High-hardness low-expansion alloy and preparation method thereof

Abstract

The invention relates to a high-hardness low-expansion alloy and a preparation method thereof, belongs to the field of precision alloy materials, and solves the technical bottleneck of insufficient hardness of the traditional low-expansion alloy in the prior art and the problem that the traditional low-expansion alloy is difficult to be used for manufacturing aerospace precision parts and high-precision instruments with higher hardness requirements. The invention relates to a high-hardness low-expansion alloy and a preparation method thereof. The high-hardness low-expansion alloy comprises the following components in percentage by mass: 0.02-0.06% of Fe, 38-45% of Cr, 0.04-1.1% of Si, less than or equal to 0.0049% of P, less than or equal to 0.0049% of S, less than or equal to 0.0019% of Mn, less than or equal to 0.049% of C, 2.9-4.6% of Al and the balance of Ni. The preparation method is characterized in that solution treatment and aging treatment are adopted, specifically, solution treatment and water cooling are conducted at the temperature of 1100-1200 DEG C, then aging treatment is conducted at the temperature of 450-650 DEG C, a lamellar alpha-Cr (50-200 nm) and granular alpha-Cr (20-80 nm) double-phase strengthening structure is generated in the alloy, and performance breakthrough is achieved through the synergistic effect of the lamellar alpha-Cr and the granular alpha-Cr. Under the condition that the thermal expansion coefficient of the alloy is smaller than or equal to 5 * 10 <-6 > / K at the temperature of 20-200 DEG C, the hardness is larger than or equal to 58 HRC, and the tensile strength is larger than

Description

TECHNICAL FIELD

[0001] The present application relates to the field of precision alloy materials, and in particular to a high-hardness low-expansion alloy and a preparation method thereof. BACKGROUND

[0002] In the high-end manufacturing field of precision instruments, aerospace thermal sensitive elements, etc., the thermal expansion performance and mechanical properties of materials are extremely demanding. An ideal material should have a low thermal expansion coefficient to ensure excellent dimensional stability in a temperature changing environment, and also have high hardness and strength to meet the mechanical performance requirements of wear resistance and deformation resistance, etc.

[0003] At present, traditional low-expansion alloys, such as Fe-Ni invar alloys, have been widely used in the above-mentioned fields because they have extremely low thermal expansion coefficients (usually ≤2×10 -6 / K) within a certain temperature range. However, these alloys generally have low hardness, usually less than 45HRC, which makes it difficult to meet the requirements of high wear resistance and high load in harsh working conditions.

[0004] In order to improve the hardness and strength of low-expansion alloys, existing technologies attempt to add strengthening elements such as chromium (Cr) and molybdenum (Mo) for alloying design. Although the addition of these elements can improve the strength of the material to some extent, it often brings new problems: on the one hand, excessive addition can significantly increase the thermal expansion coefficient of the alloy, losing its low-expansion characteristics; on the other hand, it can also cause deterioration of material properties, such as reduction of hardness and strength, bringing difficulties and challenges to actual application.

[0005] Therefore, it is necessary to develop a new type of high-hardness low-expansion alloy and a preparation method thereof to break through the above technical bottlenecks and obtain a material with excellent comprehensive performance of high hardness, low thermal expansion coefficient and high strength, thereby breaking through the existing technical bottlenecks and meeting the growing demand for high-end precision manufacturing. SUMMARY

[0006] In view of the above analysis, the present application aims to provide a high-hardness low-expansion alloy and a preparation method thereof to provide an alloy with high hardness, low thermal expansion coefficient and high strength.

[0007] In one aspect, the present application provides a high-hardness low-expansion alloy, the chemical composition of which comprises, in terms of mass percentage: Fe 0.02-0.06%, Cr 38-45%, Si 0.04-1.1%, P ≤0.0049%, S ≤0.0049%, Mn ≤0.0019%, C ≤0.049%, Al 2.9-4.6%, and the balance being Ni.

[0008] Preferably, the high hardness and low expansion alloy has a chemical composition comprising, in mass percentage: Fe 0.03-0.05%, Cr 39-44%, Si 0.05-1%, P≤0.005%, S≤0.005%, Mn≤0.002%, C≤0.05%, Al 3-4.5%, and the balance of Ni.

[0009] Further, the alloy has a structure of lamellar alpha-Cr and granular alpha-Cr dual-phase strengthening structure, and the alloy has a structure of lamellar alpha-Cr and granular alpha-Cr dual-phase strengthening structure, wherein the lamellar alpha-Cr has a particle size range of 50-200 nm, and the granular alpha-Cr has a particle size range of 20-80 nm.

[0010] Further, the alloy in solid solution state has a two-phase structure composed of a face-centered cubic austenite matrix and body-centered cubic Cr single-element particles.

[0011] Further, the alloy in solid solution state has a grain size of 24-26 μm, and the Cr particles have a size of less than 5 μm.

[0012] Further, the alloy has a thermal expansion coefficient of ≤5×10 -6 / K at 20-200°C, a hardness of ≥58 HRC, and a tensile strength of ≥1300 MPa.

[0013] In another aspect, the present application provides a method for preparing a high hardness and low expansion alloy, comprising the following steps:

[0014] S1, batching: taking metallic nickel, metallic chromium, electrolytic aluminum and industrial pure iron as raw materials, and batching according to the above-mentioned component proportions;

[0015] S2, smelting:

[0016] The batched materials are placed into a vacuum induction furnace for smelting, and then cast into electrode rods; the prepared electrode rods are ground and polished, and then subjected to vacuum self-consumption remelting to obtain self-consumption ingots;

[0017] S3, forging

[0018] The self-consumption ingots are placed in a furnace below 600°C, and the temperature is raised at a rate of ≤200°C / h; after being kept at a temperature of 1100-1180°C for an appropriate time, the ingots are broken down into rod materials;

[0019] S4, solid solution treatment of the rod materials;

[0020] S5, aging treatment.

