A forging method for improving the sensitivity of forging cracks of difficult-to-deform superalloys

Abstract

This invention relates to the field of high-temperature alloy hot working technology, specifically to a forging method that improves the forging crack sensitivity of difficult-to-deform high-temperature alloys. The method includes multi-stage treatment before, during, and after forging to achieve crack prevention: Before forging, the two ends of the steel ingot are wrapped with insulating cotton, and a three-stage stepped heating and heat preservation process is used; during forging, a four-sided and eight-sided elongation process combined with trapezoidal hammer forging is employed, with a single deformation amount of 9%–15%. The ingot is reheated in the furnace when the temperature approaches the final forging temperature, ensuring that the deformation amount of the final forging is ≥35%; after forging, slow cooling is achieved using a combination of air cooling, furnace cooling, or hood cooling, depending on the temperature range characteristics of the alloy phases. This invention can effectively reduce shear deformation stress, avoid excessively high local temperatures caused by deformation superposition, reduce the incidence of abnormal microstructure induced by local deformation, improve the uniformity of forging deformation, significantly reduce the risk of cracking, optimize the microstructure and properties of forgings, and meet aerospace requirements.

Description

Technical Field

[0001] This invention relates to the field of high-temperature alloy hot working technology, and specifically to a forging method for improving the forging crack sensitivity of difficult-to-deform high-temperature alloys. Background Technology

[0002] In modern aerospace, energy, and other high-end manufacturing fields, difficult-to-deform nickel-based superalloys (such as GH3536, GH4151, GH4169, GH4175, GH4975, and GH4738) have become core materials for manufacturing critical hot-end components due to their excellent high-temperature strength, oxidation resistance, and hot corrosion resistance. Their forging quality directly determines the service performance and safe lifespan of these high-end equipment. As high-end equipment upgrades towards "high parameters and long lifespan," the industry's demand for difficult-to-deform superalloy forgings has shifted from "formability" to "high-quality formability." Specific requirements include: near-zero forging cracks (to avoid sudden failures during component service), high microstructure uniformity (to ensure consistent high-temperature performance), and suitability for industrialized mass production (balancing efficiency and cost control). This places higher technical demands on existing forging processes.

[0003] The current mainstream technical solution in the field of free forging of difficult-to-deform high-temperature alloys is the "traditional flat anvil continuous forging process". This solution relies on conventional high-speed forging equipment and the supporting processes include: using a single-stage or two-stage or more heating mode before forging, so that the steel ingot finally reaches the forging temperature; during the forging stage, flat anvil hammers with rectangular cross sections are mostly used, and a unidirectional forging method of "continuously hammering from one end of the forging to the other end" is generally adopted, without special end heat preservation measures; after forging, single air cooling, furnace cooling or water cooling are selected. Some solutions will be supplemented with traditional processes such as cladding forging and alternating forging of four and eight directions to improve the local forming effect.

[0004] However, long-term use has revealed that the traditional flat-anvil continuous forging process has significant technical shortcomings for difficult-to-deform high-temperature alloys, for example: 1. High risk of cracking The flat anvil hammer head is in full contact with the forging. The external force applied by the flat anvil hammer head to the forging is very obvious in the vertical shear force during the forging process. Moreover, continuous forging is very easy to cause stress superposition. The high temperature alloy that is difficult to deform itself has extremely high deformation resistance and is very easy to generate shear tensile stress cracks. 2. Poor tissue uniformity Conventional forging methods lack end-heat preservation, resulting in rapid temperature drop at the ends and a high likelihood of forging cracks forming at the ends. Furthermore, continuous forging, due to the stroke length, easily leads to significant temperature differences between the starting and ending forging points, causing uneven microstructure and affecting performance. Thirdly, continuous forging can easily cause localized overheating between adjacent forging sections, resulting in a significant increase in grain size at the forging section and inducing microstructural abnormalities (such as abnormal grain growth and precipitation of harmful phases), affecting subsequent performance. Therefore, how to solve the crack sensitivity and microstructure uniformity issues in the forging of difficult-to-deform high-temperature alloys in order to meet the production needs of high-end components made of difficult-to-deform high-temperature alloys has become a core technical challenge that urgently needs to be overcome in this field. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a method to improve the crack sensitivity of forging difficult-to-deform high-temperature alloys. This method includes multi-stage treatment before, during, and after forging to achieve crack prevention and control. It can effectively reduce shear deformation stress, avoid excessively high local temperatures caused by deformation superposition, reduce the incidence of abnormal microstructure induced by local deformation, improve the deformation uniformity of forgings, significantly reduce the risk of cracking, optimize the microstructure and properties of forgings, and meet the needs of aerospace.

