An ultrafine-grained, micro-deformed, high-hardness bainite wind turbine main shaft bearing material and manufacturing process

Abstract

The present invention discloses an ultrafine-grained, micro-deformation, high-hardness bainite-type wind turbine main shaft bearing material and manufacturing process, belonging to the field of metal material processing technology. The present invention appropriately increases the content of Mo and Si elements and adds an appropriate amount of AlN elements on the basis of traditional high-carbon chromium bearing steel, and uses a bainite austempering process to produce wind turbine main shaft bearing ring forgings, thereby obtaining a lower bainite structure with higher toughness and smaller deformation, which not only ensures the high hardness and high toughness of the ring forgings, but also significantly reduces deformation and improves dimensional accuracy. The original austenite grain size of the core of the produced ring forgings is not less than 10.5 grade, the hardness is 59-61HRC, the room temperature impact value is not less than 83J, the low-temperature impact value of -40℃ is not less than 33J, the single-sided machining allowance is not more than 0.52mm, and the deformation is not more than 0.18mm / m.

Description

Technical Field

[0001] The invention relates to an ultrafine-grained, slightly deformed, high-hardness bainite wind turbine main shaft bearing material and a manufacturing process thereof, belonging to the technical field of metal material processing. Background Art

[0002] Wind turbine main shaft bearings are core components of wind turbines, requiring high strength, toughness, hardness, wear resistance, and dimensional accuracy. With the rapid scaling of wind turbines, the size of wind turbine main shaft bearings has also gradually increased. In recent years, the diameter of wind turbine main shaft bearings has increased from less than 1 meter to 2 meters or more. This places higher demands on the toughness, hardness, deformation, and uniformity of the bearings and the ring forgings before machining. Traditional wind turbine main shaft bearings are made of quenched and tempered steel and case-hardened steel. Quenched and tempered steel bearings lack the hardness and wear resistance to meet the main shaft bearing requirements of high-power wind turbines over 8MW. Even lowering the tempering temperature still results in insufficient hardness and unreliable toughness. While case-hardened steel solves the problem of matching surface hardness and toughness, the long carburizing time and significant dimensional deformation of the workpiece make it unable to meet the dimensional accuracy requirements of large wind turbine main shaft bearings.

[0003] Wind turbine main shaft bearings are usually manufactured through processes such as roughing and drawing of blanks, punching and ring rolling, heat treatment, and machining. Therefore, the hot forming process and heat treatment process of forged ring rolling have an impact on the strength, toughness, hardness, wear resistance, and dimensional accuracy of the ring forgings. Compared with quenching to martensite, the deformation caused by phase transformation expansion and thermal stress during bainite transformation is significantly smaller, and the hardness is reduced very little. Therefore, bainite austempering, as a heat treatment process with high hardness, high toughness, and low deformation, has been applied to small-sized bearings. However, the insufficient degree of microstructure refinement and homogenization after ring forging ring rolling, the deformation anisotropy caused by metal streamlines, and the lack of austempering uniformity are key factors limiting the application of bainite austempering in the manufacture of main shaft bearings for high-power wind turbines above 8MW.

[0004] Therefore, there is an urgent need for a material suitable for ultrafine-grained, micro-deformation, high-hardness bainite wind turbine main shaft bearings and the corresponding forging, ring rolling and bainite isothermal quenching processes, which can significantly refine the austenite grains of the ring forgings after ring rolling and heat treatment, improve the strength, toughness and hardness, and reduce the deformation of the ring forgings. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide a manufacturing process for ring forgings for wind turbine main shaft bearings. Mo and Si are appropriately added to the traditional 100CrMnMo material to expand the bainite austempering process window, and appropriate amounts of Al and N are added to form a secondary phase for grain refinement. Hot rotary forging technology is introduced to refine the core structure, disrupt metal flow lines, and improve structural uniformity. The austempering process is controlled to produce ultrafine-grained, micro-deformed, and high-hardness ring forgings for wind turbine main shaft bearings.

[0006] At the same time, the present invention provides an ultrafine-grained, micro-deformation, high-hardness bainite wind turbine main shaft bearing material.

[0007] At the same time, the present invention provides an application of an ultrafine-grained, micro-deformed, high-hardness bainite wind turbine main shaft bearing material in a ring forging for a wind turbine main shaft bearing.

[0008] At the same time, the present invention provides a ring forging for a wind turbine main shaft bearing, which is used in the main shaft bearing of a high-power wind turbine generator set above 8MW.

[0009] At the same time, the present invention provides a main shaft bearing ring of a high-power wind turbine with a capacity of 8MW or above, which is prepared by the manufacturing process of the ring forging for the main shaft bearing of the wind turbine according to the present invention, and the main shaft bearing ring has a lower bainite structure.

[0010] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0011] The invention discloses an ultrafine-grained, micro-deformation, high-hardness bainite wind turbine main shaft bearing material, which has the following chemical composition, measured by mass percentage: C: 0.93% to 1.05%, Si: 0.40% to 0.60%, Mn: 0.80% to 1.10%, Cr: 1.80% to 2.05%, Mo: 0.50% to 0.60%, Al: 0.02% to 0.04%, N: 0.008% to 0.012%, and the balance being Fe and unavoidable impurities.

[0012] A ring forging for a wind turbine main shaft bearing made of ultrafine-grained, micro-deformed, high-hardness bainite wind turbine main shaft bearing material. The original austenite grain size at the center of the ring forging is not less than level 10.5, the hardness is 59-61HRC, the room temperature impact value is not less than 83J, the low-temperature impact value of -40℃ is not less than 33J, the single-sided machining allowance is not more than 0.52mm, and the deformation is not more than 0.18mm / m.

