A high-strength cobalt-nickel-based alloy material and a preparation method thereof

Abstract

The application discloses a high-strength cobalt-nickel-based alloy material, which is composed of C≤0.025wt%, Mn≤0.15wt%, Si≤0.15wt%, P≤0.015wt%, S≤0.010wt%, Cr: 19.00-21.00wt%, Ni: 33.00-37.00wt%, Mo: 9.00-10.50wt%, Ti≤1.00wt%, Fe≤1.00wt% and the balance of Co and inevitable impurities, and the KAM value of the alloy material is 1.87-2.1, and the microhardness is 450-525HV.

Description

Technical Field

[0001] This invention belongs to the field of alloy material preparation technology, specifically relating to a high-strength cobalt-nickel based Co35Ni35Cr20Mo10 alloy and its preparation method. Background Technology

[0002] Co35Ni35Cr20Mo10 alloy, a typical cobalt-nickel-based ultra-high strength and corrosion-resistant alloy, achieves extremely high strength through the synergistic effect of cold deformation and age hardening. It also possesses excellent resistance to corrosion in all environments (including extreme media such as seawater, oil and gas, and bodily fluids), good biocompatibility, and low magnetic permeability. Therefore, it holds an irreplaceable position in high-end technology fields such as aerospace, medical implants, marine engineering, and oil extraction. Typical applications include key fasteners for aero-engines, elastic components for deep-sea exploration equipment, implantable medical devices, and corrosion-resistant instrument components for downhole drilling. These applications all place stringent requirements on the material's high strength, long fatigue life, and excellent corrosion resistance. However, despite the enormous performance potential of this alloy system, its industrial-scale preparation still faces a series of severe technical bottlenecks, resulting in its comprehensive performance not being fully realized and production costs remaining high. Specifically, these bottlenecks manifest in the following aspects:

[0003] 1. This alloy is a typical hot-working sensitive material, with an extremely narrow safe hot-working temperature range. During the hot rolling of ingots or bars, if the actual temperature deviates from its optimal plasticity range, or if the deformation per pass is not properly controlled, cracks are easily induced on the surface of the billet. To eliminate these defects, extensive peeling and grinding operations are often required on the hot-worked billet. This not only significantly reduces the final yield of the material, but any residual microcracks may also become fatigue crack sources during subsequent cold working and even during product service, seriously threatening the safety and lifespan of the components.

[0004] 2. The synergistic effect of cold working and aging strengthening is difficult to fully realize: The strength of this alloy largely depends on the synergistic strengthening mechanism of "cold deformation energy storage" and "aging precipitation". Theoretically, sufficient and uniform cold deformation is a prerequisite for subsequent aging treatment to achieve a several-fold increase in strength. However, under current processes, due to limitations in the initial quality of hot-worked blanks (such as surface microcracks and uneven microstructure), and concerns about the initiation of surface defects (such as scratches and microcracks) during cold drawing, the actual amount of cold deformation that can be applied is often quite conservative. This directly results in the strength of the material after aging treatment only reaching 70%-80% of its theoretical potential, which cannot meet the ultra-high strength requirements of applications such as aerospace fasteners and high-stress springs, thus severely restricting the application expansion of this alloy in cutting-edge fields.

[0005] 3. High overall manufacturing costs hinder industrialization: On the one hand, the main alloying elements such as cobalt and nickel are expensive; on the other hand, the high scrap rate in the aforementioned hot working process, the complexity of the cold working process and the multiple rework processes, as well as the cumbersome post-processing to ensure performance, all contribute to the high overall cost of alloy products. This makes its final cost far higher than that of conventional materials, greatly limiting its large-scale application in the cost-sensitive mid-to-high-end market. Currently, it can only be produced in small batches in a few cost-insensitive fields such as aerospace and medical.

[0006] In summary, while the Co35Ni35Cr20Mo10 alloy perfectly meets the stringent performance requirements of high corrosion, high load, and high cyclic fatigue, existing preparation technologies have significant shortcomings in terms of hot working stability, the synergy between cold working and aging, and overall cost control. This hinders the stable and economical realization of its excellent performance potential, thus impeding its industrialization process. Therefore, there is an urgent need in this field to develop a novel and optimized preparation process that can effectively improve the yield and reduce the overall cost while ensuring the material achieves ultra-high strength, thereby meeting the urgent demand for high-performance, corrosion-resistant, and high-strength materials in various high-end fields. Summary of the Invention

