Gear steel for high-speed transmission system and preparation method of gear steel

Abstract

The invention relates to gear steel for a high-speed transmission system and a preparation method thereof, and belongs to the technical field of steel. The gear steel comprises, by mass, 0.10%-0.25% of C, 0.1%-0.40% of Si, 0.3%-1.00% of Mn, smaller than or equal to 0.03% of P, 0.015%-0.05% of S, 1.2%-2.5% of Cr, 1.0%-2.5% of Ni, smaller than or equal to 0.5% of Mo, 0.015%-0.050% of Al, smaller than or equal to 0.0200% of N, 0.0005%-0.0050% of Ca, smaller than or equal to 0.05% of Nb, smaller than or equal to 0.2% of Cu and Fe, Al / N is larger than 3, and Al / N represents the mass ratio of Al to N. A component system of the gear steel is scientifically designed, on the basis of a low-C-Si-low-Mn-high-Cr-high-Ni component system, the content of Al, Nb, N and other elements is finely regulated and controlled, Mo is added as a hardenability regulator, and key process parameters in the preparation process are controlled, so that the purity and the structure uniformity of the steel are ensured. The prepared gear steel can stably operate under the high-speed and heavy-load conditions and bear large loads, and the requirement that the pitch circle linear speed of a gear in a high-speed gear transmission device is larger than or equal to 35 m / s and / or the rotating speed is larger than 4500 r / min is met.

Description

Technical Field

[0001] The present application relates to the field of steel technology, and in particular to a gear steel for a high-speed transmission system and a preparation method thereof. Background Art

[0002] High-speed transmission refers to the process of transferring power to machinery and equipment through various transmission methods during high-speed rotation or rotation. This includes, but is not limited to, industries such as machine tools, wind power generation, ships, trains, automobiles, and aerospace. In pursuit of ultimate operational efficiency, high-speed transmission is widely used in contemporary manufacturing.

[0003] High-speed gears are key components in engine power transmission, wind power, and electric motors, and their reliability directly impacts the functionality and structural safety of the engine. Due to the combined influence of multiple factors, such as gear and shaft stiffness, bearing clearance, and the dynamic meshing of parallel gears, gears often exhibit strong nonlinearity and transient behavior during their service life. Researchers at home and abroad have made progress in gear dynamics to understand how to reflect these complex operating states. However, beyond gear design, improving the ability of gear teeth to withstand transient loads during service, based on the fundamentals of raw materials, remains a key challenge for material scientists. Summary of the Invention

[0004] The present application provides a gear steel for a high-speed transmission system and a preparation method thereof to solve the following technical problem: how to improve the ability of gear steel to withstand large loads under high-speed and heavy-load conditions.

[0005] In the first aspect, the present application provides a gear steel for a high-speed transmission system. The chemical composition of the gear steel, measured by mass fraction, includes: C: 0.10% to 0.25%, Si: 0.1% to 0.40%, Mn: 0.3% to 1.00%, P≤0.03%, S: 0.015% to 0.05%, Cr: 1.2% to 2.5%, Ni: 1.0% to 2.5%, Mo≤0.5%, Al: 0.015% to 0.050%, N≤0.0200%, Ca: 0.0005% to 0.0050%, Nb≤0.05%, Cu≤0.2%, Fe, Al / N>3, wherein Al / N represents the mass ratio of Al and N.

[0006] Optionally, the chemical composition of the gear steel includes, by mass fraction: Al: 0.025% to 0.035%, N: 0.0100% to 0.0150%, and Ca: 0.0005% to 0.0020%.

[0007] Optionally, the gear steel can be processed to obtain a gear, and the tooth root of the gear can withstand a load-bearing capacity of a pitch linear velocity ≥35 m / s and / or a rotational speed ≥4500 r / min.

[0008] In a second aspect, the present application provides a method for preparing the gear steel for the high-speed transmission system described in the first aspect, the method comprising:

[0009] Refining the molten steel to obtain refined molten steel;

[0010] Continuously casting the refined molten steel to obtain a continuously cast billet;

[0011] heating and rolling the continuous casting billet in sequence to obtain a hot-rolled bar;

[0012] The hot-rolled bar is cooled to obtain gear steel.