[0013] The manufacturing process of the ring forging for the fan main shaft bearing includes the following steps:

[0014] S01, heat the forging billet to 1150℃~1180℃ and keep it warm for 3~5h;

[0015] S02, the forging blank is upset and stretched, the starting forging temperature is 1120-1150°C, the final forging temperature is 860-930°C, the total forging ratio is not less than 6, and the forging blank is finally upset into a pancake-shaped forging blank with a thickness not exceeding 25 cm;

[0016] S03, reheat the forging billet to 1150℃~1180℃ and keep it at this temperature for 1~2h;

[0017] In step S04, the forging blank is drilled and expanded, and ring rolling begins. The expansion mandrel is conical and connected to the vertical rod. The mandrel rotates and moves downward with the vertical rod. As the expansion is completed, the vertical rod enters the center hole of the forging blank, and then ring rolling begins. The starting temperature of ring rolling is 1120℃ to 1150℃.

[0018] S05, the inner and outer walls of the ring are first rolled using traditional vertical rods, with a single-turn reduction of not less than 20% and a total reduction of not less than 60% to form a ring forging. The wall thickness of the ring forging is 120% to 150% of the wall thickness of the final forging product. The end temperature of the traditional vertical rod ring rolling is not less than 1050°C. Subsequently, a hot forging press is introduced into the inner and outer walls of the ring forging, and air is blown to control cooling, so that the ring forging is cooled to 900°C at a cooling rate of not less than 20°C / s, and hot forging of the inner and outer walls is started until the wall thickness of the finished product is reached and the inner and outer shapes are formed. The end temperature of hot forging is 800°C to 850°C;

[0019] S06: Place the ring forging horizontally. Blow air from 2-3 meters above and below the center of the ring forging to 680°C. Then place it horizontally in a heating furnace for spheroidizing annealing, securing it with stoppers. Raise the temperature to 790-810°C at a rate no greater than 20°C / h for spheroidizing annealing. Hold the temperature at that temperature for 4-6 hours. Then cool it to 690°C at a cooling rate no greater than 20°C / h. Hold the temperature at that temperature for 2-3 hours. Finally, cool it to 400°C at a cooling rate no greater than 20°C / h. Remove the ring forging and air cool it to room temperature.

[0020] In step S07, heat the ring forging to 850°C–870°C at a rate no greater than 20°C / h and hold at that temperature for 1–2 hours. Secure the ring forging with a stopper. Place the ring forging horizontally in a nitrate quenching tank for isothermal quenching. The nitrate temperature is 220–240°C, and the temperature is maintained at that temperature for 25–30 hours. Remove the ring forging and air cool to room temperature. Clean any remaining nitrate.

[0021] A manufacturing process for an ultrafine-grained, micro-deformed, high-hardness bainite wind turbine main shaft bearing material. In S05, the hot forging punch working surface is spherical, with a diameter no greater than the width of the inner and outer walls of the finished ring forging. The hot forging reduction is no less than 20%, the punch rotation speed is no less than 120 rpm, and the punch moves in steps along the width of the ring forging, with a step interval no less than the time required to complete one full rotation of the ring forging. The step distance is half the diameter of the contact surface between the hot forging punch and the workpiece.

[0022] A manufacturing process for an ultrafine-grained, micro-deformed, high-hardness bainite wind turbine main shaft bearing material. In S05, when machining a special-shaped step, additional hot forging rams can be added above and below the existing hot forging rams for the inner and outer walls as needed. The ram diameter is no greater than 50% of the width of the machining surface, the reduction per turn is no less than 15%, the ram speed is no less than 120 rpm, and the ram moves in steps along the diameter and vertical direction of the ring forging. The step interval is no less than the time required to complete one full rotation of the ring forging, and the step distance is half the diameter of the contact surface between the hot forging ram and the workpiece.

[0023] The structure of the hot forging ram is as follows: the hot forging circular ram is connected to the ring rolling machine by a transmission rod that can be extended and adjusted in angle. The hot forging ram rotates and moves with the transmission rod as the axis. The diameter of the hot forging ram is selected according to needs and is not larger than the size of the special-shaped step or channel. The hot forging ram is made of cemented carbide.

[0024] A manufacturing process for an ultrafine-grained, micro-deformed, high-hardness bainite wind turbine main shaft bearing material. In S07, the nitrate salt is composed of 50% potassium nitrate and 50% sodium nitrate. A stirring device is installed in the quenching tank to ensure the nitrate salt maintains a fluid and uniform temperature. The ring forging is suspended horizontally, allowing the nitrate salt to circulate from top to bottom.

[0025] A manufacturing process for an ultrafine-grained, micro-deformed, high-hardness bainite wind turbine main shaft bearing material is disclosed. The ring forgings are applicable to ring forgings with a diameter of 1m to 3m and may be free of special shapes, with internal special shapes, with external special shapes, or with internal and external special shapes.

[0026] A manufacturing process for an ultrafine-grained, micro-deformed, high-hardness bainite wind turbine main shaft bearing material. The ring forgings produced have a core original austenite grain size of no less than 10.5, a hardness of 59-61HRC, a room temperature impact value of no less than 83J, a low-temperature impact value of no less than 33J at -40°C, a single-sided machining allowance of no more than 0.52mm, and a deformation of no more than 0.18mm / m.

[0027] Application of an ultrafine-grained, micro-deformed, high-hardness bainite wind turbine main shaft bearing material in ring forgings for wind turbine main shaft bearings.

