Iron-nickel-chromium heat-resistant alloy and its crack-resistant forging method

Abstract

The application discloses a kind of iron nickel chromium heat-resistant alloy and its anti-crack forging method, belong to special alloy technical field.Solve the problem of low yield rate caused by narrow hot working window and easy to produce crack in the process of forging of high alloy heat-resistant material in prior art.The method comprises smelting alloy raw material to obtain ingot, and heat preservation material is used to heat preservation treatment for ingot or intermediate forging in the process of forging.The heat preservation material is composed of heat preservation matrix material and binder;The heat preservation matrix material is aluminium silicate fiber cotton;The binder is mixed by sodium water glass and potassium water glass, wherein, according to solid effective component, the mass ratio of sodium water glass and potassium water glass is (70-80):(20-30).The application effectively slows down the temperature drop of forging by using specific heat preservation material composition and applying in multi-fire forging, significantly reduces the formation probability of forging crack of high alloy heat-resistant material, and improves product yield and processing efficiency.

Description

Technical Field

[0001] This invention relates to the field of special alloy technology, and in particular to an iron-nickel-chromium heat-resistant alloy and its crack-resistant forging method. Background Technology

[0002] Heat-resistant steels and alloys refer to special steels and alloys that possess excellent thermal strength, thermal stability, and resistance to oxidation and corrosion at high temperatures. They are widely used in key heat-resistant components in thermal power, vehicles, petrochemicals, and other fields. As energy and chemical equipment develops towards higher efficiency and higher parameters, higher requirements are placed on the operating temperature and service life of heat-resistant components.

[0003] Currently used austenitic heat-resistant steels, such as 1Cr25Ni20Si2, mainly rely on solid solution strengthening and carbide strengthening. However, their room temperature and high-temperature strength are increasingly insufficient to meet the demands of extreme working conditions. To improve strength, high levels of strengthening elements such as Al and Ti are typically added to the alloy to form the γ' phase (Ni3(Al,Ti)). However, the addition of these elements significantly deteriorates the alloy's hot workability, leading to poorer hot plasticity and a narrower hot working temperature range. In actual forging processes, high-alloy heat-resistant steel ingots or forgings cool rapidly, making them highly susceptible to surface or internal cracks near the final forging temperature due to insufficient plasticity. This not only increases subsequent processing steps and time but also severely reduces the product yield and increases production costs. Summary of the Invention

[0004] Based on the above analysis, the present invention aims to provide an iron-nickel-chromium heat-resistant alloy and its crack-resistant forging method, so as to at least solve one of the problems of high forging crack rate and low yield of existing high alloy heat-resistant materials.

[0005] On one hand, embodiments of the present invention provide a method for forging an iron-nickel-chromium heat-resistant alloy to resist cracking, comprising the following steps: S1. Smelt alloy raw materials to obtain steel ingots; S2. Forging the steel ingot; In step S2, during the forging process, the surface of the steel ingot or intermediate forging is covered with a thermal insulation material; the thermal insulation material is composed of a thermal insulation matrix material and a binder; the thermal insulation matrix material is aluminum silicate fiber cotton; the binder is a mixture of sodium silicate and potassium silicate, wherein, based on the solid effective components, the mass ratio of sodium silicate to potassium silicate is (70-80):(20-30).

[0006] Furthermore, the modulus of the sodium silicate is 2.60 to 2.90, and / or the modulus of the potassium silicate is 3.25 to 3.35.

[0007] Furthermore, the density of the aluminosilicate fiber cotton is 120-200 kg / m³.3 The thickness is 20-50mm, and it is cut into sheets. The surface of each sheet is bound together with thin iron wire to form a grid structure.

[0008] Furthermore, the sheet-like thermal insulation substrate material has a size of 600mm × 1000mm, and the unit size of the grid structure is 200mm × 200mm.

[0009] Furthermore, the mass ratio of the thermal insulation substrate material to the adhesive is 1:(0.5-2).

[0010] Furthermore, the forging process in step S2 is a multi-fire forging process, and the insulating material is covered in at least two different fires.

[0011] Furthermore, the insulation material is covered and compacted before the steel ingot is unloaded from the furnace, and is forged together with the forging, and is covered again during the hole expansion process.

[0012] Furthermore, the casting temperature in step S1 is 1510~1530℃; the initial forging temperature in step S2 is 1120~1150℃, and the final forging temperature is ≥950℃.

