Scraper chain steel and its preparation method, scraper chain and its preparation method

Abstract

This invention provides a scraper chain steel and its preparation method, as well as a scraper chain and its preparation method. The scraper chain steel of this invention, by weight percentage, comprises: C, 0.26–0.45 wt%, Si ≤ 0.5 wt%, Mn ≤ 0.5 wt%, P ≤ 0.015 wt%, S ≤ 0.008 wt%, Cr, 0.4–1.2 wt%, Ni, 0.8–3.5 wt%, Mo, 0.40–0.65 wt%, Nb ≤ 0.06 wt%, V ≤ 0.1 wt%, Al, 0.02–0.05 wt%, H ≤ 1 ppm, with the balance being Fe and unavoidable impurities. The element types and their contents in the scraper chain steel of this invention form an effective synergy, enabling the steel to be used as a material for large-scale scraper chains while simultaneously achieving high strength and toughness.

Description

Technical Field

[0001] This invention relates to the field of metallurgy, and more specifically, to a scraper chain steel material and its preparation method, and a scraper chain and its preparation method. Background Technology

[0002] Scraper chains are chains used on scraper conveyors and transfer conveyors in coal mines. They are an important component of the three main machines and one frame in coal mines, and a crucial part ensuring smooth coal extraction. With the upgrading and intelligent development of coal mining equipment, the output of fully mechanized mining faces is constantly increasing. This is sometimes achieved by increasing the face length, and sometimes by increasing the mining height. Increased output inevitably requires the use of larger scraper chains. Larger chains present greater challenges and requirements than smaller chains, both in terms of materials and manufacturing processes, and face challenges such as material hardenability, large-section flash welding, and uniform heat treatment. Therefore, producing high-quality large chains requires improvements in materials, equipment, and processes, supplemented by optimal parameters and procedures, to ensure the final product meets customer performance requirements.

[0003] Traditional scraper chains typically use low-alloy high-strength steel, combined with a medium-temperature tempering heat treatment process to achieve good strength and toughness. For example, 23MnNiMoCr 5-4, specified in DIN 17115-2012 standard, is a commonly used scraper chain steel. Its main components include 0.20–0.26% C, 1.10–1.40% Mn, 0.40–0.60% Cr, 0.9–1.1% Ni, 0.50–0.60% Mo, and other trace alloying elements. However, with the continuous increase in the size of scraper chains, this traditional scraper chain has a small performance margin and a low safety factor, which is not conducive to coping with the complex working conditions downhole, leading to an increased risk of breakage or problems with service life due to excessive wear. To address the aforementioned issues, CN113249643 discloses a high-strength carburized chain steel for mining, which optimizes the existing heat treatment process of "quenching + medium- or high-temperature tempering" for mining chain steel to a heat treatment process of "quenching + low-temperature tempering". While this can increase the product strength by lowering the tempering temperature, it leads to a decrease in the toughness of the chain, thereby reducing the chain's fatigue resistance, stress corrosion resistance, weather resistance, and other environmental properties.

[0004] Therefore, the present invention needs to provide a new scraper chain to solve the problem that existing large-size scraper chains cannot simultaneously achieve excellent strength and toughness. Summary of the Invention

[0005] The main objective of this invention is to provide a scraper chain steel material and its preparation method, as well as a scraper chain and its preparation method, to solve the problem that large-size scraper chains in the prior art cannot simultaneously achieve excellent strength and toughness.

[0006] To achieve the above objectives, according to one aspect of the present invention, a scraper chain steel is provided, comprising, by weight percentage: C, 0.26–0.45 wt%, Si ≤ 0.5 wt%, Mn ≤ 0.5 wt%, P ≤ 0.015 wt%, S ≤ 0.008 wt%, Cr, 0.4–1.2 wt%, Ni, 0.8–3.5 wt%, Mo, 0.40–0.65 wt%, Nb ≤ 0.06 wt%, V ≤ 0.1 wt%, Al, 0.02–0.05 wt%, H ≤ 1 ppm, with the balance being Fe and unavoidable impurity elements.

[0007] Furthermore, in the scraper chain steel, the total weight percentage of alloying elements other than iron is 4.5 to 5.5 wt%.

[0008] Furthermore, by weight percentage, the scraper chain steel consists of 0.40 wt% C, 0.35 wt% Si, 0.3 wt% Mn, 0.008 wt% P, 0.005 wt% S, 0.8 wt% Cr, 2.5 wt% Ni, 0.55 wt% Mo, 0.04 wt% Nb, 0.05 wt% V, 0.04 wt% Al, 0.00005 wt% H, with the balance being Fe and unavoidable. The impurity element composition; or, the scraper chain steel is composed of 0.30 wt% C, 0.5 wt% Si, 0.5 wt% Mn, 0.015 wt% P, 0.008 wt% S, 0.8 wt% Cr, 2.0 wt% Ni, 0.40 wt% Mo, 0.01 wt% Nb, 0.02 wt% V, 0.02 wt% Al, 0.00005 wt% H, with the balance being Fe and unavoidable impurities. Elemental composition; or, the scraper chain steel is composed of 0.45 wt% C, 0.1 wt% Si, 0.1 wt% Mn, 0.002 wt% P, 0.003 wt% S, 1.1 wt% Cr, 3.0 wt% Ni, 0.60 wt% Mo, 0.02 wt% Nb, 0.05 wt% V, 0.02 wt% Al, 0.00005 wt% H, balance Fe and unavoidable impurity elements. Alternatively, the scraper chain steel is composed of 0.32 wt% C, 0.35 wt% Si, 0.3 wt% Mn, 0.005 wt% P, 0.002 wt% S, 0.65 wt% Cr, 2.8 wt% Ni, 0.55 wt% Mo, 0.04 wt% Nb, 0.05 wt% V, 0.04 wt% Al, 0.00005 wt% H, with the balance being Fe and unavoidable impurity elements.

[0009] Furthermore, the center porosity and ingot segregation grades of the scraper chain steel do not exceed grade 1.5.

[0010] Furthermore, the non-metallic impurity level of the scraper chain steel shall not exceed grade 1.5.

[0011] To achieve the above objectives, according to one aspect of the present invention, a method for preparing scraper chain steel is provided, comprising: mixing raw materials in a stoichiometric ratio and sequentially performing smelting, refining, continuous casting, slow cooling, rolling and annealing to obtain scraper chain steel.

