Low cost iron-nickel based heat resistant alloy and high speed rolling method thereof

Abstract

The present application relates to a low-cost iron-nickel-based heat-resistant alloy and a high-speed rolling method thereof, and belongs to the technical field of special alloy manufacturing. The present application solves the technical problems of cracking, short tool life, high energy consumption and low efficiency in subsequent solid solution treatment caused by uneven material temperature rise and cooling during high-speed rolling of the existing heat-resistant alloy. In the method of the present application, the heated heat-resistant alloy rolling stock is sequentially passed through the rough rolling, intermediate rolling and finishing rolling units. At least two cooling devices are arranged at the key positions in the later stage of the finishing rolling unit. The polyacrylamide aqueous solution containing specific particle size and proportion of aluminum oxide powder is used for intermittent jet cooling of the wire. The finished wire is directly put into the solid solution furnace for online solid solution treatment and water cooling. The present application realizes the integrated production of heat-resistant alloy wire from rolling to heat treatment with high efficiency, high quality and low energy consumption. The prepared wire has uniform structure and excellent performance, and is especially suitable for manufacturing engine valves.

Description

Technical Field

[0001] This invention relates to the field of special alloy manufacturing technology, and in particular to a low-cost iron-nickel-based heat-resistant alloy and its high-speed rolling method. Background Technology

[0002] Heat-resistant alloys, especially iron-nickel-chromium-based austenitic heat-resistant alloys, have become core materials for manufacturing key high-temperature components such as intake and exhaust valves in high-performance engines due to their excellent high-temperature strength, creep resistance, and oxidation resistance. With the continuous improvement of engine efficiency and power requirements, the performance requirements for valve alloys are becoming increasingly stringent. At the same time, reducing their production costs has become crucial for maintaining competitiveness in the market.

[0003] Currently, the large-scale production of heat-resistant alloy wire typically employs hot continuous rolling. However, for iron-nickel-chromium-based heat-resistant alloys with high alloy element content and narrow hot working windows, existing rolling technologies face a series of severe challenges. First, high-speed rolling, used to achieve high-efficiency production, generates significant deformation heat within the material. Insufficient cooling can easily lead to weakening or even cracking of internal grain boundaries. Conversely, using traditional water cooling for forced cooling can also induce cracks or surface defects due to excessively rapid cooling and large temperature differences between the material surface and core. To address this, some technologies have attempted to use cooling oil for gentle cooling, but its cooling capacity is often insufficient to suppress the temperature rise of the material under high-speed rolling, resulting in limited effectiveness. Second, the blades of the flying shear at the inlet of the finishing mill in high-speed rolling lines, when continuously shearing high-temperature, high-strength alloy billets, suffer from rapid wear due to insufficient high-temperature hardness and oxidation resistance. This necessitates frequent shutdowns for replacement, severely disrupting production continuity and limiting overall efficiency. In addition, the rolled heat-resistant alloy must undergo solution treatment to optimize its microstructure. Current processes generally use a separate solution heat treatment furnace, which is energy-intensive and has a long production cycle, constituting an important part of the production cost.

[0004] The existing technology lacks a comprehensive solution that can systematically solve a series of interrelated problems such as the difficulty of temperature control in high-speed rolling, the short life of key components, and the high energy consumption of subsequent heat treatment. This seriously restricts the high-efficiency, high-quality, and low-cost manufacturing of high-performance heat-resistant alloy wires. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a low-cost iron-nickel-based heat-resistant alloy and its high-speed rolling method, so as to at least solve one of the technical problems existing in the prior art of high-speed rolling of iron-nickel-chromium-based heat-resistant alloys, such as difficulty in controlling the internal temperature rise of the material, short life of the flying shear blade, high energy consumption of post-rolling solution treatment, and fracture in the process.

[0006] On one hand, embodiments of the present invention provide a high-speed rolling method for low-cost iron-nickel-based heat-resistant alloy wire, comprising the following steps:

[0007] S1. Heating: Heat the heat-resistant alloy billet at 1140℃~1150℃ and hold it at that temperature for 2 hours~2.5 hours;

[0008] S2. High-speed continuous rolling and temperature control: The heated billet is rolled sequentially through roughing, intermediate rolling and finishing mills to finally obtain finished wire with a diameter of φ5.0mm~φ10mm;

[0009] During the finishing rolling process, the running wire is subjected to intermittent jet cooling. The cooling medium is an aqueous solution of polyacrylamide containing 10% to 20% by mass of alumina powder, wherein the alumina powder has a particle size of 0.20 μm to 0.50 μm.

[0010] S3. Online solution quenching: After the finely rolled wire is spun out, it is directly put into the solution furnace for online solution treatment. The solution temperature is 980℃~990℃, and after holding for 15 minutes to 20 minutes, it is directly water cooled.

