460mpa grade or above high strength and toughness thick wall forging ring, preparation method and application thereof

Abstract

This invention relates to a high-strength and high-toughness forged ring with a large wall thickness of 460MPa or above, its preparation method, and its application. It belongs to the field of forging technology and solves the problems of poor impact toughness in the core of forged rings with a wall thickness ≥100mm in the prior art, and the difficulty in achieving both high strength and excellent welding performance. The method includes the following steps: S1: Billet preparation, selecting a billet with the following chemical composition by weight percentage: C 0.08-0.12%, Si 0.10-0.20%, Mn 1.00-1.20%, Ni 1.0-1.4%, Mo 0.2-0.4%, V 0.02-0.05%, S<0.001%, P<0.006%, with the remainder being Fe and unavoidable impurities; S2: Forging the forged ring, forging the billet into a forged ring of the required size, wherein the wall thickness of the forged ring is ≥100mm; S3: Post-forging pretreatment; S4: Heat treatment, sequentially quenching, two-phase quenching, and tempering of the pretreated forged ring; S5: Finishing. This method enables the preparation of high-strength, high-toughness, thick-walled forged rings for shipbuilding, offshore platforms, or engineering machinery applications.

Description

Technical Field

[0001] This invention relates to the field of forging technology, and in particular to a high-strength and high-toughness forging ring with a wall thickness of 460MPa or higher, its preparation method, and its application. Background Technology

[0002] Forged rings, as key load-bearing components, are widely used in high-end equipment in fields such as nuclear power, hydropower, marine engineering, and shipbuilding. Their performance requirements include high strength, high toughness, good homogeneity, and weldability. With the development of larger equipment, the demand for forged rings with a wall thickness of 100mm or more is increasing, which places higher demands on the strength-toughness matching and the uniformity of core performance of forged rings.

[0003] Currently, existing forged ring manufacturing technologies include Chinese patent CN112251574A, which discloses a method for manufacturing a high-performance forged ring for tank trucks, with a tensile strength greater than 550 MPa, a yield strength greater than 400 MPa, and an elongation of not less than 21%; and Chinese patent CN112251572A, which discloses a method for manufacturing a high-performance wind turbine bearing cage forging, with a yield strength greater than 390 MPa, a tensile strength of 530-700 MPa, and a low-temperature impact energy of not less than 27 J at 0℃. All of these technologies employ conventional quenching and tempering heat treatment processes.

[0004] However, the aforementioned existing technologies mainly target forgings with a strength level of approximately 400 MPa, and do not address higher strength requirements such as 460 MPa and above. Furthermore, for thick-walled forging rings with a wall thickness ≥ 100 mm, conventional quenching and tempering heat treatment easily leads to the formation of coarse-grained bainite structures due to the slow cooling rate of the core, resulting in a significant decrease in core impact toughness, making it difficult to simultaneously achieve high strength, high toughness, and excellent weldability. In addition, the aforementioned existing technologies have a high carbon content (C ≥ 0.13%), resulting in a high carbon equivalent, which adversely affects weldability. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a high-strength and high-toughness forged ring with a large wall thickness of 460MPa or above, its preparation method, and its application, so as to at least solve at least one of the problems in the prior art, such as poor impact toughness of the core of forged rings with a wall thickness ≥100mm and difficulty in achieving both high strength and excellent welding performance.

[0006] On one hand, embodiments of the present invention provide a method for preparing a high-strength, high-toughness, thick-walled forging ring with a strength of 460 MPa or higher, comprising the following steps: S1: Raw material preparation. Select raw materials with the following chemical composition by weight percentage: C 0.08-0.12%, Si 0.10-0.20%, Mn 1.00-1.20%, Ni 1.0-1.4%, Mo 0.2-0.4%, V 0.02-0.05%, S<0.001%, P<0.006%, with the remainder being Fe and unavoidable impurities, of which Cr≤0.10%; S2: Forging ring forging, forging a blank into a forging ring of the required size, wherein the wall thickness of the forging ring is ≥100mm; S3: Post-forging pretreatment, annealing and normalizing the forged ring after forging; S4: Heat treatment, the pretreated forging ring is sequentially quenched, quenched in the two-phase region and tempered. S5: Finishing, which involves precision machining of the heat-treated forged ring.

[0007] Furthermore, in S1, the billet is an electroslag remelted billet.

[0008] Furthermore, in S4: The quenching process is as follows: heat to 900-950℃, hold for 15-20mm / h based on the forging ring wall thickness, and then water cool. The two-phase quenching process is as follows: heat to 820-860℃, hold for 15-20mm / h based on the forging ring wall thickness, and then water cool; The tempering process is as follows: heat to 650-700℃, hold for 10-15mm / h based on the wall thickness of the forging ring, and then air cool.

