Composite reinforced stellite alloy STL 6B for large shield tunneling machine as well as preparation method and application of composite reinforced stellite alloy STL 6B

Abstract

The invention provides a composite reinforced stellite alloy STL 6B for a large shield tunneling machine as well as a preparation method and application of the composite reinforced stellite alloy STL 6B. The stellite alloy STL 6B comprises the following components in percentage by weight: 0.9 to 1.8 percent of C, 27.0 to 33.0 percent of Cr, 3.0 to 6.0 percent of W, 0.5 to 2.0 percent of Mo, 1.0 to 4.0 percent of Ni, 0.2 to 2.0 percent of Si, 0.50 to 2.0 percent of Mn, 0.001 to 0.1 percent of N + B, 0.001 to 0.05 percent of Y, less than or equal to 5.0 percent of Fe, less than or equal to 0.50 percent of Al, less than or equal to 0.50 percent of Ti, less than or equal to 0.015 percent of P, less than or equal to 0.001 percent of S and the balance of Co. Through collaborative optimization of all the elements, the functions of high abrasion resistance, corrosion resistance and excellent mechanical property of the STL 6B alloy material are achieved, and the STL 6B alloy material can become an ideal material for key abrasion-resistant and long-service-life components in a large shield tunneling machine.

Description

Technical Field

[0001] This invention belongs to the technical field of special alloy material preparation for industries such as major equipment, nuclear power, petrochemicals, high-speed rail, automobiles, and aerospace. Specifically, it relates to a composite reinforced Stellite alloy STL 6B for large tunnel boring machines, its preparation method, and its application. In particular, it relates to a Stellite alloy STL 6B for wear-resistant, corrosion-resistant, and oxidation-resistant key components such as cutterheads and main bearings of large tunnel boring machines, and its preparation process by vacuum induction melting. Background Technology

[0002] A tunnel boring machine (TBM) is a large-scale tunnel construction machine that integrates functions such as tunneling, support, muck removal, and guidance. It is widely used in underground tunnel projects such as subways, railways, highways, water conservancy, and municipal engineering, and is especially suitable for efficient and safe construction under complex geological conditions. The cutterhead and main bearing are crucial core components of the TBM. The cutterhead has various cutting tools (rollers, scrapers, toothed cutters, etc.) mounted on its surface, which cut the strata through rotation. Its design and material selection directly affect construction efficiency, safety, and adaptability. The main bearing, as a core component bearing the extreme loads (axial force, radial force, overturning moment) of the TBM, must have materials that meet comprehensive performance requirements such as high strength, high toughness, wear resistance, and corrosion resistance. Ordinary iron-based metal materials are unlikely to meet these stringent usage conditions.

[0003] Currently, the main bearings of tunnel boring machines (TBMs) primarily use carburized bearing steel or high-carbon chromium bearing steel. The matrix of bearing steel is iron. When iron is exposed to high temperatures and humidity, and subjected to prolonged pressure and friction with geological materials containing certain alkalinity or acidity, its material properties deteriorate, severely impacting the service life of the cutterhead or main bearing. This can easily lead to frequent TBM equipment failures, resulting in increased costs. Furthermore, prolonged downtime of TBMs can cause geological and safety issues, including potential collapse of unsupported strata in front of the cutterhead, leading to surface subsidence; failure to maintain pressure during slurry TBM maintenance, potentially causing water and sand inrush accidents; and workers entering the cutterhead compartment for maintenance in water-rich sand layers, potentially triggering collapses or gas poisoning accidents.