[0007] To overcome the shortcomings of existing technologies, the present invention aims to provide a high-strength cobalt-nickel-based alloy material and its preparation method. The specific technical solution of the present invention is as follows: A high-strength cobalt-nickel-based alloy material, Co35Ni35Cr20Mo10, is provided, with the following composition: C≤0.025wt%, Mn≤0.15wt%, Si≤0.15wt%, P≤0.015wt%, S≤0.010wt%, Cr: 19.00-21.00wt%, Ni: 33.00-37.00wt%, Mo: 9.00-10.50wt%, Ti≤1.00wt%, Fe≤1.00wt%, and the balance being Co and unavoidable impurities. The KAM value of this alloy material is 1.87-2.1, and the microhardness is 450-525 HV. The KAM value is one of the current standards for quantifying local strain (i.e., the degree of fibrosis), and the KAM value directly corresponds to dislocation density. Microhardness is the material's ability to resist local plastic deformation and is directly related to dislocation density.

[0008] Furthermore, the room temperature tensile strength (Rm) of the alloy material is ≥1800 MPa, the room temperature yield strength (Rp0.2) is ≥1800 MPa, and the room temperature elongation (A) is ≥10%. In some embodiments, the room temperature tensile strength of the alloy material is 1850 MPa, 1900 MPa, 1950 MPa, 2000 MPa, 2050 MPa, 2100 MPa, 2150 MPa, 2250 MPa, 2300 MPa, or 2350 MPa; the room temperature yield strength is 1850 MPa, 1900 MPa, 1950 MPa, 2000 MPa, 2050 MPa, or 2100 MPa; and the room temperature elongation is 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, or 14.5%.

[0009] The present invention also provides a method for preparing the aforementioned high-strength cobalt-nickel-based alloy material, comprising the following steps:

[0010] Step S1: Steel Ingot Preparation and Hot Working: A steel ingot with uniform composition is prepared using a dual process of vacuum induction melting and vacuum consumable arc melting. The ingot is then forged and hot rolled.

[0011] Forging: Heating temperature 1150℃, holding time 4 hours, initial forging temperature not lower than 1100℃, final forging temperature not lower than 950℃, forging the steel ingot into a square billet of a certain size. Preferably, the size of the square billet is 40-80mm, which can be 40mm or 50mm or 60mm or 70mm or 80mm.

[0012] Hot rolling of round bars: The square billet after surface cleaning is rolled into an initial round bar with a diameter of Φ1 through multiple passes in one heat. The billet is heated at 1150℃ and held for 1.5 hours. The initial rolling temperature is not lower than 1120℃ and the final rolling temperature is 950~980℃.

[0013] Step S2: Annealing of the rolled bar: The round bar obtained in step S1 is annealed. The annealing process is as follows: holding at 1038℃ for 1.5 hours, followed by water cooling; using a dual melting process of "vacuum induction + vacuum self-consumption" to ensure extremely pure and uniform composition (extremely low levels of impurities such as S and P). High-temperature forging and hot rolling break down the casting structure and refine the grains, combined with annealing at 1038℃, aim to eliminate processing stress and provide a uniform initial structure for subsequent cold deformation.

[0014] Step S3: Rough drawing and solution treatment: The annealed round bar is rough drawn to a diameter of Φ2, and the ellipticity of the bar is controlled to be no more than 0.03mm; then solution treatment is performed. The solution treatment process is: heat treatment at 1045℃ for 4 hours, followed by air cooling.

[0015] Step S4: Multi-pass continuous cold drawing: The solution-treated round bar is subjected to multi-pass continuous cold drawing, with the deformation amount per pass controlled at 12%~16%. Lubricant is uniformly applied before deformation. Preferably, the lubricant can be D-380 type drawing oil produced by Beishan Chemical. Finally, a cold-drawn round bar is obtained. This step introduces extremely high density dislocation entanglement and cellular structure into the material, which makes the strength of the material (especially the yield strength) leapfrog for the first time, providing a large number of nucleation sites for the final precipitation of the strengthening phase.

[0016] Step S5: Aging Treatment: Before aging treatment, the cold-drawn round bar obtained in Step S4 is straightened, polished, and its surface inspected to ensure that there are no defects such as microcracks on the surface. Then, aging treatment is performed. The aging process is as follows: hold at 540℃ for 4 hours, followed by air cooling. Aging is performed at a relatively low temperature (540℃). This is the final step, where supersaturated solid solution elements (especially Ti, and possibly Mo, etc.) precipitate in the form of extremely fine, dispersed strengthening phases (such as γ' phase [Ni3(Ti, Al)], or / and carbides).