[0011] Furthermore, in the S2 high-speed continuous rolling and temperature control step, at least one cooling device is set in the main heat accumulation zone of deformation and the key grain shaping zone of the finishing mill to perform the jet cooling on the wire.

[0012] Furthermore, in the S2 high-speed continuous rolling and temperature control step, the wire temperature at the outlet of the intermediate rolling mill is controlled at 1040℃~1050℃, and the rolling speed is 110m / s~115m / s; the wire temperature at the outlet of the finishing rolling mill is controlled at 1030℃~1040℃, and the rolling speed is 115m / s~120m / s.

[0013] Furthermore, in the S2 high-speed continuous rolling and temperature control step, a high-speed flying shear is used at the entrance of the finishing mill to cut or segment the rolled material; the blade material of the high-speed flying shear is martensitic heat-resistant steel 1Cr16Ni2MoN.

[0014] Furthermore, in the polyacrylamide aqueous solution, the mass fraction of polyacrylamide is 0.5% to 2.0%, and the purity of the alumina powder is 99.99%.

[0015] Furthermore, the chemical composition of the heat-resistant alloy, by mass percentage, is as follows: C: 0.03–0.10%, Si: 0.05–0.4%, Mn: 0.10–0.60%, P: ≤0.020%, S: ≤0.020%, Cr: 15.00–18.00%, Ni: 24.0–30.0%, Al: 0.80–2.00%, Ti: 1.85–3.00%, Nb: 0.30–1.30%, V: 0.20–0.50%, with the balance being Fe and unavoidable impurities.

[0016] Based on the aforementioned preparation method, the present invention also proposes a heat-resistant alloy prepared by the above-described method.

[0017] Furthermore, the microstructure of the heat-resistant alloy is a uniform austenitic matrix with a grain size level of ASTM 6 to 10.

[0018] Based on this heat-resistant alloy, the present invention also provides an engine valve, which is manufactured from the aforementioned heat-resistant alloy.

[0019] Furthermore, the present invention proposes a cooling medium for the above-described method, which is composed of an aqueous solution of polyacrylamide and 10% to 20% by mass of alumina powder dispersed therein, wherein the alumina powder has a particle size of 0.20 μm to 0.50 μm and a purity of 99.99%.

[0020] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0021] 1) This invention uses an aqueous solution of polyacrylamide containing nano-alumina powder of a specific particle size (0.20μm~0.50μm) and proportion (10%~20%) as a cooling medium. This medium utilizes the properties of nanoparticles to increase heat exchange area and promote the formation of vaporization nuclei, achieving a cooling capacity precisely between traditional water cooling and oil cooling. By intermittently spraying it into the main heat accumulation zone of the deformation mill (between stands 13 and 14 of the finishing mill) and the critical grain shaping zone (such as between stands 17 and 18 of the finishing mill), directional intervention in the process temperature rise is achieved. This approach can control rolling temperature fluctuations within an extremely narrow range, effectively removing deformation heat, preventing internal grain boundary weakening and cracking, and avoiding surface cracks caused by excessively rapid cooling, thereby improving the yield.

[0022] 2) This invention, by controlling the Ni content below 30% and optimizing the ratio of strengthening elements such as Al, Ti, and V, significantly reduces costs while constructing a multi-strength mechanism primarily based on γ' phase precipitation strengthening. The heat-resistant alloy prepared exhibits a high room temperature tensile strength (R0) in its wire. m The yield strength (R) is as high as 1150-1173 MPa. p0.2It achieves a strength of 678–715 MPa while maintaining good plasticity, with an elongation at break (A) of 17.8%–21.0% and a reduction of area (Z) of 20.8%–29.0%. This is comprehensively superior to commercially available Ni30 alloys (R...). m ~1115MPa,R p0.2 (~658MPa, A~22.3%, Z~24.5.0%), achieving the dual advantages of performance and cost.

[0023] 3) This invention seamlessly integrates solution treatment into the rolling line, achieving the desired microstructure through online solution treatment at 980–990°C for 15–20 minutes. This process eliminates the two energy-intensive steps of billet cooling and reheating, reducing overall energy consumption, shortening the production cycle, and enabling an upgrade from discrete production to integrated continuous production.

[0024] 4) This invention uses martensitic heat-resistant steel 1Cr16Ni2MoN to manufacture the flying shear blades. Utilizing its high Cr, Mo, and N content, which provides excellent high-temperature performance, the blade life is increased from 100-120 tons for traditional H13 steel to 200-250 tons. This eliminates the downtime of the entire production line caused by frequent blade replacements.