[0004] Therefore, it is imperative to select special alloy materials with superior performance, such as high temperature resistance, oxidation resistance, corrosion resistance, wear resistance, and long service life. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a composite reinforced Stellite alloy STL 6B (hereinafter referred to as "STL 6B") for large tunnel boring machines, its preparation method, and its applications. This Stellite alloy possesses excellent high-temperature resistance, oxidation resistance, and corrosion resistance.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a composite reinforced Stellite alloy STL 6B for large tunnel boring machines, the chemical composition of which, by mass fraction, comprises the following components:

[0008] C: 0.9–1.8%, Cr: 27.0–33.0%, W: 3.0–6.0%, Mo: 0.5–2.0%, Ni: 1.0–4.0%, Si: 0.2–2.0%, Mn: 0.50–2.0%, N+B: 0.001–0.1%, Y: 0.001–0.05%, Fe: ≤5.0%, Al: ≤0.50%, Ti: ≤0.50%, P: ≤0.015%, S: ≤0.001%, Co: balance.

[0009] Preferably, the chemical composition of the STL 6B alloy, by mass fraction, consists of the following components:

[0010] C: 0.9–1.5%, Cr: 27.0–32.0%, W: 3.0–5.0%, Mo: 1.0–2.0%, Ni: 2.0–4.0%, Si: 0.5–2.0%, Mn: 0.50–1.5%, N+B: 0.01–0.1%, Y: 0.001–0.01%, Fe: ≤5.0%, Al: ≤0.50%, Ti: ≤0.50%, P: ≤0.015%, S: ≤0.001%, Co: balance.

[0011] The STL 6B alloy developed in this invention uses cobalt as the matrix to build structural stability, chromium, tungsten and molybdenum to enhance corrosion resistance and mechanical properties, and carbon and trace elements to regulate the microstructure, achieving comprehensive optimization of high strength, wear resistance, oxidation resistance and corrosion resistance.

[0012] Secondly, the present invention also provides a method for preparing the above-mentioned Stellite alloy, comprising the following steps:

[0013] S1: The ingredients are designed and proportioned according to the composition, and the raw materials of each element are vacuum induction melted, poured and demolded to obtain the ingot;

[0014] S2: The ingot is subjected to stress relief treatment and cooled to obtain the final product.

[0015] Preferably, in the process of ingredient preparation, Co, Cr, W, Mo and Ni are made from pure metallic elements; Y is made from Ni-Y; and B and N are made from B-Fe and CrN master alloys.

[0016] Preferably, the vacuum induction melting process is as follows:

[0017] (1) The metal raw materials of Co, Ni, W, Mo and Cr are vacuum induction melted at 1480℃±20℃ until the raw materials are clear;

[0018] (2) Lower the temperature to 1400℃±10℃, and introduce Ni-Y master alloy, B-Fe, and CrN master alloy in an inert atmosphere, and then heat the temperature to 1480℃±10℃ for vacuum induction melting.

[0019] Preferably, the vacuum degree of the vacuum induction melting in step (1) is ≤0.5Pa.

[0020] Preferably, the inert atmosphere is argon gas with a purity of ≥99.8wt%.

[0021] Preferably, the pressure of the inert atmosphere is ≥10000Pa.

[0022] Preferably, the stress relief treatment temperature is 990–1150°C, and the holding time is 6–10 hours.

[0023] Preferably, the cooling is performed to below 300°C.

[0024] Thirdly, the present invention provides an application of the above-mentioned Stellite alloy in the preparation of tunnel boring machine components.

[0025] Preferably, the tunnel boring machine components include, but are not limited to, the cutterhead and / or the main bearing.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] This invention provides a Stellite alloy, the composition of which, compared to ordinary Stellite alloys, includes the addition of boron (B), nitrogen (N), and rare earth metal yttrium (Y). Bo, as a trace element, segregates at grain boundaries, reducing grain boundary energy and inhibiting the precipitation of harmful phases (such as the σ phase). Simultaneously, B and N elements can improve the material's creep resistance, fatigue resistance, and wear resistance; however, excessive amounts can increase brittleness. Therefore, this invention limits the N+B range to 0.001–0.1 wt%. The rare earth element (Y), upon oxidation, forms a dense oxide layer such as Y₂O₃, enhancing surface oxidation resistance and simultaneously purifying the melt, reducing inclusions, and improving alloy purity. This invention achieves high wear resistance, corrosion resistance, and excellent mechanical properties in Stellite alloys by adding elements B and Y and combining them with other components, optimizing the component content within the following ranges: C: 0.9–1.8%, Cr: 27.0–33.0%, W: 3.0–6.0%, Mo: 0.5–2.0%, Ni: 1.0–4.0%, Si: 0.2–2.0%, Mn: 0.50–2.0%, N+B: 0.001–0.1%, Y: 0.001–0.05%, Fe: ≤5.0%, Al: ≤0.50%, Ti: ≤0.50%, P: ≤0.015%, S: ≤0.001%, Co: balance. Through the synergistic optimization of these elements, Stellite alloys are achieved, exhibiting high wear resistance, corrosion resistance, and excellent mechanical properties, making them an ideal material for key wear-resistant and long-life components in large tunnel boring machines. Detailed Implementation