[0017] Preferably, in step S1, taking a square billet with a size of 60mm obtained during forging as an example, the total deformation of the hot-rolled circle is controlled at 85-91%.

[0018] Furthermore, in step S3, Φ2 is generally reduced by 2mm from Φ1 in step S1, which can complete the rough drawing and rounding, achieving an ellipticity of ≤0.03mm.

[0019] Preferably, in step S4, the total deformation of the cold-drawn round bar is controlled at 50-55%.

[0020] Furthermore, after step S5, the process also includes precision straightening and polishing of the bar, and / or mechanical property testing before the final product is completed.

[0021] This application utilizes a super solid solution-strengthened Co-Ni-Cr-Mo matrix, combined with extremely high-density dislocations introduced by large deformation cold working, and finally achieves an ultimate balance between strength and plasticity through "pinning and locking" of nanoscale strengthening phases precipitated during low-temperature aging. The process follows a path of constructing an ultra-pure homogeneous alloy → hot working to refine grains → solid solution to obtain a single-phase matrix → large deformation cold drawing to introduce dislocations (first strengthening) → low-temperature aging to precipitate dispersed phases to pin the dislocations (second strengthening). The resulting alloy has a KAM value of 1.87-2.1, a microhardness of 450-525 HV, and exhibits ultra-high strength (≥1800 MPa) while maintaining good plasticity (≥10%). The strengthening strategy combining "deformation + aging" is the key to this alloy's ability to overcome the performance bottlenecks of traditional high-temperature alloys or ultra-high-strength steels. The core points are: 1. This invention explicitly limits the initial rolling temperature to no less than 1120℃ and strictly controls the final rolling temperature to 950~980℃. This design optimizes the temperature window to maintain the alloy in its best plastic state while avoiding deformation in the low-temperature brittle region; 2. By controlling the total hot rolling deformation to a high level of 85%~91% and coordinating appropriate pass arrangements, this invention ensures that the forging microstructure is fully broken down and refined, resulting in a uniform processing flow line microstructure. This uniform deformation avoids stress concentration caused by excessive local deformation or uneven microstructure, thereby mechanistically suppressing the generation of transverse surface cracks and core porosity cracks.

[0022] The beneficial technical effects of this invention are as follows:

[0023] (1) Optimization of hot working process: By controlling a relatively high initial rolling temperature (≥1120℃) and a suitable final rolling temperature (950~980℃) range, and combining it with a total deformation of 85%~91%, the as-cast structure was effectively broken up, the grains were refined, and a uniform processed structure was obtained. At the same time, cracks caused by temperature fluctuations or improper deformation were avoided, providing high-quality billets for subsequent processing. On the surface, trying to "increase the processing temperature" to solve the hot cracking problem seems to be a conceivable direction. However, this is precisely the technical bias or cognitive misconception that has long existed in this field. For ultra-high strength precipitation-strengthened alloys such as Co35Ni35Cr20Mo10, the traditional technical common sense is: in order to prevent grain coarsening, avoid the precipitation of harmful phases and retain the potential for subsequent cold deformation, hot working should be carried out at "the lowest possible temperature" to obtain fine initial grains. This "fear of heat" thinking leads existing processes to tend to carry out risky operations in the temperature range that is too low or even close to the lower limit of alloy plasticity. This is the psychological root and technical reality of the dilemma of "narrow temperature window and easy cracking" in the background technology. This invention, through systematic experiments and analysis, discovered that for this alloy, the risk of cracking caused by "low-temperature brittleness" is far more harmful than the controllable slight grain growth that may occur in a specific higher temperature range. Instead of following the conservative approach of "keeping the temperature as low as possible," this invention takes the opposite approach, actively setting the initial rolling temperature at no less than 1120℃, coupled with a relatively high final rolling temperature of 950~980℃. Its ingenuity lies in: ① It is a combined window of "lower limit of initial rolling temperature + final rolling temperature range," rather than a single temperature point. This ensures that the entire deformation process is within the high plasticity region of the material. ② Choosing 1120℃ instead of 1100℃ or 1080℃ as the lower limit is based on a precise understanding of the alloy's dynamic recrystallization critical temperature and thermoplastic recovery curve. Values ​​below this (such as 1100℃ in Comparative Example 1) are insufficient to completely avoid processing in the low-temperature brittleness region; while excessively high values ​​may lead to overheating. The window of this invention precisely balances "sufficient plasticity" and "controllable microstructure." ③ It successfully resolved the traditional contradiction between "wanting high plasticity (requiring high temperature)" and "fearing coarsening of the microstructure (requiring low temperature)," finding a repeatable process space that can stably produce defect-free billets. It fundamentally eliminated billet cracks and improved the hot working yield from the unstable state of traditional processes to a higher level; providing a defect-free, high-quality billet foundation for subsequent large deformation cold drawing (50-54%).