[0012] Furthermore, smelting is carried out in an electric furnace or converter.

[0013] Furthermore, the smelting process is carried out at a temperature of 1450–1500℃ for a duration of 0.5–1 hour.

[0014] Further refining is carried out in a ladle refining furnace, a vacuum degassing furnace, or a vacuum circulating degassing furnace.

[0015] Furthermore, the refining process is carried out at a temperature of 1600–1700℃ for 1–2 hours.

[0016] Furthermore, the initial rolling temperature is 1200–1250℃, and the final rolling temperature is 800–950℃.

[0017] Furthermore, the rolling ratio is ≥7.

[0018] Furthermore, the annealing temperature is 600–650℃; the annealing holding time is 8–12 hours.

[0019] Furthermore, after annealing, the preparation method also includes the following steps: shot blasting the surface of the annealed scraper chain steel, and then screening it through non-destructive testing to obtain scraper chain steel with no surface cracks.

[0020] To achieve the above objectives, according to one aspect of the present invention, a scraper chain is provided, wherein the scraper chain has a diameter of 48-60 mm, a pitch of 152-197 mm, and a weight of 40-75 kg / m; the scraper chain is made of the aforementioned scraper chain steel.

[0021] To achieve the above objectives, according to one aspect of the present invention, a method for preparing a scraper chain is provided. Step S1 involves processing the scraper chain steel into bars, forging a portion of the bars into multiple vertical rings, and then sawing the other portion of the bars into multiple short bars, the length of which is the circumference of a flat ring. The short bars are heated and bent into elliptical rings with an opening on one side. The elliptical rings are fitted between two vertical rings, and the openings of the elliptical rings are welded to form a flat ring. This process is repeated multiple times to form a prefabricated chain with multiple vertical rings connected sequentially to a flat ring. Step S2 involves sequentially normalizing, quenching, and tempering the prefabricated chain to obtain the scraper chain.

[0022] Furthermore, in step S1, the preparation method also includes: using a turning method to make the surface roughness of the scraper chain steel not lower than Ra3.2 grade.

[0023] Furthermore, the heating temperature of the short bar stock is 860–960°C;

[0024] Further, normalizing includes: holding the prefabricated chain at a temperature of 880-960℃ for 0.6-1h, and then air-cooling it after it is removed from the furnace to obtain the normalized material.

[0025] Furthermore, quenching includes: holding the normalized material at a temperature of 860–920℃ for 0.5–0.8 hours, and then water-cooling it after removal from the furnace to obtain the quenched material.

[0026] Furthermore, the first tempering includes: holding the quenched material at a temperature of 450-550℃ for 0.6-1h, and then water-cooling it after removal from the furnace to obtain the scraper chain.

[0027] Furthermore, after the first tempering, the preparation method also includes a step of performing a second tempering on the material after the first tempering to obtain the scraper chain.

[0028] Furthermore, the secondary tempering includes: holding the material after the primary tempering at a temperature of 450-550°C for 0.6-1 hour, and then water-cooling it after exiting the furnace to obtain the scraper chain.

[0029] The commonly used scraper chain steel in existing technology is 23MnNiMoCr 5-4, whose main components include 0.20-0.26 wt% C, 1.10-1.40 wt% Mn, 0.40-0.60 wt% Cr, 0.9-1.1 wt% Ni, 0.50-0.60 wt% Mo, and other trace alloying elements. This invention redesigns the composition of the scraper chain steel. Compared with existing scraper chain steel, the total alloy content is increased by about 1.5%, improving the material's performance margin. The proportions of each element are adjusted, resulting in an effective synergy between the types and contents of elements in the scraper chain steel. This allows the steel to maintain high strength and toughness, enabling scraper chains made from this material to simultaneously achieve excellent strength and toughness in subsequent applications, especially meeting the requirements of large-size scraper chains. Meanwhile, during the preparation of the scraper chain steel, the surface quality and internal cleanliness of the steel are controlled, which improves the fatigue resistance of the scraper chain using it as raw material in subsequent applications. Furthermore, during the scraper chain preparation process, the parameters of its heat treatment process are appropriately adjusted to maintain the scraper chain at suitable temperatures for appropriate holding times. This improves the mechanical properties of the weld seams, eliminates processing stress, and enhances the uniformity and toughness of the scraper chain's microstructure. This results in a scraper chain with excellent comprehensive properties, such as superior strength, toughness, stress corrosion resistance, weather resistance, and fatigue resistance, enabling it to cope with complex working conditions and offering better prospects for industrial applications. Detailed Implementation

[0030] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0031] As described in the background section of this application, existing large-scale scraper chains cannot simultaneously achieve excellent strength and toughness. To address this issue, this application provides a scraper chain steel, comprising, by weight percentage: C, 0.26–0.45 wt%, Si ≤ 0.5 wt%, Mn ≤ 0.5 wt%, P ≤ 0.015 wt%, S ≤ 0.008 wt%, Cr, 0.4–1.2 wt%, Ni, 0.8–3.5 wt%, Mo, 0.40–0.65 wt%, Nb ≤ 0.06 wt%, V ≤ 0.1 wt%, Al, 0.02–0.05 wt%, H ≤ 1 ppm, with the balance being Fe and unavoidable impurity elements.

[0032] The commonly used steel for scraper chains in the prior art is 23MnNiMoCr 5-4, whose main components include 0.20-0.26 wt% C, 1.10-1.40 wt% Mn, 0.40-0.60 wt% Cr, 0.9-1.1 wt% Ni, 0.50-0.60 wt% Mo, and other trace alloying elements. This invention redesigns the composition of the scraper chain steel, adjusting the proportions of each element. In subsequent applications, scraper chains made from this material can simultaneously maintain excellent strength and toughness, especially meeting the requirements for large-scale scraper chains. The applicant further elaborates on the beneficial effects brought about by the aforementioned element types and dosages as follows:

[0033] C: C is the main factor determining the strength of steel. Increasing the C content helps improve hardenability, thereby increasing the strength of the chain; it can also appropriately improve the wear resistance of the chain; however, excessively high C content will reduce the weldability and toughness of the scraper chain. Based on this, the C content of the scraper chain steel in this invention is controlled at 0.26-0.45 wt% to increase the strength and wear resistance of the scraper chain.