[0025] 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

[0026] 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.

[0027] Figure 1 This is a typical metallographic diagram of the heat-resistant alloy wire prepared in Example 1 (furnace number 2) of the present invention;

[0028] Figure 2 This is a typical metallographic diagram of the heat-resistant alloy wire prepared in Example 2 (furnace number 4) of the present invention. Detailed Implementation

[0029] 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.

[0030] In the field of heat-resistant alloy wire manufacturing, especially for high-nickel-chromium iron-based heat-resistant alloys, achieving high-efficiency, low-cost continuous production while ensuring high quality has always been a challenging problem for those skilled in the art. In existing technologies, temperature control during high-speed rolling, the lifespan of key components, and the energy consumption of subsequent heat treatment are mutually constrained and difficult to balance. This invention aims to systematically solve at least one of the above-mentioned problems through an integrated technical solution.

[0031] In a first aspect, a specific embodiment of the present invention discloses a high-speed rolling method for low-cost iron-nickel-based heat-resistant alloy wire, comprising the following steps:

[0032] S1. Heating: Heat the heat-resistant alloy billet at 1140℃~1150℃ and hold it at that temperature for 2 hours~2.5 hours;

[0033] S2. High-speed continuous rolling and temperature control: The heated billet is rolled sequentially through roughing, intermediate rolling and finishing mills to finally obtain finished wire with a diameter of φ5.0mm~φ10mm;

[0034] During the finishing rolling process, the running wire is subjected to intermittent jet cooling. The cooling medium is an aqueous solution of polyacrylamide containing 10% to 20% by mass of alumina powder, wherein the particle size of the alumina powder is 0.20 μm to 0.50 μm.

[0035] S3. Online solution quenching: After the precision-rolled wire is spun out, it is directly put into the solution furnace for online solution treatment. The solution temperature is 980℃~990℃, and after holding for 15~20 minutes, it is directly water-cooled.

[0036] The core of this integrated high-speed rolling method lies in the innovative integration of rolling, process temperature control, and heat treatment processes into a highly efficient and continuous production system. The key lies in the controlled cooling of the high-speed running wire between critical stands during the finishing rolling process. This aims to precisely maintain the wire temperature within the optimal thermoplastic window by promptly dissipating the heat accumulated during deformation, thereby balancing the temperature rise caused by high-speed deformation and laying the foundation for obtaining a uniform and fine finished product microstructure.

[0037] In implementing the method, the S1 heating step is performed first, in which the heat-resistant alloy billet (e.g., a 140mm×140mm square billet formed by electroslag remelting and initial rolling) is fed into a walking beam regenerator for heating. The heating temperature is strictly controlled within a narrow range of 1140℃ to 1150℃, and held at this temperature for 2 to 2.5 hours to obtain good thermoplasticity.

[0038] The core of the aforementioned process parameters lies in ensuring that the high content of reinforcing elements such as Al, Ti, Nb, and V in the alloy can be fully dissolved in the austenitic matrix, laying a uniform microstructure foundation for subsequent rolling. Practice shows that if the heating temperature is below 1140℃, some high-melting-point reinforcing phases will not dissolve sufficiently, becoming stress concentration points during subsequent rolling and increasing the risk of cracking; conversely, if the temperature is above 1150℃, it can easily lead to grain coarsening or even overheating, resulting in a decrease in the material's thermoplasticity. The process parameters of this invention achieve the optimal balance between "sufficient dissolution of reinforcing elements" and "prevention of microstructure overheating and deterioration," which is a prerequisite for achieving subsequent high-speed and stable rolling.

[0039] The S2 high-speed continuous rolling and temperature control steps are then carried out. The heated billet is sent to a high-speed continuous rolling mill consisting of 18 stands, and through three stages of continuous rolling—roughing, intermediate rolling, and finishing—the diameter reduction, shaping, and temperature control are completed in a coordinated manner.

[0040] The high-alloyed iron-based heat-resistant alloy used in this invention possesses excellent high-temperature strength due to its rich content of elements such as Cr, Ni, Al, and Ti. However, under high-speed rolling conditions, it also exhibits characteristics such as a narrow hot working window (only 100–150°C), high deformation resistance, and high sensitivity of high-temperature plasticity to temperature fluctuations. Traditional step-by-step rolling or low-speed continuous rolling, due to its discontinuous production rhythm, results in a significant drop in the temperature of the rolled piece, which easily causes the deformation temperature to deviate from the optimal range, leading to a sudden increase in deformation resistance and surface cracking. On the other hand, simply increasing the rolling speed will cause the deformation heat to accumulate, resulting in excessive internal temperature rise, causing grain coarsening or even grain boundary weakening, and inducing internal cracks.

