High-wear-resistance high-toughness carburizing alloy steel material and driving tooth

Abstract

The application relates to a high-wear-resistance high-toughness carburizing alloy steel material and a driving tooth, and belongs to the technical field of alloy materials. The alloy steel material is based on a Cr-Mn system, and is compounded with Ni, Mo, Nb, V and Ce-La mixed rare earth, and meanwhile, the contents of Si, P, S, O and N and the relations of Ni / Mo, Mo / (Nb+V) and (Ce+La) / (O+S) are controlled. Ni-Mo improves the hardenability and toughness of the core, Nb-V-Mo constructs a multi-temperature zone stable precipitation system to inhibit mixed crystals during carburizing, Ce-La converts long strip sulfides and sharp corner oxides into fine dispersed inclusions, low-silicon cleaning and strong penetration-diffusion segmented carbon potential treatment are matched, the depth of the carburized layer, hardness, residual austenite and carbide distribution are more uniform, and the obtained driving tooth has high surface wear resistance, anti-peeling property and high core impact toughness.

Description

Technical Field

[0001] This invention belongs to the field of alloy materials technology, specifically relating to a high wear-resistant and high toughness carburized alloy steel and a drive gear. Background Technology

[0002] Drive teeth in engineering machinery, mining equipment, and tracked walking mechanisms are subjected to cyclic meshing impacts, tooth root bending loads, and abrasive wear caused by sand and gravel media during service. To extend the service life of drive teeth, low-carbon alloy steel is typically used to prepare tooth blanks, which are then carburized, quenched, and subjected to low-temperature tempering to form a high-carbon, high-hardness structure on the surface, while maintaining relatively high strength and toughness in the core.

[0003] Cr-Mn carburizing steel has the advantages of readily available raw materials, moderate cost, and good hardenability, making it a commonly used basic material system for drive gears. However, simply relying on increasing the Cr and Mn content to achieve hardenability can easily exacerbate solidification segregation and banded structure. During long-term high-temperature carburizing, the original austenite grains are prone to uneven growth, and the local coarse-grained and fine-grained regions exhibit significant differences in carbon diffusion, phase transformation, and retained austenite formation, resulting in large fluctuations in the depth, hardness, and spalling resistance of the carburized layer.

[0004] Existing technologies typically improve hardenability and toughness by adding Ni or Mo alone, or refine grains by adding microalloying elements such as Nb, V, and Ti. Some technologies also use rare earth elements to modify inclusions. These individual improvement methods act on the matrix structure, austenite grains, or inclusion state respectively, and fail to fully solve the problems of "insufficient core toughness, uneven carburized layer structure, and difficulty in simultaneously achieving surface wear resistance and spalling resistance" in Cr-Mn carburized steel.

[0005] Therefore, it is necessary to carry out integrated design from aspects such as alloy element synergy, clean smelting, precipitate phase stabilization, inclusion control and carburizing regime matching, so as to improve the core toughness while maintaining the economy and basic hardenability of the Cr-Mn system, and make the carburized layer form a more consistent carbon concentration gradient and quenched structure at different positions of complex tooth shape. Summary of the Invention

[0006] In order to solve the technical problems mentioned in the background art, the purpose of this invention is to provide a high wear-resistant and high toughness carburized alloy steel and a drive gear.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] A high-wear-resistant and high-toughness carburized alloy steel is obtained by carburizing a base alloy steel; the weight percentage composition of the base alloy steel is as follows:

[0009] C: 0.18-0.22%, Si: 0.06-0.16%, Mn: 1.05-1.35%, Cr: 1.05-1.35%, Ni: 0.45-0.80%, Mo: 0.1 8-0.32%, Nb: 0.025-0.045%, V: 0.05-0.12%, Ce+La: 0.006-0.015%, Al: 0.010-0.025%, N: 0. 0.004-0.008%, P≤0.012%, S≤0.005%, O≤0.0015%, with the balance being Fe and unavoidable impurities; wherein, the content of each element satisfies the following relationships: 1.8≤Ni / Mo≤3.2, 1.6≤Mo / (Nb+V)≤2.8, 0.8≤(Ce+La) / (O+S)≤2.5, and the element content in each relationship is calculated by substituting the corresponding element's mass percentage value.