[0034] Si: Si can appropriately improve the strength of steel through solid solution strengthening, but Si is detrimental to chain link welding, easily forming oxides and reducing weld performance. Therefore, the Si content of the scraper chain steel in this invention is controlled to be ≤0.5wt%.

[0035] Mn: Mn can improve the hardenability of steel, thereby increasing the strength of the chain; however, Mn is also an element that is prone to segregation, which may lead to uneven performance of the chain links. Therefore, the scraper chain steel of this invention controls Mn ≤ 0.5 wt%, which can reduce segregation and thus increase the uniformity of the performance distribution of the scraper chain.

[0036] P: P can cause grain boundary segregation in steel, reducing the binding energy of the grain boundaries and increasing temper brittleness during heat treatment, thereby reducing impact toughness. Therefore, the P content of the scraper chain steel in this invention is controlled to be ≤0.015wt%.

[0037] S: S easily forms sulfide inclusions, affecting the fatigue performance and stress corrosion resistance of the chain. Therefore, the S content of the scraper chain steel in this invention is controlled to be ≤0.008wt%.

[0038] Cr: Cr can improve the hardenability of steel, thereby increasing the strength of the chain, and can also appropriately improve wear resistance and corrosion resistance. However, its carbides tend to coarsen during tempering, which is detrimental to impact toughness. Therefore, the scraper chain steel of this invention controls the Cr content to be 0.4-1.2 wt%, which can increase the strength of the scraper chain and improve its wear resistance and corrosion resistance.

[0039] Ni: Ni can expand the austenite region, refine the grain size, and improve the toughness, corrosion resistance, and fatigue resistance of steel. Simultaneously, Ni is less prone to burn-off in flash welds, thus improving weld performance. However, excessively high nickel content negatively impacts cost-effectiveness. Therefore, the scraper chain steel of this invention controls the Ni content to 0.8–3.5 wt%, which expands the austenite region, refines the grain size, and improves the toughness, corrosion resistance, and fatigue resistance of the scraper chain, enabling it to better handle complex working conditions.

[0040] Mo: Mo is beneficial for refining grains, reducing temper brittleness, and improving the mechanical properties of steel. However, excessive content can affect cost-effectiveness and increase deformation resistance, which is detrimental to processing. Therefore, the Mo content of the scraper chain steel in this invention is controlled at 0.40–0.65 wt%.

[0041] Nb: Nb is a grain-refining element, reducing temper brittleness and improving the toughness of steel. However, it is also a carbide-forming element; excessive content can lead to carbide coarsening, affecting mechanical properties. Therefore, the Nb content in the scraper chain steel of this invention is controlled to ≤0.06wt%.

[0042] V: V is a microalloying element and a strong carbide-forming element, but excessive content has no positive effect. Therefore, the V content of the scraper chain steel in this invention is controlled to be ≤0.1wt%.

[0043] Al: Al is a grain-refining element, but it easily forms alumina inclusions during flash welding, which is detrimental to weld toughness. Therefore, the Al content of the scraper chain steel in this invention is controlled at 0.02-0.05 wt%.

[0044] H: For large-size, high-strength scraper chains, excessive hydrogen content may lead to hydrogen embrittlement. Therefore, the scraper chain steel of this invention controls the H content to be ≤1ppm.

[0045] More importantly, the scraper chain steel of this invention forms an effective synergy between the types and contents of each element. By reducing the content of Mn, this invention can alleviate the decline in weld performance caused by Mn segregation. However, since Mn is the main alloying element that improves hardenability and toughness, its reduction will affect the strength of the steel. Therefore, this invention synergistically increases the content of Ni to compensate for the insufficient strength caused by the reduction of Mn content. At the same time, increasing the content of Ni can also improve the stability of welding and heat treatment of the steel, especially the performance stability of large-size scraper steel. Furthermore, by controlling the content of Ni, Cr, and Mo, this invention enables the steel to maintain high strength and toughness through the synergistic effect of the three elements, resulting in excellent weldability and improved stress corrosion resistance. In scraper chain steel, through the synergistic effect of the elements, this invention can further increase the content of C, promoting the precipitation of carbides in the steel. While maintaining good weldability and toughness, it can also further improve the strength and wear resistance of the material. Moreover, in addition to playing their own roles, each element is more in line with the overall design requirements, making them indispensable for comprehensively improving the overall performance of large-size scraper chains.

[0046] In a preferred embodiment, the total weight percentage of alloying elements other than iron in the scraper chain steel is 4.5–5.5 wt%. Compared with existing conventional scraper chain steel, the alloying element content in the scraper steel of the present invention is increased by about 1.5%, which, while giving the product suitable toughness, can further increase the performance margin of the scraper chain, improve the mechanical properties of the scraper chain, and has a high safety factor, which is beneficial for coping with complex working conditions downhole.

[0047] To further improve the overall performance of the material, in some preferred embodiments, the scraper chain steel, by weight percentage, consists of 0.40 wt% C, 0.35 wt% Si, 0.3 wt% Mn, 0.008 wt% P, 0.005 wt% S, 0.8 wt% Cr, 2.5 wt% Ni, 0.55 wt% Mo, 0.04 wt% Nb, 0.05 wt% V, 0.04 wt% Al, and 0.000 The scraper chain steel consists of 0.30 wt% H, balance Fe and unavoidable impurity elements; or, the scraper chain steel consists of 0.30 wt% C, 0.5 wt% Si, 0.5 wt% Mn, 0.015 wt% P, 0.008 wt% S, 0.8 wt% Cr, 2.0 wt% Ni, 0.40 wt% Mo, 0.01 wt% Nb, 0.02 wt% V, 0.02 wt% Al, 0.00005 wt% H, balance... The scraper chain steel is composed of 0.45 wt% C, 0.1 wt% Si, 0.1 wt% Mn, 0.002 wt% P, 0.003 wt% S, 1.1 wt% Cr, 3.0 wt% Ni, 0.60 wt% Mo, 0.02 wt% Nb, 0.05 wt% V, 0.02 wt% Al, 0.00005 wt% H, with the balance being Fe and unavoidable impurities. Impurity element composition; or, the scraper chain steel is composed of 0.32 wt% C, 0.35 wt% Si, 0.3 wt% Mn, 0.005 wt% P, 0.002 wt% S, 0.65 wt% Cr, 2.8 wt% Ni, 0.55 wt% Mo, 0.04 wt% Nb, 0.05 wt% V, 0.04 wt% Al, 0.00005 wt% H, balance Fe and unavoidable impurity elements.

