A forging method of a 90kN level high-performance mooring post based on a tug

Abstract

The present application relates to the field of metal material forging and heat treatment process, disclose a kind of based on tug 90kN level high-performance bitt's forging method, including preparation by industrial deionized water, film-forming main agent A, film-forming auxiliary agent B, sodium molybdate dihydrate, polyethylene glycol 400 and triethanolamine are quenched medium and heated constant temperature;After alloy structural steel blank is heated to heat, multiple-pass forging is carried out to obtain forgings;The forgings are pre-cooled to the first temperature, immersed in the quenching medium for first stage cooling, and the flow rate is controlled to maintain the first circulation flow rate;When the surface temperature of the forgings decreases to the second temperature, switch and maintain the second circulation flow rate for second stage cooling;When the core temperature of the forgings decreases to the water temperature, the forgings are lifted out and naturally cooled in still air, and the residual sensible heat is used to complete the self-tempering of the residual heat.The present application balances the cooling rate, avoids surface microcracks and improves the core hardenability.

Description

Technical Field

[0001] This invention relates to the field of metal material forging and heat treatment processes, specifically a forging method based on a 90kN-class high-performance bollard for tugboats. Background Technology

[0002] As a core load-bearing component of a ship's mooring system, the 90kN-class high-performance bollard for tugboats needs to withstand enormous mooring tensile loads and random impact forces generated during berthing and unberthing. These components are typically forged from large-section low-alloy high-strength structural steel. For such thick forgings, whose effective cross-sectional thickness often exceeds 300mm, existing forging and associated heat treatment processes have significant limitations in achieving balanced control of the cooling rate.

[0003] In the initial high-temperature immersion stage of traditional quenching processes, due to the lack of effective intervention in heat conduction at the solid-liquid interface, conventional quenching media will undergo intense heat exchange with the high-temperature metal surface, causing a sharp drop in the surface temperature of the forging. Because the core heat of large-section forgings cannot be conducted outward in time due to the physical thickness limitation, an excessive thermal stress difference will be generated between the inside and outside of the cross-section. This often induces quenching microcracks on the surface of the forging, directly damaging the fatigue life of the component.

[0004] As the cooling process continues and enters the mid-to-low temperature phase transformation region, the thickness of the large cross-section itself becomes an obstacle to heat dissipation. Existing quenching systems typically employ fixed medium flow rates or a single cooling mode, which cannot provide the sudden, high-intensity heat transfer required to rapidly extract heat from the core during the critical stages of metal phase transformation. This results in the cooling curve of the core of thick forgings frequently passing through the pearlite transformation zone, failing to generate sufficient martensite or bainite structures, ultimately manifesting as insufficient hardenability in the core, severely weakening the overall load-bearing capacity of the tie rod.

[0005] Conventional heat treatment practices involve leaving forgings in the quenching tank until they cool to room temperature or a lower temperature. This thorough cooling method not only causes residual phase transformation stress to accumulate within the metal, but also necessitates transferring the forgings back to a tempering furnace for a separate, lengthy tempering process to restore toughness. This traditional process completely ignores the enormous thermal energy naturally contained within the core of large-section forgings, failing to utilize the internal temperature gradient for spontaneous adjustment. This results in a long process flow, high energy consumption, and difficulty in achieving a natural transition and uniformity of the mechanical properties of the forging cross-section. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a forging method for 90kN-class high-performance bollards for tugboats, which solves the problems of difficulty in controlling the cooling rate evenly, easy generation of surface quenching microcracks, and insufficient hardenability of the core structure in the forging and heat treatment of large-section low-alloy high-strength steel.

[0007] To achieve the above objectives, the present invention provides a forging method for a 90kN-class high-performance bollard for tugboats, employing the following technical solution: A forging method for a 90kN-class high-performance bollard for tugboats includes the following steps: A quenching medium is prepared in a quenching tank. The quenching medium consists of 77.2-88.2 parts of industrial deionized water, 6.0-10.0 parts of film-forming agent A, 3.0-6.0 parts of film-forming auxiliary agent B, 0.3-0.8 parts of sodium molybdate dihydrate, 1.5-3.5 parts of polyethylene glycol 400, and 1.0-2.5 parts of triethanolamine by weight. The quenching medium is then heated to a constant temperature. The alloy structural steel billet is heated and held at a temperature until the core of the alloy structural steel billet is thoroughly heated to obtain a high-temperature billet. The high-temperature billet is forged in multiple passes, and the reduction rate and final forging temperature are controlled in the last pass to obtain the forging. The forging is pre-cooled in air to a preset first temperature, and then immersed in quenching medium for the first stage of cooling, while controlling the flow rate of the circulating pump in the quenching tank to maintain the first circulation flow rate. During the first stage of cooling, when the surface temperature of the forging drops to the preset second temperature, the circulation pump flow rate is switched and maintained at the second circulation flow rate for the second stage of cooling. During the second stage of cooling, the core temperature of the forging drops to the outlet water temperature. The forging is then lifted out of the quenching tank and allowed to cool naturally in still air. The residual sensible heat in the core of the forging is used to complete the residual heat self-tempering.

[0008] By employing the above technical solution, this invention combines a specific multi-component water-based polymer quenching medium with a two-stage variable flow rate cooling process. In the initial stage of quenching, the multi-component water-based quenching medium undergoes a synergistic film-forming reaction. Specifically, the film-forming main agent A and film-forming auxiliary agent B contained in the quenching medium system are both polyether polymers with anti-solubility characteristics. Because they contain different proportions of ethylene oxide and propylene oxide polymer segments, when the high-temperature forging, pre-cooled to a preset first temperature, is immersed in the quenching tank, the fluid temperature at the contact interface rapidly exceeds the cloud point of the polymer. At this time, the film-forming main agent A and film-forming auxiliary agent B detach from the aqueous phase and adhere to the surface of the forging, forming a polymer coating film.

[0009] To maintain the stability of the aforementioned film, during the first stage of high-temperature cooling, the circulation pump flow rate needs to be controlled at a relatively low initial circulation rate to reduce the mechanical erosion of the forging surface by the fluid. This relatively complete coating effectively isolates the fluid from the metal substrate, thereby suppressing the rapid cooling phenomenon in the high-temperature zone, avoiding excessive thermal stress differences between the inside and outside of large-section forgings, and preventing surface cracking. In the later stages of cooling, triethanolamine and sodium molybdate dihydrate in the medium will form an inorganic-organic composite passivation layer on the metal surface, which, together with the polymer film, adjusts the thermal conductivity coefficient of the solid-liquid interface.

[0010] As the cooling process progresses, when the surface of the forging drops to a preset second temperature, the metal structure begins to enter the phase transformation zone. At this point, the flow rate is switched to a higher second circulation rate, utilizing mechanical turbulence to disperse the polymer coating film adhering to the forging surface, causing the cooling state to transition to the nucleation boiling and convective heat transfer stage. This high heat transfer rate can quickly extract heat from the core of the forging, enabling the thick cross-section core to smoothly cross the pearlite transformation zone, thereby obtaining a dense martensite or bainite structure.

