Microalloyed gear steel with high contact fatigue performance and method for producing gears

Abstract

The application provides a kind of microalloyed high contact fatigue performance gear steel and the method of producing gear, C:0.16-0.21%, Si:0.20-0.37%, Mn:0.50-0.80%, Cr:1.5-1.8%, Mo:0.25-0.35%, V:0.10-0.20%, Ni:1.4-1.7%, P≤0.010%, S:0.015-0.035%, Al:0.015-0.025%, [N]:60-110ppm, the rest is Fe and inevitable impurity element, the application is optimized by microalloying, induction heat treatment process etc., gear steel contact fatigue performance is improved by more than 50%, i.e. under the condition that compressive stress is 4.0GPa, rated fatigue life L10≥8×10 7 , median fatigue life L50≥10×10 7 .

Description

Technical Field

[0001] The present invention belongs to the field of gear steel, and relates to a microalloyed gear steel with high contact fatigue performance and a method for producing the gear. The produced gear is used in the fields of wind power and railway transportation. Background Art

[0002] Gear steel is a critical material with high demand and high volume in the specialty steel sector, widely used in machinery, transportation, energy, and other fields. The performance requirements of gear steel not only impact technical and economic indicators such as equipment lifespan, but also influence operational safety and other requirements. Gears operate in complex and harsh environments, with primary failure modes including wear on the meshing surfaces, pitting and spalling caused by contact fatigue, and cracking or fracture due to bending fatigue at the tooth root. Materials are generally required to possess excellent strength, toughness, and wear resistance, so contact fatigue can be used to reflect material performance.

[0003] In the existing technology, Ma Li et al. mentioned in "Contact Fatigue Performance of Microalloyed Carburized Gear Steel" that a lower oxygen content can effectively reduce the number of oxide inclusions and gears, which is beneficial to improving the contact fatigue performance of gear steel; at the same time, the Nb content can control the grain size of the carburized layer of gear steel, increase the hardness of the carburized layer, and thus increase the resistance to fatigue crack initiation and expansion, which is one of the reasons for the better contact fatigue performance after Nb microalloying. Fan Liming et al. showed in the article "Study on the Effect of Ti on the Contact Fatigue Performance of 20CrMnTiH Gear Steel" that low titanium-nitrogen product (0.0001352) has better contact fatigue performance than high titanium-nitrogen product (0.0004320), which is roughly improved by about an order of magnitude. Wang Yan et al. mentioned in the article "Research on Carbides and High-Temperature Contact Fatigue Life in High-Temperature Bearing Steel" that the contact fatigue rated life and median fatigue life can be effectively improved by improving the unevenness of carbides and reducing the size of carbides. Xu Fan et al.

[0004] "The Effect of Carbon and Chromium Content on the Structure and Contact Fatigue Life of Stainless Bearing Steel" believes that a certain carbon and chromium content can effectively improve contact fatigue performance. Non-metallic inclusions and coarse eutectic carbides are prone to stress concentration under contact stress and become fatigue sources, affecting fatigue life.

[0005] A Chinese patent, publication number CN 101319294 A, published on December 10, 2008, discloses a fine-grained carburized gear steel and a method for manufacturing the same. The disclosed chemical composition (weight %) of the steel is: C 0.15-0.25%, Si ≤ 0.35%, Mn 0.60-0.90%, P ≤ 0.015%, S ≤ 0.010%, Cr 0.80-1.20%, Mo 0.15-0.35%, Nb 0.02-0.08%, B 0.0005-0.0035%, Al 0.02-0.06%, Ti 0.01-0.04%, [N] ≤ 0.015%, [O] ≤ 0.0015%, and the remainder is Fe and unavoidable impurities. At the same time, Ti ≥ 2 [N] and B ≥ ( [N] - Ti / 3.4) / 1.4 + 0.001 are required. A rolling production process with a final rolling temperature below 900 ° C is used. Compared with the existing carburized gear steel 20CrMoH, the grain size after carburizing and quenching is greater than 10 grades, the bending fatigue strength (σ - 1) is increased by more than 15%, and the contact fatigue life (L10) is increased by more than 30%. However, its rated contact fatigue is only 2.0 × 10 7 Around, with the gradual improvement of the performance requirements of high-performance gear steel in industries such as high-speed rail and wind power, it can no longer meet the current demand for high contact fatigue performance materials, so it is necessary to develop carburized gear steel with better performance. Summary of the Invention

[0006] The purpose of the present invention is to provide a microalloyed gear steel with high contact fatigue performance and a method for producing gears. Through optimization of microalloying and induction heat treatment processes, the contact fatigue performance of the gear steel is improved by more than 50%, that is, under the condition of compressive stress of 4.0 GPa, the rated fatigue life L10≥8×10 7 , median fatigue life L50≥10×10 7 .

[0007] The specific technical solutions of the present invention are as follows:

[0008] A microalloyed gear steel with high contact fatigue performance comprises the following components in mass percentage: C: 0.16-0.21%, Si: 0.20-0.37%, Mn: 0.50-0.80%, Cr: 1.5-1.8%, Mo: 0.25-0.35%, V: 0.10-0.20%; Ni: 1.4-1.7%, P≤0.010%, S: 0.015-0.035%, Al: 0.015-0.025%, [N]: 60-110 ppm, and the remainder being Fe and unavoidable impurity elements.