[0013] Furthermore, the chemical composition of the iron-nickel-chromium heat-resistant alloy, by mass percentage, is as follows: C: 0.02~0.10%, Si: 0.01~0.30%, Mn: 0.30~0.80%, P: ≤0.015%, S: ≤0.015%, Cr: 17.0~22.0%, Ni: 23.0~30.0%, Al: 1.00~1.80%, Ti: 1.80~2.80%, Nb: 0.30~1.50%, V: 0.10~0.40%, Zr: 0.010~0.050%, Ce: 0.010~0.030%, with the remainder being Fe and unavoidable impurities.

[0014] On the other hand, the present invention proposes an iron-nickel-chromium heat-resistant alloy, which is prepared by the method described above.

[0015] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: 1) Existing high-alloy heat-resistant steels, such as iron-nickel-chromium heat-resistant alloys, have poor hot working properties and prominent forging cracking problems, which seriously restrict their yield and application. Conventional solutions often focus on optimizing alloy composition or forging process parameters alone, but the effects are limited. Unlike existing technologies, this invention applies a dynamic, sacrificial insulation layer to the forging during the forging process. This insulation layer is transported with the forging and participates in the early forging deformation. In the early stages of forging, it can adapt to a certain degree of deformation or local damage on the surface of the forging, thus continuously playing a heat-insulating role in the critical stage. This slows down heat loss in the forging, especially in intermediate forgings with large surface areas, during operation, allowing it to remain in the high-temperature range with good thermoplasticity (≥950℃) for a longer period of time. This suppresses the tendency for surface and internal cracks to occur when the temperature drops to the low-temperature plasticity zone, thereby significantly improving the product yield.

[0016] 2) In the forging process, this invention uses an insulation material made of aluminosilicate fiber cotton and a sodium silicate-potassium silicate binder in a specific ratio to cover the forging. The mass ratio of the binder, based on its solid effective components, is (70-80):(20-30). This specific ratio has been experimentally proven to have excellent bonding performance at high temperatures, ensuring that the insulation cotton remains firmly in place during forging, transport, and deformation. This reduces heat loss from the forging during operation and suppresses the tendency for surface and internal cracks to form due to temperature drop to the low-temperature plastic zone, thereby significantly improving the product yield.

[0017] 3) Existing high-alloy heat-resistant steels often incorporate excessive amounts of strengthening elements such as Al and Ti to achieve high strength, leading to deterioration in hot working properties and prominent forging cracking problems, severely restricting their yield and applications. This invention precisely controls the Al and Ti content in the alloy composition within the ranges of 1.00~1.80% and 1.80~2.80%, respectively, and combines them with 0.30~1.50% Nb and 0.10~0.40% V. This ensures sufficient precipitation of high-strength γ' phase (Ni3(Al,Ti)) and fine NbC / VC carbides as strengthening phases during subsequent aging treatment, thereby endowing the alloy with excellent room temperature and high-temperature strength. Crucially, this composition design avoids the devastating impact of excessively high Al and Ti content on thermoplasticity, laying the foundation for successful hot forging and resolving the technical contradiction that high-strength alloys are often difficult to forge.

[0018] 4) This invention systematically integrates optimized alloy composition, specific heat-insulating materials, and a multi-forging process (including an initial forging temperature of 1120~1150℃, a final forging temperature ≥950℃, and covering with heat-insulating materials in at least two forging cycles). This process not only extends the effective forging time window and improves the processing efficiency of a single furnace run through heat preservation measures, but also ensures that the final forging possesses both superior performance and excellent internal structure and surface quality through the matching of composition and process. This integrated approach provides a stable and reliable technical path for producing high-performance heat-resistant alloy components, reducing the overall production costs caused by scrap and rework.

[0019] 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

[0020] 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. Figure 1 This is a macroscopic surface morphology diagram of the forging obtained in Embodiment 1 of the present invention; Figure 2 This is a macroscopic surface morphology diagram of the forging obtained in Comparative Example 4 of the present invention. Detailed Implementation

[0021] 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.

[0022] In pursuing high strength, existing high-alloy heat-resistant steels often suffer from deteriorated hot-working properties and prominent forging cracking problems due to the addition of strengthening elements such as Al and Ti, severely restricting their yield and applications. Conventional solutions often focus on optimizing alloy composition or forging process parameters individually, but with limited effectiveness. This invention aims to provide a complete solution that combines specific alloy composition with a dedicated forging process, solving the forging cracking problem while ensuring the alloy possesses excellent high-temperature strength.

[0023] In one specific embodiment of the present invention, a method for forging an iron-nickel-chromium heat-resistant alloy to resist cracking is disclosed, comprising the following steps: S1. Smelt alloy raw materials to obtain steel ingots; S2. Forging the steel ingot; In step S2, during the forging process, the surface of the steel ingot or intermediate forging is covered with heat-insulating material. The thermal insulation material is composed of a thermal insulation matrix material and an adhesive; The insulation substrate material is aluminum silicate fiber cotton; The adhesive is a mixture of sodium silicate and potassium silicate, wherein, based on the solid active ingredients, the mass ratio of sodium silicate to potassium silicate is (70-80):(20-30), for example 70:30, 72:28, 75:25, 78:22, 80:20.