[0024] (2) Reduction of raw material loss: By adopting a rough drawing and rounding process instead of the traditional peeling after annealing, the ellipticity of the bar is directly controlled within 0.03 mm, significantly reducing raw material loss. For example, if the diameter of a hot-rolled round bar billet is 26.5 mm, and it is peeled to a diameter of 23 mm after annealing, the loss is approximately 24.7%. If the rough drawing and rounding process of this application is used, and the bar is polished from a diameter of 16.2 mm to a diameter of 14.8 mm after cold drawing deformation, the loss is approximately 16.5%.

[0025] (3) Synergistic optimization of cold deformation and aging strengthening: The design of 12%~16% single-pass cold drawing deformation is within the safe window for cold working of this alloy. This not only effectively avoids defects such as tearing and peeling, ensuring a high yield (>90%), but also achieves a total deformation of 50%~54% through multiple passes, uniformly introducing high-density dislocations and twins. This lays a solid foundation for the large-scale and uniform precipitation of nanoscale strengthening phases during aging, thereby stably achieving high strength indicators of Rm≥1800MPa and Rp0.2≥1800MPa, while maintaining good plasticity and toughness. This solves the primary problem of "high cost" in the background technology—by eliminating hot working cracks and scrapping, it significantly reduces raw material loss and overall cost. Attached Figure Description

[0026] Figure 1 This is a metallographic diagram of the structure after solution treatment in step S5 of Example 1.

[0027] Figure 2 Metallographic photograph of the alloy rod prepared in Example 1;

[0028] Figure 3 This is a local orientation difference distribution diagram of the alloy rod prepared in Example 1;

[0029] Figure 4 Metallographic photograph of the alloy rod prepared in Example 2;

[0030] Figure 5 This is a local orientation difference distribution diagram of the alloy rods prepared in Example 2;

[0031] Figure 6 Metallographic photograph of the alloy rod obtained in Example 3;

[0032] Figure 7 The image shows the local orientation difference distribution of the alloy rod prepared in Example 3.

[0033] Figure 8 Metallographic images of alloy rods were prepared for Comparative Example 2;

[0034] Figure 9 The local orientation difference distribution diagram of the alloy rod prepared in Comparative Example 2;

[0035] Figure 10Metallographic images of alloy rods prepared for Comparative Example 3;

[0036] Figure 11 The alloy rods prepared in Comparative Example 3 are shown in the local orientation difference distribution diagram.

[0037] Figure 12 A photograph of the alloy obtained in step S5 of Comparative Example 1. Detailed Implementation

[0038] The technical solutions described above in this application will be explained in detail below through specific embodiments.

[0039] Example 1

[0040] This embodiment provides a method for preparing a high-strength cobalt-nickel based alloy material Co35Ni35Cr20Mo10. The alloy comprises the following components by mass: C=0.001wt%, Mn=0.013wt%, Si=0.005wt%, P=0.004wt%, S<0.001wt%, Cr=20.17wt%, Ni=35.66wt%, Mo=10.11wt%, Ti=0.71wt%, Fe=0.16wt%, with the balance being Co and unavoidable impurities.

[0041] Alloy rods are prepared using the following method:

[0042] Step S1: Forging: Heat the steel ingot with the above composition to 1150℃ and hold for 4 hours. After taking it out of the furnace, forge it. The initial forging temperature is 1140℃, and the final forging temperature is 980℃. Forge it into a 60mm square billet and remove the surface oxide scale and impurities.

[0043] Step S2: Hot rolling to round shape: Heat the 60mm square billet to 1150℃, hold it at that temperature for 1.5 hours, and then perform a single-pass hot rolling to Φ1=26.5mm. The initial rolling temperature is 1140℃ and the final rolling temperature is 970℃.

[0044] Step S3: Annealing treatment: The hot-rolled round bar is annealed by low-temperature loading and heating with the furnace, holding at 1038℃ for 1.5 hours, and then water-cooled after being taken out of the furnace.

