A high-strength wear-resistant shell alloy material and a preparation method thereof

Abstract

This invention belongs to the field of surface engineering of metallic materials and provides a high-strength wear-resistant shell alloy material and its preparation method. The invention employs a synergistic process route of alloy composition optimization design, surface mechanical rolling, and gas nitriding composite strengthening. By constructing a double-layer gradient structure of a gradient nanocrystalline strengthening zone and a nitriding diffusion zone on a carbon-manganese-silicon-chromium-molybdenum-nickel-vanadium-niobium alloy matrix, a gradient match is achieved between the ultra-hard surface (850-1100 HV0.1) and the core (350-550 HV1). The gradient nanocrystalline strengthening zone thickness is 50-300 μm, and the nitriding diffusion zone thickness is 0.30-0.60 mm. The room temperature tensile strength is 1100-1600 MPa, and the elongation after fracture is 8-20%. This invention solves the cross-domain coupling contradiction of balancing extremely high surface hardness and overall toughness, and the difficulty in controlling residual stress gradient and dimensional stability in wear-resistant shell materials. It has wide application value in the manufacture of wear-resistant components such as shells, housings, and protective covers under high-intensity wear conditions.

Description

Technical Field

[0001] This invention relates to the field of surface engineering of metallic materials, specifically to a high-strength wear-resistant shell alloy material and its preparation method. Background Technology

[0002] In consumer electronics, communication equipment, precision instruments, and smart terminals, electronic hardware housings and brackets, as core structural components and protective parts, endure complex conditions such as frequent assembly and disassembly, surface friction and wear, drop impacts, and fatigue loads during long-term use. These products require high surface hardness to resist scratches and wear from screw tightening, snap-fitting during assembly, and daily use, maintaining appearance quality and dimensional accuracy. Simultaneously, they require a sufficiently deep hardened layer to support the surface load and prevent assembly interference or functional failure caused by localized plastic deformation. Furthermore, they must maintain high core strength and good toughness to resist drop impacts, bending deformation, and impact loads during transportation, ensuring structural integrity and reliability. Traditional surface treatment methods such as electroplating, anodizing, or single nitriding treatment are insufficient to meet the multi-level synergistic requirements of "high surface hardness and wear resistance, deep subsurface support, and a strong and impact-resistant core." Gas nitriding can form a high-hardness nitride reinforcement layer on the surface of steel materials, significantly improving wear resistance. However, the depth and hardness gradient control of conventional nitriding layers are limited by diffusion kinetics, and the nitrogen concentration gradient introduced by nitriding generates a complex residual stress distribution during cooling, which may lead to deformation of thin-walled structures or a decrease in dimensional accuracy. Surface mechanical rolling and other plastic deformation strengthening technologies can induce nanocrystalline structures on the surface through intense plastic deformation, achieving improvements in hardness and fatigue performance. However, the thickness of the mechanical deformation strengthening layer is limited and its thermal stability is insufficient. Developing composite surface engineering technologies that can achieve the synergistic effect of surface nitriding strengthening and nanocrystalline plastic deformation strengthening, construct multi-level gradient structures, precisely control the hardness gradient and residual stress distribution, and ensure dimensional stability is of great significance for meeting the high-end application requirements of electronic hardware housings and brackets.

[0003] To address the surface strengthening requirements of electronic hardware casings and brackets, various technical solutions have been researched and applied. For example, Chinese patent CN107553812B discloses a method for manufacturing curved casings of electronic products, using surface hardening to increase surface hardness. However, this method has a steep hardness gradient, which can easily lead to stress concentration at the interface between the hardened layer and the substrate, causing cracking or peeling, when the thin-walled structure is subjected to assembly stress or drop impact. Furthermore, traditional methods for preparing high-strength metal casings through surface mechanical strengthening treatment can achieve a strengthening effect on the surface layer, but the mechanically deformed strengthening layer is prone to recrystallization during subsequent heat treatment or service, leading to a decline in the strengthening effect. It also fails to effectively solve the problem of hardness matching between the surface layer and the core, making the interface prone to cracking under impact. Existing technologies have limited research on combining nitriding treatment with surface plastic deformation strengthening processes. There is a lack of systematic research on key issues such as how to achieve synergistic effects between the two strengthening mechanisms through process sequence optimization, how to control the thermal stability of gradient nanocrystals during nitriding, and how to construct a continuous gradient transition from the ultra-hard surface region to the strong core region to avoid interface stress concentration and ensure the dimensional stability of the thin-walled structure. Existing electronic hardware casing and bracket materials generally suffer from shortcomings such as difficulty in achieving both high surface hardness and overall toughness, difficulty in controlling residual stress gradient and dimensional stability, and insufficient bonding strength between the surface reinforcement layer and the substrate, making them prone to peeling.

[0004] The purpose of this invention is to provide a high-strength wear-resistant shell alloy material and its preparation method, which solves the pain point problem of cross-domain coupling contradictions in current shell wear-resistant materials, such as the difficulty in balancing extremely high surface hardness and overall toughness, and the difficulty in controlling residual stress gradient and dimensional stability.

[0005] This invention adopts a synergistic approach of "alloy composition control + heat treatment optimization + surface mechanical rolling + gas nitriding". By first implementing surface rolling to induce a gradient nanocrystalline strengthening zone on a high-strength and tough matrix, and then performing gas nitriding to form a nitriding diffusion zone, a multi-level gradient synergy is achieved, which includes ultra-hard and wear-resistant surface layer, deep support of subsurface layer, and strong and tough impact resistance of core. It constructs a continuous hardness gradient and optimized stress distribution from nanocrystalline ultra-hard surface layer to the toughened core of retained austenite, thus solving the contradiction of multiple performances that are difficult to achieve with a single strengthening method. Summary of the Invention

[0006] To achieve the above objectives, the present invention provides the following technical solution: A high-strength wear-resistant shell alloy material, comprising, by mass fraction: 0.18-0.32 wt% carbon, 0.8-1.8 wt% manganese, 0.6-1.5 wt% silicon, 1.2-3.0 wt% chromium, 0.25-0.70 wt% molybdenum, 0.20-1.50 wt% nickel, 0.05-0.25 wt% vanadium, 0.02-0.08 wt% niobium, with the balance being iron and unavoidable impurities; The surface of the alloy material has a gradient nanocrystalline strengthening region and a nitriding diffusion region. The thickness of the gradient nanocrystalline strengthening region is 50-300 μm, and the thickness of the nitriding diffusion region is 0.30-0.60 mm. The thickness of the nitriding diffusion region is the thickness of the diffusion layer measured from the surface of the alloy material along the normal direction inward. The gradient nanocrystalline strengthening region is located on the surface of the alloy material and is at least partially within the thickness range of the nitriding diffusion region.

[0007] The surface Vickers hardness HV0.1 of the alloy material is 850-1100, and the core Vickers hardness HV1 is 350-550. The core Vickers hardness HV1 is the Vickers hardness value measured at a depth greater than the thickness of the nitriding diffusion zone from the surface of the alloy material. Both the surface Vickers hardness HV0.1 and the core Vickers hardness HV1 are based on values ​​measured in the finished product state.

[0008] Furthermore, the volume fraction of retained austenite in the core of the alloy material is 5-20 vol%, and the volume fraction of retained austenite is determined by taking a sample at a depth greater than the thickness of the nitriding diffusion zone from the surface of the alloy material, and determining the volume fraction by X-ray diffraction, wherein the sampling is performed in the finished product state.

[0009] Furthermore, the room temperature tensile strength of the alloy material is 1100-1600 MPa, and the room temperature elongation after fracture is 8-20%. Both the room temperature tensile strength and the room temperature elongation after fracture are mechanical property indicators obtained by room temperature tensile test.

[0010] As a concept of this invention, it employs a multi-element alloying design of carbon, manganese, silicon, chromium, molybdenum, nickel, vanadium, and niobium, combined with a surface mechanical rolling-gas nitriding composite strengthening process. This is primarily used to enhance the surface hardness, wear resistance, core toughness, and overall service reliability of wear-resistant outer shell components. A carbon content of 0.18-0.32 wt% forms the basis for quenching martensitic transformation and distribution treatment, ensuring both hardenability and matrix strength while regulating the stability of retained austenite to improve core toughness. Manganese and silicon synergistically improve hardenability and solid solution strengthen the matrix; manganese stabilizes retained austenite, while silicon inhibits cementite precipitation and promotes carbon distribution. Chromium-molybdenum composite strengthening significantly improves hardenability, tempering resistance, and corrosion resistance; chromium promotes surface nitride formation, while molybdenum refines grains and improves high-temperature stability. Nickel improves toughness and stabilizes retained austenite, lowering the martensitic transformation temperature and reducing quenching stress. Vanadium-niobium microalloying enhances strength through the synergistic effect of precipitation strengthening and grain refinement. Vanadium nitrides disperse and precipitate during nitriding to strengthen the nitrided layer, while niobium carbonitrides pin grain boundaries to stabilize the gradient nanocrystalline structure. Surface mechanical rolling introduces intense plastic deformation into the surface of the heat-treated billet, inducing the formation of a 50-300 μm gradient nanocrystalline strengthening zone. Grain refinement and dislocation strengthening synergistically improve surface hardness. Subsequent gas nitriding forms a 0.30-0.60 mm nitriding diffusion zone on the gradient nanocrystalline base. Nitrogen atoms diffuse rapidly along grain boundaries to form dispersed nitride distribution. The high-density grain boundaries of the gradient nanocrystalline accelerate nitrogen diffusion, while the precipitation of vanadium-niobium carbonitrides pins the grain boundaries, maintaining the thermal stability of the nanocrystalline structure. The dual-layer gradient structure works together to achieve a surface hardness of 850-1100HV0.1, a core hardness of 350-550HV1, and 5-20 vol% of retained austenite, forming a continuous hardness gradient to avoid stress concentration at the interface. The superposition of nitriding compressive stress and nanocrystalline residual compressive stress optimizes the surface stress state, ultimately achieving a balance between tensile strength of 1100-1600MPa and elongation of 8-20%.

[0011] This invention also discloses a method for preparing a high-strength wear-resistant shell alloy material, comprising the following steps: S1 Melting and Billet Forming: Iron, carbon, manganese, silicon, chromium, molybdenum, nickel, vanadium and niobium are provided as raw materials. After being mixed according to chemical composition, they are melted in an induction furnace or electric arc furnace under a nitrogen protective atmosphere. The melting temperature is 1550-1650℃, and the temperature is held for 10-40 minutes. The alloy billet is then cast. S2 Heat Treatment: The alloy billet is heated to 880-950℃ under a nitrogen protective atmosphere and held for 20-60 minutes, then quenched. The quenching medium is water or a 5-25 wt% polyethylene glycol aqueous solution. Subsequently, a distribution treatment or tempering treatment is performed at a temperature of 320-480℃ and a time of 30-180 minutes to obtain a heat-treated billet. After subsequent steps S3 and S4, the core Vickers hardness HV1 of the alloy material is 350-550. The core Vickers hardness HV1 is the Vickers hardness value measured at a depth greater than the thickness of the nitrided diffusion zone from the surface of the alloy material, and the core Vickers hardness HV1 is based on the value measured in the finished product state.

[0012] S3 Surface mechanical rolling: The surface of the heat-treated blank is subjected to surface mechanical rolling, the rolling pressure is 200-800MPa, the rolling pressure is the average contact pressure between the rolling tool and the workpiece surface contact area, and the rolling passes are 3-20 passes to form a gradient nanocrystalline reinforced region with a thickness of 50-300μm. S4 Gas Nitriding: The billet treated in step S3 is placed in a nitriding furnace and ammonia gas is introduced for gas nitriding. The nitriding temperature is 500-560℃, the nitriding time is 10-25h, and the nitriding pressure is 0.08-0.12MPa. The nitriding pressure is the absolute pressure inside the nitriding furnace, so as to form a nitriding diffusion zone with a thickness of 0.30-0.60mm and make the surface Vickers hardness HV0.1 reach 850-1100.