[0024] Specifically, this method applies a dynamic, sacrificial insulation layer to the forging during the forging process. This insulation layer is transported with the forging and participates in the early forging deformation. Its unique structure and adhesion allow it to undergo a certain degree of adaptive deformation or localized damage to the forging surface in the early stages of forging, thus continuously playing an insulation role in the critical stages.

[0025] Specifically, the preparation method of the thermal insulation material is as follows: Step 1: Cut the rolled aluminum silicate fiber cotton into sheets of the predetermined size.

[0026] Step 2: Use thin iron wire to bind the sheet material horizontally and vertically to form a regular grid structure.

[0027] Step 3: Prepare the binder according to the ratio: Mix sodium silicate solid and potassium silicate solid at a mass ratio of (70-80):(20-30), add water and stir to form a homogeneous aqueous solution.

[0028] Step 4: Apply the prepared adhesive evenly to the surface of the sheet insulation cotton treated in Step 2 to obtain the required insulation material.

[0029] Specifically, in step 1, the preferred dimensions of the aluminosilicate fiber cotton are 600mm × 1000mm, with a thickness of 20-50mm (e.g., 20mm, 30mm, 40mm, 50mm) and a density of 120-200 kg / m³. 3 (e.g., 120 kg / m 3 140 Kg / m 3 160Kg / m 3 180 Kg / m 3 200 Kg / m 3 ).

[0030] The preferred size range (600mm × 1000mm) is designed based on the following considerations: On the one hand, this size is moderate, which facilitates manual or mechanical handling, cutting and covering operations, improving construction efficiency; on the other hand, this size can effectively match the surface contour of conventional steel ingots and intermediate forgings, enabling efficient full coverage or splicing coverage, reducing heat loss at the joints, while avoiding incomplete coverage or cumbersome operation due to excessively small sheets, and also preventing material waste and operational inconvenience caused by excessively large sheets.

[0031] Density parameters are controlled between 120-200 kg / m³ 3 Within this range, the insulation cotton has sufficient porosity to achieve excellent thermal insulation, while also possessing enough structural strength to resist minor mechanical compression. A thickness of 20-50mm provides effective thermal resistance without being excessively bulky and interfering with forging operations and observation.

[0032] In step 2, the purpose of bundling is to enhance the structural integrity of the individual insulation cotton pieces, preventing them from tearing or deforming due to insufficient strength during coating, handling, and covering. The iron wire has an extremely fine diameter, preferably φ0.08mm, which oxidizes rapidly at the high forging temperature, and the trace residue has no substantial impact on the subsequent forging process or alloy quality. The final grid structure formed on the surface of the insulation cotton preferably has a unit size of 200mm×200mm.

[0033] This structural design has multiple advantages: First, the grid acts like a skeleton, enhancing the overall integrity of the sheet insulation cotton; second, the grid divides the surface of the insulation cotton into multiple small areas, effectively increasing the surface area and roughness, allowing the adhesive to be more firmly anchored to the insulation cotton; third, the grid structure itself has a certain buffering effect, allowing the insulation layer to undergo a certain degree of adaptive deformation when the forging is deformed.

[0034] The adhesive is a mixture of sodium silicate and potassium silicate. Crucially, the mass ratio of the two, based on their solid active ingredients, is (70-80):(20-30). This specific ratio is key to achieving excellent high-temperature adhesion. As shown in subsequent embodiments of this application, deviations from this ratio will cause the insulation layer to detach during transport or forging, while ratios within this range achieve excellent "non-detachment" results, demonstrating the necessity of this ratio for maintaining effective adhesion of the insulation layer under forging thermal shock and mechanical vibration conditions. When adding water and stirring to form an aqueous solution, it is preferable to prepare it to a saturated or near-saturated state to obtain optimal initial bond strength and workability.

[0035] The adhesive prepared according to this method has a viscosity of approximately 0.8~1.5 Pa·S when measured by a rotational viscometer at 20°C. This state makes it a homogeneous viscous liquid with good coatability and adhesion, which facilitates construction and ensures initial bond strength.