[0013] Optionally, the refining adopts LF process, and the mass of Al out of the refined station is 0.035% to 0.055% of the total mass of the molten steel.

[0014] Optionally, the oxygen activity of the molten steel at the end of the refining outside the furnace is ≤3ppm.

[0015] Optionally, the refining uses steel slag, and the basicity of the steel slag is 2-4.

[0016] Optionally, the steel slag contains Al2O3 and CaO, wherein the mass of the Al2O3 is 20% to 35% of the total mass of the steel slag, and the mass of the CaO is 50% to 65% of the total mass of the steel slag.

[0017] Optionally, refining the molten steel to obtain refined molten steel includes:

[0018] Refining the molten steel to obtain initial refined molten steel;

[0019] The initial refined molten steel is vacuum degassed to obtain refined molten steel; the LF process is adopted for the refining, and the mass of Al discharged from the refined station is 0.045% to 0.055% of the total mass of the molten steel.

[0020] Optionally, the heating temperature is 1150° C. to 1200° C., and the heating time is 2.5 h to 3.5 h.

[0021] Optionally, the starting rolling temperature is 1050°C to 1100°C, and the finishing rolling temperature is 950°C to 1000°C.

[0022] Optionally, the hot-rolled bar has a grain size range of ≤3, and the hot-rolled bar has a hardenability J10 point Rockwell hardness of 35HRC to 50HRC.

[0023] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0024] The present application provides a gear steel for a high-speed transmission system. The chemical composition of the gear steel includes, by mass fraction: C: 0.10% to 0.25%, Si: 0.1% to 0.40%, Mn: 0.3% to 1.00%, P≤0.03%, S: 0.015% to 0.05%, Cr: 1.2% to 2.5%, Ni: 1.0% to 2.5%, Mo≤0.5%, Al: 0.015% to 0.050%, N≤0.0200%, Ca: 0.0005% to 0.0050%, Nb≤0.05%, Cu≤0.2%, Fe, Al / N>3, wherein Al / N represents the mass ratio of Al to N. By scientifically designing the gear steel's compositional system, based on a low-C-Si-low-Mn-high-Cr-high-Ni compositional system, the contents of elements such as Al, Nb, and N are carefully controlled, and Mo is added as a hardenability modifier. By controlling key process parameters during the production process, the purity and structural uniformity of the steel are ensured. This results in gear steel that can operate stably and withstand heavy loads under high-speed and heavy-load conditions, meeting the requirements of high-speed gear transmissions with pitch speeds greater than or equal to 35 m / s and / or speeds greater than 4500 r / min. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0026] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0027] Figure 1 A schematic flow chart of a method for preparing gear steel for a high-speed transmission system provided in an embodiment of the present application. DETAILED DESCRIPTION

[0028] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0029] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range; for example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range; in addition, whenever a numerical range is indicated in this document, it is meant to include any cited number (fractional or integer) within the indicated range.

[0030] As used herein, the terms "including," "comprising," and the like mean "including but not limited to." Relational terms such as "first" and "second" are used solely to distinguish one entity or operation from another, and do not necessarily require or imply any actual relationship or order between these entities or operations. "And / or" describes the association relationship between associated objects, indicating that three relationships can exist. For example, "A and / or B" can mean: A exists alone, A and B exist at the same time, and B exists alone; where A and B can be singular or plural. "At least one" means one or more, "plurality" means two or more; "at least one," "at least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items; for example, "at least one of a, b, or c" or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can each be single or plural. "Parts" notation, such as parts by weight or parts by mass, indicates the proportional relationship between components. In this article, the parameters described by ratio should be understood as the first term of the proportional formula, in the order in which they are described, and the proportional figures should be understood as the second term. For example, if the weight ratio of substances A, B, and C is 1:2:3, then substances A, B, and C should correspond to the proportional figures in the proportional formula, in the order in which they are described: that is, the weight of substance A: the weight of substance B: the weight of substance C = 1:2:3.

[0031] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this article can be purchased from the market or prepared by existing methods.