[0028] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0029] To address the problems of poor wear resistance, corrosion resistance, and short service life of key components in major equipment such as tunnel boring machines, this invention proposes a composite reinforced STL 6B alloy material composition and preparation method for tunnel boring machines. It has significant specialization and uniqueness, and is an ideal material for key components such as cutterheads and main bearings of large tunnel boring machines.

[0030] Specifically, the present invention provides a composite reinforced Stellite alloy STL 6B for large tunnel boring machines, the chemical composition of which, by mass fraction, consists of the following components:

[0031] C: 0.9–1.8%, Cr: 27.0–33.0%, W: 3.0–6.0%, Mo: 0.5–2.0%, Ni: 1.0–4.0%, Si: 0.2–2.0%, Mn: 0.50–2.0%, N+B: 0.001–0.1%, Y: 0.001–0.05%, Fe: ≤5.0%, Al: ≤0.50%, Ti: ≤0.50%, P: ≤0.015%, S: ≤0.001%, Co: balance.

[0032] In some embodiments of the present invention, the chemical composition of the STL 6B alloy preferably consists of the following components by mass fraction:

[0033] C: 0.9–1.5%, Cr: 27.0–32.0%, W: 3.0–5.0%, Mo: 1.0–2.0%, Ni: 2.0–4.0%, Si: 0.5–2.0%, Mn: 0.50–1.5%, N+B: 0.01–0.1%, Y: 0.001–0.01%, Fe: ≤5.0%, Al: ≤0.50%, Ti: ≤0.50%, P: ≤0.015%, S: ≤0.001%, Co: balance.

[0034] In some embodiments of the present invention, the chemical composition of the Stellite alloy is as follows:

[0035] C: 1.2%, Cr: 30%, W: 4%, Mo: 1.0%, Ni: 2.0%, Si: 0.5%, Mn: 1.5%, N+B: 0.002%, Y: 0.001%, Fe: 1%, Al: 0.2%, Ti: 0.2%, P: 0.01%, S≤0.001%, Co: balance;

[0036] or

[0037] C: 1.5%, Cr: 32.0%, W: 5.0%, Mo: 1.0%, Ni: 2.0%, Si: 0.5%, Mn: 1.5%, N+B: 0.01%, Y: 0.001%, Fe: 2%, Al: 0.1%, Ti: 0.1%, P: 0.01%, S≤0.0008%, Co: balance.

[0038] In this invention, the design concept of the Stellite STL 6B alloy is as follows:

[0039] Cobalt (Co), as a matrix element, provides excellent room temperature and high temperature structural stability and superior corrosion resistance. Currently, the main bearings of tunnel boring machines mainly use carburized bearing steel or high-carbon chromium bearing steel. Both are improved by adding a high content of carbon to the iron matrix to form carbides (such as (Fe,Cr)3C) to improve wear resistance. However, iron-based materials have poor oxidation and corrosion resistance and cannot be compared with cobalt-based materials. Chromium (Cr) is controlled within the range of 27.0% to 33.0%. It can form a dense Cr2O3 oxide film, resisting corrosion from acids, alkalis, and salts, preventing matrix oxidation and sulfide corrosion. Furthermore, Cr dissolves in the Co matrix and forms a large number of carbides with C, ensuring the good wear resistance of STL 6B alloy. Tungsten (W) has a large atomic radius, effectively hindering dislocation movement. It also forms WC with C, which is beneficial for solid solution strengthening and carbide strengthening to improve the hardness and wear resistance of the material. Furthermore, W and Cr together form (CoCrW)6C-type carbides, which can refine grain boundaries and prevent slip, thereby improving the durability and strength of the material. The design range is 3.0–6.0%. Molybdenum (Mo) has a similar effect to W, also improving the strength and toughness of the material through solid solution strengthening, but its effect is slightly weaker than W. Excessive Mo can easily form a brittle Laves phase; therefore, the Mo content range is 0.5–2.0%. Carbon (C) content is controlled within the range of 0.9–1.8%, and its core function is to form MC and M with Cr, W, etc. 23Carbides of the C6 type provide second-phase reinforcement, ensuring the excellent wear resistance of STL 6B alloy. However, excessive C will reduce the alloy's plasticity and toughness, leading to processing difficulties and reduced material yield. Metallic nickel (Ni) partially replaces cobalt, stabilizing the austenitic structure and improving the toughness of STL 6B alloy, while also helping to reduce material costs. The Ni content is designed to range from 1.0% to 4.0%. Silicon (Si) and manganese (Mn) act as deoxidizers during alloy smelting, reducing oxide inclusions in the alloy and improving its fluidity. Mn strengthens the alloy matrix, improving its strength and toughness. The designed control range is Si: 0.2%–2.0% and Mn: 0.50%–2.0%. Boron (B), as a trace element, segregates at grain boundaries, reducing grain boundary energy and inhibiting the precipitation of harmful phases (such as σ phase). Nitrogen (N) and boron (B) elements enhance creep resistance, fatigue resistance, and wear resistance; however, excessive amounts can increase material brittleness. The design range for N+B is 0.001–0.1%. Rare earth element yttrium (Y), after oxidation, forms a dense oxide layer such as Y₂O₃, enhancing surface oxidation resistance and purifying the melt to reduce inclusions and improve alloy purity. Iron (Fe) content is limited to no more than 5.0%, as excessive Fe reduces corrosion resistance and promotes the formation of harmful phases (such as the Laves phase). Aluminum (Al) and titanium (Ti) content are controlled within the range of ≤0.5%, mainly because Co, as a matrix element, cannot utilize Al and Ti to form effective strengthening phases (such as the γ' phase) and instead leads to harmful precipitation, reducing the alloy's wear resistance. Phosphorus (P) and sulfur (S) are harmful elements that need to be limited in cobalt-based alloys; the lower the content, the better. Therefore, P: ≤0.015%; S: ≤0.001%.

[0040] The present invention also provides a method for preparing the above-mentioned Stellite alloy STL 6B, comprising the following steps:

[0041] S1: The ingredients are designed and proportioned according to the composition, and the raw materials of each element are vacuum induction melted, poured and demolded to obtain the ingot;

[0042] S2: The ingot is subjected to stress relief treatment and cooled to obtain the final product.

[0043] First, the ingredients are designed according to the composition. When formulating the ingredients, it is necessary to select the grade of the raw materials.

[0044] In this invention, Co, Cr, W, Mo, and Ni are pure metallic elements. Specifically, Co is selected from similar pure metallic materials with a content of not less than 99.5 wt% or a quality not less than Co995; W is selected from pure metallic W of grade TW-1 or higher; Mo is selected from pure metallic Mo of grade Mo-1 or higher; Ni is of grade Ni9996 or equivalent purity; C is selected from electrode graphite with a purity ≥99%; rare earth element Y is selected from a nickel-yttrium (Ni-Y) master alloy; B is selected from a boron-iron (B-Fe) master alloy; and N is selected from a chromium-nitrogen (Cr-N) master alloy.

