A mine chain steel, chain and method of manufacturing the same

Abstract

This invention discloses a mining chain steel, which contains Fe and unavoidable impurities, and also contains the following chemical elements in the following mass percentages: C: 0.18-0.28%, Si: 0.2-0.6%, Mn: 0.9-1.6%, Cr: 0.4-0.8%, Ni: 0.9-1.6%, Mo: 0.4-0.9%, Cu: 0.02-0.25%, Al: 0.01-0.04%, Nb: 0.004-0.02%, V: 0.01-0.2%, N: 0.004-0.012%. Accordingly, the present invention also discloses a chain made of the above-mentioned mining chain steel and a corresponding manufacturing method, which specifically includes the following steps: (1) smelting and casting; (2) heating and rolling; (3) ring welding; (4) quenching heat treatment: the quenching heating temperature is 840~980℃, the holding time is 1~3h, and then water cooling is performed; (5) pickling; (6) preheating: the preheating temperature is 380~450℃, and the preheating time is ≥0.5h; (7) hot-dip galvanizing; (8) cooling and passivation: the cooling water temperature during chain cooling is 20-60℃, and the passivation time of the chain coating surface is ≥2min.

Description

Technical Field

[0001] This invention relates to a type of steel and a method for manufacturing the same, and more particularly to a chain steel and a method for manufacturing the same. Background Technology

[0002] Mining round link chains are crucial components used in mechanized coal mining underground. They are commonly used as drive chains in scraper conveyors, scraper transfer machines, coal mining machines, and coal planers, serving a transmission function. In practical applications, mining round link chains require high strength and toughness, fatigue resistance, and wear resistance to ensure normal operation. Furthermore, because coal mines are often located underground in humid and corrosive environments, mining round link chains typically also need good corrosion resistance.

[0003] In the existing technology, the mining round link chain steel commonly used in the coal mining industry is usually the mining 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).

[0004] Currently, in order to meet market demand, major steel mills in China have developed a series of high-strength steels for mining chains based on the different needs of downstream users.

[0005] For example, Chinese patent document CN110714164A, published on January 21, 2020, entitled "A High-Quality Cr54 Steel for Coal Mine Chain Links and Its Production Method", discloses a high-quality Cr54 steel for coal mine chain links. It improves the weldability of the chain steel and enhances its resistance to cold and hot brittleness by introducing carbon equivalent, cold crack sensitivity coefficient, and hot crack sensitivity coefficient.

[0006] For example, Chinese patent document CN104532143A, published on April 22, 2015, entitled "A Large-Size, High-Strength Chain Steel for Mining and Its Preparation Method", discloses an improved large-size chain steel for mining with a diameter of 40-100mm, yield strength ≥980MPa, tensile strength ≥1180MPa, elongation ≥13%, reduction of area ≥50%, and room temperature Charpy impact energy >100J.

[0007] In addition, some patent documents have optimized the steel based on the composition of 54 steel. For example, Chinese patent document with publication number CN111101078A and publication date of May 5, 2020, entitled "A Nickel-Free High-Strength Mining Round Link Chain Steel and Its Production Method", discloses a high-strength mining round link chain steel without Ni element. By reducing the content of precious metal element Ni alloy and increasing the content of C, Si, Cr and Mo alloy elements, the production cost is significantly reduced while ensuring mechanical properties.

[0008] Referring to the aforementioned existing patent literature and combining it with the current improvement solutions, it is not difficult to find that researchers in this field mainly prepare high-strength mining chain steel through composition optimization design, so as to improve the wear resistance of mining chains made of mining chain steel and enable them to achieve a longer service life.

[0009] Mining chains are mainly divided into two types: mining round link chains and mining compact chains. Mining round link chains are composed of welded links connected together, with completely consistent geometric dimensions. Mining compact chains consist of welded flat links and forged vertical links. The dimensions and type of the flat links are consistent with those of mining round link chains, while the vertical links are flat on both sides and have a smaller outer width than those of mining round link chains. The chain manufacturing process mainly includes round steel cutting, link braiding, welding, heat treatment, and pre-stretching. Link braiding mainly involves bending bars of specified length onto corresponding molds to achieve the process dimensions and shape requirements of the chain links to be welded. Welding mainly uses flash welding to weld the braided chain links into rings. Heat treatment mainly involves quenching and tempering processes to give the chain complex and contradictory comprehensive mechanical properties such as high strength, high toughness, wear resistance, and corrosion resistance, as well as strict requirements for microstructure and hardness. After heat treatment, the chain is pre-stretched to make the chain links more symmetrical and the structure more reasonable. This effectively controls the chain size, ensuring that the chain link size meets the standard requirements and guarantees the dimensional requirements of the chain segment length, total length, and pairing tolerances.