[0032] In the first aspect, the present application provides a gear steel for a high-speed transmission system. The chemical composition of the gear steel, measured by mass fraction, includes: C: 0.10% to 0.25%, Si: 0.1% to 0.40%, Mn: 0.3% to 1.00%, P≤0.03%, S: 0.015% to 0.05%, Cr: 1.2% to 2.5%, Ni: 1.0% to 2.5%, Mo≤0.5%, Al: 0.015% to 0.050%, N≤0.0200%, Ca: 0.0005% to 0.0050%, Nb≤0.05%, Cu≤0.2%, Fe, Al / N>3, wherein Al / N represents the mass ratio of Al and N.

[0033] In some embodiments, the chemical composition of the gear steel includes, by mass fraction, Al: 0.025% to 0.035%, N: 0.0100% to 0.0150%, and Ca: 0.0005% to 0.0020%.

[0034] Drawing on the nonlinear dynamics theory of high-speed, heavy-load gear transmissions, this paper conducted an in-depth analysis of the dynamic performance of gears, examining abnormal phenomena such as dynamic overload, increased meshing force, decreased meshing stability, and low-frequency resonance. Based on these analysis results, a rational selection and design of material strength was made to ensure that the gears can operate stably and withstand heavy loads under high-speed, heavy-load conditions. This application designs the chemical composition of gear steel based on the application requirements of high-speed transmissions.

[0035] The positive effects of limiting the carbon content to 0.10% to 0.25%: Carbon is one of the most important strengthening elements in steel. A carbon content of 0.10% to 0.25% can significantly improve the hardness and strength of steel, which is crucial for high-speed transmission gears that must withstand high loads and operate at high speeds. However, a carbon content above 0.25% may reduce the toughness of the steel. Therefore, limiting the carbon content to 0.10% to 0.25% achieves a balance between hardness, strength, and toughness, achieving optimal mechanical properties. Furthermore, high-speed operation of gears generates significant friction and wear. A carbon content of 0.10% to 0.25% can increase the wear resistance of the steel and extend the service life of the gears. This is of great significance for improving the reliability and stability of the entire transmission system. For example, the carbon content may be 0.10%, 0.12%, 0.15%, 0.18%, 0.21%, 0.23%, 0.25%, etc.

[0036] The positive effects of limiting the Si content to 0.1% to 0.40% are: Si can improve the strength and hardness of gear steel, while also helping to refine grains and increase the toughness of the steel. The Si content can be 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, etc.

[0037] The positive effects of limiting the Mn content to 0.3% to 1.00% are: Mn primarily enhances the strength and toughness of steel, while also helping to improve its hardenability. For example, the Mn content can be 0.30%, 0.40%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.00%, etc.

[0038] The positive effect of limiting the phosphorus content to ≤ 0.03% is that phosphorus is a harmful element in steel and its content should be minimized to improve the toughness of the steel. For example, the phosphorus content can be 0.005%, 0.01%, 0.015%, 0.02%, 0.025%, 0.03%, etc.

[0039] The positive effects of limiting the S content to 0.015% to 0.05% are as follows: controlling the S content within the range of 0.015% to 0.05% can effectively exert the influence of S on the performance of steel, improve the purity and overall quality of steel, and a S content of 0.015% to 0.05% helps to improve the cutting performance of steel. However, if the S content is higher than 0.05%, the addition amount will be too high, which will have a negative effect on the steel matrix. Therefore, limiting the S content to the range of 0.015% to 0.05% can avoid the negative effects of S while ensuring the processing performance. For example, the S content can be 0.015%, 0.02%, 0.025%, 0.03%, 0.035%, 0.04%, 0.045%, 0.05%, etc.

[0040] The positive effects of limiting the Cr content to 1.2% to 2.5% are as follows: Cr is one of the important alloying elements in steel and can significantly increase the hardness and strength of steel. Adding 1.2% to 2.5% Cr to gear steel can effectively enhance the gear's load-bearing capacity, especially under high-speed and high-load conditions, maintaining good mechanical properties. Cr can also enhance the steel's wear resistance because it forms hard carbides in the steel, which act as a strong anti-wear agent on the gear surface. This is particularly important for high-speed transmission system gears that need to operate for long periods of time, significantly extending their service life. For example, the Cr content can be 1.20%, 1.40%, 1.60%, 1.80%, 2.0%, 2.2%, 2.4%, 2.5%, etc.

