Gradient composite structure material for wear-resistant accessories of oversized excavator and preparation method of gradient composite structure material

Abstract

The invention discloses a gradient composite structure material for a wear-resistant part of an oversized excavator and a preparation method of the gradient composite structure material. The material adopts a multi-layer gradient structure design, a surface layer is mainly made of nanoscale VC precipitated phase enhanced fine grain martensite, the grain size is larger than or equal to 8 grades, a transition layer is a mixed structure of bainite and tempered sorbite, and a core part is a combination of ferrite and pearlite. A component system comprises alloy elements including 0.20%-0.50% of C, 0.80%-2.00% of Cr, 0.50%-1.50% of Ni and 0.10%-0.50% of Mo, the performance is optimized through the synergistic matching of the Cr / Ni ratio of 1.2-1.8 and the Mo / V ratio of 1.5-3.0, and the content of S and the content of P are controlled to be smaller than or equal to 0.030%. According to the preparation method, a gradient cooling mold is innovatively adopted to control the cooling rate, a two-stage tempering process and subzero treatment are combined, a fine grain enhancer is introduced, and continuous gradient distribution of material components and structures is achieved. The final material has high strength and toughness, the gradient hardness characteristic is presented from the surface layer to the core part, the hardness of the surface layer and the core part are reasonably matched, a welding heat affected zone has no intergranular crack tendency, and the strict requirement of wear-resisting parts of the oversized excavator for the comprehensive performance is met.

Description

Technical Field

[0001] This invention relates to composite materials for wear-resistant parts, and more particularly to a gradient composite structural material for wear-resistant parts of ultra-large excavators and its preparation method. Background Technology

[0002] With the continuous expansion of mining and large-scale engineering construction, wear-resistant parts for ultra-large excavators face extreme working conditions. During operation, they are subjected to impact loads exceeding 2000 MPa and are subjected to multiple damage coupling effects, including abrasive wear and corrosive wear. Traditional materials such as high-manganese steel and bimetallic composite castings generally present a contradiction between achieving both surface hardness and core toughness: when a single homogeneous material increases its surface hardness to above 45 HRC, its elongation often drops below 8%; while surface strengthening technologies such as welding and spraying suffer from low interfacial strength and easy peeling, easily leading to interlayer cracking failure under frequent impacts.

[0003] In recent years, gradient materials technology has provided new ideas for this field, but existing gradient structure materials still have significant technical bottlenecks: First, the alloy system design mostly adopts simple element superposition and has not established a mechanism for controlling the gradient stability of key element ratios such as Cr / Ni and Mo / V, which is prone to compositional segregation during thermal cycling; Second, the single cooling rate in the casting process leads to abrupt changes in the microstructure from the surface to the core, with grain size differences exceeding 4 levels, causing stress concentration; Third, conventional heat treatment processes are difficult to achieve continuous gradient control of the martensite lath width from 0.1 μm on the surface to 1.0 μm in the core, and the volume fraction of nanoscale VC precipitates is less than 1%, which restricts the synergistic improvement of the material's strength and toughness.

[0004] Patent CN111069610A proposes a gradient structure cemented carbide ball tooth and its preparation method. The tooth consists of a top layer, a diffusion layer, and a substrate layer composed of WC, Co, and grain growth inhibitors. The surface layer has a high inhibitor content and fine WC grains, while the core layer has reduced inhibitors and coarser grains, forming a gradient structure with decreasing hardness and increasing toughness. During preparation, a mixture of upper and lower layers is packaged, with a high inhibitor content on the top layer and a low inhibitor content on the bottom layer. The gradient distribution is achieved through two loading processes, one pressing, and high-temperature sintering, simplifying the process and making it suitable for mass production. Its advantages include: high surface hardness improves wear resistance, coarse grains in the core enhance impact resistance, and service life is increased by 30% compared to conventional ball teeth; the process reduces interfacial stress, and a diffusion layer thickness of ≥2mm reduces the risk of cracking. However, limitations exist: the fixed type and ratio of inhibitors restrict performance optimization; stringent requirements for sintering temperature and wet grinding parameters can easily lead to uneven gradients; and the wide WC particle size range may affect applicability in high-precision applications. This technology balances performance and cost through material and process innovation, but further improvements are needed in refined control and long-term stability.

[0005] Patent CN114559044B discloses a designable multilayer composite armor plate and its preparation method. This method achieves a multilayer integrated structure by alternately stacking tough metal layers and ceramic particle-reinforced composite layers (such as boron carbide, silicon carbide, or alumina), combined with hot pressing sintering and hot rolling processes. The tough layer uses metal powder, while the hard layer is composed of ceramic particles and a metal matrix, with powder particle sizes ranging from 0.5 micrometers to 50 micrometers. The preparation process includes powder mixing, alternating layering, cold pressing, high-temperature hot pressing, preheating, and multi-pass rolling, ultimately forming multilayer, sandwich, or gradient configurations. Its advantages include: the hard layer enhances ballistic performance, the tough layer effectively disperses impact stress, and the interlayer bonding strength reaches 370 to 450 MPa, more than 30% higher than traditional processes; the structural design is flexible and adaptable to different protection requirements. However, the process is highly complex, requiring precise control of mixing time, hot pressing temperature fluctuations, and rolling parameters (2 to 20 passes). The multi-step high-temperature processing is energy-intensive, and the interface brittleness increases significantly when the ceramic content exceeds 45%. Furthermore, the particle size of the metal powder limits its high-precision applications. Although this technology improves performance through innovative structure, the stringent process parameters and long process flow restrict industrialization efficiency.