[0045] In some embodiments of the present invention, after selecting raw materials according to the above grades, the batching is designed according to the composition of STL 6B alloy. All material types are required to be weighed by weighers, and then inspectors re-inspect each material grade and weight and make records.

[0046] After the ingredients are prepared, the raw materials of each element are subjected to vacuum induction melting according to the present invention. The power of the vacuum induction melting adopts a high-low-high scheme, which can reduce the loss of volatile elements and accurately control the alloy composition. In some embodiments of the present invention, it is preferred to perform vacuum induction melting of Co, Ni, W, Mo, and Cr metal raw materials at 1480℃±20℃ (e.g., 1460℃, 1470℃, 1480℃, 1490℃, 1500℃) until the raw materials are clear; then the temperature is lowered to 1400℃±10℃ (e.g., 1390℃, 1395℃, 1400℃, 1405℃, 1410℃, etc.), and Ni-Y master alloy, B-Fe master alloy, and CrN master alloy are introduced in an inert atmosphere, and the temperature is raised to 1480℃±10℃ (e.g., 1470℃, 1475℃, 1480℃, 1485℃, 1490℃, etc.) for vacuum induction melting.

[0047] In some specific embodiments of the present invention, it is preferable to load the batched raw materials into a vacuum induction melting furnace for melting. During the melting process, based on the crucible capacity, Co, Ni, W, Mo, and Cr metallic raw materials are first loaded into the crucible. Refractory elements W and Mo are placed in the upper middle part of the crucible material as much as possible to improve melting efficiency. It is anticipated that multiple batches of metal material will be added using a feeder. The equipment is evacuated, requiring the vacuum degree of the melting chamber of the induction furnace to be ≤0.5 Pa. Then, power is supplied to begin heating and melting the metal material. After the materials are cleaned, reduce the power supply to 80%–90% of the normal melting power, and fill the melting chamber with inert gas, preferably high-purity argon (Ar ≥ 99.8 wt%), with an argon pressure greater than or equal to 10000 Pa. Then add Ni-Y master alloy and B-Fe master alloy, and increase the power to 100% of the normal melting power of the equipment. Stir the alloy melt for ≥ 5 min. After the master alloy is cleaned and homogenized, pour the STL 6B alloy melt into the ingot mold. After the ingot cools in the ingot mold chamber for ≥ 30 min, it is removed from the furnace.

[0048] Then, the STL 6B alloy ingot, which has solidified in the ingot mold, is demolded.

[0049] After demolding, stress relief treatment is performed according to the present invention.

[0050] In some embodiments of the present invention, it is preferable to quickly place the demolded ingot into a high-temperature furnace for stress relief treatment. The process parameters are 990–1150°C, such as 990°C, 1000°C, 1030°C, 1050°C, 1080°C, 1100°C, 1120°C, or 1150°C; the holding time is 6 hours to 10 hours, such as 6 hours, 8 hours, 9 hours, or 10 hours. The above temperature range exceeds the carbide aging precipitation temperature (700–900°C) of STL 6B alloy, which can avoid increasing the amount of precipitated phase, leading to increased strength and decreased plasticity.

[0051] After the stress relief treatment is completed, the above-mentioned ingots are preferably furnace cooled to below 300°C, and then covered with insulation cotton to cool slowly to room temperature after being taken out of the furnace.

[0052] In this invention, after cooling to below 300°C, the ingot undergoes compositional testing. Specifically, a chemical composition analysis sample is machined from the head of the ingot and sent for testing. This invention requires the test results to meet the designed composition range of the aforementioned alloy. Ingots that pass the inspection are placed in the material warehouse for later use.