[0009] The composition of the microalloyed high contact fatigue performance gear steel meets the following conditions: Al / [N]: 2.0-4.0;

[0010] The composition of the microalloyed high contact fatigue performance gear steel meets the following conditions: 0.60≤

[0011] [C+Mn / 4+Si / 2 / +(Cr+V) / 10]≤0.70; This formula is a component guarantee for the strength of locomotive gears, but too high will increase the hardenability of the gears, bringing adverse effects and easily causing cold cracks. Therefore, under the premise of ensuring strength, the formula range is strictly controlled to 0.60≤[C+Mn / 4+Si / 2 / +(Cr+V) / 10]≤0.70; preferably [C+Mn / 4+Si / 2 / +(Cr+V) / 10]=0.65-0.70, more preferably

[0012] [C+Mn / 4+Si / 2 / +(Cr+V) / 10] = 0.67-0.70. Since each element plays a strengthening role in gear steel, the coefficient matching is based on the different strengthening effects of each element.

[0013] The present invention provides a method for producing a micro-alloyed gear with high contact fatigue performance, which includes the following process flow: electric arc furnace smelting → LF refining → RH vacuum treatment → round billet continuous casting → round billet forging → heating → rolling → heat treatment → machining → induction quenching of the gear outer diameter surface → testing → packaging.

[0014] In the heating, the soaking temperature of the steel billet in the heating furnace is controlled at 1200-1240° C., and the total time of preheating, heating and soaking is controlled at 5.0 h-8.0 h.

[0015] The rolling process has a starting temperature of 1030-1050°C and a finishing temperature of 850-880°C.

[0016] Slow cooling after rolling, specifically: after rolling, the stack is dropped, air-cooled to no less than 500℃ and then put into the furnace.

[0017] The heat treatment specifically comprises the following steps: loading the rolled blank gear into a furnace, heating the blank gear at a temperature of 870-900°C for 4-5 hours to fully austenitize the blank gear in order to improve the banded structure caused by the segregation of alloy elements; removing the fully austenitized gear from the furnace, cooling the blank gear with water to ensure a cooling rate of 3-5°C / s, and then tempering the blank gear at 650-680°C for 4-6 hours, and finally machining and induction quenching the gear to obtain the finished gear.

[0018] The gear outside The induction hardening of the outer diameter of the gear is carried out at a speed of 400-450 mm / min. Preferably, when the gear is subjected to surface induction hardening, the heating sensor and the water spray ring are fine-tuned in the horizontal direction to ensure that the gear is in the center of the heat sensor coil; the heating sensor and the water spray ring are moved axially at a uniform speed along the gear.

[0019] When the gear is subjected to surface induction hardening, the gear rotates at 40-60r / min;

[0020] When the gear is subjected to surface induction hardening, the quenching and water spraying should be carried out from bottom to top, and the water pressure should be

[0021] 0.40-0.50MPa, the water spraying time is consistent with the heating time; the heating time is 20-50s;

[0022] The gear is subjected to surface induction hardening. The larger the diameter D (unit: mm) of the part is, the lower the selected frequency is. For large-sized parts, the current frequency is selected to be 1000-3000 Hz; the depth of the hardened layer is 15-20 mm.

[0023] After surface induction hardening, the gears are tempered at 180-200℃ to eliminate internal stress;

[0024] After tempering is completed, the gear surface is finely ground.

[0025] The microalloyed high contact fatigue performance gear provided by the present invention is produced by the above method, and has a structure of more than 90% pearlite and a small amount of ferrite;

[0026] The microalloyed high contact fatigue performance gear has a grain size of ≥11.0 and a grain size of ≤6 μm; a core grain size of ≥9 and a grain size of ≤15 μm; and a rated fatigue life L10 of ≥8×10 under a compressive stress of 4.0 GPa. 7 , median fatigue life L50≥10×10 7 ; Tensile strength ≥1000-1100Mpa, yield strength ≥900Mpa, U2 notch impact on gear outer diameter surface ≥50J, surface hardness 280-320HB.

[0027] The design ideas of the present invention are as follows:

[0028] C: C is the most basic and effective strengthening element in steel and the element that most effectively affects hardenability. In order to ensure sufficient strength and hardenability of gear steel, the C content cannot be lower than 0.16%. Since gear steel must ensure toughness, the C content cannot be higher than 0.21%, so the C content is determined to be 0.16-0.21%.

[0029] Si: Si is a deoxidizer that increases the hardness of steel through solid solution strengthening and can also improve the hardenability of gear steel. The Si content cannot be lower than 0.20%. However, excessive silicon increases the activity of C, promoting decarburization and graphitization during rolling and heat treatment, making the carburized layer susceptible to oxidation. Therefore, the Si content cannot be higher than 0.37%. The Si content is controlled at 0.20-0.37%.

[0030] Mn: Mn is soluble in ferrite, increasing the hardness and strength of both ferrite and austenite in steel. It also improves the stability of the austenite structure and significantly enhances the hardenability of the steel. However, excessive Mn reduces the steel's plasticity and toughness during hot rolling. The Mn content should be controlled within a range of 0.50-0.80%.

[0031] The addition of Si and Mn can play a role in solid solution strengthening, while improving the thermal stability of gear steel, thereby reducing the sensitivity of gear materials to rolling contact fatigue and ratcheting effect, and slowing down the initiation of fatigue cracks. Silicon is a non-carbide-forming element. It does not exist in cementite but is mainly dissolved in ferrite with a body-centered cubic lattice. The large size difference between silicon and iron atoms causes a strong distortion of the ferrite lattice, forming solid solution strengthening. This solid solution strengthening effect is not only reflected in the proeutectoid ferrite of gear steel, but also exists in pearlite ferrite. The microstructure of gear steel is mainly pearlite structure. Therefore, the addition of silicon will increase the overall strength of gear steel, and compared with carbon, it will reduce the plasticity of the material less.