[0028] The ring forgings for wind turbine main shaft bearings obtained by the manufacturing process of the present invention are used in main shaft bearings of high-power wind turbine generator sets above 8MW.

[0029] A main shaft bearing ring of a high-power wind turbine generator set with a capacity of 8MW or more is prepared by the manufacturing process of the present invention. The main shaft bearing ring has a lower bainite structure.

[0030] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0031] (1) The bainite isothermal quenching process is used to produce the fan main shaft bearing ring forgings, obtaining a lower bainite structure with higher toughness and smaller phase transformation deformation, which not only ensures the high hardness and toughness of the ring forgings, but also significantly reduces deformation and improves dimensional accuracy. The present invention adopts an isothermal quenching process in which the ring forgings are placed horizontally in a salt bath and the nitrate salt is circulated vertically. The phase transformation temperature of the ring forgings is stable and uniform, further reducing the additional deformation caused by uneven temperature and uneven phase transformation, and achieving higher dimensional accuracy. When the ring forgings are air-cooled, air is blown from the center of the circle at the same time. The heating rate is limited during spheroidizing annealing, quenching heating and nitrate salt quenching, and a limit block is used to further reduce the possible dimensional deformation. During spheroidizing annealing cooling, the isothermal temperature is maintained at 690℃ for 2-3 hours, so that the size of the spherical cementite obtained is more uniform and the size of the ferrite grains is closer, improving the phase transformation uniformity during quenching heating and isothermal heating, thereby improving the uniformity of the organizational properties and reducing dimensional deformation.

[0032] (2) The forging heating temperature and deformation temperature are significantly reduced and controlled within a narrow range, which refines the austenite grains from the source. In the ring rolling process, hot forging is introduced. In addition to the normal flow of the ring metal toward the direction of expanding the diameter, the local metal in contact with the hot forging punch also produces flow along the direction of the punch rotation, which significantly increases the metal deformation and deformation penetration efficiency, breaks the ring forging structure, and makes the ring forging present ultrafine graining, providing a finer microstructure foundation for subsequent heat treatment processes. At the same time, the ring rolling temperature is further reduced to enter the two-phase region, and the newly generated carbides are fully broken by hot forging to achieve a fine dispersed distribution effect, improve toughness, and realize online spheroidizing annealing, significantly shortening the spheroidizing annealing time. In addition, hot forging also destroys the metal streamlines of the ring forging, making defects such as segregation uniformly distributed, avoiding structural anisotropy, and further reducing the deformation of bainite after austempering.

[0033] (3) By adding an appropriate amount of AlN to the material, its large-scale precipitation during hot forging is controlled, further hindering the growth of austenite grains during hot forging and subsequent spheroidizing annealing and quenching heating, and refining the austempering structure. Increasing the content of Mo and Si elements in the material expands the bainite transformation temperature range and the bainite isothermal transformation process window, making the bainite transformation more uniform and sufficient, reducing the content of retained austenite, and improving the dimensional stability of the ring forging.

[0034] The main principles of the present invention are as follows:

[0035] The forging blank is heated to 1150-1180°C and held for 3-5 hours before being upset and stretched. This prevents excessive heating temperatures from causing the austenite grains in the blank to fully grow before forging, which is beneficial for grain refinement. The initial forging temperature is 1120-1150°C, the final forging temperature is 860-930°C, and the total forging ratio is no less than 6. This is to fully heat and break up the as-cast structure of the forging blank and weld together internal defects. The final upset is a pancake-shaped forging blank with a thickness of no more than 25 cm, which facilitates the subsequent drilling, reaming, and ring rolling. It avoids problems such as excessive thickness, which makes drilling and reaming difficult, and the inability of the ring rolling rod to enter the center hole.

[0036] The integrated drilling, reaming, and ring rolling process significantly shortens forming time. After ring rolling, hot rotary forging is used, resulting in low deformation temperature and excellent deformation penetration. This fully refines the core structure of the ring forging, breaks down carbides formed during deformation in the two-phase region, disrupts metal flow lines, improves the uniformity of defects such as segregation, and avoids uneven deformation during austempering. By adding multiple sets of hot rotary forging rams, the shape and size of the internal and external profiles of the ring forging can be independently and precisely controlled, improving dimensional accuracy and reducing subsequent machining allowances.

[0037] During the hot forging process, in order to ensure that all positions of the ring forging can be fully deformed during the ring rolling process, the hot forging ram adopts step-by-step displacement, that is, it is ensured that the hot forging is completed at least one circle of the ring forging before stepping and the displacement is half of the diameter of the contact surface between the hot forging ram and the workpiece, ensuring that the hot forging deformation can cover each position of the workpiece twice, so that the deformation is uniform, and the surface quality and surface dimensional accuracy are uniform.

[0038] The end temperature of traditional vertical rod ring rolling is above 1050℃, at which point aluminum nitride precipitation begins. Replacing the hot forging head and cooling with air blowing to 900℃ inhibits aluminum nitride precipitation in this temperature range to form a large second phase. Instead, it induces aluminum nitride to precipitate below 900℃ to form a finer and more dispersed second phase. This improves the resistance to austenite grain boundary migration during spheroidizing annealing and quenching, further refining the austenite grains.