[0036] The sodium silicate glass is primarily composed of sodium silicate (chemical composition expressed as Na₂O·mSiO₂). Its core parameter, modulus (m, i.e., the molar ratio of SiO₂ to Na₂O), is 2.60–2.90 (e.g., 2.60, 2.70, 2.80, 2.90). This modulus range ensures that the binder can form a silicon-oxygen network with a balance of strength and toughness. When using a liquid product, its concentration is typically expressed in Baume degrees. This invention preferably uses sodium silicate glass with a Baume degree of 44.0–46.0°Bé (e.g., 44.0, 44.5, 45.0, 45.5, 46.0). This concentration corresponds to its solid content; specifically, its indicators are typically: SiO₂ content (wt%): 25.7–29.2%; Na₂O content (wt%): 10.2%–12.8%.

[0037] The potassium silicate glass described herein is primarily composed of potassium silicate (chemical composition expressed as K₂O·mSiO₂). It has a higher modulus, ranging from 3.25 to 3.35 (e.g., 3.25, 3.28, 3.30, 3.32, 3.35). This high modulus contributes to the formation of a denser, more heat-resistant silicon-oxygen network structure. The corresponding liquid commercial specifications are typically: density (20°C) ≥ 1.362 g / cm³. 3 Approximately equivalent to a Baumé degree of not less than 38.5°Bé; K2O content (wt%): 11.5-13.5; SiO2 content (wt%): 25.5-28.5; viscosity (20°C) ≥ 0.9 Pa·S.

[0038] Modulus is a core parameter of silicate adhesives. The modulus range selected in this invention ensures that the adhesive can form a high-strength, heat-resistant silicon-oxygen network structure at high temperatures. Specifically, the adhesive forms a three-dimensional silicon-oxygen (Si–O–Si) network structure through a dehydration condensation reaction at high temperatures. During heating, the system loses water, and the silanol groups condense to form a stable inorganic silicon-oxygen bond network, ultimately forming a stable adhesive layer at high temperatures.

[0039] If the properties of the water glass do not meet the above requirements, it will have adverse effects: low SiO2 content will lead to a decrease in modulus, insufficient bonding strength, and easy detachment of the insulation layer; abnormal Na2O or K2O content will also cause modulus imbalance and affect high-temperature stability; excessive iron content (such as Fe content >0.09% in sodium water glass) may introduce impurities and affect alloy purity; low viscosity will lead to uneven coating and reduced adhesion.

[0040] In practice, alloy steel ingots with precisely controlled composition are first obtained through S1 smelting. The smelting can be performed using a vacuum induction furnace or a non-vacuum induction furnace. The raw materials are preferably 50% pure metal and 50% recycled material, which must be baked to remove grease before use. The loading follows the principle of "dense at the bottom, loose at the top," meaning smaller pieces are placed at the bottom and larger pieces at the top to facilitate uniform melting and reduce burning loss. The pouring temperature is controlled at 1510~1530℃ (e.g., 1510℃, 1515℃, 1518℃, 1520℃, 1525℃, 1530℃), the pouring time is 5-6 minutes, and the demolding time is 3-4 hours. After annealing, the obtained steel ingots need to be trimmed at the top and bottom to remove parts with more impurities, and the surface is then polished and cleaned.

[0041] In the S2 forging process, pre-treated and adhesive-coated insulating material is applied to the surface of the high-temperature steel ingot or intermediate forging and then compacted. Alumina silicate fiber cotton itself has extremely low thermal conductivity, making it a highly efficient thermal insulator. The binder, a mixture of sodium silicate and potassium silicate, loses water at high temperatures and forms a hard, high-temperature-resistant three-dimensional silica-oxygen network inorganic binder layer through the condensation reaction of silanol groups. This inorganic binder layer firmly adheres the fiber cotton to the forging surface, preventing it from falling off during transport and forging operations; it also constitutes an additional thermal barrier. This significantly reduces the rate of heat loss from the core of the forging, thereby extending the duration of its optimal thermoplastic temperature range.

[0042] Compared to existing technologies, the forging method provided in this embodiment directly addresses the root cause of forging cracks in high-alloy steel—rapid temperature drop—by introducing a dynamic insulation layer. This is a process insulation technology closely integrated with the forging process. It allows operators more time to complete complex forging operations, preventing cracking caused by the rapid drop in surface temperature of the forging to the thermoplastic deterioration range. Therefore, the beneficial effects of this method are direct and significant: the probability of forging crack formation is greatly reduced, directly translating into improved product yield and processing efficiency.

[0043] Furthermore, the forging process in step S2 is a multi-pass forging process, with the insulating material covered in at least two different passes. Forging high-alloy steel ingots typically requires multiple passes. As forging progresses, the shape of the forging changes, the surface area increases, heat dissipation accelerates, and in subsequent passes (such as reaming), the forging may become thinner, increasing its susceptibility to cracking. Therefore, covering with insulating material only in the first forging pass is insufficient.