[0011] When the core of the forging cools to the outlet water temperature, it is removed from the cooling tank. At this point, the surface temperature of the cross-section has dropped to a low level, but the core still retains a high amount of heat. In the subsequent static air cooling state, the sensible heat that has not been completely dissipated from the core will be conducted to the surface. Utilizing the temperature gradient existing in the forging body, the hardened structure that has already formed on the surface is tempered in situ, thereby eliminating residual phase transformation stress and improving the overall toughness of the forging.

[0012] Preferably, the alloy structural steel billet is 35CrMo alloy structural steel or 42CrMo alloy structural steel with an effective cross-sectional thickness of 300-320mm; the heating rate of the alloy structural steel billet is 80-120℃ / h, and the target heating temperature is 1150-1200℃. When forging the high-temperature billet in multiple passes, the reduction rate applied in the last pass is controlled at 25%-35%, and the final forging temperature is 850-880℃.

[0013] By adopting the above technical solution, the limited heating rate restricts the tendency of large-section billets to crack in the early stage of heating. During the forging stage, setting the reduction rate of the final pass to 25%-35%, while controlling the final forging temperature at 850-880℃, promotes the transmission of deformation shear force towards the core, thereby breaking up coarse dendrite structures and refining austenite grains. This parameter ratio also avoids forging cracks caused by excessively high final forging temperatures leading to coarse grains or excessively low temperatures, thus providing sufficient deformation energy and a fine-grained microstructure for subsequent heat treatment processes.

[0014] Preferably, the quenching medium comprises, by weight, 77.0-88.5 parts industrial deionized water; 7.0-9.0 parts film-forming agent A; 4.0-5.0 parts film-forming auxiliary agent B; 0.4-0.6 parts sodium molybdate dihydrate; 2.0-3.0 parts polyethylene glycol 400; and 1.5-2.0 parts triethanolamine. The raw materials for preparing film-forming agent A comprise, by weight, 0.8-1.2 parts 1,2-propanediol; 0.3-0.4 parts potassium hydroxide; 68-85 parts ethylene oxide; 90-112 parts propylene oxide; and 0.35-0.45 parts glacial acetic acid. The preparation method of film-forming agent A includes the following steps: 1,2-propanediol and potassium hydroxide are added to a high-pressure reactor, and nitrogen gas is introduced into the reactor to replace the air inside; the high-pressure reactor is heated to 110-130℃, and the reaction pressure is controlled at 0.3-0.5MPa. A mixture of ethylene oxide and propylene oxide is continuously added dropwise; after the addition is completed, the reactor is kept at a constant temperature of 110-130℃ and a pressure of 0.3-0.5MPa until the pressure inside the high-pressure reactor no longer decreases; the high-pressure reactor is cooled to 70-90℃, and glacial acetic acid is added for neutralization; unreacted residual monomers are removed under vacuum conditions to obtain film-forming agent A. The raw materials for preparing film-forming agent B, by weight, include: 0.8-1.2 parts 1,2-propanediol; 0.08-0.12 parts potassium hydroxide; 11-17 parts ethylene oxide; 14.5-22.5 parts propylene oxide; and 0.09-0.13 parts glacial acetic acid. The preparation method for film-forming agent B is the same as that for film-forming agent A.

[0015] By employing the above technical solution, both the film-forming agent A and the film-forming auxiliary agent B use 1,2-propanediol as the initiator, and initiate the anionic ring-opening polymerization reaction of ethylene oxide and propylene oxide under the catalysis of potassium hydroxide to generate polyether compounds. Due to the difference in proportions, the proportion of propylene oxide in film-forming agent A is higher than that in film-forming auxiliary agent B, resulting in a lower cloud point for film-forming agent A. This allows it to preferentially precipitate from the aqueous phase at higher temperatures, forming a dense inner polymer film. In contrast, the higher cloud point of film-forming auxiliary agent B causes it to begin precipitating only at slightly lower temperatures, thus forming a relatively loose outer film. The physical combination of these two agents can spontaneously form a bilayer polymer layer with a phase change gradient on the surface of the forging, effectively enhancing the vapor film stability during the high-temperature cooling stage. Furthermore, the use of glacial acetic acid to neutralize residual alkali in the system and to remove monomers maintains the chemical stability of the polymer material.

[0016] Preferably, the operation of preparing the quenching medium in the quenching tank includes: injecting industrial deionized water into a quenching tank equipped with mechanical stirring, and heating it to 43-47℃; adding film-forming agent A, film-forming auxiliary agent B, sodium molybdate dihydrate, polyethylene glycol 400, and triethanolamine sequentially at a stirring speed of 300-500 rpm to dissolve and form a homogeneous liquid. The quenching medium is heated to a constant temperature of 43-47℃, and the outlet water temperature is 200-250℃; the preset first temperature is 800-840℃, and the first circulation flow rate is 0.15-0.25 m / s; the preset second temperature is 340-360℃, and the second circulation flow rate is 1.2-1.8 m / s.

[0017] By adopting the above technical solution, the initial temperature of the quenching medium is maintained at 43-47℃, reducing the temperature difference between the fluid and the polymer's cloud point. This helps to improve the response speed of polymer precipitation when the pre-cooled forging is immersed in water. Regarding temperature range control, setting the first temperature to 800-840℃ ensures that the workpiece does not undergo a proeutectoid transformation before immersion in water. Combined with a first circulation flow rate of 0.15-0.25 m / s, the surface film is kept in a relatively stable dynamic equilibrium state. When the temperature drops to 340-360℃, near the martensitic transformation initiation temperature, it is used as the second temperature node. At this point, the flow rate is increased to 1.2-1.8 m / s to break the liquid film, forcing the forging into a high-cooling-rate region. Finally, the outlet water temperature is controlled within the phase transformation range of 200-250℃ and the workpiece is removed from the water-cooled environment. This allows the core to retain a certain amount of sensible heat and continuously conduct it to the outside, relying on its own residual heat to transform the surface structure into tempered martensite. This enables the 90kN-class tugboat bollard to obtain matching tensile and impact mechanical properties.

[0018] This invention provides a forging method for a 90kN-class high-performance bollard for tugboats. It offers the following advantages: 1. This invention uses a water-based quenching medium formulated with a film-forming main agent A and a film-forming auxiliary agent B containing different propylene oxide polymerization ratios. By utilizing the difference in their cloud points, a gradient double-layer polymer coating film is preferentially precipitated and formed when the high-temperature forging is immersed in water. It can maintain dynamic stability at a low circulation flow rate in the first stage, effectively isolating the fluid from the metal matrix, reducing the cooling rate of the forging in the high-temperature stage, thereby reducing the thermal stress difference between the inside and outside of the thick cross-section forging and avoiding the generation of surface quenching microcracks.