[0048] In a preferred embodiment, the center porosity and ingot segregation grade of the scraper chain steel do not exceed level 1.5 (GB / T1979-2001); preferably, the non-metallic impurity grade of the scraper chain steel does not exceed level 1.5 (GB / T 10561-2005). This invention, by controlling the cleanliness and uniformity of the steel, helps to reduce micro-fatigue crack nucleation and extend the fatigue life of the scraper chain.

[0049] The present invention also provides a method for preparing the above-mentioned scraper chain steel, comprising: mixing the raw materials for preparing scraper chain steel in a stoichiometric ratio and sequentially performing smelting, refining, continuous casting, slow cooling, rolling and annealing treatment to obtain scraper chain steel.

[0050] For the reasons stated above, the scraper chain steel prepared in this application possesses excellent strength and toughness, making it suitable as a raw material for large-scale scraper chains. This meets the practical application requirements of large-scale scraper chains and enhances their safety when dealing with complex downhole conditions. Furthermore, the preparation method described above is simple to operate and has higher utilization efficiency.

[0051] Furthermore, the smelting, refining, continuous casting, slow cooling, rolling, and annealing processes described in this application are not specifically limited, and those skilled in the art can handle them according to their own process requirements. In a preferred embodiment, to improve smelting efficiency, smelting is carried out in an electric furnace or converter; the smelting temperature is 1450–1500°C, and the processing time is 0.5–1 hour. To improve refining efficiency, refining is carried out in a ladle refining furnace, a vacuum degassing furnace, or a vacuum circulating degassing furnace; the refining temperature is 1600–1700°C, and the processing time is 1–2 hours. Based on considerations of grain refinement, the initial rolling temperature is 1200–1250°C, and the final rolling temperature is 800–950°C. When the rolling temperature is limited to the above range in this invention, the rolling process is carried out within the austenite recrystallization temperature range, which can achieve the purpose of grain refinement. Preferably, the rolling ratio is ≥7. The present invention limits the rolling ratio to ≥7 because if the rolling ratio is too small, the density and microstructure quality of the central part of the scraper chain steel will decrease, which will in turn lead to a decrease in the strength of the scraper chain during subsequent manufacturing. More preferably, the rolling ratio is 7 to 9. Since the upper limit of the rolling ratio is limited by the initial ingot size, the rolling ratio is controlled within the above range.

[0052] In a preferred embodiment, the annealing temperature is 600–650°C, and the annealing holding time is 8–12 hours. The hot-rolled microstructure of round steel is predominantly bainite, with small amounts of martensite and ferrite. Annealing allows carbon to be extracted from the bainite and martensite, resulting in a ferrite microstructure with dispersed carbide particles on the ferrite matrix. This microstructure increases austenite nucleation sites. This invention controls the annealing temperature within the above range, which is more conducive to refining the austenite grain size, thereby improving the toughness of the material after heat treatment.

[0053] In a preferred embodiment, after annealing, the surface of the annealed scraper chain steel is shot-blasted, and then non-destructive testing is used to screen for scraper chain steel with no surface cracks. This invention uses shot blasting to improve the cleanliness and uniformity of the scraper chain steel surface, and adds a non-destructive testing screening step, which can remove defective materials in advance, improving the fatigue resistance of the scraper chain and extending its fatigue life.

[0054] To further improve the fatigue resistance of the material, the shot blasting time is 0.5 to 1 hour.

[0055] The present invention also provides a scraper chain with a diameter of 48-60 mm, a pitch of 152-197 mm, a weight of 40-75 kg / m, and the scraper chain is made of the aforementioned scraper chain steel.

[0056] For the reasons mentioned above, the scraper chain steel with excellent strength and toughness is particularly suitable for manufacturing large-scale scraper chains. This allows large-scale scraper chains to have excellent comprehensive performance, such as superior strength, toughness, stress corrosion resistance, weather resistance, and fatigue resistance, thus enabling them to cope with complex working conditions and have better prospects for industrial application.

[0057] The present invention also provides a method for preparing the above-mentioned scraper chain, comprising the following steps: Step S1, processing the scraper chain steel into bars, forging a portion of the bars into multiple vertical rings, and then sawing the other portion of the bars into multiple short bars, the length of which is the circumference of the flat ring; heating and bending the short bars into elliptical rings with an opening on one side, fitting the elliptical rings between two vertical rings, and then welding the opening of the elliptical rings to form a flat ring; then sequentially fitting the elliptical rings between two vertical rings, and then welding the opening of the elliptical rings to form a flat ring; repeating this process multiple times to form a prefabricated chain with multiple vertical rings-flat rings-vertical rings connected in sequence; Step S2, sequentially normalizing, quenching, and tempering the prefabricated chain to obtain the scraper chain.

[0058] For the reasons stated above, the resulting product exhibits both good strength and toughness, as well as excellent fatigue resistance, stress corrosion resistance, and weather resistance. This type of scraper chain is particularly suitable for complex working conditions, offering high safety and reliability.

[0059] The scraper chain prepared using the above method can achieve the following performance characteristics: yield strength ≥1000MPa, tensile strength ≥1200MPa, elongation ≥12%, shrinkage ≥50%, impact energy at the Charpy notch base material at 20℃ ≥60J, and impact energy at the Charpy notch weld at 20℃ ≥45J. Under a stress range of 50–250MPa, the fatigue cycle count is no less than 100,000 cycles; the breaking stress of the scraper chain is no less than 850MPa, and the ratio of the shrinkage rate in simulated corrosive media to the shrinkage rate in air is no less than 0.85.

[0060] To further improve the surface quality of the scraper chain steel and thus enhance its fatigue resistance, step S1 further includes the following preparation method: using turning to ensure that the surface roughness of the scraper chain steel is not lower than Ra3.2 (the above test is conducted in accordance with the standard GB / T 1031-2009).

[0061] To further improve the processability of the product, the short bar stock is heated to a temperature of 860–960°C.

