Cr to significantly improve the hardenability of steel. Adding an appropriate amount of Ni to steel can lower the carbon content at the eutectoid point, which is beneficial for improving the strength of the steel. Furthermore, as shown by the carbon equivalent formula, Ni has a relatively small coefficient and therefore has a smaller impact on weldability. However, Ni is a valuable alloying element, and adding too much Ni will increase production costs. Therefore, to obtain excellent performance while ensuring low production costs, the Ni content is controlled at 2.5-3.5%.

[0023] Mo: Mo mainly exists in steel in solid solution form, which can exert a solid solution strengthening effect, improve the hardenability of steel, and facilitate the formation of martensite during quenching. However, excessive Mo should not be added to steel. Too much Mo significantly increases the carbon equivalent of the material, which is detrimental to the flash welding performance of chain steel; moreover, Mo is a valuable alloying element, and excessive Mo addition leads to increased production costs. Therefore, the Mo content is controlled at 0.2-0.5%.

[0024] Cu: Adding an appropriate amount of Cu can significantly improve the corrosion resistance of steel and reduce its susceptibility to hydrogen-induced cracking. However, it should be noted that excessive Cu content is detrimental to the weldability of steel and can easily cause copper embrittlement, deteriorating the surface properties of the steel. Therefore, the Cu content is controlled at 0.03-0.2%.

[0025] Al: Al primarily functions as a deoxidizer and nitrogen fixator. Al can combine with nitrogen to form AlN, which effectively refines grain size. However, it's important to note that excessive Al content in steel can negatively impact its casting properties and toughness. Therefore, the Al content is controlled at 0.01-0.05%.

[0026] Nitrogen (Nb): As a strong carbide-forming element, Nb can inhibit recrystallization in steel, thus effectively refining the grain size. However, it's important to note that the Nb content in steel should not be too high. Excessive Nb content can lead to the formation of coarse NbC particles under high-temperature tempering conditions, deteriorating the steel's low-temperature impact resistance. Therefore, the Nb content is controlled at 0.008-0.025%.

[0027] V: As a strong carbide-forming element, V can significantly improve the strength of steel through dispersed precipitation. However, if the addition amount is too high, it will reduce the toughness and weldability of the steel. Based on this, the content of V is controlled at 0.03-0.25%.

[0028] Nitrogen (N): Nitrogen is an austenite-forming element and also an MX-type precipitate-forming element. To avoid nitrogen accumulation in steel, the steel should not contain excessive amounts of N. Furthermore, nitrogen enrichment occurs during the addition of alloying elements and the casting process. However, excessively low N content increases production costs and is detrimental to steel microstructure refinement. Therefore, the N content is controlled at 0.002-0.008%.

[0029] Preferably, in the chain steel of the present invention, the content of impurity elements by mass percentage satisfies: P≤0.012%, S≤0.01%, O≤0.002%, H≤0.00015%.

[0030] In this invention, elements P, S, O, and H are all impurity elements in steel. Where technically feasible, the content of impurity elements in the material should be reduced as much as possible to obtain steel with better performance and superior quality.

[0031] Both phosphorus (P) and sulfur (S) are unavoidable harmful elements in steel, and both deteriorate its properties. Although P can improve the corrosion resistance of steel, its negative effects outweigh its negative ones overall. Therefore, the P content is controlled to no more than 0.012%, and the S content is controlled to no more than 0.01%.

[0032] O (oxygen) is an impurity element that can combine with deoxidizing elements such as Al in steel to form oxides and complex inclusions, which are detrimental to the steel's properties. Therefore, the O content is controlled to not exceed 0.0015%.

[0033] Impurity element hydrogen (H) tends to accumulate at defects in steel. High-strength steels, especially those with tensile strengths exceeding 1000 MPa, are particularly sensitive to H content. Hydrogen-induced delayed fracture caused by H can lead to premature chain failure. Therefore, the H content is controlled to no more than 0.00015%.

[0034] In other embodiments, the steel may also contain other harmful elements, such as As, Pb, Sn, Sb, Bi, etc. The content of these harmful elements should be reduced as much as possible in accordance with national laws, regulations, and standards.

[0035] In this invention, the strength and toughness of steel are adjusted by combining Mn, Ni, Mo, Cr, V, Cu, and C elements, thereby obtaining high-strength and high-toughness chain steel. These alloying elements have different coefficients of influence on strength and toughness. Cr and V elements mainly strengthen the matrix by forming precipitates with C and N elements; Ni, Mn, Mo, Cu, and other elements mainly solid-solve with Fe elements, improving strength through solid solution strengthening.