[0019] 2. This invention employs a two-stage variable flow rate cooling process. When the surface temperature of the forging drops to a second temperature near the martensitic transformation zone, the flow rate of the circulating pump is switched to a higher second circulation flow rate. The increased mechanical turbulence disperses the polymer coating film on the surface of the forging, forcing the cooling state to quickly transition to the nucleation boiling and convective heat transfer stage. Through the abrupt high heat transfer rate, the heat in the core of the forging is rapidly extracted, enabling the thick cross-section core to smoothly cross the pearlite transformation zone, effectively improving the hardenability of the core structure of the forging.

[0020] 3. This invention controls the timing of the forging's exit from the water. Within the phase transformation range when the core temperature of the forging drops to the exit water temperature, it removes the forging from the quenching tank and allows it to cool naturally in still air. This preserves the sensible heat that has not yet been completely dissipated from the core. By utilizing the inherent temperature gradient of the large-section forging, heat is conducted from the inside to the surface. The hardened structure already formed on the surface is then subjected to residual heat self-tempering in situ. This not only eliminates residual stress from the phase transformation but also improves the overall toughness of the tie rod and eliminates the need for a subsequent independent tempering heating process. Attached Figure Description

[0021] Figure 1 This is a test diagram of the continuous cooling curve associated with dynamic variable flow rate in Test Example 1 of the present invention; Figure 2 This is the inversion test diagram of the surface heat transfer coefficient at the solid-liquid interface in Test Example 2 of the present invention; Among them, (a) is a curve of surface heat transfer coefficient as a function of surface temperature, and (b) is a comparison of the local changes in heat transfer coefficient before and after the flow rate abrupt change point at 350℃. Figure 3 This is a comparative test diagram of the macroscopic mechanical properties of the large cross-section core of Test Example 3 of the present invention. Among them, (a) is a distribution diagram of the core strength index of the forging, (b) is a comparison diagram of the core impact toughness at -40℃, and (c) is a distribution diagram of the core elongation after fracture of the forging. Figure 4 This is a test graph comparing the quenching cracking rate and macroscopic surface residual stress of the forging in Test Example 4 of the present invention. Among them, (a) is a bar chart of the microcrack detection rate distribution of each batch of forgings, and (b) is a scatter plot of the average maximum principal stress on the surface of the corresponding batch of forgings. Figure 5 This is a graph showing the overall energy consumption and production cycle evaluation in Test Example 5 of the present invention; Among them, (a) is a stacked area diagram of the energy consumption per ton of forgings for each scheme, and (b) is a scatter plot of the total manufacturing cycle time for each scheme. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Preparation Examples 1-6: Preparation Example 1: This preparation example provides a method for preparing film-forming agent A1, including the following steps: Add 1 part by weight of 1,2-propanediol and 0.3 parts by weight of potassium hydroxide to a high-pressure reactor, seal the reactor, and purge the air with nitrogen. Heat the reactor to 120°C, control the reaction pressure at 0.4 MPa, and slowly and continuously add a mixture of 68 parts by weight of ethylene oxide and 90 parts by weight of propylene oxide. After the addition is complete, continue the reaction at the above temperature and pressure until the pressure inside the reactor no longer decreases. Then, cool the reaction system to 80°C and add 0.35 parts by weight of glacial acetic acid for neutralization. Finally, remove unreacted residual monomers under vacuum to obtain the film-forming agent A1.

[0024] Preparation Example 2: This preparation example provides a method for preparing film-forming agent A2, including the following steps: Add 1 part by weight of 1,2-propanediol and 0.35 parts by weight of potassium hydroxide to a high-pressure reactor, seal the reactor, and purge the air with nitrogen. Heat the reactor to 120°C, control the reaction pressure at 0.4 MPa, and slowly and continuously add a mixture of 77 parts by weight of ethylene oxide and 101 parts by weight of propylene oxide. After the addition is complete, continue the reaction at the above temperature and pressure until the pressure inside the reactor no longer decreases. Then, cool the reaction system to 80°C and add 0.4 parts by weight of glacial acetic acid for neutralization. Finally, remove unreacted residual monomers under vacuum to obtain the film-forming agent A2.

[0025] Preparation Example 3: This preparation example provides a method for preparing film-forming agent A3, including the following steps: Add 1 part by weight of 1,2-propanediol and 0.4 parts by weight of potassium hydroxide to a high-pressure reactor, seal the reactor, and purge the air with nitrogen. Heat the reactor to 120°C, control the reaction pressure at 0.4 MPa, and slowly and continuously add a mixture of 85 parts by weight of ethylene oxide and 112 parts by weight of propylene oxide. After the addition is complete, continue the reaction at the above temperature and pressure until the pressure inside the reactor no longer decreases. Then, cool the reaction system to 80°C and add 0.45 parts by weight of glacial acetic acid for neutralization. Finally, remove unreacted residual monomers under vacuum to obtain the film-forming agent A3.

[0026] Preparation Example 4: This preparation example provides a method for preparing film-forming agent B1, including the following steps: Add 1 part by weight of 1,2-propanediol and 0.08 parts by weight of potassium hydroxide to a high-pressure reactor, seal the reactor, and purge the air with nitrogen. Heat the reactor to 120°C, control the reaction pressure at 0.4 MPa, and slowly and continuously add a mixture of 11 parts by weight of ethylene oxide and 14.5 parts by weight of propylene oxide. After the addition is complete, continue the reaction at the above temperature and pressure until the pressure inside the reactor no longer decreases. Then, cool the reaction system to 80°C and add 0.09 parts by weight of glacial acetic acid for neutralization. Finally, remove unreacted residual monomers under vacuum to obtain film-forming agent B1.

[0027] Preparation Example 5: This preparation example provides a method for preparing film-forming agent B2, including the following steps: Add 1 part by weight of 1,2-propanediol and 0.1 part by weight of potassium hydroxide to a high-pressure reactor, seal the reactor, and purge the air with nitrogen. Heat the reactor to 120°C, control the reaction pressure at 0.4 MPa, and slowly and continuously add a mixture of 14 parts by weight of ethylene oxide and 18.5 parts by weight of propylene oxide. After the addition is complete, continue the reaction at the above temperature and pressure until the pressure inside the reactor no longer decreases. Then, cool the reaction system to 80°C and add 0.11 parts by weight of glacial acetic acid for neutralization. Finally, remove unreacted residual monomers under vacuum to obtain film-forming agent B2.