[0013] Furthermore, step S1 includes the following operations: S11 Raw Material Acceptance: The purity of the iron shall not be less than 99.5 wt%, the fixed carbon content of the carbon shall not be less than 98 wt%, and the purity of the manganese, silicon, chromium, molybdenum, nickel, vanadium and niobium shall not be less than 98 wt%. S12 Ingredients: Weigh and prepare ingredients according to their chemical composition, with the weighing error controlled within ±0.5%; S13 Melting: Under nitrogen protection, heat to 1550-1650℃ and hold for 10-40 minutes; S14 Casting: The molten material is poured into a metal mold or sand mold to obtain the alloy billet; S15 post-processing: Remove the riser from the alloy billet and machine to remove 0.5-3mm of skin; S16 Quality Control: The chemical composition of the alloy billet is inspected to confirm that the contents of carbon, manganese, silicon, chromium, molybdenum, nickel, vanadium and niobium are all within the above range.

[0014] Furthermore, step S3 includes the following operations: S31 Pretreatment: The surface of the heat-treated blank is degreased and cleaned with acetone for 2-10 minutes, and then dried until no cleaning agent residue is visible on the surface of the workpiece. S32 Rolling: The surface mechanical rolling is performed at 15-35℃, the rolling pressure is 200-800MPa, the rolling pressure is the average contact pressure between the rolling tool and the workpiece surface, the rolling speed is 0.05-0.50m / s, the number of rolling passes is 3-20, and the feed rate is 0.05-0.50mm / pass. S33 Endpoint Criterion: The endpoint criterion is that the Vickers hardness of the surface after rolling increases by 80-250 HV0.1 compared with that before rolling; by controlling the rolling pressure, rolling passes and feed rate, the thickness of the gradient nanocrystalline reinforced region can reach 50-300 μm; S34 Post-treatment: After rolling, remove surface debris until there are no visible debris on the workpiece surface, and then dry; S35 Quality Control: Randomly inspect the increase in surface Vickers hardness and the thickness of the gradient nanocrystalline reinforced region to confirm that they meet the endpoint criteria of operation S33 and the limit on the thickness of the gradient nanocrystalline reinforced region, respectively.

[0015] Furthermore, step S4 includes the following operations: S41 Pretreatment: Before nitriding, the product is degreased and cleaned with acetone and then dried; S42 heating: Heat to 500-560℃ in a nitriding furnace at a heating rate of 1-10℃ / min; S43 Ammonia Nitrification: Ammonia gas is introduced, the nitriding pressure is 0.08-0.12 MPa, the nitriding pressure is the absolute pressure inside the nitriding furnace, and the nitriding time is 10-25 h; S44 Cooling: After nitriding, furnace cooling or cooling to no higher than 200°C while maintaining the furnace atmosphere before unloading; S45 endpoint criterion: The endpoint criterion is that the thickness of the nitrided diffusion zone reaches 0.30-0.60 mm and the surface Vickers hardness HV0.1 reaches 850-1100. S46 Quality Control: Randomly inspect the thickness of the nitriding diffusion zone and the surface Vickers hardness HV0.1 to ensure compliance with requirements.

[0016] Furthermore, acetone is used as the cleaning agent for both the degreasing and cleaning processes in steps S3 and S4, and the cleaning time is 2-10 minutes.

[0017] Furthermore, the quenching medium is water, and after quenching, it enters the distribution process or the tempering process within 10-60 seconds.

[0018] Furthermore, the quenching medium is an aqueous solution of polyethylene glycol, and the mass fraction of polyethylene glycol in the aqueous solution is 5-25 wt%.

[0019] Furthermore, the gradient nanocrystalline strengthening region is a grain size gradient structure region formed by surface mechanical rolling, wherein the grain size gradually increases from the nanometer level on the surface of the alloy material to the submicrometer level.

[0020] Furthermore, the nitriding diffusion zone is a nitrogen concentration gradient diffusion zone formed by gas nitriding, wherein the nitrogen concentration gradually decreases from the surface of the alloy material inward.

[0021] Furthermore, the gradient nanocrystal reinforcement region is characterized by transmission electron microscopy or electron backscatter diffraction, and the grain size distribution is determined by cross-sectional microstructure observation.

[0022] Furthermore, the X-ray diffraction test of the retained austenite volume fraction was performed using Cu-Kα rays with a scanning angle range of 40-100°. The volume fraction of the retained austenite was calculated by integrating the intensity of the 111, 200, and 220 diffraction peaks of austenite and the 110, 200, and 211 diffraction peaks of ferrite or martensite.

[0023] Furthermore, the room temperature tensile test was conducted in accordance with GB / T 228.1-2021 standard, with the specimen being a round bar tensile specimen, the gauge length diameter being 5-10 mm, the beam displacement rate being 1-10 mm / min, and the room temperature being 15-25℃.

[0024] Furthermore, the heating in step S2 is carried out under a nitrogen protective atmosphere or under vacuum conditions; when heating under vacuum conditions, the vacuum degree is 10-100 Pa, the vacuum time is 10-30 min, and then the temperature is increased.

[0025] Furthermore, the molecular weight of the polyethylene glycol is 200-10000.

[0026] Furthermore, in step S4, the ammonia flow rate is 5-50 L / h, and the ammonia decomposition rate is controlled at 20-40%.

[0027] Furthermore, the nitriding diffusion zone of the alloy material is composed of a diffusion layer in which nitrides are dispersed, and the nitrogen concentration gradually decreases from 0.5-2.0 wt% on the surface to 0.05-0.2 wt% inward.

[0028] Furthermore, the rolling equipment in step S3 is one of cryogenic rolling equipment, ultrasonic rolling equipment, or conventional mechanical rolling equipment.

[0029] Furthermore, the alloy material is suitable for manufacturing shells, housings, protective covers, or wear-resistant parts that withstand high-intensity wear conditions.

[0030] Furthermore, the boundary of the nitriding diffusion zone is determined by the disappearance of nitride dispersion or the reduction of nitrogen concentration to the matrix level, and is determined by metallographic observation or microhardness gradient measurement.

[0031] Furthermore, the gradient nanocrystalline reinforced region formed in step S3 still maintains the nanocrystalline gradient structure after nitriding treatment in step S4. The thermal stability of the nanocrystalline gradient structure is achieved through the grain boundary pinning effect of alloying elements and the inhibition effect of nitrides precipitated during nitriding on grain boundary migration.

[0032] Furthermore, the ammonia decomposition rate in step S4 is determined by online analysis of the composition of the exhaust gas in the furnace or by periodic sampling analysis, and is controlled by adjusting the ammonia flow rate and the exhaust gas volume in the furnace.

[0033] Furthermore, when step S2 employs a partitioning process, the partitioning process is a carbon partitioning process based on a quenching-partitioning process. By holding the temperature at the partitioning process temperature, carbon diffuses from martensite to retained austenite, stabilizing the retained austenite and regulating the hardness and toughness of the core structure.

[0034] As another aspect of this invention, a four-step preparation process of "melting and billet formation → quenching-distribution heat treatment → surface mechanical rolling → gas nitriding" is adopted. This process is mainly used to enhance the microstructure control precision, process stability, and product consistency of the outer shell alloy material preparation process. In step S1, the billet is smelted in an induction furnace or electric arc furnace at 1550-1650℃ for 10-40 minutes under nitrogen protection. The precise batching error is ≤±0.5%. After casting, the billet is machined to remove 0.5-3mm of the outer layer and the chemical composition is inspected to ensure that the alloy element content is within the target range, laying the compositional foundation for subsequent heat treatment and surface strengthening. Step S2 heat treatment adopts a quenching-distribution or quenching-tempering route. Under nitrogen protection or vacuum conditions, it is heated at 880-950℃ and held for 20-60 min, followed by water quenching or quenching with polyethylene glycol aqueous solution. Then, it is distributed or tempered at 320-480℃ for 30-180 min to obtain a high-strength and tough matrix with a core Vickers hardness of 350-550 HV1 and 5-20 vol% retained austenite, providing a reliable support basis for surface strengthening. Step S3, surface mechanical rolling, involves intense plastic deformation at room temperature (15-35℃) with a rolling pressure of 200-800MPa, a rolling speed of 0.05-0.50m / s, 3-20 passes, and a feed rate of 0.05-0.50mm / pass. This induces the formation of a 50-300μm gradient nanocrystalline reinforcement zone on the surface of the heat-treated blank. The surface grains are refined to the nanoscale and gradually transition inward. The endpoint is defined as an increase in surface hardness of 80-250HV0.1. Acetone degreasing pretreatment and posttreatment ensure surface cleanliness. In step S4, gas nitriding, ammonia gas is introduced into the nitriding furnace, and the temperature is raised to 500-560℃ at a rate of 1-10℃ / min and held for 10-25h. The nitriding pressure is 0.08-0.12MPa, the ammonia flow rate is 5-50L / h, and the decomposition rate is 20-40%. Nitrogen atoms diffuse rapidly along the high-density grain boundaries of the gradient nanocrystals to form a nitriding diffusion zone with a thickness of 0.30-0.60mm. The nitrogen concentration decreases from 0.5-2.0wt% on the surface to 0.05-0.2wt% inward. Vanadium and niobium nitrides are dispersed and precipitated to pin the grain boundaries and maintain the thermal stability of the nanocrystals. Finally, the surface hardness reaches 850-1100HV0.1. After nitriding, the furnace is cooled to ≤200℃ before being removed from the furnace. The process sequence of rolling followed by nitriding enables the gradient nanocrystals to obtain nitride pinning reinforcement during nitriding and maintain the thermal stability of the nanostructure. This avoids the risk of cracking of the brittle nitride layer caused by nitriding followed by rolling, and achieves the synergistic construction and performance optimization of the double-layer gradient structure.

[0035] In this invention, the gradient nanocrystalline strengthening zone and the nitriding diffusion zone, as a double-layer surface gradient structure, play a synergistic role in the outer shell alloy material, with each having a clear focus and main function and supporting each other. The gradient nanocrystalline strengthening zone mainly achieves surface grain refinement to the nanoscale through intense plastic deformation induced by surface mechanical rolling. Relying on the grain refinement strengthening and high-density dislocation strengthening mechanism, it significantly improves the surface hardness, fatigue strength, and crack initiation resistance. Its thickness of 50-300 μm provides the first ultra-hard protective barrier for the surface layer. The nitriding diffusion zone mainly achieves strengthening through nitrogen atom diffusion during gas nitriding and the formation of dispersed nitrides by alloying elements such as vanadium and niobium. Its thickness of 0.30-0.60 mm provides a deep load-bearing support layer for the subsurface. The nitride dispersion strengthening and solid solution nitrogen strengthening synergistically improve the subsurface hardness and continuously transition towards the core. The high-density grain boundaries of the gradient nanocrystalline strengthening zone provide short-circuit diffusion channels for rapid nitrogen atom diffusion, accelerating the nitriding process and preferentially precipitating nitrides at the nanograin boundaries, thus enhancing the nitriding effect. During nitriding, the precipitation of vanadium-niobium carbonitrides at the grain boundaries of nanocrystals exerts a strong pinning effect on grain boundary migration, inhibiting the growth of nanocrystals at nitriding temperatures of 500-560℃, maintaining the thermal stability of the gradient nanocrystal structure, and avoiding the degradation of the strengthening effect caused by nanocrystal recrystallization. The surface compressive stress introduced by nitriding and the residual compressive stress generated by the gradient nanocrystals superimpose to optimize the surface stress state, further inhibiting the initiation and propagation of fatigue cracks. The double-layer gradient structure transitions from the ultra-hard region of the surface nanocrystals through the nitrided subsurface to the core toughened by residual austenite, forming a continuous hardness gradient and stress gradient distribution. This avoids abrupt hardness changes and stress concentrations at the interface between a single strengthening layer and the matrix, improves the bonding strength and anti-stripping performance between the surface strengthening layer and the matrix, and ultimately achieves multi-level synergistic performance optimization of ultra-hard and wear-resistant surface, deep support and load-bearing capacity, and strong and impact-resistant core.

[0036] Beneficial technical effects 1. Significantly improves surface hardness and wear resistance: Through a dual-layer composite reinforcement design that induces a gradient nanocrystalline reinforcement zone by surface mechanical rolling and forms a nitriding diffusion zone by gas nitriding, a nanocrystalline ultrahard layer with a thickness of 50-300μm and a nitride dispersion reinforcement layer with a thickness of 0.30-0.60mm are constructed on the surface of the alloy material, achieving an ultra-high surface hardness of 850-1100HV0.1. Compared with conventional nitriding or single surface strengthening processes, the surface hardness is increased by more than 30%, exhibiting excellent resistance to abrasive cutting and ploughing under high-intensity abrasive wear conditions, and significantly extending the wear life of shell components.