[0021] Further, the solid solution treatment: the rod materials are placed in a non-vacuum resistance furnace, heated to 1100-1200°C at a temperature raising rate of 80-120°C / min, and kept for 0.5-1.5 h.

[0022] Further, the aging treatment is that the bar is placed in a non-vacuum resistance furnace again, heated to 450-650 DEG C at a heating rate of 80-120 DEG C / min, and kept for 4-6 hours.

[0023] Further, with the increase of the aging temperature, lamellar alpha-Cr begins to precipitate again, and then fine granular alpha-Cr precipitates at the grain boundaries.

[0024] Compared with the prior art, the present application can achieve at least one of the following beneficial effects:

[0025] 1. The present application provides a component basis for the dual-phase strengthening structure of "lamellar alpha-Cr" and "granular alpha-Cr" by strictly controlling the Cr content (38-45%) and the ultra-low impurity elements (P, S, Mn≤0.005%), while ensuring the low expansion property.

[0026] 2. The solid solution state structure of the present application is a two-phase structure composed of face-centered cubic austenite matrix and body-centered cubic Cr single element particles, the grain size is about 25 μm, and the Cr particle size is below 5 μm. With the increase of the aging temperature, lamellar alpha-Cr begins to precipitate again, and then fine granular alpha-Cr precipitates at the grain boundaries. After a period of aging, the amount of granular alpha-Cr precipitates increases and the size becomes larger, and the alloy hardness rapidly increases.

[0027] 3. The alloy structure obtained by the solid solution and aging treatment of the preparation method of the present application is the dual-phase strengthening structure of "lamellar alpha-Cr" and "granular alpha-Cr". The two forms of precipitates play different strengthening roles (lamellar hinders dislocation slip, granular pins the grain boundary to inhibit high-temperature grain growth), and produce a synergistic effect. Lamellar alpha-Cr hinders dislocation slip to increase the strength; granular alpha-Cr pins the grain boundary to inhibit high-temperature grain growth; the synergistic effect of the two makes the hardness break through 58HRC (the traditional invar alloy ≤45HRC), while maintaining a low thermal expansion coefficient ≤5×10 -6 / K and high tensile strength (≥1300 MPa).

[0028] 4. The preparation method of the present application forms the structure of austenite matrix + granular Cr single element in the solid solution stage. With the increase of the aging temperature, lamellar alpha-Cr begins to precipitate again, and then fine granular alpha-Cr precipitates at the grain boundaries. The obtained alloy has excellent comprehensive performance of high hardness (≥58HRC), low thermal expansion coefficient (≤5.0×10 -6 / K) and high tensile strength (≥1300 MPa), can still maintain excellent dimensional stability in a temperature change environment, and also has high hardness and strength to meet the mechanical performance requirements of wear resistance, deformation resistance and the like, and expands the application in some aerospace precision parts and high-precision instrument manufacturing which require high hardness.

[0029] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description and the accompanying drawings. Attached Figure Description

[0030] Figure 1 It is a solid solution metallographic structure of a high-hardness, low-expansion alloy.

[0031] Figure 2 The microstructure of a high-hardness, low-expansion alloy aged at 600℃ for 5 hours. Detailed Implementation

[0032] Exemplary embodiments of the present invention will now be described in more detail. While exemplary embodiments of the present invention are shown in the following examples, it should be understood that the present invention may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0033] Traditional low-expansion alloys (such as Fe-Ni Invar alloys) have low expansion characteristics, but their hardness is generally below 45 HRC, making it difficult to meet the requirements of high wear resistance. Existing technologies strengthen alloys by adding elements such as Cr and Mo, but this can easily lead to an increase in the coefficient of thermal expansion or a deterioration in performance.

[0034] Therefore, it is necessary to develop a new type of alloy and its preparation method to break through the above-mentioned technical bottlenecks and obtain a material with excellent comprehensive properties, including high hardness, low coefficient of thermal expansion and high strength, thereby breaking through the existing technical bottlenecks and meeting the growing demand for high-end precision manufacturing.

[0035] On one hand, the present invention provides a high-hardness, low-expansion alloy, wherein the chemical composition of the high-hardness, low-expansion alloy comprises, by mass percentage: Fe 0.02-0.06%, Cr 38-45%, Si 0.04-1.1%, P≤0.0049%, S≤0.0049%, Mn≤0.0019%, C≤0.049%, Al 2.9-4.6%, and the balance being Ni.

[0036] Preferably, the chemical composition of the high-hardness, low-expansion alloy, by mass percentage, includes: Fe 0.03-0.05%, Cr 39-44%, Si 0.05-1%, P≤0.005%, S≤0.005%, Mn≤0.002%, C≤0.05%, Al 3-4.5%, with the balance being Ni.

[0037] Specifically, the role played by each element and the reason for the amount are:

[0038] Cr: form reinforcing phase: chromium is the main precipitated strengthening element in the alloy. Through a specific solid solution + aging heat treatment process, Cr is precipitated in the form of lamellar α-Cr and granular α-Cr from the nickel matrix, forming a "dual-phase strengthening structure". If the Cr content in the alloy is too low, it cannot precipitate a sufficient number and size of α-Cr phase during aging, resulting in insufficient strengthening effect. Too high Cr content will significantly increase the thermal expansion coefficient of the alloy, destroy its low expansion characteristics and increase the cost. Considering comprehensively, the Cr element amount of the present application is 38-45%.

[0039] Ni: a key element for controlling the expansion of the alloy, the Ni content in the alloy needs to be strictly controlled, and too low or too high Ni content in the alloy will cause the expansion coefficient of the alloy to be too high, which seriously affects the performance of the alloy.