[0041] The positive effects of limiting the Ni content to 1.0% to 2.5% are: Ni primarily enhances the toughness of steel and also helps improve its fatigue resistance. For example, the Ni content can be 1.0%, 1.3%, 1.5%, 1.7%, 1.9%, 2.1%, 2.3%, 2.5%, etc.

[0042] The positive effect of limiting the Mo content to ≤ 0.5% is that Mo is a strong carbide-forming element that improves the hardenability and hot strength of steel. However, a content above 0.5% may reduce the toughness of the steel. For example, the Mo content can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, etc.

[0043] The positive effects of limiting the Al content to 0.015% to 0.050% are: Al is an effective grain-refining element in steel. An Al content of 0.015% to 0.050% can form fine grains in the steel, helping to improve the steel's strength and toughness. For gear steel used in high-temperature transmission systems, fine grains can more effectively resist fatigue damage under high-speed operation and heavy load conditions. Additionally, Al can reduce the steel's tendency to hot cracking during hot working. During hot working processes such as continuous casting and rolling, Al helps form a dense oxide film, reducing the oxygen content and inclusions in the steel, thereby reducing the risk of hot cracking. For example, the Al content can be 0.015%, 0.02%, 0.025%, 0.03%, 0.035%, 0.04%, 0.045%, 0.050%, etc.

[0044] The positive effects of limiting the N content to ≤ 0.0200% are: Nitrogen easily forms nitride inclusions in steel, which can become crack sources and reduce the toughness and fatigue life of the steel. Limiting the N content can reduce the number of these inclusions, thereby improving the purity and toughness of the steel. Furthermore, reducing the N content helps avoid or mitigate microstructural deterioration caused by nitride precipitation, maintaining the uniformity and stability of the steel structure. For example, the N content can be 0.0040%, 0.0080%, 0.0120%, 0.0160%, 0.0200%, etc.

[0045] The positive effects of limiting the Ca content to 0.0005% to 0.0050% are as follows: Calcium is a trace element that helps improve the metallurgical quality and mechanical properties of steel. However, excessively high Ca content increases the risk of CaS formation in steel. Therefore, limiting the Ca content to 0.0005% to 0.0050% can provide limited improvement in fatigue resistance. For example, the Ca content can be 0.0005%, 0.0010%, 0.0015%, 0.0020%, 0.0025%, 0.0030%, 0.0035%, 0.0040%, 0.0045%, 0.0050%, etc.

[0046] The positive effect of limiting the Nb content to ≤0.05%: Nb can form fine precipitates in steel, which can hinder grain growth and thus refine the grains of the steel. Refined grains help improve the strength and toughness of steel, which is especially important for gear steel used in high-speed transmission systems that need to withstand high-speed operation and heavy loads. In addition, Nb precipitates can also act as a strengthening phase to increase the yield strength and tensile strength of steel while maintaining good toughness. This precipitation strengthening effect helps to improve the overall performance of gears. For example, the Nb content can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, etc.

[0047] The positive impact of limiting the Cu content to ≤ 0.2%: In gear steels used in high-speed transmission systems, Cu content above 0.2% can act as an impurity, affecting the steel's purity. By limiting the Cu content, the adverse effects of excessive impurities on steel properties can be reduced. For example, the Cu content can be 0.04%, 0.08%, 0.12%, 0.16%, 0.2%, and so on.

[0048] The specific content / content range of Fe can be obtained by the upper and lower limit formula of the component, namely:

[0049] The sum of the percentages of the contents of each component in a composition should be equal to 100%, and the content ranges of several components should meet the following conditions: the upper limit of a component + the lower limit of other components ≤ 100; the lower limit of a component + the upper limit of other components ≥ 100.

[0050] In some embodiments, the gear steel can be processed to obtain a gear, and the tooth root of the gear can withstand a load-bearing capacity of a pitch linear velocity ≥35 m / s and / or a rotational speed ≥4500 r / min.