[0032] Cr: Cr improves the hardenability and strength of steel. It also reduces the activity of carbon and reduces the tendency of surface decarburization during heating, rolling, and heat treatment, contributing to high fatigue resistance. Therefore, the Cr content should not be less than 1.5%. Excessive Cr content reduces the toughness of the steel and results in the formation of large amounts of carbides in the carburized layer, affecting its properties. Therefore, the Cr content should not exceed 1.8%. Cr is a carbide-forming element. During pearlite formation, alloying elements diffuse and redistribute at the interface between ferrite and cementite, and between ferrite and cementite. The chemical composition of cementite can vary widely, and it can form alloyed cementite with other elements. While the crystal structure of cementite is not altered, alloying elements have very low diffusion coefficients, which reduce the diffusion coefficient of carbon in austenite, thereby delaying cementite formation and austenite homogenization. This significantly increases the temperature of the pearlite-to-austenite transformation, delaying the austenite-to-pearlite transformation, and reducing the interlamellar spacing of pearlite.

[0033] Mo is an element with similar or stronger effects than Cr, and is used to improve the hardening properties of steel and prevent the strength of heat-treated materials from decreasing. However, when Mo is added in amounts less than 0.25%, it is difficult to ensure the hardening properties of the steel. When added in amounts greater than 0.35%, a structure with weak low-temperature toughness is formed, and temper embrittlement occurs. Therefore, the Mo content is preferably limited to 0.25% to 0.35%.

[0034] Ni: Ni dissolves into steel, increasing its yield strength and fatigue strength after hot forging and heat treatment. It also improves its toughness after hot forging and heat treatment. Ni content above 1.4% achieves optimal results, so the lower limit is set at 1.4%. Excessive Ni content increases manufacturing costs, so the Ni content is controlled within a range of 1.4-1.7%.

[0035] Vanadium (V): Vanadium is an important strong carbonitride-forming element in gear steel. Through heating, dissolution, and cooling, precipitation, it forms interstitial VC, V4C3, and nitrogen-rich V(C,N) second-phase particles in the steel, resulting in strong precipitation strengthening and grain refinement, significantly improving yield strength. Furthermore, the formation of vanadium-containing second-phase particles promotes the formation of proeutectoid ferrite due to the carbon-poor microregions surrounding the particles and a smaller lattice mismatch with the ferrite, which moderately increases the wear rate. This balances the competitive relationship between contact fatigue and wear, improving the surface contact fatigue resistance of gears. The present invention sets the vanadium content range to 0.10%-0.20%. The rationale is that, on the one hand, vanadium contents exceeding this value require higher heating temperatures to achieve a significant strengthening effect. Otherwise, the combined effects of low solid-solution V content and low matrix carbon content significantly limit the strength-enhancing effect of V microalloying, or even produce a negative effect. On the other hand, too low a vanadium content will not significantly enhance precipitation strengthening. In addition, if the heat treatment regime is inappropriate, vanadium may deprive the matrix of carbon, resulting in a decrease in strength. In addition, the V carbonitrides on the grain boundaries strongly pin the grain boundaries and refine the grains, thereby improving the morphology, quantity and distribution of proeutectoid ferrite, and refining the austenite grain size makes it easier for cracks to bend and passivate at grain boundaries or pearlite boundaries, increasing the crack propagation resistance, and thus playing a role in improving the strength-toughness match.

[0036] Al: Al is an effective deoxidizer and can form AlN to refine grains. When the Al content is below 0.015%, its effect is not significant. When it is above 0.025%, it tends to form coarse inclusions, deteriorating the properties of the steel. Therefore, the Al content should be controlled within 0.015-0.025%.

[0037] [N]: It can form compounds with Al, refining grains. A reasonable Al / [N] ratio significantly contributes to grain refinement, while excessively high [N] can cause continuous casting defects such as bubbles. Therefore, the [N] content should be controlled between 60-110 ppm. At the same time, the Al / [N] ratio should be controlled between 2.0-4.0.

[0038] P and S: Sulfur easily forms MnS inclusions with manganese in steel, causing hot brittleness. However, adding a small amount of S can significantly improve the cutting performance of gear steel without affecting product performance. MnS also has the effect of refining the grain size. P is an element with a strong tendency to segregate, increasing cold brittleness and reducing plasticity, which is detrimental to the uniformity of the product's structure and properties. Control P ≤ 0.010%, and S: 0.015-0.035%.

[0039] Compared with the existing technology, the present invention improves the contact fatigue performance of gear steel by more than 50% through optimization of microalloying and induction heat treatment process, that is, under the condition of compressive stress of 4.0GPa, the rated fatigue life L10≥8×10 7 , median fatigue life L50≥10×10 7 . BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The actual grains on the surface of the rolled gear blank in Example 1;

[0041] Figure 2 The grain size of tempered austenite in Example 1;

[0042] Figure 3 The actual grains on the surface of the rolled gear blank in comparative example 1;

[0043] Figure 4 This is the tempered austenite grain size of Comparative Example 1. DETAILED DESCRIPTION

[0044] The present invention provides a microalloyed high contact fatigue performance gear steel, comprising the following components in percentage by mass:

[0045] C: 0.16-0.21%, Si: 0.20-0.37%, Mn: 0.50-0.80%, Cr: 1.5-1.8%, Mo: 0.25-0.35%, V: 0.10-0.20%; Ni: 1.4-1.7%, P≤0.010%, S: 0.015-0.035%, Al: 0.015-0.025%, [N]: 60-110ppm, the rest are Fe and unavoidable impurity elements.