[0006] This invention addresses the shortcomings of existing gradient materials in wear-resistant components of engineering machinery by proposing an innovative solution: segregation is suppressed by optimizing the Cr / Ni and Mo / V element ratios, and a continuous transition from fine-grained martensite on the surface to ferrite + pearlite in the core is achieved through gradient cooling of the ZrO2 coating mold; the width of the martensite laths is precisely controlled by employing two-stage tempering and cryogenic treatment. The final material exhibits a tensile strength ≥1800MPa, an impact toughness ≥30J at -40℃, and a hardness gradient from the surface to the core with hardness fluctuation in the weld zone ≤5HRC. This overcomes the challenges of strength-toughness imbalance, abrupt microstructure changes, and process instability inherent in traditional technologies, thus improving service life. Summary of the Invention

[0007] In order to overcome the defects of the prior art, the present invention provides a gradient composite structural material for wear-resistant parts of ultra-large excavators and its preparation method. By optimizing the element ratio, gradient cooling casting and two-stage heat treatment, the problems of imbalance of strength and toughness, abrupt changes in structure and unstable process of traditional wear-resistant materials are solved, thereby improving service life.

[0008] The objective of this invention can be achieved through the following technical solutions:

[0009] A gradient composite structural material for wear-resistant parts of ultra-large excavators, comprising: C 0.20%–0.50%, Si 0.10%–0.50%, Mn 0.50%–1.50%, Cr 0.80%–2.00%, Ni 0.50%–1.50%, Mo 0.10%–0.50%, V 0.05%–0.30%, Ti 0.01%–0.10%, Nb 0.02%–0.15%, W 0.05%–0.30%, (La+Ce+Y) 0.01%–0.15%, S≤0.030%, P≤0.030%, with the balance being Fe and unavoidable impurities.

[0010] Preferably, the gradient composite structural material for wear-resistant parts of ultra-large excavators has the following chemical composition by weight percentage: C 0.25%–0.40%, Si 0.15%–0.30%, Mn 0.80%–1.20%, Cr 1.00%–1.80%, Ni 0.80%–1.20%, Mo 0.15%–0.35%, V 0.08%–0.20%, Ti 0.02%–0.08%, Nb 0.05%–0.12%, W 0.10%–0.25%, (La+Ce+Y) 0.03%–0.10%, S≤0.025%, P≤0.025%, with the balance being Fe and unavoidable impurities.

[0011] Furthermore, a gradient composite structural material for wear-resistant parts of ultra-large excavators has the following weight percentages of S and P elements: S≤0.005%, P≤0.005%.

[0012] Furthermore, a gradient composite structural material for wear-resistant parts of ultra-large excavators is characterized in that the amounts of Cr, Ni, Mo, V, and W elements added satisfy the following proportional relationships: Cr / Ni = 1.2 to 1.8, Mo / V = 1.5 to 3.0, Nb / Ti = 1.0 to 2.5, and the W content is 0.6 to 1.2 times the Mo content.

[0013] A method for preparing a gradient composite structural material for wear-resistant parts of ultra-large excavators includes the following steps:

[0014] (1) Alloy smelting

[0015] The ingredients as described in claim 1 are blended and smelted into molten steel, and then deoxidized and refined.

[0016] (2) Refine grain strengthening treatment

[0017] Add a fine-grain strengthening agent to the molten steel, stir, and let stand.

[0018] (3) Casting and molding

[0019] A gradient cooling mold is used for casting to create a gradient in composition or structure;

[0020] (4) Heat treatment

[0021] The castings are subjected to quenching, tempering, and gradient-controlled heat treatment.

[0022] Preferably, a method for preparing a gradient composite structural material for wear-resistant parts of ultra-large excavators includes the following steps:

[0023] (1) Alloy smelting

[0024] The ingredients according to claim 1 are smelted into molten steel at a smelting temperature of 1580-1650℃ and a deoxidation and refining time of ≥20min.

[0025] (2) Refine grain strengthening treatment

[0026] Add a fine grain strengthening agent to the molten steel, stir and let stand. The fine grain strengthening agent is added 5 to 10 minutes after refining and before casting.

[0027] (3) Casting and molding

[0028] The casting process employs a gradient cooling mold with a casting temperature of 1500–1550℃ and a gradient cooling rate of 10–50℃ / s.

[0029] (4) Heat treatment

[0030] The castings are quenched at 880–920℃ for 1.0–2.0 h and then oil-cooled; then tempered at 550–650℃ for 2.0–4.0 h and subjected to gradient control treatment.