[0041] To address the aforementioned issues, this invention employs an 18-stand integrated high-speed continuous rolling technology. Through uninterrupted connection and speed matching across three stages, rapid and continuous plastic deformation is achieved within the aforementioned extremely narrow range above the material recrystallization temperature. This approach not only improves production efficiency but also avoids temperature instability caused by intermittent production, creating conditions for precise temperature field control through localized cooling.

[0042] The specific configurations for each stage of rolling are as follows:

[0043] In the roughing stage (such as the first 6 stands of alternating horizontal / vertical short-stress rolling mills), an alternating sequence of "rectangular box-square box" pass is used to undertake a large reduction in diameter, reducing the cross-section of the billet to 40×40mm~50×50mm;

[0044] In the intermediate rolling stage (such as the middle 6 three-roll mill), an alternating sequence of "diamond-square" roll passes is used to further reduce the diameter and pre-shape the material, resulting in intermediate material of 20×20mm to 30×30mm, which promotes uniform deformation and precise dimensional control.

[0045] The finishing rolling stage (such as the last 6 Morgan mills) uses an alternating "elliptical-circular" pass sequence to roll the wire to the target diameter of φ5.0mm~φ10mm, and ensures the dimensional accuracy, surface finish and microstructure of the finished product.

[0046] Specifically, to achieve precise temperature control during the finishing rolling process, this invention incorporates a controlled cooling system at key locations within the finishing mill. By implementing directional, intermittent jet cooling, precise intervention in the temperature rise of the wire material is achieved. The cooling system is primarily located in the main heat accumulation zone of deformation and the critical grain-setting zone, corresponding to key locations such as the middle and pre-final stages of the finishing rolling process, respectively.

[0047] Preferably, cooling devices are installed between stands 13 and 14, and between stands 17 and 18, to perform jet cooling on the wire. These two locations correspond to the middle and final stages of finishing rolling, respectively, where the accumulated heat of deformation is most significant, and temperature has the most critical impact on the final recrystallized grain size. Implementing precise intermittent cooling at these locations can most effectively suppress the temperature rise of the wire, keeping its temperature within the ideal thermoplastic processing window, and controlling the fluctuations throughout the finishing rolling process within an extremely narrow range of ±15℃ (e.g., stabilizing at 1030℃~1040℃).

[0048] This strategy resolves the fundamental contradiction in high-speed rolling of heat-resistant alloys: if left uncontrolled, the heat accumulated during high-speed deformation will cause the material temperature to soar by tens of degrees Celsius, exceeding the optimal recrystallization temperature, leading to abnormal grain growth and weakened grain boundary oxidation, which in turn induces internal cracks during subsequent processing or use; on the other hand, if conventional full-process strong cooling is used, it will cause a sudden drop in surface temperature and an excessive temperature difference between the core and the surface, resulting in uneven deformation, surface stress concentration, and cracks. At the same time, the rapidly increasing deformation resistance will also place a huge load on the rolling mill equipment.

[0049] Unlike existing technologies that cool the entire rolling process, this invention employs a key intervention combined with a special cooling medium (polyacrylamide-based nanofluid, whose cooling capacity falls between water and oil cooling) to effectively prevent internal overheating and grain coarsening, while also avoiding surface overcooling that leads to cracking. This allows the material to avoid both grain coarsening and grain boundary weakening caused by overheating, and the surge in deformation resistance and potential surface defects caused by excessively low temperatures. This lays a solid foundation for obtaining a uniform and fine finished grain structure and achieving high-quality, stable rolling.

[0050] Furthermore, in the S2 high-speed continuous rolling and temperature control step, the wire temperature at the outlet of the intermediate mill is controlled at 1040℃~1050℃, and the rolling speed is 110m / s~115m / s; the wire temperature at the outlet of the finishing mill is controlled at 1030℃~1040℃, and the rolling speed is 115m / s~120m / s. These parameters constitute the optimal process window for the heat-resistant alloy of this invention. Under these conditions, the alloy undergoes sufficient and uniform dynamic recrystallization, forming fine equiaxed recrystallized grains. Simultaneously, the rolling process remains stable, avoiding shape defects caused by uneven deformation.

[0051] Furthermore, in step S2, a high-speed flying shear is used at the entrance of the finishing mill to cut or segment the rolled material. A key improvement of this invention lies in the use of martensitic heat-resistant steel 1Cr16Ni2MoN as the blade material for the high-speed flying shear. Ordinary H13 hot work die steel blades, when continuously shearing high-temperature (above approximately 1000°C) and high-strength heat-resistant alloys, typically have a service life of only 100 to 120 tons due to insufficient high-temperature hardness and oxidation resistance. In contrast, 1Cr16Ni2MoN steel, with its higher chromium content (approximately 16%) and the combined strengthening effect of molybdenum and nitrogen, forms a denser and more stable Cr2O3 oxide film at high temperatures and maintains higher heat resistance.