[0009] Furthermore, in S3: The annealing process is as follows: heat the forged ring that has been cooled to a surface temperature ≤300℃ to 600-650℃, hold it for 15-20mm / h based on the wall thickness of the forged ring, and then air cool it to room temperature; The normalizing process is as follows: heat the annealed forging ring to 900-950℃, hold for 25-30mm / h based on the forging ring wall thickness, and then air cool.

[0010] Furthermore, the billet selected in S1 has a carbon equivalent Ceq ≤ 0.50%, where Ceq = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15.

[0011] Furthermore, in S2, a hydraulic press is used to freely forge the billet into shape through multiple firing cycles.

[0012] On the other hand, embodiments of the present invention provide a high-strength, high-toughness, large-wall-thickness forged ring with a strength of 460 MPa or higher, which is prepared using the method described above.

[0013] Furthermore, the performance of the forged ring meets the following requirements: yield strength ≥ 460 MPa, tensile strength ≥ 600 MPa, elongation after fracture ≥ 20%, and impact energy at -20℃ ≥ 100 J.

[0014] Furthermore, the impact energy of the core of the forged ring at -20℃ is ≥180J.

[0015] The high-strength, high-toughness, and thick-walled forged rings with a strength of 460MPa or higher described above can be applied to the fields of shipbuilding, offshore platforms, or engineering machinery.

[0016] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: 1) This invention controls the carbon content of thick-walled forged rings to 0.08-0.12%, which is about 30% lower than the commonly used 0.13-0.17% carbon content in existing forged rings. The carbon equivalent (Ceq) is ≤0.50%, effectively reducing the sensitivity to cold cracking during welding. Simultaneously, by adding 1.0-1.4% Ni, 0.2-0.4% Mo, and 0.02-0.05% V, solid solution strengthening and precipitation strengthening are used to compensate for the strength loss caused by the reduced carbon content. The measured yield strength of the thick-walled forged ring is 523-568 MPa, and the tensile strength is 624-659 MPa, achieving a strength requirement of 460 MPa or higher while ensuring weldability.

[0017] 2) To address the problem of coarse granular bainite forming in the core and poor toughness in thick-walled forged rings (≥100mm) after conventional quenching and tempering, this invention employs a "quenching + two-phase zone quenching + tempering" QLT process. The two-phase zone treatment introduces a soft ferrite phase into the microstructure, reducing the damage to toughness caused by granular bainite. Actual measurements show that the impact energy of the core of the thick-walled forged ring at -20℃ reaches 203-265J, far exceeding the conventional level (approximately 60-100J) of existing thick-walled forged rings of the same grade, achieving performance uniformity from the surface to the core of the thick-walled forged ring.

[0018] 3) This invention, through a low-carbon composition design combined with QLT process, can reduce the generation of welding cracks, making the strength and toughness of the welded joint essentially the same as the base material. Its welded joint can achieve an impact energy of 175-221J at -20℃, far superior to products manufactured using conventional processes. Its low-temperature toughness meets practical application requirements and is suitable for welding applications in fields such as shipbuilding and offshore platforms.

[0019] 4) This invention adds only one two-phase quenching process to the conventional forging and precision machining processes. No special equipment is required, and it is compatible with existing tempering heat treatment production lines, exhibiting high versatility. The above performance can be achieved using a 12000t hydraulic press and a conventional heat treatment furnace, demonstrating good process scalability.

[0020] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0021] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0022] Figure 1 Metallographic photograph of the core of the forged ring prepared in Example 1 of this invention; Figure 2 Metallographic photograph of the core of the forged ring prepared in Example 2 of this invention; Figure 3 Metallographic image of the core of the forged ring prepared for Comparative Example 1. Detailed Implementation

[0023] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0024] Existing forged ring manufacturing technologies primarily target forgings with strength levels of approximately 400 MPa, employing conventional quenching and tempering heat treatment processes. For thick-walled forged rings with a wall thickness ≥ 100 mm, conventional quenching and tempering heat treatment easily leads to the formation of coarse-grained bainite structures due to slow core cooling rates, resulting in a significant decrease in core impact toughness. Furthermore, existing technologies have high carbon content (C ≥ 0.13%), resulting in a high carbon equivalent, which adversely affects weldability. This invention addresses these technical problems by proposing a high-strength and high-toughness forged ring with a wall thickness of 460 MPa or higher, its manufacturing method, and its applications.