[0006] The objective of this invention is achieved through the following approach: A forging method for improving the forging crack sensitivity of difficult-to-deform high-temperature alloys includes the following steps: 1) Pre-forging heating and heat preservation At room temperature, the two ends of the difficult-to-deform high-temperature alloy steel ingot are wrapped with heat-insulating cotton, and the steel ingot is heated in three stages and kept warm until the steel ingot is fully heated before it is opened. 2) Multi-directional elongation forging Using a trapezoidal hammerhead, the blank is forged in a step-by-step forging method, with a single forging deformation of 9% to 15%. 2-1) The lower end of the trapezoidal hammer head is the small end of the trapezoid, and the small end of the trapezoidal hammer head is a rectangular plane. When each side is lengthened, first make the short side of the rectangular plane of the small end of the trapezoidal hammer head parallel to the forging direction. Use intermittent forging to start hammering from a distance of 1 / 2 of the diameter of the blank from the end of the blank. Then hammer again at a distance of 2 times the length of the short side of the trapezoidal hammer head every time until there is no longer a distance of 2 times the length of the short side at the end of the blank. This completes one forging stroke using the short side of the hammer head to lengthen the blank. 2-2) After one short-side lengthening forging stroke of the hammer head is completed, rotate the trapezoidal hammer head horizontally by 90 degrees so that the long side of the rectangular plane at the lower end of the trapezoidal hammer head is parallel to the forging direction. Then, starting from the end of the blank, use the long side of the rectangular plane at the lower end of the trapezoidal hammer head to forge the gaps where the short side has not been forged until the end of the blank, thus completing the long-side lengthening forging stroke of the hammer head. 2-3) Following the steps 2-1) and 2-1), the blank is forged in all directions until the blank of the target size is obtained; 3) Slow cooling after forging Based on the temperature variation characteristics of the alloy's constituent phases, a combination of air cooling, furnace cooling, or hood cooling is used for slow cooling after forging.

[0007] Preferably, in step 1), the specific method of the three-stage stepped heating is as follows: the first temperature platform is 600℃, the second temperature platform is 900℃, and the third temperature platform is 1130℃~1170℃, and the heating rate of the three-stage stepped heating is 100℃ / hour~200℃ / hour.

[0008] Preferably, in step 2), during the forging process, when the billet temperature is close to the final forging temperature, it needs to be returned to the furnace to be heated through to the third-level temperature platform before proceeding with the subsequent forging process.

[0009] Preferably, in step 2), the final forging temperature is ≥950℃.

[0010] Preferably, in step 2), the deformation amount of the blank in the last firing cycle is ≥35%, calculated according to the following formula: C = (AB) / A; In the formula, C is the deformation amount of the last forging, A is the actual cross-sectional area of ​​the blank before the last forging, and B is the cross-sectional area of ​​the blank of the target size.

[0011] Preferably, in step 2), the ratio of the long side to the short side of the rectangular plane at the small end of the trapezoidal hammer head is 3 to 3.5, and the long side of the small end of the trapezoidal hammer head has the same side length as the sides of the large end of the trapezoidal hammer head.

[0012] Preferably, the angle between the short side of the rectangular plane at the small end of the trapezoidal hammer head and the hypotenuse of the trapezoid is set as an arc-shaped chamfer.

[0013] Preferably, the ratio of the radius of the arc-shaped chamfer to the short side of the rectangular plane at the small end of the trapezoidal hammer head is 0.43 to 0.57.