[0010] In the composition design of this matrix alloy steel, the C content ensures sufficient strength and hardenability of the core, while avoiding excessive carbon content in the core that would reduce impact toughness; Si is used for deoxidation and solid solution strengthening, but is controlled within a low range to mitigate selective internal oxidation during gas carburizing; Mn and Cr form the basic hardenability system and improve the hardness and wear resistance of the carburized layer; Ni is mainly dissolved in the matrix, improving the plasticity and crack propagation resistance of the low-carbon core; Mo improves hardenability and resistance to tempering softening, and promotes the high-temperature stability of Nb-V composite carbonitrides.

[0011] Nb preferentially forms high-temperature stable Nb(C,N) to pin austenite grain boundaries; V supplements the formation of finer-sized and more numerous V(C,N) or Nb-V composite carbonitrides during controlled rolling cooling and subsequent heating; Mo reduces the particle coarsening rate through solid solution dragging and precipitation phase interface stabilization.

[0012] The control of Ni / Mo ratio from 1.8 to 3.2 aims to: Ni primarily improves the toughness and plasticity of the low-carbon core and reduces the tendency for brittle fracture; Mo primarily improves hardenability, resistance to tempering softening, and stabilizes Nb-V precipitates. If Ni / Mo is less than 1.8, the relatively high Mo content easily leads to carbide enrichment in the alloy, coarsening of the carbide layer, and insufficient improvement in core toughness. If Ni / Mo is greater than 3.2, the relatively high Ni content easily increases the amount of residual austenite in the carburized layer, decreases surface hardness, and increases the risk of dimensional instability. Controlling Ni / Mo within the range of 1.8-3.2 balances core toughening with the stability of the carburized layer structure.

[0013] The control of 1.6≤Mo / (Nb+V)≤2.8 aims to ensure that Nb and V provide a basis for grain refinement and precipitation strengthening, while Mo improves the hardenability of the core and inhibits the coarsening of Nb-V composite carbonitrides during high-temperature carburizing. If Mo / (Nb+V) is less than 1.6, Mo is relatively insufficient, making it difficult to effectively stabilize the precipitated phase. Microalloying elements are more likely to form coarse primary precipitates, reducing the grain refinement effect and carburizing uniformity. If Mo / (Nb+V) is greater than 2.8, Mo is relatively excessive, which not only increases costs but may also exacerbate segregation and carbide enrichment, hindering the dispersed distribution of carbides in the carburized layer.

[0014] The control of 0.8 ≤ (Ce+La) / (O+S) ≤ 2.5 aims to ensure that this ratio reflects the degree of matching between rare earth elements and the total amount of oxygen and sulfur to be modified. If it is less than 0.8, there is insufficient rare earth element, making it difficult for inclusions such as MnS and Al2O3 to be sufficiently spheroidized and refined; if it is greater than 2.5, there is an excess of rare earth element, which easily forms coarse rare earth oxide sulfide inclusions, which can become crack initiation sites. Controlling this ratio between 0.8 and 2.5 can obtain fine, dispersed, near-spherical inclusion morphology, reduce stress concentration, and improve microstructure uniformity.

[0015] Preferably, the mass ratio of Ce to La is 1.5-3.0:1.

[0016] A drive gear based on high wear-resistant and high-toughness carburized alloy steel is prepared by the following method:

[0017] Step S1: The target components of the base alloy steel are prepared and initially refined, followed by LF refining and RH vacuum treatment. After deoxidation, desulfurization and vacuum treatment are completed, Ce-La mixed rare earth is added, and the billet is obtained by protective casting continuous casting.