[0051] Figure 1 A schematic flow chart of a method for preparing gear steel for a high-speed transmission system provided in an embodiment of the present application.

[0052] See Figure 1 In a second aspect, the present application provides a method for preparing the gear steel for the high-speed transmission system described in the first aspect, the method comprising:

[0053] S1, refining molten steel to obtain refined molten steel;

[0054] In some embodiments, molten steel needs to be smelted before being refined. The smelting can be carried out by electric furnace or converter smelting. After smelting, lime, fluorite, silicon carbide, aluminum ingots, refining slag, quartz sand, etc. are added. Then, the LF process is used for refining to further remove impurities and gases in the steel. Al wire can be fed into the refining seat to control the aluminum content. According to the required target nitrogen content, operations such as adding nitrogen-enhancing alloy raw materials can be selected to ensure that the Al:N ratio in the continuous casting process reaches 3 or more.

[0055] In some embodiments, the refining adopts the LF process, and the mass of Al at the refined output is 0.035% to 0.055% of the total mass of the molten steel.

[0056] Al is a commonly used deoxidizer in steel. Controlling the Al content within this range can ensure that the molten steel is fully deoxidized, reduce the oxygen content in the steel, and thus improve the purity and quality of the steel. In addition, Al can react with oxygen in the steel to form oxides such as aluminum oxide (Al2O3), most of which will float up and be removed, thereby reducing inclusions in the steel and improving the mechanical properties of the steel. For example, the mass of Al at the refining station can be 0.035%, 0.039%, 0.043%, 0.047%, 0.051%, 0.055%, etc. of the total mass of the molten steel.

[0057] In some embodiments, the oxygen activity of the molten steel at the end of the external refining is ≤3 ppm.

[0058] Lowering the oxygen activity in molten steel means reducing the dissolved oxygen content in the molten steel, thereby reducing the oxidation reaction of the molten steel that may be caused by excessive oxygen content, helping to remove non-metallic inclusions (such as oxide inclusions) in the steel and improving the purity and cleanliness of the molten steel. For gear steel used in high-speed transmission systems, reducing oxide inclusions in the steel is crucial to improving the wear resistance, fatigue resistance and service life of the gears. Molten steel with low oxygen activity helps reduce the risk of early failure of gears during use. For example, the oxygen activity of the molten steel at the end of refined off-furnace refining can be 0.5ppm, 1ppm, 1.5ppm, 2ppm, 2.5ppm, 3ppm, etc.

[0059] In some embodiments, the refining uses steel slag, and the basicity of the steel slag is 2-4.

[0060] During the refining process, basicity generally refers to the inverse of the mass ratio of basic oxides to acidic oxides in the slag. Basicity has a significant impact on the deoxidation and deoxidation effects of molten steel and the quality of steel. Too high a basicity may affect the deoxidation effect, while too low a basicity may affect the deoxidation effect. In the first 1 / 2 control stage of the refining process, the basicity of the steel slag is 4.8-7.5, at which time the desulfurization rate of the refining reaches 65%-82%. In the last 1 / 2-3 / 4 control stages of the refining process, the basicity of the steel slag is 2-4. For example, the basicity of the refined steel slag can be 2, 2.5, 3, 3.5, 4, etc.

[0061] In some embodiments, the steel slag contains Al2O3 and CaO, wherein the mass of the Al2O3 is 20% to 35% of the total mass of the steel slag, and the mass of the CaO is 50% to 65% of the total mass of the steel slag.

[0062] Al2O3 has a certain melting point in steel slag. An appropriate amount of Al2O3 content can help stabilize the melting point of steel slag, allowing it to maintain a certain viscosity at high temperatures, which is beneficial to the fluidity and removal of steel slag. This helps to reduce inclusions in molten steel and improve the purity of molten steel. During the LF refining process, the addition of Al helps deoxidation and desulfurization reactions, generating corresponding oxides and sulfides that enter the steel slag. Limiting the content of Al2O3 in steel slag can ensure that there is enough Al to react with oxygen and sulfur in the molten steel during the refining process, thereby improving refining efficiency and reducing refining time and cost. For example, the mass of Al2O3 in steel slag can be 20%, 23%, 26%, 29%, 32%, 35%, etc. of the total mass of the steel slag.