[0062] In a preferred embodiment, normalizing includes: holding the prefabricated chain at a temperature of 880–960°C for 0.6–1 hour, followed by air cooling after removal from the furnace to obtain the normalized material. This invention holds the prefabricated chain at the aforementioned high-temperature range for a relatively long time, allowing for sufficient diffusion of elements in the weld area, compensating for alloy element loss caused by flash welding, and achieving the purpose of eliminating processing stress and improving the uniformity of the microstructure.

[0063] In a preferred embodiment, quenching includes: holding the normalized material at a temperature of 860–920°C for 0.5–0.8 hours, followed by water cooling after removal from the furnace to obtain the quenched material. This invention controls the quenching temperature and holding time within the aforementioned range, enabling the scraper chain to absorb sufficient heat during quenching, fully realizing the austenite transformation, particularly improving the mechanical properties of the weld, and also ensuring that the chain achieves the expected transformation of the internal material structure during subsequent tempering.

[0064] In a preferred embodiment, the first tempering includes: holding the quenched material at a temperature of 450–550°C for 0.6–1 hour, followed by water cooling to obtain the scraper chain. This invention controls the temperature and holding time of the first tempering within the above range, enabling the chain to achieve a better combination of strength and toughness, and ensuring that the mechanical properties of the ring back and weld are similar, thus avoiding local performance fluctuations that could affect the performance.

[0065] For different application scenarios, a secondary tempering step can be flexibly selected. When the product's operating environment has high requirements for toughness and stress corrosion resistance, a secondary tempering is performed after the primary tempering. This secondary tempering can further reduce quenching stress, increase carbide precipitation, improve the microstructure and toughness, and enhance the overall performance of the product.

[0066] To further improve the overall performance of the product, secondary tempering includes: holding the material after primary tempering at a temperature of 450-550℃ for 0.6-1 hour, and then water-cooling it after exiting the furnace to obtain the scraper chain.

[0067] To provide consumers with a better product experience and improve the appearance quality and fatigue life of the product, the scraper chain can be shot blasted before leaving the factory to ensure that the surface cleanliness of the scraper chain is not lower than Sa2.5 grade (GB / T 8923.1-2011).

[0068] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0069] Example 1

[0070] Preparation of scraper chain steel:

[0071] The chemical composition of the scraper chain steel, by weight percentage, is as follows: C, 0.40 wt%, Si, 0.35 wt%, Mn, 0.3 wt%, P, 0.008 wt%, S, 0.005 wt%, Cr, 0.8 wt%, Ni, 2.5 wt%, Mo, 0.55 wt%, Nb, 0.04 wt%, V, 0.05 wt%, Al, 0.04 wt%, H, 0.00005 wt%, with the balance being Fe and unavoidable impurities; the total weight percentage of alloying elements other than iron is 4.97 wt%. The center porosity and ingot segregation grade of the scraper chain steel is 1.0 (GB / T1979-2001), and the non-metallic impurity grade of the scraper chain steel is 1.0 (GB / T 10561-2005).

[0072] The preparation method of scraper chain steel is as follows: scraper chain steel is smelted in an electric furnace (1500℃, 0.8h), refined in a ladle refining furnace (1650℃, 1.5h), refined in a vacuum circulating degassing furnace, and continuously cast to obtain steel billets that meet the chemical composition requirements; the steel billets are then slowly cooled for 20h; after slow cooling, the steel billets are rolled again, with an initial rolling temperature of 1200℃, a final rolling temperature of 800℃, and a rolling ratio of 9; after being rolled into round bars, they are annealed at 600℃ for 10h; after annealing, the surface of the scraper chain steel is shot blasted for 1h, and then non-destructive testing is used to screen for scraper chain steel with no surface cracks.

[0073] Preparation of scraper chain:

[0074] The preparation method of the scraper chain is as follows: First, the surface roughness of the scraper chain steel is Ra4 grade by turning; the scraper chain steel is processed into bars, a part of the bars is forged into multiple vertical rings, and then the other part of the bars is sawn into multiple short bars, the length of which is the circumference of the flat ring, which is 620mm; the short bars are heated to 950℃ and bent into elliptical rings with an opening on one side, the elliptical rings are fitted between two vertical rings, and then the opening of the elliptical rings is welded to form a flat ring; then the elliptical rings are fitted between two vertical rings in sequence, and the opening of the elliptical rings is welded to form a flat ring; this process is repeated multiple times to form a prefabricated chain with multiple vertical rings-flat rings-vertical rings connected in sequence;

[0075] The prefabricated chain is normalized (normalizing temperature is 960℃, holding time is 0.8h), and then air-cooled after removal from the furnace to obtain normalized material; the normalized material is then quenched (quenching temperature is 920℃, holding time is 0.7h); after being water-cooled after removal from the furnace to obtain quenched material; the quenched material is then tempered once (tempering temperature is 550℃, holding time is 0.8h), and after being water-cooled after removal from the furnace to obtain tempered material; after being water-cooled after removal from the furnace to obtain scraper chain.

[0076] The scraper chain has a diameter of 56mm, a pitch of 187mm, and a weight of 60Kg / m.

[0077] Example 2

[0078] The only difference from Example 1 is the chemical composition of the scraper chain steel. By weight percentage, the chemical composition of the scraper chain steel is: C, 0.30 wt%, Si, 0.5 wt%, Mn, 0.5 wt%, P, 0.015 wt%, S, 0.008 wt%, Cr, 0.8 wt%, Ni, 2.0 wt%, Mo, 0.40 wt%, Nb, 0.01 wt%, V, 0.02 wt%, Al, 0.02 wt%, H, 0.00005 wt%, with the balance being Fe and unavoidable impurity elements; the total weight percentage of alloying elements other than iron is 4.57 wt%.

[0079] Example 3

[0080] The only difference from Example 1 is the chemical composition of the scraper chain steel. By weight percentage, the chemical composition of the scraper chain steel is: C, 0.45 wt%, Si, 0.1 wt%, Mn, 0.1 wt%, P, 0.002 wt%, S, 0.003 wt%, Cr, 1.1 wt%, Ni, 3.0 wt%, Mo, 0.60 wt%, Nb, 0.02 wt%, V, 0.05 wt%, Al, 0.02 wt%, H, 0.00005 wt%, with the balance being Fe and unavoidable impurity elements; the total weight percentage of alloying elements other than iron is 5.45 wt%.