[0040] Fe: as a base element of the alloy, Fe element has the advantages of wide source, low price and excellent plasticity. If the Fe content is too high, it will change the phase equilibrium of the Ni-Cr-Al system, which may promote the undesirable phase transition or change the precipitation dynamics, and cause uncontrollable effects on the stable low expansion characteristics and hardness. Considering comprehensively, the Fe content of the present application is controlled at 0.02-0.06%. Exemplarily, Fe: 0.02%, 0.03%, 0.04%, 0.05%, 0.06%

[0041] Si: as an element that can reduce the Curie point of the alloy, appropriate low Si content can effectively reduce its effect on the Curie point of the alloy, and high Si content also has adverse effects on the thermal plasticity of the alloy, but a certain amount of Si can form an oxide film on the surface of the alloy to prevent metal oxidation. Considering comprehensively, the Si content of the present application is controlled at 0.04-1.1%. Exemplarily, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 1.0%, 1.1%.

[0042] Al: aluminum can form ordered intermetallic compounds with nickel (such as Ni3Al), which have high temperature stability and significant precipitation strengthening effect, further improving the strength and hardness of the alloy. If the content is too high, the overall thermal expansion coefficient of the alloy may be significantly exceeded; if the content is too low, the strength and hardness are reduced, which cannot meet the wear-resistant working conditions. Considering comprehensively, the Al content of the present application is controlled at 2.9-4.6%. Exemplarily, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%.

[0043] Mn: the appropriate amount of Mn element in the alloy can effectively improve the thermal plasticity of the alloy, improve the comprehensive performance of the alloy, but too high Mn content will cause a large number of MnS inclusions in the alloy. Reduce the purity of the alloy, prone to cracking during hot working. Comprehensive consideration, the present application controls Mn≤0.0019%.

[0044] P and S: as impurity elements, try to reduce their content in the alloy as much as possible under the condition of equipment and production cost, which can effectively curb the hot and cold brittle defects generated in the alloy. If the content of P is too high, P: has a strong grain boundary segregation tendency, significantly increases the grain boundary brittleness of the alloy, causes the room temperature and low temperature toughness to decrease sharply, and is easy to occur brittle fracture. If the content of S is too high, sulfide inclusions are formed with Mn and other elements, which will extend along the rolling direction during hot working, form anisotropy, and seriously damage the transverse toughness and fatigue resistance. Comprehensive consideration, the present application controls P≤0.0049%, S≤0.0049%.

[0045] C is a chemical element in iron.

[0046] On the other hand, the present application provides a high hardness and low expansion alloy preparation method, comprising the following steps: batching, smelting, forging, solid solution treatment, aging treatment.

[0047] S1, batching: taking metal nickel, metal chromium, electrolytic aluminum and industrial pure iron as raw materials, batching according to the above component proportion;

[0048] S2, smelting:

[0049] The batching is put into a vacuum induction furnace for smelting, and is poured into an electrode bar; the surface of the prepared electrode bar is ground and polished, and then vacuum consumable remelting is carried out, to obtain a consumable ingot;

[0050] Specifically, in the above step S2, in the vacuum induction smelting process, the material is strictly allocated according to the designed composition, and the loss on ignition of various alloy elements and the content of impurity elements are strictly controlled; and in the pouring process, argon is filled to 4000-6000 Pa to form a protective atmosphere for pouring into an electrode rod. After the composition analysis of the electrode rod meets the requirements, the surface of the electrode rod is polished, and vacuum consumable remelting is performed. In the smelting process, a constant melting drop control technology is used, the current is 2.0-4.7 KA, the voltage is 21.5-24.5 V, the melting speed is 5-9 kg / min, and the vacuum degree is ≤0.1 Pa. By stabilizing the current and voltage, the liquid drop formation and drop process are stable, the smelting process is extremely stable, the removal of harmful elements is ensured, and the alloy composition is purified. If the vacuum degree is too low, the gas elements in the alloy cannot be fully removed, and if the vacuum degree is too high, the equipment conditions cannot be met, and the normal service life of the equipment will be affected. The main role of step S2 is to accurately control the chemical composition, reduce the inclusion and gas content in the alloy, ensure the purity of the alloy, and then obtain a consumable ingot that meets the preset formula.

[0051] S3, forging:

[0052] The consumable ingot is loaded into the furnace below 600℃, the heating rate is ≤200℃ / h, and after being kept at 1100℃-1180℃ for a proper time, the rod material is formed.

[0053] Specifically, the loading temperature is controlled below 600℃, and after being kept for 2h, the consumable ingot is preheated to ensure that the inside and outside can be completely heated; the heating furnace has a heating rate of ≤200℃, and the heating rate should not be too fast. If the heating rate is too fast, the temperature difference between the inside and outside of the steel ingot will be large, which will cause cracking during forging. If the heating rate is too slow, energy will be wasted; the forging heating temperature is controlled at 1100-1180℃. The forging heating temperature should not be too low or too high. If it is too low, it will cause cracking during forging, and if it is too high, it will cause overheating or overburning.

[0054] Further, the S4 solid solution treatment: the rod material is placed in a non-vacuum resistance furnace, heated to 1100-1200℃ at a heating rate of 80-120℃ / min, kept for 0.5-1.5h, and water-cooled.

[0055] For example, the solid solution heating rate is 80℃ / min, 90℃ / min, 100℃ / min, 110℃ / min, 120℃ / min, the temperature is 1100℃, 1110℃, 1120℃, 1130℃, 1140℃, 1150℃, 1160℃, 1170℃, 1180℃, 1190℃, 1200℃; the holding time is 0.5h, 0.6h, 0.7h, 0.8h, 0.9h, 1.0h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h.