[0053] Let me reiterate the advantages of this invention:

[0054] (1) A STL 6B alloy composition for key wear-resistant and oxidation-resistant components of tunnel boring machines was successfully designed and implemented. By adding multiple main elements and trace elements and precisely designing and controlling the content of each element, the STL 6B alloy achieved a good combination of high wear resistance, corrosion resistance, and optimized mechanical properties. Through composite strengthening of carbide + (W, Mo) solid solution + boron and its compounds, a significant synergistic strengthening mechanism was observed, making the designed STL 6B alloy an ideal material for key wear-resistant and long-life components of large tunnel boring machines. Specifically, the core role of C in the STL 6B alloy is to form MC and M with Cr, W, etc. 23 Carbides of types such as C6 provide second-phase reinforcement, ensuring the excellent wear resistance of STL 6B alloy. Element Si and Mn act as deoxidizers during alloy smelting, reducing oxide inclusions and improving alloy fluidity. Mn, in particular, strengthens the alloy matrix, improving its strength and toughness. B, as a trace element, segregates at grain boundaries, reducing grain boundary energy and inhibiting the precipitation of harmful phases (such as σ phase). At the same time, N+B elements enhance the material's creep resistance, fatigue resistance, and wear resistance. Rare earth element (Y) forms a dense oxide layer such as Y2O3 after oxidation, enhancing surface oxidation resistance, purifying the melt, reducing inclusions, and improving alloy purity.

[0055] (2) Stress relief treatment at a specific temperature in the preparation method. In this invention, the demolded STL 6B alloy ingot is rapidly placed into a heat treatment furnace for high-temperature stress relief treatment. The process requires a temperature of 990–1150°C and a holding time of ≥6 hours. This is because the STL 6B alloy ingot has high internal stress after solidification. If the stress cannot be eliminated or relieved, it can easily lead to cracking and scrapping of the ingot. The temperature range and time specified in this invention can prevent the precipitation of secondary carbide phases in the STL 6B alloy ingot, significantly reducing the internal stress of the ingot.

[0056] In summary, the STL 6B alloy composition designed in this invention, compared with the traditional Stellite alloy composition process, solves the problems of poor oxidation resistance, corrosion resistance, and wear resistance of key components such as the main bearing and cutterhead of domestic tunnel boring machines, improves the service life of materials, and significantly reduces production costs.

[0057] To further illustrate the present invention, the following embodiments provide a detailed description. The experimental materials used in the following embodiments of the present invention are all commercially available products.

[0058] Example 1

[0059] (1) STL 6B alloy composition design: C: 1.2 (weight percentage, wt%, the same below); Cr: 30.0; W: 4.0; Mo: 1.0; Ni: 2.0; Si: 0.5; Mn: 1.5; N+B: 0.002; Y: 0.001; small amount of impurities (total content: 4), Co: balance;

[0060] Co, Cr, W, Mo, and Ni are made from pure metallic elements. Specifically, Co is selected from Co995 grade or higher; Cr from JCr99 grade or higher; W from TW-1 grade or higher; Mo from Mo-1 grade or higher; Ni from Ni9996 grade or equivalent and higher; C from electrode graphite with a purity of 99.5%; rare earth element Y from a nickel-yttrium (Ni-Y) master alloy; and B and N from boron-iron (B-Fe) and chromium-nitrogen (Cr-N) master alloys. The materials are distributed according to the design of the STL 6B alloy. After weighing all materials, the weigher must verify the weight of each material, and the verification personnel must record the results.

[0061] (2) Vacuum Induction Melting of STL 6B Alloy: The prepared raw materials are loaded into a vacuum induction melting furnace for melting. During the melting process, based on the crucible capacity, Co, Ni, W, Mo, and Cr metal raw materials are first loaded into the crucible. Refractory elements W and Mo are placed in the upper middle part of the crucible material as much as possible to improve melting efficiency. It is expected that the metal material will be added in multiple batches using a feeder. The equipment is evacuated, requiring a vacuum degree of 0.2 Pa in the melting chamber of the induction furnace. Then, power is supplied to start heating and melting the metal material. After the material is cleared, the power supply is reduced to 90% of the normal melting power, and high-purity argon gas (Ar≥99.8wt%) is introduced into the melting chamber. The argon gas pressure is 10000 Pa, and then intermediate alloys such as Ni-Y and B-Fe are added. Increase the power to 100% of the normal melting power of the equipment, stir the alloy melt for 5 minutes, and after the intermediate alloying is clear and uniform, pour the STL 6B alloy melt into the steel ingot mold. The ingot is cooled in the ingot mold chamber for 30 minutes before being taken out of the furnace.