[0081] Example 4

[0082] The only difference from Example 1 is the chemical composition of the scraper chain steel: by weight percentage, the chemical composition of the scraper chain steel is: C, 0.40 wt%, Si, 0.35 wt%, Mn, 0.3 wt%, P, 0.008 wt%, S, 0.005 wt%, Cr, 0.8 wt%, Ni, 3.5 wt%, Mo, 0.55 wt%, Nb, 0.04 wt%, V, 0.05 wt%, Al, 0.04 wt%, H, 0.00005 wt%, with the balance being Fe and unavoidable impurity elements; the total weight percentage of alloying elements other than iron is 6.0 wt%.

[0083] Example 5

[0084] The chemical composition of the scraper chain steel, by weight percentage, is as follows: C, 0.32 wt%, Si, 0.35 wt%, Mn, 0.3 wt%, P, 0.005 wt%, S, 0.002 wt%, Cr, 0.65 wt%, Ni, 2.8 wt%, Mo, 0.55 wt%, Nb, 0.04 wt%, V, 0.05 wt%, Al, 0.04 wt%, H, 0.00005 wt%, with the balance being Fe and unavoidable impurities; the total weight percentage of alloying elements other than iron is 5.1 wt%.

[0085] Example 6

[0086] The only difference from Example 1 is that the center porosity and ingot segregation grade of the scraper chain steel is grade 2 (GB / T1979-2001), and the non-metallic impurity grade of the scraper chain steel is grade 2 (GB / T 10561-2005).

[0087] Example 7

[0088] The only difference from Example 1 is that the preparation method of the scraper chain steel does not include shot blasting and non-destructive testing screening steps.

[0089] Example 8

[0090] The only difference from Example 1 is that in the preparation method of the scraper chain, the normalizing temperature is 880°C and the holding time is 0.6h.

[0091] Example 9

[0092] The difference from Example 1 is that in the preparation method of the scraper chain, the quenching temperature is 860℃ and the holding time is 0.5h.

[0093] Example 10

[0094] The difference from Example 1 is that in the preparation method of the scraper chain, the first tempering temperature is 450°C and the holding time is 0.6h.

[0095] Example 11

[0096] The difference from Example 1 is that in the preparation method of the scraper chain: after the first tempering, the material after the first tempering is subjected to a second tempering, the second tempering temperature is 475℃, and the holding time is 0.6h.

[0097] Example 12

[0098] The difference from Example 1 is that in the preparation method of the scraper chain, the normalizing temperature is 800°C and the holding time is 1 hour.

[0099] Example 13

[0100] The difference from Example 1 is that in the preparation method of the scraper chain, the quenching temperature is 800℃ and the holding time is 0.8h.

[0101] Example 14

[0102] The difference from Example 1 is that in the preparation method of the scraper chain, the first tempering temperature is 300°C and the holding time is 1 hour.

[0103] Comparative Example 1

[0104] The only difference from Example 1 is that the scraper chain steel is 23MnNiMoCr 5-4, with the following chemical composition: C, 0.23wt%, Si, 0.15wt%, Mn, 1.3wt%, P, 0.006wt%, S, 0.002wt%, Cr, 0.50wt%, Ni, 1.0wt%, Mo, 0.55%, Nb, 0.03wt%, V, 0.03wt%, Al, 0.03wt%, H, balance Fe and unavoidable impurity elements; the total weight percentage of alloying elements other than iron is 3.83wt%.

[0105] Comparative Example 2

[0106] The only difference from Example 1 is the chemical composition of the scraper chain steel: by weight percentage, the chemical composition of the scraper chain steel is: C, 0.2wt%, Si, 0.35wt%, Mn, 1.35%, P, 0.008wt%, S, 0.005wt%, Cr, 1.5wt%, Ni, 1.1wt%, Mo, 0.55wt%, Nb, 0.04wt%, V, 0.05wt%, Al, 0.04wt%, H, balance Fe and unavoidable impurity elements; the total weight percentage of alloying elements other than iron is 4.85wt%.

[0107] Performance characterization:

[0108] Mechanical properties of the scraper chains in the above embodiments and comparative examples were tested. Yield strength, tensile strength, elongation and shrinkage were tested according to GB / T 228.1-2021 standard. Impact energy of the Charpy notch base material at 20℃ (excluding the weld seam of the chain, i.e. the back of the chain ring) and impact energy of the Charpy notch weld seam at 20℃ were tested according to GB / T 229-2020 standard. The test results are shown in Table 1.

[0109] Table 1

[0110]

[0111] The scraper chains of the above embodiments and comparative examples were subjected to fatigue cycle counts (tested according to GB / T 12718 standard under a stress range of 50–250 MPa), breaking stress (tested according to GB / T 12718 standard), and performance tests on the reduction of area Z1 in simulated corrosive media and the reduction of area Z2 in air (tested according to GB / T 15970.7 standard). The reduction of area is equal to the shrinkage of the cross-sectional area at the fracture point within the gauge length divided by the original cross-sectional area. The ratio of Z1 / Z2 was used to evaluate the stress corrosion resistance of the scraper chain. The test results are shown in Table 2.

[0112] Table 2

[0113]

[0114] From the performance data in Tables 1 and 2 above, the following conclusions can be drawn: By comparing Examples 1-5 with Comparative Example 1, it can be found that when the total weight percentage of alloying elements other than iron in the scraper chain steel is not in the range of 4.5-5.5 wt%, for example, when the total weight percentage of alloying elements other than iron in the scraper chain of Example 4 is 6.0%, its yield strength is 1165 MPa, tensile strength is 1339 MPa, elongation is 13%, shrinkage rate is 58%, the impact energy of the Charpy notch base material at 20°C is 71 J, and the impact energy of the Charpy notch weld at 20°C is 5 J. The fatigue cycle count is 103558, the breaking stress is 895MPa, and the Z1 / Z2 ratio is 0.90. For example, when the total weight percentage of alloying elements other than iron in the scraper chain of Comparative Example 1 is 3.83%, its yield strength is 1094MPa, tensile strength is 1191MPa, elongation is 15%, shrinkage rate is 58%, the impact energy of the Charpy notch base material at 20℃ is 86J, the impact energy of the Charpy notch weld at 20℃ is 52J, the fatigue cycle count is 79366, the breaking stress is 818MPa, and the Z1 / Z2 ratio is 0.93.