[0025] A specific embodiment of the present invention discloses a method for preparing a high-strength, high-toughness, thick-walled forging ring with a strength of 460 MPa or higher, such as... Figure 1-3 As shown, it includes the following steps: S1: Raw material preparation. Select raw materials with the following chemical composition by weight percentage: C 0.08-0.12%, Si 0.10-0.20%, Mn 1.00-1.20%, Ni 1.0-1.4%, Mo 0.2-0.4%, V 0.02-0.05%, S<0.001%, P<0.006%, with the remainder being Fe and unavoidable impurities; S2: Forging ring forging, forging a blank into a forging ring of the required size, wherein the wall thickness of the forging ring is ≥100mm, for example, 100mm, 120mm, 150mm, 180mm, 200mm, or 250mm. S3: Post-forging pretreatment, annealing and normalizing the forged ring after forging; S4: Heat treatment, the pretreated forging ring is sequentially quenched, quenched in the two-phase region and tempered. S5: Finishing, which involves precision machining of the heat-treated forged ring.

[0026] It should be noted that the chemical composition described in step S1, with the C content controlled within a low range of 0.08-0.12%, aims to reduce the carbon equivalent of the forging ring, thereby ensuring weldability. Since a decrease in C content leads to strength loss, this invention compensates by adding 1.0-1.4% Ni, 0.2-0.4% Mo, and 0.02-0.05% V: Ni primarily improves low-temperature toughness, Mo enhances strength through solid solution strengthening, and V generates precipitation strengthening through the formation of carbonitrides. S and P, as impurity elements, are strictly controlled at S < 0.001% and P < 0.006% to ensure material purity. In step S2, a wall thickness ≥ 100 mm falls into the category of large wall thickness. At this size, conventional heat treatment processes struggle to guarantee the uniformity of core properties.

[0027] The following explains the basis for selecting the parameter ranges in the technical solution of this invention: Carbon content 0.08-0.12%: Carbon is the most effective element for improving strength, but excessive carbon will deteriorate weldability and low-temperature toughness. When the carbon content is below 0.08%, even with the addition of other alloying elements, it is difficult to achieve the strength requirement of 460 MPa or higher; when the carbon content is above 0.12%, the carbon equivalent easily exceeds 0.58, affecting weldability. Therefore, a range of 0.08-0.12% is selected.

[0028] Si content 0.10-0.20%: Si has a deoxidizing effect, but excessive Si will reduce toughness and weldability. This range is lower than that of conventional forged rings (Si 0.15-0.40%), mainly to further improve weldability.

[0029] Mn content 1.00-1.20%: Mn can improve hardenability and strength, but excessive Mn will promote grain growth and reduce toughness. This range is moderate and can be used in combination with low C and high Ni.

[0030] Ni content 1.0-1.4%: Ni is a key element for improving low-temperature toughness and also enhances hardenability. When Ni content is below 1.0%, it is difficult to consistently achieve an impact energy of over 100J at -20℃; when Ni content is above 1.4%, the cost increases significantly and the performance improvement slows down. Therefore, a range of 1.0-1.4% is chosen.

[0031] Mo content 0.2-0.4%: Mo can improve hardenability, produce solid solution strengthening, and suppress temper brittleness. When Mo is below 0.2%, the strengthening effect is not obvious; when Mo is above 0.4%, the cost increases and coarse carbides may form. Therefore, a range of 0.2-0.4% is selected.

[0032] V content 0.02-0.05%: V strengthens the grains by forming V(C,N) precipitates. This range is considered microalloying addition; excessive V will reduce toughness and weldability.

[0033] Regarding the absence of Cr: Cr is a commonly used element to improve hardenability, but it significantly increases the carbon equivalent, impairing weldability. This invention compensates for hardenability with Ni and Mo, eliminating the need for Cr addition, which is one of the key measures to achieve Ceq≤0.50%.

[0034] In practice, the billet is first prepared according to the chemical composition requirements of S1, and a high-purity billet can be obtained using electroslag remelting. The billet is then heated and sent to a hydraulic press for forging, undergoing multiple passes to form a ring. After forging, the ring is cooled to a surface temperature not exceeding 300°C, and then annealed and normalized according to S3 to eliminate forging stress and refine the grain size. Subsequently, heat treatment is performed according to S4: first, quenching is performed in the austenitic region to obtain a bainitic matrix; then, a second quenching is performed in the two-phase region (ferrite + austenite coexistence region) to introduce a certain amount of soft ferrite phase into the microstructure; finally, tempering is performed to eliminate quenching stress and stabilize the microstructure. After heat treatment, precision machining is performed according to S5 to obtain the finished forged ring.