[0044] In different forging cycles, the forging temperature, deformation method, and shape and size of the forgings all change, which places corresponding requirements on the covering method and size of the insulation material. In principle, the insulation material should be adapted to the specific shape and size of the forging in the current forging cycle to ensure that the insulation layer is intact and effective.

[0045] The present invention requires covering in at least two different heat treatments, for example, covering at the beginning of the billet forging and during the subsequent reaming process, to systematically control the temperature drop through dynamic and continuous heat preservation.

[0046] For example, the forging process may specifically include: Before the first forging (bill opening): Before loading the steel ingot into the furnace, the pre-treated and adhesive-coated insulation cotton is completely covered and compacted on the surface of the steel ingot. The mass ratio of the insulation matrix material (alumina silicate fiber cotton) to the adhesive is controlled within the range of 1:(0.5-2), for example, 1:0.8, 1:1, or 1:1.5. This ratio ensures that the adhesive fully impregnates the fiber cotton to obtain the best bonding strength, while avoiding oversaturation that could lead to softening of the material structure.

[0047] This covering requires the use of pre-treated (i.e., cut, bundled and coated with adhesive as described above) complete sheets of insulation material (600mm × 1000mm) to ensure that the surface of the steel ingot is completely covered.

[0048] Forging is carried out on a 2000-ton high-speed forging mill, with the steel ingot and insulation material exiting the furnace together. The initial forging temperature is 1120~1150℃ (e.g., 1120℃, 1130℃, 1140℃, 1150℃). After exiting the furnace, the steel ingot is placed vertically on the worktable, head down, and the tail is compressed using a flat anvil. The first compression is to 70-75% of the original height, and then the ingot is trimmed to maintain a cylindrical shape. After this forging, the insulation material is often damaged. After completion, the ingot is returned to the furnace and held at 1150℃ for 1-1.5 hours.

[0049] Before the second forging (drawing): After the forging is removed from the heating furnace, its surface is immediately covered with new insulation material.

[0050] This covering requires the use of new, pre-treated insulation material. Since the shape of the forging has changed after the initial forging, the standard-sized insulation material sheet (600mm×1000mm) can be appropriately cut according to the actual size and shape of the current forging before covering, but it is still necessary to ensure that the insulation layer is intact and firmly bonded.

[0051] Place the forging horizontally, with the manipulator holding the head and the tail one-third on the table. Compress the forging gradually from head to tail using a flat anvil, rotating as you press to maintain a cylindrical shape. Once two-thirds of the forging is compressed, stand the ingot upright and change the direction of the forging head. Continue forging until the ingot reaches 85-90% of its original length. Stop forging and return the ingot to the furnace for 1-1.5 hours. The final forging temperature must be ≥950℃ (e.g., 950℃, 960℃, 970℃, 980℃, 990℃, 1000℃).

[0052] The third forging process (upsetting and forming): Upsetting is performed to the required dimensions, followed by punching and reaming. Especially during the reaming process, because the forging becomes thinner and dissipates heat extremely quickly, it is necessary to supplement the critical parts of the forging (such as the hole wall) with insulation cotton for localized reinforcement. This stage mainly focuses on localized insulation, and smaller, pre-treated insulation material sheets can be used to selectively cover the thin areas where heat dissipates quickly.

[0053] After forging, the obtained blank forgings are heat-treated to obtain the required mechanical properties: First, solution treatment is performed, in which the forgings are heated to 1050–1150℃ and held for 1–2 hours to allow the alloying elements to fully dissolve in the matrix, followed by rapid cooling by water or air cooling; then, aging treatment is performed, in which the solution-treated forgings are held at 700–800℃ for 8–16 hours, followed by air cooling. During this process, nanoscale γ' phase [Ni3(Al,Ti)] and fine carbide reinforcing phases precipitate in the alloy, thereby giving the alloy excellent room temperature and high temperature strength.

[0054] This meticulous and standardized forging process, closely integrated with the dynamic and repeated application of thermal insulation materials, ensures effective temperature protection for the forgings at critical moments when their shape undergoes significant changes and heat dissipation intensifies. This, in turn, guarantees the success rate of the entire complex forging process and the intrinsic quality of the final forgings.

[0055] Based on the above method, the present invention prepares an iron-nickel-chromium heat-resistant alloy.

[0056] The chemical composition of the iron-nickel-chromium heat-resistant alloy, by mass percentage, is as follows: C: 0.02~0.10%, Si: 0.01~0.30%, Mn: 0.30~0.80%, P: ≤0.015%, S: ≤0.015%, Cr: 17.0~22.0%, Ni: 23.0~30.0%, Al: 1.00~1.80%, Ti: 1.80~2.80%, Nb: 0.30~1.50%, V: 0.10~0.40%, Zr: 0.010~0.050%, Ce: 0.010~0.030%, with the remainder being Fe and unavoidable impurities.