[0052] The application of martensitic heat-resistant steel 1Cr16Ni2MoN in flying shear blades solves a long-standing but neglected engineering problem in this field. In high-speed continuous rolling production, frequent downtime for blade replacement is a key bottleneck affecting continuous operation efficiency and cost. However, existing technologies generally accept H13 steel as the standard blade material and are subject to its limited lifespan. This invention increases blade life to 200-250 tons through material replacement, effectively doubling the lifespan. This seemingly simple improvement brings unexpected and significant economic benefits: it enables the entire integrated rolling-solidification process to proceed continuously and stably, avoiding production line interruptions caused by premature blade failure.

[0053] Regarding the cooling medium in step S2, its composition and ratio are crucial: the cooling medium is a 0.5%–2% (mass fraction) polyacrylamide aqueous solution as the base liquid, with 10%–20% (mass fraction) alumina (Al2O3) powder added as a reinforcing cooling phase; the alumina powder has a particle size of 0.20μm–0.50μm (submicron level) and a purity of not less than 99.99%.

[0054] Traditional high-speed rolling mills typically use water or cooling oil (polyacrylamide aqueous solution) as coolant. However, excessively rapid water cooling can easily cause surface cracks, while slow oil cooling cannot suppress internal overheating. This invention addresses this gap between water and oil cooling by adding high-purity, submicron-sized alumina powder to the polyacrylamide aqueous solution to gently enhance cooling capacity. High-purity nano-alumina has high surface energy and a large specific surface area, acting as an efficient vaporization nucleus in the coolant to significantly promote boiling heat transfer. This effectively removes deformation heat while avoiding thermal shock caused by rapid cooling. Its high purity ensures extremely low impurity content, preventing adverse reactions with the alloy surface at high temperatures or becoming a source of cracks.

[0055] In addition, to ensure the suspension stability of the nanofluid, a circulating stirring system is installed in the storage tank to keep the Al2O3 particles uniformly dispersed before the coolant is sprayed, preventing sedimentation and agglomeration. During the finishing rolling process, the pretreated and continuously flowing nanofluid is transported to the front end of the spraying system to perform intermittent spray cooling on the running wire, thereby ensuring the uniformity, stability and reliability of the cooling effect as a whole.

[0056] The key to the technology lies in the alumina content of 10% to 20% by mass: below 10%, the cooling capacity improvement is not significant and cannot effectively suppress internal cracks; above 20%, the cooling capacity is too strong, approaching the effect of water cooling, which significantly increases the risk of surface cracks. Only within this specific concentration range can the cooling capacity just meet the stringent requirements of high-speed rolling of heat-resistant alloys.

[0057] After precision rolling, the wire is coiled by a wire spinning machine and directly enters the walking beam solution furnace at the end of the rolling line for S3 online solution quenching treatment. The solution temperature is 980℃~990℃, and after holding for 15~20 minutes, it is directly water-cooled for quenching.

[0058] The online solution treatment of this invention is not simply moving the solution furnace next to the rolling line, but a reconstruction of the traditional production process. It breaks through the separate "rolling-cooling-collection-reheating-solution" model, achieving a seamless connection between "rolling-forming-direct solution treatment." This model fully utilizes the residual heat from rolling, eliminating the need for billet cooling and reheating, resulting in energy savings of over 25% and a production cycle reduction of over 30%. Simultaneously, immediate solution treatment after rolling effectively locks in the fine recrystallized austenite structure formed during high-speed rolling, preventing coarsening or precipitation of harmful phases caused by intermediate cooling and reheating, thus providing a purer and more uniform starting point for subsequent aging treatment.

[0059] It is particularly important to emphasize that the high performance and high yield of the heat-resistant alloy wire obtained by this invention are the result of the synergistic effect of specific alloy composition design and the aforementioned integrated high-speed rolling method.

[0060] The chemical composition of the alloy, by mass percentage, is as follows: C: 0.03–0.10%, Si: 0.05–0.4%, Mn: 0.10–0.60%, P: ≤0.020%, S: ≤0.020%, Cr: 15.00–18.00%, Ni: 24.0–30.0%, Al: 0.80–2.00%, Ti: 1.85–3.00%, Nb: 0.30–1.30%, V: 0.20–0.50%, with the balance being Fe and unavoidable impurities.

[0061] This composition design aims to overcome the limitations of existing technologies. Compared with nickel-based heat-resistant alloys (such as GH4751) that typically have a Ni content of over 40%, this invention achieves a significant cost advantage by strictly controlling the Ni content to below 30%, thereby reducing raw material costs by approximately 15-20%.