[0056] Specifically, the role of the solution treatment is to fully dissolve the alloying elements (especially Cr) into the nickel matrix to form a solid solution state organization of austenite matrix + granular Cr element (such as Figure 1 ), the grain size is about 25 μm, and the Cr particle size is below 5 μm, obtaining a uniform and fine initial organization: through high-temperature holding, the composition is homogenized, and through rapid cooling (water cooling), the high-temperature state is "fixed" to prepare for subsequent precipitation. The solid solution state is a two-phase organization composed of an austenite matrix of face-centered cubic and Cr element particles of body-centered cubic.

[0057] The solution treatment temperature range is selected at 1100-1200℃: this temperature range ensures that Cr, Al and other elements have enough diffusion energy and can be fully dissolved into the Ni matrix. If the temperature is too low, the dissolution is not sufficient, and the subsequent aging is not uniform or the amount of precipitated phase is insufficient; if the temperature is too high, it may cause the grains to grow rapidly, which damages the toughness and strength of the material.

[0058] If the solution treatment temperature is too low: Cr and other elements are not fully dissolved, and there are undissolved coarse Cr phases in the matrix. These phases cannot be transformed into the required nanoscale lamellar / particle structure during subsequent aging, which greatly reduces the strengthening effect and the hardness and strength cannot meet the standard.

[0059] If the solution treatment temperature is too high: the austenite grains will coarsen rapidly. Coarse grains will reduce the strength of the material, and may also cause element segregation, which will also affect the uniform distribution of the subsequent precipitated phase, thus affecting the strength and hardness.

[0060] The solution holding time is 0.5-1.5 hours, which ensures that the alloying elements are fully dissolved and the composition is uniform at a given temperature.

[0061] If the solution treatment holding time is too short: the element dissolution and diffusion are not sufficient, the composition is not uniform, and the strength and hardness of the material are not good.

[0062] If the solution treatment holding time is too long: under the premise of ensuring dissolution, the long holding time provides more time for grain growth, which may cause grain coarsening, and the strength and hardness of the material are not greatly improved and the energy consumption is increased.

[0063] The role of water cooling: rapid cooling is to prevent the alloying elements from precipitating too early and slowly during cooling. The purpose is to retain the supersaturated solid solution state at high temperature to room temperature, which lays the foundation for the uniform and dispersed precipitation of nanoscale strengthening phase during subsequent aging. If the cooling is slow, the Cr element will precipitate coarse particles at the grain boundaries, which will consume the strengthening elements in the matrix and make the aging treatment ineffective.

[0064] The solution treatment heating rate is selected to be 80-120℃ / min, because the alloy will undergo recovery, recrystallization and other microstructure transformation during heating. A controllable heating rate helps these transformations to proceed uniformly and fully, providing a more uniform starting point for the subsequent solution dissolution stage.

[0065] If the heating rate is too slow, part of the strengthening elements (such as Cr) will precipitate prematurely and slowly before reaching the solution temperature, forming coarse and unevenly distributed precipitates. These "inborn defects" may be difficult to completely dissolve during the subsequent solution holding stage, thereby consuming elements (such as Cr) used to form ideal nano-strengthening phases, damaging the final strengthening effect and possibly having a slight negative impact on the microstructure.

[0066] If the heating rate is too fast, it may lead to poor temperature uniformity: the surface has reached or even exceeded the solution temperature, while the core temperature is still very low. This will cause surface grain coarsening: the surface area stays at high temperature for too long, and the grains begin to grow, while the core structure has not yet been transformed. The composition is not uniformly dissolved: the strengthening elements in the surface area have been dissolved, while the core has not. Within the specified holding time, it may not be enough to completely homogenize the core composition, ultimately leading to reduced strength and hardness performance.

[0067] Further, the aging treatment S5 places the rod again in a non-vacuum resistance furnace, heats it to 450-650℃ at a heating rate of 80-120℃ / min, and holds it for 4-6 hours.

[0068] For example, the aging heating rate is 80℃ / min, 90℃ / min, 100℃ / min, 110℃ / min, 120℃ / min, the temperature is 450℃, 460℃, 470℃, 480℃, 490℃, 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, 590℃, 600℃, 610℃, 620℃, 630℃, 640℃, 650℃; the holding time is 4.1h, 4.2h, 4.3h, 4.4h, 4.5h, 4.6h, 4.7h, 4.8h, 4.9h, 5h, 5.1h, 5.2h, 5.3h, 5.4h, 5.5h, 5.6h, 5.7h, 5.8h, 5.9h, 6h.

[0069] The core purpose of the aging treatment is to promote the controlled precipitation of a large number of fine and dispersed strengthening phases from the supersaturated solid solution through medium temperature heating. This is the most critical step to achieve performance breakthroughs (high hardness, high strength, low thermal expansion coefficient). With the increase of aging temperature, lamellar α-Cr begins to precipitate again; followed by the precipitation of fine granular α-Cr at the grain boundaries (such as Figure 2), after a period of aging treatment, the number of granular α-Cr precipitates increases and the size becomes larger, and the hardness of the alloy rapidly increases. Finally, the alloy can generate two ideal strengthening phases simultaneously: lamellar α-Cr (50-200 nm): usually precipitates in the grain, can effectively hinder dislocation movement, and is the main force to improve strength and hardness. Granular α-Cr (20-80 nm): usually precipitates in the grain and in the grain, can pin the grain boundary, inhibit the growth of the grain at high temperature, stabilize the structure, and at the same time contribute to the improvement of hardness. The synergistic effect of this "dual-phase strengthening structure" is the key to realizing high hardness (≥58HRC), high tensile strength (≥1323MPa) while maintaining thermal expansion coefficient ≤5×10 -6 / K.

[0070] If the aging treatment temperature is too low: the atomic diffusion ability is insufficient, and the lamellar α-Cr is difficult to effectively precipitate, or the number of precipitates is extremely small and the size is too small, resulting in insufficient strengthening effect and insufficient hardness and strength improvement.