[0010] However, it should be noted that in actual applications, underground coal mines are mostly humid working environments. High-strength mining chains are inevitably affected by environmental corrosion during use. Moreover, high-strength mining chains have high stress and are also more sensitive to stress corrosion. During use, they are very prone to corrosion fatigue fracture (frequent low-load brittle fractures can occur in as little as a few days or even a few months), causing premature failure of the mining chains.

[0011] Based on this, the present invention aims to obtain a new type of mining chain steel with excellent comprehensive performance. It not only has high strength but also excellent toughness-plasticity matching. After coating treatment, it has excellent corrosion resistance. It can be effectively used to manufacture chains, thereby solving the problem of the service life of existing mining chains due to the mismatch between strength, toughness-plasticity, weldability and corrosion resistance. Summary of the Invention

[0012] One of the objectives of this invention is to provide a mining chain steel with good strength and toughness. After being made into a chain and subjected to quenching and coating treatment, it can achieve a high strength-plasticity ratio and excellent corrosion resistance. It can effectively solve the problem of service life affected by the mismatch between strength, toughness, plasticity and corrosion resistance in existing mining chains.

[0013] To achieve the above objectives, this invention provides a mining chain steel containing Fe and unavoidable impurities, as well as the following chemical elements in the following mass percentages:

[0014] C: 0.18~0.28%, Si: 0.2~0.6%, Mn: 0.9~1.6%, Cr: 0.4~0.8%, Ni: 0.9~1.6%, Mo: 0.4~0.9 %, Cu: 0.02~0.25%, Al: 0.01~0.04%, Nb: 0.004~0.02%, V: 0.01~0.2%, N: 0.004~0.012%.

[0015] Furthermore, in the mining chain steel described in this invention, the mass percentage content of each chemical element is as follows:

[0016] C: 0.18–0.28%, Si: 0.2–0.6%, Mn: 0.9–1.6%, Cr: 0.4–0.8%, Ni: 0.9–1.6%, Mo: 0.4–0.9%, Cu: 0.02–0.25%, Al: 0.01–0.04%, Nb: 0.004–0.02%, V: 0.01–0.2%, N: 0.004–0.012%; balance Fe and unavoidable impurities.

[0017] The design principles of each chemical element in the mining chain steel described in this invention are as follows:

[0018] C: In the mining chain steel described in this invention, carbon (C) is an essential element for ensuring the strength of the steel. Increasing the C content in the steel will increase the non-equilibrium transformation capacity of the steel, thereby significantly improving the strength of the steel. However, it should be noted that 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 also significantly increase the carbon equivalent of the material, deteriorating the weldability of the steel. Based on this, in the mining chain steel described in this invention, the mass percentage of C is controlled between 0.18% and 0.28%.

[0019] Si: In the mining chain steel described in this invention, Si can dissolve in the steel to improve its strength and hardness, and reduce the diffusion ability of C in ferrite, thereby inhibiting the precipitation of cementite. Furthermore, adding an appropriate amount of Si to the steel can improve the stability of austenite during cooling, thus preventing the formation of coarse carbides. However, it should be noted that the Si content in the steel should not be too high, as excessive Si content will increase the brittleness of the steel. Therefore, in the mining chain steel described in this invention, the mass percentage of Si is controlled between 0.2% and 0.6%.

[0020] Mn: In the mining chain steel described in this invention, adding an appropriate amount of Mn can not only improve the stability of austenite in the steel, but also improve the hardenability of the steel. Furthermore, in this invention, Mn can also play a role in solid solution strengthening, which can increase the strength of martensite in the steel, 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 easily during quenching and heating, and can promote the segregation of harmful elements at grain boundaries. Based on this, in the mining chain steel described in this invention, the mass percentage of Mn is controlled between 0.9% and 1.6%.

[0021] Cr: In the mining chain steel described in this invention, adding an appropriate amount of Cr not only improves the hardenability of the steel but also forms a hardened martensitic structure, thereby improving the strength of the steel. Furthermore, Cr carbides can slow down grain growth in the heat-affected zone at the weld joint, which is very beneficial to the weld structure of the mining chain. Adding appropriate amounts of Cr and Ni to the steel is beneficial to improving its corrosion resistance. However, it should be noted that the Cr content in the steel should not be too high. When the Cr content is too high, the carbides generated during heat treatment will consume a large amount of C in the steel, which is not conducive to the formation of retained austenite. Moreover, 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, in the mining chain steel described in this invention, the mass percentage of Cr is controlled between 0.4% and 0.8%.