[0115] Compared to the scraper chains of Examples 1-3 and Example 5, tests on yield strength, tensile strength, and breaking stress revealed that the scraper chain of Example 4 showed improved strength, while the scraper chain of Comparative Example 1 showed a significant decrease in strength. Tests on elongation and shrinkage revealed a decrease in plasticity in both Examples 4 and Comparative Example 1. Tests on impact energy at 20°C Charpy notch in the base material and at 20°C Charpy notch in the weld showed a decrease in toughness in both Examples 4 and Comparative Example 1, with Example 4 showing a greater decrease. Tests on fatigue cycle count, reduction of area in simulated corrosive media (Z1), and reduction of area in air (Z2) showed a significant decrease in fatigue resistance in both Examples 4 and Comparative Example 1, with Comparative Example 1 showing a greater decrease. Stress corrosion resistance in both Examples 4 and Comparative Example 1 also showed a significant decrease. In contrast, the scraper chains of Examples 1-3 and Example 5 simultaneously exhibited superior toughness and strength, as well as superior fatigue resistance and stress corrosion resistance. This is because when the total weight percentage of alloying elements other than iron in the scraper chain steel is not within the range of 4.5–5.5 wt%, a higher total weight percentage of alloying elements can improve weld performance and lead to a certain increase in material strength, but it will affect the uniformity of the material's microstructure, significantly reducing its toughness, fatigue resistance, and stress corrosion resistance. Conversely, a lower total weight percentage of alloying elements will reduce the performance margin, leading not only to a decrease in strength but also in toughness, fatigue resistance, and stress corrosion resistance.

[0116] By comparing Examples 1, 6, and 7, it can be found that the fatigue resistance of Examples 6 and 7 decreased significantly. This is because Example 1 controlled the cleanliness and uniformity of the steel during the preparation of the scraper chain steel, which is beneficial to reducing the nucleation of apparent fatigue cracks and extending the fatigue life of the scraper chain.

[0117] Comparing Examples 1, 8, and 12, it can be found that in Example 8, the impact energy of the base material with a Charpy notch at 20°C is 89J, the impact energy of the weld joint with a Charpy notch at 20°C is 56J, and the number of fatigue cycles is 123,542. In Example 12, the impact energy of the base material with a Charpy notch at 20°C is 83J, the impact energy of the weld joint with a Charpy notch at 20°C is 48J, and the number of fatigue cycles is 10,239. Compared with Examples 1 and 8, the toughness and fatigue resistance of the scraper chain in Example 12 are both reduced, with a greater decrease in fatigue resistance. This is because the normalizing temperature in Example 12 is too low, which does not allow sufficient diffusion of elements in the weld area, resulting in a decrease in the uniformity of the microstructure and thus a decrease in the toughness and fatigue resistance of the scraper chain.

[0118] Comparing Examples 1, 9, and 13, it can be found that Example 13 has a yield strength of 1123 MPa, a tensile strength of 1235 MPa, a breaking stress of 853 MPa, an impact energy of 85 J at the Charpy notch base material at 20°C, an impact energy of 43 J at the Charpy notch weld at 20°C, and a fatigue cycle count of 98083. Compared to Examples 1 and 9, the scraper chain in Example 13 exhibits decreased strength, toughness, and fatigue resistance. This is because the quenching temperature in Example 13 was too low, preventing the scraper chain from absorbing sufficient heat during quenching and hindering the austenite transformation. Consequently, the chain failed to achieve the expected transformation of the internal material structure during subsequent tempering, leading to a decrease in strength, toughness, and fatigue resistance.

[0119] Comparing Examples 1, 10, and 14, it can be observed that Example 14 exhibits a yield strength of 1258 MPa, a tensile strength of 1465 MPa, an elongation of 11%, a shrinkage rate of 55%, an impact energy of 51 J at the Charpy notch base material at 20°C, an impact energy of 35 J at the Charpy notch weld joint at 20°C, a fatigue cycle count of 53437, a breaking stress of 937 MPa, and a Z1 / Z2 ratio of 0.77. Compared to Examples 1 and 10, Example 14 shows improved scraper chain strength, but significantly reduced toughness, fatigue resistance, and stress corrosion resistance. This is because the tempering temperature in Example 14 is too low, resulting in insufficient martensitic tempering of the steel. This leads to an increase in scraper chain strength but a decrease in toughness, and an increased susceptibility to chain link cracking. Under fatigue loads, it is more prone to cracking due to stress concentration, reducing fatigue life. Simultaneously, the increased strength leads to increased hydrogen embrittlement sensitivity, resulting in a significant decrease in the scraper chain's resistance to stress corrosion during use.

[0120] By comparing Examples 1 and 11, it can be found that Example 11 has a yield strength of 1103 MPa, a tensile strength of 1236 MPa, an impact energy of 92 J at the Charpy notch base material at 20°C, an impact energy of 65 J at the Charpy notch weld at 20°C, a fatigue cycle count of 137025, a breaking stress of 855 MPa, and a Z1 / Z2 ratio of 0.98. Compared with Example 1, Example 11 shows improved fatigue resistance and stress corrosion resistance. This is because secondary tempering can reduce quenching stress, increase carbide precipitation, and improve the fatigue resistance and stress corrosion resistance of the scraper chain.

[0121] Comparing Example 1 and Comparative Example 2, it can be found that the yield strength of Comparative Example 2 is 1168 MPa, the tensile strength is 1280 MPa, the impact energy of the Charpy notch base metal at 20℃ is 51 J, the impact energy of the Charpy notch weld at 20℃ is 35 J, the number of fatigue cycles is 82505, the breaking stress is 880 MPa, and the Z1 / Z2 ratio is 0.85. Compared with Example 1, the strength of Comparative Example 2 is only slightly improved, but the toughness and fatigue resistance are significantly reduced. This is because the scraper chain steel of Comparative Example 2 contains more Mn and Cr elements. Mn and Cr elements can improve the strength to a certain extent, but too much Mn will lead to segregation, which will reduce the weld performance and the uniformity of the microstructure. Too much Cr will cause it to coarsen during the subsequent tempering process of the scraper chain, thus leading to a significant decrease in the toughness and fatigue resistance of the scraper chain of Comparative Example 2.