[0031] Furthermore, a method for preparing a gradient composite structural material for wear-resistant parts of an ultra-large excavator is provided, wherein the fine-grained reinforcing agent is a crystal-controlling mixture of Re, B, and Ti, and its chemical composition by mass percentage is: Re 0.03-0.05%, B 0.01-0.05%, Ti 0.01-0.02%, with the remainder being Fe.

[0032] Furthermore, a method for preparing a gradient composite structural material for wear-resistant parts of an ultra-large excavator, wherein the inner wall of the gradient cooling mold is coated with a ZrO2 heat-insulating coating to control the difference in cooling rate.

[0033] Furthermore, a method for preparing a gradient composite structural material for wear-resistant parts of an ultra-large excavator is characterized by a tempering process consisting of two stages: the first stage involves holding at 600–650℃ for 0.5–1.0 h followed by air cooling; the second stage involves holding at 550–600℃ for 1.5–3.0 h followed by furnace cooling to below 200℃.

[0034] Furthermore, a method for preparing a gradient composite structural material for wear-resistant parts of an ultra-large excavator involves adding a deep cryogenic treatment after tempering, at -80 to -196℃, for 2.0 to 6.0 hours.

[0035] Furthermore, a gradient composite structural material for wear-resistant parts of ultra-large excavators has a multi-layer gradient structure: the surface layer is mainly martensite with a grain size ≥ 8, containing nano-sized VC precipitates with a size ≤ 50 nm and a volume fraction of 1-3%; the transition layer is mainly a mixture of bainite and tempered sorbite with a grain size of 6-8; and the core is mainly ferrite + pearlite with a grain size of 4-6.

[0036] Furthermore, in a gradient composite structural material for wear-resistant parts of ultra-large excavators, the C, Cr, and Mo content decreases continuously from the transition layer to the core, and the width of the martensitic laths increases from 0.1–0.3 μm in the surface layer to 0.5–1.0 μm in the core.

[0037] Furthermore, a gradient composite structural material for wear-resistant parts of ultra-large excavators has the following mechanical properties: tensile strength ≥1800MPa, yield strength ≥1600MPa, elongation ≥10%, impact toughness at -40℃ ≥30J, surface hardness 45~50HRC, and core hardness 25~30HRC.

[0038] Furthermore, a gradient composite structural material for wear-resistant parts of ultra-large excavators has a hardness fluctuation of ≤5HRC in the weld heat-affected zone and no tendency for intergranular cracks.

[0039] Compared with the prior art, the present invention has the following advantages:

[0040] 1. By precisely controlling the proportions of key elements such as Cr / Ni, Mo / V, and Nb / Ti, compositional segregation during thermal cycling is suppressed. Combined with Re-B-Ti grain refiner to promote the precipitation of nanoscale VC phase, the composition-structure synergistic optimization of the surface fine-grained martensite and the core ferrite + pearlite is achieved.

[0041] 2. A gradient cooling mold coated with ZrO2 heat-insulating coating is used to precisely control the cooling rate and form a continuous gradient structure: high-hardness martensite on the surface layer → bainite + tempered sorbite in the transition layer → tough ferrite + pearlite in the core, which solves the stress concentration problem caused by abrupt changes in the structure in traditional casting.

[0042] 3. An innovative two-stage tempering combined with cryogenic treatment is used to achieve continuous gradient control of the martensitic lath width from 0.1 to 0.3 μm on the surface to 0.5 to 1.0 μm in the core; the final material has a tensile strength ≥1800 MPa, an impact toughness ≥30 J at -40℃, and a hardness fluctuation of ≤5 HRC in the weld heat-affected zone with no intergranular cracks. Its comprehensive performance is significantly better than that of existing technologies. Attached Figure Description

[0043] Figure 1 A process flow diagram of the preparation method of the present invention is shown;

[0044] Figure 2 A photograph of the surface area tissue of Example 1 is shown;

[0045] Figure 3 A photograph of the surface area tissue of Example 1 is shown;

[0046] Figure 4 A photograph of the tissue morphology of the transition region in Example 1 is shown;

[0047] Figure 5 A photograph of the tissue morphology of the transition region in Example 1 is shown;

[0048] Figure 6 A photograph of the tissue morphology of the core region of Example 1 is shown;

[0049] Figure 7 A photograph of the tissue morphology of the core region of Example 1 is shown. Detailed Implementation

[0050] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. It should be noted that those skilled in the art can make various changes and modifications without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0051] This invention provides a gradient composite structural material for wear-resistant parts of ultra-large excavators and its preparation method.

[0052] Example 1

[0053] The alloy composition of the gradient composite structural material used in the wear-resistant parts of the super-large excavator is as follows: C 0.20%, Si 0.50%, Mn 0.5%, Cr 1.5%, Ni 1.0%, Mo 0.50%, V 0.30%, Ti 0.01%, Nb 0.02%, W 0.30%, (La+Ce+Y) 0.01%, S≤0.005%, P≤0.005%, and the balance Fe. The ratios are: Cr / Ni = 1.5, Mo / V = 1.67, Nb / Ti = 2.0, and the W content is 0.6 times that of Mo.