[0022] Ni: In the mining chain steel described in this invention, Ni is an austenite-forming element that can exist in the steel in solid solution form. Ni can be used in combination with Cr to significantly improve the hardenability of the steel. Adding an appropriate amount of Ni to the steel can reduce the C content at the eutectoid point and increase the volume fraction of pearlite, which is beneficial to improving the strength of the steel. In addition, Ni has a relatively small effect on weldability, but Ni is a valuable alloying element. Therefore, in order to ensure a low production cost, the mass percentage of Ni in the mining chain steel described in this invention is controlled between 0.9% and 1.6%.

[0023] Mo: In the mining chain steel described in this invention, Mo mainly exists in the steel in a solid solution form. It can play a solid solution strengthening role and is beneficial to improving the hardenability of the steel, so that the steel can form martensite during quenching. However, it should be noted that excessive Mo should not be added to the steel. When too much Mo is added to the steel, it will significantly increase the carbon equivalent of the material, which is detrimental to the flash welding performance of the chain steel. In addition, Mo is also a valuable alloying element, and adding too much Mo will lead to an increase in production costs. Based on this, in the mining chain steel described in this invention, the mass percentage of Mo is controlled between 0.4% and 0.9%.

[0024] Cu: In the mining chain steel described in this invention, adding an appropriate amount of Cu can significantly improve the corrosion resistance of the steel and reduce its susceptibility to hydrogen-induced cracking. However, it should be noted that excessive Cu content in the steel not only negatively impacts its weldability but also easily leads to copper embrittlement, deteriorating the surface properties of the steel. Therefore, in the mining chain steel described in this invention, the mass percentage of Cu is controlled between 0.02% and 0.25%.

[0025] Al: In the mining chain steel described in this invention, Al mainly functions as a deoxidizer and nitrogen fixer. Al can combine with N to form AlN, which effectively refines the grain size. However, it is important to note that the Al content in the steel should not be too high. Excessive Al content not only affects the steel's casting properties but also impairs its toughness. Therefore, in the mining chain steel described in this invention, the mass percentage of Al is controlled between 0.01% and 0.04%.

[0026] Nb: In the mining chain steel described in this invention, Nb, as a strong carbide-forming element, can inhibit recrystallization of the steel by adding an appropriate amount, thereby effectively refining the grains and improving the quality of the weld. However, the Nb content in the steel should not be too high. When the Nb content is too high, Nb will combine to form coarse NbC particles under high-temperature tempering conditions, which will not only weaken the grain refinement function but also deteriorate the impact performance of the steel. Therefore, in order to maximize the beneficial effects of Nb, the mass percentage of Nb in the mining chain steel described in this invention is controlled between 0.004% and 0.02%.

[0027] V: In the mining chain steel described in this invention, V, as a strong carbide-forming element, can effectively refine the steel's microstructure and grain size, and can significantly improve the steel's strength through dispersed precipitation. However, it should be noted that the V content in the steel should not be too high. When the amount of V added to the steel is too high, it will reduce the steel's toughness and weldability. Therefore, in the mining chain steel described in this invention, the mass percentage of V is controlled between 0.01% and 0.2%.

[0028] N: In the mining chain steel described in this invention, N is an austenite-forming element and also an MX-type precipitate-forming element. N can combine with Nb to form Nb(C,N) particles in the steel, effectively refining the microstructure, preventing coarsening of the microstructure during welding, and improving welding quality. It is important to note that the N content in the steel should not be too high. Excessive N content can lead to premature precipitation and growth of MX-type precipitates, reducing the microstructure refinement effect and decreasing the impact toughness and fatigue performance of the mining chain steel. Therefore, in the mining chain steel described in this invention, the mass percentage of N is controlled between 0.004% and 0.012%.

[0029] Furthermore, in the mining chain steel described in this invention, among the unavoidable impurities, P≤0.015%, S≤0.01%, O≤0.0015%, and H≤0.0002%.

[0030] In the above technical solution, P, S, O and H are all impurity elements in steel. Under the condition that the technical conditions permit, in order to obtain mining chain steel with better performance and higher quality, the content of impurity elements in the material should be reduced as much as possible.

[0031] In the mining chain steel described in this invention, both phosphorus (P) and sulfur (S) are unavoidable harmful impurities in the steel and both deteriorate its performance. Although P can improve the corrosion resistance of the steel, its negative effects are greater overall. Therefore, in this invention, the P content is controlled to be P≤0.015%, and the S content is controlled to be S≤0.01%.