[0071] If the aging treatment temperature is too high: the atomic diffusion is too fast, resulting in rapid coarsening and aggregation of the precipitated phase. Small particles merge into large particles, and the lamellar structure degenerates. The strengthening effect (pinning dislocation ability) of the coarse precipitated phase is much lower than that of the fine dispersed nanophase. As a result, the hardness and strength decrease significantly. At the same time, the aging temperature is too high, which will also make the matrix itself recover and reduce the strength. In addition, the coarsening of the precipitated phase will change the composition of the matrix, which may have an adverse effect on the low expansion characteristics, resulting in an increase in the thermal expansion coefficient. Too high a temperature will also cause energy waste.

[0072] The aging treatment holding time is 4-6 hours: at a certain temperature, the holding time determines how large the precipitated phase can grow and whether the precipitation process can be completed.

[0073] If the aging treatment holding time is too short: the lamellar α-Cr (50-200 nm) and the granular α-Cr (20-80 nm) precipitated phase is not completely precipitated, and the performance is reduced.

[0074] If the aging treatment holding time is too long: similar to the temperature being too high, it will cause the coarsening of the fine phase that has been precipitated, and the phase will change from a strengthening phase to a weakening phase, and the hardness and strength will decrease, and energy will be wasted.

[0075] The effect of the aging treatment heating rate of 80-120°C / min realizes synchronous and uniform precipitation: heating to the aging temperature at a moderate and controllable rate means that the core and surface of the alloy bar reach the target temperature almost simultaneously. In this way, the precipitation process in the entire workpiece almost starts simultaneously. This ensures that the precipitation phase ("lamellar α-Cr" and "granular α-Cr" dual-phase strengthening) is uniformly distributed and has consistent size throughout the material, thereby obtaining uniform mechanical properties (hardness, strength). This is the key to achieving high performance and consistent performance, and can avoid heterogeneous precipitation and non-uniform nucleation: during slow and uniform heating, the precipitation phase nucleates uniformly, which helps to form the ideal dual-phase strengthening structure. It can reduce internal stress and maintain dimensional stability: similar to solid solution treatment, a controllable heating rate can reduce thermal stress caused by the temperature difference between the core and the surface, which is crucial for precision parts that require extremely high dimensional stability.

[0076] If the aging treatment heating rate is too slow, it may cause pre-precipitation during the heating process: when passing through the low-temperature interval (such as 300-500°C) at a very slow rate, atoms have enough diffusion ability to preferentially precipitate at some defects (such as dislocations, grain boundaries) before reaching the target aging temperature. These prematurely precipitated phases tend to be large and unevenly distributed, and also disrupt the uniformity of subsequent ideal nanometer precipitates, resulting in peak strength, hardness that cannot be achieved, and lower performance.

[0077] If the aging treatment heating rate is too fast, it may cause explosive and non-uniform precipitation: rapid heating makes the workpiece quickly skip the low-temperature zone and directly "rush" to the aging temperature. This is equivalent to giving the system a sudden "shock", which will cause the precipitation phase to nucleate in a small number of high-energy locations (such as grain boundaries). The precipitation phase is excessively concentrated in the grain boundaries, and the grain boundary precipitates are too large and the intragranular precipitates are insufficient. This uneven structure cannot provide uniform and effective strengthening, which may result in reduced strength and hardness, or uneven performance.

[0078] In summary, solid solution treatment is to uniformly dissolve all alloy elements into the (matrix); aging treatment is to control the temperature and holding time to allow the alloy elements to precipitate in the form of "lamellar α-Cr" and "granular α-Cr", forming a dual-phase strengthening structure with lamellar α-Cr (50-200nm) and granular α-Cr (20-80nm), which has excellent performance of high hardness (≥58HRC), low thermal expansion coefficient (≤5.0×10 -6 / K) and high tensile strength (≥1300MPa) to meet the mechanical performance requirements of wear resistance, deformation resistance, etc. and expand the application in some aerospace precision parts and high-precision instrument manufacturing that require higher hardness.

[0079] In order to more clearly describe the present application, the following examples and comparative examples are further illustrated.

[0080] Example 1

[0081] A high hardness and low expansion alloy, the chemical composition is as follows in terms of percentage by weight:

[0082]

[0083] A kind of high hardness and low expansion alloy is prepared A round bar is prepared by the following method:

[0084] S1, batching:

[0085] Metal nickel, metal chromium, electrolytic aluminum and industrial pure iron are used as raw materials, and the materials are batched according to the above component ratio;

[0086] S2, smelting:

[0087] The batched materials are placed into a vacuum induction furnace for smelting, and poured into an electrode bar; after the surface of the prepared electrode bar is ground, vacuum consumable remelting is carried out, and a consumable ingot is obtained.

[0088] During the vacuum induction smelting process, the materials are strictly batched according to the designed components, and the loss on ignition and impurity element content of various alloy elements are strictly controlled; and during the pouring process, argon is filled to 4000-6000 Pa to form a protective atmosphere for pouring into an electrode bar. After the composition analysis of the electrode bar meets the requirements, the surface of the electrode bar is polished, vacuum consumable remelting is carried out, and during the smelting process, constant melting drop control technology is adopted, the current is 3 KA, the voltage is 23 V, the melting speed is 6 kg / min, and the vacuum degree is ≤0.1 Pa.

[0089] S3, forging:

[0090] The consumable ingot is heated below 600℃, the heating rate is ≤200℃ / h, the billet is opened after being kept at 1100℃ for a proper time, and the bar material is formed.

[0091] S4 solid solution treatment:

[0092] The bar material is placed in a non-vacuum resistance furnace (RX-60-12), heated to 1180℃ at a heating rate of 80℃ / min, kept for 1h, and water cooled.

[0093] S5 aging treatment:

[0094] The bar material is again placed in a non-vacuum resistance furnace (RX-60-12), heated to 650℃ at a heating rate of 80℃ / min, and kept for 5 hours.