[0057] The alloy of this invention is an iron-nickel-chromium austenitic heat-resistant alloy that achieves a balance between strength and hot workability through precise compositional design. Its high Ni content (23.0~30.0%) and Cr content (17.0~22.0%) ensure a stable austenitic matrix and excellent resistance to oxidation and corrosion. The core of achieving this balance lies in the precise selection and control of the types and content ranges of elements such as Al, Ti, Nb, and V. This is not only to ensure sufficient strengthening phase formation during subsequent heat treatment to guarantee strength, but more importantly, by limiting the Al and Ti contents to specific ranges (Al: 1.00~1.80%, Ti: 1.80~2.80%), and supplementing with Nb and V, excessive formation of harmful phases and a sharp decline in hot workability are avoided, thus enabling this high-strength alloy to be successfully processed through specific subsequent forging processes.

[0058] The strengthening mechanism of this alloy after solution treatment and aging is mainly based on two aspects: (1) γ' phase strengthening: Ni reacts with Al and Ti in strictly controlled amounts to form a coherent intermetallic compound strengthening phase γ', namely Ni3(Al,Ti). This phase is extremely stable at high temperatures and its strength increases with increasing temperature, making it the most important high-temperature strengthening phase of the alloy.

[0059] (2) Carbide strengthening: Strong carbide-forming elements Nb and V combine with C in the alloy to precipitate fine, dispersed NbC and VC particles during aging. These carbides, as a second strengthening phase, can effectively pin dislocations and hinder their movement, thereby providing additional strength contributions.

[0060] Zr and Ce are microalloying elements, mainly used to purify grain boundaries and improve thermoplasticity.

[0061] It is precisely because of the synergistic strengthening effect of the γ' phase and carbides that the alloy of the present invention achieves strength indicators that are far higher than those of the traditional austenitic heat-resistant steel 1Cr25Ni20Si2 at both room temperature and high temperature.

[0062] Furthermore, the iron-nickel-chromium heat-resistant alloy is prepared by the aforementioned method. Existing high-alloy heat-resistant steels often incorporate strengthening elements such as Al and Ti to achieve high strength. Due to their high Al and Ti content, their as-cast microstructure exhibits poor thermoplasticity, making them highly susceptible to cracking when using conventional forging processes. The specific crack-resistant forging method described in this invention (especially the dynamic heat preservation technology) allows for the successful processing of this alloy into defect-free forgings, realizing its excellent high-temperature strength potential. Therefore, alloy products prepared by this method possess higher commercial value and reliability.

[0063] 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.

[0064] Preparation Example This embodiment provides a specific method for preparing the thermal insulation material, the steps of which are as follows: Step 1: Take a roll with a density of 160 kg / m³ 3 Aluminum silicate fiber cotton with a thickness of 30mm is cut into several rectangular sheets with a size of 600mm (width) × 1000mm (length).

[0065] Step 2: Take one of the pieces and use a thin iron wire with a diameter of φ0.08mm to tie it horizontally and vertically at a spacing of 200mm, so as to form a stable 200mm×200mm grid structure on its surface.

[0066] Step 3: Take 750 grams of sodium silicate with a modulus of 2.75 and a Baume degree of 45.0°Bé, and 250 grams of potassium silicate with a modulus of 3.30. Place both in a container and stir using a mechanical stirrer. During stirring, add water as needed to adjust the viscosity of the mixture until a homogeneous, saturated or nearly saturated, and easily brushable viscous liquid is obtained, which is the desired adhesive.

[0067] Step 4: Apply the prepared adhesive evenly to the surface of the sheet insulation substrate material treated in Step 2. During application, ensure the adhesive fully saturates the surface fibers of the insulation cotton while avoiding oversaturation that could damage the material structure. By controlling the amount applied, maintain a 1:1 mass ratio of insulation substrate material to adhesive, resulting in a final adhesive coating thickness of approximately 2mm on the insulation cotton surface.

[0068] Example 1 This embodiment provides an iron-nickel-chromium heat-resistant alloy and its crack-resistant forging method. The alloy chemical composition (furnace number 2) by mass percentage is: C: 0.045%, Si: 0.17%, Mn: 0.32%, P: 0.013%, S: 0.007%, Cr: 18.22%, Ni: 28.33%, Al: 1.41%, Ti: 2.25%, Nb: 1.06%, V: 0.30%, Zr: 0.022%, Ce: 0.018%, with the balance being Fe and unavoidable impurities.