[0032] Furthermore, in this invention, 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 steel. Therefore, in this invention, the O element is controlled to satisfy O≤0.0015%.

[0033] Furthermore, impurity element hydrogen (H) tends to accumulate at defects in steel, especially in high-strength steels with tensile strengths exceeding 1000 MPa. These steels are particularly sensitive to H content, as it can cause hydrogen-induced delayed fracture and easily lead to premature chain failure. Therefore, in this invention, the H content is controlled to be H ≤ 0.0002%.

[0034] Of course, in some other implementations, the steel may contain other harmful elements, such as As, Pb, Sn, Sb, Bi, etc., and the content of these harmful elements should be reduced as much as possible.

[0035] Accordingly, another objective of the present invention is to provide a chain with excellent performance, which has a high strength-to-plasticity ratio and excellent corrosion resistance, and can be widely used in engineering machinery, mining and marine engineering and other occasions that require high strength, toughness and high corrosion resistance chains.

[0036] To achieve the above objectives, the present invention proposes a chain, which is specifically made of the mining chain steel described above.

[0037] Furthermore, in the chain described in this invention, its microstructure is needle-shaped tempered martensite.

[0038] Furthermore, in the chain described in this invention, the length of the needle-like tempered martensite is ≤25μm.

[0039] Furthermore, the chain described in this invention satisfies the following performance requirements: yield strength R p0.2 ≥1100MPa, tensile strength R m ≥1250MPa, elongation A≥13%, reduction of area Z≥50%, room temperature impact energy A KV ≥70J.

[0040] Furthermore, in the chain described in this invention, the zinc layer thickness on the chain surface after coating treatment is 30-500 μm, and its resistance to neutral salt spray corrosion rate is ≤0.25 mm / a.

[0041] Furthermore, another object of the present invention is to provide a method for manufacturing the above-mentioned chain, which is simple to produce and the chain obtained has high strength, excellent toughness-plasticity matching and excellent corrosion resistance.

[0042] To achieve the above objectives, the present invention provides a method for manufacturing the aforementioned chain, comprising the following steps:

[0043] (1) Smelting and casting;

[0044] (2) Heating and rolling;

[0045] (3) Ring welding;

[0046] (4) Quenching heat treatment: The quenching heating temperature is 840~980℃, the holding time is 1~3h, and then water cooling is performed;

[0047] (5) Pickling;

[0048] (6) Preheating: The preheating temperature is 380~450℃, and the preheating time is ≥0.5h;

[0049] (7) Hot-dip galvanizing;

[0050] (8) Cooling and passivation: The cooling water temperature during chain cooling is 20-60℃, and the passivation time of the chain coating surface is ≥2min.

[0051] In this invention, the inventors, through the rational design of alloying elements and optimized manufacturing processes, fully utilize the influence of various alloying elements and the processing techniques of mining chains on the microstructure, precisely controlling the microstructure of the mining chain steel of this invention. In this manufacturing process, after quenching heat treatment, the steel forms a acicular martensite structure. Through preheating and hot-dip galvanizing of the chain, fine carbides are dispersed and precipitated in the supersaturated solid solution formed by quenching, improving the chain's performance; simultaneously, a zinc layer of a certain thickness is formed on the chain surface, thereby improving the chain's corrosion resistance.

[0052] In the chain manufacturing process of this invention, the traditional chain quenching and tempering process is combined with the hot-dip galvanizing process, eliminating the chain tempering process. The precipitation of carbides in the steel is fully utilized during the hot-dip galvanizing process, so that the mining chain steel of this invention has both high strength and ductility, as well as good corrosion resistance. This also makes the chain made based on this mining chain steel have excellent performance.

[0053] In step (1) of the manufacturing method of the present invention, the smelting operation can be carried out in an electric furnace or converter, and the steel can be refined by LF and VD or RH vacuum refining so that the chemical composition meets the design requirements of the present invention before casting. Accordingly, in the casting process, continuous casting process can be used to cast ingots, and the superheat of the molten steel in the tundish can be controlled at 15-40°C, and the casting speed of the continuous casting machine can be 0.4-0.8 m / min.

[0054] Furthermore, in step (2) of the manufacturing method of the present invention, the ingot can be heated and rolled into finished product size using a rolling process, and the finished product size range can be Φ26~100mm. In the rolling process, the billet heating temperature can preferably be controlled to be ≥1150℃, the heating time to be 3~6h, the final rolling temperature to be ≥850℃, and the billet can be air-cooled or slowly cooled to room temperature after rolling.