[0045] Step S4: Rough drawing and rounding: Rough drawing and rounding the annealed rolled round to Φ2=24mm, controlling the ovality to be no more than 0.03mm;

[0046] Step S5: Solution treatment: The round bar after rough drawing and rounding is subjected to solution treatment. The solution treatment process is to hold at 1045℃ for 4 hours and then air cool after being taken out of the furnace.

[0047] Step S6: Cold drawing deformation: The solution-treated round bar is subjected to multiple consecutive drawing passes. The deformation amounts for each pass are as follows: the first pass draws to Φ3=22mm (deformation approximately 16.0%), the second pass draws to Φ4=20.3mm (deformation approximately 14.9%), the third pass draws to Φ5=18.8mm (deformation approximately 14.2%), the fourth pass draws to Φ6=17.4mm (deformation approximately 14.3%), and the fifth pass draws to Φ73=16.2mm (deformation approximately 13.3%). The total deformation is 54.4%. Subsequently, the cold-drawn round bar is straightened and polished to obtain a cold-drawn round bar with a diameter of Φ8=14.8mm.

[0048] Step S7: Aging Treatment: The straightened and polished bars are subjected to aging treatment at 540℃ for 4 hours, followed by air cooling. Subsequently, they are finely straightened, polished, and the alloy properties are tested. The measured performance data are shown in Table 1.

[0049] Example 2

[0050] Unlike Example 1:

[0051] In step S2, the material is hot-rolled in multiple passes to Φ1=25.5mm, with a final rolling temperature of 975℃.

[0052] In step S4, the rough drawing is rounded to Φ2=23mm;

[0053] In step S6, the drawing process is as follows: the first pass draws to Φ3=21.3mm (deformation approximately 14.2%), the second pass draws to Φ4=19.8mm (deformation approximately 13.6%), the third pass draws to Φ5=18.4mm (deformation approximately 13.6%), the fourth pass draws to Φ6=17.1mm (deformation approximately 13.6%), and the fifth pass draws to Φ7=15.9mm (deformation approximately 13.5%), with a total deformation of 52.2%. After straightening and polishing, the diameter is Φ8=14.5mm.

[0054] Example 3

[0055] Unlike Example 1:

[0056] In step S2, the material is hot-rolled in multiple passes to Φ1=24.5mm, with a final rolling temperature of 975℃.

[0057] In step S4, the rough drawing is rounded to Φ2=22mm;

[0058] In step S6, the drawing process is as follows: the first pass draws to Φ3=20.5mm (deformation approximately 13.2%), the second pass draws to Φ4=19.1mm (deformation approximately 13.2%), the third pass draws to Φ5=17.8mm (deformation approximately 13.1%), the fourth pass draws to Φ6=16.6mm (deformation approximately 13.0%), and the fifth pass draws to Φ7=15.5mm (deformation approximately 12.8%), with a total deformation of 50.4%. After straightening and polishing, the diameter is Φ8=14.1mm.

[0059] Comparative Example 1

[0060] This comparative example uses the same raw materials as Example 1, the difference being the control of hot rolling process parameters:

[0061] In step S2, the initial rolling temperature is 1100℃ and the final rolling temperature is 920℃.

[0062] Subsequent steps S3 to S5 are the same as in Example 1. After completing step S5 (solution treatment), a batch of microcracks appeared on the surface of the bar, as shown in [the image / description]. Figure 12 Subsequent cold drawing processing is impossible if the billet has initial cracks. Any subsequent strong deformation and aging will be meaningless if these cracks are present. This indicates that exceeding the hot rolling temperature window set by this invention will lead to material cracking and a significant reduction in yield. The comparative example showed "batch-sized surface microcracks," making further processing impossible. This conversely proves that the hot working parameters defined by this invention are necessary and effective in solving the aforementioned hot working cracking problem. The hot working steps of this invention are a "key prerequisite" for unlocking the ultimate performance potential of this alloy, and have a direct and decisive causal relationship with ultimately achieving an ultra-high strength of 1800 MPa.

[0063] Comparative Example 2

[0064] This comparative example uses the same raw materials and hot rolling, annealing, and solution treatment processes as Example 1. The main difference is that the total deformation amount during cold drawing is insufficient.

[0065] In step S6, the cold drawing process is as follows: the first pass to Φ3=22.1mm (deformation approximately 15.2%), the second pass to Φ4=20.4mm (deformation approximately 14.8%), the third pass to Φ5=19.0mm (deformation approximately 13.3%), and the fourth pass to Φ6=17.8mm (deformation approximately 12.2%), with a total deformation of 45.0%. After straightening and polishing, the diameter is approximately 14.8mm.