[0028] Preparation Example 6: This preparation example provides a method for preparing film-forming agent B3, including the following steps: Add 1 part by weight of 1,2-propanediol and 0.12 parts by weight of potassium hydroxide to a high-pressure reactor, seal the reactor, and purge the air with nitrogen. Heat the reactor to 120°C, control the reaction pressure at 0.4 MPa, and slowly and continuously add a mixture of 17 parts by weight of ethylene oxide and 22.5 parts by weight of propylene oxide. After the addition is complete, continue the reaction at the above temperature and pressure until the pressure inside the reactor no longer decreases. Then, cool the reaction system to 80°C and add 0.13 parts by weight of glacial acetic acid for neutralization. Finally, remove unreacted residual monomers under vacuum to obtain film-forming agent B3.

[0029] Examples 1-4: Example 1

[0030] This embodiment provides a forging method for a 90kN-class high-performance bollard for tugboats, including the following steps: 82.7 parts by weight of industrial deionized water were injected into a quenching tank equipped with mechanical stirring, and the temperature control system was turned on to heat it to 45°C. Under a stirring speed of 400 rpm, 8.0 parts by weight of film-forming agent A2, 4.5 parts by weight of film-forming auxiliary agent B2, 0.5 parts by weight of sodium molybdate dihydrate, 2.5 parts by weight of polyethylene glycol 400, and 1.8 parts by weight of triethanolamine were added slowly in sequence. After complete dissolution to form a homogeneous liquid, the temperature of the main body of the quenching medium in the tank was kept constant at 45°C for later use. Select 35CrMo alloy structural steel billets with an effective cross-sectional thickness of 300mm and feed them into a natural gas heating furnace. Heat them to 1180℃ at a heating rate of 100℃ / h and hold them at that temperature for 300 minutes until the core is fully heated. High-temperature billets are forged in multiple passes using a hydraulic forging machine. The final forging temperature of the last pass is strictly controlled at 865℃, and a reduction rate of 30% is applied in this pass to retain a high-density deformation dislocation network inside the billet. After forging, when the surface temperature of the forging is 820℃, the forging is steadily immersed in the pre-prepared quenching tank. During the moment of immersion and the high-temperature cooling stage, the flow rate of the circulating pump in the quenching tank is set to 0.2m / s. The surface temperature of the forging is monitored in real time by a temperature measurement system. When the surface temperature drops to 350℃, the flow rate of the circulating pump is switched instantly and maintained at 1.5m / s. When the system determines that the core temperature of the forging has dropped to 225°C, the forging is lifted out of the quenching tank and placed in still air to cool naturally, using the residual heat in the core that has not been completely dissipated to complete the residual heat self-tempering process. Example 2

[0031] This embodiment provides a forging method for a 90kN-class high-performance bollard for tugboats, including the following steps: 88.2 parts by weight of industrial deionized water were injected into a quenching tank equipped with mechanical stirring, and the temperature control system was turned on to heat it to 43°C. Under a stirring speed of 400 rpm, 6.0 parts by weight of film-forming agent A1, 3.0 parts by weight of film-forming auxiliary agent B1, 0.3 parts by weight of sodium molybdate dihydrate, 1.5 parts by weight of polyethylene glycol 400, and 1.0 part by weight of triethanolamine were added slowly in sequence. After complete dissolution to form a homogeneous liquid, the temperature of the main body of the quenching medium in the tank was kept constant at 43°C for later use. 42CrMo alloy structural steel billets with an effective cross-sectional thickness of 320mm were selected and fed into a natural gas heating furnace. They were heated to 1150℃ at a heating rate of 80℃ / h and held at that temperature for 256 minutes until the core was fully heated. High-temperature billets are forged in multiple passes using a hydraulic forging machine. The final forging temperature of the last pass is strictly controlled at 850℃, and a reduction rate of 25% is applied in this pass to retain a high-density deformation dislocation network inside the billet. After forging, when the surface temperature of the forging is 800℃, the forging is steadily immersed in the pre-prepared quenching tank. During the moment of immersion and the high-temperature cooling stage, the flow rate of the circulating pump in the quenching tank is set to 0.15m / s. The surface temperature of the forging is monitored in real time by a temperature measurement system. When the surface temperature drops to 340℃, the flow rate of the circulating pump is switched instantly and maintained at 1.2m / s. When the system determines that the core temperature of the forging has dropped to 200℃, the forging is lifted out of the quenching tank and placed in still air to cool naturally, using the residual heat in the core that has not been completely dissipated to complete the residual heat self-tempering process. Example 3

[0032] This embodiment provides a forging method for a 90kN-class high-performance bollard for tugboats, including the following steps: 77.2 parts by weight of industrial deionized water were injected into a quenching tank equipped with mechanical stirring, and the temperature control system was turned on to heat it to 47°C. Under a stirring speed of 400 rpm, 10.0 parts by weight of film-forming agent A3, 6.0 parts by weight of film-forming auxiliary agent B3, 0.8 parts by weight of sodium molybdate dihydrate, 3.5 parts by weight of polyethylene glycol 400, and 2.5 parts by weight of triethanolamine were added slowly in sequence. After complete dissolution to form a homogeneous liquid, the temperature of the main body of the quenching medium in the tank was kept constant at 47°C for later use. Select 35CrMo alloy structural steel billets with an effective cross-sectional thickness of 300mm and feed them into a natural gas heating furnace. Heat them to 1200℃ at a heating rate of 120℃ / h and hold them at that temperature for 360 minutes until the core is fully heated. High-temperature billets are forged in multiple passes using a hydraulic forging machine. The final forging temperature of the last pass is strictly controlled at 880℃, and a reduction rate of 35% is applied in this pass to retain a high-density deformation dislocation network inside the billet. After forging, when the surface temperature of the forging is 840℃, the forging is steadily immersed in the pre-prepared quenching tank. During the moment of immersion and the high-temperature cooling stage, the flow rate of the circulating pump in the quenching tank is set to 0.25m / s. The surface temperature of the forging is monitored in real time by a temperature measurement system. When the surface temperature drops to 360℃, the flow rate of the circulating pump is switched instantly and maintained at 1.8m / s. When the system determines that the core temperature of the forging has dropped to 250℃, the forging is lifted out of the quenching tank and placed in still air to cool naturally, using the residual heat in the core that has not been completely dissipated to complete the residual heat self-tempering process. Example 4

[0033] This embodiment provides a forging method for a 90kN-class high-performance bollard for tugboats, including the following steps: 77.2 parts by weight of industrial deionized water were injected into a quenching tank equipped with mechanical stirring, and the temperature control system was turned on to heat it to 45°C. Under a stirring speed of 400 rpm, 10.0 parts by weight of film-forming agent A3, 6.0 parts by weight of film-forming auxiliary agent B3, 0.8 parts by weight of sodium molybdate dihydrate, 3.5 parts by weight of polyethylene glycol 400, and 2.5 parts by weight of triethanolamine were added slowly in sequence. After complete dissolution to form a homogeneous liquid, the temperature of the main body of the quenching medium in the tank was kept constant at 45°C for later use. Select 42CrMo alloy structural steel billets with an effective cross-sectional thickness of 300mm and feed them into a natural gas heating furnace. Heat them to 1150℃ at a heating rate of 100℃ / h and hold them at that temperature for 240 minutes until the core is fully heated. High-temperature billets are forged in multiple passes using a hydraulic forging machine. The final forging temperature of the last pass is strictly controlled at 850℃, and a reduction rate of 25% is applied in this pass to retain a high-density deformation dislocation network inside the billet. After forging, when the surface temperature of the forging is 800℃, the forging is steadily immersed in the pre-prepared quenching tank. During the moment of immersion and the high-temperature cooling stage, the flow rate of the circulating pump in the quenching tank is set to 0.15m / s. The surface temperature of the forging is monitored in real time by a temperature measurement system. When the surface temperature drops to 340℃, the flow rate of the circulating pump is switched instantly and maintained at 1.2m / s. When the system determines that the core temperature of the forging has dropped to 200℃, the forging is lifted out of the quenching tank and placed in still air to cool naturally, using the residual heat in the core that has not been completely dissipated to complete the residual heat self-tempering process.