[0018] Step S2: After homogenizing the billet, it is rolled and controlled rolling and cooling are used to obtain the base alloy steel.

[0019] Step S3: Perform preheating and machining on the alloy steel to produce a drive gear blank.

[0020] Step S4: The drive gear blank is subjected to segmented carburizing treatment in the strong diffusion stage and the diffusion stage, followed by quenching and low-temperature tempering to obtain the drive gear.

[0021] Furthermore, in step S1, the RH vacuum degree is not higher than 100 Pa, and the vacuum holding time is 15-25 min; the refining endpoint is controlled with S≤0.005% and O≤0.0015%; Ce-La mixed rare earth is added after deoxidation, desulfurization and vacuum treatment are completed, and after addition, it is weakly stirred for 3-8 min and then allowed to stand for 5-10 min.

[0022] Furthermore, the superheating temperature for continuous casting is 20-35℃.

[0023] Furthermore, in step S2, the homogenization temperature of the billet is 1180-1210℃, and the time is 3-5h.

[0024] Furthermore, the initial rolling temperature is 1050-1100℃, the final rolling temperature is 840-880℃, and after final rolling, it is cooled to 620-680℃ at 2-5℃ / s, and then air-cooled to room temperature. The rolling ratio is not less than 4.0.

[0025] Furthermore, in step S3, the preheating temperature is 880-910℃ and the time is 1.5-2.5h, followed by air cooling.

[0026] Furthermore, in step S4, the temperature of the strong infiltration stage is 940-960℃, the carbon potential is 1.05-1.15%, and the time is 1.5-2.5h; the temperature of the diffusion stage is 930-950℃, the carbon potential is 0.75-0.90%, and the time is 4-7h. By rapidly establishing the surface carbon concentration through a high carbon potential in the early stage, and then reducing the carbon potential to allow excess carbon on the surface to diffuse into the interior, the formation of continuous network carbides and excess retained austenite on the surface is avoided.

[0027] Furthermore, oil quenching is used, and the temperature is held at 840-860℃ for 20-40 minutes before quenching; the tempering temperature is 170-190℃ and the tempering time is 2-3 hours.

[0028] The beneficial effects of this invention are:

[0029] 1. This invention does not involve single-element strengthening of Cr-Mn steel. Instead, it utilizes Ni-Mo, Nb-V-Mo, and Ce-La to act on the core phase transformation, austenite grain boundaries, and inclusion interfaces, respectively. Furthermore, the dual action of Mo links matrix toughening with the stability of the carburized structure. Ni improves the plasticity and crack propagation resistance of the low-carbon core, while Mo supplements the hardenability of the large-section core and inhibits tempering softening, allowing the core to maintain high toughness without increasing the carbon content.

[0030] 2. Nb-V-Mo synergistically refines grains. Nb(C,N) provides stable grain boundary pinning at high carburizing temperatures, V(C,N) replenishes the number of fine particles during controlled rolling cooling and reheating, and Mo both generates solute drag and slows down the coarsening of Nb-V composite carbonitrides. Together, these three elements reduce the original austenite grain size distribution, avoid localized abnormal grain growth, and make carbon diffusion and quenched microstructure more consistent at different locations, thereby significantly improving carburizing uniformity.

[0031] 3. The synergistic effect of Ce-La mixed rare earth elements and low S and low O purification control transforms elongated MnS and sharp-angled Al2O3 into fine, dispersed, near-spherical rare earth oxide sulfides, reducing stress concentration at the tips of tooth root inclusions and longitudinal and transverse performance differences. At the same time, the uniform and fine inclusions reduce local abnormal nucleation and local microstructure fluctuations, providing a more stable and consistent matrix for Nb-V-Mo precipitates and segmented carbon potential carburization.