[0063] CaO is the main alkaline oxide in steel slag, and its content directly affects the basicity of the steel slag. When the CaO content is within the range of 50% to 65%, the steel slag can be ensured to have a moderate basicity, which helps the steel slag maintain stable performance and reduce fluctuations during the refining and continuous casting processes. Therefore, controlling the CaO content in steel slag helps promote the desulfurization reaction, improve the steel slag's ability to absorb inclusions, and thus improve the quality of molten steel. For example, the mass of CaO in the steel slag can be 50%, 53%, 56%, 59%, 62%, 65%, etc. of the total mass of the steel slag.

[0064] In some embodiments, refining the molten steel to obtain refined molten steel comprises:

[0065] Refining the molten steel to obtain initial refined molten steel;

[0066] The initial refined molten steel is vacuum degassed to obtain refined molten steel; the LF process is adopted for the refining, and the mass of Al discharged from the refined station is 0.045% to 0.055% of the total mass of the molten steel.

[0067] After refining and before continuous casting, vacuum degassing can be performed to further reduce the gas content in the steel and improve its purity. Vacuum degassing can be performed using either a VD or RH process. The Al content of the refined steel can be adjusted to 0.045% to 0.055% of the total mass of the molten steel.

[0068] S2, continuously casting the refined molten steel to obtain a continuously cast billet;

[0069] S3, heating and rolling the continuous casting billet in sequence to obtain a hot-rolled bar;

[0070] In some embodiments, the heating temperature is 1150° C. to 1200° C., and the heating time is 2.5 h to 3.5 h.

[0071] The positive effect of limiting the heating temperature to 1150°C to 1200°C is that it ensures good plastic deformation of the steel billet during rolling, reduces rolling resistance and energy consumption, and improves rolling efficiency. For example, the heating temperature can be 1150°C, 1160°C, 1170°C, 1180°C, 1190°C, 1200°C, etc.

[0072] The positive effect of limiting the heating time to 2.5 to 3.5 hours: A heating time of 2.5 to 3.5 hours can prevent grain coarsening caused by excessive heating of the billet, ensuring the microstructure and properties of the rolled product. For example, the heating time can be 2.5, 2.7, 2.9, 3.1, 3.3, or 3.5 hours.

[0073] In some embodiments, the starting rolling temperature is 1050°C to 1100°C, and the finishing rolling temperature is 950°C to 1000°C.

[0074] The positive effect of limiting the starting rolling temperature to 1050°C to 1100°C is that starting rolling within this temperature range maintains the steel in a good plastic state, which facilitates smooth rolling. For example, the starting rolling temperature can be 1050°C, 1060°C, 1070°C, 1080°C, 1090°C, 1100°C, etc.

[0075] The positive effects of limiting the finishing rolling temperature to 950°C to 1000°C: Finishing rolling within this temperature range helps refine and homogenize the internal structure of the steel. The high temperature and deformation during the finishing rolling process further refine the austenite grains and reduce internal defects such as inclusions and pores, thereby improving the mechanical properties and wear resistance of the steel. For example, the finishing rolling temperature can be 950°C, 960°C, 970°C, 980°C, 990°C, 1000°C, etc.

[0076] In some embodiments, the hot-rolled bar has a grain size range of ≤3, and a Rockwell hardness of the hot-rolled bar at J10 point of hardenability of 35HRC to 50HRC.

[0077] S4. Cooling the hot-rolled bar to obtain gear steel.

[0078] In some embodiments, the cooling method is air cooling.

[0079] The present application is further described below with reference to specific examples. Experimental methods in the following examples where specific conditions are not specified are generally measured in accordance with national / industry standards. If there are no corresponding national / industry standards, the methods are carried out in accordance with commonly used international standards, conventional conditions, or conditions recommended by the manufacturer.