[0055] In addition, in step (2) above, the billet can be controlled to start rolling after being descaled by high-pressure water after leaving the heating furnace, and air cooling or slow cooling can be used after rolling.

[0056] It should be noted that in the manufacturing method of the present invention, ring welding is required in step (3). The round steel cut to a fixed length can be braided into a single ring on a braiding machine and then welded into a complete ring by flash welding.

[0057] In step (4) of the manufacturing method described in this invention, the chain needs to undergo quenching heat treatment, specifically controlling the quenching heating temperature to be 840–980°C and the holding time to be 1–3 hours, followed by water quenching. In step (4), after the quenching heat treatment process, the matrix structure of the mining chain steel changes from austenite at high temperature to acicular martensite, and the length of the acicular martensite is ≤25μm. The fine acicular martensite is beneficial for the precipitation of fine and dispersed carbides from the steel during subsequent preheating and plating, thereby improving the mechanical properties of the chain.

[0058] In the manufacturing method described above, the chain needs to be pickled in step (5). Specifically, a 15% sulfuric acid solution or a 20% hydrochloric acid solution can be used for pickling to remove the oxide scale from the chain surface. After pickling, the chain needs to be cleaned to remove any adhering substances from its surface.

[0059] In the manufacturing method described above, the chain needs to be preheated in step (6) to prevent problems such as zinc explosion during hot-dip galvanizing. Specifically, the preheating temperature of the chain is controlled at 380-450°C, and the preheating time is ≥0.5h. During the preheating process, the supersaturated martensite structure formed by chain quenching begins to precipitate carbides, which will reduce its strength, but the elongation and impact toughness will begin to increase.

[0060] In the manufacturing method of the present invention, in step (8), the chain needs to be cooled and passivated to improve the corrosion resistance of the galvanized surface layer. Therefore, in the cooling and passivation process, the cooling water temperature during chain cooling is specifically controlled at 20-60℃, and the passivation time of the chain coating surface is controlled at ≥2min.

[0061] The mining chain steel described in this invention controls the alloy element content to give the steel good mechanical properties. By performing a compact quenching and galvanizing treatment on the manufactured chain, the quenching and tempering heat treatment of the chain is combined with the hot-dip galvanizing process, which can form a galvanized layer on the surface of the chain, thereby significantly improving the corrosion resistance of the mining chain, preventing corrosion cracking during service, and extending the service life.

[0062] Furthermore, in the manufacturing method described in this invention, during the casting process in step (1), a continuous casting process is used to cast the ingot, the superheat of the molten steel in the tundish is controlled to be 15-40°C, and the casting speed of the continuous casting machine is 0.4-0.8 m / min.

[0063] Furthermore, in the manufacturing method described in this invention, in step (2), the ingot is heated and then rolled into the finished product size; the heating temperature of the billet is controlled to be ≥1150℃, the heating time is 3~6h, and the final rolling temperature is ≥850℃; after rolling, it is cooled to room temperature.

[0064] Furthermore, in the manufacturing method described in this invention, in step (2), the finished product size range is Φ26~100mm.

[0065] Furthermore, in the manufacturing method described in this invention, in step (7), the temperature of the zinc liquid is controlled to be 410–530°C.

[0066] In the above technical solution of the present invention, the chain needs to be hot-dip galvanized in step (7). The zinc liquid temperature can preferably be controlled at 410-530°C so that the zinc layer thickness on the surface of the chain after coating is controlled between 30-500μm.

[0067] Compared with the prior art, the mining chain steel, chain, and manufacturing method of the present invention have the following advantages and beneficial effects:

[0068] The mining chain steel described in this invention employs a rational chemical composition design and optimized manufacturing process, fully utilizing the influence of various alloying elements and the processing techniques of mining chains on the microstructure, thus precisely controlling the microstructure of the chain. After quenching heat treatment, the prepared steel forms a chain with a acicular martensitic structure. Preheating and hot-dip galvanizing of the chain not only allows fine carbides to disperse and precipitate in the supersaturated solid solution formed by quenching, improving the chain's performance, but also forms a zinc layer of a certain thickness on the chain surface, thereby enhancing the chain's corrosion resistance.

[0069] Applying a zinc coating to the chain surface isolates corrosive media from the chain substrate, improving the chain's corrosion resistance. Even when the coating wears off in some areas, the zinc layer in other areas still provides anodic protection, preventing corrosion during use and extending the chain's lifespan.