[0066] The performance test results after aging treatment are shown in Table 1, which indicate that the material strength failed to reach the optimal level required by the present invention due to insufficient energy storage during cold deformation.

[0067] Comparative Example 3

[0068] This comparative example uses the same raw materials and hot rolling, annealing, and solution treatment processes as Example 1. The difference lies in the excessively large total deformation during cold drawing.

[0069] In step S6, the cold drawing process is as follows: the first pass to Φ3=22mm (deformation approximately 16.0%), the second pass to Φ4=20.2mm (deformation approximately 15.7%), the third pass to Φ5=18.5mm (deformation approximately 16.1%), the fourth pass to Φ6=16.9mm (deformation approximately 16.5%), and the fifth pass to Φ7=15.5mm (deformation approximately 15.9%), with a total deformation of 58.3%. After straightening and polishing, the diameter is approximately 14.1mm.

[0070] Table 1 shows the performance test results after aging treatment. It compares the performance measured in Examples 1-3 with those in Comparative Examples 2 and 3. It was found that although excessive single-pass deformation can achieve high strength, it may lead to a decrease in plasticity reserve or an increase in processing risk.

[0071] All room temperature tensile properties (tensile strength Rm, yield strength Rp0.2, elongation after fracture A) in this invention are tested in accordance with ASTM E8 standards and are directly measured by an Instron 5982 tensile testing machine.

[0072] In particular, when the alloy obtained in this application is mainly used to prepare high-stress springs, special attention is paid to the above-mentioned performance indicators. This is because tensile strength means the ultimate safety line, ensuring that the spring does not undergo catastrophic fracture under extreme working conditions; yield strength ensures that the spring does not undergo permanent deformation (permanent relaxation) during long-term cycling; and elongation after fracture is the process bottom line, ensuring that the spring can be manufactured smoothly and has basic impact toughness.

[0073] The following methods were used to test the above performance in this application:

[0074] Tensile strength (Rm): Calculated by reading the maximum force (Fm) from the recorded curve and dividing it by the original cross-sectional area of ​​the specimen (S0), i.e., Rm = Fm / S0. Yield strength (Rp0.2): Measured after the elastic segment on the curve, corresponding to the stress value at which 0.2% residual plastic deformation occurs. Usually determined on the load-displacement curve using an automatic extensometer or software algorithm. Elongation after fracture (A): Calculated by measuring the final gauge length (Lu) after the specimen has fractured and the fracture surfaces are tightly joined, using the formula A = [(Lu - L0) / L0] × 100%.

[0075] Table 1

[0076]

[0077] In high-end fields such as aerospace, medical implants, and the nuclear industry, excellent performance in a single mechanical property is insufficient to meet application requirements; tensile strength, yield strength, and elongation must achieve a synergistic balance. These fields have multi-dimensional requirements for materials, typically needing to maintain sufficient plasticity and toughness while ensuring extremely high strength. Only Examples 1-3 meet the requirements for use in these fields; the comparative examples do not. A comprehensive analysis of the results shown in Table 1 demonstrates the superior effectiveness of the preparation process described in this invention. Specifically, by controlling the initial and final rolling temperatures of hot rolling within a relatively high and suitable range, excessive accumulation of residual stress during rolling is effectively avoided, significantly reducing the risk of initial crack initiation on the surface of the round bar. Simultaneously, the rough drawing and rounding process replaces traditional peeling, reducing raw material loss. In particular, the elongation of Examples 1-3 is ≥10%, meaning that while maintaining high strength, it still retains considerable work hardening potential and fracture resistance. Typically, a high KAM state corresponds to extremely high yield strength and low elongation. In this application, through overall process design, the intermetallic compound particles precipitated during aging treatment are very fine and uniformly distributed. These particles can pin dislocations to provide strength without becoming crack initiators like large particles, thus maintaining a high elongation. This achieves both high hardness and ductility, making the material both hard (wear-resistant, compressive-resistant) and tough (fracture-resistant) under extreme conditions.

[0078] Regarding further quantification of the degree of fibrillation, this invention uses KAM (Kernel Average Misorientation) diagrams, and the local orientation difference distribution diagrams of Examples 1-3 and Comparative Examples 2-3 are shown below. Figure 2-11 As shown, microhardness is used to characterize it.

[0079] Correlation of KAM diagrams: This is one of the current standards for quantifying local strain (i.e., the degree of fibrosis), and KAM values ​​directly correspond to dislocation density.