[0080] Example 1

[0081] In this embodiment, the gear steel has the following chemical composition, by mass: C: 0.18%, Si: 0.30%, Mn: 0.70%, P: 0.008%, S: 0.018%, Cr: 1.6%, Ni: 1.6%, Al: 0.025%, N: 0.0100%, Mo: 0.04%, Nb: 0.01%, and Ca: 0.0005%. Electric furnace smelting is employed. During the LF refining process, 6 m / t of Al wire is fed into the refining ladle to control the aluminum content to 0.055%. During the first half of the refining process, the slag basicity is controlled at 5.5, at which point the desulfurization rate reaches 81%. During the last half to three-quarters of the refining process, the oxygen activity in the steel is 2 ppm, and the slag basicity is 2.8. The Al2O3 content in the slag is 33% and the CaO content is 61%, meeting the aluminum and sulfur content requirements for the VD process. Using the VD process, the sulfur content at the end of VD is 0.020%. The continuous cast slab enters a heating furnace at 1180°C for 2.5 hours. After exiting the furnace, it undergoes high-pressure water descaling. After descaling, it enters the hot rolling mill with an initial rolling temperature of 1150°C and a finishing temperature of 980°C.

[0082] The obtained hot-rolled bar has a grain size range of 2.5, a hardenability of the hot-rolled bar at J10 point of Rockwell hardness of 40HRC, an impact load impact energy of 113J, a tensile strength of 1270MPa, and an elongation of 12%. After cooling, the hot-rolled bar has a surface hardness of 65HRC, a core hardness of 37HRC, and a retained austenite level of 1.

[0083] Example 2

[0084] In this embodiment, the gear steel has the following chemical composition, by mass: C: 0.16%, Si: 0.24%, Mn: 0.60%, P: 0.008%, S: 0.030%, Cr: 1.4%, Ni: 2.0%, Al: 0.025%, N: 0.0090%, Mo: 0.3%, Nb: 0.01%, and Ca: 0.0020%. Electric furnace smelting is employed. During the LF refining process, 6 m / t of Al wire is fed into the refining ladle to control the aluminum content to 0.045%. During the first half of the refining process, the slag basicity is controlled at 6.5, achieving a desulfurization rate of 68% in the off-furnace refining. During the last half to third quarter of the refining process, the oxygen activity in the steel is 3 ppm, and the slag basicity is 2.4. The Al2O3 content in the slag is 29%, and the CaO content is 59%. At this point, the aluminum and sulfur contents meet the quantitative requirements for VD operation. The VD process is used, and the sulfur content at the end of VD is 0.020%. The continuous casting billet enters the heating furnace at a temperature of 1170°C for 3 hours. After exiting the heating furnace, it undergoes high-pressure water descaling. After descaling, it enters the hot rolling mill with an initial rolling temperature of 1140°C and a finishing temperature of 980°C.

[0085] The obtained hot-rolled bar has a grain size range of 2.5, a hardenability of the hot-rolled bar at J10 point of Rockwell hardness of 38HRC, an impact load impact energy of 135J, a tensile strength of 1360MPa, and an elongation of 11%. After cooling, the hot-rolled bar has a surface hardness of 68HRC, a core hardness of 35HRC, and a retained austenite level of 1.

[0086] Comparative Example 1

[0087] The comparison steel grade is 20CrMnTi, whose chemical composition includes: C: 0.20%, Si: 0.28%, Mn: 0.93%, P: 0.015%, S: 0.016%, Cr: 1.050%, Al: 0.015%, and N: 0.0080%. It is smelted in an electric furnace, with a tapping end-point C content of 0.06%, a P content of 0.012%, and an oxygen activity of 660 ppm. Lime, fluorite, silicon carbide, aluminum ingots, refining slag, and quartz sand are added during tapping. 3 m / t of Al wire is fed into the refining ladle to control the Al content to 0.035%. Vacuum degassing is performed using a VD process, with Al wire added before vacuum degassing to achieve an Al content of 0.045%. The refined molten steel has a basicity of 2.5 and an oxygen activity of 7 ppm. The refined slag contains 15% Al2O3 and 45% CaO. The molten steel is poured under protective conditions throughout the entire process at a pouring temperature of 1580°C. Two-stage electromagnetic stirring and a suitable cooling system are employed to solidify the slab into a continuous casting. The slab enters a heating furnace at 1160°C for 2.5 hours. After exiting the furnace, it undergoes high-pressure water descaling. After descaling, it enters the hot rolling mill with an initial rolling temperature of 1000°C and a finishing temperature of 900°C.