[0035] Compared with existing technologies, the preparation method provided in this embodiment solves the problem of poor toughness in the core of thick-walled forged rings through the synergistic effect of low-C composition design and QLT heat treatment process. Specifically, the low-C design ensures that the carbon equivalent Ceq ≤ 0.50%, giving the forged ring good weldability; the alloying of Ni, Mo, and V compensates for the strength loss caused by the reduction in C; the two-phase quenching in the QLT process introduces a soft ferrite phase, effectively suppressing the damage to toughness caused by granular bainite, thus achieving a balance between high strength, high toughness, and good weldability.

[0036] Preferably, in S1, the billet is an electroslag remelted billet.

[0037] The advantages of using electroslag remelted billets are as follows: the electroslag remelting process can effectively remove non-metallic inclusions from the molten steel, significantly reduce the content of impurity elements such as sulfur (S) and phosphorus (P), and improve the uniformity and density of the ingot structure. For high-toughness forged rings requiring an impact energy ≥100J at -20℃, the purity of the billet is fundamental to ensuring toughness. In this embodiment, the impurity levels of S <0.001% and P <0.006% were achieved through the electroslag remelting process. Therefore, using electroslag remelted billets provides a raw material guarantee for obtaining high and stable impact toughness in thick-walled forged rings.

[0038] Furthermore, in S4: the quenching process is as follows: heating to 900-950℃, for example, heating to 900℃, 910℃, 920℃, 930℃, 940℃, or 950℃, with holding time calculated based on the forging ring wall thickness of 15-20mm / h, for example, based on the forging ring wall thickness of 15mm / h, 16mm / h, 17mm / h, 18mm / h, 19mm / h, or 20mm / h, followed by water cooling; the two-phase quenching process is as follows: heating to 820-860℃, for example, heating to 820℃, 830℃, or 950℃, with holding time calculated based on the forging ring wall thickness of 15mm / h, 16mm / h, 17mm / h, 18mm / h, 19mm / h, or 20mm / h, followed by water cooling; The holding time is calculated based on a forging ring wall thickness of 15-20 mm / h, followed by water cooling. The tempering process is as follows: heat to 650-700℃, for example, heat to 650℃, 660℃, 670℃, 680℃, 690℃, 700℃, and hold for 10-15 mm / h, for example, based on a forging ring wall thickness of 10 mm / h, 11 mm / h, 12 mm / h, 13 mm / h, 14 mm / h, 15 mm / h, followed by air cooling.

[0039] The above process parameters are specifically optimized for forging rings with a wall thickness ≥100mm. The quenching temperature of 900-950℃ is chosen to ensure complete austenitization and full dissolution of alloying elements. The holding time is calculated at 15-20 mm / h; for example, 1.5-2 hours for a 100mm wall thickness. This time ensures core heating while preventing excessive grain growth. The two-phase quenching temperature is selected at 820-860℃. This temperature range is within the coexistence region of ferrite and austenite. By controlling the heating temperature in the two-phase region, the ratio of ferrite to bainite in the microstructure can be adjusted: lower temperatures result in more ferrite, reducing strength; higher temperatures result in less ferrite, weakening the improvement in toughness. Experiments have verified that the 820-860℃ range can significantly improve toughness while maintaining strength. A tempering temperature of 650-700℃ is selected, which falls within the high-temperature tempering range and can obtain a tempered bainitic structure, maintaining a good balance of strength and toughness while eliminating quenching stress. The holding time is calculated at 10-15 mm / h, which is slightly shorter than the holding time for quenching and two-phase quenching because the microstructure transformation is completed faster during tempering than during quenching.

[0040] Furthermore, in S3: the annealing process is as follows: the forged ring cooled to a surface temperature ≤300℃ is heated to 600-650℃, for example, to 600℃, 610℃, 620℃, 630℃, 640℃, or 650℃. The holding time is calculated based on the forged ring wall thickness of 15-20mm / h, for example, based on forged ring wall thicknesses of 15mm / h, 16mm / h, 17mm / h, 18mm / h, 19mm / h, or 20mm / h. The process involves heating the annealed forged ring to 900-950℃, for example, to 900℃, 910℃, 920℃, 930℃, 940℃, or 950℃. The holding time is calculated based on the forged ring wall thickness of 25-30mm / h, for example, based on the forged ring wall thickness of 25mm / h, 26mm / h, 27mm / h, 28mm / h, 29mm / h, or 30mm / h. The ring is then air-cooled.