[0046] The composition of the above microalloyed high contact fatigue performance gear steel meets the following requirements:

[0047] 0.60≤[C+Mn / 4+Si / 2 / +(Cr+V) / 10]≤0.70, Al / [N]: 2.0-4.0.

[0048] The microalloyed high contact fatigue performance gear provided by the present invention is produced using the above-mentioned microalloyed high contact fatigue performance gear steel. The specific production process is as follows:

[0049] Electric arc furnace smelting → LF refining → RH vacuum treatment → round billet continuous casting → round billet forging → heating → rolling → heat treatment → machining → gear outer diameter surface induction quenching → testing → packaging.

[0050] The specific process conditions are as follows:

[0051] 1) Metallurgy uses electromagnetic stirring and optimized heat treatment process control to improve the banded structure of the material. To ensure higher density of the gear blank and increase the forging ratio of the gear blank steel, the continuous casting blank with a cross section of Φ600mm is converted into Φ380 or Φ280mm round steel through forging and rolling to give the rolled blank an initial forging ratio.

[0052] 2) Heating: The soaking temperature of the steel billet in the heating furnace is controlled at 1200-1240°C, and the total time of preheating, heating and soaking is controlled at 5.0h-8.0h.

[0053] 3) Rolling: starting rolling temperature 1030-1050℃, finishing rolling temperature 850-880℃.

[0054] 4) Slow cooling: After rolling, the steel is unstacked and air-cooled to a temperature not lower than 500°C before being put into the furnace.

[0055] 5) Heat treatment: The rolled gear blank is loaded into a furnace and heated at 870-900°C for 4-5 hours to fully austenitize in order to improve the banded structure caused by alloy element segregation. The fully austenitized gear is removed from the furnace and water-cooled to ensure a cooling rate of 3-5°C / s. It is then tempered at 650-680°C and finally machined and induction hardened to obtain the finished gear.

[0056] 6) Gear outside Induction hardening of the outer diameter surface of the gear: the outer diameter surface of the gear is induction hardened; the heating sensor and the water spray ring are fine-tuned in the horizontal direction to ensure that the gear is in the center of the coil; the heating sensor and the water spray ring are moved axially at a uniform speed along the gear, and the quenching speed is 400-450mm / min; when the outer diameter surface of the gear is induction hardened, the quenching machine drives the gear to rotate at 40-60r / min to ensure uniform heating and cooling of the gear; quenching and water spraying need to be carried out from bottom to top, the water pressure is 0.40-0.50MPa, and the water spraying time is consistent with the heating time (20-50s); the larger the part diameter D (unit: mm), the lower the selected frequency. For large-size gears, the current frequency is selected as 1000-3000Hz; the depth of the hardened layer is 15-20mm.

[0057] 7) After surface induction quenching, low temperature tempering at 180-200℃ is carried out to eliminate internal stress. After tempering, the gear surface is finely ground.

[0058] The microalloyed high contact fatigue performance gear produced according to the above composition and production method has a structure of more than 90% pearlite and a small amount of ferrite; the grain size is ≥11.0 grade, the grain size is ≤6μm; the core grain size is ≥9 grade, the grain size is ≤15μm; under the condition of compressive stress of 4.0GPa, the rated fatigue life L10 is ≥8×10 7 , median fatigue life L50≥10×10 7 ;Tensile strength ≥1000-1100Mpa, yield strength ≥900Mpa, gear outside The impact of U2 notch on the radial surface is ≥50J, and the surface hardness is 280-320HB.

[0059] The present invention is further described in detail below with reference to several specific cases.

[0060] Example 1

[0061] A microalloyed high contact fatigue performance gear steel comprising the following components in percentage by mass:

[0062] C: 0.17%, Si: 0.25%, Mn: 0.72%, Cr: 1.52%, Mo: 0.25%, V: 0.11%; Ni: 1.42%, P: 0.01%, S: 0.016%, Al: 0.015%, [N]: 60ppm, [C+Mn / 4+Si / 2 / +(Cr+V) / 10]=0.64, Al / [N]: 2.50, the rest are Fe and unavoidable impurity elements.

[0063] The method for producing a microalloyed high contact fatigue performance gear using the microalloyed high contact fatigue performance gear steel of Example 1 includes the following process flow:

[0064] Electric arc furnace smelting → LF refining → RH vacuum treatment → round billet continuous casting → round billet forging → heating → rolling → heat treatment → processing → gear outer diameter surface induction quenching → testing → packaging. The specific process conditions are as follows:

[0065] After sawing, the continuous casting slab is preheated at 1230°C for a total of 6.5 hours, followed by preheating, heating, and soaking. Round steel rolling begins at 1047°C and ends at 863°C. After rolling, it is cooled on a cooling bed to 632°C before being slow-cooled in a pit for 10 hours. Heat treatment is performed at 880°C for 4.5 hours to achieve full austenitization. The fully austenitized gear is removed from the furnace and water-cooled, maintaining a cooling rate of 3°C / s. It is then tempered at 650°C for 4.5 hours before being machined and induction hardened to produce the finished gear. Among them, induction quenching is specifically as follows: surface induction quenching of the gear; fine-tuning of the heating sensor and the water spray ring in the horizontal direction to ensure that the gear is in the center of the coil; the heating sensor and the water spray ring are moved axially at a uniform speed along the gear, and the quenching speed is 420mm / min; when the outer diameter surface of the gear is induction quenched, the quenching machine drives the gear to rotate at 45r / min to ensure uniform heating and cooling of the gear; quenching and water spraying need to be carried out from bottom to top, the water pressure is 0.45MPa, and the water spraying time is consistent with the heating time of 40s; the current frequency f of the induction quenching equipment is 1000Hz, and the depth of the hardened layer d is 16:mm; the larger the part diameter D (unit: mm), the lower the selected frequency. The gear is a large-size part. After surface induction quenching, it is subjected to low-temperature tempering at 180℃ to eliminate internal stress. After tempering, the gear surface is fine-ground.