[0036] Preferably, the alloying coefficient A of the chain steel is... I Satisfy: A I= 4.0 - 5.0, where A I = 0.3×Mn+Cr+1.2×Mo+2×V+0.7×Ni+0.5×Cu, where each chemical element represents its content as a percentage by mass. Note: When calculating, the value before the percentage sign should be substituted. For example, when Mn=1.2%, Cr=0.9%, Mo=0.2%, V=0.03%, Ni=3.5%, Cu=0.2%, A I =0.3×1.2+0.9+1.2×0.2+2×0.03+0.7×3.5+0.5×0.2=4.11.

[0037] Without being bound by any theory, when the content of various chemical elements (e.g., C, Si, Mn, etc.) in the chain steel meets the range defined in claim 1, chain steel with excellent performance can be obtained, resulting in a yield strength R of the chain steel. p0.2 ≥1200MPa, tensile strength R m ≥1350MPa, elongation A≥12%, reduction of area Z≥50%, and room temperature impact energy A KV ≥80J.

[0038] Preferably, by satisfying 4.0≤A I A yield strength ≤5.0 can further improve the performance of the chain steel, increasing the yield strength R of the chain steel. p0.2 ≥1260MPa, tensile strength R m ≥1385MPa, elongation A≥13%, reduction of area Z≥53%, and room temperature impact energy A KV ≥85J.

[0039] Specifically, after conducting extensive experimental analysis, the inventors discovered that when the alloying coefficient A of the steel... I Satisfy A I When A = 4.0-5.0, fine, dispersed nanoscale carbides can be formed in the steel after heat treatment, precipitating within the lamellar tempered martensite structure. This further improves the steel's strength, while also enhancing its plasticity and toughness. When A... I When A < 4.0, the content of alloying elements in the steel is relatively low, which is not conducive to further improving the strength of the steel after heat treatment; when A I When the temperature is >5.0, the content of alloying elements in the steel is relatively high, which makes it prone to temper brittleness and is not conducive to further improving toughness and plasticity.

[0040] Preferably, the microstructure of the chain steel (i.e., the finished chain steel obtained after quenching and tempering in step 3 below) is tempered martensite, wherein the size of the interlaminar carbides in the martensite is ≤250nm.

[0041] Preferably, the chain steel has the following properties: yield strength R p0.2 ≥1200MPa, tensile strength R m ≥1350MPa, elongation A≥12%, reduction of area Z≥50%, room temperature impact energy A KV ≥80J. More preferably, the chain steel has the following properties: yield strength R p0.2 ≥1260MPa, tensile strength R m ≥1385MPa, elongation A≥13%, reduction of area Z≥53%, and room temperature impact energy A KV ≥85J.

[0042] On the other hand, the present invention relates to a method for manufacturing the above-mentioned chain steel, the method comprising the following steps:

[0043] (1) The molten steel is smelted and cast to obtain a billet;

[0044] (2) The billet is heated and rolled to obtain steel.

[0045] (3) The steel is quenched and tempered twice. During the quenching process, the heating temperature is 850-950℃ and the holding time is 1-4h. The tempering includes the first tempering and the second tempering. The tempering temperature of the first tempering is 350-550℃ and the holding time is 0.5-3h. After the first tempering, the steel is water-cooled to room temperature and then tempered twice. The tempering temperature of the second tempering is 200-350℃ and the holding time is 0.5-3h. After the second tempering, the steel is water-cooled to room temperature.

[0046] Preferably, in step (1), the molten steel is smelted using an electric furnace or converter, wherein the molten steel is subjected to LF and VD or RH vacuum refining.

[0047] Preferably, in step (2), during the heating operation, the heating temperature is 1150-1250℃ and the holding time is 3-10h.

[0048] Preferably, in step (2), during the rolling operation, the initial rolling temperature is ≥1050℃ and the final rolling temperature is 850-980℃.

[0049] Preferably, in step (2), the rolled steel has a specification of Φ35-150mm.

[0050] Preferably, in step (2), the billet is descaled by high-pressure water after heating and before rolling.

[0051] Preferably, in step (2), after rolling, the steel is slowly cooled in an insulation pit for ≥24 hours.

[0052] Preferably, in step (2), the microstructure of the rolled steel is bainite with an average grain size of less than 28 μm. In this paper, the "average grain size" is determined according to the standard GB / T 6394 "Method for determination of average grain size of metals".

[0053] In the above manufacturing method, heating temperature and tempering temperature refer to the set temperature of the heating furnace; initial rolling temperature and final rolling temperature refer to the surface temperature of the steel.