[0032] 4. The low-Si design reduces surface alloy depletion caused by selective Si oxidation during gas carburizing, while the strong carburizing-diffusion segmented carbon potential regime avoids the formation of network carbides and excessive retained austenite due to the continuous high carbon potential in Cr, Mo, and V enriched areas. Composition homogenization, grain stabilization, inclusion modification, and carbon potential regulation promote each other: a clean and uniform matrix ensures consistent carbon diffusion and phase change, stable fine grains enable the segmented carbon potential to form a gentle carbon gradient, and the Ni-Mo toughened core can withstand the impact load transmitted by the high-hardness carburized layer, ultimately achieving a synergistic improvement of "high core toughness - high carburized layer uniformity - high surface wear resistance - high interface spalling resistance". Attached Figure Description

[0033] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 Metallographic image of the cross-section of the carburized layer of the drive tooth in Example 3;

[0035] Figure 2 Metallographic image of the surface microstructure of Example 3. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] The present invention provides three sets of embodiments, and Table 1 below shows the composition of the base alloy steel;

[0038] Table 1. Chemical composition (wt%) of the base alloy steel in the examples.

[0039]

[0040] Example 1: Preparation of high wear-resistant and high toughness drive teeth. The specific implementation process is as follows:

[0041] Step S1, Smelting and Continuous Casting: Materials were prepared according to the target composition in Example 1 of Table 1, and subjected to primary smelting in an electric arc furnace, refining in an LF furnace, and RH vacuum treatment at a vacuum degree of 90 Pa for 15 min. After deoxidation, desulfurization, and vacuum treatment, Ce-La mixed rare earth elements were added, and the mixture was gently stirred for 3 min and allowed to stand for 5 min. Protective casting was used for continuous casting at a superheat of 20°C to obtain the cast billet.

[0042] Step S2, homogenization and controlled rolling and cooling: The billet is held at 1180℃ for 5 hours with a rolling ratio of 4.5; the initial rolling temperature is 1050℃, the final rolling temperature is 840℃, and after final rolling, it is cooled to 620℃ at 2℃ / s, and then air-cooled to room temperature to obtain the base alloy steel.

[0043] Step S3, Preparatory heat treatment and processing: After holding the alloy steel at 880℃ for 2.5h, air cool it, machine it and remove the oxide scale to make a drive gear blank.

[0044] Step S4, carburizing and quenching and tempering: The drive gear blank is strongly carburized at 940℃ and carbon potential of 1.05% for 2.5h, and then diffused at 930℃ and carbon potential of 0.75% for 7h; then cooled to 840℃ and held for 40min, quenched in quenching oil at 70℃, and tempered at 170℃ for 3h. The tempering is repeated twice to obtain the drive gear of Example 1.

[0045] Example 2: Preparation of high wear-resistant and high toughness drive teeth. The specific implementation process is as follows:

[0046] Step S1, Smelting and Continuous Casting: Materials were prepared according to the target composition in Example 2 of Table 1, and subjected to primary smelting in an electric arc furnace, refining in an LF furnace, and RH vacuum treatment at 80 Pa for 25 min. After deoxidation, desulfurization, and vacuum treatment, Ce-La mixed rare earth elements were added, gently stirred for 8 min, and allowed to stand for 10 min. Protective casting was used for continuous casting at a superheat of 35°C to obtain the cast billet.

[0047] Step S2, homogenization and controlled rolling and cooling: The billet is held at 1210℃ for 3 hours with a rolling ratio of 5; the initial rolling temperature is 1100℃ and the final rolling temperature is 880℃. After final rolling, it is cooled to 680℃ at 5℃ / s and then air-cooled to room temperature to obtain the base alloy steel.

[0048] Step S3, Preliminary heat treatment and processing: After holding the alloy steel at 910℃ for 1.5h, air cool it, machine it and remove the oxide scale to make a drive gear blank.

[0049] Step S4, carburizing and quenching and tempering: The drive gear blank is strongly carburized at 960℃ and carbon potential of 1.15% for 1.5h, and then diffused at 950℃ and carbon potential of 0.90% for 4h; then cooled to 860℃ and held for 20min, quenched in quenching oil at 100℃, and tempered at 190℃ for 2h. The tempering is repeated twice to obtain the drive gear of Example 2.