[0034] Comparative Examples 1-5: Comparative Example 1: Compared with Example 1, the difference is that the conventional heat treatment process is adopted, which involves air cooling to room temperature after forging, reheating in the furnace to 860°C for austenitization, quenching with pure quenching oil, and finally tempering in a high-temperature tempering furnace. All other aspects are the same.

[0035] Comparative Example 2: Compared with Example 1, the difference is that polyethylene glycol 400 is not added in the preparation of the quenching medium, and its corresponding weight part is made up with industrial deionized water, while the rest are the same.

[0036] Comparative Example 3: Compared with Example 1, the difference is that triethanolamine is not added in the preparation of the quenching medium, and its corresponding weight parts are made up with industrial deionized water, while the rest are the same.

[0037] Comparative Example 4: Compared with Example 1, the difference is that the flow rate of the circulating pump in the quenching tank is constantly set to 0.8 m / s during the water immersion and the entire quenching and cooling stage, without any sudden change in flow rate. All other aspects are the same.

[0038] Comparative Example 5: Compared with Example 1, the difference is that in the forging process, the final forging temperature of the last pass is controlled at 950°C, and only a 10% reduction rate is applied in this pass, while the rest are the same.

[0039] Test Examples 1-5: Test Example 1: This test case verifies the actual cooling mechanism under the synergistic effect of composition components and process parameters by measuring the thermal conduction behavior of the surface and core of the test block through temperature inversion.

[0040] A 35CrMo alloy structural steel with an effective cross-sectional thickness of 300mm was used as an experimental specimen. Two blind holes with a diameter of 6mm were drilled at the center height of the side of the specimen, with depths of 5mm and 150mm from the surface of the specimen, respectively, to represent the near-surface layer and the core position.

[0041] Insert the K-type armored thermocouple into the bottom of the blind hole, seal the hole with refractory putty, and connect the thermocouple tail end to a multi-channel data acquisition instrument with the sampling frequency set to 100Hz.

[0042] According to the process parameters of each embodiment and comparative example, the test block with thermocouple is sent into the heating furnace for austenitization and heat preservation, and the final forging is completed on the hydraulic forging machine. When the surface temperature of the test block drops to the set water immersion temperature, the test block is steadily immersed in the corresponding quenching medium.

[0043] Cooling is performed according to the set flow rate program, and the data acquisition instrument synchronously records the temperature and time data of the test block throughout the quenching process. Data acquisition is terminated when the core temperature drops to 200℃.

[0044] Import the temperature time series data into the analysis software, obtain the continuous cooling rate through first-order differential calculation, and extract the maximum cooling rate and average cooling rate within a specific temperature range.

[0045] Table 1. Test results of near-surface cooling rate in specific temperature ranges for each scheme

[0046] According to Table 1 and Figure 1 The test data for Examples 1 to 4 show that the maximum cooling rate remained between 79.1°C / s and 92°C / s in the high-temperature range of 800°C to 500°C; while in the low-temperature range of 350°C to 200°C, the average cooling rate decreased to approximately 5°C / s. This segmented cooling rate characteristic is consistent with the expected heat transfer design. In the high-temperature stage, Comparative Example 1, treated with conventional quenching oil, achieved a maximum cooling rate of only 31.24°C / s, significantly limiting the heat transfer efficiency of large-section workpieces. Comparative Example 2, by removing polyethylene glycol 400 from its formulation, reduced the maximum cooling rate in the high-temperature zone to 45.71°C / s. This data indicates that the lack of the microplasticizing effect of polyethylene glycol 400 on the PAG crosslinking network resulted in a polyether film with excessive rigidity formed at high temperatures, failing to adhere tightly to the metal surface to suppress vapor film formation, thus causing the initial heat transfer efficiency to fall short of the levels of the examples.

[0047] When entering the low-temperature cooling stage from 350℃ to 200℃, the circulation flow rate switched from low to high. In this example, the cooling rate not only did not increase with the enhancement of forced convection, but instead showed a significant decreasing trend. Compared to Comparative Example 3 without triethanolamine, after performing the same flow rate increase operation, the average cooling rate in the low-temperature region reached as high as 22.37℃ / s. This difference indicates that, in the absence of triethanolamine as a competing agent for hydrogen bond reconstruction, the original polymer film structure maintained high stability. Increasing the flow rate at this point mainly enhanced the forced convection heat transfer caused by physical scouring, resulting in a higher cooling rate in the low-temperature region, which is detrimental to the control of phase transformation stress. In this example, due to the participation of triethanolamine, the high-flow-rate shearing action promoted the high hydration and large-volume swelling of the polymer film, forming a viscous, water-rich gel barrier layer on the metal surface, changing the contact state of the solid-liquid interface, thereby effectively slowing down the heat transfer process.

[0048] For Comparative Example 4, which uses a constant flow rate of 0.8 m / s throughout, the cooling rates in both the high-temperature and low-temperature sections are at a moderate level. This verifies that relying solely on the chemical formulation without introducing a variable flow rate process is insufficient to meet the differentiated cooling requirements of the workpiece in different phase transition temperature ranges. The macroscopic performance of the temperature measurement data confirms the actual impact of the synergistic effect of the medium composition and specific operating conditions on the heat transfer process.

[0049] Test Example 2: This test case aims to convert the experimentally collected temperature sequence into the surface heat transfer coefficient through nonlinear inverse heat conduction numerical calculation, thereby quantitatively characterizing the heat transfer efficiency of the quenching medium under different temperature ranges and flow field interventions.

[0050] The experimental object was a 35CrMo alloy structural steel specimen with a thickness of 300mm. The real-time temperature-time raw data collected by the thermocouple at a distance of 5mm from the surface in Test Example 1 was used as the input boundary condition for the reverse heat conduction calculation.