[0095] Example 2

[0096] A high hardness and low expansion alloy, the chemical composition is as follows in percentage by weight:

[0097]

[0098] Preparation of a Round bar, the preparation method is as follows:

[0099] S1, batching:

[0100] Metal nickel, metal chromium, electrolytic aluminum and industrial pure iron are used as raw materials, and the materials are batched according to the above component proportion;

[0101] S2, smelting:

[0102] The batched materials are put into a vacuum induction furnace for smelting, and are poured into electrode bars; after the surface of the prepared electrode bar is ground, vacuum consumable remelting is carried out, and a consumable ingot is obtained.

[0103] During the vacuum induction smelting process, the materials are strictly batched according to the designed components, and the loss on ignition and impurity element content of various alloy elements are strictly controlled; and during the pouring process, argon is filled to 4000-6000 Pa to form a protective atmosphere for pouring into electrode bars. After the composition analysis of the electrode bars meets the requirements, the surface of the electrode bars is polished, vacuum consumable remelting is carried out, and during the smelting process, constant melting drop control technology is adopted, the current is 3.5 KA, the voltage is 23.5 V, the melting speed is 6 kg / min, and the vacuum degree is ≤0.1 Pa.

[0104] S3, forging:

[0105] The consumable ingot is heated below 600℃, the heating rate is ≤200℃ / h, and after being heated at 1120℃ for a proper time, a bar material is formed. S4 solid solution treatment:

[0106] The obtained bar material is placed in a non-vacuum resistance furnace (RX-60-12), heated to 1120℃ at a heating rate of 120℃ / min, and kept for 1.5h, and then water-cooled.

[0107] S5 aging treatment:

[0108] The bar material is again placed in a non-vacuum resistance furnace (RX-60-12), heated to 600℃ at a heating rate of 120℃ / min, and kept for 6 hours.

[0109] Example 3

[0110] A high hardness and low expansion alloy, the chemical composition is as follows in percentage by weight:

[0111]

[0112] Preparation of a Round bar, the preparation method is as follows:

[0113] S1, batching:

[0114] Metal nickel, metal chromium, electrolytic aluminum and industrial pure iron are used as raw materials, and are batched according to the above component proportion;

[0115] S2, smelting:

[0116] The batched materials are placed into a vacuum induction furnace for smelting, and are poured into electrode rods; after the surface of the prepared electrode rods is ground, vacuum consumable remelting is performed, and a consumable ingot is obtained.

[0117] During the vacuum induction smelting process, the materials are strictly batched according to the designed components, and the loss on ignition of various alloy elements and the content of impurity elements are strictly controlled; and during the pouring process, argon is filled to 4000-6000 Pa for protection atmosphere pouring into electrode rods. After the component analysis of the electrode rods meets the requirements, the surface of the electrode rods is polished, vacuum consumable remelting is performed, and during the smelting process, constant melting drop control technology is adopted, the current is 4 KA, the voltage is 23 V, the melting speed is 5.5 kg / min, and the vacuum degree is ≤0.1 Pa.

[0118] S3, forging:

[0119] The consumable ingot is heated to 600℃ or lower, the heating rate is ≤200℃ / h, after holding at 1130℃ for an appropriate time, the billet is formed into a rod.

[0120] S4, solid solution treatment:

[0121] The round rod is placed in a non-vacuum resistance furnace (RX-60-12), heated to 1150℃ at a heating rate of 100℃ / min, held for 1h, and water-cooled.

[0122] S5, aging treatment:

[0123] The round rod is again placed in a non-vacuum resistance furnace (RX-60-12), heated to 600℃ at a heating rate of 100℃ / min, and held for 6 hours.

[0124] Example 4

[0125] A high-hardness low-expansion alloy, the chemical components are as follows in terms of percentage by weight:

[0126]

[0127] A kind of Round rod, the preparation method is as follows:

[0128] S1, batching:

[0129] Metal nickel, metal chromium, electrolytic aluminum and industrial pure iron are used as raw materials, and are batched according to the above component proportion;

[0130] S2, smelting:

[0131] The ingredients are put into a vacuum induction furnace for smelting and casting into an electrode rod; the surface of the prepared electrode rod is ground and polished, and then vacuum consumable remelting is performed to obtain a consumable ingot.

[0132] In the vacuum induction smelting process, the materials are strictly matched according to the designed composition, and the loss on ignition and the content of impurity elements of various alloy elements are strictly controlled; and in the casting process, argon is filled to 4000-6000 Pa for protection atmosphere casting into an electrode rod. After the composition analysis of the electrode rod meets the requirements, the surface of the electrode rod is polished, vacuum consumable remelting is performed, and in the smelting process, constant melting drop control technology is adopted, the current is 3 KA, the voltage is 22.5 V, the melting speed is 6 kg / min, and the vacuum degree is ≤0.1 Pa.

[0133] S3, forging:

[0134] The consumable ingot is heated below 600℃, the heating rate is ≤200℃ / h, after holding at 1140℃ for an appropriate time, the billet is formed into a rod.

[0135] S4, solid solution treatment:

[0136] The round rod is placed in a non-vacuum resistance furnace (RX-60-12), heated to 1120℃ at a heating rate of 80℃ / min, held for 0.5h, and water-cooled.

[0137] S5, aging treatment:

[0138] The round rod is again placed in a non-vacuum resistance furnace (RX-60-12), heated to 630℃ at a heating rate of 80℃ / min, and held for 4 hours.

[0139] Example 5

[0140] A high-hardness low-expansion alloy, the chemical composition is as follows in terms of percentage by weight:

[0141]

[0142] A kind of Round rod, the preparation method is as follows:

[0143] S1, ingredient:

[0144] Metallic nickel, metallic chromium, electrolytic aluminum and industrial pure iron are used as raw materials, and the ingredients are matched according to the above component ratio;

[0145] S2, smelting:

[0146] The ingredients are put into a vacuum induction furnace for smelting and casting into an electrode rod; the surface of the prepared electrode rod is ground and polished, and then vacuum consumable remelting is performed to obtain a consumable ingot.