[0037] 2. Achieving gradient matching and synergistic optimization of surface superhardness and core toughness: A high-strength and tough matrix with a Vickers hardness of 350-550 HV1 and a retained austenite volume fraction of 5-20 vol% is obtained by quenching-distribution or quenching-tempering heat treatment. Combined with a double-layer gradient strengthening structure on the surface, a continuous hardness gradient distribution is formed from the surface nanocrystalline superhard zone through the nitrided strengthening sub-surface layer to the core toughened by retained austenite. This avoids abrupt hardness changes and stress concentrations at the interface between a single strengthening layer and the matrix, achieving a balance between room temperature tensile strength of 1100-1600 MPa and elongation at break of 8-20%. When subjected to impact loads, the core provides reliable strong and tough support and absorbs impact energy, inhibiting crack propagation from the surface to the core, and significantly improving the impact crack resistance and overall reliability of shell components.

[0038] 3. Optimizing residual stress distribution and improving fatigue performance and anti-stripping reliability: The residual compressive stress introduced by surface mechanical rolling and the surface compressive stress generated by nitrogen atom diffusion during gas nitriding work synergistically to form a favorable compressive stress state on the surface, inhibiting the initiation and propagation of fatigue cracks and significantly improving the fatigue strength and fatigue life of the material. Simultaneously, the continuous transition between the gradient nanocrystalline reinforcement zone and the nitriding diffusion zone, as well as the pinning effect of vanadium-niobium carbonitrides at the nanocrystalline grain boundaries, enhances the interfacial bonding strength between the surface reinforcement layer and the substrate, avoiding the spalling failure problem that easily occurs under impact loads in traditional single nitriding layers or coatings, ensuring the long-term stability and reliability of shell components under complex service conditions.

[0039] 4. Ensuring the thermal stability and process controllability of the gradient nanocrystalline structure: By designing a process sequence of surface mechanical rolling followed by gas nitriding, the dispersed precipitation of vanadium-niobium carbonitrides at the grain boundaries of the gradient nanocrystals during nitriding exerts a strong pinning effect on grain boundary migration, inhibiting the growth and recrystallization of nanocrystals at the nitriding temperature of 500-560℃. This maintains the thermal stability of the gradient nanocrystalline structure and preserves its strengthening effect, avoiding the brittle nitride layer cracking problem that may occur with nitriding followed by rolling. Simultaneously, quality control measures such as precise ingredient proportioning, strict control of melting and heat treatment parameters, and setting endpoint criteria for rolling and nitriding ensure the precision of microstructure control and product consistency during the preparation process, improving the stability and reproducibility of the process.

[0040] 5. Expanding application scope and improving economic benefits: The high-strength wear-resistant shell alloy material prepared by this invention has multi-level synergistic properties, including ultra-hard and wear-resistant surface, deep support and load-bearing capacity, and strong and impact-resistant core. It is suitable for manufacturing shells, housings, protective covers and other wear-resistant parts that are subjected to high-intensity wear conditions in fields such as engineering machinery, mining equipment, heavy-duty transportation and protective equipment. Compared with traditional materials, it can significantly extend the service life of parts, reduce maintenance costs and improve equipment operating efficiency, and has broad market application prospects and good economic benefits. Attached Figure Description

[0041] Figure 1 The XRD patterns of Example 1, Comparative Example 4, and Comparative Example 5 are shown in comparison.

[0042] Figure 2 This is a comparison chart of the residual austenite volume fraction in Example 1, Comparative Example 4, and Comparative Example 5.

[0043] Figure 3 The image shows a comparison of the microhardness gradients of Example 1, Comparative Example 4, and Comparative Example 5.

[0044] Figure 4 The TEM statistical equivalent grain diameter distribution diagram of the surface layer of Example 1, the sub-surface layer of Example 1, and the surface layer of Comparative Example 4 is shown.

[0045] Figure 5 The TEM statistical cumulative distribution of equivalent grain diameters of the surface layer of Example 1, the subsurface layer of Example 1, and the surface layer of Comparative Example 4 are shown.

[0046] Figure 6 This is a cumulative distribution diagram of the equivalent diameter of dimples in the tensile fracture surface of Comparative Example 1.

[0047] Figure 7 This is a cumulative distribution diagram of the equivalent diameter of the quasi-solution cleavage feature of the tensile fracture surface in Comparative Example 2 of Example 1.

[0048] Figure 8 This is a comparison diagram of the residual stress depth distribution in Example 1 and Comparative Example 5.

[0049] Figure 9 This is a comparison of the XPS chemical state N1s high-resolution spectra of Comparative Example 7 of Example 1.

[0050] Figure 10 This is a comparison of the XPS chemical state Cr2p high-resolution spectra of Comparative Example 7 in Example 1.

[0051] Figure 11 This is a comparison of the XPS chemical state Fe2p high-resolution spectra of Comparative Example 7 in Example 1. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Example

[0053] This embodiment provides a high-strength wear-resistant shell alloy material. By mass fraction, the alloy material in this embodiment includes: 0.25wt% carbon, 1.3wt% manganese, 1.0wt% silicon, 2.1wt% chromium, 0.48wt% molybdenum, 0.85wt% nickel, 0.15wt% vanadium, 0.05wt% niobium, with the balance being iron and unavoidable impurities.

[0054] The alloy material of this embodiment has a gradient nanocrystalline strengthening region and a nitriding diffusion region on its surface. The thickness of the gradient nanocrystalline strengthening region in this embodiment is 150 μm, and the thickness of the nitriding diffusion region in this embodiment is 0.45 mm. The thickness of the nitriding diffusion region in this embodiment is the thickness of the diffusion layer measured from the surface of the alloy material inward along the normal direction. The gradient nanocrystalline strengthening region in this embodiment is located on the surface layer of the alloy material and is at least partially within the thickness range of the nitriding diffusion region. The gradient nanocrystalline strengthening region in this embodiment is a grain size gradient structure region formed by surface mechanical rolling. The grain size in this embodiment gradually increases from the nanometer level on the surface of the alloy material to the submicrometer level. The nitriding diffusion region in this embodiment is a nitrogen concentration gradient diffusion region formed by gas nitriding. The nitrogen concentration in this embodiment gradually decreases from the surface layer of the alloy material inward.

[0055] The surface Vickers hardness HV0.1 of the alloy material in this embodiment is 950, and the core Vickers hardness HV1 is 450. The core Vickers hardness HV1 in this embodiment is the Vickers hardness value measured at a depth greater than the thickness of the nitriding diffusion zone at the surface of the alloy material in this embodiment. The surface Vickers hardness HV0.1 and the core Vickers hardness HV1 in this embodiment are based on the values ​​measured in the finished product state.

[0056] The volume fraction of retained austenite in the core of the alloy material in this embodiment is 12 vol%. The volume fraction of retained austenite in this embodiment is determined as follows: a sample is taken at a depth greater than the thickness of the nitriding diffusion zone from the surface of the alloy material in this embodiment, and the volume fraction is determined by X-ray diffraction. The sampling in this embodiment is performed in the finished product state. The X-ray diffraction test for the volume fraction of retained austenite in this embodiment uses Cu-Kα rays with a scanning angle range of 40-100°. The volume fraction of retained austenite in this embodiment is calculated by the integrated intensity of the 111, 200, and 220 diffraction peaks of austenite and the 110, 200, and 211 diffraction peaks of ferrite or martensite.

[0057] The room temperature tensile strength of the alloy material in this embodiment is 1350 MPa, and the room temperature elongation after fracture is 14%. Both the room temperature tensile strength and the room temperature elongation after fracture in this embodiment are mechanical property indicators obtained by room temperature tensile testing. The room temperature tensile test in this embodiment was conducted according to GB / T 228.1-2021 standard. The specimen was a round bar tensile specimen with a gauge length diameter of 8 mm, a beam displacement rate of 5 mm / min, and a room temperature of 20℃.

[0058] The preparation method of the high-strength wear-resistant shell alloy material in this embodiment includes the following steps: S1 Melting and Billet Forming: Iron, carbon, manganese, silicon, chromium, molybdenum, nickel, vanadium and niobium are provided as raw materials. After being distributed according to chemical composition, they are melted in an induction furnace under a nitrogen protective atmosphere at a melting temperature of 1600℃ for 25 minutes, and then cast to obtain alloy billets. Step S1 includes the following operations: S11 Raw material acceptance: The purity of iron in this embodiment is not less than 99.5 wt%, the fixed carbon content of carbon in this embodiment is not less than 98 wt%, and the purity of manganese, silicon, chromium, molybdenum, nickel, vanadium, and niobium in this embodiment is not less than 98 wt%; S12 Batching: Weigh and batch the materials according to the chemical composition of this embodiment, with the weighing error controlled within ±0.3%; S13 Melting: Heat to 1600℃ under nitrogen protection and hold for 25 minutes; S14 Casting: Cast the melt into a metal mold to obtain the alloy billet of this embodiment; S15 Post-processing: Remove the riser of the alloy billet of this embodiment and machine to remove 1.5 mm of skin; S16 Quality control: Perform chemical composition acceptance on the alloy billet of this embodiment to confirm that the contents of carbon, manganese, silicon, chromium, molybdenum, nickel, vanadium, and niobium are all within the range of this embodiment.

[0059] S2 Heat Treatment: The alloy billet of this embodiment is heated to 915°C under a nitrogen protective atmosphere and held for 40 minutes before quenching. The quenching medium in this embodiment is water. Subsequently, tempering is performed at 400°C for 105 minutes to obtain a heat-treated billet with a core Vickers hardness HV1 of 450. The core Vickers hardness HV1 of 450 in this embodiment is determined by measurement at a depth greater than the thickness of the nitrided diffusion zone in the finished product state. In this embodiment, the tempering process is performed within 30 seconds after quenching. The heating in step S2 is carried out under a nitrogen protective atmosphere.

[0060] S3 Surface Mechanical Rolling: Surface mechanical rolling is performed on the surface of the heat-treated blank in this embodiment. The rolling pressure is 500 MPa, which is the average contact pressure between the rolling tool and the workpiece surface. The rolling passes are 12 times to form a gradient nanocrystalline reinforced region with a thickness of 150 μm. This step S3 includes the following operations: S31 Pretreatment: The surface of the heat-treated blank in this embodiment is degreased and cleaned with acetone for 5 minutes, followed by drying until no visible cleaning agent residue is visible on the workpiece surface; S32 Rolling: Surface mechanical rolling is performed at 25°C, with a rolling pressure of 500 MPa. The rolling pressure in this embodiment is the average contact pressure between the rolling tool and the workpiece surface. The rolling speed is 0.25 m / s, the rolling passes are 12 times, and the feed rate is 0.25 mm / pass; S33 Endpoint Judgment According to the criteria, the Vickers hardness of the surface after rolling increased by 150 HV0.1 compared to before rolling. By controlling the rolling pressure, number of rolling passes, and feed rate, the thickness of the gradient nanocrystalline reinforced zone in this embodiment reached 150 μm. S34 Post-processing: After rolling, surface debris was removed until no visible debris remained on the workpiece surface, and then the workpiece was dried. S35 Quality control: The increase in surface Vickers hardness and the thickness of the gradient nanocrystalline reinforced zone in this embodiment were randomly checked to confirm that they met the endpoint criterion of operation S33 and the thickness limit of the gradient nanocrystalline reinforced zone in this embodiment, respectively. The rolling equipment in step S3 of this embodiment is a conventional mechanical rolling equipment.

[0061] S4 Gas Nitriding: The billet treated in step S3 is placed in a nitriding furnace and ammonia gas is introduced for gas nitriding. The nitriding temperature is 530°C, the nitriding time is 17.5 h, and the nitriding pressure is 0.10 MPa. In this embodiment, the nitriding pressure is the absolute pressure inside the nitriding furnace, in order to form a nitriding diffusion zone with a thickness of 0.45 mm and to achieve a surface Vickers hardness of HV0.1 of 950. Step S4 includes the following operations: S41 Pretreatment: Before nitriding, acetone is used for degreasing, cleaning, and drying for 5 minutes; S42 Heating: The temperature is raised to 530°C in the nitriding furnace at a rate of 5°C / min; S43 Ammonia nitriding: Ammonia gas is introduced at a nitriding pressure of 0.10 MPa (in this embodiment, the nitriding pressure is the absolute pressure inside the nitriding furnace), and the nitriding time is 17.5 hours; S44 Cooling: After nitriding, the furnace is cooled to a temperature not exceeding 200°C before removal; S45 Endpoint criterion: The endpoint criterion is that the thickness of the nitrided diffusion zone reaches 0.45 mm and the surface Vickers hardness HV0.1 reaches 950; S46 Quality control: The thickness of the nitrided diffusion zone and the surface Vickers hardness HV0.1 are randomly checked to ensure compliance with requirements. In step S4 of this embodiment, the ammonia flow rate is 25 L / h, and the ammonia decomposition rate is controlled at 30%.