[0014] The beneficial effects of this invention are as follows: 1. This invention uses insulating cotton to wrap both ends of the steel ingot, which effectively slows down the temperature drop rate of the ends during transportation and forging, preventing the end temperature from rapidly deviating from the suitable forging temperature range. This avoids the problem of a sudden increase in deformation resistance due to insufficient temperature, greatly reducing the risk of shear crack initiation at the ends. This invention employs a three-stage stepped heating process: First, preheating at 600℃ ensures that the core and surface temperatures of the steel ingot are sufficiently uniform, avoiding internal cracking caused by a sudden temperature rise; second, a 900℃ platform further uniformizes the core and surface temperatures, minimizing subsequent temperature differences due to variations in heat transfer; finally, holding at 1130℃~1170℃ until the steel ingot is fully heated ensures uniform radial and axial temperatures. Simultaneously, a heating rate of 100℃~200℃ / hour allows for separate control of temperature differences at each stage, matching the alloy softening process, ensuring heating efficiency, and reducing process debugging costs and equipment modification requirements for industrial production.

[0015] 2. This invention employs a trapezoidal hammer for intermittent forging of the billet, transforming the concentrated vertical shear force of traditional flat anvils into a more dispersed combination of oblique tensile and compressive forces, significantly reducing the risk of cracking caused by concentrated internal shear stress in the billet. First, by setting the starting position and the reserved length at the end, this invention precisely avoids the low-temperature, high-resistance region at the end, preventing cracking due to deformation inconsistency. Second, by controlling the movement distance of the trapezoidal hammer and the amount of deformation per pass, it can suppress microstructural defects caused by local overheating and precisely match the load-bearing limit of the alloy's hot plasticity, gradually optimizing the internal structure to prevent billet cracking. Finally, by rotating the trapezoidal hammer horizontally by 90 degrees, forging the previously skipped protrusions from the starting position of the billet while simultaneously flattening the beginning and end of the billet, it eliminates the thickness difference between the protrusions and the forged section, avoiding overload problems in local deformation during subsequent drawing, thus balancing process efficiency and crack prevention.

[0016] Specifically, when using the intermittent forging method to forge a fully heated billet, the forging logic of "segmented pressure application - reserved transition - rotary forging" must be strictly followed to ensure the coordination of force transmission and structural deformation. First, the rectangular plane of the small end of the trapezoidal hammer head is tightly fitted to the surface of the billet, and the short side of the rectangular plane of the small end of the trapezoidal hammer head is kept parallel to the forging direction. This allows the forging force to form a dispersed oblique stress field along the inclined side of the trapezoid, avoiding stress concentration. Meanwhile, the forging starting point is set at half the diameter from the end of the blank. This position avoids the low-temperature, high-resistance area formed at the end due to heat loss, significantly reducing the risk of cracking due to deformation inconsistency. Each press during forging creates a 9%–15% deformation recess on the blank surface. This deformation matches the alloy's hot-state plastic bearing capacity limit, ensuring that insufficient deformation leads to inadequate microstructure optimization, while preventing localized stress concentration caused by excessive deformation. The length of the recess along the forging direction is equal to the shorter side of the rectangular plane at the small end of the trapezoidal hammerhead. Complete consistency is ensured to guarantee the regularity of the deformation area each time. After completing one pressing, the trapezoidal hammer head moves forward along the forging direction by a distance twice the length of the short side of the rectangular plane at the small end of the trapezoidal hammer head for the next forging. This interval between two pressings forms the raised transition zone for subsequent forging, avoiding excessive heat concentration and overheating defects caused by continuous forging. At the same time, the tail end of the blank, which is less than twice the length of the short side, is temporarily left unforged to avoid the risk of deformation in the low-temperature area, until a forging stroke using the short side of the hammer head is completed.