[0041] The forging process includes a pretreatment step of annealing and normalizing to prepare the microstructure for subsequent QLT heat treatment. Specifically, after the forged ring is cooled to a surface temperature not exceeding 300℃, it is placed in the furnace for annealing. This aims to eliminate residual stress generated during forging and prevent stress accumulation leading to cracking. The annealing temperature is selected at 600-650℃, which falls within the low-temperature annealing range, effectively eliminating stress without causing significant microstructure coarsening. After annealing, normalizing is performed by heating to 900-950℃ followed by air cooling. This homogenizes the microstructure and refines the grains, providing a uniform initial microstructure for subsequent quenching. The normalizing holding time is calculated at 25-30 mm / h, slightly longer than the annealing holding time, to ensure sufficient austenitization. It should be noted that the normalizing temperature range (900-950℃) is consistent with the subsequent quenching temperature range. This design ensures that the microstructure after normalizing is similar to that before quenching, which is beneficial for stabilizing quenching quality.

[0042] Furthermore, the billet selected in S1 has a carbon equivalent Ceq ≤ 0.50%, where Ceq = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15.

[0043] Carbon equivalent is an important indicator for evaluating the weldability of steel. This invention controls the carbon equivalent to ≤0.50%, corresponding to a low C (0.08-0.12%) and low Cr (no deliberate addition, only residual levels) composition design. Currently, the carbon equivalent of forged rings with a strength of 460 MPa or higher is typically between 0.60-0.70. This invention significantly reduces the carbon equivalent by lowering the C content and avoiding the addition of Cr. According to the carbon equivalent formula recommended by the International Institute of Welding (IIW), steel with Ceq ≤0.50% has lower cold cracking sensitivity under conventional welding conditions and generally does not require complex preheating and post-weld heat treatment measures. This is of great significance for the manufacture of large welded structural components such as ships and offshore platforms.

[0044] Furthermore, in S2, a hydraulic press is used to freely forge the billet into shape through multiple firing cycles.

[0045] Thick-walled forged rings require significant forging force to ensure complete penetration. In this embodiment, a 12000t hydraulic press is used for forging. Multiple forging passes (e.g., 5, 6, or 7 passes) are performed, each pass including heating, forging, and cooling. Through repeated upsetting and drawing, the as-cast structure is broken up, and internal pores are welded together to obtain a dense forged structure. After forging, the forged ring achieves a grain size of grade 5 or higher, with a microstructure consisting of forged pearlite and ferrite, providing a uniform initial microstructure for subsequent heat treatment.

[0046] Furthermore, the forged ring is used in the fields of ships, offshore platforms, or engineering machinery.

[0047] The common requirements for forged rings in the aforementioned fields are: bearing complex loads, operating in harsh environments (especially low-temperature environments), and requiring extensive welding assembly. The forged ring of this invention possesses a yield strength of 460 MPa or higher, an impact toughness of ≥100 J at -20℃, and excellent weldability with Ceq≤0.50%, perfectly meeting the performance requirements of critical load-bearing forged rings in the shipbuilding, offshore platform, and engineering machinery fields.

[0048] Another specific embodiment of the present invention discloses a high-strength and high-toughness forged ring with a wall thickness of 460MPa or higher, which is prepared by the above-described method.

[0049] Specifically, because the forged ring is prepared using the above method, it has the compositional characteristics of low C, high Ni, and no Cr, as well as the process characteristics of QLT heat treatment, thus possessing both high strength, high toughness, and good weldability.

[0050] Furthermore, the performance of the forged ring meets the following requirements: yield strength ≥ 460 MPa, tensile strength ≥ 600 MPa, elongation after fracture ≥ 20%, and impact energy at -20℃ ≥ 100 J.

[0051] The above performance indicators represent the minimum performance thresholds of this invention. Yield strength ≥ 460 MPa is the definition of "above 460 MPa"; tensile strength ≥ 600 MPa ensures sufficient strength reserve; elongation after fracture ≥ 20% reflects good plasticity; and impact energy ≥ 100 J at -20℃ is the low-temperature toughness requirement, meeting the needs of ships and marine engineering equipment operating in cold sea areas. It should be noted that the actual performance indicators obtained in the embodiments of this invention are significantly higher than the above threshold values.

[0052] Furthermore, the impact energy of the core of the forged ring at -20℃ is ≥180J.

[0053] For thick-walled forged rings, the core is the weakest point during heat treatment, and the impact energy of the core directly reflects the uniformity of the ring's performance. In the embodiments of this invention, the measured impact energy of the core of a 100mm thick-walled forged ring at -20℃ reached 203-265J, which is much higher than the 67J obtained by the conventional quenching and tempering process in the comparative example, fully demonstrating the technical advantages of this invention in improving the toughness of the core of thick-walled forged rings.