[0062] In this embodiment, acetone is used as the cleaning agent for degreasing and cleaning in steps S3 and S4, and the cleaning time is 5 minutes for both steps.

[0063] In this embodiment, the nitriding diffusion zone of the alloy material consists of a diffusion layer with dispersed nitride distribution, and the nitrogen concentration gradually decreases from 1.2 wt% on the surface to 0.12 wt% inward. The boundary of the nitriding diffusion zone in this embodiment is determined by the disappearance of the dispersed nitride distribution or the nitrogen concentration decreasing to the matrix level, and is determined by metallographic observation or microhardness gradient measurement. The gradient nanocrystalline reinforced zone formed in step S3 of this embodiment retains its nanocrystalline gradient structure after nitriding treatment in step S4. The thermal stability of the nanocrystalline gradient structure in this embodiment is achieved through the grain boundary pinning effect of alloying elements and the inhibition of grain boundary migration by nitrides precipitated during nitriding. The ammonia decomposition rate in step S4 of this embodiment is determined by online analysis of the furnace exhaust composition and controlled by adjusting the ammonia flow rate and the furnace exhaust volume.

[0064] The gradient nanocrystalline reinforced region in this embodiment was characterized using transmission electron microscopy, and the grain size distribution was determined by cross-sectional microstructure observation. The alloy material in this embodiment is suitable for preparing shells, housings, protective covers, or wear-resistant parts that withstand high-intensity wear conditions.

[0065] Features of Example 1: This embodiment employs a moderate chemical composition ratio, with 0.25 wt% carbon, 1.3 wt% manganese, and 2.1 wt% chromium. A martensitic and retained austenitic microstructure is obtained through quenching at 915℃ and tempering at 400℃, ensuring good core toughness with a core hardness of 450 HV1. A 150 μm thick gradient nanocrystalline reinforcement zone is formed on the surface through 12 passes of rolling at 500 MPa moderate pressure. Subsequently, a 0.45 mm thick nitriding diffusion zone is formed through nitriding at 530℃ for 17.5 hours, achieving a surface hardness of 950 HV0.1. This embodiment achieves a good match between a tensile strength of 1350 MPa and an elongation after fracture of 14%, with 12 vol% retained austenite providing excellent toughness reserves. The process parameters of this embodiment are robust and controllable, suitable for components such as shells and protective covers subjected to moderate impact and wear conditions. It is particularly suitable for stable mass production scenarios and can be widely used in the manufacture of wear-resistant shells in engineering machinery, mining equipment, and conveying equipment. Example

[0066] This embodiment provides a high-strength wear-resistant shell alloy material. By mass fraction, the alloy material of this embodiment includes: 0.28wt% carbon, 1.5wt% manganese, 1.2wt% silicon, 2.5wt% chromium, 0.60wt% molybdenum, 0.60wt% nickel, 0.20wt% vanadium, 0.06wt% niobium, with the balance being iron and unavoidable impurities.

[0067] The alloy material of this embodiment has a gradient nanocrystalline strengthening region and a nitriding diffusion region on its surface. The thickness of the gradient nanocrystalline strengthening region in this embodiment is 220 μm, and the thickness of the nitriding diffusion region in this embodiment is 0.52 mm. The thickness of the nitriding diffusion region in this embodiment is the thickness of the diffusion layer measured from the surface of the alloy material inward along the normal direction. The gradient nanocrystalline strengthening region in this embodiment is located on the surface layer of the alloy material and is at least partially within the thickness range of the nitriding diffusion region. The gradient nanocrystalline strengthening region in this embodiment is a grain size gradient structure region formed by surface mechanical rolling. The grain size in this embodiment gradually increases from the nanometer level on the surface of the alloy material to the submicrometer level. The nitriding diffusion region in this embodiment is a nitrogen concentration gradient diffusion region formed by gas nitriding. The nitrogen concentration in this embodiment gradually decreases from the surface layer of the alloy material inward.

[0068] In this embodiment, the surface Vickers hardness HV0.1 of the alloy material is 1050, and the core Vickers hardness HV1 is 500. The core Vickers hardness HV1 in this embodiment is the Vickers hardness value measured at a depth greater than the thickness of the nitriding diffusion zone at the surface of the alloy material. Both the surface Vickers hardness HV0.1 and the core Vickers hardness HV1 in this embodiment are based on values ​​measured in the finished product state.

[0069] The volume fraction of retained austenite in the core of the alloy material in this embodiment is 8 vol%. The volume fraction of retained austenite in this embodiment is determined as follows: a sample is taken at a depth greater than the thickness of the nitrided diffusion zone from the surface of the alloy material in this embodiment, and the volume fraction is determined by X-ray diffraction. The sampling in this embodiment is performed in the finished product state. The X-ray diffraction test for the volume fraction of retained austenite in this embodiment uses Cu-Kα rays with a scanning angle range of 40-100°. The volume fraction of retained austenite in this embodiment is calculated by the integrated intensity of the 111, 200, and 220 diffraction peaks of austenite and the 110, 200, and 211 diffraction peaks of ferrite or martensite.

[0070] The room temperature tensile strength of the alloy material in this embodiment is 1500 MPa, and the room temperature elongation after fracture is 10%. Both the room temperature tensile strength and the room temperature elongation after fracture in this embodiment are mechanical property indicators obtained by room temperature tensile testing. The room temperature tensile test in this embodiment was conducted according to GB / T 228.1-2021 standard. The specimen was a round bar tensile specimen with a gauge length diameter of 6 mm, a beam displacement rate of 7 mm / min, and a room temperature of 22℃.

[0071] The preparation method of the high-strength wear-resistant shell alloy material in this embodiment includes the following steps: S1 Melting and Billet Forming: Iron, carbon, manganese, silicon, chromium, molybdenum, nickel, vanadium and niobium are provided as raw materials. After being mixed according to chemical composition, they are melted in an electric arc furnace under a nitrogen protective atmosphere. The melting temperature is 1620℃, and the temperature is held for 30 minutes. The alloy billet is then cast. Step S1 includes the following operations: S11 Raw material acceptance: The purity of iron in this embodiment is not less than 99.5 wt%, the fixed carbon content of carbon in this embodiment is not less than 98 wt%, and the purity of manganese, silicon, chromium, molybdenum, nickel, vanadium, and niobium in this embodiment is not less than 98 wt%; S12 Batching: Weigh and batch the materials according to the chemical composition of this embodiment, with the weighing error controlled within ±0.4%; S13 Melting: Heat to 1620℃ under nitrogen protection and hold for 30 minutes; S14 Casting: Cast the melt into a sand mold to obtain the alloy billet of this embodiment; S15 Post-processing: Remove the riser of the alloy billet of this embodiment and machine to remove 2.0 mm of skin; S16 Quality control: Perform chemical composition acceptance on the alloy billet of this embodiment to confirm that the contents of carbon, manganese, silicon, chromium, molybdenum, nickel, vanadium, and niobium are all within the range of this embodiment.

[0072] S2 Heat Treatment: The alloy billet of this embodiment is heated to 930°C under a nitrogen protective atmosphere and held for 50 minutes, followed by quenching. The quenching medium in this embodiment is a 10 wt% polyethylene glycol aqueous solution. Subsequently, a distribution treatment is performed at 350°C for 120 minutes to obtain a heat-treated billet with a core Vickers hardness HV1 of 500. The core Vickers hardness HV1 of 500 in this embodiment is determined by measurement at a depth greater than the thickness of the nitrided diffusion zone in the finished product. The polyethylene glycol in this embodiment has a mass fraction of 10 wt% in the polyethylene glycol aqueous solution and a molecular weight of 4000. The heating in step S2 is performed under a nitrogen protective atmosphere. When step S2 uses a partitioning process, the partitioning process in this embodiment is a carbon partitioning process based on quenching-partitioning technology. By holding the temperature at the partitioning temperature in this embodiment, carbon diffuses from martensite to retained austenite, stabilizing the retained austenite and regulating the hardness and toughness of the core structure.

[0073] S3 Surface Mechanical Rolling: Surface mechanical rolling is performed on the surface of the heat-treated blank in this embodiment. The rolling pressure is 700 MPa, which is the average contact pressure between the rolling tool and the workpiece surface. The rolling passes are 16 times to form a gradient nanocrystalline reinforced region with a thickness of 220 μm. This step S3 includes the following operations: S31 Pretreatment: The surface of the heat-treated blank in this embodiment is degreased and cleaned with acetone for 6 minutes, followed by drying until no visible cleaning agent residue is visible on the workpiece surface; S32 Rolling: Surface mechanical rolling is performed at 28°C, with a rolling pressure of 700 MPa. The rolling pressure in this embodiment is the average contact pressure between the rolling tool and the workpiece surface. The rolling speed is 0.35 m / s, the rolling passes are 16 times, and the feed rate is 0.35 mm / pass; S33 Endpoint Judgment According to the criteria, the Vickers hardness of the surface after rolling increased by 200 HV0.1 compared to before rolling. By controlling the rolling pressure, number of rolling passes, and feed rate, the thickness of the gradient nanocrystalline reinforced zone in this embodiment reached 220 μm. S34 Post-processing: After rolling, surface debris was removed until no visible debris remained on the workpiece surface, and then the workpiece was dried. S35 Quality control: The increase in surface Vickers hardness and the thickness of the gradient nanocrystalline reinforced zone in this embodiment were randomly checked to confirm that they met the endpoint criterion of operation S33 and the thickness limit of the gradient nanocrystalline reinforced zone in this embodiment, respectively. The rolling equipment in step S3 of this embodiment is an ultrasonic rolling device.

[0074] S4 Gas Nitriding: The billet treated in step S3 is placed in a nitriding furnace and ammonia gas is introduced for gas nitriding. The nitriding temperature is 550°C, the nitriding time is 22 hours, and the nitriding pressure is 0.11 MPa. In this embodiment, the nitriding pressure is the absolute pressure inside the nitriding furnace, in order to form a nitriding diffusion zone with a thickness of 0.52 mm and to achieve a surface Vickers hardness of HV0.1 of 1050. Step S4 includes the following operations: S41 Pretreatment: Before nitriding, acetone is used for degreasing, cleaning, and drying for 6 minutes; S42 Heating: The temperature is raised to 550°C in the nitriding furnace at a rate of 7°C / min; S43 Ammonia nitriding: Ammonia gas is introduced at a nitriding pressure of 0.11 MPa (in this embodiment, the nitriding pressure is the absolute pressure inside the nitriding furnace), and the nitriding time is 22 hours; S44 Cooling: After nitriding, the temperature is cooled to no higher than 200°C while maintaining the furnace atmosphere before being removed from the furnace; S45 Endpoint criterion: The endpoint criterion is that the thickness of the nitrided diffusion zone reaches 0.52 mm and the surface Vickers hardness HV0.1 reaches 1050; S46 Quality control: The thickness of the nitrided diffusion zone and the surface Vickers hardness HV0.1 are randomly checked to ensure they meet the requirements. In step S4 of this embodiment, the ammonia flow rate is 35 L / h, and the ammonia decomposition rate is controlled at 32%.

[0075] In this embodiment, acetone was used as the cleaning agent for degreasing and cleaning in steps S3 and S4, and the cleaning time was 6 minutes for both steps.

[0076] In this embodiment, the nitriding diffusion zone of the alloy material consists of a diffusion layer with dispersed nitride distribution, and the nitrogen concentration gradually decreases from 1.6 wt% on the surface to 0.15 wt% inward. The boundary of the nitriding diffusion zone in this embodiment is determined by the disappearance of the dispersed nitride distribution or the nitrogen concentration decreasing to the matrix level, and is determined by microhardness gradient measurement. The gradient nanocrystalline reinforced zone formed in step S3 of this embodiment retains its nanocrystalline gradient structure after nitriding treatment in step S4. The thermal stability of the nanocrystalline gradient structure in this embodiment is achieved through the grain boundary pinning effect of alloying elements and the inhibition of grain boundary migration by nitrides precipitated during nitriding. The ammonia decomposition rate in step S4 of this embodiment is determined by periodic sampling analysis and controlled by adjusting the ammonia flow rate and the furnace exhaust volume.