[0069] The specific steps are as follows: S1. Smelting and Casting: Smelting is carried out in a vacuum induction furnace. The raw materials are pure metal and recycled materials, each accounting for 50%. The casting temperature is controlled at 1528℃ and the casting time is 5.5 minutes. After demolding, steel ingots are obtained.

[0070] S2. Forging and Insulation: After annealing, trimming, and surface cleaning, the steel ingot undergoes multiple forging processes. During forging, an insulation material prepared as described in Preparation Example 1 is used for covering.

[0071] First forging (opening): Before loading the steel ingot into the furnace, a full-size (600mm × 1000mm) insulation material is completely wrapped around the surface of the ingot and compacted. The ingot, along with the insulation material, is removed from the furnace and forged on a 2000-ton high-speed forging mill. The initial forging temperature is 1125℃. The ingot is compressed to 70% of its original height in the first forging. After completion, it is returned to the furnace and held at 1150℃ for 1.5 hours.

[0072] Before the second forging (drawing): After removing the forging from the heating furnace, immediately re-cover its surface with new, trimmed insulation material to fit the current shape of the forging. The initial forging temperature is 1120℃, the length after forging reaches 85% of the original length, and the final forging temperature is 972℃. The forging is then returned to the furnace for 1.0 hour of heat treatment.

[0073] The third forging process (upsetting and forming): Upsetting is performed to the required dimensions, followed by punching and reaming. During the reaming process, small pieces of insulation material are added to critical areas such as the hole walls and end faces to provide localized insulation.

[0074] The final product is a blank forging with good surface quality and no macroscopic cracks (see...). Figure 1 ).

[0075] S3. Heat treatment: The obtained blank forgings are first subjected to solution treatment at 1100℃ for 2 hours and water cooling; then subjected to aging treatment at 750℃ for 16 hours and air cooling.

[0076] Example 2 This embodiment aims to illustrate the universality of the method of the present invention for alloys with different compositions. Six heats (with chemical compositions corresponding to heat numbers 1-6 in Table 1) of iron-nickel-chromium heat-resistant alloy were smelted in a vacuum induction furnace. All heats employed the same heat-holding forging process as in Example 1. The casting process parameters and initial ingot quality are recorded in Table 2, and the forging process parameters and forging quality are recorded in Table 5. The room temperature and high-temperature mechanical properties of this alloy were compared with those of commercial austenitic heat-resistant steel 1Cr25Ni20Si2, which served as a comparative example. The results are shown in Table 3.

[0077] Table 1 Chemical composition (wt%) of embodiments of the present invention

[0078] Table 2 Casting process parameters and ingot quality

[0079] Table 3 Comparison of mechanical properties of embodiments of the present invention and commonly used austenitic heat-resistant steels

[0080] Table 4. Adhesive ratio and bonding effect of thermal insulation material in embodiments of the present invention.

[0081] Table 5 Forging process parameters and results of embodiments of the present invention

[0082] As shown in Table 2, under the casting process parameters described in this invention, all heats yielded steel ingots with good surface quality, providing qualified raw materials for subsequent forging.

[0083] As shown in Table 5, all heat numbers were processed under the forging parameters described in this invention, and all of them ultimately obtained forgings of "good" quality. This proves that the forging process of this invention has good stability and repeatability in solving the problem of forging cracks in high alloy steel, and directly leads to a significant improvement in product yield.

[0084] As shown in Table 3, the alloy forgings (heater numbers 1-6) forged using the method of this invention and conforming to the composition range of this invention achieve an excellent combination of high strength and good plasticity in their mechanical properties: Room temperature (23°C) properties: The tensile strength (R) of the alloy of this invention m The yield strength (R) is as high as 1155~1212MPa. p0.2 The pressure reaches 715~782MPa, which is much higher than the 705MPa and 412MPa of the comparative steel.

[0085] Its high-temperature strength is particularly outstanding, with high-temperature performance at 600℃: the R of the alloy of this invention m Maintain at 1005~1066MPa, R p0.2 The pressure remains between 685 and 702 MPa, which is more than 2.3 times that of the comparative steel (431 MPa, 208 MPa). High-temperature performance at 700℃: The R of the alloy of this invention... m It can still maintain 802~824MPa, R p0.2 It maintains a pressure of 635~670 MPa, which is more than 2.4 times that of the comparative steel (343MPa, 127MPa).

[0086] Although the room temperature elongation (A) and reduction of area (Z) of the alloy of the present invention are slightly lower than those of the comparative steel, this is a reasonable result expected in the art, accompanying the high strength strengthening achieved through the γ' phase and carbides. The plasticity properties of all embodiments remain at a good level suitable for practical engineering applications (A>20%, Z>20%). Furthermore, at a high temperature of 700°C, the plasticity (A, Z) of the alloy of the present invention recovers to a level comparable to or even better than that of the comparative steel, indicating a more reliable guarantee of toughness under high-temperature service conditions.