[0054] In the above manufacturing method, the inventors optimized the quenching and tempering heat treatment process in step (3). In step (3), after the steel undergoes quenching heat treatment, a martensitic structure with fine lamellar structure can be formed. The alloying elements in the steel exist in the martensite in the form of supersaturated solid solutions. The steel has high strength but relatively poor plasticity and impact toughness. By adopting an optimized secondary tempering heat treatment, the supersaturated alloying elements in the martensite are dispersed and precipitated in the form of nanoscale carbides between the martensite lamellars. The size of the interlamellar carbides is ≤250nm. This can significantly improve the strength of the steel, while avoiding temper brittleness, so that the steel has both high strength and excellent impact performance.

[0055] Preferably, in step (3), the microstructure of the steel obtained after quenching and secondary tempering is tempered martensite, and the size of the interlaminar carbides is ≤250nm.

[0056] In this article, “size” in relation to a carbide refers to the size of a single carbide, specifically the length of the longest line segment passing through the center of the carbide, such as the diameter (when the carbide is spherical or nearly spherical), the major axis (when the carbide is ellipsoidal or nearly ellipsoidal), or other length (when the carbide is of other shapes).

[0057] Compared to existing technologies, the inventors have developed a superior chain steel by employing a reasonable chemical composition design (e.g., optimizing the design of strengthening elements such as Si, Mn, Ni, Cr, and Mo in the steel) and optimizing the manufacturing process (especially a reasonable quenching + secondary tempering heat treatment process), which gives the steel a good balance of strength and toughness.

[0058] The chain steel of this invention has a reasonable chemical composition and process design, a wide process window, and is easy to manufacture, enabling mass commercial production. The chain steel obtained by the manufacturing method of this invention has good strength and toughness, and can be widely used in mining, marine engineering, and other applications requiring high-strength and high-toughness steel. Attached Figure Description

[0059] Figure 1 This is a photograph of the microstructure of the chain steel in Embodiment 1 of the present invention after rolling.

[0060] Figure 2 This is a photograph of the microstructure of the chain steel in Embodiment 1 of the present invention after heat treatment. Detailed Implementation

[0061] The chain steel and its manufacturing method described in this invention will be further explained and illustrated below with reference to specific embodiments. However, the following description is illustrative and intended to explain the invention, and is not intended to limit the scope of the invention to the scope of this description.

[0062] Examples 1-6 and Comparative Examples 1-2

[0063] The chain steel in Examples 1-6 was obtained through the following steps:

[0064] (1) The molten steel is smelted and continuously cast according to the formula shown in Table 1 below to obtain a billet. Specifically, the smelting can be carried out in an electric furnace or converter, and the molten steel undergoes LF refining and VD or RH vacuum treatment;

[0065] (2) The billet is heated and rolled into steel with finished dimensions (Φ35-150mm). The steel is then placed in a heat-insulating pit for slow cooling for ≥24 hours. Specifically, the billet heating temperature is 1150-1250℃, the holding time is 3-10 hours, and after descaling by high-pressure water, the billet is rolled, with an initial rolling temperature ≥1050℃ and a final rolling temperature of 850-980℃; and

[0066] (3) Quenching and secondary tempering of steel. Specifically, during quenching, the heating temperature is 850-950℃ and the holding time is 1-4h; secondary tempering includes first tempering and second tempering. The tempering temperature of the first tempering is 350-550℃ and the holding time is 0.5-3h. After the first tempering, the steel is water-cooled to room temperature and then subjected to second tempering. The tempering temperature of the second tempering is 200-350℃ and the holding time is 0.5-3h. After the second tempering, the steel is water-cooled to room temperature.

[0067] The chain steel of Comparative Examples 1-2 was prepared using the same method as described above, according to the formulation shown in Table 1 below, except that one or more of the chemical element content or manufacturing process parameters of Comparative Examples 1-2 did not meet the requirements of the present invention.

[0068] Table 1 lists the chemical compositions of the chain steels of Examples 1-6 and Comparative Examples 1-2.