[0077] The gradient nanocrystalline reinforcement region in this embodiment was characterized using electron backscatter diffraction, and the grain size distribution was determined by cross-sectional microstructure observation. The alloy material in this embodiment is suitable for preparing shells, housings, protective covers, or wear-resistant parts that withstand high-intensity wear conditions.

[0078] Features of Example 2: This embodiment employs a high-strength chemical composition ratio, with 0.28 wt% carbon combined with 2.5 wt% high chromium, 0.60 wt% high molybdenum, and 0.20 wt% high vanadium. Through high-temperature quenching at 930℃ and low-temperature partitioning treatment at 350℃, a multiphase microstructure of high-carbon martensite and 8 vol% low-residual austenite is obtained, achieving a core hardness of 500 HV1. The surface is reinforced with a 220 μm thick gradient nanocrystalline zone through 700 MPa high rolling pressure and 16 passes. Subsequently, a 0.52 mm thick nitriding diffusion zone is formed through nitriding treatment at 550℃ for 22 hours, achieving a surface hardness of 1050 HV0.1. This embodiment achieves a high tensile strength of 1500 MPa, with a moderate sacrifice of elongation after fracture to 10%. This embodiment prioritizes surface hardness and wear resistance, making it suitable for shell components subjected to extreme abrasive wear and high-stress sliding wear conditions. It is particularly suitable for high-strength wear-resistant applications such as crusher liners, ball mill liners, and wear-resistant pipes, and can be widely used in the manufacture of high-wear components in industries such as mining, cement, and metallurgy. Example

[0079] This embodiment provides a high-strength wear-resistant shell alloy material. By mass fraction, the alloy material of this embodiment includes: 0.21 wt% carbon, 1.1 wt% manganese, 0.8 wt% silicon, 1.6 wt% chromium, 0.35 wt% molybdenum, 1.20 wt% nickel, 0.10 wt% vanadium, 0.04 wt% niobium, with the balance being iron and unavoidable impurities.

[0080] The alloy material of this embodiment has a gradient nanocrystalline strengthening region and a nitriding diffusion region on its surface. The thickness of the gradient nanocrystalline strengthening region in this embodiment is 120 μm, and the thickness of the nitriding diffusion region in this embodiment is 0.38 mm. The thickness of the nitriding diffusion region in this embodiment is the thickness of the diffusion layer measured from the surface of the alloy material inward along the normal direction. The gradient nanocrystalline strengthening region in this embodiment is located on the surface layer of the alloy material and is at least partially within the thickness range of the nitriding diffusion region. The gradient nanocrystalline strengthening region in this embodiment is a grain size gradient structure region formed by surface mechanical rolling. The grain size in this embodiment gradually increases from the nanometer level on the surface of the alloy material to the submicrometer level. The nitriding diffusion region in this embodiment is a nitrogen concentration gradient diffusion region formed by gas nitriding. The nitrogen concentration in this embodiment gradually decreases from the surface layer of the alloy material inward.

[0081] In this embodiment, the surface Vickers hardness HV0.1 of the alloy material is 900, and the core Vickers hardness HV1 is 400. The core Vickers hardness HV1 in this embodiment is the Vickers hardness value measured at a depth greater than the thickness of the nitriding diffusion zone at the surface of the alloy material. Both the surface Vickers hardness HV0.1 and the core Vickers hardness HV1 in this embodiment are based on values ​​measured in the finished product state.

[0082] The volume fraction of retained austenite in the core of the alloy material in this embodiment is 16 vol%. The volume fraction of retained austenite in this embodiment is determined as follows: a sample is taken at a depth greater than the thickness of the nitrided diffusion zone from the surface of the alloy material in this embodiment, and the volume fraction is determined by X-ray diffraction. The sampling in this embodiment is performed in the finished product state. The X-ray diffraction test for the volume fraction of retained austenite in this embodiment uses Cu-Kα rays with a scanning angle range of 40-100°. The volume fraction of retained austenite in this embodiment is calculated by the integrated intensity of the 111, 200, and 220 diffraction peaks of austenite and the 110, 200, and 211 diffraction peaks of ferrite or martensite.

[0083] The room temperature tensile strength of the alloy material in this embodiment is 1250 MPa, and the room temperature elongation after fracture is 17%. Both the room temperature tensile strength and the room temperature elongation after fracture in this embodiment are mechanical property indicators obtained by room temperature tensile testing. The room temperature tensile test in this embodiment was conducted according to GB / T 228.1-2021 standard. The specimen was a round bar tensile specimen with a gauge length diameter of 9 mm, a beam displacement rate of 4 mm / min, and a room temperature of 18℃.

[0084] The preparation method of the high-strength wear-resistant shell alloy material in this embodiment includes the following steps: S1 Melting and Billet Forming: Iron, carbon, manganese, silicon, chromium, molybdenum, nickel, vanadium and niobium are provided as raw materials. After being mixed according to chemical composition, they are melted in an induction furnace under a nitrogen protective atmosphere. The melting temperature is 1580℃, and the temperature is held for 18 minutes. The alloy billet is then cast. Step S1 includes the following operations: S11 Raw material acceptance: The purity of iron in this embodiment is not less than 99.5 wt%, the fixed carbon content of carbon in this embodiment is not less than 98 wt%, and the purity of manganese, silicon, chromium, molybdenum, nickel, vanadium, and niobium in this embodiment is not less than 98 wt%; S12 Batching: Weigh and batch the materials according to the chemical composition of this embodiment, with the weighing error controlled within ±0.3%; S13 Melting: Heat to 1580℃ under nitrogen protection and hold for 18 minutes; S14 Casting: Cast the melt into a metal mold to obtain the alloy billet of this embodiment; S15 Post-processing: Remove the riser of the alloy billet of this embodiment and machine to remove 1.0 mm of skin; S16 Quality control: Perform chemical composition acceptance on the alloy billet of this embodiment to confirm that the contents of carbon, manganese, silicon, chromium, molybdenum, nickel, vanadium, and niobium are all within the range of this embodiment.

[0085] S2 Heat Treatment: The alloy billet of this embodiment is heated to 895°C under a nitrogen protective atmosphere and held for 30 minutes before quenching. The quenching medium in this embodiment is water. Subsequently, tempering is performed at 450°C for 80 minutes to obtain a heat-treated billet with a core Vickers hardness HV1 of 400. The core Vickers hardness HV1 of 400 in this embodiment is measured at a depth greater than the thickness of the nitrided diffusion zone in the finished product state. In this embodiment, the tempering process is performed within 25 seconds after quenching. The heating in step S2 is carried out under a nitrogen protective atmosphere.

[0086] S3 Surface Mechanical Rolling: Surface mechanical rolling is performed on the surface of the heat-treated blank in this embodiment. The rolling pressure is 350 MPa, which is the average contact pressure between the rolling tool and the workpiece surface. The rolling passes are 8 times to form a gradient nanocrystalline reinforced region with a thickness of 120 μm. This step S3 includes the following operations: S31 Pretreatment: The surface of the heat-treated blank in this embodiment is degreased and cleaned with acetone for 4 minutes, followed by drying until no visible cleaning agent residue is visible on the workpiece surface; S32 Rolling: Surface mechanical rolling is performed at 20°C, with a rolling pressure of 350 MPa. The rolling pressure in this embodiment is the average contact pressure between the rolling tool and the workpiece surface. The rolling speed is 0.15 m / s, the rolling passes are 8 times, and the feed rate is 0.15 mm / pass; S33 Endpoint Judgment According to the criteria, the increase in Vickers hardness after rolling by 100 HV0.1 compared to before rolling is used as the endpoint. By controlling the rolling pressure, number of rolling passes, and feed rate, the thickness of the gradient nanocrystalline reinforced zone in this embodiment reaches 120 μm. S34 Post-processing involves removing surface debris after rolling until no visible debris remains on the workpiece surface, followed by drying. S35 Quality control involves randomly checking the increase in surface Vickers hardness and the thickness of the gradient nanocrystalline reinforced zone in this embodiment to confirm that they meet the endpoint criteria of operation S33 and the thickness limit of the gradient nanocrystalline reinforced zone in this embodiment, respectively. The rolling equipment in step S3 of this embodiment is a cryogenic rolling equipment.

[0087] S4 Gas Nitriding: The billet treated in step S3 is placed in a nitriding furnace and ammonia gas is introduced for gas nitriding. The nitriding temperature is 515°C, the nitriding time is 14 hours, and the nitriding pressure is 0.09 MPa. In this embodiment, the nitriding pressure is the absolute pressure inside the nitriding furnace, in order to form a nitriding diffusion zone with a thickness of 0.38 mm and to achieve a surface Vickers hardness of HV0.1 of 900. Step S4 includes the following operations: S41 Pretreatment: Before nitriding, acetone is used for degreasing, cleaning, and drying for 4 minutes; S42 Heating: The temperature is raised to 515°C in the nitriding furnace at a rate of 3°C / min; S43 Ammonia nitriding: Ammonia gas is introduced at a nitriding pressure of 0.09 MPa (in this embodiment, the nitriding pressure is the absolute pressure inside the nitriding furnace), and the nitriding time is 14 hours; S44 Cooling: After nitriding, the furnace is cooled to a temperature not exceeding 200°C before removal; S45 Endpoint criterion: The endpoint criterion is that the thickness of the nitrided diffusion zone reaches 0.38 mm and the surface Vickers hardness HV0.1 reaches 900; S46 Quality control: The thickness of the nitrided diffusion zone and the surface Vickers hardness HV0.1 are randomly checked to ensure compliance with requirements. In step S4 of this embodiment, the ammonia flow rate is 18 L / h, and the ammonia decomposition rate is controlled at 26%.

[0088] In this embodiment, acetone is used as the cleaning agent for degreasing and cleaning in steps S3 and S4, and the cleaning time is 4 minutes.

[0089] In this embodiment, the nitriding diffusion zone of the alloy material consists of a diffusion layer with dispersed nitride distribution, and the nitrogen concentration gradually decreases from 0.9 wt% on the surface to 0.08 wt% inward. The boundary of the nitriding diffusion zone in this embodiment is determined by the disappearance of the dispersed nitride distribution or the nitrogen concentration decreasing to the matrix level, and is determined by metallographic observation. The gradient nanocrystalline strengthening zone formed in step S3 of this embodiment retains its nanocrystalline gradient structure after nitriding treatment in step S4. The thermal stability of the nanocrystalline gradient structure in this embodiment is achieved through the grain boundary pinning effect of alloying elements and the inhibition of grain boundary migration by nitrides precipitated during nitriding. The ammonia decomposition rate in step S4 of this embodiment is determined by online analysis of the furnace exhaust composition and controlled by adjusting the ammonia flow rate and the furnace exhaust volume.

[0090] The gradient nanocrystalline reinforced region in this embodiment was characterized using transmission electron microscopy, and the grain size distribution was determined by cross-sectional microstructure observation. The alloy material in this embodiment is suitable for preparing shells, housings, protective covers, or wear-resistant parts that withstand high-intensity wear conditions.

[0091] Features of Example 3: This embodiment employs a chemical composition with a relatively high toughness profile, combining 0.21 wt% low carbon with 1.20 wt% high nickel and 1.1 wt% medium manganese. A multiphase microstructure of low-carbon martensite and 16 vol% high retained austenite is obtained through quenching at 895℃ and tempering at 450℃. The core hardness is only 400 HV1 to ensure excellent core toughness. A relatively thin 120 μm gradient nanocrystalline reinforcement zone is formed on the surface through 8 passes of rolling at a relatively low pressure of 350 MPa. Subsequently, a nitriding treatment at 515℃ for a moderate time of 14 hours forms a 0.38 mm nitriding diffusion zone, achieving a surface hardness of 900 HV0.1. This embodiment achieves an excellent match between a moderate tensile strength of 1250 MPa and a high elongation after fracture of 17%. The 16 vol% high retained austenite imparts good impact toughness and deformation-induced plasticity to the material. This embodiment prioritizes comprehensive mechanical properties and impact resistance, making it suitable for shell components subjected to impact wear and complex stress states. It is particularly suitable for scenarios requiring both wear resistance and impact resistance, such as vibrating screens, conveyor chains, and protective covers. It can be widely used in the manufacture of wear-resistant and impact-resistant components in industries such as building materials, food processing, and logistics transportation. Example

[0092] This embodiment provides a high-strength wear-resistant shell alloy material. By mass fraction, the alloy material of this embodiment includes: 0.30 wt% carbon, 0.9 wt% manganese, 1.4 wt% silicon, 2.8 wt% chromium, 0.50 wt% molybdenum, 0.25 wt% nickel, 0.08 wt% vanadium, 0.07 wt% niobium, with the balance being iron and unavoidable impurities.