[0039] Because hot rotary forging produces greater deformation and better deformation penetration, and the deformation temperature is lower than the material's Acm temperature, carbides formed during deformation are fully broken down, improving material toughness and increasing the number of carbide nucleation sites. This allows ring forgings to be directly placed in a heating furnace for spheroidizing annealing, rather than cooling to room temperature to form lamellar pearlite before spheroidizing annealing. This reduces the traditional spheroidizing annealing time from approximately 20 hours to 4-6 hours, significantly shortening the spheroidizing annealing process cycle and energy consumption. After the ring rolling is completed, the ring forging is air-cooled to 680℃ to inhibit the continued precipitation of carbides, and then spheroidized annealing temperature is 790℃~810℃, isothermal for 4-6h, and then cooled to 690℃ at a cooling rate of no more than 20℃ / h, isothermal for 2-3h, with the broken carbides as the core, precipitated to form granular carbides, and then cooled to 400℃ at a cooling rate of no more than 20℃ / h. After being taken out, it is air-cooled to room temperature to avoid the formation of lamellar pearlite in the untransformed structure, completing the spheroidizing annealing.

[0040] The bainite isothermal quenching heating temperature is 850℃~870℃, and the temperature is kept for 1~2h. After that, it is placed horizontally in a nitrate quenching tank for isothermal quenching. The nitrate temperature is 220-240℃ and the temperature is kept at this temperature for 25-30h. The ring forging is partially austenitized in the two-phase region, and the C element content entering the austenite is controlled to obtain a lower bainite structure with better performance, high hardness, high toughness and low deformation. At the same time, fine carbides are retained to improve the hardness and wear resistance of the bearing. The material of the present invention expands the temperature range of bainite transformation, especially lower bainite transformation, by increasing the Mo and Si content, so that the ring forging is fully transformed into lower bainite without producing harmful structures such as upper bainite. By circulating nitrate and long-term temperature balancing, the austenite is transformed into lower bainite as much as possible, and it will not be retained in the bearing and cause deformation.

[0041] The ring forgings applicable to the present invention have diameters ranging from 1m to 3m and may be non-shaped, internally shaped, externally shaped, or both. Smaller ring forgings can be adequately quenched using conventional martensitic quenching processes, and the present invention does not significantly improve performance. Larger ring forgings are limited by equipment capacity, and forging heating and thermal deformation temperatures cannot be controlled to the lower temperature range required by the present invention. Upsetting and drawing may require multiple reheating cycles, which cannot guarantee microstructure refinement. Furthermore, larger ring forgings experience greater deformation after austempering, which cannot be controlled to the range required by the present invention.

[0042] This invention utilizes a bainite austempering process to produce fan main shaft bearing ring forgings by appropriately increasing the Mo and Si content and adding an appropriate amount of AlN based on traditional high-carbon chromium bearing steel. This process results in a lower bainite structure with enhanced toughness and reduced deformation. This ensures the ring forgings' high hardness and toughness while significantly reducing deformation and improving dimensional accuracy. The resulting ring forgings have a core austenite grain size of no less than 10.5, a hardness of 59-61 HRC, an impact strength of no less than 83J at room temperature and no less than 33J at -40°C, a single-side machining allowance of no more than 0.52mm, and a deformation of no more than 0.18mm / m. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 The phase transition law calculated for the material in Example 1;

[0044] Figure 2 The AlN solid solution precipitation law calculated for the material in Example 1;

[0045] Figure 3 TTT curve calculated for the material of Example 1;

[0046] Figure 4 This is the original austenite grain morphology of the spindle bearing core in Example 1;

[0047] Figure 5 This is the lower bainite structure and a small amount of white retained austenite in the core of the spindle bearing of Example 1. DETAILED DESCRIPTION

[0048] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention is further described in detail below with reference to the accompanying drawings, comparative examples and embodiments. The specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0049] Example 1

[0050] A manufacturing process for an ultrafine-grained, micro-deformed, high-hardness bainite wind turbine main shaft bearing material is disclosed. Specifically, a ring forging for a wind turbine main shaft bearing with internal and external special shapes is manufactured, with a final size requirement of Φ2100*Φ1840*193 mm (wherein Φ2100 is the outer diameter of the ring forging, Φ1840 is the inner diameter of the ring forging, and 193 mm is the height of the ring forging, i.e., the height of the cross section, perpendicular to the wall thickness). The material used has the following chemical composition, calculated by mass percentage: C: 1.0%, Si: 0.5%, Mn: 1.0%, Cr: 1.95%, Mo: 0.55%, Al: 0.02%, N: 0.01%, and the balance being Fe and unavoidable impurities.

[0051] The forging blank is first heated to 1160℃ and held for 3.5 hours. After being taken out, it is upsetting and drawing at 1130℃, with a total forging ratio of upsetting and drawing of 7. The final forging temperature is 900℃. Finally, it is upset into a pancake-shaped forging blank with a thickness of about 20cm.

[0052] The forging blank is reheated to 1160°C and held for 1 hour before drilling. After completion, it moves to the hole-reaming and ring-rolling station. The reaming mandrel is conical and connected to the vertical rod. The mandrel rotates and moves downward with the vertical rod, completing the hole-reaming process simultaneously with the punching process, allowing the vertical rod to enter the center hole of the forging blank. Ring rolling then begins. The starting temperature for ring rolling is approximately 1130°C.

[0053] The inner and outer ring walls are first rolled using traditional vertical rods, with a single turn reduction of 25% and a total reduction of 65%. This results in a ring forging with a wall thickness of approximately 130% of the final forging wall thickness (approximately 260mm). The final temperature of traditional vertical rod rolling is 1070°C. Hot forging rams are then introduced to the inner and outer ring walls, while controlled cooling is achieved by blowing air. The ring forging is cooled to 900°C at a cooling rate of 25°C / s. Hot forging of the inner and outer walls then begins until the final wall thickness is achieved and the inner and outer profiles are formed. The final temperature of the hot forging is 820°C.