[0054] The preparation method of the gradient composite structural material for wear-resistant parts of ultra-large excavators includes the following steps:

[0055] (1) Alloy smelting: The above alloy components are proportioned to form raw materials, and the raw materials are smelted into molten steel at 1600℃ and deoxidized and refined for 25 minutes;

[0056] (2) Fine grain strengthening treatment: Add Re-B-Ti strengthening agent (Re 0.04%, B 0.03%, Ti 0.015%) 8 minutes after refining, stir and let stand;

[0057] (3) Gradient casting: The ZrO2 coated mold of claim 8 is used for casting at 1520℃, and the cooling rate is controlled at 30℃ / s;

[0058] (4) Heat treatment:

[0059] Quenching: Hold at 900℃ for 1.5 hours, then oil quench;

[0060] Two-stage tempering: the first stage is held at 620℃ for 0.8h and then air-cooled; the second stage is held at 580℃ for 2.5h and then cooled to 180℃ in the furnace.

[0061] Cryogenic treatment: Keep warm at -150℃ for 4 hours.

[0062] The surface microstructure of the obtained wear-resistant parts material is fine-grained martensite with a grain size of grade 9, containing 2.5% nano-VC precipitates, and an average grain size of 40 nm. Figure 2 As shown; the transition layer is a bainite + tempered sorbite structure with a grain size of grade 7, as... Figure 3 As shown, the core is composed of ferrite and pearlite with a grain size of grade 5; the material has a yield strength of 1650 MPa, a tensile strength of 1850 MPa, and an elongation of 12.0%; low-temperature impact toughness Akv2 = 35 J; surface hardness 48 HRC; and core hardness 28 HRC. Therefore, the microstructure of the material used for the wear-resistant parts of the ultra-large excavator is a multi-layered gradient structure.

[0063] Example 2

[0064] The alloy composition of the gradient composite structural material used in the wear-resistant parts of the super-large excavator is as follows: C 0.25%, Si 0.15%, Mn 0.80%, Cr 1.00%, Ni 0.80%, Mo 0.15%, V 0.08%, Ti 0.02%, Nb 0.05%, W 0.10%, (La+Ce+Y) 0.03%, S≤0.004%, P≤0.004%, and the balance Fe. The ratio of Cr / Ni is 1.25, Mo / V is 1.88, Nb / Ti is 2.5, and the W content is 0.67 times that of Mo.

[0065] The preparation method of the gradient composite structural material for wear-resistant parts of ultra-large excavators includes the following steps:

[0066] (1) Alloy smelting: The above alloy components are proportioned to form raw materials and smelted into molten steel at 1580℃, and then deoxidized and refined for 20 minutes.

[0067] (2) Fine grain strengthening treatment: Add Re-B-Ti strengthening agent (Re 0.03%, B 0.01%, Ti 0.01%) 5 minutes after refining, stir and let stand;

[0068] (3) Gradient casting: The ZrO2 coated mold of claim 8 is used for casting at 1500℃, and the cooling rate is controlled at 10℃ / s;

[0069] (4) Heat treatment:

[0070] Quenching: Hold at 880℃ for 1.0h, then oil quench;

[0071] Two-stage tempering: the first stage is held at 600℃ for 0.5h and then air-cooled; the second stage is held at 550℃ for 2.0h and then cooled to 200℃ in the furnace.

[0072] Cryogenic treatment: -80℃ for 2.0h.

[0073] The surface microstructure of the obtained wear-resistant parts material is fine-grained martensite with a grain size of grade 8, containing 1.2% nano-VC precipitates, and an average grain size of 45 nm; the transition layer is bainite + tempered sorbite with a grain size of grade 6; the core is ferrite + pearlite with a grain size of grade 4; the material has a yield strength of 1600 MPa, a tensile strength of 1800 MPa, an elongation of 10.0%; a low-temperature impact toughness Akv2 = 30 J; a surface hardness of 45 HRC; and a core hardness of 25 HRC.

[0074] Example 3

[0075] The alloy composition of the gradient composite structural material used in the wear-resistant parts of the super-large excavator is as follows: C 0.40%, Si 0.30%, Mn 1.20%, Cr 1.80%, Ni 1.20%, Mo 0.35%, V 0.20%, Ti 0.08%, Nb 0.12%, W 0.25%, (La+Ce+Y) 0.10%, S≤0.025%, P≤0.025%, and the balance Fe. The ratios are: Cr / Ni = 1.50, Mo / V = 1.75, Nb / Ti = 1.5, and the W content is 0.71 times that of Mo.

[0076] The preparation method of the gradient composite structural material for wear-resistant parts of ultra-large excavators includes the following steps:

[0077] (1) Alloy smelting: The above alloy components are proportioned to form raw materials, which are then smelted into molten steel at 1650°C and deoxidized and refined for 30 minutes.