[0066] Example 2

[0067] A microalloyed high contact fatigue performance gear steel comprising the following components in percentage by mass:

[0068] C: 0.17%, Si: 0.25%, Mn: 0.73%, Cr: 1.66%, Mo: 0.30%, V: 0.15%; Ni: 1.61%, P: 0.01%, S: 0.025%, Al: 0.02%, [N]: 100ppm, [C+Mn / 4+Si / 2 / +(Cr+V) / 10]=0.66, Al / [N]: 2.00, the rest are Fe and unavoidable impurity elements.

[0069] The method for producing a microalloyed high contact fatigue performance gear using the microalloyed high contact fatigue performance gear steel of Example 2 includes the following process flow:

[0070] Electric arc furnace smelting → LF refining → RH vacuum treatment → round billet continuous casting → round billet forging → heating → rolling → heat treatment → processing → gear outer diameter surface induction quenching → testing → packaging. The specific process conditions are as follows:

[0071] After sawing, the continuous casting slab is preheated at 1217°C for a total of 6.5 hours, followed by a controlled soaking time. Round steel rolling begins at 1038°C and ends at 857°C. After rolling, it is cooled on a cooling bed to 633°C before being placed in a pit for 10 hours of slow cooling. Heat treatment is performed at 880°C for 4.5 hours to achieve full austenitization. The fully austenitized gear is removed from the furnace and water-cooled, maintaining a cooling rate of 4°C / s. It is then tempered at 670°C for 4.5 hours before being machined and induction hardened to produce the finished gear. Among them, induction quenching is specifically as follows: surface induction quenching of the gear; fine-tuning of the heating sensor and the water spray ring in the horizontal direction to ensure that the gear is in the center of the coil; the heating sensor and the water spray ring are moved axially at a uniform speed along the gear, and the quenching speed is 440mm / min; when the outer diameter surface of the gear is induction quenched, the quenching machine drives the gear to rotate at 50r / min to ensure uniform heating and cooling of the gear; quenching and water spraying need to be carried out from bottom to top, with a water pressure of 0.45MPa, and the water spraying time is consistent with the heating time of 32s; the current frequency f of the induction quenching equipment is 1500Hz, the depth of the hardened layer d is 18mm, and after surface induction quenching, low-temperature tempering at 180℃ is performed to eliminate internal stress. After tempering, the gear surface is fine-ground.

[0072] Example 3

[0073] A microalloyed high contact fatigue performance gear steel comprising the following components in percentage by mass:

[0074] C: 0.18%, Si: 0.25%, Mn: 0.75%, Cr: 1.78%, Mo: 0.34%, V: 0.19%; Ni: 1.68%, P: 0.01%, S: 0.032%, Al: 0.025%, [N]: 105ppm, [C+Mn / 4+Si / 2 / +(Cr+V) / 10]=0.69, Al / [N]: 2.38, the rest are Fe and unavoidable impurity elements.

[0075] The method for producing a microalloyed high contact fatigue performance gear using the microalloyed high contact fatigue performance gear steel of Example 3 includes the following process flow:

[0076] Electric arc furnace smelting → LF refining → RH vacuum treatment → round billet continuous casting → round billet forging → heating → rolling → heat treatment → processing → gear outer diameter surface induction quenching → testing → packaging. The specific process conditions are as follows:

[0077] After sawing, the continuous casting slab is preheated at 1239°C for a total of 7.0 hours, followed by round rolling. The rolling starts at 1050°C and ends at 879°C. After rolling, it is cooled on a cooling bed to 636°C before being slow-cooled in a pit for 10 hours. Heat treatment is performed at 880°C for 4.5 hours to achieve full austenitization. The fully austenitized gear is removed from the furnace and water-cooled, maintaining a cooling rate of 5°C / s. It is then tempered at 680°C for 4.5 hours before being machined and induction hardened to obtain the finished gear. Among them, induction quenching is specifically as follows: surface induction quenching of the gear; fine-tuning of the heating sensor and the water spray ring in the horizontal direction to ensure that the gear is in the center of the coil; the heating sensor and the water spray ring are moved axially at a uniform speed along the gear, and the quenching speed is 430mm / min; when the outer diameter surface of the gear is induction quenched, the quenching machine drives the gear to rotate at 60r / min to ensure uniform heating and cooling of the gear; quenching and water spraying need to be carried out from bottom to top, with a water pressure of 0.45MPa, and the water spraying time is consistent with the heating time of 25s; the current frequency f of the induction quenching equipment is 2500Hz, the depth of the hardened layer d is 18mm, and after surface induction quenching, low-temperature tempering at 180℃ is performed to eliminate internal stress. After tempering, the gear surface is fine-ground.

[0078] Comparative Example 1

[0079] A microalloyed high contact fatigue performance gear steel comprising the following components in percentage by mass:

[0080] C：0.26％ , Si: 0.42% , Mn: 0.70%, Cr：1.2％， Mo: 0.28%, V:0.08％ ; Ni: 1.63%, P: 0.010%, S: 0.015%, Al：0.034％ , [N]: 95ppm, Al / [N]: 3.58, [C+Mn / 4+Si / 2 / +(Cr+V) / 10]= 0.77， The rest is Fe and unavoidable impurity elements, and conforms to the formula.