[0054] The hot forging ram's working surface is spherical, with a diameter no larger than the width of the finished ring forging's inner and outer walls. The hot forging reduction is 20%, the ram's rotation speed is 120 rpm, and the ram moves in steps across the ring forging's width. The step interval is no less than the time required to complete one full rotation of the ring forging, and the step distance is half the diameter of the contact surface between the hot forging ram and the workpiece.

[0055] When machining irregularly shaped steps in this embodiment, additional hot forging rams can be added above and below the existing hot forging rams for the inner and outer walls as needed. The ram diameter is 50% of the machining surface width, the single-turn reduction is 15%, the ram speed is 120 rpm, and the ram moves in steps along the diameter and vertical directions of the ring forging. The step interval is no less than the time required to complete one full rotation of the ring forging, and the step distance is half the diameter of the contact surface between the hot forging ram and the workpiece.

[0056] The ring forging was placed horizontally. Air was blown from 2 meters above and below the center of the ring forging to 680°C. The forging was then placed horizontally in a heating furnace for spheroidizing annealing, secured with stoppers. The temperature was raised to 800°C at a rate of 15°C / h for spheroidizing annealing. The forging was then isothermaled for 5 hours. The forging was then cooled to 690°C at a rate of 15°C / h, isothermaled for 2.5 hours, and finally cooled to 400°C at a rate of 10°C / h. After removal, the forging was air-cooled to room temperature.

[0057] The ring forgings were heated to 860°C at a rate of 15°C / h, held at that temperature for 1 hour, and then placed horizontally in a nitrate quenching tank for austempering. Support blocks were placed in the nitrate to secure the ring forgings. The nitrate was heated to 230°C and held at that temperature for 26 hours. After removal, the ring forgings were air-cooled to room temperature and the attached nitrate was cleaned.

[0058] The nitrate salt is made of 50% potassium nitrate and 50% sodium nitrate. A stirring device is installed in the quenching tank to ensure that the nitrate salt is in a fluid and uniform temperature state. The ring forging is placed horizontally in the air, and the nitrate salt circulates from top to bottom.

[0059] This embodiment obtains an ultrafine-grained, slightly deformed, high-hardness bainite wind turbine main shaft bearing material.

[0060] The ultrafine-grained, slightly deformed, high-hardness bainite wind turbine main shaft bearing material obtained in this embodiment is used in ring forgings for wind turbine main shaft bearings.

[0061] The ring forgings for wind turbine main shaft bearings obtained by the manufacturing process of this embodiment are used in main shaft bearings of high-power wind turbines above 8MW.

[0062] A main shaft bearing ring of a high-power wind turbine generator set with a capacity of 8 MW or more is prepared by the manufacturing process of this embodiment. The main shaft bearing ring has a lower bainite structure.

[0063] The material phase transformation law, AlN solid solution precipitation law and TTT curve of this embodiment are shown in Figures 1 to 3 .from Figure 1 It can be seen that the A1 temperature is about 750℃ and the Acm temperature is about 900℃. For hypereutectoid bearing steel, the quenching heating temperature should be between A1 and Acm to ensure that the remaining undissolved carbides increase wear resistance. Figure 2 It can be seen that the AlN precipitation temperature range is about 1100℃~780℃, among which the AlN precipitated at high temperature tends to grow, significantly reducing the effect of refining austenite grains. Therefore, hot forging dies are introduced into the inner and outer walls of the ring forging, and air is blown to control cooling, so that the ring forging is cooled to 900℃ at a cooling rate of 25℃ / s, forming finer and more dispersed AlN, improving the inhibitory effect on austenite grain boundary migration during spheroidizing annealing and quenching heating, and further refining the austenite grains. Figure 3 It can be seen that the transformation temperature range of lower bainite is about 210-300℃. In order to obtain finer bainite and less retained austenite, the austempering temperature is selected to be 230℃. Figure 3 It can also be seen that the bainite transformation starts at 230℃ no earlier than 3h, and the transformation completion time is significantly longer, so the temperature is kept at 26h.

[0064] The original austenite grain morphology and microstructure morphology of the core of the ring forging are as follows: Figure 4 、 Figure 5 As shown, Figure 4 As shown in Figure 2, the austenite grains are very fine and uniform. Figure 5 As shown in the figure, a very small amount of white retained austenite is visible on the bainite matrix. The austenite grain size, hardness, impact resistance, single-side machining allowance and deformation are shown in Table 1.

[0065] Example 2

[0066] A manufacturing process for an ultrafine-grained, micro-deformed, high-hardness bainite wind turbine main shaft bearing material is disclosed. Specifically, a ring forging for a wind turbine main shaft bearing having a final size requirement of Φ1200*Φ1000*85 mm is manufactured. The material used has the following chemical composition, calculated by mass percentage: C: 0.93%, Si: 0.4%, Mn: 0.8%, Cr: 1.8%, Mo: 0.50%, Al: 0.04%, N: 0.008%, and the balance being Fe and unavoidable impurities.

[0067] The forging blank is first heated to 1150℃ and kept at this temperature for 3 hours. After being taken out, it is upsetting and drawing at 1120℃. The total forging ratio of upsetting and drawing is 6, and the final forging temperature is 860℃. Finally, it is upset into a pancake-shaped forging blank with a thickness of about 6cm.