[0080] Correlation of microhardness (HV): Hardness is the ability of a material to resist local plastic deformation, which is directly related to dislocation density.

[0081] Table 2 lists the KAM values ​​and microhardness values ​​of the alloys obtained in Examples 1-3 and Comparative Examples 2-3:

[0082] Table 2

[0083]

[0084] As shown in Table 2: Examples 1-3 (deformation amount 50-54%): The KAM diagrams show a high average KAM value, indicating uniform strain and high dislocation density, which intuitively quantifies the full and uniform fibrous deformation state.

[0085] Comparative Example 2 (deformation 45%): The KAM plot shows a low average KAM value and a light color distribution, indicating insufficient strain accumulation and low dislocation density, consistent with the observation of "insufficient fiberization".

[0086] Comparative Example 3 (deformation amount 58.3%): The KAM value may be very high, but the distribution may show local extreme high value regions (shear bands), reflecting that excessive deformation may lead to severe local lattice distortion or damage.

[0087] As a microscopic projection of macroscopic strength, microhardness directly reflects the degree of work hardening. From Comparative Example 2 to the Examples, and then to Comparative Example 3, microhardness monotonically increases with increasing total deformation. The key finding is that within the window of this invention (Examples), the hardness reaches a high and stable plateau region, which perfectly matches the trend of strength properties. While Comparative Example 3 exhibits high hardness, it may be accompanied by a sharp drop in plasticity.

[0088] Compared with Comparative Example 2 (total deformation 45%), Examples 1-3 (total deformation 50-54%) have a larger deformation, resulting in more complete grain elongation and fibrosis. Therefore, the visual proportion of "flocculent fibers" is higher and the continuity is better. After multiple cold drawing passes, the original equiaxed grains are drastically elongated and twisted along the drawing direction, the grain boundaries become blurred, and high-density dislocation entanglements and deformed twins are generated in the grains, thus presenting this flocculent and fibrous morphology under an optical microscope - a highly deformed grain (or subgrain) structure.

[0089] Summary of deformation patterns:

[0090] 1. With the increase of total cold deformation, the microstructure exhibits a clear evolutionary sequence: equiaxed crystals → elongation along the deformation direction → fibrous / streamlined structure. The greater the deformation, the more pronounced the fibrosis and the more blurred the grain boundaries (i.e., "more flocculent").

[0091] 2. An optimal deformation window exists: the total cold deformation of 50%-54% defined in this invention (Examples 1-3) embodies this window. Within this window: Microstructure characteristics: A fully homogeneous fibrous structure is obtained, with high dislocation and twin density, providing a large number of uniform nucleation sites for subsequent aging precipitation. Performance results: Correspondingly, the material achieves an optimal match between strength (≥1800MPa) and plasticity (elongation ≥10%).

[0092] 3. Microstructure and Performance Verification Deviating from the Optimal Window: Insufficient deformation leads to inadequate microfibrillation and weak "flocculent" characteristics, resulting in insufficient dislocation energy storage, limited aging strengthening effect, and substandard strength. Excessive deformation may cause over-fibrillation or even microcrack tendency. Although the strength may still be high, the plasticity reserve will decrease, and the process risk will increase.

[0093] In the cold deformation stage, by controlling the deformation amount of a single cold drawing to 12%~16% and the total cold deformation amount to 50%~55%, the tensile strength and yield strength of the alloy were successfully increased to over 1800MPa while ensuring good plasticity, thus achieving the successful preparation of high-strength and high-toughness bars.

[0094] By comparing the embodiments with comparative examples, the core process window of the present invention is further clarified:

[0095] Hot rolling window: The initial rolling temperature should not be lower than 1120℃, and the final rolling temperature should be maintained at 950~980℃. Temperatures below this range are prone to surface cracks in the rolled bar, increasing material loss and processing risks.

[0096] Cold deformation window: The total cold deformation amount should be controlled between 50% and 55%. Insufficient deformation will lead to a significant reduction in strength; while excessive deformation will impair the plasticity of the material.

[0097] In summary, this invention, through systematic optimization of key process steps such as hot working, annealing and solution treatment, rough drawing and rounding, and cold deformation aging, not only effectively overcomes the technical difficulties of high material loss and low yield in traditional manufacturing processes, but also achieves a significant improvement in alloy strength through precise control of cold deformation. The prepared alloy bars exhibit excellent comprehensive performance, fully meeting the stringent requirements for ultra-high strength materials in high-end fields such as aerospace fasteners and high-stress springs.