[0078] (2) Fine grain strengthening treatment: 10 minutes after refining, add Re-B-Ti strengthening agent (Re 0.05%, B 0.05%, Ti 0.02%), stir and let stand;

[0079] (3) Gradient casting: The ZrO2 coated mold of claim 8 is used for casting at 1550℃, and the cooling rate is controlled at 50℃ / s;

[0080] (4) Heat treatment:

[0081] Quenching: Hold at 920℃ for 2.0h, then oil quench;

[0082] Two-stage tempering: the first stage is held at 650℃ for 1.0h and then air-cooled; the second stage is held at 600℃ for 4.0h and then cooled to 150℃ in the furnace.

[0083] Cryogenic treatment: -196℃ for 6.0h.

[0084] The surface microstructure of the obtained wear-resistant parts material is fine-grained martensite with a grain size of grade 10, containing 3.0% nano-VC precipitates, and an average grain size of 30 nm; the transition layer is bainite + tempered sorbite with a grain size of grade 8; the core is ferrite + pearlite with a grain size of grade 6; the material has a yield strength of 1700 MPa, a tensile strength of 1900 MPa, an elongation of 12.5%; a low-temperature impact toughness Akv2 = 40 J; a surface hardness of 50 HRC; and a core hardness of 30 HRC.

[0085] Example 4

[0086] The alloy composition of the gradient composite structural material used in the wear-resistant parts of the super-large excavator is as follows: C 0.30%, Si 0.20%, Mn 1.00%, Cr 1.20%, Ni 0.90%, Mo 0.20%, V 0.10%, Ti 0.04%, Nb 0.08%, W 0.15%, (La+Ce+Y) 0.05%, S≤0.005%, P≤0.005%, and the balance Fe. The ratio of Cr / Ni is 1.33, Mo / V is 2.00, Nb / Ti is 2.0, and the W content is 0.75 times that of Mo.

[0087] The preparation method of the gradient composite structural material for wear-resistant parts of ultra-large excavators includes the following steps:

[0088] (1) Alloy smelting: The above alloy components are proportioned to form raw materials, which are then smelted into molten steel at 1600°C and deoxidized and refined for 25 minutes.

[0089] (2) Fine grain strengthening treatment: 7 minutes after refining, add Re-B-Ti strengthening agent (Re 0.04%, B 0.03%, Ti 0.015%), stir and let stand;

[0090] (3) Gradient casting: The ZrO2 coated mold of claim 8 is used for casting at 1530℃, and the cooling rate is controlled at 25℃ / s;

[0091] (4) Heat treatment:

[0092] Quenching: Hold at 900℃ for 1.5 hours, then oil quench;

[0093] Two-stage tempering: the first stage is held at 620℃ for 0.8h and then air-cooled; the second stage is held at 580℃ for 2.5h and then cooled to 180℃ in the furnace.

[0094] Cryogenic treatment: -120℃ for 4.0h.

[0095] The surface microstructure of the obtained wear-resistant parts material is fine-grained martensite with a grain size of grade 9, containing 2.0% nano-VC precipitates, and an average grain size of 35 nm; the transition layer is bainite + tempered sorbite with a grain size of grade 7; the core is ferrite + pearlite with a grain size of grade 5; the material has a yield strength of 1630 MPa, a tensile strength of 1820 MPa, an elongation of 11.2%; a low-temperature impact toughness Akv2 = 33 J; a surface hardness of 47 HRC; and a core hardness of 27 HRC.

[0096] Example 5

[0097] The alloy composition of the gradient composite structural material used in the wear-resistant parts of the super-large excavator is as follows: C 0.28%, Si 0.18%, Mn 0.90%, Cr 1.10%, Ni 0.85%, Mo 0.18%, V 0.09%, Ti 0.03%, Nb 0.06%, W 0.12%, (La+Ce+Y) 0.04%, S≤0.003%, P≤0.003%, and the balance Fe. The ratio of Cr / Ni is 1.29, Mo / V is 2.00, Nb / Ti is 2.0, and the W content is 0.67 times that of Mo.

[0098] The preparation method of the gradient composite structural material for wear-resistant parts of ultra-large excavators includes the following steps:

[0099] (1) Alloy smelting: The above alloy components are proportioned to form raw materials, which are then smelted into molten steel at 1590°C and deoxidized and refined for 22 minutes.

[0100] (2) Fine grain strengthening treatment: 6 minutes after refining, add Re-B-Ti strengthening agent (Re 0.035%, B 0.02%, Ti 0.012%), stir and let stand;

[0101] (3) Gradient casting: The ZrO2 coated mold of claim 8 is used for casting at 1510℃, and the cooling rate is controlled at 12℃ / s;

[0102] (4) Heat treatment:

[0103] Quenching: Hold at 890℃ for 1.2 hours, then oil quench;

[0104] Two-stage tempering: the first stage is held at 610℃ for 0.6h and then air-cooled; the second stage is held at 560℃ for 2.2h and then cooled to 190℃ in the furnace.

[0105] Cryogenic treatment: -100℃ for 3.0h.