[0093] The alloy material of this embodiment has a gradient nanocrystalline strengthening region and a nitriding diffusion region on its surface. The thickness of the gradient nanocrystalline strengthening region in this embodiment is 70 μm, and the thickness of the nitriding diffusion region in this embodiment is 0.55 mm. The thickness of the nitriding diffusion region in this embodiment is the thickness of the diffusion layer measured from the surface of the alloy material inward along the normal direction. The gradient nanocrystalline strengthening region in this embodiment is located on the surface layer of the alloy material and is at least partially within the thickness range of the nitriding diffusion region. The gradient nanocrystalline strengthening region in this embodiment is a grain size gradient structure region formed by surface mechanical rolling. The grain size in this embodiment gradually increases from the nanometer level on the surface of the alloy material to the submicrometer level. The nitriding diffusion region in this embodiment is a nitrogen concentration gradient diffusion region formed by gas nitriding. The nitrogen concentration in this embodiment gradually decreases from the surface layer of the alloy material inward.

[0094] The surface Vickers hardness HV0.1 of the alloy material in this embodiment is 1075, and the core Vickers hardness HV1 is 530. The core Vickers hardness HV1 in this embodiment is the Vickers hardness value measured at a depth greater than the thickness of the nitriding diffusion zone at the surface of the alloy material in this embodiment. Both the surface Vickers hardness HV0.1 and the core Vickers hardness HV1 in this embodiment are based on values ​​measured in the finished product state.

[0095] The volume fraction of retained austenite in the core of the alloy material in this embodiment is 6 vol%. The volume fraction of retained austenite in this embodiment is determined as follows: a sample is taken at a depth greater than the thickness of the nitrided diffusion zone from the surface of the alloy material in this embodiment, and the volume fraction is determined by X-ray diffraction. The sampling in this embodiment is performed in the finished product state. The X-ray diffraction test for the volume fraction of retained austenite in this embodiment uses Cu-Kα rays with a scanning angle range of 40-100°. The volume fraction of retained austenite in this embodiment is calculated by the integrated intensity of the 111, 200, and 220 diffraction peaks of austenite and the 110, 200, and 211 diffraction peaks of ferrite or martensite.

[0096] The room temperature tensile strength of the alloy material in this embodiment is 1560 MPa, and the room temperature elongation after fracture is 9%. Both the room temperature tensile strength and the room temperature elongation after fracture in this embodiment are mechanical property indicators obtained by room temperature tensile testing. The room temperature tensile test in this embodiment was conducted according to GB / T 228.1-2021 standard. The specimen was a round bar tensile specimen with a gauge length diameter of 5.5 mm, a beam displacement rate of 9 mm / min, and a room temperature of 24℃.

[0097] The preparation method of the high-strength wear-resistant shell alloy material in this embodiment includes the following steps: S1 Melting and Billet Forming: Iron, carbon, manganese, silicon, chromium, molybdenum, nickel, vanadium and niobium are provided as raw materials. After being distributed according to chemical composition, they are melted in an electric arc furnace under a nitrogen protective atmosphere. The melting temperature is 1645℃, and the temperature is held for 38 minutes. The alloy billet is then cast. Step S1 includes the following operations: S11 Raw material acceptance: The purity of iron in this embodiment is not less than 99.5 wt%, the fixed carbon content of carbon in this embodiment is not less than 98 wt%, and the purity of manganese, silicon, chromium, molybdenum, nickel, vanadium, and niobium in this embodiment is not less than 98 wt%; S12 Batching: Weigh and batch the materials according to the chemical composition of this embodiment, with the weighing error controlled within ±0.5%; S13 Melting: Heat to 1645℃ under nitrogen protection and hold for 38 minutes; S14 Casting: Cast the melt into a metal mold to obtain the alloy billet of this embodiment; S15 Post-processing: Remove the riser of the alloy billet of this embodiment and machine to remove 0.8 mm of skin; S16 Quality control: Perform chemical composition acceptance on the alloy billet of this embodiment to confirm that the contents of carbon, manganese, silicon, chromium, molybdenum, nickel, vanadium, and niobium are all within the range of this embodiment.

[0098] S2 Heat Treatment: The alloy billet of this embodiment is heated to 940°C under a nitrogen protective atmosphere and held for 56 minutes, followed by quenching. The quenching medium in this embodiment is a 22wt% polyethylene glycol aqueous solution. Subsequently, tempering is performed at 330°C for 45 minutes to obtain a heat-treated billet with a core Vickers hardness HV1 of 530. The core Vickers hardness HV1 of 530 for the alloy material in this embodiment is measured at a depth greater than the thickness of the nitrided diffusion zone in the finished product state. The polyethylene glycol in this embodiment has a mass fraction of 22wt% in the polyethylene glycol aqueous solution and a molecular weight of 8000. The heating in step S2 is performed under a nitrogen protective atmosphere.

[0099] S3 Surface Mechanical Rolling: Surface mechanical rolling is performed on the surface of the heat-treated blank in this embodiment. The rolling pressure is 250 MPa, which is the average contact pressure between the rolling tool and the workpiece surface. Five rolling passes are performed to form a gradient nanocrystalline reinforced region with a thickness of 70 μm. This step S3 includes the following operations: S31 Pretreatment: The surface of the heat-treated blank in this embodiment is degreased and cleaned with acetone for 8 minutes, followed by drying until no visible cleaning agent residue is visible on the workpiece surface; S32 Rolling: Surface mechanical rolling is performed at 18°C, with a rolling pressure of 250 MPa, which is the average contact pressure between the rolling tool and the workpiece surface. The rolling speed is 0.08 m / s, five rolling passes are performed, and the feed rate is 0.08 mm / pass; S33 Endpoint. The criterion is that the Vickers hardness of the surface after rolling increases by 90 HV0.1 compared to before rolling. By controlling the rolling pressure, number of rolling passes, and feed rate, the thickness of the gradient nanocrystalline reinforced zone in this embodiment reaches 70 μm. S34 Post-processing involves removing surface debris after rolling until no visible debris remains on the workpiece surface, followed by drying. S35 Quality control involves randomly checking the increase in surface Vickers hardness and the thickness of the gradient nanocrystalline reinforced zone in this embodiment to confirm that both the endpoint criterion of operation S33 and the thickness limit of the gradient nanocrystalline reinforced zone in this embodiment are met. The rolling equipment in step S3 of this embodiment is a conventional mechanical rolling equipment.

[0100] S4 Gas Nitriding: The billet treated in step S3 is placed in a nitriding furnace and ammonia gas is introduced for gas nitriding. The nitriding temperature is 555℃, the nitriding time is 24h, and the nitriding pressure is 0.115MPa. In this embodiment, the nitriding pressure is the absolute pressure inside the nitriding furnace, so as to form a nitriding diffusion zone with a thickness of 0.55mm and make the surface Vickers hardness HV0.1 reach 1075. Step S4 includes the following operations: S41 Pretreatment: Before nitriding, acetone is used for degreasing, cleaning, and drying for 8 minutes; S42 Heating: The temperature is raised to 555°C in the nitriding furnace at a rate of 9°C / min; S43 Ammonia nitriding: Ammonia gas is introduced at a nitriding pressure of 0.115 MPa (in this embodiment, the nitriding pressure is the absolute pressure inside the nitriding furnace), and the nitriding time is 24 hours; S44 Cooling: After nitriding, the temperature is cooled to no higher than 200°C while maintaining the furnace atmosphere before being removed from the furnace; S45 Endpoint criterion: The endpoint criterion is that the thickness of the nitrided diffusion zone reaches 0.55 mm and the surface Vickers hardness HV0.1 reaches 1075; S46 Quality control: The thickness of the nitrided diffusion zone and the surface Vickers hardness HV0.1 are randomly checked to ensure they meet the requirements. In step S4 of this embodiment, the ammonia flow rate is 45 L / h, and the ammonia decomposition rate is controlled at 38%.

[0101] In this embodiment, acetone was used as the cleaning agent for degreasing and cleaning in steps S3 and S4, and the cleaning time was 8 minutes for both steps.

[0102] In this embodiment, the nitriding diffusion zone of the alloy material consists of a diffusion layer with dispersed nitride distribution, and the nitrogen concentration gradually decreases from 1.8 wt% on the surface to 0.18 wt% inward. The boundary of the nitriding diffusion zone in this embodiment is determined by the disappearance of the dispersed nitride distribution or the nitrogen concentration decreasing to the matrix level, and is determined by microhardness gradient measurement. The gradient nanocrystalline reinforced zone formed in step S3 of this embodiment retains its nanocrystalline gradient structure after nitriding treatment in step S4. The thermal stability of the nanocrystalline gradient structure in this embodiment is achieved through the grain boundary pinning effect of alloying elements and the inhibition of grain boundary migration by nitrides precipitated during nitriding. The ammonia decomposition rate in step S4 of this embodiment is determined by periodic sampling analysis and controlled by adjusting the ammonia flow rate and the furnace exhaust volume.

[0103] The gradient nanocrystalline reinforcement region in this embodiment was characterized using electron backscatter diffraction, and the grain size distribution was determined by cross-sectional microstructure observation. The alloy material in this embodiment is suitable for preparing shells, housings, protective covers, or wear-resistant parts that withstand high-intensity wear conditions.

[0104] Features of Example 4: This embodiment employs a multi-boundary combination design of chemical composition and process parameters, combining a high carbon content of 0.30 wt% with high chromium of 2.8 wt%, high silicon of 1.4 wt%, high niobium of 0.07 wt%, low manganese of 0.9 wt%, and low nickel of 0.25 wt%. Through high-temperature melting at 1645℃, high-temperature quenching at 940℃, and low-temperature tempering at 330℃, an ultra-high strength multiphase microstructure of high-carbon martensite and 6 vol% low-residual austenite is obtained, achieving a core hardness of 530 HV1. A 70 μm thin gradient nanocrystalline reinforcement zone is formed on the surface through low rolling pressure of 250 MPa and 5 passes of rolling. Subsequently, a 0.55 mm thick nitriding diffusion zone is formed through high-temperature nitriding at 555℃ for 24 hours and high-pressure nitriding at 0.115 MPa, achieving a surface hardness of 1075 HV0.1. This embodiment achieves an ultra-high tensile strength of 1560 MPa, with an elongation after fracture of 9%, which is at a relatively low level allowed by the technical specifications. This embodiment utilizes a complementary design of gradient nanocrystalline region thickness and nitriding diffusion region thickness. The thin surface reinforcement region, combined with the thick nitriding diffusion layer, forms a unique surface reinforcement gradient, suitable for high-performance housing components subjected to extreme high-stress wear and fretting wear conditions. It is particularly suitable for ultra-high strength wear-resistant scenarios such as precision mechanical guide rails, high-speed impact hammers, and high-stress gear protective covers, and can be widely used in the manufacture of wear-resistant components under extreme working conditions in aerospace, precision equipment, and high-end manufacturing fields.

[0105] Comparative Example 1: Basically the same as Example 1, except that the carbon content is 0.15wt%, while the amounts of other components and preparation conditions remain unchanged.

[0106] Comparative Example 2: Basically the same as Example 1, except that the carbon content is 0.35wt%, while the amounts of other components and preparation conditions remain unchanged.

[0107] Comparative Example 3: Basically the same as Example 1, except that the chromium content is 1.0 wt%, while the amounts of other components and preparation conditions remain unchanged.

[0108] Comparative Example 4: Basically the same as Example 1, except that the surface mechanical rolling process in step S3 was omitted, and the gas nitriding in step S4 was performed directly after the heat treatment in step S2. No gradient nanocrystal reinforcement region was formed, and other preparation conditions remained unchanged.

[0109] Comparative Example 5: Basically the same as Example 1, except that step S4 gas nitriding process is omitted, and only step S3 surface mechanical rolling is performed to obtain the finished product. No nitriding diffusion zone is formed. Other preparation conditions remain unchanged.