[0070] Therefore, the mining chain steel described in this invention has excellent comprehensive performance. The chain made from this mining chain steel not only has high strength, but also excellent toughness and plasticity matching. After coating treatment, the chain has excellent corrosion resistance, which can effectively solve the problem of the service life of existing mining chains due to the mismatch between strength, toughness and plasticity, weldability and corrosion resistance.

[0071] Accordingly, during the manufacturing process, the chemical composition of the mining chain steel described in this invention and its process design in chain preparation are reasonable, with a wide process window and convenient production, enabling mass commercial production. This mining chain steel can be made into various high-performance industrial chains for mining, mooring, etc., and is widely used in engineering machinery, mining, and marine engineering, where high-strength, high-toughness, and high-corrosion-resistant chains are required. Attached Figure Description

[0072] Figure 1 The image shows the microstructure of the finished chain made of mining chain steel according to Example 1 under a 1000x electron microscope. Detailed Implementation

[0073] The mining chain steel, chain, and manufacturing method of the present invention will be further explained and described below with reference to the accompanying drawings and specific embodiments. However, such explanation and description do not constitute an undue limitation on the technical solution of the present invention.

[0074] Examples 1-6 and Comparative Examples 1-2

[0075] The chains in Examples 1-6 were all prepared using the following steps:

[0076] (1) Slabs are obtained by smelting and continuous casting according to the chemical composition shown in Table 1 below. Smelting can be carried out by electric furnace or converter, and the steel is tapped after LF refining and VD or RH vacuum treatment. During casting, the molten steel is cast into ingots by continuous casting process, and the superheat of the molten steel in the tundish is controlled at 15-40℃, and the casting speed of the continuous casting machine is 0.4-0.8m / min.

[0077] (2) Heating and rolling: The billet is heated in a walking beam furnace and then rolled into finished size. The finished size range can be Φ26~100mm. Specifically, the billet heating temperature is ≥1150℃, the heating time is 3~6h, the final rolling temperature is ≥850℃, and the billet is air-cooled or slowly cooled to room temperature after rolling.

[0078] (3) Ring welding: After the round steel cut to a fixed length is braided into a single ring on a braiding machine, it is welded into a complete ring by flash welding.

[0079] (4) Quenching heat treatment: control the heating temperature of the ore chain to 840-980℃, hold for 1-3 hours, and then perform water quenching.

[0080] (5) Pickling: Pickling is performed using 15% sulfuric acid solution or 20% hydrochloric acid solution to remove the oxide scale on the surface of the chain, and the chain is cleaned to remove the surface deposits.

[0081] (6) Preheating treatment: The preheating temperature (tempering temperature) of the chain is controlled at 380-450℃, and the preheating time (tempering time) is ≥0.5h.

[0082] (7) Hot-dip galvanizing: The chain is hot-dip galvanized and the temperature of the zinc bath is controlled between 410 and 530°C to control the thickness of the zinc layer on the chain surface to be 30-500 μm.

[0083] (8) Cooling and passivation: Cool the hot-dip galvanized chain to room temperature and control the cooling water temperature during chain cooling to 20-60℃; passivate the chain coating surface with chromate and control the passivation time of the chain coating surface to ≥2min.

[0084] In this invention, based on the mining chain steel of Examples 1-6, the chains corresponding to the mining chain steel of each example can be effectively obtained by using the above steps (1)-(8). In this invention, the chemical composition design and related processes of the mining chain steel used to prepare the chains of Examples 1-6 all meet the design specifications of this invention, and its chemical composition design can be found in Table 1 below.

[0085] Correspondingly, the comparative steels used in the chains prepared in Comparative Examples 1-2 are finished steels from different manufacturers. The chemical composition of the comparative steels used in Comparative Examples 1-2 all have parameters that do not meet the design specifications of this invention, and the chains are produced using a traditional quenching and tempering heat treatment process.

[0086] Table 1 lists the mass percentage of each chemical element in the mining chain steel of Examples 1-6 and the comparative steel of Comparative Examples 1-2.

[0087] Table 1. (wt.%, balance Fe and other unavoidable impurities other than P, S, O and H)

[0088]

[0089] It should be noted that, in this invention, the chain preparation process differs from that of Examples 1-6 above, and the processing technology used in Comparative Examples 1-2 is different from the manufacturing process used in Examples 1-6. The heat treatment processing technology used in Comparative Examples 1-2 is based on the parameters recommended by the supplier.

[0090] Tables 2-1 and 2-2 list the specific process parameters for the manufacturing process of the mining chain steel of Examples 1-6 and the comparative steel of Comparative Examples 1-2.