[0062] (3) Demolding of ingot: Demolding the STL 6B alloy ingot that has solidified in the ingot mold;

[0063] (4) Hot annealing: The demolded ingot is quickly placed into a heat treatment furnace for high-temperature stress relief treatment. The process is 990℃ and held for 10 hours.

[0064] (5) Composition Inspection: After annealing, the STL 6B alloy ingots are furnace cooled to below 300°C, covered with insulation cotton, and slowly cooled to room temperature before composition inspection. A chemical composition analysis sample is machined at the ingot head and sent for testing. The composition test results must meet the required range. Qualified ingots are stored for later use, while unqualified ingots are returned to the furnace for remelting.

[0065] This embodiment uses a common Stellite alloy as a comparison, with the following specific composition: C: 0.9-1.4%, Cr: 28.0-32.0%, W: 3.5-5.5%, Si: 0.5-2.0%, Mn: 0.50-2.0%, Fe: ≤3.0%, P: ≤0.04%, S: ≤0.03%, Co: balance. The preparation method is the same as described above.

[0066] Hardness and abrasion resistance tests were conducted in accordance with GB / T 230.1-2009 "Metallic materials Rockwell hardness test - Part 1: Test method" and JB / T 7705-1995 "Test method for wear of loose abrasive particles - Rubber wheel method".

[0067] The test results are shown in Table 1 below:

[0068] Table 1

[0069]

[0070] Example 2

[0071] (1) STL 6B alloy composition design: C: 1.5 (weight percentage, wt%, the same below); Cr: 32.0; W: 5.0; Mo: 1.0; Ni: 2.0; Si: 0.5; Mn: 1.5; N+B: 0.01; Y: 0.001; small amount of impurities (total impurity content: 3), Co: balance;

[0072] Co, Cr, W, Mo, and Ni are made from pure metallic elements. Co is Co995 grade; Cr is JCr99 grade; W is TW-1 grade; Mo is Mo-1 grade; Ni is Ni9997 grade; C is electrode graphite with a purity of 99.8%; rare earth element Y is made from Ni-Y master alloy; B and N are made from boron-iron (B-Fe) and chromium-nitrogen (Cr-N) master alloys. The materials are distributed according to the design of STL 6B alloy. After weighing all materials, the weigher must weigh them, and the inspector must verify the grade and weight of each material and record the results.

[0073] (2) STL 6B alloy vacuum induction melting: The prepared raw materials are loaded into the vacuum induction melting furnace for melting. During the melting process, based on the crucible capacity, Co, Ni, W, Mo, and Cr metal raw materials are first loaded into the crucible. Refractory elements W and Mo are placed in the upper middle part of the crucible material as much as possible to improve melting efficiency. It is expected that the metal material will be added in multiple batches using a feeder. The equipment is evacuated, requiring a vacuum degree of 0.2 Pa in the melting chamber of the induction furnace. Then, power is supplied to start heating and melting the metal material. After the material is cleaned, the power supply is reduced to 90% of the normal melting power, and high-purity argon gas (Ar≥99.8wt%) is introduced into the melting chamber at a pressure of 11000 Pa. Then, intermediate alloys such as Ni-Y and B-Fe are added. Increase the power to 100% of the equipment's normal smelting power, stir the alloy melt for 8 minutes, and after the intermediate alloying is clear and uniform, pour the STL 6B alloy melt into the steel ingot mold. After the ingot cools in the ingot mold chamber for 50 minutes, it is taken out of the furnace; the ingot is demolded.