[0106] The surface microstructure of the obtained wear-resistant parts material is fine-grained martensite with a grain size of grade 8, containing 1.8% nano-VC precipitates, and an average grain size of 42 nm; the transition layer is bainite + tempered sorbite with a grain size of grade 6; the core is ferrite + pearlite with a grain size of grade 4; the material has a yield strength of 1610 MPa, a tensile strength of 1810 MPa, an elongation of 10.8%; a low-temperature impact toughness Akv2 = 31 J; a surface hardness of 46 HRC; and a core hardness of 26 HRC.

[0107] Example 6

[0108] The alloy composition of the gradient composite structural material used in the wear-resistant parts of the super-large excavator is as follows: C 0.45%, Si 0.40%, Mn 1.40%, Cr 1.90%, Ni 1.10%, Mo 0.40%, V 0.25%, Ti 0.09%, Nb 0.14%, W 0.28%, (La+Ce+Y) 0.12%, S≤0.025%, P≤0.025%, and the balance Fe. The ratios are: Cr / Ni = 1.73, Mo / V = 1.60, Nb / Ti = 1.56, and the W content is 0.70 times that of Mo.

[0109] The preparation method of the gradient composite structural material for wear-resistant parts of ultra-large excavators includes the following steps:

[0110] (1) Alloy smelting: The above alloy components are proportioned to form raw materials, which are then smelted into molten steel at 1640°C and deoxidized and refined for 28 minutes.

[0111] (2) Fine grain strengthening treatment: After refining, add Re-B-Ti strengthening agent (Re 0.048%, B 0.045%, Ti 0.019%) 9 minutes later, stir and let stand;

[0112] (3) Gradient casting: The ZrO2 coated mold of claim 8 is used for casting at 1540℃, and the cooling rate is controlled at 48℃ / s;

[0113] (4) Heat treatment:

[0114] Quenching: Hold at 915℃ for 1.9 hours, then oil quench;

[0115] Two-stage tempering: the first stage is held at 640℃ for 0.9h and then air-cooled; the second stage is held at 590℃ for 3.5h and then cooled to 170℃ in the furnace.

[0116] Cryogenic treatment: -170℃ for 5.5 hours.

[0117] The surface microstructure of the obtained wear-resistant parts material is fine-grained martensite with a grain size of grade 9, containing 2.8% nano-VC precipitates, and an average grain size of 38 nm; the transition layer is bainite + tempered sorbite with a grain size of grade 7; the core is ferrite + pearlite with a grain size of grade 5; the material has a yield strength of 1680 MPa, a tensile strength of 1860 MPa, an elongation of 11.7%; a low-temperature impact toughness Akv2 = 35 J; a surface hardness of 49 HRC; and a core hardness of 29 HRC.

[0118] Example 7

[0119] The alloy composition of the gradient composite structural material used in the wear-resistant parts of the super-large excavator is as follows: C 0.32%, Si 0.25%, Mn 1.10%, Cr 1.60%, Ni 1.00%, Mo 0.28%, V 0.14%, Ti 0.05%, Nb 0.10%, W 0.22%, (La+Ce+Y) 0.07%, S≤0.004%, P≤0.004%, and the balance Fe. The ratio of Cr / Ni is 1.60, Mo / V is 2.00, Nb / Ti is 2.0, and the W content is 0.79 times that of Mo.

[0120] A method for preparing gradient composite structural materials for wear-resistant parts of ultra-large excavators includes the following steps:

[0121] (1) Alloy smelting: The above alloy components are proportioned to form raw materials, which are then smelted into molten steel at 1615°C and deoxidized and refined for 26 minutes.

[0122] (2) Fine grain strengthening treatment: After refining, add Re-B-Ti strengthening agent (Re 0.042%, B 0.035%, Ti 0.016%) 8 minutes later, stir and let stand;

[0123] (3) Gradient casting: The ZrO2 coated mold of claim 8 is used for casting at 1525℃, and the cooling rate is controlled at 35℃ / s;

[0124] (4) Heat treatment:

[0125] Quenching: Hold at 905℃ for 1.7 hours, then oil quench;

[0126] Two-stage tempering: the first stage is held at 630℃ for 0.7h and then air-cooled; the second stage is held at 570℃ for 2.7h and then cooled to 185℃ in the furnace.

[0127] Cryogenic treatment: -130℃ for 4.8 hours.

[0128] The surface microstructure of the obtained wear-resistant parts material is fine-grained martensite with a grain size of grade 9, containing 2.2% nano-VC precipitates, and an average grain size of 37 nm; the transition layer is bainite + tempered sorbite with a grain size of grade 7; the core is ferrite + pearlite with a grain size of grade 5; the material has a yield strength of 1645 MPa, a tensile strength of 1835 MPa, an elongation of 11.3%; a low-temperature impact toughness Akv2 = 34 J; a surface hardness of 47 HRC; and a core hardness of 27 HRC.