[0147] The material is strictly allocated according to the designed component in the vacuum induction smelting process, and the burning loss of various alloy elements and the content of impurity elements are strictly controlled; and in the pouring process, the electrode rod is poured into a protective atmosphere by argon filling at 4000-6000 Pa. After the component analysis of the electrode rod meets the requirements, the surface of the electrode rod is polished, vacuum consumable remelting is performed, and in the smelting process, constant melting drop control technology is adopted, the current is 4 KA, the voltage is 23 V, the melting speed is 6 kg / min, and the vacuum degree is less than or equal to 0.1 Pa.

[0148] S3, forging:

[0149] The consumable ingot is less than 600 DEG C and is loaded into a furnace, the heating rate is less than or equal to 200 DEG C / h, after being kept at 1150 DEG C for a proper time, the billet is formed.

[0150] S4, solid solution treatment:

[0151] The obtained rod is placed in a non-vacuum resistance furnace (RX-60-12), heated to 1120 DEG C at a heating rate of 100 DEG C / min, kept for 1 h, and water-cooled.

[0152] S5, aging treatment:

[0153] The round rod is placed again in a non-vacuum resistance furnace (RX-60-12), heated to 610 DEG C at a heating rate of 100 DEG C / min, and kept for 4.5 h.

[0154] Example 6

[0155] A high-hardness low-expansion alloy, the chemical components are as follows in terms of percentage by weight:

[0156]

[0157]

[0158] A kind of Round rod, the preparation method is as follows:

[0159] S1, batching:

[0160] Metal nickel, metal chromium, electrolytic aluminum and industrial pure iron are used as raw materials, and the batching is performed according to the above component proportion;

[0161] S2, smelting:

[0162] The batching is placed into a vacuum induction furnace for smelting, and an electrode rod is poured; after the surface of the prepared electrode rod is polished, vacuum consumable remelting is performed, and a consumable ingot is obtained.

[0163] The vacuum induction melting process requires that the materials are strictly allocated according to the designed composition, the loss on ignition of various alloy elements and the content of impurity elements are strictly controlled; and in the pouring process, the argon is filled to 4000-6000 Pa to form a protective atmosphere for pouring the electrode rod. After the composition analysis of the electrode rod meets the requirements, the surface of the electrode rod is polished, and then vacuum consumable remelting is performed. In the melting process, the constant melting drop control technology is used, the current is 3 KA, the voltage is 23 V, the melting speed is 6 kg / min, and the vacuum degree is less than or equal to 0.1 Pa.

[0164] S3, forging:

[0165] The consumable ingot is less than 600 DEG C and is loaded into a furnace, the heating rate is less than or equal to 200 DEG C / h, after being kept at 1130 DEG C for an appropriate time, the billet is formed.

[0166] S4, solution treatment:

[0167] The rod is placed in a non-vacuum resistance furnace (RX-60-12), heated to 1120 DEG C at a heating rate of 120 DEG C / min, kept for 1 h, and water-cooled.

[0168] S5, aging treatment:

[0169] The round rod is again placed in a non-vacuum resistance furnace (RX-60-12), heated to 550 DEG C at a heating rate of 120 DEG C / min, and kept for 5 h.

[0170] The inventor has carried out a large number of experimental researches in the research process, and some results of bad schemes are taken as comparative examples.

[0171] Comparative Example 1

[0172] The chemical composition does not meet the range of the application; the rest is the same as Example 1. The chemical composition of Comparative Example 1 is as follows in terms of weight percentage:

[0173]

[0174] Comparative Example 2

[0175] S4, solution treatment: the rod is placed in a non-vacuum resistance furnace (RX-60-12), heated to 1120 DEG C at a heating rate of 150 DEG C / min, kept for 1 h, and water-cooled; the rest is the same as Example 1.

[0176] Comparative Example 3

[0177] S4, solution treatment: the rod is placed in a non-vacuum resistance furnace (RX-60-12), heated to 1000 DEG C at a heating rate of 80 DEG C / min, kept for 1 h, and water-cooled; the rest is the same as Example 1.

[0178] Comparative Example 4

[0179] S4 solution treatment: the rod is placed in a non-vacuum resistance furnace (RX-60-12) and heated to 1120℃ at a heating rate of 80℃ / min, and held for 2h, and water-cooled; the rest is the same as example 1.

[0180] Comparative example 5

[0181] S5 aging treatment: the rod is again placed in a non-vacuum resistance furnace (RX-60-12) and heated to 650℃ at a heating rate of 150℃ / min, and held for 5h; the rest is the same as example 1.

[0182] Comparative example 6

[0183] S5 aging treatment: the rod is again placed in a non-vacuum resistance furnace (RX-60-12) and heated to 400℃ at a heating rate of 80℃ / min, and held for 5h; the rest is the same as example 1.

[0184] Comparative example 7

[0185] S5 aging treatment: the rod is again placed in a non-vacuum resistance furnace (RX-60-12) and heated to 650℃ at a heating rate of 80℃ / min, and held for 3h; the rest is the same as example 1.

[0186] Performance test

[0187] The tensile properties of examples 1-6 and comparative examples 1-7 above are tested according to GB / T 228.1-2010, the hardness is tested according to GB / T 230.1-2018, the thermal expansion coefficient is tested according to GB / T 4339-2008, and the results are shown in Table 1, the microstructure is tested according to GB / T 5168-2020, and the results are shown in Table 2. Figure 1 and Figure 2

[0188] Table 4 performance test results of examples and comparative examples

[0189]

[0190]

[0191] From Table 4, it can be seen that the performance of the alloy prepared by the present application is high hardness (≥55HRC), low thermal expansion coefficient (≤5.0×10 -6 / K) and high tensile strength (≥1300MPa).