[0017] After one forging stroke involving the short side of the hammerhead, the trapezoidal hammerhead is rotated 90 degrees horizontally around its own axis, maintaining contact between the rectangular plane of the small end of the trapezoidal hammerhead and the workpiece. The only change is that the short side of the rectangular plane at the small end of the trapezoidal hammerhead is perpendicular to the forging direction, meaning the long side of the rectangular plane at the small end of the trapezoidal hammerhead remains parallel to the forging direction. This change in the hammerhead's orientation allows for the full coverage and flattening of the reserved ends and protrusions by utilizing the length advantage of the long side of the rectangular plane at the small end of the trapezoidal hammerhead. The length of the trapezoidal hammerhead is designed to be more than three times the length of the short side of the rectangular plane at the small end of the trapezoidal hammerhead, providing a structural basis for covering two adjacent protrusions in one pass. Forging begins at the end of the blank. With each press, the long side of the rectangular plane at the small end of the trapezoidal hammer head can cover an area at least three times the length of the short side of the rectangular plane at the small end of the trapezoidal hammer head along the forging direction. It is also necessary to ensure that the exact center of the rectangular plane at the small end of the trapezoidal hammer head is precisely aligned with the exact center of the end of the blank. Through this method of applying pressure in the center, the initially protruding part at the end is smoothly pressed down to be flush with the previously formed depression, eliminating the initial height difference. Subsequently, the previously reserved protrusions are forged. Each time the hammer is pressed down, the center of the rectangular plane at the small end of the trapezoidal hammer head must be aligned with the geometric center of the protrusion. This ensures that the working surface of the trapezoidal hammer head completely covers the short side length of three adjacent and continuous rectangular planes, achieving a smooth transition between the protrusion and the recess. The unforged area at the tail end of the blank is forged flat in the same way. The entire forging process does not require additional heating, and the plasticity can be guaranteed by relying on the residual heat of the blank itself. Finally, the overall cross-section of the blank reaches a uniform and consistent near-square shape, providing a regular blank base for the subsequent square drawing process.

[0018] 3. This invention employs a square-octagonal elongation process for forging the billet, effectively breaking the directional growth trend of the texture. Multi-dimensional stress release reduces accumulated internal stress from previous forging processes, lowering the risk of stress concentration-induced cracks. Simultaneously, forging the billet to a near-square cross-section after each process effectively avoids excessive local deformation due to irregular shapes, preventing structural defects such as abnormally coarse grains and non-uniform distribution of precipitates. When the forging temperature approaches the final forging temperature, this invention employs a reheating process to restore the billet's temperature uniformity and hot plasticity, effectively preventing "hard forging" cracking. Furthermore, the final forging cycle with a deformation of ≥35% completely breaks up any remaining coarse grain structure and precipitate agglomeration areas, ensuring that the final billet meets the stringent mechanical property requirements of high-temperature alloy forgings in the aerospace field.

[0019] 4. Based on the temperature range variation characteristics of the constituent phases of difficult-to-deform high-temperature alloys, this invention adopts a combination of suitable air cooling, furnace cooling, or hood cooling slow cooling methods to further reduce residual stress after forging and avoid cracks caused by stress release during the cooling process.

[0020] Glossary Intermittent forging method: In this invention, the intermittent forging method is a precision forging process designed for difficult-to-deform high-temperature alloys. It employs a trapezoidal hammer with a rectangular lower end (the ratio of the long side to the short side is 3-3.5, and the angle between the short side and the trapezoidal hypotenuse is an arc-shaped chamfer with a chamfer radius ratio of 0.43-0.57 to the short side). Following the logic of "segmented pressure application - reserved transition - rotary forging," the blank is forged in all directions. Specific operations include: for each direction of forging, first aligning the short side of the rectangular plane at the small end of the trapezoidal hammer with the forging direction, starting the hammering from a distance of 1 / 2 the diameter of the blank from the end of the blank, and then applying pressure in stages at intervals twice the length of the short side of the trapezoidal hammer. The deformation is controlled at 9% to 15% per cycle until the end of the blank no longer has a distance twice the length of the short side, completing the short side elongation stroke of the hammer head. Then, the trapezoidal hammer head is rotated horizontally by 90 degrees so that the long side of the rectangular plane at the small end is parallel to the forging direction. Starting from the end of the blank, the unforged interval area of ​​the short side and the reserved parts at the beginning and end are forged until the cross-section of the blank is uniform. This process can transform the concentrated vertical shear force of the traditional flat anvil into a dispersed oblique tensile and compressive force, avoiding the low temperature and high resistance area at the end, avoiding stress superposition and local overheating caused by continuous forging, significantly reducing the risk of cracking and improving the uniformity of the blank structure, providing a regular blank for subsequent multi-directional elongation forging. Attached Figure Description

[0021] Figure 1 This is a flowchart of a forging method for improving the forging crack sensitivity of difficult-to-deform high-temperature alloys according to the present invention. Figure 2 This is a three-dimensional structural diagram of the trapezoidal hammer head in an embodiment of the present invention; Figure 3 This is a schematic diagram of the installation and connection between the trapezoidal hammer and the forging press in an embodiment of the present invention; Figure 4 This is a schematic diagram showing the external dimensions of the cylindrical blank in an embodiment of the present invention; Figure 5 This is a schematic diagram of the shape of the blank after intermittent initial forging in an embodiment of the present invention; Figure 6 This is a schematic diagram of the blank's external dimensions during the intermediate stage of the forging process in an embodiment of the present invention; Figure 7 for Figure 6 A schematic diagram of the cross-sectional dimensions of the blank during the intermediate stage of the forging process. Detailed Implementation