[0054] The present invention will be described in more detail below through specific embodiments. These embodiments are merely descriptions of the best implementation of the invention and do not limit the scope of the invention in any way.

[0055] Example 1 This embodiment provides a method for preparing a high-strength, high-toughness, thick-walled forging ring with a strength of 460 MPa or higher, as detailed below: S1: Billet Preparation: Electroslag remelted billet was selected, with the following chemical composition by weight percentage: C 0.08%, Si 0.10%, Mn 1.00%, Ni 1.0%, Mo 0.2%, V 0.02%, S 0.0008%, P 0.005%, with the remainder being Fe and unavoidable impurities. The calculated carbon equivalent (Ceq) is 0.36%.

[0056] S2: Forging of Forged Rings: The billet is freely forged into a ring shape using a 12000t hydraulic press through 6 forging cycles. The wall thickness of the forged ring is 100mm. During the forging process, repeated upsetting and drawing are used to break up the as-cast structure and weld the internal pores. After forging, the grain size reaches level 5 or above.

[0057] S3: Post-forging pretreatment: Heat the forged ring, which has been cooled to a surface temperature ≤300℃, to 600℃ and hold for 5 hours (calculated based on a wall thickness of 100mm), then air cool to room temperature. Then heat the annealed forged ring to 950℃ and hold for 3 hours (calculated based on a wall thickness of 100mm), then air cool.

[0058] S4: Heat treatment: Heat the normalized forging ring to 900℃ and hold for 5 hours based on a wall thickness of 100mm, then water cool; then heat to 820℃ and hold for 5 hours based on a wall thickness of 100mm, then water cool; finally heat to 650℃ and hold for 7 hours based on a wall thickness of 100mm, then air cool.

[0059] S5: Finishing: The heat-treated forged ring is precision machined.

[0060] Example 2 This embodiment provides a method for preparing a high-strength, high-toughness, thick-walled forging ring with a strength of 460 MPa or higher, as detailed below: S1: Billet Preparation: Electroslag remelted billet was selected, with the following chemical composition by weight percentage: C 0.12%, Si 0.18%, Mn 1.20%, Ni 1.4%, Mo 0.4%, V 0.05%, S 0.0007%, P 0.005%, with the remainder being Fe and unavoidable impurities. The calculated carbon equivalent (Ceq) is 0.50%.

[0061] S2: Forging of forged rings: The billet is freely forged into shape using a 12000t hydraulic press in 6 passes, with a ring wall thickness of 100mm. During the forging process, repeated upsetting and drawing are performed to break up the as-cast structure and weld the internal pores, resulting in a grain size of grade 5 or higher after forging.

[0062] S3: Post-forging pretreatment: Heat the forged ring, which has been cooled to a surface temperature ≤300℃, to 650℃ and hold for 6 hours (calculated based on a wall thickness of 100mm), then air cool to room temperature. Then heat the annealed forged ring to 900℃ and hold for 4 hours (calculated based on a wall thickness of 100mm), then air cool.

[0063] S4: Heat treatment: Heat the normalized forging ring to 950℃ and hold for 6 hours based on a wall thickness of 100mm, then water cool; then heat to 860℃ and hold for 6 hours based on a wall thickness of 100mm, then water cool; finally heat to 650℃ and hold for 10 hours based on a wall thickness of 100mm, then air cool.

[0064] S5: Finishing: The heat-treated forged ring is precision machined.

[0065] Example 3 This embodiment provides a method for preparing a high-strength, high-toughness, thick-walled forging ring with a strength of 460 MPa or higher, as detailed below: S1: Billet Preparation: Electroslag remelted billets were selected, with the following chemical composition by weight percentage: C 0.09%, Si 0.20%, Mn 1.18%, Ni 1.4%, Mo 0.3%, V 0.03%, S 0.0008%, P 0.004%, with the remainder being Fe and unavoidable impurities. The calculated carbon equivalent (Ceq) is 0.45%.

[0066] S2: Forging of forged rings: The billet is freely forged into shape using a 12000t hydraulic press in 6 passes, with a ring wall thickness of 100mm. During the forging process, repeated upsetting and drawing are performed to break up the as-cast structure and weld the internal pores, resulting in a grain size of grade 5 or higher after forging.

[0067] S3: Post-forging pretreatment: The forged ring, cooled to a surface temperature ≤300℃, is heated to 600℃ and held for 7 hours based on a wall thickness of 100mm (based on a flow rate of 15-20mm / h, taking 15mm / h as approximately 6.7 hours, but actually taking 7 hours). It is then air-cooled to room temperature. The annealed forged ring is then heated to 910℃ and held for 4 hours based on a wall thickness of 100mm, followed by air cooling.