[0081] The method for producing a microalloyed high contact fatigue performance gear using the microalloyed high contact fatigue performance gear steel of Comparative Example 1 includes the following process flow:

[0082] Electric arc furnace smelting → LF refining → RH vacuum treatment → round billet continuous casting → round billet forging → heating → rolling → heat treatment → processing → testing → packaging. The specific process conditions are as follows:

[0083] After continuous casting billet is sawn 1187 After heating and holding for 8.0h, round steel rolling is carried out. The rolling temperature is: 1027 ℃, final rolling temperature 841℃, after rolling, it is cooled to 638℃ in the cooling bed and then put into the pit for slow cooling, the slow cooling time is 10h. 880 ℃, heating time 4.5 hours, fully austenitized; the fully austenitized gear is taken out of the furnace, cooled by water to ensure the cooling rate of the blank gear is 3.5℃ / s, and then tempered at 670℃ for 4.5 hours, and then machined. No entry Surface induction hardening.

[0084] Comparative Example 2

[0085] A microalloyed high contact fatigue performance gear steel comprising the following components in percentage by mass:

[0086] C: 0.18%, Si: 0.26%, Mn: 0.72%, Cr：2.3％ , Mo: 0.27%, V:0.24％ ; Ni: 1.61%, P: 0.010%, S: 0.015%, Al：0.035％ , [N]: 60ppm, Al / [N]: 5.83 , [C+Mn / 4+Si / 2+(Cr+V) / 10]= 0.74， The rest is Fe and unavoidable impurity elements, and conforms to the formula.

[0087] The method for producing a microalloyed high contact fatigue performance gear using the microalloyed high contact fatigue performance gear steel of Comparative Example 2 includes the following process flow:

[0088] Electric arc furnace smelting → LF refining → RH vacuum treatment → round billet continuous casting → round billet forging → heating → rolling → heat treatment → processing → testing → packaging. The specific process conditions are as follows:

[0089] After continuous casting billet is sawn 1284 After heating and holding for 6.5 hours, round steel rolling is carried out. The rolling temperature is: 1083 ℃, final rolling temperature 895 ℃, after rolling, it is cooled to 633℃ on the cooling bed and then put into the pit for slow cooling, and the slow cooling time is 10h. The heat treatment is carried out at a temperature of 880℃ and the heating time is 4.5 hours to fully austenitize. The fully austenitized gear is taken out of the furnace and cooled by water to ensure that the cooling rate of the blank gear is 3.5℃ / s, and then tempered at 680℃ for a period of time. 4.5 hours, and then machined. No entry Surface induction hardening.

[0090] Comparative Example 3

[0091] A microalloyed high contact fatigue performance gear steel comprising the following components in percentage by mass:

[0092] C: 0.17%, Si: 0.34%, Mn: 0.78%, Cr: 1.7%, Mo: 0.25%, V: 0.11%; Ni: 1.42%, P: 0.01%, S: 0.025%, Al: 0.015%, [N]: 60ppm, [C+Mn / 4+Si / 2 / +(Cr+V) / 10]=0.72 , Al / [N]: 2.50, and the rest are Fe and inevitable impurity elements.

[0093] The method for producing a microalloyed high contact fatigue performance gear using the microalloyed high contact fatigue performance gear steel of Comparative Example 3 includes the following process flow:

[0094] Electric arc furnace smelting → LF refining → RH vacuum treatment → round billet continuous casting → round billet forging → heating → rolling → heat treatment → processing → gear outer diameter surface induction quenching → testing → packaging. The specific process conditions are as follows:

[0095] After sawing, the continuous casting slab is preheated at 1230°C for a total of 6.5 hours, followed by a controlled soaking time. Round steel rolling begins at 1047°C and ends at 863°C. After rolling, it is cooled on a cooling bed to 632°C before being slow-cooled in a pit for 10 hours. Heat treatment is performed at 880°C for 4.5 hours to achieve full austenitization. The fully austenitized gear is removed from the furnace and water-cooled, maintaining a cooling rate of 3.5°C / s. It is then tempered at 650°C for 4.5 hours before machining and induction hardening to obtain the finished gear. Among them, induction quenching is specifically as follows: surface induction quenching of the gear; fine-tuning of the heating sensor and the water spray ring in the horizontal direction to ensure that the gear is in the center of the coil; the heating sensor and the water spray ring are moved axially at a uniform speed along the gear, and the quenching speed is 440mm / min; when the outer diameter surface of the gear is induction quenched, the quenching machine drives the gear to rotate at 50r / min to ensure uniform heating and cooling of the gear; quenching and water spraying need to be carried out from bottom to top, the water pressure is 0.45MPa, and the water spraying time is consistent with the heating time of 32s; the current frequency f of the induction quenching equipment is 1500Hz, and the depth of the hardened layer d is 18:mm; the larger the part diameter D (unit: mm), the lower the selected frequency. The gear is a large-size part. After surface induction quenching, it is subjected to low-temperature tempering at 180℃ to eliminate internal stress. After tempering, the gear surface is fine-ground.

[0096] Comparative Example 4

[0097] A microalloyed high contact fatigue performance gear steel comprising the following components in percentage by mass:

[0098] C: 0.17%, Si: 0.25%, Mn: 0.73%, Cr: 1.66%, Mo: 0.30%, V: 0.15%; Ni: 1.61%, P: 0.01%, S: 0.032%, Al: 0.02%, [N]: 100ppm, [C+Mn / 4+Si / 2 / +(Cr+V) / 10]=0.66, Al / [N]: 2.00, the rest are Fe and unavoidable impurity elements.