[0091] Table 2-1.

[0092]

[0093] Table 2-2.

[0094]

[0095] Therefore, in order to analyze the structure and properties of the finished chains of Examples 1-6, the present invention samples the chains of Examples 1-6 obtained after step (8) and samples the chains of Comparative Examples 1-2 to obtain chain samples corresponding to each example and comparative example. The chain samples of each example and comparative example steel are observed, their microstructure is analyzed, and the mechanical properties of the chain samples of Examples 1-6 and Comparative Examples 1-2 are further measured.

[0096] When observing the chain steel samples of Examples 1-6 and Comparative Examples 1-2, it was found that the microstructure of the finished chains made from the mining chain steel of Examples 1-6 consisted entirely of acicular tempered martensite, and these tempered martensite particles were extremely fine. Table 3 lists the observed lengths of the acicular tempered martensite in the chains of Examples 1-6.

[0097] Table 3.

[0098]

[0099] As can be seen from Table 3 above, the acicular tempered martensite of the chains obtained in Examples 1-6 of this invention is very fine, and the length of the acicular tempered martensite is specifically between 16 and 24 μm.

[0100] Accordingly, after completing the observation of the chains of each embodiment and comparative example, in order to verify the performance of the chains, the inventors further tested the performance of the finished chains of Examples 1-6 and the comparative chains of Comparative Examples 1-2, and conducted tensile tests, impact performance tests and neutral salt spray corrosion performance tests, respectively, to obtain the performance of the chains of Examples 1-6 and the comparative chains of Comparative Examples 1-2. The specific tests are listed in Table 4 below.

[0101] The specific testing methods for the relevant tensile tests, Charpy impact tests, and neutral salt spray corrosion tests are as follows:

[0102] Tensile test: The steels of each example and the comparative example were sampled from hot-rolled round steel in accordance with the national standard GB / T 2975 and made into tensile specimens. Tensile properties were tested in accordance with the national standard GB / T 228.1 to determine the yield strength Rp0.2, tensile strength Rm, elongation A and reduction of area Z of the chains of Examples 1-6 and the comparative chains of Comparative Examples 1-2.

[0103] Charpy impact test: Steel samples from hot-rolled round steel were taken according to national standard GB / T 2975 to prepare impact specimens, and impact performance tests were conducted according to national standard GB / T 229. The impact energy (AKV) of the chains in Examples 1-6 and Comparative Examples 1-2 at room temperature was measured.

[0104] Neutral salt spray corrosion test: A 150mm long chain round steel sample was taken from the steel and sealed with silicone rubber at both ends. A 5wt% NaCl salt spray corrosion test was conducted according to GB / T 10125 standard (laboratory temperature 35℃, saturated tank temperature 47℃, corrosive medium 5 wt.% NaCl aqueous solution, pH=6.5, test sample longitudinally at a 20° angle, test time 120h, continuous spraying, salt spray deposition rate 1.5 mL / (h 80 cm). 2 After the 120-hour neutral salt spray test, the test samples were removed, the silicone rubber at both ends was peeled off, surface corrosion products were removed, the samples were dried, and their mass was recorded as M'. The salt spray corrosion rate R of the chain samples in each embodiment and comparative example was then calculated.

[0105] R = (M - M') / (S·T)

[0106] Where M is the initial mass of the sample, in g; M' is the mass of the sample after drying to remove corrosion products, in g; and S is the corrosion test area of ​​the sample, in m². 2 T represents corrosion time, with dimensions in hours; R represents salt spray corrosion rate, with dimensions in g / m³. 2 .h

[0107] Table 4 lists the test results of the chains in Examples 1-6 and Comparative Examples 1-2.

[0108] Table 4.

[0109]

[0110] As can be seen from Table 4, the chains of Examples 1-6 of this invention possess excellent comprehensive performance, exhibiting not only high strength but also excellent toughness-ductility matching, and after coating treatment, they also possess excellent corrosion resistance. The yield strength R of the chains of Examples 1-6 of this invention... p0.2 Between 1125-1230 MPa, the tensile strength R m Between 1285-1388 MPa, elongation A is between 14-17.5%, reduction of area Z is between 55-65%, and room temperature impact energy A... KV Between 75-101 J, its salt spray corrosion rate is 0.17-0.22 g / m. 2 Between .h

[0111] Accordingly, as can be seen from Table 4, the overall performance of the chains of Examples 1-6 of the present invention is significantly better than that of the chains of Comparative Examples 1-2, which use existing comparative steel as the base material.