[0022] like Figure 1 As shown, a forging method for improving the forging crack sensitivity of difficult-to-deform high-temperature alloys is characterized by comprising the following steps: 1) Pre-forging heating and heat preservation Under normal temperature conditions, the two ends of the steel ingot made of difficult-to-deform high-temperature alloy (including nickel-based high-temperature alloys such as GH3536, GH4151, GH4169, GH4175 and GH4975) are wrapped with heat-insulating cotton. The steel ingot is heated in three stages: the first stage temperature plateau is 600℃, the second stage temperature plateau is 900℃, and the third stage temperature plateau is 1130℃~1170℃. The heating rate is 100℃~200℃ / hour. The third stage temperature plateau is held until the steel ingot is fully heated before it is opened. 2) Multi-directional elongation forging Using a trapezoidal hammerhead, the blank is forged in all directions using an intermittent forging method, with a single-direction forging deformation of 9% to 15%. 2-1) The lower end of the trapezoidal hammer head is the small end of the trapezoid, and the small end of the trapezoidal hammer head is a rectangular plane. Each time the length is drawn, the short side of the rectangular plane of the small end of the trapezoidal hammer head is first made parallel to the forging direction. The hammer is started from a distance of 1 / 2 of the diameter of the blank at the end of the blank using intermittent forging. Then the hammer is dropped again at a distance of twice the length of the short side of the trapezoidal hammer head every time, until there is no longer a distance of twice the length of the short side at the end of the blank, thus completing one forging stroke using the short side of the hammer head to draw the length. 2-2) After one short-side lengthening forging stroke of the hammer head is completed, rotate the trapezoidal hammer head horizontally by 90 degrees so that the long side of the rectangular plane at the lower end of the trapezoidal hammer head is parallel to the forging direction. Then, starting from the end of the blank, use the long side of the rectangular plane at the lower end of the trapezoidal hammer head to forge the gaps where the short side has not been forged until the end of the blank, thus completing the long-side lengthening forging stroke of the hammer head. 2-3) Following the steps 2-1) and 2-1), the blank is forged in all directions until the blank of the target size is obtained.

[0023] During the forging process, it must be ensured that the deformation of the billet in the last heat treatment is ≥35%, and the deformation of the billet in the last heat treatment is calculated according to the following formula: C = (AB) / A; In the formula, C is the deformation amount of the last forging, A is the actual cross-sectional area of ​​the blank before the last forging, and B is the cross-sectional area of ​​the blank of the target size. In addition, when the billet temperature is close to the final forging temperature (final forging temperature ≥ 950℃), it needs to be returned to the furnace to the third temperature platform for thorough heating before proceeding with the subsequent forging process.

[0024] It is worth noting that the lower part of the trapezoidal hammer head is an inverted trapezoidal structure, the upper end of which is the large end of the trapezoid, and the upper end of the inverted trapezoidal structure is a square plane; the ratio of the long side to the short side of the rectangular plane at the small end of the trapezoidal hammer head is 3 to 3.5, and the long side of the small end of the trapezoidal hammer head is the same as the side of the large end of the trapezoidal hammer head; and the angle between the short side of the rectangular plane at the small end of the trapezoidal hammer head and the hypotenuse of the trapezoid is set as an arc chamfer, the ratio of the radius of the arc chamfer to the short side of the rectangular plane at the small end of the trapezoidal hammer head is 0.43 to 0.57.