[0051] Establish a database of thermal properties parameters for this steel grade, including thermal conductivity as a function of temperature. ), specific heat capacity ( ) and density ( The database of thermal property parameters of steel grades is imported into a discrete calculation program based on the numerical inversion algorithm (IHCP).

[0052] The calculation step size is set to be consistent with the experimental sampling frequency. The heat transfer equation inside the test block is implicitly solved by the finite difference method, and the heat flux density of the metal surface at each instantaneous temperature is calculated.

[0053] According to Newton's law of cooling, dividing the instantaneous heat flux density by the temperature difference between the surface and the quenching medium yields the surface heat transfer coefficient that varies with surface temperature. ).

[0054] For Example 1 and Comparative Examples 2, 3, and 4, we focused on extracting and comparing the characteristic heat transfer coefficient values ​​of the surface temperature range of 800°C to 650°C (corresponding to the initial stage of film formation) and the range of 350°C to 250°C (corresponding to the flow rate switching period).

[0055] Table 2. Calculation results of surface heat transfer coefficient at different surface temperature nodes

[0056] According to Table 2 and Figure 2 The heat transfer coefficient evolution data and the aforementioned inverted heat transfer coefficient evolution trend verify the heat transfer control mechanism of the present invention within a specific temperature range. During the high-temperature film formation stage from 800℃ to 650℃, the inverted heat transfer coefficient of Example 1 was recorded as 4862.4 (W / (m²)) at 750℃. 2·K), compared to 2145.6 (W / (m)) in Comparative Example 2. 2 The K)) exhibits significant advantages. This numerical difference indicates that the introduction of polyethylene glycol 400 into the composition significantly improves the physical morphology of the polyether film at high temperatures by plasticizing the PAG polymer chains, allowing the medium to enter the nucleation boiling stage earlier and thus providing a significantly enhanced heat transfer intensity in the initial cooling phase. This phenomenon is particularly important for large-section bobbin forgings, as it ensures rapid heat dissipation from the core, providing the necessary thermodynamic conditions for subsequent microstructural transformation.

[0057] When the cooling process entered the low-temperature region below 350°C, the trend of the experimental data revealed the crucial role of the synergy between the components and the flow field. After implementing the flow rate switching operation, the heat transfer coefficient of Example 1 at 300°C remained at 1145.7 (W / (m²)). 2 The heat transfer coefficient of the control group (specifically, the control group lacking triethanolamine) was at a lower level, while that of the control group (specifically, the control group lacking triethanolamine) increased to 6842.3 W / (m³) at the same flow rate. 2 According to the mechanism design of this scheme, the low heat transfer characteristics exhibited by the embodiment in the low-temperature region are due to the hydrogen bond competition between triethanolamine and PAG ether bonds under strong shear force, which induces macroscopic water absorption and swelling of polymer segments, thickening the thermal resistance layer at the solid-liquid interface. This change in the solid-liquid interface state hinders convective heat dissipation from the metal surface, allowing the workpiece to pass through the martensitic phase transformation region in a near-quasi-isothermal manner.

[0058] For Comparative Example 4, which uses a constant flow rate throughout, the heat transfer coefficient decreases linearly with decreasing temperature due to the lack of specific chemical component intervention, making it impossible to achieve the differentiated heat transfer characteristics of high-temperature rapid cooling and low-temperature slow cooling required by this process. These physical quantities, obtained from measured temperature inversion, demonstrate the technical feasibility of controlling the metal phase transformation process by adjusting the boundary layer heat transfer coefficient through chemical composition.

[0059] Test Example 3: This test case aims to verify the actual effect of the process combination on strengthening and toughening the microstructure of thick cross-section metals by sampling and testing the core region of the tie rod forging, especially to evaluate the synergistic contribution of the dislocation network generated by deformation and the segmented cooling control to the core parameters.

[0060] Selected forgings from each batch that had undergone heat treatment and cooled to room temperature, and longitudinally cut rod-shaped blanks at 1 / 2R of the effective cross-section of the forging (approximately 150mm from the surface) using a deep hole drill. The sampling process avoided shrinkage cavities and porous areas at the ends of the forgings to ensure the representativeness of the test data.

[0061] The cut blanks are processed into proportional specimens conforming to GB / T228.1 standard. The specimen diameter is set to 10 mm and the gauge length is 50 mm for room temperature tensile testing.

[0062] Simultaneously process 10mm×10mm×55mm standard Charpy V-notch specimens conforming to GB / T229 standard for low-temperature impact testing.

[0063] The yield strength of the specimen was determined using a microcomputer-controlled electronic universal testing machine. ) and tensile strength ( ), and record the elongation after fracture ( ).

[0064] The samples were subjected to impact tests at -40℃ using a low-temperature impact testing machine. The average value of three samples in each group was taken as the impact energy of the batch. The final measurement results.

[0065] Table 3. Test results of macroscopic mechanical properties of the core of forgings in each embodiment and comparative example.

[0066] According to the experimental data shown in Table 3, Examples 1 to 4 maintained an impact energy of over 55 J at -40℃ while maintaining a yield strength above 680 MPa, reflecting a good balance of strength and toughness in the core structure. This performance is directly related to deformation control during the forging stage and the subsequent segmented cooling process. The examples induced a large accumulation of dislocations within the austenite by applying a large reduction rate at a temperature slightly above the phase transformation point. Rapid cooling in the high-temperature zone locked these dislocation networks, providing high-density active sites for heterogeneous nucleation in the medium- and low-temperature zones. In contrast, Comparative Example 5, due to its higher final forging temperature and a reduction rate of only 10%, lacked sufficient deformation-induced defects in the core, resulting in a final yield strength of only 552.4 MPa and a corresponding decrease in impact energy. This demonstrates that relying solely on chemical composition without the accumulation of deformation energy is insufficient to achieve the desired fine-grain strengthening effect.

[0067] As can be seen from the data in Comparative Example 1, the impact energy of the core of the forging treated with traditional quenching and tempering process is as low as 22.1 J. The cooling rate of large-section steel in conventional quenching oil is limited by the physical heat transfer limit, and the core cooling curve usually passes through the ferrite or pearlite transformation zone, resulting in a coarse microstructure. In this example, by introducing polyethylene glycol 400 and controlling the flow field, the interfacial heat transfer efficiency was improved at high temperatures, successfully achieving a strengthened microstructure dominated by bainite in the core. Although Comparative Example 3 achieved a yield strength of 705.1 MPa through rapid cooling, its impact energy was only 28.4 J. This coexistence of high strength and low toughness indicates that the lack of a buffering effect of triethanolamine on heat transfer in the low-temperature region led to the ineffective release of phase transformation stress, inducing microcracks or high residual tensile stress within the microstructure. This data comparison confirms that the linkage between chemical composition adjustment and variable flow rate conditions plays an important role in improving the toughness of thick-section metals while ensuring strength.