[0069] Table 1 (wt%, balance Fe and other unavoidable impurities other than P, S, N, O and H)

[0070] C Si Mn Cr Ni Mo Cu Al Nb V N P S O H <![CDATA[A I ]]> Example 1 0.21 0.34 0.71 1.57 2.75 0.31 0.04 0.026 0.021 0.05 0.0077 0.007 0.007 0.0019 0.00015 4.20 Example 2 0.25 0.47 0.98 0.53 2.91 0.49 0.12 0.011 0.024 0.25 0.0067 0.012 0.008 0.0016 0.0001 4.01 Example 3 0.19 0.3 0.82 1.08 3.09 0.41 0.15 0.048 0.017 0.14 0.0048 0.006 0.005 0.0007 0.00014 4.34 Example 4 0.27 0.41 0.35 1.36 2.54 0.28 0.18 0.017 0.013 0.18 0.0055 0.01 0.009 0.0005 0.00015 4.03 Example 5 0.29 0.25 1.17 0.82 3.47 0.22 0.11 0.042 0.011 0.21 0.0035 0.009 0.002 0.0015 0.00012 4.34 Example 6 0.23 0.21 0.51 1.78 3.29 0.39 0.08 0.035 0.008 0.09 0.0026 0.012 0.002 0.0012 0.00011 4.92 Comparative Example 1 0.25 0.15 1.3 0.55 0.98 0.56 0.11 0.027 0.003 0.005 0.0086 0.008 0.006 0.0012 0.0002 2.36 Comparative Example 2 0.22 0.32 0.48 0.81 3.02 0.55 0.02 0.03 0.02 0.05 0.01 0.013 0.006 0.0015 0.0002 3.84

[0071] Note: A I =0.3×Mn+Cr+1.2×Mo+2×V+0.7×Ni+0.5×Cu, where each chemical element represents the content of the corresponding element as a percentage by mass. When calculating, the value before the percentage sign of the mass percentage content should be substituted.

[0072] Tables 2-1 and 2-2 list the specific process parameters in the methods described above for manufacturing the chain steel of Examples 1-6 and Comparative Examples 1-2.

[0073] Table 2-1

[0074]

[0075] Table 2-2

[0076]

[0077] Samples were taken from the chain steels of Examples 1-6 and Comparative Examples 1-2, respectively, to obtain corresponding samples. Tensile tests and Charpy impact tests were performed on the obtained steel samples to obtain performance data for the chain steels of the examples and comparative examples. The test results of the steels of each example and comparative example are listed in Table 3.

[0078] The testing methods for the relevant performance parameters are as follows:

[0079] Tensile test: According to national standard GB / T 2975, the chain steel of Examples 1-6 and Comparative Examples 1-2 were sampled and made into tensile specimens, and tensile properties were tested according to national standard GB / T 228.1.

[0080] Charpy impact test: According to national standard GB / T 2975, chain steel samples from Examples 1-6 and Comparative Examples 1-2 were taken and impact test specimens were prepared. Impact performance was tested according to national standard GB / T 229.

[0081] Table 3 lists the test results of the chain steel in Examples 1-6 and Comparative Examples 1-2.

[0082] Table 3

[0083]

[0084] As can be seen from Table 3, the chain steel of Examples 1-6 of the present invention exhibits excellent comprehensive performance, and the yield strength R of the chain steel is [missing information]. p0.2 ≥1260MPa, tensile strength R m The chain steel of Examples 1-6 of this invention exhibits a comprehensive performance significantly superior to that of Comparative Examples 1-2, with an elongation of ≥1385 MPa, elongation A≥13.5%, reduction of area Z≥50%, and room temperature impact energy AKV≥80 J.

[0085] As can be seen from Tables 1 and 3, compared with the chain steel of Comparative Examples 1-2, the chemical composition (especially the alloying coefficient) of the chain steel of Examples 1-6 of the present invention falls within the scope of protection. At the same time, the optimized quenching + secondary tempering heat treatment process is adopted, so it has excellent impact toughness while obtaining high strength.

[0086] The present invention uses an optical microscope to observe the microstructure of the chain steel of Example 1 after rolling, and the results are as follows. Figure 1 As shown. By Figure 1 It can be seen that the chain steel of Embodiment 1 of the present invention has a bainitic microstructure after rolling, with an average grain size of less than 28 μm.

[0087] Furthermore, the present invention uses scanning electron microscopy to observe the microstructure of the chain steel of Example 1 after quenching and secondary tempering heat treatment, and the results are as follows: Figure 2 As shown. By Figure 2 As can be seen, the microstructure of the chain steel in Embodiment 1 of the present invention after heat treatment is tempered martensite with small interlamellar spacing, and fine, dispersed nanoscale carbides precipitated between the martensite lamellars, with a carbide size ≤250nm. These fine nanoscale carbides can significantly improve the strength and toughness of the steel, thereby obtaining a high-strength, high-toughness mining chain steel with excellent properties.