[0192] ​The element range of Cr element of the comparative example 1 is out of the range of the present application, which can fundamentally change the matrix characteristics of the alloy and cause the loss of low expansion performance. The aging treatment stage precipitates coarse Cr phase rapidly and unevenly, and it is difficult to form uniform and fine lamellar / particle dual-phase structure in the whole grain, which causes the decrease of strength and hardness.

[0193] The solution treatment of the comparative example 2 is too fast, which is out of the range of the present application and can cause poor temperature uniformity: the surface has reached or even exceeded the solution temperature, while the core temperature is still very low. This can cause surface grain coarsening: the surface area stays at high temperature for too long, and the grains begin to grow, while the core structure has not been transformed. The composition is not dissolved uniformly: the strengthening elements in the surface area have been dissolved, while the core has not been dissolved. In the specified holding time, it can not be enough to completely homogenize the core composition, which finally causes the decrease of strength and hardness performance.

[0194] The solution temperature of the comparative example 3 is too low, and the elements such as Cr are not completely dissolved, and there are undissolved coarse Cr phases in the matrix. These phases cannot be transformed into the required nanoscale lamellar / particle structure in the subsequent aging, which causes the great discount of strengthening effect and cannot meet the requirements of hardness and strength.

[0195] The solution holding time of the comparative example 4 is too long, which causes grain coarsening, and the strength and hardness performance of the material is not greatly improved and the energy consumption is increased.

[0196] The aging temperature of the comparative example 5 is too fast, which causes the precipitation phase to be excessively concentrated in the grain boundary, and the grain boundary precipitation phase is too coarse and the intragranular precipitation is insufficient. This uneven structure cannot provide uniform and effective strengthening, which can cause the decrease of strength and hardness.

[0197] The aging temperature of the comparative example 6 is too low, and the number and size of the precipitates are too small, which causes insufficient strengthening effect and insufficient improvement of hardness and strength.

[0198] The aging holding time of the comparative example 7 is too short, and the lamellar α-Cr and granular α-Cr (20-80 nm) precipitates are not completely precipitated, which causes the decrease of performance.

[0199] The above only describes the preferred embodiments of the present application and does not limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

[0200] Other features and advantages of the present application will be set forth in the following description, and in part will become apparent to those skilled in the art from the description, or can be learned by practice of the present application. The objects and other advantages of the present application can be achieved and obtained by the structure particularly pointed out in the written description and the accompanying drawings.

Claims

1. A high-hardness, low-expansion alloy characterized by, The high-hardness low-expansion alloy has a chemical composition including, in mass percentage, Fe 0.02-0.06%, Cr 38-45%, Si 0.04-1.1%, P≤0.0049%, S≤0.0049%, Mn≤0.0019%, C≤0.049%, Al 2.9-4.6%, and the balance of Ni.

2. The high-hardness, low-expansion alloy of claim 1, wherein, The high-hardness low-expansion alloy has a chemical composition including, in mass percentage, Fe 0.03-0.05%, Cr 39-44%, Si 0.05-1%, P≤0.005%, S≤0.005%, Mn≤0.002%, C≤0.05%, Al 3-4.5%, and the balance of Ni.

3. The high-hardness, low-expansion alloy of claim 1, wherein, The alloy has a duplex strengthening structure of lamellar α-Cr and granular α-Cr, with the lamellar α-Cr having a particle size ranging from 50 nm to 200 nm and the granular α-Cr having a particle size ranging from 20 nm to 80 nm.

4. The high-hardness, low-expansion alloy of claim 1, wherein, The alloy has a two-phase solid solution structure composed of a face-centered cubic austenite matrix and body-centered cubic Cr single-element particles.

5. The high-hardness, low-expansion alloy of claim 4, wherein, The alloy has a solid solution grain size of 24-26 μm and a Cr single-element particle size of less than 5 μm.

6. The high-hardness, low-expansion alloy of claim 1, wherein, The obtained alloy has a thermal expansion coefficient of ≤5*10 -6 / K at 20-200℃, hardness ≥58HRC, tensile strength ≥1300Mpa.

7. A method of producing the high-hardness low-expansion alloy as claimed in any one of claims 1 to 6, characterized by, The method comprises the following steps: S1, batching: using metallic nickel, metallic chromium, electrolytic aluminum and industrial pure iron as raw materials and batching according to the above component proportions; S2, smelting: The batching is placed into a vacuum induction furnace for smelting and cast into an electrode rod; the prepared electrode rod is ground and then subjected to vacuum consumable remelting to obtain a consumable ingot; S3, forging The consumable ingot is charged into a furnace below 600 ℃ at a heating rate of ≤200 ℃ / h, and after being kept at 1100-1180 ℃ for a proper time, is broken down into a rod; S4, solid solution treatment of the rod; S5, aging treatment.

8. The method of claim 7, wherein the high hardness, low expansion alloy is prepared by the steps of: The solid solution treatment comprises: placing the rod in a non-vacuum resistance furnace, heating to 1100-1200 ℃ at a heating rate of 80-120 ℃ / min, and keeping for 0.5-1.5 h.

9. The method of claim 7, wherein the high-hardness, low-expansion alloy is prepared by the steps of: The aging treatment comprises: again placing the rod in a non-vacuum resistance furnace, heating to 450-650 ℃ at a heating rate of 80-120 ℃ / min, and keeping for 4-6 h.

10. The high-hardness, low-expansion alloy of claim 7, wherein, With the increase of the aging temperature, lamellar α-Cr starts to precipitate, and then fine granular α-Cr precipitates at the grain boundaries; with the increase of the amount of the precipitated granular α-Cr and the increase of the size of the granular α-Cr, the hardness of the alloy rapidly increases.

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