[0068] The forging blank is reheated to 1150°C and held for 2 hours before drilling. The process then moves to the hole-reaming and ring-rolling station. The cone-shaped reaming mandrel, connected to the vertical rod, rotates and moves downward with the vertical rod. This simultaneously expands the hole and allows the vertical rod to enter the center hole of the forging blank. Ring rolling then begins. The starting temperature for ring rolling is approximately 1120°C.

[0069] The inner and outer ring walls are first rolled using traditional vertical rods, with a single turn reduction of 20% and a total reduction of 60%. This results in a ring forging with a wall thickness of approximately 120% of the final forged wall thickness. The final temperature for traditional vertical rod rolling is 1050°C. Hot forging rams are then introduced to the inner and outer ring walls, while controlled cooling is achieved by blowing air. The ring forging is cooled to 900°C at a cooling rate of 20°C / s. Hot forging of the inner and outer walls then begins until the final wall thickness is achieved. The final temperature for hot forging is 800°C.

[0070] The hot forging ram's working surface is spherical, with a diameter no larger than the width of the finished ring forging's inner and outer walls. The hot forging reduction is 25%, the ram's rotation speed is 150 rpm, and the ram moves in steps across the ring forging's width. The step interval is no less than the time required to complete one full rotation of the ring forging, and the step distance is half the diameter of the contact surface between the hot forging ram and the workpiece.

[0071] The ring forging is placed horizontally. Air is blown from 3 meters above and below the center of the ring forging to 680°C. The forging is then placed horizontally in a heating furnace for spheroidizing annealing, secured with stoppers. The temperature is raised to 790°C at a rate of 20°C / hour for spheroidizing annealing. The forging is then isothermal for 4 hours. The forging is then cooled to 690°C at a rate of 20°C / hour, isothermal for 2 hours, and finally cooled to 400°C at a rate of 20°C / hour. After removal, the forging is air-cooled to room temperature.

[0072] The ring forgings are heated to 850°C at a rate of 20°C / h, held at that temperature for 2 hours, and then placed horizontally in a nitrate quenching tank for austempering. Support blocks are provided to secure the ring forgings in the nitrate, which is at 220°C for 25 hours. After removal, they are air-cooled to room temperature and cleaned of any attached nitrate.

[0073] The nitrate salt is made of 50% potassium nitrate and 50% sodium nitrate. A stirring device is installed in the quenching tank to ensure that the nitrate salt is in a fluid and uniform temperature state. The ring forging is placed horizontally in the air, and the nitrate salt circulates from top to bottom.

[0074] This embodiment obtains an ultrafine-grained, slightly deformed, high-hardness bainite wind turbine main shaft bearing material.

[0075] The ultrafine-grained, slightly deformed, high-hardness bainite wind turbine main shaft bearing material obtained in this embodiment is used in ring forgings for wind turbine main shaft bearings.

[0076] The ring forgings for wind turbine main shaft bearings obtained by the manufacturing process of this embodiment are used in main shaft bearings of high-power wind turbines above 8MW.

[0077] A main shaft bearing ring of a high-power wind turbine generator set with a capacity of 8 MW or more is prepared by the manufacturing process of this embodiment. The main shaft bearing ring has a lower bainite structure.

[0078] Example 3

[0079] A manufacturing process for an ultrafine-grained, micro-deformed, high-hardness bainite wind turbine main shaft bearing material is disclosed. Specifically, a ring forging for a wind turbine main shaft bearing having a final size requirement of Φ3000*Φ2640*350 mm is manufactured. The material used has the following chemical composition, calculated by mass percentage: C: 1.05%, Si: 0.6%, Mn: 1.10%, Cr: 2.05%, Mo: 0.60%, Al: 0.03%, N: 0.012%, and the balance being Fe and unavoidable impurities.

[0080] The forging blank is first heated to 1180°C and held for 5 hours. After being taken out, it is upsetting and drawing at 1150°C. The total forging ratio of upsetting and drawing is 7, and the final forging temperature is 930°C. Finally, it is upset into a pancake-shaped forging blank with a thickness of about 24 cm.

[0081] The forging blank is reheated to 1180°C and held for 1.5 hours before drilling. The blank is then moved to the hole-reaming and ring-rolling station. The reaming mandrel is conical and connected to the vertical rod. The mandrel rotates and moves downward with the vertical rod, completing the hole-reaming process while simultaneously punching and allowing the vertical rod to enter the center hole of the forging blank. Ring rolling then begins. The starting temperature for ring rolling is approximately 1150°C.

[0082] The inner and outer ring walls are first rolled using traditional vertical rods, with a single turn reduction of 25% and a total reduction of 70%. This results in a ring forging with a wall thickness approximately 150% of the final forged wall thickness. The final temperature for traditional vertical rod rolling is 1080°C. Hot forging rams are then introduced to the inner and outer ring walls, while controlled cooling is achieved by blowing air. The ring forging is cooled to 900°C at a cooling rate of 30°C / s. Hot forging of the inner and outer walls then begins until the final wall thickness is achieved. The final temperature for hot forging is 850°C.

[0083] The hot forging ram's working surface is spherical, with a diameter no larger than the width of the finished ring forging's inner and outer walls. The hot forging reduction is 25%, the ram's rotation speed is 140 rpm, and the ram moves in steps across the ring forging's width. The step interval is no less than the time required to complete one full rotation of the ring forging, and the step distance is half the diameter of the contact surface between the hot forging ram and the workpiece.