Claims

1. A high-strength cobalt-nickel-based alloy material, characterized in that, Its composition is C≤0.025wt%, Mn≤0.15wt%, Si≤0.15wt%, P≤0.015wt%, S≤0.010wt%, Cr: 19.00-21.00wt%, Ni: 33.00-37.00wt%, Mo: 9.00-10.50wt%, Ti≤1.00wt%, Fe≤1.00wt%, and the balance being Co and unavoidable impurities. This high-strength cobalt-nickel-based alloy material has a KAM value of 1.87-2.1, a microhardness of 450-525HV, a room temperature tensile strength ≥1800 MPa, a room temperature yield strength ≥1800 MPa, and a room temperature tensile elongation ≥10%. The preparation method of this high-strength cobalt-nickel-based alloy material is as follows: Step S1: Preparation and Hot Working of Alloy Ingots: Alloy ingots are prepared using a dual process of vacuum induction melting and vacuum consumable arc melting. The alloy ingots are then forged and hot rolled. Specifically, forging is performed first: the heating temperature is 1150℃, the holding time is 4 hours, the initial forging temperature is not lower than 1100℃, and the final forging temperature is not lower than 950℃, forging the alloy ingot into a square billet of a certain size. Then, hot rolling is performed: the surface-cleaned square billet is rolled into an initial round bar through multiple passes in one heat. The billet heating temperature is 1150℃, the holding time is 1.5 hours, the initial rolling temperature is not lower than 1120℃, and the final rolling temperature is 950~980℃. Step S2: Anneal the rolled round obtained in step S1. The annealing conditions are: holding at 1038℃ for 1.5 hours, followed by water cooling. Step S3: Rough drawing and solution treatment: The annealed rolled round is rough drawn and rounded to control the ellipticity of the bar to be no more than 0.03 mm; then solution treatment is performed under the following conditions: heat treatment at 1045℃ for 4 hours, followed by air cooling. Step S4: Multi-pass continuous cold drawing: The solution-treated round bar is subjected to multi-pass continuous cold drawing, with the deformation amount of each pass controlled at 12%~16%, to obtain a cold-drawn round bar. The total deformation amount of the cold-drawn round bar is controlled at 50~55%. Step S5: Aging treatment: Before aging treatment, the cold-drawn round bar is straightened, polished and inspected to ensure that there are no micro-cracks on the surface; then aging treatment is carried out under the following conditions: heat treatment at 540℃ for 4 hours, followed by air cooling.

2. A method for preparing a high-strength cobalt-nickel-based alloy material as described in claim 1, characterized in that, Includes the following steps: Step S1: Preparation and Hot Working of Alloy Ingots: Alloy ingots are prepared using a dual process of vacuum induction melting and vacuum consumable arc melting. The alloy ingots are then forged and hot rolled. Specifically, forging is performed first: the heating temperature is 1150℃, the holding time is 4 hours, the initial forging temperature is not lower than 1100℃, and the final forging temperature is not lower than 950℃, forging the alloy ingot into a square billet of a certain size. Then, hot rolling is performed: the surface-cleaned square billet is rolled into an initial round bar through multiple passes in one heat. The billet heating temperature is 1150℃, the holding time is 1.5 hours, the initial rolling temperature is not lower than 1120℃, and the final rolling temperature is 950~980℃. Step S2: Anneal the rolled round obtained in step S1. The annealing conditions are: holding at 1038℃ for 1.5 hours, followed by water cooling. Step S3: Rough drawing and solution treatment: The annealed rolled round is rough drawn and rounded to control the ellipticity of the bar to be no more than 0.03 mm; then solution treatment is performed under the following conditions: heat treatment at 1045℃ for 4 hours, followed by air cooling. Step S4: Multi-pass continuous cold drawing: The solution-treated round bar is subjected to multi-pass continuous cold drawing, with the deformation amount of each pass controlled at 12%~16%, to obtain a cold-drawn round bar. The total deformation amount of the cold-drawn round bar is controlled at 50~55%. Step S5: Aging treatment: Before aging treatment, the cold-drawn round bar is straightened, polished and inspected to ensure that there are no micro-cracks on the surface; then aging treatment is carried out under the following conditions: heat treatment at 540℃ for 4 hours, followed by air cooling.

3. The method for preparing the high-strength cobalt-nickel-based alloy material according to claim 2, characterized in that, After step S5, the process also includes precision straightening and polishing of the bar stock and / or mechanical property testing before the final product is completed.

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