[0050] Example 3: Preparation of high wear-resistant and high toughness drive teeth. The specific implementation process is as follows:

[0051] Step S1, Smelting and Continuous Casting: Materials were prepared according to the target composition in Example 3 of Table 1, and subjected to primary smelting in an electric arc furnace, refining in an LF furnace, and RH vacuum treatment at a vacuum degree of 85 Pa for 20 min. After deoxidation, desulfurization, and vacuum treatment, Ce-La mixed rare earth elements were added, gently stirred for 5 min, and allowed to stand for 8 min. Protective casting was used for continuous casting at a superheat of 28°C to obtain the cast billet.

[0052] Step S2, homogenization and controlled rolling and cooling: The billet is held at 1200℃ for 4 hours with a rolling ratio of 4.8; the initial rolling temperature is 1080℃ and the final rolling temperature is 860℃. After final rolling, it is cooled to 650℃ at 3.5℃ / s and then air-cooled to room temperature to obtain the base alloy steel.

[0053] Step S3, Preparatory heat treatment and processing: After holding the alloy steel at 895℃ for 2 hours, air cool it, machine it and remove the oxide scale to make a drive gear blank.

[0054] Step S4, carburizing and quenching and tempering: The drive gear blank is strongly carburized at 950℃ and carbon potential of 1.10% for 2 hours, and then diffused at 940℃ and carbon potential of 0.82% for 5.5 hours; then cooled to 850℃ and held for 30 minutes, quenched in quenching oil at 85℃, and tempered at 180℃ for 2.5 hours. The tempering is repeated twice to obtain the drive gear of Example 3.

[0055] The comparative examples are set as follows. Except for the differences that are explicitly stated, the smelting, controlled rolling and cooling, preheating, drive gear machining and heat treatment conditions of each comparative example are the same as those in Example 3. The specific differences are shown in Table 2.

[0056] Table 2. Main differences between the comparative example and Example 3

[0057]

[0058] Samples were taken from the drive teeth prepared in the examples and comparative examples, and the following tests were performed:

[0059] (1) Effective carburized layer depth and uniformity: 12 test points were selected on the working tooth surface, tooth top, two sides of the tooth surface and tooth root of each drive tooth. The microhardness was measured along the cross section. The depth corresponding to 550HV was taken as the effective carburized layer depth. The average value and coefficient of variation of the 12 test values ​​were calculated. At the same time, the surface Rockwell hardness of each point was tested and the range was calculated.

[0060] (2) Microstructure test: The original austenite grain boundaries were reconstructed by metallography, and the average grain size and the area ratio of coarse grains with an equivalent diameter greater than 40 μm were statistically analyzed. The volume fraction of residual austenite in the diffusion layer was determined by X-ray diffraction. The average equivalent diameter of carbides and the presence of continuous network carbides were statistically analyzed by scanning electron microscopy. The maximum depth of the inner oxide layer was observed in cross section.

[0061] (3) Mechanical property test: room temperature tensile test and V-notch impact test were performed on the core sample treated in the same furnace as the drive tooth; the tensile test was performed according to the method specified in GB / T 228.1-2021, and the impact test was performed according to the method specified in GB / T 229-2020.

[0062] (4) Wear test: A penetration layer sample was prepared from the working tooth surface. The dry sand rubber wheel abrasive wear method was adopted. The load was 130N, the abrasive was quartz sand with a particle size of 0.20-0.30mm, the rubber wheel speed was 6000rpm, and the mass difference before and after wear was measured.

[0063] (5) Peeling test: Run for 100 hours on a meshing wear tester containing quartz sand, and determine the proportion of the peeling area of ​​the working tooth surface to the area of ​​the test area.