[0074] (3) Demolding of ingot: Demolding the STL 6B alloy ingot that has solidified in the ingot mold;

[0075] (4) Hot annealing: The demolded ingot is quickly placed into a heat treatment furnace for high-temperature stress relief treatment. The heating temperature is 1150℃, and the holding time is 8 hours;

[0076] (5) Composition Inspection: After the STL 6B alloy ingot is processed, it is furnace cooled to 200℃, then covered with insulation cotton and slowly cooled to room temperature; composition inspection is then performed. A chemical composition analysis test piece is processed at the ingot head and sent for testing. The composition test results are required to meet the required range. Qualified ingots are stored for later use, while unqualified ingots are returned to the furnace for remelting.

[0077] This embodiment uses the common Stellite alloy mentioned in the previous embodiment as a comparison, and the preparation method is the same as described above.

[0078] The hardness and abrasion resistance tests were performed in the same manner as in Example 1.

[0079] The test results are shown in Table 2 below:

[0080] Table 2

[0081]

[0082] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A composite reinforced Stellite alloy STL 6B for large tunnel boring machines, characterized in that, The chemical composition, by mass fraction, consists of the following components: C: 0.9–1.8%, Cr: 27.0–33.0%, W: 3.0–6.0%, Mo: 0.5–2.0%, Ni: 1.0–4.0%, Si: 0.2–2.0%, Mn: 0.50–2.0%, N+B: 0.001–0.1%, Y: 0.001–0.05%, Fe: ≤5.0%, Al: ≤0.50%, Ti: ≤0.50%, P: ≤0.015%, S: ≤0.001%, Co: balance.

2. The Stellite alloy STL 6B according to claim 1, characterized in that, The chemical composition, by mass fraction, consists of the following components: C: 0.9–1.5%, Cr: 27.0–32.0%, W: 3.0–5.0%, Mo: 1.0–2.0%, Ni: 2.0–4.0%, Si: 0.5–2.0%, Mn: 0.50–1.5%, N+B: 0.01–0.1%, Y: 0.001–0.01%, Fe: ≤5.0%, Al: ≤0.50%, Ti: ≤0.50%, P: ≤0.015%, S: ≤0.001%, Co: balance.

3. A method for preparing Stellite alloy STL 6B as described in claim 1 or 2, characterized in that, Includes the following steps: S1: The ingredients are designed and proportioned according to the composition, and the raw materials of each element are vacuum induction melted, poured and demolded to obtain the ingot; S2: The ingot is subjected to stress relief treatment and cooled to obtain the final product.

4. The preparation method according to claim 3, characterized in that, In the process of ingredient preparation, Co, Cr, W, Mo and Ni are used as raw materials made from pure metallic elements; Y uses Ni-Y as a raw material; B and N are made from B-Fe and CrN master alloys.

5. The preparation method according to claim 4, characterized in that, The vacuum induction melting process is as follows: (1) The metal raw materials of Co, Ni, W, Mo and Cr are vacuum induction melted at 1480℃±20℃ until the raw materials are clear; (2) Lower the temperature to 1400℃±10℃ and introduce Ni-Y, B-Fe, CrN master alloys in an inert atmosphere, and then heat the temperature to 1480℃±10℃ for vacuum induction melting.

6. The preparation method according to claim 5, characterized in that, The vacuum degree of the vacuum induction melting in step (1) is ≤0.5Pa.

7. The preparation method according to claim 5 or 6, characterized in that, The inert atmosphere is argon gas with a purity of ≥99.8wt%; The pressure of the inert atmosphere is ≥10000Pa.

8. The preparation method according to any one of claims 4 to 7, characterized in that, The stress relief treatment temperature is 990–1150℃, and the holding time is 6–10 hours. The temperature is then cooled to below 300°C.

9. The application of Stellite alloy STL 6B as described in claim 1 or 2, or Stellite alloy STL 6B prepared by the preparation method according to any one of claims 3 to 8, in the preparation of tunnel boring machine components.

10. The application according to claim 9, characterized in that, The tunnel boring machine components include, but are not limited to, the cutterhead and / or the main bearing.

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