[0025] Meanwhile, the upper part of the trapezoidal hammerhead of the present invention is cylindrical, and an inner cavity is provided at the axis of the cylinder. The upper opening of the inner cavity is rectangular, and the lower part of the inner cavity is a cylindrical cavity. The diameter of the cylindrical cavity is equal to the long side of the rectangular opening. By inserting the cross arm of the T-shaped rod into the cylindrical cavity through the rectangular opening and then rotating it 90° clockwise, the T-shaped rod and the trapezoidal hammerhead can be connected and locked. A spring is provided at the lower end of the T-shaped rod, and the upper end of the spring is connected and fixed to the slider of the forging press, thereby completing the assembly of the trapezoidal hammerhead and the forging press. By adjusting the extension and retraction of the hydraulic rod on the slider of the forging press, the trapezoidal hammerhead and the forging press can be firmly installed. The support cylinder on the slider of the forging press can constrain the working stroke of the trapezoidal hammerhead, ensuring that the trapezoidal hammerhead does not wobble during the up and down reciprocating motion, thus playing a role in positioning and stabilization.

[0026] In other words, the trapezoidal hammer head described in this invention is installed and connected to the forging press in a known manner, that is, the hammer head is connected to the slider on the hydraulic forging press through a spring and a T-shaped rod, which can absorb the forging impact and protect the equipment.

[0027] 3) Slow cooling after forging Based on the temperature variation characteristics of the constituent phases after forging of difficult-to-deform high-temperature alloys, a combination of air cooling, furnace cooling, or hood cooling is used for slow cooling after forging.

[0028] The following is an example of using the above method: like Figures 2 to 7 As shown, a forging method for improving the forging crack sensitivity of difficult-to-deform high-temperature alloys includes the following specific steps: (1) Making a trapezoidal hammerhead The working part of the trapezoidal hammerhead is the rectangular plane at the small end of the hammerhead, which is the only part that directly contacts the workpiece and bears the forging pressure. Specifically, the inverted trapezoidal structure at the bottom of the hammerhead has the following parameters: the upper end (large end of the trapezoid) is a square plane with a side length of 1000mm; the lower end (small end of the trapezoid) is a rectangular plane with a short side length of 330mm and a long side length of 1000mm; the height of the inverted trapezoidal structure is 330mm; the angle between the short side of the rectangular plane at the small end of the hammerhead and the hypotenuse of the trapezoid is approximately 135 degrees, with a rounded chamfer at the angle, the radius of which is controlled between 150 and 200mm (to avoid stress concentration).

[0029] The upper part of the trapezoidal hammer head is cylindrical, with a height of 400mm. An inner cavity is located at the center of the cylinder. The upper opening of this inner cavity is rectangular, with a length of 260mm, a width of 90mm, and a height of 300mm. The lower part of this inner cavity is a cylindrical cavity with a diameter equal to the long side of the rectangular opening, which is 260mm, and a height of 100mm.

[0030] (2) Pretreatment of difficult-to-deform nickel-based superalloys GH4169 nickel-based superalloy (difficult-to-deform nickel-based superalloy) steel ingots with a diameter of 400mm and a length of 1200mm were selected. Before forging, diffusion annealing was performed to eliminate compositional segregation and internal stress generated during the ingot casting process. The specific operating procedure is as follows: The steel ingots are placed smoothly into a bogie-type resistance furnace at room temperature. Multiple sets of thermocouples are placed inside the furnace, evenly distributed throughout the furnace cavity. Diffusion annealing is then performed according to the following process curve: ① Room temperature → 600℃: Heating time is 4 hours, and after reaching 600℃, the temperature is held for 2 hours. This can effectively eliminate the initial thermal stress after the cold steel ingot is loaded into the furnace and avoid internal cracking caused by temperature difference. ② 600℃→980℃: The heating time is 3 hours, and after reaching 980℃, the temperature is held for 4 hours. This can promote a more uniform temperature inside and outside the steel ingot and is more conducive to reducing the difference between the temperature of the steel ingot core and the target heating temperature. ③ 980℃→1150℃: The heating time is 2 hours, and after reaching 1150℃, it is held for 30 hours. This can effectively carry out Nb diffusion, greatly consume the laves phase, and improve the uniformity of the alloy composition of the steel ingot. ④ 1150℃→1190℃: Heating time is 2 hours, and after reaching 1190℃, it is held for 50 hours, which can further enhance the homogenization of various alloying elements; ⑤ 1190℃→600℃: Furnace cooling is adopted, and the cooling rate is controlled at ≤50℃ / h to avoid the generation of new internal stress due to excessively rapid cooling; ⑥ When the temperature drops below 600℃, open the furnace and air-cool it to room temperature to complete the diffusion annealing process.