[0110] Comparative Example 6: Basically the same as Example 1, except that the rolling pressure in step S3 is 150 MPa, the number of rolling passes is 6, the thickness of the gradient nanocrystal reinforcement region is 40 μm, and other preparation conditions remain unchanged.

[0111] Comparative Example 7: Basically the same as Example 1, except that the nitriding temperature in step S4 is 480℃, the nitriding time is 12h, the thickness of the nitriding diffusion zone is 0.22mm, the surface Vickers hardness HV0.1 is 780, and other preparation conditions remain unchanged.

[0112] Comparative Example 8: Basically the same as Example 1, except that the nickel content is 1.80 wt% and the manganese content is 0.6 wt%, while the amounts of other components and preparation conditions remain unchanged.

[0113] Performance testing: Experiment 1: Surface Vickers Hardness Test Test Object: The surface layer of finished alloy materials. Test Purpose: To evaluate the Vickers hardness of the surface and verify the extremely high hardness and wear resistance of the surface layer. Test Principle: A Vickers hardness tester uses a diamond indenter to press into the material surface under a specified load. The hardness value is calculated based on the diagonal length of the indentation, reflecting the material surface's resistance to plastic deformation. Experimental Method: A Vickers hardness tester is used, with a load of 0.98 N (HV0.1) and a holding time of 10-15 seconds. The test is conducted at a depth of 0.05 mm from the surface. At least 5 points are tested for each sample, and the average value is taken. Before testing, the sample is sanded and polished to a mirror finish. Key Parameters: Room temperature 23±2℃, relative humidity ≤60%, load accuracy ±1%, indentation diagonal measurement accuracy ±0.5 μm. Data Processing: The mean and standard deviation (n≥5) are calculated. Outliers deviating from the mean by more than 10% are removed, and the data is recalculated.

[0114] Experiment 2: Vickers hardness test of the heart Test Object: The core of the finished alloy material. Test Purpose: To evaluate the Vickers hardness of the core and verify the overall toughness and support capacity. Test Principle: The Vickers hardness tester measures the hardness of the core structure under a large load, reflecting the degree of strength-toughness matching of the matrix. Experimental Method: A Vickers hardness tester is used, with a load of 9.8 N (HV1) and a holding time of 10-15 s. Testing is conducted at a depth greater than the thickness of the nitrided diffusion zone (≥0.7 mm from the surface), with a test point every 0.5 mm radially. At least three points are tested for each sample, and the average value is taken. Before testing, the sample is axially cut and mechanically polished. Key Parameters: Room temperature 23±2℃, relative humidity ≤60%, load accuracy ±1%, test position depth from the surface ≥0.7 mm. Data Processing: Calculate the mean and standard deviation (n≥3), and plot the hardness gradient distribution curve.

[0115] Experiment 3: Room Temperature Tensile Properties Test Test Object: Finished alloy material. Test Objective: To evaluate room temperature tensile strength and elongation at fracture, and verify the synergistic matching of strength and toughness. Test Principle: The tensile strength, yield strength, and elongation at fracture of the material are determined by a uniaxial tensile test, reflecting the overall mechanical properties of the material. Experimental Method: A universal testing machine is used. The specimen is a round bar tensile specimen with a gauge length of 50 mm and a gauge diameter of 5-10 mm. The beam displacement rate is 5 mm / min, the room temperature is 20 ± 2℃, and three parallel samples are tested in each group. The specimen surface should have no obvious machining marks. The test continues until the specimen breaks. Key Parameters: Room temperature 20 ± 2℃, relative humidity ≤ 70%, beam displacement rate 5 ± 0.5 mm / min, load accuracy ± 0.5%. Data Processing: Calculate the tensile strength Rm, yield strength Rp0.2, and elongation at fracture A, and take the average of the three samples ± standard deviation.

[0116] Experiment 4: Abrasive Wear Performance Test Test Object: The surface of finished alloy materials. Test Objective: To evaluate wear resistance and verify the contribution of extremely high surface hardness to wear-bearing capacity. Test Principle: The wear mass loss of the material is determined by abrasive wear testing. After friction over a specified distance under specified load and abrasive conditions, the mass loss is measured, reflecting the material's resistance to abrasive wear. Experimental Method: An MLS-225 abrasive wear testing machine was used. The abrasive was 120-mesh brown corundum. The load was 20 N, the rotation speed was 200 r / min, the wear time was 30 min, the wear distance was approximately 500 m, and the sample size was 30 mm × 25 mm × 10 mm. Samples were cleaned with anhydrous ethanol and dried to constant weight before and after testing. Three parallel samples were tested in each group. Key Parameters: Room temperature 23 ± 2℃, relative humidity ≤ 60%, load accuracy ± 2%, rotation speed stability ± 5 r / min, abrasive particle size 120 ± 5 mesh. Data processing: Calculate the wear mass loss Δm and relative wear resistance ε = (wear amount of control sample / wear amount of sample), and take the average value of 3 samples ± standard deviation.

[0117] Experiment 5: Residual Stress Gradient Distribution Test Test Object: The surface to core of the finished alloy material. Test Objective: To evaluate the residual stress gradient distribution and verify the surface's resistance to spalling and dimensional stability. Test Principle: X-ray diffraction residual stress testing is based on the change in interplanar spacing. Residual stress is calculated by measuring the diffraction peak displacements at different tilt angles, reflecting the stress gradient from the surface to the core. Experimental Method: An X-ray residual stress analyzer with Cu-Kα rays was used. The test angle range was 2θ = 150-160° (α-Fe 211 crystal plane), with five tilt angles ψ = 0° to 45°. Testing was performed every 0.05 mm of electrolytic removal along the depth direction, starting from the surface, up to a depth of 0.6 mm. At least three points were tested at each depth. Key Parameters: Tube voltage 30kV, tube current 10mA, scan rate 2° / min, collimator diameter 2mm, electrolytic removal rate controlled at 0.01-0.02mm / min. Data processing: The sin²ψ method was used to calculate the residual stress, the residual stress-depth distribution curve was plotted, and the stress gradient (MPa / mm) was calculated.

[0118] Experiment 6: Test of Nitriding Diffusion Zone Thickness and Nitrogen Concentration Gradient Test Object: A cross-section of the finished alloy material from the surface to the core. Test Objective: To evaluate the thickness of the nitriding diffusion zone and the nitrogen concentration gradient, and to verify the strengthening effect of the deep nitriding layer on the surface. Test Principle: The boundary of the nitriding diffusion zone is determined by metallographic observation combined with microhardness gradient measurement. The nitriding diffusion zone appears as a bright white layer with dispersed nitride distribution and a transitional diffusion layer. Experimental Method: The sample is cut along the cross-section, mounted, and then sequentially polished to a mirror finish using 400-2000 grit sandpaper. It is then etched with a 4% nitric acid alcohol solution for 3-8 seconds, and the morphology of the nitrided layer is observed under an optical microscope. Simultaneously, a microhardness tester (HV0.1 load) is used to test at points every 0.05 mm along the depth direction from the surface until the hardness value drops to the core hardness level. The thickness of the nitriding diffusion zone is determined at the point where the dispersed nitride distribution disappears or at the inflection point of the hardness gradient. Key Parameters: Etching time 3-8 seconds, microhardness test interval 0.05 mm, magnification 200-500x. Data processing: The thickness of the nitrided diffusion zone was measured and a microhardness-depth curve was plotted. Three lines were tested for each sample, and the average value ± standard deviation was taken.

[0119] As can be seen from the performance of the examples and comparative examples in Table 1, the technical solution of the present invention achieves synergistic optimization of surface hardness, core toughness, and wear resistance. The surface hardness HV0.1 of Examples 1-4 all reach 900-1075, which is significantly higher than that of Comparative Example 4 (720) and Comparative Example 5 (605) which lack the key process. The relative wear resistance reaches 1.91-3.00, and the wear mass loss is only 14-22mg, which is far better than that of Comparative Examples 1-7 (35-55mg). Comparative Example 1, with its low-carbon design, resulted in insufficient core and surface hardness, severely deteriorating wear resistance. Comparative Example 2, with its high-carbon design, improved hardness but reduced elongation after fracture to 6.5%, indicating insufficient toughness reserves. Comparative Example 3, with its low-chromium design, weakened hardenability and nitride formation ability. Comparative Example 4, omitting surface mechanical rolling, resulted in a surface hardness of only 720, failing to form a gradient nanocrystalline reinforcement zone, leading to a significant decrease in wear resistance. Comparative Example 5, omitting gas nitriding, resulted in a sharp drop in surface hardness to 605, losing the deep nitride reinforcement effect. Comparative Example 6, with insufficient rolling parameters, resulted in a gradient nanocrystalline zone thickness of only 40 μm, weakening the surface hardening effect. Comparative Example 7, with its excessively low nitriding temperature, resulted in a nitrided layer thickness of only 0.22 mm, reducing surface hardness to 780. Comparative Example 8, with its unbalanced nickel-manganese ratio, resulted in reduced core hardness and excessive toughness. The embodiments, through the composite design of gradient nanocrystalline reinforcement zone and nitriding diffusion zone, achieve a synergistic effect of surface hardness 850-1100HV0.1 and excellent wear resistance while ensuring core hardness of 400-530HV1 and elongation after fracture of 9-17%, thus verifying the superiority of the technical solution of the present invention.

[0120] Figure 1The XRD patterns of Examples 1, 4, and 5 are shown for comparison. The fixed parameters were that the matrix material and sample size were consistent, the XRD testing conditions were consistent, and the same instrument and scanning range were used to obtain the diffraction intensity versus 2θ curves. The varying parameters were the different combinations of surface treatment processes, including the presence and order of nitriding and surface plastic deformation treatments. In Example 1, the curves show more distinct surface reaction phase-related peaks in addition to the matrix phase characteristic peaks, accompanied by peak shape changes. This indicates that nitriding and surface plastic deformation treatments synergistically introduce stable surface microstructure and phase composition differences, verifying from a phase evidence perspective that this scheme can form a surface structure basis different from the control group.

[0121] Figure 2 The figures show a comparison of the retained austenite volume fraction in Examples 1, 4, and 5. The parameters were fixed as the same material system, the same method for quantifying retained austenite, and the same data processing flow. The only variation was the combination of nitriding and surface plastic deformation treatments. In Example 1, the retained austenite volume fraction remained at a level comparable to the control group with minimal dispersion, indicating that this approach maintained reasonable phase stability and microstructure uniformity while strengthening the surface layer. This provides accurate phase composition support for subsequent improvements in hardness gradient and mechanical properties.

[0122] Figure 3 The figures show a comparison of the microhardness gradients of Examples 1, 4, and 5. The fixed parameters were: consistent microhardness test load and holding time; consistent sampling direction and test line position; and testing at equal depth intervals from the surface to the center. The varying parameters were the differences in surface strengthening methods due to the presence or absence of nitriding and surface plastic deformation treatments. Example 1 showed a high-hardness zone on the surface with a continuously decreasing gradient distribution inwards and a greater effective hardened layer depth. This demonstrates that the scheme can simultaneously achieve significant surface strengthening and gradient transition, thereby reducing the risk of stress concentration caused by abrupt interface changes, and verifying its rationality in the synergistic design of strength and toughness.

[0123] Figure 4 The TEM statistical equivalent grain diameter distribution of the surface layer of Example 1, the subsurface layer of Example 1, and the surface layer of Comparative Example 4 is shown. The parameters were fixed: consistent TEM sample preparation and imaging conditions, and the same statistical aperture was used to calculate the equivalent grain diameter. The varying parameters were the differences in grain refinement between the surface and subsurface layers caused by different processes. In Example 1, the surface layer distribution is concentrated at the nanoscale and significantly shifted to the left compared to Comparative Example 4. In Example 1, the subsurface layer distribution is located at the submicron scale and forms a hierarchical refinement structure with the surface layer. This demonstrates that this scheme can construct a nanocrystalline layer on the surface and transition inward to a fine-grained region, proving the correctness of its strengthening mechanism at the microstructural level.

[0124] Figure 5The TEM statistical cumulative distribution of equivalent grain diameters for the surface layer of Example 1, the sub-surface layer of Example 1, and the surface layer of Comparative Example 4 is shown. The parameters are fixed as the same equivalent grain diameter dataset and the same cumulative probability calculation method. The varying parameters are the overall quantile differences in grain size caused by different processing methods. In Example 1, the cumulative distribution at the same probability level corresponds to significantly smaller grain sizes and a steeper curve, reflecting a finer and more uniform grain population. This indicates that the scheme not only achieves grain refinement but also improves the uniformity of the surface structure, further verifying the stability and repeatability of nanocrystalline layer formation from a statistical perspective.