[0064] The specific test results are shown in Tables 3-5:

[0065] Table 3. Results of Grain and Carburization Uniformity Tests

[0066]

[0067] Table 4. Composition of carburized layer phases and carbide states

[0068]

[0069] Table 5 Mechanical properties and wear test results

[0070]

[0071] As can be seen from the test results in Tables 3-5, the examples have fine grains, high alloy strength and toughness, uniform carburization, and excellent surface wear resistance.

[0072] like Figure 1The image shown is a metallographic image of the cross-section of the carburized layer of the drive tooth in Example 3. From the surface inward, it includes a surface carburized layer, a transition zone, and a core. The microstructure gradient from the surface to the core is continuous, and no obvious abnormal grain growth is observed.

[0073] like Figure 2 The image shown is a metallographic microstructure of the surface layer in Example 3. It is mainly composed of fine tempered martensite, with residual austenite distributed diffusely, and fine dispersed carbides are visible. No continuous network carbides are observed.

[0074] In the description of this specification, the references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0075] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A high wear-resistant and high-toughness carburized alloy steel, obtained by carburizing a base alloy steel, characterized in that, The weight percentage composition of the base alloy steel is as follows: C: 0.18-0.22%, Si: 0.06-0.16%, Mn: 1.05-1.35%, Cr: 1.05-1.35%, Ni: 0.45-0.80%, Mo: 0.18-0.32%, Nb: 0.025-0.045%, V: 0.05-0.12%, Ce+La: 0.006-0.015%, Al: 0.010-0.025%, N: 0.004-0.008%, P≤0.012%, S≤0.005%, O≤0.0015%, with the balance being Fe and unavoidable impurities; The content of each element satisfies the following relationship: 1.8≤Ni / Mo≤3.2, 1.6≤Mo / (Nb+V)≤2.8, 0.8≤(Ce+La) / (O+S)≤2.

5. The content of each element in each relationship is calculated by substituting the mass percentage of the corresponding element.

2. A drive gear, characterized in that, It is prepared by machining and shaping a base alloy steel followed by carburizing. The specific preparation method includes the following steps: Step S1: The target composition of the base alloy steel is prepared and initially refined, followed by LF refining and RH vacuum treatment. After deoxidation, desulfurization and vacuum treatment are completed, Ce-La mixed rare earth is added, and the billet is obtained by protective casting continuous casting. Step S2: After homogenizing the billet, it is rolled and controlled rolling and cooling are used to obtain the base alloy steel; Step S3: Perform preheating and machining on the alloy steel to produce a drive gear blank; Step S4: The drive gear blank is subjected to segmented carburizing treatment in the strong infiltration stage and the diffusion stage, followed by quenching and low-temperature tempering to obtain the drive gear.

3. A drive gear according to claim 2, characterized in that, The RH vacuum degree is not higher than 100Pa, the vacuum holding time is 15-25min, and the refining endpoint is controlled with S≤0.005% and O≤0.0015%.

4. A drive gear according to claim 2, characterized in that, The homogenization temperature of the billet is 1180-1210℃, and the time is 3-5h.

5. A drive gear according to claim 2, characterized in that, The initial rolling temperature is 1050-1100℃, the final rolling temperature is 840-880℃, and after final rolling, it is cooled to 620-680℃ at 2-5℃ / s, and then air-cooled to room temperature. The rolling ratio is not less than 4.

0.

6. A drive gear according to claim 2, characterized in that, The preheating temperature is 880-910℃ and the time is 1.5-2.5h.

7. A drive gear according to claim 2, characterized in that, The temperature of the strong infiltration stage is 940-960℃, the carbon potential is 1.05-1.15%, and the time is 1.5-2.5h; the temperature of the diffusion stage is 930-950℃, the carbon potential is 0.75-0.90%, and the time is 4-7h.

8. A drive gear according to claim 2, characterized in that, The quenching process uses oil quenching, and the temperature is held at 840-860℃ for 20-40 minutes before quenching; the tempering temperature is 170-190℃ and the tempering time is 2-3 hours.

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