[0088] The obtained hot-rolled bar has a hardenability of 28HRC at J10 point of Rockwell hardness, impact load impact energy>45J, tensile strength>1080Mpa, and elongation>9%. After the hot-rolled bar is cooled, the core hardness reaches above 30HRC.

[0089] A comprehensive comparison between the embodiments of the present application and the comparative examples shows that the embodiments of the present application are improved in terms of impact energy, elongation, tensile strength, etc. in terms of impact load resistance, and can meet the requirements of bearing larger loads under high-speed and heavy-load conditions.

[0090] One or more technical solutions in the embodiments of the present invention may have at least the following technical effects or advantages:

[0091] The gear steel can be processed to obtain a gear, and the tooth root of the gear can withstand a bearing capacity of a pitch circle linear velocity ≥35m / s or a rotational speed ≥4500r / min.

[0092] The foregoing is merely a list of specific embodiments of the present application, intended to enable those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but rather is intended to conform to the broadest scope consistent with the principles and novel features claimed herein.

Claims

1. A gear steel for a high-speed transmission system, characterized in that: Measured in mass fraction, the chemical composition of the gear steel includes: C: 0.10% to 0.25%, Si: 0.1% to 0.40%, Mn: 0.3% to 1.00%, P≤0.03%, S: 0.015% to 0.05%, Cr: 1.2% to 2.5%, Ni: 1.0% to 2.5%, Mo≤0.5%, Al: 0.015% to 0.050%, N≤0.0200%, Ca: 0.0005% to 0.0050%, Nb≤0.05%, Cu≤0.2%, Fe, Al / N>3, where Al / N represents the mass ratio of Al to N.

2. The gear steel according to claim 1, characterized in that: Calculated by mass fraction, the chemical composition of the gear steel includes: Al: 0.025% to 0.035%, N: 0.0100% to 0.0150%, and Ca: 0.0005% to 0.0020%.

3. The gear steel according to claim 1, characterized in that: The gear steel can be processed to obtain a gear, and the tooth root of the gear can withstand a bearing capacity of a pitch circle linear velocity ≥35m / s and / or a rotational speed ≥4500r / min.

4. A method for preparing gear steel according to any one of claims 1 to 3, characterized in that: The method comprises: Refining the molten steel to obtain refined molten steel; Continuously casting the refined molten steel to obtain a continuously cast billet; heating and rolling the continuous casting billet in sequence to obtain a hot-rolled bar; The hot-rolled bar is cooled to obtain gear steel.

5. The method according to claim 4, characterized in that The refining adopts LF process, and the mass of Al in the refined steel output is 0.035% to 0.055% of the total mass of the molten steel; and / or, The oxygen activity of the molten steel at the end of the refining process outside the furnace is ≤3ppm.

6. The method according to claim 4, characterized in that The refining uses steel slag, and the basicity of the steel slag is 2 to 4; and / or, The steel slag contains Al2O3 and CaO, wherein the mass of the Al2O3 accounts for 20% to 35% of the total mass of the steel slag, and the mass of the CaO accounts for 50% to 65% of the total mass of the steel slag.

7. The method according to claim 4, characterized in that The molten steel is refined to obtain refined molten steel, comprising: Refining the molten steel to obtain initial refined molten steel; The initial refined molten steel is vacuum degassed to obtain refined molten steel; the LF process is adopted for the refining, and the mass of Al discharged from the refined station is 0.045% to 0.055% of the total mass of the molten steel.

8. The method according to claim 4, characterized in that The heating temperature is 1150° C. to 1200° C., and the heating time is 2.5 hours to 3.5 hours.

9. The method according to claim 4, characterized in that The starting rolling temperature is 1050°C to 1100°C, and the finishing rolling temperature is 950°C to 1000°C.

10. The method according to claim 4, characterized in that The grain size range of the hot-rolled bar is ≤3, and the hardenability J10 point Rockwell hardness of the hot-rolled bar is 35HRC to 50HRC.

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