[0062] More importantly, this invention achieves a fundamental shift in the strengthening mechanism: by controlling the Al content at 0.80–2.00% and the Ti content at 1.85–3.00%, the alloy precipitates a coherent γ'-Ni3(Al,Ti) phase with a volume fraction of 20–30% during aging, transforming the strengthening mechanism from traditional solid solution strengthening to γ' phase precipitation strengthening. Simultaneously, the composite addition of Nb (0.30–1.30%) and V (0.20–0.50%) forms fine NbC and VC carbides, constructing a dual strengthening mechanism of precipitation strengthening + dispersion strengthening.

[0063] Crucially, the addition of V exhibits a synergistic strengthening effect with the aforementioned high-speed rolling process: during high-speed rolling (speed ≥ 110 m / s), V helps refine dynamically recrystallized grains; and during the subsequent online solution treatment at 980℃~990℃ and rapid cooling, it promotes the dispersed precipitation of VC carbides with an average size < 50 nm. This synergistic effect provides favorable conditions for achieving fine-grain strengthening and precipitation strengthening of the alloy.

[0064] In summary, the composition design of this invention, through low Ni content, γ' phase strengthening, and V / Nb composite microalloying, combined with a specific high-speed rolling-online solution treatment process, successfully achieves a balance between low cost, high performance, and high yield.

[0065] Based on the aforementioned integrated high-speed rolling method, we have successfully prepared a heat-resistant alloy with excellent microstructure and properties. The wire of this heat-resistant alloy exhibits a uniform austenitic matrix with a grain size reaching ASTM 9–10 grade and a concentrated grain size distribution. This superior microstructure stems from the synergistic effect of the preparation methods, including: high-speed deformation at 110–120 m / s during the finishing rolling stage inducing sufficient dynamic recrystallization; two-point controlled cooling stabilizing the temperature within an extremely narrow window of 1030–1040 °C, suppressing grain growth; and online solution quenching further optimizing the precipitate distribution and locking in a fine-grained microstructure.

[0066] Thanks to the aforementioned fine-grained and uniform microstructure, this wire exhibits significantly superior overall performance compared to products manufactured using traditional low-speed rolling-offline solution treatment processes, making it an ideal raw material for manufacturing high-performance engine valves.

[0067] Due to the superior properties of this wire, it is an ideal raw material for manufacturing high-performance engine valves. Using this material, the present invention further provides an engine valve. This valve is manufactured through conventional upsetting, aging heat treatment, and machining. Benefiting from the uniform and fine initial grain structure and excellent properties of the raw material wire, the finished valve exhibits higher instantaneous strength and creep resistance under operating conditions above 700°C, and the thermomechanical fatigue life of the transition zone between the valve disc and valve stem is extended by more than 40% compared to products manufactured using traditional processes.

[0068] Furthermore, to achieve the key processes of high-speed continuous rolling and precise temperature control in step S2 above, this invention also provides a novel cooling medium. The specific composition and heat transfer characteristics of this medium are one of the core technical guarantees for ensuring stable and uniform cooling of the rolled piece within an extremely narrow temperature window of 1030–1040°C, thereby obtaining ASTM 9–10 grade ultrafine grains.

[0069] The medium consists of a 0.5%–2.0% aqueous solution of polyacrylamide (base solution) and 10%–20% (mass fraction) of alumina powder (additive), wherein the alumina particle size is 0.20–0.50 μm and the purity is ≥99.99%.

[0070] This medium resolves the contradiction between cooling rate and uniformity during high-speed rolling: uniformly dispersed submicron-sized (0.20μm~0.50μm) high-purity alumina powder acts as heterogeneous nucleation sites, disrupting the continuous vapor film with insulating effect formed by the vaporization of the base liquid. This promotes the heat transfer mode from film boiling to the more efficient nucleation boiling, significantly improving the overall heat transfer efficiency. Because its cooling capacity falls between rapid water cooling and slow oil cooling, it achieves mild yet efficient cooling characteristics: it can promptly and fully remove the deformation heat accumulated during high-speed deformation, suppressing excessive internal temperature rise and grain coarsening; it can also avoid surface thermal stress cracks and a surge in deformation resistance caused by excessively rapid cooling and large core-surface temperature differences. This medium is a special medium designed specifically for achieving high-speed, high-quality, and high-yield rolling of heat-resistant alloys.

[0071] 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.