[0099] The method for producing a microalloyed high contact fatigue performance gear using the microalloyed high contact fatigue performance gear steel of Comparative Example 4 includes the following process flow:

[0100] Electric arc furnace smelting → LF refining → RH vacuum treatment → round billet continuous casting → round billet forging → heating → rolling → heat treatment → processing → testing → packaging. The specific process conditions are as follows:

[0101] After sawing, the continuous casting billet is preheated at 1226℃, and the total preheating, heating and soaking time is controlled at 6.5h before round steel rolling. The starting rolling temperature is 1040℃, the final rolling temperature is 858℃, and after rolling, it is cooled to 635℃ on the cooling bed and then slowly cooled in the pit for 10h. The heat treatment is carried out at a temperature of 850℃ and a heating time of 4.5 hours for full austenitization. The fully austenitized gear is taken out of the furnace and cooled by water to ensure that the cooling rate of the blank gear is 6℃ / s. It is then tempered at 660℃ for 4.5 hours and then machined. No surface induction hardening is performed.

[0102] Comparative Example 5

[0103] A microalloyed high contact fatigue performance gear steel comprising the following components in percentage by mass:

[0104] C: 0.18%, Si: 0.25%, Mn: 0.75%, Cr: 1.78%, Mo: 0.34%, V: 0.19%; Ni: 1.68%, P: 0.01%, S: 0.033%, Al: 0.025%, [N]: 105ppm, [C+Mn / 4+Si / 2 / +(Cr+V) / 10]=0.69, Al / [N]: 2.38, the rest are Fe and unavoidable impurity elements.

[0105] The method for producing a microalloyed high contact fatigue performance gear using the microalloyed high contact fatigue performance gear steel of Comparative Example 5 includes the following process flow:

[0106] Electric arc furnace smelting → LF refining → RH vacuum treatment → round billet continuous casting → round billet forging → heating → rolling → heat treatment → processing → gear outer diameter surface induction quenching → testing → packaging. The specific process conditions are as follows:

[0107] After sawing, the continuous casting slab is preheated at 1217°C for a total of 6.5 hours, followed by a controlled soaking time. Round steel rolling begins at 1038°C and ends at 857°C. After rolling, it is cooled on a cooling bed to 633°C before being slow-cooled in a pit for 10 hours. Heat treatment is performed at 880°C for 4.5 hours to achieve full austenitization. The fully austenitized gear is removed from the furnace and water-cooled, maintaining a cooling rate of 2.5°C / s. It is then tempered at 660°C for 4.5 hours before being machined and induction hardened to produce the finished gear. Among them, induction quenching is specifically as follows: surface induction quenching of the gear; fine-tuning of the heating sensor and the water spray ring in the horizontal direction to ensure that the gear is in the center of the coil; the heating sensor and the water spray ring are moved axially at a uniform speed along the gear, and the quenching speed is 430mm / min; when the outer diameter surface of the gear is induction quenched, the quenching machine drives the gear to rotate at 60r / min to ensure uniform heating and cooling of the gear; quenching and water spraying need to be carried out from bottom to top, the water pressure is 0.45MPa, and the water spraying time is consistent with the heating time of 25s; the current frequency f of the induction quenching equipment is 2500Hz, and the depth of the hardened layer d is 18:mm; the larger the part diameter D (unit: mm), the lower the selected frequency. The gear is a large-size part. After surface induction quenching, it is subjected to low-temperature tempering at 180℃ to eliminate internal stress. After tempering, the gear surface is fine-ground.

[0108] Table 1 Chemical composition of the present invention (unit: [N] is ppm, the rest is %)

[0109] C Si Mn P S Cr Mo Ni Al V [N] Al / [N] formula Example 1 0.17 0.25 0.72 0.01 0.016 1.52 0.25 1.42 0.015 0.11 60 2.50 0.64 Example 2 0.17 0.25 0.73 0.01 0.025 1.66 0.30 1.61 0.020 0.15 100 2.00 0.66 Example 3 0.18 0.25 0.75 0.01 0.032 1.78 0.34 1.68 0.025 0.19 105 2.38 0.69 Comparative Example 1 <![CDATA[ 0.26 ]]> <![CDATA[ 0.42 ]]> 0.70 0.01 0.015 <![CDATA[ 1.2 ]]> 0.28 1.63 <![CDATA[ 0.034 ]]> <![CDATA[ 0.08 ]]> 95 3.58 <![CDATA[ 0.77 ]]> Comparative Example 2 0.18 0.26 0.72 0.01 0.015 <![CDATA[ 2.3 ]]> 0.27 1.61 <![CDATA[ 0.035 ]]> <![CDATA[ 0.24 ]]> 60 <![CDATA[ 5.83 ]]> <![CDATA[ 0.74 ]]> Comparative Example 3 0.17 0.34 0.78 0.01 0.025 1.7 0.25 1.42 0.015 0.11 60 2.50 <![CDATA[ 0.72 ]]> Comparative Example 4 0.17 0.25 0.73 0.01 0.032 1.66 0.30 1.61 0.020 0.15 100 2.00 0.66 Comparative Example 5 0.18 0.25 0.75 0.01 0.033 1.78 0.34 1.68 0.025 0.19 105 2.38 0.69

[0110] Table 2 Steel rolling production process parameters

[0111]

[0112]

[0113] Table 3 Heat treatment process of each embodiment and comparative example

[0114]

[0115] Table 4 Surface induction quenching process of each embodiment and comparative example

[0116]

[0117] The grain size and performance tests of the gears of various embodiments and comparative examples are shown in Tables 5 and 6.