[0112] In terms of corrosion resistance, the neutral salt spray corrosion rate of the chains in Examples 1-6 of this invention is only 1 / 10 to 1 / 8 of that in Comparative Examples 1-2. This indicates that the corrosion resistance of the chains made from the mining chain steel of Examples 1-6 designed by this invention is significantly better than that of the chains made from the existing comparative steels selected in Comparative Examples 1-2.

[0113] In summary, this invention, through rational chemical composition design and the combination of chain heat treatment and subsequent galvanizing processes, forms an optimized quenching and hot-dip galvanizing process, resulting in high-performance mining chains. The chain designed in this invention exhibits excellent overall performance, possessing not only high strength but also a superior balance of toughness and plasticity. When manufactured into a mining chain, it demonstrates excellent corrosion resistance, effectively solving the problem of service life limitations caused by the mismatch between strength, toughness, plasticity, and corrosion resistance in existing mining chains.

[0114] In practical applications, the mining chain steel described in this invention can be made into various high-performance industrial chains for mining, mooring, etc., and is widely used in engineering machinery, mining and marine engineering and other occasions that require high-strength, high-toughness and high-corrosion-resistant chains.

[0115] Figure 1 The image shows the microstructure of the finished chain made of mining chain steel according to Example 1 under a 1000x electron microscope.

[0116] like Figure 1 As shown, in this invention, the microstructure of the mining chain steel of Example 1 is acicular tempered martensite. Analysis revealed that the length of the acicular martensite in the mining chain steel of Example 1 is ≤25μm.

[0117] It should be noted that the combination of the technical features in this case is not limited to the combination methods described in the claims of this case or the combination methods described in the specific embodiments. All technical features described in this case can be freely combined or combined in any way, unless they contradict each other.

[0118] It should also be noted that the embodiments listed above are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made thereto are those that can be directly derived or easily conceived by those skilled in the art from the content disclosed in the present invention, and should all fall within the protection scope of the present invention.

Claims

1. A chain, characterized in that It is made of mining chain steel, and the mass percentage of each chemical element in the mining chain steel is as follows: C: 0.18–0.28%, Si: 0.2–0.6%, Mn: 0.9–1.6%, Cr: 0.4–0.8%, Ni: 0.9–1.6%, Mo: 0.4–0.9%, Cu: 0.02–0.25%, Al: 0.01–0.04%, Nb: 0.004–0.02%, V: 0.01–0.2%, N: 0.004–0.012%; balance Fe and unavoidable impurities. The microstructure of the chain is acicular tempered martensite, wherein the length of the acicular tempered martensite is ≤25μm; The chain has the following performances: yield strength R p0.2 ≥ 1100 MPa, tensile strength R m ≥ 1250 MPa, elongation A ≥ 13%, reduction of area Z ≥ 50%, room temperature impact energy A KV ≥ 70 J; after plating treatment, the chain surface zinc layer thickness is 30-500 μm, and neutral salt spray corrosion rate is ≤ 0.25 mm / a.

2. The chain of claim 1 wherein, In the unavoidable impurities of the mining chain steel, P≤0.015%, S≤0.01%, O≤0.0015%, H≤0.0002%.

3. The chain manufacturing method according to any one of claims 1-2, characterized by, It includes the following steps: (1) Smelting and casting; (2) Heating and rolling; (3) Ring welding; (4) Quenching heat treatment: The quenching heating temperature is 840~980℃, the holding time is 1~3h, and then water cooling is performed; (5) Pickling; (6) Preheating: The preheating temperature is 380~450℃, and the preheating time is ≥0.5h; (7) Hot-dip galvanizing; (8) Cooling and passivation: The cooling water temperature during chain cooling is 20-60℃, and the passivation time of the chain coating surface is ≥2min.

4. The chain manufacturing method according to claim 3, wherein In the casting process of step (1), the continuous casting process is used to cast the ingot into billets, and the superheat of the molten steel in the tundish is controlled to be 15-40℃, and the casting speed of the continuous casting machine is 0.4-0.8m / min.

5. The chain manufacturing method according to claim 3, wherein In step (2), the ingot is heated and rolled into finished size; the heating temperature of the billet is controlled at ≥1150℃, the heating time is 3~6h, and the final rolling temperature is ≥850℃; after rolling, it is cooled to room temperature.

6. The chain manufacturing method according to claim 5, wherein In step (2), the finished product size range is Φ26~100mm.

7. The chain manufacturing method according to claim 3, wherein In step (7), the temperature of the zinc liquid is controlled to be 410-530℃.

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