[0068] S4: Heat treatment: Heat the normalized forging ring to 923℃ and hold for 7 hours based on a wall thickness of 100mm, then water cool; then heat to 840℃ and hold for 7 hours based on a wall thickness of 100mm, then water cool; finally heat to 700℃ and hold for 8 hours based on a wall thickness of 100mm, then air cool.

[0069] S5: Finishing, which involves precision machining of the heat-treated forged ring.

[0070] Comparative Example 1 This comparative example uses a conventional quenching and tempering heat treatment process and is compared with Examples 1-3.

[0071] S1: Raw material preparation: The chemical composition is basically the same as in Example 3: C 0.09%, Si 0.17%, Mn 1.15%, Ni 1.3%, Mo 0.3%, V 0.05%, S 0.0008%, P 0.005%, with the remainder being Fe and unavoidable impurities. Carbon equivalent Ceq = 0.44%.

[0072] S2: Forging of forged rings: The billet is freely forged into shape using a 12000t hydraulic press in 6 passes, with a ring wall thickness of 100mm. During the forging process, repeated upsetting and drawing are performed to break up the as-cast structure and weld the internal pores, resulting in a grain size of grade 5 or higher after forging.

[0073] S3: Post-forging pretreatment: The forged ring cooled to a surface temperature ≤300℃ is heated to 620℃ and held for 6 hours based on a wall thickness of 100mm, then air-cooled to room temperature. Then the annealed forged ring is heated to 917℃ and held for 4 hours based on a wall thickness of 100mm, then air-cooled.

[0074] S4: Conventional quenching and tempering heat treatment: The normalized forged ring is heated to 921℃ and held for 5 hours (based on a wall thickness of 100mm), followed by water cooling; then heated to 660℃ and held for 7 hours (based on a wall thickness of 100mm), followed by air cooling. The difference from the embodiment is that there is no two-phase quenching process; that is, the traditional "quenching + tempering" process is used.

[0075] S5: Finishing: Same as Examples 1-3.

[0076] Comparative Example 2 The chemical composition of this comparative example is basically the same as that of Example 1, except that Ni is not actively added (Ni exists only as a residual element).

[0077] S1: Billet Preparation: Electroslag remelted billets were selected, with the following chemical composition by weight percentage: C 0.08%, Si 0.10%, Mn 1.00%, Ni ≤0.01% (not actively added, only residual level), Mo 0.2%, V 0.02%, S 0.0008%, P 0.005%, with the remainder being Fe and unavoidable impurities. The calculated carbon equivalent, Ceq, is 0.29%.

[0078] S2: Forging of forged rings: Same as in Example 1.

[0079] S3: Post-forging pretreatment: Same as in Example 1.

[0080] S4: Heat treatment: Same as in Example 1.

[0081] S5: Finishing: Same as Example 1.

[0082] Characterization results and analysis Performance tests were conducted on the forged rings prepared in Examples 1-3 and Comparative Examples 1-2, with the core sampling location being the center of the forged ring wall thickness. All performance tests were performed according to relevant national standards, including the impact energy of the center and welded joint at -20℃ (using the Charpy V-notch test, referring to GB / T 2650-2022 standard). The test results are shown in Table 1 below.

[0083] Table 1. Mechanical property test results of the examples and comparative examples

[0084] As can be seen from Table 1: The yield strength of Examples 1-3 is 523-568 MPa, the tensile strength is 624-659 MPa, the elongation after fracture is 23.5-24.5%, and the impact energy at -20℃ is 203-265 J, all of which are significantly higher than the minimum threshold values ​​set by this invention (yield strength ≥ 460 MPa, tensile strength ≥ 600 MPa, elongation after fracture ≥ 20%, impact energy at -20℃ ≥ 100 J).

[0085] In contrast, the -20℃ impact energy of the core of Comparative Example 1 was only 67J, and that of Comparative Example 2 was only 38J, both of which did not meet the requirement of ≥100J. The yield strength (365MPa) and tensile strength (452MPa) of Comparative Example 2 also did not meet the threshold values, indicating that when the Ni content is less than 1.0%, even if the QLT process is used, it is difficult to meet the requirements for strength and low-temperature toughness.

[0086] Furthermore, the impact energy of the welded joints in Examples 1-3 at -20°C was 175-221J, which was much higher than that of Comparative Example 1 (24J) and Comparative Example 2 (7J), indicating that the forging ring of the present invention still maintains good low-temperature toughness after welding.