[0125] Figure 6 The image shows the cumulative distribution of the equivalent dimple diameter on the tensile fracture surface of Comparative Example 1 (Example 1). The parameters were fixed to ensure that the tensile test and fracture surface SEM characterization conditions were consistent, and the same measurement and statistical rules were used to extract the equivalent dimple diameter. The varying parameters were the differences in plastic deformation and micropore nucleation and growth behavior caused by different processing conditions. The curve in Example 1 shifts overall towards the smaller size range while maintaining a high cumulative rate at the mid-to-high quantiles, indicating finer dimple features and a more complete micropore aggregation plastic fracture process. This demonstrates that the scheme can maintain a good plastic energy dissipation mechanism while improving the surface load-bearing capacity, verifying the fracture surface evidence of its strength-toughness synergy.

[0126] Figure 7 The diagram shows the cumulative distribution of equivalent diameters of quasi-cleavage features on the tensile fracture surface of Example 1 compared to Comparative Example 2. The parameters were fixed: the tensile conditions and fracture surface SEM statistical method were consistent, and feature dimensions were extracted under the same magnification and threshold rules. The varying parameters were the differences in brittle fracture tendency and cleavage feature scale caused by different processing methods. Compared to Comparative Example 2, the feature dimensions in Example 1 are generally smaller and more concentrated, indicating that brittle cleavage features are suppressed and a more refined fracture element scale is presented. From the perspective of failure modes, this demonstrates that the scheme can reduce the possibility of large-scale cleavage propagation and improve resistance to instability.

[0127] Figure 8 This is a comparison diagram of the residual stress depth distribution between Example 1 and Comparative Example 5. The parameters were fixed, with consistent XRD sin²ψ residual stress testing conditions and a layer-by-layer removal method to obtain the same depth sequence data. The varying parameters were the different depths and amplitudes of compressive stress introduced due to differences in the combination of surface plastic deformation and nitriding. Example 1 introduced a higher level of compressive residual stress on the surface layer, which gradually attenuated inwards and had a greater impact depth. This indicates that this scheme can establish a more favorable compressive stress field to counteract external tensile stress and delay crack initiation and propagation, verifying its correctness in improving fatigue and crack resistance from a stress field perspective.

[0128] Figure 9The image shows a high-resolution XPS spectrum comparison of the N1s chemical state in Example 1 and Comparative Example 7. The parameters were fixed, with consistent XPS testing conditions and the same energy calibration and background processing methods used to obtain the binding energy versus intensity curves. The varying parameters were the differences in nitrogen-containing chemical bonding states caused by different nitriding temperatures and surface plastic deformation coupling modes. Example 1 exhibits a more significant signal and clearer peak shape in the metal nitride-related binding energy region, indicating that this scheme can promote the formation and stable existence of nitrogen-related chemical states on the surface, thus verifying the rationality of the surface strengthening source from a chemical state perspective.

[0129] Figure 10 The image shows a comparison of the XPS high-resolution spectra of the Cr2p chemical state in Example 1 and Comparative Example 7. The parameters were fixed, with consistent XPS light source and power supply conditions, and the same data processing workflow. The varying parameters were the differences in the proportion of chromium-related chemical states caused by different nitriding process conditions. Example 1 exhibits peak intensity and shape differences that better reflect the trend of nitride formation, indicating that this method can promote the interaction between chromium and nitrogen on the surface and form a more stable reaction-related chemical state. This supports the correctness of surface hardening and improved wear and corrosion resistance from the perspective of elemental chemical environment.

[0130] Figure 11 The image shows a high-resolution XPS spectrum comparison of Fe2p in the chemical state with Comparative Example 7 of Example 1. The XPS test area and acquisition parameters were kept constant, and the same fitting and normalization strategy was used to characterize the chemical state changes of iron. The varying parameters were the differences in the regulation of the key binding environment of the iron phase by nitriding temperature and surface plastic deformation. Example 1 showed a more significant spectral response in the binding energy range related to nitrogen interaction, consistent with the trends of N1s and Cr2p. This indicates that the scheme formed a chemical state structure coordinated with the nitriding reaction on the surface of the iron matrix. From the perspective of multi-spectral consistency, this jointly proves that the scheme forms a closed-loop evidence chain regarding the chemical state stress field and fracture mechanism of the microstructure, thus verifying the correctness and effectiveness of the overall scheme.

[0131] Table 1 Performance Comparison Summary Table

[0132] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that any equivalent structural transformations made under the concept of the present invention and using the contents of the specification and drawings of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A high-strength, wear-resistant shell alloy material, characterized in that, The alloy material comprises, by mass fraction: 0.18-0.32 wt% carbon, 0.8-1.8 wt% manganese, 0.6-1.5 wt% silicon, 1.2-3.0 wt% chromium, 0.25-0.70 wt% molybdenum, 0.20-1.50 wt% nickel, 0.05-0.25 wt% vanadium, 0.02-0.08 wt% niobium, with the balance being iron and unavoidable impurities; The surface of the alloy material has a gradient nanocrystalline strengthening region and a nitriding diffusion region. The thickness of the gradient nanocrystalline strengthening region is 50-300 μm, and the thickness of the nitriding diffusion region is 0.30-0.60 mm. The thickness of the nitriding diffusion region is the thickness of the diffusion layer measured from the surface of the alloy material along the normal direction inward. The gradient nanocrystalline strengthening region is located on the surface of the alloy material and is at least partially within the thickness range of the nitriding diffusion region. The surface Vickers hardness HV0.1 of the alloy material is 850-1100, and the core Vickers hardness HV1 is 350-550. The core Vickers hardness HV1 is the Vickers hardness value measured at a depth greater than the thickness of the nitriding diffusion zone from the surface of the alloy material. Both the surface Vickers hardness HV0.1 and the core Vickers hardness HV1 are based on values ​​measured in the finished product state. The volume fraction of retained austenite in the core of the alloy material is 5-20 vol%. The volume fraction of retained austenite is determined by taking a sample at a depth greater than the thickness of the nitriding diffusion zone from the surface of the alloy material and determining the volume fraction by X-ray diffraction. The sampling is performed in the finished product state.

2. The high-strength wear-resistant shell alloy material as described in claim 1, characterized in that, The room temperature tensile strength of the alloy material is 1100-1600 MPa, and the room temperature elongation after fracture is 8-20%. Both the room temperature tensile strength and the room temperature elongation after fracture are mechanical property indicators obtained by room temperature tensile test.

3. A method for preparing a high-strength wear-resistant outer shell alloy material as described in any one of claims 1-2, characterized in that, Includes the following steps: S1 Melting and Billet Forming: Iron, carbon, manganese, silicon, chromium, molybdenum, nickel, vanadium and niobium are provided as raw materials. After being mixed according to chemical composition, they are melted in an induction furnace or electric arc furnace under a nitrogen protective atmosphere. The melting temperature is 1550-1650℃, and the temperature is held for 10-40 minutes. The alloy billet is then cast. S2 heat treatment: The alloy billet is heated to 880-950℃ under a nitrogen protective atmosphere and held for 20-60 minutes, then quenched. The quenching medium is water or a polyethylene glycol aqueous solution with a mass fraction of 5-25 wt%. Subsequently, a distribution treatment or tempering treatment is performed. The temperature of the distribution treatment or the temperature of the tempering treatment is 320-480℃, and the time of the distribution treatment or the tempering treatment is 30-180 minutes, to obtain a heat-treated billet. After subsequent steps S3 and S4, the Vickers hardness HV1 of the core of the alloy material is 350-550. The Vickers hardness HV1 of the core is the Vickers hardness value measured at a depth greater than the thickness of the nitriding diffusion zone from the surface of the alloy material. The Vickers hardness HV1 of the core is based on the value measured in the finished product state. S3 Surface mechanical rolling: The surface of the heat-treated blank is subjected to surface mechanical rolling, the rolling pressure is 200-800MPa, the rolling pressure is the average contact pressure between the rolling tool and the workpiece surface contact area, and the rolling passes are 3-20 passes to form a gradient nanocrystalline reinforced region with a thickness of 50-300μm. S4 Gas Nitriding: The billet treated in step S3 is placed in a nitriding furnace and ammonia gas is introduced for gas nitriding. The nitriding temperature is 500-560℃, the nitriding time is 10-25h, and the nitriding pressure is 0.08-0.12MPa. The nitriding pressure is the absolute pressure inside the nitriding furnace, so as to form a nitriding diffusion zone with a thickness of 0.30-0.60mm and make the surface Vickers hardness HV0.1 reach 850-1100.

4. The preparation method according to claim 3, characterized in that, Step S1 includes the following operations: S11 Raw Material Acceptance: The purity of the iron shall not be less than 99.5 wt%, the fixed carbon content of the carbon shall not be less than 98 wt%, and the purity of the manganese, silicon, chromium, molybdenum, nickel, vanadium and niobium shall not be less than 98 wt%. S12 Ingredients: Weigh and prepare ingredients according to their chemical composition, with the weighing error controlled within ±0.5%; S13 Melting: Under nitrogen protection, heat to 1550-1650℃ and hold for 10-40 minutes; S14 Casting: The molten material is poured into a metal mold or sand mold to obtain the alloy billet; S15 post-processing: Remove the riser from the alloy billet and machine to remove 0.5-3mm of skin; S16 Quality Control: The chemical composition of the alloy billet is inspected to confirm that the contents of carbon, manganese, silicon, chromium, molybdenum, nickel, vanadium and niobium are all within the above range.

5. The preparation method according to claim 3, characterized in that, Step S3 includes the following operations: S31 Pretreatment: The surface of the heat-treated blank is degreased and cleaned with acetone for 2-10 minutes, and then dried until no cleaning agent residue is visible on the surface of the workpiece. S32 Rolling: The surface mechanical rolling is performed at 15-35℃, the rolling pressure is 200-800MPa, the rolling pressure is the average contact pressure between the rolling tool and the workpiece surface, the rolling speed is 0.05-0.50m / s, the number of rolling passes is 3-20, and the feed rate is 0.05-0.50mm / pass. S33 Endpoint Criterion: The endpoint criterion is that the Vickers hardness of the surface after rolling increases by 80-250 HV0.1 compared with that before rolling; by controlling the rolling pressure, rolling passes and feed rate, the thickness of the gradient nanocrystalline reinforced region can reach 50-300 μm; S34 Post-treatment: After rolling, remove surface debris until there are no visible debris on the workpiece surface, and then dry; S35 Quality Control: Randomly inspect the increase in surface Vickers hardness and the thickness of the gradient nanocrystalline reinforced region to confirm that they meet the endpoint criteria of operation S33 and the limit on the thickness of the gradient nanocrystalline reinforced region, respectively.

6. The preparation method according to claim 3, characterized in that, Step S4 includes the following operations: S41 Pretreatment: Before nitriding, the product is degreased and cleaned with acetone and then dried; S42 heating: Heat to 500-560℃ in a nitriding furnace at a heating rate of 1-10℃ / min; S43 Ammonia Nitrification: Ammonia gas is introduced, the nitriding pressure is 0.08-0.12 MPa, the nitriding pressure is the absolute pressure inside the nitriding furnace, and the nitriding time is 10-25 h; S44 Cooling: After nitriding, furnace cooling or cooling to no higher than 200°C while maintaining the furnace atmosphere before unloading; S45 endpoint criterion: The endpoint criterion is that the thickness of the nitrided diffusion zone reaches 0.30-0.60 mm and the surface Vickers hardness HV0.1 reaches 850-1100. S46 Quality Control: Randomly inspect the thickness of the nitriding diffusion zone and the surface Vickers hardness HV0.1 to ensure compliance with requirements.

7. The preparation method according to claim 3, characterized in that, In both steps S3 and S4, acetone is used as the cleaning agent for degreasing and cleaning, and the cleaning time is 2-10 minutes.

8. The preparation method according to claim 3, characterized in that, The quenching medium is water, and after quenching, it enters the distribution process or the tempering process within 10-60 seconds.

9. The preparation method according to claim 3, characterized in that, The quenching medium is a polyethylene glycol aqueous solution, and the mass fraction of polyethylene glycol in the polyethylene glycol aqueous solution is 5-25 wt%.

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