[0088] In summary, this invention, through rational chemical composition design and optimized process, yields high-strength and high-toughness mining chain steel with excellent performance, which can be widely used in marine engineering, mining machinery and other fields requiring high-strength steel.

[0089] It should be noted that all technical features described in this application can be freely combined or combined in any way, unless they contradict each other. Various modifications and variations can be made to this invention without departing from its scope, as will be apparent to those skilled in the art. For example, features shown or described as part of one embodiment can be used with another embodiment to produce yet another embodiment. Therefore, this invention is intended to cover these modifications and variations falling within the scope of the appended claims and their equivalents.

Claims

1. A type of chain steel, characterized in that, In addition to containing over 90% Fe and unavoidable impurities, it also contains the following chemical elements by mass percentage: C: 0.18-0.30%, Si: 0.2-0.5%, Mn: 0.3-1.2%, Cr: 0.5-1.8%, Ni: 2.5-3.5%, Mo: 0.2-0.5% , Cu: 0.03-0.2%, Al: 0.01-0.05%, Nb: 0.008-0.025%, V: 0.03-0.25%, N: 0.002-0.008%; The alloying coefficient A of the chain steel I Satisfy: A I =4.00-5.00, where A I =0.3×Mn+Cr+1.2×Mo+2×V+0.7×Ni+0.5×Cu, where each chemical element represents the value before the percentage sign of the mass percentage content of the corresponding chemical element.

2. The chain steel according to claim 1, characterized in that, The chain steel contains the following chemical elements by mass percentage: C: 0.18-0.30%, Si: 0.2-0.5%, Mn: 0.3-1.2%, Cr: 0.5-1.8%, Ni: 2.5-3.5%, Mo: 0.2-0.5%, Cu: 0.03-0.2%, Al: 0.01-0.05%, Nb: 0.008-0.025%, V: 0.03-0.25%, N: 0.002-0.008%; balance Fe and unavoidable impurities; The alloying coefficient A of the chain steel I Satisfy: A I =4.00-5.00, where A I =0.3×Mn+Cr+1.2×Mo+2×V+0.7×Ni+0.5×Cu, where each chemical element represents the value before the percentage sign of the mass percentage content of the corresponding chemical element.

3. The chain steel according to claim 1, characterized in that, The content of impurity elements, expressed as a percentage by mass, shall meet the following requirements: P≤0.012%, S≤0.01%, O≤0.002%, H≤0.00015%.

4. The chain steel according to claim 1, characterized in that, The microstructure of the chain steel is tempered martensite, wherein the size of the interlaminar carbides is ≤250nm.

5. The chain steel according to any one of claims 1-4, characterized in that, The chain steel meets the following performance requirements: yield strength R p0.2 ≥1200MPa, tensile strength R m ≥1350MPa, elongation A≥12%, reduction of area Z≥50%, room temperature impact energy A KV ≥80J.

6. A method for manufacturing chain steel according to any one of claims 1-5, characterized in that, The method includes the following steps: (1) The molten steel is smelted and cast to obtain a billet; (2) Heating and rolling the billet to obtain steel; and (3) The steel is quenched and tempered twice. During the quenching process, the heating temperature is 850-950℃ and the holding time is 1-4h. The second tempering includes the first tempering and the second tempering. The tempering temperature of the first tempering is 350-550℃ and the holding time is 0.5-3h. After the first tempering, the steel is water-cooled to room temperature and then tempered twice. The tempering temperature of the second tempering is 200-350℃ and the holding time is 0.5-3h. After the second tempering, the steel is water-cooled to room temperature.

7. The method according to claim 6, characterized in that, In step (1), the molten steel is smelted using an electric furnace or converter, and the molten steel is vacuum refined using LF and VD or RH.

8. The method according to claim 6, characterized in that, In step (2), during the heating operation, the heating temperature is 1150-1250℃ and the holding time is 3-10h.

9. The method according to claim 6, characterized in that, In step (2), during the rolling operation, the initial rolling temperature is ≥1050℃ and the final rolling temperature is 850-980℃.

10. The method according to claim 6, characterized in that, In step (2), after heating and before rolling, the billet is descaled by high-pressure water.

11. The method according to any one of claims 6-10, characterized in that, In step (2), after rolling, the steel is slowly cooled in a heat preservation pit for ≥24 hours.

12. The method according to any one of claims 6-10, characterized in that, In step (2), the microstructure of the rolled steel is bainite with an average grain size of less than 28 μm.

13. The method according to any one of claims 6-10, characterized in that, In step (3), the microstructure of the steel obtained after quenching and secondary tempering is tempered martensite, and the size of the interlaminar carbides is ≤250nm.

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