[0118] Table 5 Grain size of the embodiment of the present invention

[0119]

[0120] Table 6 Contact fatigue rated fatigue life and median fatigue life

[0121] Sample number Contact stress / GPa L10 / cycle L50 / cycle Example 1 4.0 <![CDATA[8.12×10 7 ]]> <![CDATA[10.08×10 7 ]]> Example 2 4.0 <![CDATA[8.63×10 7 ]]> <![CDATA[10.64×10 7 ]]> Example 3 4.0 <![CDATA[8.65×10 7 ]]> <![CDATA[10.76×10 7 ]]> Comparative Example 1 4.0 <![CDATA[ 3.36×10 7 ]]> <![CDATA[ 5.20×10 7 ]]> Comparative Example 2 4.0 <![CDATA[ 3.48×10 7 ]]> <![CDATA[ 5.32×10 7 ]]> Comparative Example 3 4.0 <![CDATA[ 5.37×10 7 ]]> <![CDATA[ 7.37×10 7 ]]> Comparative Example 5 4.0 <![CDATA[ 3.75×10 7 ]]> <![CDATA[ 6.01×10 7 ]]>

[0122] The underlined data above are data that do not meet the requirements of the present invention.

[0123] It can be seen from Table 5 that after heat treatment, the gear steels described in Examples 1-3 of the present invention have a grain size of above 11.0, a grain size of 5.1-5.6 μm, and a grain size of 9.0-16.3 μm for the comparative example; the core grain size of the embodiments is above 9.5, a grain size of 12.7-14.2 μm, and the grain size of the comparative example is 8.0-8.5, a grain size of 17.2-20.4 μm.

[0124] Table 6 shows the contact fatigue comparison between the embodiment and the comparative example. Through optimization such as microalloying and induction hardening, the contact fatigue performance of the gear steel of the embodiment is improved by more than 50% compared with that of the comparative example. Under the condition of compressive stress of 4.0 GPa, the rated fatigue life L10≥8×10 7 , median fatigue life L50≥10×10 7 .

Claims

1. A microalloyed high contact fatigue performance gear, characterized in that: The microalloyed high contact fatigue performance gear steel comprises the following components in percentage by mass: C: 0.16-0.21%, Si: 0.20-0.37%, Mn: 0.50-0.80%, Cr: 1.5-1.8%, Mo: 0.25-0.35%, V: 0.10-0.20%; Ni: 1.4-1.7%, P≤0.010%, S: 0.015-0.035%, Al: 0.015-0.025%, [N]: 60-110ppm, the rest is Fe and unavoidable impurity elements; The composition of the microalloyed high contact fatigue performance gear steel meets the following conditions: 0.60≤[C+Mn / 4+Si / 2 / +(Cr+V) / 10]≤0.70; The production method of the micro-alloyed high contact fatigue performance gear includes the following process flow: electric arc furnace smelting → LF refining → RH vacuum treatment → round billet continuous casting → round billet forging → heating → rolling → heat treatment → machining → gear outer diameter surface induction quenching → testing → packaging; The heat treatment is specifically as follows: the rolled gear blank is charged into a furnace, heated at 870-900°C for 4-5 hours, cooled by water after being taken out of the furnace to ensure a cooling rate of 3-5°C / s, and then tempered at 650-680°C for 5-6 hours; The outer diameter surface of the gear is induction hardened. When the gear is surface induction hardened, the quenching speed is 400-450mm / min; the gear rotates at 40-60r / min; when the gear is surface induction hardened, quenching and water spraying must be carried out from bottom to top, the water pressure is 0.40-0.50MPa, and the water spraying time is consistent with the heating time; the heating time is 20-50s.

2. The microalloyed high contact fatigue performance gear according to claim 1, characterized in that: The composition of the microalloyed high contact fatigue performance gear steel meets the following conditions: Al / [N]: 2.0-4.

0.

3. A method for producing the microalloyed high contact fatigue performance gear according to claim 1 or 2, characterized in that: The production method includes the following process flow: electric arc furnace smelting → LF refining → RH vacuum treatment → round billet continuous casting → round billet forging → heating → rolling → heat treatment → machining → gear outer diameter surface induction quenching → testing → packaging; The heat treatment is specifically as follows: the rolled gear blank is charged into a furnace, heated at 870-900°C for 4-5 hours, cooled by water after being taken out of the furnace to ensure a cooling rate of 3-5°C / s, and then tempered at 650-680°C for 5-6 hours; The outer diameter surface of the gear is induction hardened. When the gear is surface induction hardened, the quenching speed is 400-450mm / min; the gear rotates at 40-60r / min; when the gear is surface induction hardened, quenching and water spraying must be carried out from bottom to top, the water pressure is 0.40-0.50MPa, and the water spraying time is consistent with the heating time; the heating time is 20-50s.

4. The production method according to claim 3, characterized in that In the heating, the soaking temperature of the steel billet in the heating furnace is controlled at 1200-1240° C., and the total time of preheating, heating and soaking is controlled at 5.0 h-8.0 h.

5. The production method according to claim 3, characterized in that The rolling process has a starting temperature of 1030-1050°C and a finishing temperature of 850-880°C.

6. The production method according to claim 3, characterized in that The current frequency of surface induction hardening is selected to be 1000-3000Hz; the depth of hardened layer is 15-20mm.

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