[0084] The ring forging was placed horizontally. Air was blown to 680°C from 2.5m above and below the center of the ring forging. The ring forging was then placed horizontally in a heating furnace for spheroidizing annealing, secured with stoppers. The temperature was raised to 810°C at a rate of 20°C / h for spheroidizing annealing. The temperature was then isothermal for 6 hours. The ring forging was then cooled to 690°C at a rate of 10°C / h, isothermal for 3 hours, and finally cooled to 400°C at a rate of 15°C / h. After removal, the ring forging was air-cooled to room temperature.

[0085] The ring forgings were heated to 870°C at a rate of 15°C / h, held at that temperature for 1.5 hours, and then placed horizontally in a nitrate quenching tank for austempering. The nitrate was infused with support blocks to secure the ring forgings. The nitrate was heated to 240°C and held at that temperature for 30 hours. After removal, the ring forgings were air-cooled to room temperature and the attached nitrate was cleaned.

[0086] The nitrate salt is made of 50% potassium nitrate and 50% sodium nitrate. A stirring device is installed in the quenching tank to ensure that the nitrate salt is in a fluid and uniform temperature state. The ring forging is placed horizontally in the air, and the nitrate salt circulates from top to bottom.

[0087] This embodiment obtains an ultrafine-grained, slightly deformed, high-hardness bainite wind turbine main shaft bearing material.

[0088] The ultrafine-grained, slightly deformed, high-hardness bainite wind turbine main shaft bearing material obtained in this embodiment is used in ring forgings for wind turbine main shaft bearings.

[0089] The ring forgings for wind turbine main shaft bearings obtained by the manufacturing process of this embodiment are used in main shaft bearings of high-power wind turbines above 8MW.

[0090] A main shaft bearing ring of a high-power wind turbine generator set with a capacity of 8 MW or more is prepared by the manufacturing process of this embodiment. The main shaft bearing ring has a lower bainite structure.

[0091] Example 4

[0092] The difference between this embodiment and embodiment 1 is that:

[0093] The ring forging was placed horizontally. Air was blown from 2 meters above and below the center of the ring forging to 680°C. The forging was then placed horizontally in a heating furnace for spheroidizing annealing, secured with stoppers. The temperature was raised to 800°C at a rate of 15°C / h for spheroidizing annealing. The forging was then isothermaled for 4.5 hours. The forging was then cooled to 690°C at a rate of 20°C / h, isothermaled for 3 hours, and finally cooled to 400°C at a rate of 15°C / h. After removal, the forging was air-cooled to room temperature.

[0094] Comparative Example 1

[0095] The final workpiece dimensions, material, and heating schedule were the same as those in Example 1. This comparative example differed from Example 1 only in that the workpiece was heated to 800°C at a rate of 15°C / h for spheroidizing annealing, held isothermal for 5 hours, then cooled to 700°C at a cooling rate of 15°C / h, held isothermal for 18 hours, and finally cooled to 400°C at a cooling rate of 25°C / h. After removal, the workpiece was air-cooled to room temperature. The original austenite grain size, hardness, impact resistance, single-side machining allowance, and deformation of the ring forging core are shown in Table 1.

[0096] Comparative Example 2

[0097] The final workpiece dimensions, material, and heating schedule were the same as those in Example 1. The only difference between this comparative example and Example 1 was that the ring forgings were heated to 860°C at a rate of 15°C / h, held at that temperature for 1 hour, then placed horizontally in a quenching tank. After cooling to 150°C, they were removed and tempered in a 200°C furnace for 7 hours. After removal, they were air-cooled to room temperature. The original austenite grain size, hardness, impact resistance, single-side machining allowance, and deformation of the ring forgings are shown in Table 1.

[0098] Comparative Example 3

[0099] The final workpiece dimensions, material, and heating schedule were the same as in Example 1. The only difference between this comparative example and Example 1 was that the ring forgings were heated to 860°C at a rate of 15°C / h, held at that temperature for 1 hour, and then placed horizontally in a nitrate quenching tank for austempering. The nitrate was held at 200°C for 35 hours with support blocks. After removal, the ring forgings were air-cooled to room temperature and cleaned of any adhering nitrate. The original austenite grain size, hardness, impact resistance, single-sided machining allowance, and deformation of the ring forgings are shown in Table 1.

[0100] Comparative Example 4

[0101] The final workpiece dimensions, material, and heating schedule were the same as in Example 1. The only difference between this comparative example and Example 1 was that the ring forgings were heated to 860°C at a rate of 15°C / h, held at that temperature for 1 hour, and then placed horizontally in a nitrate quenching tank for austempering. The nitrate was held at 250°C for 23 hours with support blocks. After removal, the ring forgings were air-cooled to room temperature and cleaned of any adhering nitrate. The original austenite grain size, hardness, impact resistance, single-sided machining allowance, and deformation of the ring forgings are shown in Table 1.

[0102] Comparative Example 5

[0103] The final workpiece dimensions and hot working procedures were the same as in Example 1, differing only in the material. The chemical composition of the materials used, expressed in mass percentage, is as follows: C: 1.0%, Si: 0.25%, Mn: 1.0%, Cr: 1.95%, Mo: 0.15%, with the remainder being Fe and unavoidable impurities; no Al, N, or other elements were added. The original austenite grain size, hardness, impact resistance, single-side machining allowance, and deformation of the ring forging core are shown in Table 1.

[0104] Table 1 Grain size, hardness, impact resistance, machining allowance and deformation of ring forgings

[0105]

[0106] Note: The austenite grain size refers to the national standard GB / T 6394-2017 "Method for determination of average grain size of metals".

[0107] The impact energy refers to the national standard GB / T 229-2020 "Charpy Pendulum Impact Test Method for Metallic Materials".