[0031] Then, the GH4169 steel ingots after diffusion annealing are cold-charged into the furnace (room temperature charging to avoid local temperature differences caused by charging into a hot furnace). The two ends of the steel ingots are completely wrapped and sealed with insulating cotton to reduce heat loss at the ends of the steel ingots and ensure the uniformity of the overall temperature of the steel ingots.

[0032] (3) Pre-forging heating (three-stage stepped heating) treatment After completing the heat preservation measures for the pre-forging furnace and the end of the steel ingot, the heating furnace is started to enter the first heating stage: the steel ingot is heated from room temperature to a temperature platform of 600℃ along with the furnace. In this stage, there is no need to deliberately control the heating rate. After reaching the target temperature (i.e. 600℃), it is held for 60 minutes to eliminate the initial temperature difference between the inside and outside of the cold steel ingot after it is loaded into the furnace, and to avoid the risk of thermal stress initiation in the low temperature stage. After the first stage of heat preservation, the steel ingot is heated from 600℃ to 900℃ at a steady heating rate of 110℃ / hour, which effectively avoids internal stress concentration caused by a sudden temperature rise. After the temperature transition is completed, the second stage of heating begins: the temperature plateau at 900℃ is maintained for 60 minutes. This process promotes preliminary dynamic softening of the alloy, effectively reducing the internal stress concentration problem that may occur in the subsequent high-temperature heating stage, and laying a stable foundation for high-temperature heating.

[0033] After the second stage of heat preservation is completed, the temperature continues to rise slowly from 900℃ to 1140℃ at a rate of 110℃ / hour. Then, the critical third stage of heating (heat penetration) begins: the high-temperature platform of 1140℃ needs to be held for 120 minutes. Sufficient heat preservation time ensures that the temperature of the core and surface of the steel ingot is completely consistent, achieving overall heat penetration. This provides sufficient and stable hot plasticity for subsequent forging processes, ensuring the smooth progress of the forging process.

[0034] After heating, a robotic arm is used to quickly remove the steel ingot from the forging heating furnace and transfer it to the high-speed forging machine station for billet preparation. This reduces heat loss of the billet in the air and ensures that the billet temperature meets the process requirements during forging.

[0035] It is worth noting that this heating and holding process was specifically designed for GH4169 steel ingots with a diameter of 400mm and a length of 1200mm. In actual production, it is necessary to make targeted adjustments to parameters such as the heating rate and holding time at each temperature plateau based on the specific grade of the difficult-to-deform high-temperature alloy (such as GH3536, GH4151, etc.), the specifications and dimensions of the steel ingot, and the characteristics of the heating furnace, in order to ensure the heating effect at this stage.

[0036] (4) Intermittent forging Intermittent forging is performed using a trapezoidal hammer head, ensuring that the rectangular plane at the small end of the trapezoidal hammer head is in contact with the billet (i.e., the hot-through steel ingot after pre-forging heat treatment), and that the short side of the rectangular plane at the small end of the trapezoidal hammer head is parallel to the forging direction (i.e., along the length of the billet). The hammer is lowered starting 200mm from the end of the billet, and the hammer head moves forward 600mm to 700mm each time (approximately twice the length of the short side of the rectangular plane at the small end of the trapezoidal hammer head). The single pressing amount is between 20mm and 40mm. When forging to the other end of the billet, a 200mm tail end is left unforged temporarily. Then, keeping the blank position unchanged, rotate the trapezoidal hammer head horizontally by 90 degrees (i.e., rotate it 90 degrees around an axis perpendicular to the forging surface of the blank). After rotation, ensure that the short side of the rectangular plane at the small end of the trapezoidal hammer head is perpendicular to the forging direction. Start forging from the original reserved end of the blank, and forge the unforged protrusions one by one until they are flat. Finally, forge the other end of the blank that was originally reserved at the same time.