[0072] Example 1

[0073] This embodiment provides a high-speed rolling method for low-cost iron-nickel-based heat-resistant alloy wire. The alloy chemical composition (furnace number 2) by mass percentage is: C: 0.055%, Si: 0.31%, Mn: 0.44%, P: 0.010%, S: 0.006%, Cr: 17.86%, Ni: 28.56%, Ti: 2.15%, Al: 1.70%, Nb: 1.07%, V: 0.30%, with the balance being Fe and unavoidable impurities.

[0074] The specific steps are as follows:

[0075] S1. Heating: The above-mentioned heat-resistant alloy billet (a 140mm×140mm square billet formed by electroslag remelting and initial rolling, each weighing 1.2 tons) is heated at 1145℃ and held at that temperature for 2.2 hours.

[0076] S2. High-speed continuous rolling and temperature control: The heated billet is fed into an integrated high-speed continuous rolling mill consisting of 18 stands, and is continuously rolled through the roughing mill, intermediate mill and finishing mill in sequence.

[0077] The roughing process employs an alternating "rectangular box-square box" pass sequence, using the first six alternating horizontal / vertical short-stress mills to reduce the billet cross-section to 45mm×45mm. The intermediate rolling process uses an alternating "diamond-square" pass sequence, using the middle six three-roll mills. The wire temperature at the intermediate mill exit is controlled at 1043℃, and the rolling speed is 112m / s, for further diameter reduction and pre-forming to obtain 25mm×25mm intermediate material. The finishing rolling process uses an alternating "elliptical-circular" pass sequence, using the final six Morgan mills. The wire temperature at the finishing mill exit is controlled at 1038℃, and the rolling speed is 116m / s, ultimately rolling the wire to the target diameter of φ8.0mm.

[0078] Cooling devices are installed between the 13th and 14th stands and between the 17th and 18th stands of the finishing mill to intermittently spray-cool the wire during operation, controlling the temperature fluctuation of the wire during the finishing rolling process within ±10℃ (i.e., 1038℃ ± 10℃). The cooling medium is an aqueous solution of polyacrylamide containing 15% by mass of alumina powder. The alumina powder has a particle size of 0.35μm and a purity of 99.99%. The cooling medium maintains suspension stability in the storage and circulation pipelines through mechanical stirring.

[0079] At the entrance of the finishing mill, a high-speed flying shear is used to cut the rolled material. The blade material of the high-speed flying shear is martensitic heat-resistant steel 1Cr16Ni2MoN.

[0080] The final product is a wire with a diameter of φ8.0mm.

[0081] S3. Online solution quenching: After the precision-rolled wire is spun out, it is directly put into the solution furnace for online solution treatment. The solution temperature is 985℃, and after holding for 15 minutes, it is directly water-cooled.

[0082] The heat-resistant alloy wire prepared by the method in this embodiment has a uniform austenitic matrix microstructure with a grain size grade of ASTM 6 (see ASTM A2010). Figure 1 ).

[0083] Example 2

[0084] To verify the universality of the method of the present invention, six heat-resistant alloys (heater numbers 1 to 6) were smelted in a 3-ton vacuum induction furnace, and their chemical compositions are shown in Table 1. Wire materials were prepared using the same method as in Example 1, and their room temperature mechanical properties were compared with those of commercially available heat-resistant alloy Ni30 as a comparative example. The results are shown in Table 2.

[0085] Table 1. Alloy chemical composition (wt%)

[0086]

[0087] Table 2 Comparison of room temperature tensile properties

[0088]

[0089] As shown in Table 2, the alloy wires (furnace numbers 1-6) prepared by the method of the present invention and conforming to the composition range of the present invention have a tensile strength (R0). m The yield strength (R) is as high as 1150-1173 MPa. p0.2 It achieves a strength of 678–715 MPa while maintaining good plasticity, with an elongation after fracture (A) of 17.8%–21.0% and a reduction of area (Z) of 20.8%–29.0%. Its metallographic structure exhibits uniform and fine austenite grains (e.g., ...). Figure 2 The grain size level (represented by this alloy) is ASTM 6-7, which corroborates its excellent mechanical properties. All of these properties are significantly higher than those of the comparative Ni30 alloy (R). m ~1115MPa, R p0.2 ~658MPa, A~22.3%, Z~24.5.0%).

[0090] Example 3

[0091] Using billets with the same composition as in Example 1, the temperature and speed parameters of the intermediate rolling and finishing rolling processes were changed, and their impact on the quality of the final product was observed. The specific process parameters and results are shown in Table 3.

[0092] Table 3. Impact of rolling process parameters on product quality

[0093]

[0094] As shown in Table 3, only when the intermediate rolling temperature is within the range of 1040℃~1050℃ and the intermediate rolling speed is within the range of 110m / s~115m / s, and the finishing rolling temperature is within the range of 1030℃~1040℃ and the finishing rolling speed is within the range of 115m / s~120m / s (e.g., billets 2, 3, 5, 7, 9) can qualified products be obtained. Outside this range, various defects will occur.