[0129] Example 8

[0130] The alloy composition of the gradient composite structural material used in the wear-resistant parts of the super-large excavator is as follows: C 0.50%, Si 0.10%, Mn 1.50%, Cr 0.80%, Ni 0.50%, Mo 0.10%, V 0.05%, Ti 0.10%, Nb 0.10%, W 0.12%, (La+Ce+Y) 0.15%, S≤0.030%, P≤0.030%, and the balance Fe. The ratio of Cr / Ni is 1.60, Mo / V is 2.0, Nb / Ti is 1.0, and the W content is 1.2 times that of Mo.

[0131] The preparation method of the gradient composite structural material for wear-resistant parts of ultra-large excavators includes the following steps:

[0132] (1) Alloy smelting: The above alloy components are proportioned to form raw materials, which are then smelted into molten steel at 1650°C and deoxidized and refined for 30 minutes.

[0133] (2) Fine grain strengthening treatment: 10 minutes after refining, add Re-B-Ti strengthening agent (Re 0.05%, B 0.05%, Ti 0.02%), stir and let stand;

[0134] (3) Gradient casting: The ZrO2 coated mold of claim 8 is used for casting at 1550℃, and the cooling rate is controlled at 50℃ / s;

[0135] (4) Heat treatment:

[0136] Quenching: Hold at 920℃ for 2.0h, then oil quench;

[0137] Two-stage tempering: the first stage is held at 650℃ for 1.0h and then air-cooled; the second stage is held at 600℃ for 4.0h and then cooled to 150℃ in the furnace.

[0138] Cryogenic treatment: -196℃ for 6.0h.

[0139] The surface microstructure of the obtained wear-resistant parts material is fine-grained martensite with a grain size of grade 9, containing 3.0% nano-VC precipitates, and an average grain size of 25 nm; the transition layer is bainite + tempered sorbite with a grain size of grade 8; the core is ferrite + pearlite with a grain size of grade 6; the material has a yield strength of 1700 MPa, a tensile strength of 1900 MPa, an elongation of 12.5%; a low-temperature impact toughness Akv2 = 32 J; a surface hardness of 50 HRC; and a core hardness of 30 HRC.

[0140] Example 9

[0141] The alloy composition according to claim 1 is as follows: C 0.35%, Si 0.25%, Mn 1.10%, Cr 1.40%, Ni 1.00%, Mo 0.30%, V 0.15%, Ti 0.06%, Nb 0.09%, W 0.27%, (La+Ce+Y) 0.08%, S≤0.006%, P≤0.006%, and the balance Fe. The ratio of Cr / Ni is 1.40, Mo / V is 2.00, Nb / Ti is 1.50, and the W content is 0.90 times that of Mo.

[0142] The preparation method of the gradient composite structural material for wear-resistant parts of ultra-large excavators includes the following steps:

[0143] (1) Alloy smelting: The above alloy components are proportioned to form raw materials, which are then smelted into molten steel at 1620°C and deoxidized and refined for 26 minutes.

[0144] (2) Fine grain strengthening treatment: 7 minutes after refining, add Re-B-Ti strengthening agent (Re 0.045%, B 0.04%, Ti 0.018%), stir and let stand;

[0145] (3) Gradient casting: The ZrO2 coated mold of claim 8 is used for casting at 1530℃, and the cooling rate is controlled at 35℃ / s;

[0146] (4) Heat treatment:

[0147] Quenching: Hold at 910℃ for 1.6 hours, then oil quench;

[0148] Two-stage tempering: the first stage is held at 630℃ for 0.8h and then air-cooled; the second stage is held at 580℃ for 2.8h and then cooled to 190℃ in the furnace.

[0149] Cryogenic treatment: -140℃ for 4.5 hours.

[0150] The surface microstructure of the obtained wear-resistant parts material is fine-grained martensite with a grain size of grade 9, containing 2.3% nano-VC precipitates, and an average grain size of 36 nm; the transition layer is bainite + tempered sorbite with a grain size of grade 7; the core is ferrite + pearlite with a grain size of grade 5; the material has a yield strength of 1650 MPa, a tensile strength of 1850 MPa, an elongation of 12.0%; a low-temperature impact toughness Akv2 = 35 J; a surface hardness of 48 HRC; and a core hardness of 28 HRC.

[0151] The materials used for wear-resistant parts of the super-large excavator described in Examples 1 to 9 above all have a multi-layered gradient structure.

[0152] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A gradient composite structural material for wear-resistant parts of ultra-large excavators, wherein the weight percentage of its chemical composition is as follows: C 0.20%–0.50%, Si 0.10%–0.50%, Mn 0.50%–1.50%, Cr 0.80%–2.00%, Ni 0.50%–1.50%, Mo 0.10%–0.50%, V 0.05%–0.30%, Ti 0.01%–0.10%, Nb 0.02%–0.15%, W 0.05%–0.30%, (La+Ce+Y) 0.01%–0.15%, S≤0.030%, P≤0.030%, with the balance being Fe and unavoidable impurities.