[0087] Using steel ingots with the same composition as in Example 1 (furnace number 2), the ratio of the thermal insulation material binder was changed during the forging process to investigate its effect on the forging process and the quality of the forgings. The specific ratio and results are shown in Table 4.

[0088] As shown in Table 4, qualified products can only be obtained when the mass ratio of sodium silicate to potassium silicate in the binder is within the range of (70-80):(20-30) (numbers 3-6). Exceeding this range will cause the insulation layer to fall off and trigger cracking of the forging.

[0089] Comparative Example To verify the key role of the heat-insulating forging method of the present invention, the same alloy composition, smelting process (casting parameters are the same as those in heat number 2 in Table 2) and forging temperature parameters were used as in Example 1 (furnace number 2), but the heat-insulating material described in the present invention was not covered during the subsequent forging process, so as to serve as a comparative example.

[0090] The results showed that in this comparative example, during the second forging (drawing) process, the forging temperature rapidly dropped to approximately 850°C, leading to severe surface cracking of the forging. Even after subsequent processing and grinding, deep defects remained at the cracked areas (see...). Figure 2 This forced the forging process to be halted, resulting in the product being scrapped. This contrasts sharply with the excellent forging obtained in Example 1.

[0091] In summary, this invention successfully forges high-performance iron-nickel-chromium heat-resistant alloy forgings by combining optimized alloy composition with a specialized heat-insulating forging process. This method overcomes the industry-wide problem of forging cracks in high-alloy heat-resistant steels caused by the addition of Al and Ti elements, resulting in a high product yield. The prepared alloy achieves an optimal balance between high strength and good plasticity, with its room temperature and high temperature strength (especially tensile strength and yield strength at 600℃ and 700℃) significantly increased, outperforming traditional austenitic heat-resistant steels. This provides a reliable material solution for components operating under higher stress and temperature environments.

[0092] 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 forging an iron-nickel-chromium heat-resistant alloy to resist cracking, characterized in that, Includes the following steps: S1. Smelt alloy raw materials to obtain steel ingots; S2. Forging the steel ingot; In step S2, during the forging process, the surface of the steel ingot or intermediate forging is covered with heat-insulating material. The thermal insulation material is composed of a thermal insulation matrix material and an adhesive; The insulation substrate material is aluminum silicate fiber cotton; The adhesive is composed of sodium silicate and potassium silicate, wherein, based on the solid effective components, the mass ratio of sodium silicate to potassium silicate is (70-80):(20-30); The modulus of the sodium silicate is 2.60 to 2.90, and the modulus of the potassium silicate is 3.25 to 3.

35.

2. The forging method according to claim 1, characterized in that, The density of the aluminum silicate fiber cotton is 120-200 kg / m³. 3 The thickness is 20-50mm, and it is cut into sheets. The surface of each sheet is bound together with thin iron wire to form a grid structure.

3. The forging method according to claim 2, characterized in that, The sheet-like thermal insulation substrate material has a size of 600mm × 1000mm, and the unit size of the grid structure is 200mm × 200mm.

4. The forging method according to claim 1, characterized in that, The mass ratio of the thermal insulation substrate material to the adhesive is 1:(0.5-2).

5. The forging method according to claim 1, characterized in that, The forging process in step S2 is a multi-fire forging process, and the insulating material is covered in at least two different fires.

6. The forging method according to claim 5, characterized in that, The insulation material is covered and compacted before the steel ingot is unloaded from the furnace, and is forged together with the forging. It is then covered again during the hole expansion process.

7. The forging method according to claim 1, characterized in that, The casting temperature in step S1 is 1510~1530℃; the initial forging temperature in step S2 is 1120~1150℃, and the final forging temperature is ≥950℃.

8. The forging method according to any one of claims 1-7, characterized in that, The chemical composition of the iron-nickel-chromium heat-resistant alloy, by mass percentage, is as follows: C: 0.02~0.10%, Si: 0.01~0.30%, Mn: 0.30~0.80%, P: ≤0.015%, S: ≤0.015%, Cr: 17.0~22.0%, Ni: 23.0~30.0%, Al: 1.00~1.80%, Ti: 1.80~2.80%, Nb: 0.30~1.50%, V: 0.10~0.40%, Zr: 0.010~0.050%, Ce: 0.010~0.030%, with the remainder being Fe and unavoidable impurities.

9. A heat-resistant iron-nickel-chromium alloy, characterized in that, The iron-nickel-chromium heat-resistant alloy is prepared by the method described in claim 8.

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