[0108] It should be understood that in order to streamline the present disclosure and aid understanding of one or more of the various inventive aspects, in the above description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together into a single embodiment, figure, or description thereof. However, this disclosed method should not be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as reflected in the claims, inventive aspects lie in less than all of the features of the previously disclosed embodiments. Accordingly, the claims that follow the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of the invention.

[0109] Although the present invention has been described with respect to a limited number of embodiments, it will be apparent to those skilled in the art, having benefit of the foregoing description, that other embodiments are contemplated within the scope of the invention thus described. Furthermore, it should be noted that the language used in this specification has been selected primarily for readability and didactic purposes, rather than for the purpose of explaining or limiting the subject matter of the present invention. Consequently, many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims. The disclosure of the present invention is intended to be illustrative rather than restrictive of the scope of the invention, which is defined by the appended claims.

[0110] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A ring forging for a fan main shaft bearing, characterized in that: The chemical composition, in mass percentage, is as follows: C: 0.93%~1.05%, Si: 0.40%~0.60%, Mn: 0.80%~1.10%, Cr: 1.80%~2.05%, Mo: 0.50%~0.60%, Al: 0.02%~0.04%, N: 0.008%~0.012%, and the balance is Fe and unavoidable impurities; The original austenite grain size of the ring forging core shall not be less than grade 10.5, the hardness shall be 59-61HRC, the room temperature impact value shall not be less than 83J, the low temperature impact value at -40℃ shall not be less than 33J, the single-sided machining allowance shall not exceed 0.52mm, and the deformation shall not exceed 0.18mm / m.

2. The manufacturing process of the ring forging for the fan main shaft bearing according to claim 1 is characterized in that: The following steps are involved: S01, heat the forging billet to 1150℃~1180℃ and keep it warm for 3~5h; S02, the forging blank is upset and stretched, the starting forging temperature is 1120~1150℃, the final forging temperature is 860~930℃, the total forging ratio is not less than 6, and the forging blank is finally upset into a pancake-shaped forging blank with a thickness not exceeding 25cm; S03, reheat the forging billet to 1150℃~1180℃ and keep it warm for 1~2h; S04, drilling and expanding the forging blank and starting ring rolling, the ring rolling starting temperature is 1120℃~1150℃; S05: The inner and outer walls of the ring are first rolled using traditional vertical rods, with a single-turn reduction of no less than 20% and a total reduction of no less than 60%, to form a ring forging. The wall thickness of the ring forging is 120%-150% of the final wall thickness of the forged product. The final temperature of the traditional vertical rod ring rolling is no less than 1050°C. Subsequently, a hot forging ram is introduced into the inner and outer walls of the ring forging, and air is blown to control cooling, so that the ring forging is cooled to 900°C at a cooling rate of no less than 20°C / s. The inner and outer walls are then hot forged until the wall thickness reaches the final product and the inner and outer shapes are formed. The final temperature of the hot forging is 800°C-850°C. S06: Place the ring forging horizontally, blow air from 2-3m above and below the center of the ring forging to 680°C, then place it horizontally in a heating furnace for spheroidizing annealing. Use a stopper to fix the ring forging. Raise the temperature to 790-810°C at a rate of no more than 20°C / h for spheroidizing annealing. Hold the temperature at this temperature for 4-6 hours. Then cool it to 690°C at a cooling rate of no more than 20°C / h. Hold the temperature at this temperature for 2-3 hours. Finally, cool it to 400°C at a cooling rate of no more than 20°C / h. Remove the ring forging and air cool it to room temperature. S07, the ring forging is heated to 850-870°C at a rate of no more than 20°C / h, kept warm for 1-2h, fixed with a limit block, and then placed horizontally in a nitrate quenching tank for isothermal quenching. The nitrate has a support limit block to fix the ring forging, the nitrate temperature is 220-240°C, and the temperature is kept warm for 25-30h; after being taken out, it is air-cooled to room temperature and the attached nitrate is cleaned to obtain the product.

3. The manufacturing process according to claim 2, characterized in that In S05, the working surface of the hot forging ram is spherical, and the diameter of the spherical working surface is not greater than the width of the inner and outer walls of the finished ring forging; the hot forging reduction is not less than 20%, the ram rotation speed is not less than 120 rpm, the ram is stepped along the width direction of the ring forging, the step interval is not less than the time required for the ring forging to roll one circle, and the step distance is half the diameter of the contact surface between the hot forging ram and the workpiece.

4. The manufacturing process according to claim 2, characterized in that In S07, the nitrate salt used is 50% potassium nitrate + 50% sodium nitrate. A stirring device is provided in the quenching tank to ensure that the nitrate salt is in a flowing and uniform temperature state. The ring forging is placed horizontally in the air, and the nitrate salt circulates from top to bottom.

5. The manufacturing process according to claim 2, characterized in that: The diameter of ring forgings is 1m~3m.

6. The manufacturing process according to claim 2, characterized in that: In S04, the hole expansion core mold is conical and connected to the vertical rod. The hole expansion core mold rotates and moves downward with the vertical rod. While completing the hole expansion, the vertical rod enters the center hole of the forging blank and then starts ring rolling.

7. Use of the ring forging for wind turbine main shaft bearing obtained by the manufacturing process according to any one of claims 2 to 6 in the main shaft bearing of a high-power wind turbine set above 8 MW.

8. A main shaft bearing ring for a high-power wind turbine with a capacity of 8 MW or above, produced by the manufacturing process according to any one of claims 2 to 6, wherein the main shaft bearing ring has a lower bainite structure.

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