[0068] Test Example 4: This test case mainly uses non-destructive testing methods and blind hole stress release tests to evaluate the ability of different cooling control schemes to alleviate phase transformation stress in large-volume solid metals, and to verify the actual effect of the medium formulation in suppressing microcracks on the workpiece surface and regulating the properties of the residual stress field.

[0069] The experimental subjects were full-size solid 90kN-class high-performance bollard forgings produced in Examples 1 to 4 and Comparative Examples 1 to 5. All tests were conducted after the forgings had been completely cooled to room temperature and left to stand for 24 hours.

[0070] An ultrasonic flaw detector, in conjunction with a magnetic particle flaw detector, was used to perform 100% surface and near-surface defect scanning on each batch of forgings. The proportion of workpieces found to have microcracks was statistically analyzed and recorded, and the microcrack detection rate of the batch was calculated.

[0071] At three characteristic locations on the surface of the cylindrical forging, namely the upper end, middle part, and root of the variable cross-section, the oxide scale on the surface is removed using a grinding machine until the metallic luster is exposed, and then degreasing is performed with anhydrous ethanol.

[0072] Macroscopic residual stress was measured using the blind hole method. Special strain rosettes were attached to the three treated locations and connected to a static strain gauge for initial zeroing. A blind hole with a diameter of 2.0 mm and a depth of 2.0 mm was drilled at the center of the strain rosette using a special drilling device, and the anisotropic micro-strain data generated by stress release around the hole were recorded.

[0073] Based on the strain release and the material's elastic modulus and Poisson's ratio, the maximum principal stress values ​​at each measuring point are calculated. The algebraic average of the maximum principal stresses at the three measuring points is taken as the representative surface residual stress of this batch of forgings. In the data record, tensile stress is defined as positive (+) and compressive stress as negative (-).

[0074] Table 4. Detection rate of microcracks and test data of macroscopic surface residual stress in forgings for each scheme.

[0075] According to the test data in Table 4, the residual stress distribution on the surface of the forging is closely related to the phase transformation kinetics control at the end of cooling. Large-section steel undergoes significant volumetric expansion in the martensitic or lower bainitic phase transformation zone below 350℃. The significant temperature gradient between the surface and the core not only generates thermal stress but also leads to asynchronous martensitic / bainitic phase transformation. The superposition of these two factors easily forms destructive residual tensile stress on the surface. The test results of Examples 1 to 4 show that the average principal stress on the surface is stable within the compressive stress range of -162.75 MPa to -210.38 MPa, and the microcrack detection rate is zero. Combined with the aforementioned temperature inversion test, it can be found that this scheme triggers the water absorption and swelling thickening of the polymer film in the low-temperature region through variable flow rate, weakening the heat transfer efficiency of the solid-liquid interface and establishing a quasi-isothermal cooling environment for thick and large sections. This heat transfer mechanism allows the phase transformation expansion of the core and the surface contraction to compensate each other over time, resulting in residual compressive stress on the surface when cooling is complete. This effectively improves the fatigue resistance of forgings under alternating loads.

[0076] Comparative Example 3, lacking triethanolamine, exhibited a macroscopic residual stress of +684.95 MPa, along with a microcrack detection rate of 18.62%. During actual flaw detection, these microcracks were observed to be primarily concentrated in stress concentration areas such as the root of the variable cross-section. This data reflects that, in the absence of a competing hydrogen bond remodeling agent, even with the circulation pump flow rate increased to 1.5 m / s, the polymer film adhering to the workpiece surface remained in a rigid contraction state, failing to undergo effective hydration and thickening. The enhanced convective heat transfer resulting from the high flow rate led to rapid surface cooling and martensitic hardening, followed by phase transformation expansion in the core. The resulting internal tensile stress exceeded the yield limit of the surface structure, which had already lost some plastic deformation capacity, thus inducing surface cracking. Furthermore, Comparative Example 4, maintaining a constant flow rate throughout, measured a tensile stress of +412.37 MPa. This indicates that relying solely on the natural heat transfer attenuation of the quenching medium at low flow rates is insufficient to balance the differences in thermal inertia within thick forgings. Specific chemical compositions, in conjunction with changes in shear force in fluid dynamics, are required to alter the heat transfer state at the interface within the target temperature range. Surface mechanical properties and flaw detection statistics obtained from testing validate, from an engineering service perspective, the synergistic regulation of flow field intervention and chemical composition in suppressing quenching cracking.

[0077] Test Example 5: This test case mainly monitors the time span and power consumption in the actual production process to evaluate the manufacturing efficiency and economy of different process combinations in the actual workshop environment, and verifies the comprehensive energy consumption performance of the coupled deformation heat treatment and variable flow rate quenching scheme in the mass production of large parts.

[0078] The experimental subjects were the entire manufacturing batches of the 90kN-class high-performance bollard forgings involved in Examples 1 to 4 and Comparative Examples 1 to 5. The test scope covered the complete processing flow from steel ingot heating, forging, quenching to tempering and unloading.

[0079] Actual operating data is extracted from the three-phase power quality analyzer and smart meter nodes configured on the production line. The monitoring equipment mainly includes austenitizing heating furnace, hydraulic forging machine, quenching tank circulating water pump system and high temperature tempering furnace.

[0080] Record the actual time consumed at each process stage for each batch. The total manufacturing cycle is calculated from the moment the forging blank is heated in the furnace to the moment it is finally tempered and removed from the furnace. Non-process waiting time caused by workshop crane scheduling is deducted during the calculation.

[0081] The energy consumption of a single forging is statistically analyzed in segments during the heating and forging stage, the quenching medium circulation stage, and the tempering stage. The total energy consumption is divided by the actual net weight of the batch of forgings to calculate the energy consumption index per ton (kWh / t).

[0082] Summarize the time and energy consumption data. For comparative examples where residual stress was too high or microstructure defects were found in the previous tests, record the additional stress-relief tempering time and corresponding energy consumption required to meet the factory technical requirements.

[0083] Table 5. Calculation results of comprehensive manufacturing cycle and energy consumption per ton for each forging scheme

[0084] According to the data calculated in Table 5, different process paths show significant differences in actual production cycle and energy consumption. The total manufacturing cycle of Examples 1 to 4 averages around 28.5 hours, with total energy consumption per ton ranging from 538 to 552 kWh / t. In contrast, Comparative Example 1, which uses a conventional offline quenching process, takes 45.2 hours and consumes as much as 876.5 kWh / t. In actual workshop operations, if large-section forgings are cooled to room temperature and then re-furnace for austenitization, a long period of heat treatment is often required to prevent thermal stress cracking caused by the temperature difference between the inside and outside. This results in significantly higher energy consumption during the heating stage of Comparative Example 1. The example scheme utilizes the residual heat from forging for quenching, connecting the forming process with the phase transformation heat treatment, thus eliminating the energy consumption of secondary heating.