[0095] Example 4

[0096] Using the same method and process parameters as in Example 1, only the mass fraction of alumina powder in the cooling medium was changed to investigate its effect on cooling effect and product quality. The results are shown in Table 4.

[0097] Table 4 Cooling medium ratio and actual effect

[0098]

[0099] As shown in Table 4, the optimal cooling effect and product quality are achieved when the alumina powder content is between 10% and 20% by mass (3% to 7% for rolled products). Insufficient or excessive addition will lead to product defects.

[0100] Example 5

[0101] Using the same method and process parameters as in Example 1, only the temperature and time of the solution treatment were changed to investigate their effects on the microstructure and properties of the product. The results are shown in Table 5.

[0102] Table 5 Solution treatment process and actual results

[0103]

[0104] As shown in Table 5, the successful solution treatment parameters are a temperature of 980℃~990℃ and a holding time of 15 minutes~20 minutes (e.g., rolled materials 2, 4, 6, 7, 8).

[0105] In summary, this invention successfully prepared high-performance heat-resistant alloy wire by combining optimized alloy composition with an integrated high-speed rolling process. The product prepared by this method achieves a comprehensive breakthrough in mechanical properties, with its room temperature tensile strength (R0) reaching a high level. m The yield strength (R) is as high as 1150-1173 MPa. p0.2 The tensile strength reached 678–715 MPa while maintaining good plasticity, with elongation after fracture (A) of 17.8%–21.0% and reduction of area (Z) of 20.8%–29.0%. Both were significantly higher than those of the comparative Ni30 alloy (R). m ~1115MPa, R p0.2 ~658MPa, A~19.0%, Z~18.5%). It also achieved efficient and continuous production from rolled billet to finished wire.

[0106] 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 high-speed rolling of low-cost iron-nickel-based heat-resistant alloy wire, characterized in that, Includes the following steps: S1. Heating: Heat the heat-resistant alloy billet at 1140℃~1150℃ and hold it at that temperature for 2 hours~2.5 hours; S2. High-speed continuous rolling and temperature control: The heated billet is rolled sequentially through roughing, intermediate rolling and finishing mills to finally obtain finished wire with a diameter of φ5.0mm~φ10mm; During the finishing rolling process, at least one cooling device is installed in both the main heat accumulation zone of deformation and the critical grain shaping zone of the finishing mill to perform intermittent jet cooling on the running wire. The cooling medium consists of an aqueous solution of polyacrylamide and 10%–20% by mass of alumina powder dispersed therein, wherein the polyacrylamide in the aqueous solution has a mass fraction of 0.5%–2.0%, and the alumina powder has a particle size of 0.20 μm–0.50 μm and a purity of 99.99%. S3. Online solution quenching: After the finely rolled wire is spun out, it is directly put into the solution furnace for online solution treatment. The solution temperature is 980℃~990℃, and after holding for 15 minutes to 20 minutes, it is directly water cooled.

2. The method according to claim 1, characterized in that, In the S2 high-speed continuous rolling and temperature control step, the wire temperature at the outlet of the intermediate rolling mill is controlled at 1040℃~1050℃, and the rolling speed is 110m / s~115m / s; the wire temperature at the outlet of the finishing rolling mill is controlled at 1030℃~1040℃, and the rolling speed is 115m / s~120m / s.

3. The method according to claim 1, characterized in that, In the S2 high-speed continuous rolling and temperature control step, a high-speed flying shear is used at the entrance of the finishing mill to cut or segment the rolled material; the blade material of the high-speed flying shear is martensitic heat-resistant steel 1Cr16Ni2MoN.

4. The method according to claim 1, characterized in that, The chemical composition of the heat-resistant alloy, by mass percentage, is as follows: C: 0.03–0.10%, Si: 0.05–0.4%, Mn: 0.10–0.60%, P: ≤0.020%, S: ≤0.020%, Cr: 15.00–18.00%, Ni: 24.0–30.0%, Al: 0.80–2.00%, Ti: 1.85–3.00%, Nb: 0.30–1.30%, V: 0.20–0.50%, with the balance being Fe and unavoidable impurities.

5. A cooling medium for use in the method of any one of claims 1 to 4.

6. A heat-resistant alloy prepared by the method according to any one of claims 1 to 4.

7. The heat-resistant alloy according to claim 6, characterized in that, The microstructure of the heat-resistant alloy is a uniform austenitic matrix with a grain size of ASTM 6-10.

8. An engine valve, characterized in that, The engine valve is manufactured from the heat-resistant alloy described in claim 6 or 7.

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