2. The gradient composite structural material for wear-resistant parts of ultra-large excavators according to claim 1, wherein the weight percentage of its chemical composition is as follows: C 0.25%~0.40%, Si 0.15%~0.30%, Mn 0.80%~1.20%, Cr 1.00%~1.80%, Ni 0.80%~1.20%, Mo 0.15%~0.35%, V 0.08%~0.20%, Ti 0.02%~0.08%, Nb 0.05%~0.12%, W 0.10%~0.25%, (La+Ce+Y) 0.03%~0.10%, S≤0.025%, P≤0.025%, with the balance being Fe and unavoidable impurities.

3. The gradient composite structural material for wear-resistant parts of ultra-large excavators according to claim 2, characterized in that, The weight percentages of S and P elements are: S ≤ 0.005%, P ≤ 0.005%.

4. A gradient composite structural material for wear-resistant parts of ultra-large excavators according to claims 1-2, characterized in that, The amounts of Cr, Ni, Mo, V, and W added meet the following proportional relationships: Cr / Ni = 1.2 to 1.8, Mo / V = 1.5 to 3.0, Nb / Ti = 1.0 to 2.5, and the W content is 0.6 to 1.2 times the Mo content.

5. A method for preparing a gradient composite structural material for wear-resistant parts of ultra-large excavators, characterized in that, Includes the following steps: (1) Alloy smelting The ingredients as described in claim 1 are blended and smelted into molten steel, and then deoxidized and refined. (2) Refine grain strengthening treatment Add a fine-grain strengthening agent to the molten steel, stir, and let stand. (3) Casting and molding A gradient cooling mold is used for casting to create a gradient in composition or structure; (4) Heat treatment The castings are subjected to quenching, tempering, and gradient-controlled heat treatment.

6. The method for preparing a gradient composite structural material for wear-resistant parts of ultra-large excavators according to claim 5, characterized in that, Includes the following steps: (1) Alloy smelting The ingredients according to claim 1 are smelted into molten steel at a smelting temperature of 1580-1650℃ and a deoxidation and refining time of ≥20min. (2) Refine grain strengthening treatment Add a fine grain strengthening agent to the molten steel, stir and let stand. The fine grain strengthening agent is added 5 to 10 minutes after refining and before casting. (3) Casting and molding The casting process employs a gradient cooling mold with a casting temperature of 1500–1550℃ and a gradient cooling rate of 10–50℃ / s. (4) Heat treatment The castings are quenched at 880–920℃ for 1.0–2.0 h and then oil-cooled; followed by tempering at 550–650℃ for 2.0–4.0 h and gradient-controlled heat treatment.

7. The method for preparing a gradient composite structural material for wear-resistant parts of ultra-large excavators according to claim 5, characterized in that, The fine-grain strengthening agent is a crystal-controlling mixture of Re, B, and Ti, with the following mass percentages of chemical composition: Re 0.03–0.05%, B 0.01–0.05%, Ti 0.01–0.02%, and the remainder being Fe.

8. The method for preparing a gradient composite structural material for wear-resistant parts of ultra-large excavators according to claim 5, characterized in that, The inner wall of the gradient cooling mold is coated with a ZrO2 heat-insulating coating to control the difference in cooling rate.

9. The method for preparing a gradient composite structural material for wear-resistant parts of ultra-large excavators according to claim 5, characterized in that, The tempering process is divided into two stages: the first stage involves holding at 600-650℃ for 0.5-1.0h and then air cooling; the second stage involves holding at 550-600℃ for 1.5-3.0h and then cooling with the furnace to below 200℃.

10. The method for preparing a gradient composite structural material for wear-resistant parts of ultra-large excavators according to claim 5, characterized in that, After the tempering, a deep cryogenic treatment is added, using a liquid nitrogen tank for insulation at a temperature of -196°C to -80°C for 2.0 to 6.0 hours.

11. A gradient composite structural material for wear-resistant parts of ultra-large excavators according to any one of claims 1 to 4, characterized in that, Its microstructure is a multi-layered gradient structure: the surface layer is mainly martensite with a grain size ≥ 8, containing nanoscale VC precipitates with a size ≤ 50 nm and a volume fraction of 1-3%; the transition layer is mainly a mixture of bainite and tempered sorbite with a grain size of 6-8; the core is mainly ferrite + pearlite with a grain size of 4-6.

12. The gradient composite structural material for wear-resistant parts of ultra-large excavators according to claim 11, characterized in that, The C, Cr, and Mo contents decrease in a continuous gradient from the transition layer to the core, and the width of the martensite laths increases from 0.1–0.3 μm in the surface layer to 0.5–1.0 μm in the core.

13. The gradient composite structural material for wear-resistant parts of ultra-large excavators according to claim 1, characterized in that, Its mechanical properties meet the following requirements: tensile strength ≥1800MPa, yield strength ≥1600MPa, elongation ≥10%, impact toughness at -40℃ ≥30J, surface hardness HRC 45~50, and core hardness HRC 25~30.

14. The gradient composite structural material for wear-resistant parts of ultra-large excavators according to claim 1, characterized in that, Its weld heat-affected zone hardness fluctuation is ≤5HRC, and it has no tendency for intergranular cracks.

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