[0037] (5) Multi-directional elongation forging The cross-section of the blank is gradually reduced by using an alternating four-sided and eight-sided drawing process. 5-1) Rotate the blank 90 degrees and forge it according to step (4); 5-2) Repeat step 5-1) forging until a straight bar with a nearly square billet cross-section of 300mm×300mm is formed; 5-3) Rotate the straight bar of the near square billet with a cross section of 300mm×300mm by 45 degrees and forge it according to step (4); 5-4) Repeat step 5-1) forging until a straight bar with a near square billet cross-section of 250mm×250mm is formed; The deformation amount for the final firing cycle is calculated as follows: The actual cross-sectional area of ​​the blank before forging is A=πr 2 =3.14×200×200mm 2 =125600mm 2 The target cross-sectional area B = 250mm × 250mm = 62500mm 2 Deformation calculation: C = (AB) / A = (125600 - 62500) / 125600 = 63100 / 125600 = 50.24%; (6) Post-forging treatment After forging, the nearly square billet straight bar of 250mm×250mm is subjected to slow cooling by natural air cooling. During cooling, contact with humid / strong wind environments should be avoided to prevent local temperature difference cracks.

[0038] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications made to the present invention by those skilled in the art without departing from the spirit of the present invention shall fall within the protection scope of the present invention.

Claims

1. A forging method for improving the forging crack sensitivity of difficult-to-deform high-temperature alloys, characterized in that, Includes the following steps: 1) Pre-forging heating and heat preservation The two ends of the difficult-to-deform high-temperature alloy steel ingot are wrapped with heat-insulating cotton. The steel ingot is heated in three stages and kept warm until it is fully heated before it is opened. 2) Multi-directional elongation forging Using a trapezoidal hammerhead, the blank is forged in all directions using an intermittent forging method, with a single-direction forging deformation of 9% to 15%. 2-1) The lower end of the trapezoidal hammer head is the small end of the trapezoid, and the small end of the trapezoidal hammer head is a rectangular plane. Each time the length is drawn, the short side of the rectangular plane of the small end of the trapezoidal hammer head is first made parallel to the forging direction. The hammer is started from a distance of 1 / 2 of the diameter of the blank at the end of the blank using intermittent forging. Then the hammer is dropped again at a distance of twice the length of the short side of the trapezoidal hammer head every time, until there is no longer a distance of twice the length of the short side at the end of the blank, thus completing one forging stroke using the short side of the hammer head to draw the length. 2-2) After one short-side lengthening forging stroke of the hammer head is completed, rotate the trapezoidal hammer head horizontally by 90 degrees so that the long side of the rectangular plane at the lower end of the trapezoidal hammer head is parallel to the forging direction. Then, starting from the end of the blank, use the long side of the rectangular plane at the lower end of the trapezoidal hammer head to forge the gaps where the short side has not been forged until the end of the blank, thus completing the long-side lengthening forging stroke of the hammer head. 2-3) Following the steps 2-1) and 2-1), the blank is forged in all directions until the blank of the target size is obtained; 3) Slow cooling after forging Based on the temperature variation characteristics of the alloy's constituent phases, a combination of air cooling, furnace cooling, or hood cooling is used for slow cooling after forging.

2. The forging method according to claim 1, characterized in that, In step 1), the specific method of the three-stage stepped heating is as follows: the first temperature platform is 600℃, the second temperature platform is 900℃, and the third temperature platform is 1130℃~1170℃. The heating rate of the three-stage stepped heating is 100℃ / hour~200℃ / hour.

3. The forging method according to claim 1, characterized in that, Step 2) During the forging process, when the billet temperature is close to the final forging temperature, it needs to be returned to the furnace to the third temperature platform for thorough heating before proceeding with the subsequent forging process.

4. The forging method according to claim 3, characterized in that, The final forging temperature is ≥950℃.

5. The forging method according to claim 1, characterized in that, In step 2), the deformation of the blank in the last firing cycle is ≥35%, calculated according to the following formula: C = (AB) / A; In the formula, C is the deformation amount of the last forging, A is the actual cross-sectional area of ​​the blank before the last forging, and B is the cross-sectional area of ​​the blank of the target size.

6. The forging method according to claim 1, characterized in that, The ratio of the long side to the short side of the rectangular plane at the small end of the trapezoidal hammer head is 3 to 3.5, and the long side of the small end of the trapezoidal hammer head has the same side length as the sides of the large end of the trapezoidal hammer head.

7. The forging method according to claim 1, characterized in that, The angle between the short side of the rectangular plane at the small end of the trapezoidal hammer head and the hypotenuse of the trapezoid is set as an arc chamfer.

8. The forging method according to claim 7, characterized in that, The ratio of the radius of the arc-shaped chamfer to the shorter side of the rectangular plane at the small end of the trapezoidal hammer head is 0.43 to 0.57.

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