[0087] Combining metallographic photographs ( Figures 1-3 )analyze: Figure 1 (Example 1) and Figure 2 (Example 2) The core tissue mainly consists of tempered martensite + ferrite, with the ferrite being fine and diffusely distributed; while Figure 3 (Comparative Example 1) contains a large amount of coarse granular bainite in its core microstructure. Granular bainite consists of a ferrite matrix and martensite / austenite islands (MA islands). During deformation, stress concentration easily occurs at the interface between the MA islands and the ferrite matrix, leading to early crack initiation and propagation, resulting in poor toughness. This invention, through two-phase quenching, introduces an appropriate amount of soft ferrite phase into the microstructure, reducing the damage to toughness caused by granular bainite and thus significantly improving impact toughness.

[0088] In summary, this invention ensures a carbon equivalent (Ceq) of ≤0.50% through a low-C composition design (0.08-0.12%), giving the forged ring excellent weldability. The addition of Ni (1.0-1.4%), Mo (0.2-0.4%), and V (0.02-0.05%) compensates for the strength loss caused by the reduced C content, resulting in a measured yield strength of 523-568 MPa and a tensile strength of 624-659 MPa. Furthermore, by employing the QLT heat treatment process, for forged rings with a wall thickness ≥100 mm, a ferrite soft phase is introduced into the core, effectively suppressing the damage to toughness caused by granular bainite. This significantly increases the impact energy at -20℃ from 67 J in conventional quenching and tempering processes to 203-265 J, achieving a balance between high strength, high toughness, and good weldability for forged rings with a wall thickness of ≥460 MPa. This meets the application requirements of high-strength, high-toughness, and thick-walled forged rings in fields such as shipbuilding, offshore platforms, and engineering machinery.

[0089] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a high-strength, high-toughness, thick-walled forging ring with a strength of 460 MPa or higher, characterized in that, Includes the following steps: S1: Raw material preparation. Select raw materials with the following chemical composition by weight percentage: C 0.08-0.12%, Si 0.10-0.20%, Mn 1.00-1.20%, Ni 1.0-1.4%, Mo 0.2-0.4%, V 0.02-0.05%, S<0.001%, P<0.006%, with the remainder being Fe and unavoidable impurities, of which Cr≤0.10%; S2: Forging ring forging, forging a blank into a forging ring of the required size, wherein the wall thickness of the forging ring is ≥100mm; S3: Post-forging pretreatment, annealing and normalizing the forged ring after forging; S4: Heat treatment, the pretreated forging ring is sequentially quenched, quenched in the two-phase region and tempered. S5: Finishing, which involves precision machining of the heat-treated forged ring.

2. The method according to claim 1, characterized in that, In S1, the billet is an electroslag remelted billet.

3. The method according to claim 1, characterized in that, In S4: The quenching process is as follows: heat to 900-950℃, hold for 15-20mm / h based on the forging ring wall thickness, and then water cool. The two-phase quenching process is as follows: heat to 820-860℃, hold for 15-20mm / h based on the forging ring wall thickness, and then water cool; The tempering process is as follows: heat to 650-700℃, hold for 10-15mm / h based on the wall thickness of the forging ring, and then air cool.

4. The method according to claim 1, characterized in that, In S3: The annealing process is as follows: heat the forged ring that has been cooled to a surface temperature ≤300℃ to 600-650℃, hold it for 15-20mm / h based on the wall thickness of the forged ring, and then air cool it to room temperature; The normalizing process is as follows: heat the annealed forging ring to 900-950℃, hold for 25-30mm / h based on the forging ring wall thickness, and then air cool.

5. The method according to claim 1, characterized in that, The billet selected in S1 has a chemical composition with a carbon equivalent Ceq ≤ 0.50%, where Ceq = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15.

6. The method according to claim 1, characterized in that, In step S2, a hydraulic press is used to forge the billet into shape through multiple firing cycles.

7. A high-strength, high-toughness, thick-walled forged ring with a strength of 460 MPa or higher, characterized in that... Prepared using the method described in any one of claims 1-6.

8. The forging ring according to claim 7, characterized in that, The forged ring has the following performance requirements: yield strength ≥ 460 MPa, tensile strength ≥ 600 MPa, elongation after fracture ≥ 20%, and impact energy at -20℃ ≥ 100 J.

9. The forging ring according to claim 8, characterized in that, The core of the forged ring has an impact energy of ≥180J at -20℃.

10. The application of a high-strength, high-toughness, thick-walled forged ring with a strength of 460 MPa or higher, obtained by the preparation method according to any one of claims 1-6, or a high-strength, high-toughness, thick-walled forged ring with a strength of 460 MPa or higher, as described in any one of claims 7-9, characterized in that... The forged ring is used in the fields of ships, offshore platforms or engineering machinery.

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