[0085] Actual calculation data shows that the microstructure and stress state established during the quenching and cooling stage directly affect the resource input of the subsequent tempering process. In Comparative Example 3, due to the absence of triethanolamine, a high residual tensile stress formed on the surface after quenching. To prevent delayed cracking of the high-stress workpiece during transfer, it was loaded into the furnace as soon as possible after quenching, and the holding time for stress-relief tempering was appropriately extended. This increased the tempering energy consumption of Comparative Example 3 to 349.6 kWh / t, and extended the total cycle to 34.7 hours. The Example, however, utilizes the flow field frequency conversion and dielectric film hydration and swelling mechanism to induce residual compressive stress on the surface at the end of quenching, allowing the tempering process to focus on simple hardness adjustment and reducing the ineffective time spent in the high-temperature furnace. Although the Example increased the operating frequency of the circulating pump in a specific temperature range, resulting in slightly higher circulating pumping energy consumption than Comparative Example 1 (approximately 15.8 kWh / t vs. 8.5 kWh / t), this increased energy consumption accounts for a very small percentage of the total energy consumption. The comparison of the above energy consumption and time data confirms that a reasonable match between chemical media and fluid dynamics conditions can effectively shorten the manufacturing period and reduce energy consumption in the heat treatment process while ensuring the mechanical properties of forgings.

Claims

1. A forging method for a 90kN-class high-performance bollard for tugboats, characterized in that, Includes the following steps: A quenching medium is prepared in a quenching tank. The quenching medium is composed of 77.2-88.2 parts by weight of industrial deionized water, 6.0-10.0 parts by weight of film-forming agent A, 3.0-6.0 parts by weight of film-forming auxiliary agent B, 0.3-0.8 parts by weight of sodium molybdate dihydrate, 1.5-3.5 parts by weight of polyethylene glycol 400, and 1.0-2.5 parts by weight of triethanolamine. The quenching medium is then heated to a constant temperature. The alloy structural steel billet is heated and held at a temperature until the core of the alloy structural steel billet is thoroughly heated to obtain a high-temperature billet. The high-temperature billet is forged in multiple passes, and the reduction rate and final forging temperature are controlled in the last pass to obtain the forging. The forging is pre-cooled in air to a preset first temperature, and then immersed in the quenching medium for the first stage of cooling, while the flow rate of the circulating pump in the quenching tank is controlled to be maintained at the first circulation flow rate. During the first stage of cooling, when the surface temperature of the forging drops to a preset second temperature, the flow rate of the circulating pump is switched and maintained at the second circulation flow rate for the second stage of cooling. During the second stage of cooling, the core temperature of the forging drops to the outlet water temperature. The forging is then lifted out of the quenching tank and allowed to cool naturally in still air. The residual sensible heat in the core of the forging is used to complete the residual heat self-tempering.

2. The forging method for a 90kN-class high-performance bollard for a tugboat according to claim 1, characterized in that, The alloy structural steel billet is 35CrMo alloy structural steel or 42CrMo alloy structural steel with an effective cross-sectional thickness of 300-320mm. The heating rate of the alloy structural steel billet is 80-120℃ / h, and the target heating temperature is 1150-1200℃.

3. The forging method for a 90kN-class high-performance bollard for a tugboat according to claim 1, characterized in that, The preset first temperature is 800-840℃, and the first circulation flow rate is 0.15-0.25m / s; The preset second temperature is 340-360℃, and the second circulation flow rate is 1.2-1.8m / s.

4. The forging method for a 90kN-class high-performance bollard for a tugboat according to claim 1, characterized in that, The raw materials for preparing the film-forming agent A include, by weight: 1,2-Propanediol: 0.8-1.2 parts; Potassium hydroxide: 0.3-0.4 parts; Ethylene oxide: 68-85 parts; Propylene oxide: 90-112 parts; Glacial acetic acid: 0.35-0.45 parts.

5. The forging method for a 90kN-class high-performance bollard for a tugboat according to claim 4, characterized in that, The preparation method of the film-forming agent A includes the following steps: Add the 1,2-propanediol and the potassium hydroxide to a high-pressure reactor, and then introduce nitrogen gas to replace the air in the high-pressure reactor in a sealed manner. The high-pressure reactor is heated to 110-130℃, the reaction pressure is controlled at 0.3-0.5MPa, and the mixture of ethylene oxide and propylene oxide is continuously added dropwise. After the addition is complete, the reaction is continued at a constant temperature of 110-130℃ and a pressure of 0.3-0.5MPa until the pressure inside the high-pressure reactor no longer decreases; The high-pressure reactor is cooled to 70-90°C, and then glacial acetic acid is added to neutralize it. Unreacted residual monomers are removed under vacuum conditions to obtain the film-forming agent A.

6. The forging method for a 90kN-class high-performance bollard for a tugboat according to claim 1, characterized in that, The raw materials for preparing the film-forming agent B include, by weight: 1,2-Propanediol: 0.8-1.2 parts; Potassium hydroxide: 0.08-0.12 parts; Ethylene oxide: 11-17 parts; Propylene oxide: 14.5-22.5 parts; Glacial acetic acid: 0.09-0.13 parts.

7. A forging method for a 90kN-class high-performance bollard for a tugboat according to claim 6, characterized in that, The preparation method of the film-forming agent B includes the following steps: Add the 1,2-propanediol and the potassium hydroxide to a high-pressure reactor, and then introduce nitrogen gas to replace the air in the high-pressure reactor in a sealed manner. The high-pressure reactor is heated to 110-130℃, the reaction pressure is controlled at 0.3-0.5MPa, and the mixture of ethylene oxide and propylene oxide is continuously added dropwise. After the addition is complete, the reaction is continued at a constant temperature of 110-130℃ and a pressure of 0.3-0.5MPa until the pressure inside the high-pressure reactor no longer decreases; The high-pressure reactor is cooled to 70-90°C, and then glacial acetic acid is added to neutralize it. Unreacted residual monomers were removed under vacuum conditions to obtain the film-forming agent B.

8. The forging method for a 90kN-class high-performance bollard for a tugboat according to claim 1, characterized in that, The operation of preparing the quenching medium in the quenching tank includes: The industrial deionized water is injected into the quenching tank equipped with mechanical stirring and heated to 43-47°C; At a stirring speed of 300-500 rpm, the film-forming main agent A, the film-forming auxiliary agent B, the sodium molybdate dihydrate, the polyethylene glycol 400, and the triethanolamine are added sequentially to dissolve and form a homogeneous liquid.

9. A forging method for a 90kN-class high-performance bollard for a tugboat according to claim 1, characterized in that, When the high-temperature billet is forged in multiple passes, the reduction rate applied in the last pass is controlled to be 25%-35%, and the final forging temperature is 850-880℃.

10. A forging method for a 90kN-class high-performance bollard for a tugboat according to claim 1, characterized in that, The quenching medium is heated to a constant temperature of 43-47℃, and the outlet water temperature is 200-250℃.

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