[0122] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A scraper chain steel material, characterized in that, The scraper chain steel, by weight percentage, comprises: C, 0.26~0.45wt%, Si≤0.5wt%, Mn≤0.5wt%, P≤0.015wt%, S≤0.008wt%, Cr, 0.4~1.2wt%, Ni, 0.8~3.5wt%, Mo, 0.40~0.65wt%, Nb≤0.06wt%, V≤0.1wt%, Al, 0.02~0.05wt%, H≤1ppm, with the balance being Fe and unavoidable impurity elements; The total weight percentage of alloying elements other than iron is 4.5~5.5 wt%; the center porosity and ingot segregation grade of the scraper chain steel do not exceed 1.5; and the non-metallic impurity grade of the scraper chain steel does not exceed 1.

5.

2. The scraper chain steel according to claim 1, characterized in that, By weight percentage, the scraper chain steel comprises 0.40 wt% C, 0.35 wt% Si, 0.3 wt% Mn, 0.008 wt% P, 0.005 wt% S, 0.8 wt% Cr, 2.5 wt% Ni, 0.55 wt% Mo, 0.04 wt% Nb, 0.05 wt% V, 0.04 wt% Al, 0.00005 wt% H, with the balance being Fe and unavoidable impurity elements; or, The scraper chain steel is composed of 0.30 wt% C, 0.5 wt% Si, 0.5 wt% Mn, 0.015 wt% P, 0.008 wt% S, 0.8 wt% Cr, 2.0 wt% Ni, 0.40 wt% Mo, 0.01 wt% Nb, 0.02 wt% V, 0.02 wt% Al, 0.00005 wt% H, with the balance being Fe and unavoidable impurity elements; or, The scraper chain steel is composed of 0.45 wt% C, 0.1 wt% Si, 0.1 wt% Mn, 0.002 wt% P, 0.003 wt% S, 1.1 wt% Cr, 3.0 wt% Ni, 0.60 wt% Mo, 0.02 wt% Nb, 0.05 wt% V, 0.02 wt% Al, 0.00005 wt% H, with the balance being Fe and unavoidable impurity elements; or, The scraper chain steel is composed of 0.32wt% C, 0.35wt% Si, 0.3wt% Mn, 0.005wt% P, 0.002wt% S, 0.65wt% Cr, 2.8wt% Ni, 0.55wt% Mo, 0.04wt% Nb, 0.05wt% V, 0.04wt% Al, 0.00005wt% H, with the balance being Fe and unavoidable impurity elements.

3. A method for preparing the scraper chain steel according to claim 1 or 2, characterized in that, include: The raw materials are mixed according to the stoichiometric ratio and then sequentially smelted, refined, continuously cast, slowly cooled, rolled and annealed to obtain the scraper chain steel.

4. The method for preparing scraper chain steel according to claim 3, characterized in that, The smelting is carried out in an electric furnace or converter; the initial rolling temperature is 1200~1250℃, and the final rolling temperature is 800~950℃.

5. The method for preparing scraper chain steel according to claim 4, characterized in that, The smelting process is carried out at a temperature of 1450~1500℃ for 0.5~1h.

6. The method for preparing scraper chain steel according to claim 3, characterized in that, The refining is carried out in a ladle refining furnace, a vacuum degassing furnace, or a vacuum circulating degassing furnace.

7. The method for preparing scraper chain steel according to claim 6, characterized in that, The refining process is carried out at a temperature of 1600~1700℃ for 1~2 hours.

8. The method for preparing scraper chain steel according to claim 3, characterized in that, The rolling ratio is ≥7.

9. The method for preparing scraper chain steel according to claim 3, characterized in that, The annealing temperature is 600~650℃; the annealing holding time is 8~12h.

10. The method for preparing scraper chain steel according to claim 3, characterized in that, After the annealing, the preparation method further includes the following steps: shot blasting the surface of the annealed scraper chain steel, and then screening it through non-destructive testing to obtain scraper chain steel with no surface cracks.

11. A scraper chain, characterized in that, The scraper chain has a diameter of 48~60mm, a pitch of 152~197mm, and a weight of 40~75Kg / m per meter; the scraper chain is made of the scraper chain steel as described in claim 1 or 2.

12. A method for preparing the scraper chain according to claim 11, characterized in that, The preparation method includes the following steps: Step S1: First, the scraper chain steel material as described in claim 1 or 2 is processed into bar stock. A portion of the bar stock is forged into multiple vertical rings. Then, another portion of the bar stock is sawn into multiple short bars, the length of which is the circumference of the flat ring. The short bars are heated and bent into elliptical rings with an opening on one side. The elliptical rings are fitted between two vertical rings, and the openings of the elliptical rings are welded to form flat rings. Then, the elliptical rings are fitted between two vertical rings in sequence, and the openings of the elliptical rings are welded to form flat rings. This process is repeated multiple times to form a prefabricated chain with multiple vertical rings-flat rings-vertical rings connected in sequence. Step S2: The prefabricated chain is sequentially normalized, quenched, and tempered once to obtain the scraper chain.

13. The method for preparing the scraper chain according to claim 12, characterized in that, In step S1, the preparation method further includes: using a turning method to make the surface roughness of the scraper chain steel not lower than Ra3.2 grade.

14. The method for preparing the scraper chain according to claim 12, characterized in that, The short bar stock is heated to a temperature of 860~960℃.

15. The method for preparing the scraper chain according to claim 12, characterized in that, The normalizing process includes: holding the prefabricated chain at a temperature of 880~960℃ for 0.6~1h, and then air-cooling it after it is removed from the furnace to obtain the normalized material.

16. The method for preparing the scraper chain according to claim 15, characterized in that, The quenching process includes: holding the normalized material at a temperature of 860~920℃ for 0.5~0.8h, and then water-cooling it after removal from the furnace to obtain the quenched material.

17. The method for preparing the scraper chain according to claim 16, characterized in that, The first tempering process includes: holding the quenched material at a temperature of 450~550℃ for 0.6~1h, and then water-cooling it after removal from the furnace to obtain the scraper chain.

18. The method for preparing the scraper chain according to claim 12, characterized in that, The scraper chain is obtained by performing a second tempering step after the first tempering.

19. The method for preparing the scraper chain according to claim 18, characterized in that, The secondary tempering is carried out at a temperature of 450~550℃ for 0.6~1h, and the scraper chain is obtained after water cooling after being taken out of the furnace.

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