Medium-temperature forming preparation method of heavy-load carburized part and heavy-load carburized part

Abstract

The invention discloses a medium-temperature forming preparation method of a heavy-load carburized part and the heavy-load carburized part, belongs to the technical field of metal material forming manufacturing and surface heat treatment strengthening, and solves the problems that surface carburizing heat treatment of a traditional heavy-load carburized part needs extremely long in-furnace diffusion time, the production efficiency is low, the energy consumption is high, and the cost is low. Carburizing heat treatment strength and hardness are insufficient, and obdurability and wear resistance are limited to be improved. The preparation method comprises the steps that carburizing steel is subjected to preforming treatment, and a part blank is obtained; removing a surface decarburized layer of the part blank; carburizing the part blank; the carburized part blank is cooled to the temperature below the recrystallization temperature; and a medium-temperature die forging machining method is adopted, a heavy-load carburized part is obtained, quenching cooling is conducted immediately, and deep cooling and tempering treatment are conducted. The method can be used for preparing heavy-duty gears, shafts, bearings and other parts needing deep carburized layers.

Description

Technical Field

[0001] The invention relates to the technical field of metal material forming and manufacturing and surface heat treatment strengthening, and in particular to a medium-temperature forming preparation method for a heavy-loaded carburized part and the heavy-loaded carburized part. Background Art

[0002] Heavy-duty carburizing steel is mostly used in the production of large equipment parts, such as heavy-duty gears, shafts, bearing support rings, etc. The carburized layer depth of parts is usually required to reach more than 3mm. In order to obtain high wear resistance of the carburized layer, the traditional preparation process includes long-term carburizing and subsequent high-temperature tempering, quenching, etc. The high hardness and high strength of the carburized layer mainly rely on the high carbon content of the carburized layer quenching martensite structure. However, in order to avoid the inherent brittleness of high-carbon martensite, the actual carburized layer matrix solid solution carbon content usually needs to be diluted through multiple high-temperature tempering to prevent quenching cracks, but this also limits the room for improvement of the hardness and strength of the carburized layer.

[0003] The existing carburizing and subsequent heat treatment process technology requires high-temperature austenitizing treatment above 900°C. The strengthening factors introduced by the previous forging deformation process have been basically eliminated, and the long-term carburizing and heat preservation cause the austenite grains to be relatively coarse, further limiting the way to improve the strength and toughness of the carburized layer of heavy-loaded gears. Summary of the invention

[0004] In view of the above situation, the present invention aims to provide a medium-temperature forming preparation method for heavy-loaded carburized parts and heavy-loaded carburized parts, which can at least solve one of the following technical problems: traditional surface carburizing heat treatment of heavy-loaded carburized parts requires extremely long diffusion time in the furnace, low production efficiency, high energy consumption, insufficient strength and hardness of carburizing heat treatment, and limited improvement in toughness and wear resistance.

[0005] The purpose of the present invention is mainly achieved through the following technical solutions:

[0006] The present invention provides a medium temperature forming preparation method for a heavy-load carburized part, the preparation method comprising:

[0007] Step 1: Carburizing steel is preformed by hot pressure processing to obtain a part blank;

[0008] Step 2: Process the part blank to remove the surface decarburized layer;

[0009] Step 3: Carburizing the part blank;

[0010] Step 4: Cool the carburized part blank to a temperature below the recrystallization temperature;

[0011] Step 5: Below the recrystallization temperature, a medium-temperature die forging method is used to obtain heavy-load carburized parts, which are then quenched and cooled, and deep-cooled and tempered.

[0012] Furthermore, the height H of the part blank in the forming direction in step 1 and the height h of the final part in the forming direction in step 5 meet the following relationship:

[0013] Wherein, T is the carburized layer depth of the part blank in step 3, and t is the effective hardened layer depth of the final part.

[0014] Furthermore, the value of H / h ranges from 1.1 to 2.

[0015] Furthermore, step 4 is executed immediately after step 3 is completed, and step 5 is executed immediately after step 4 is completed.

[0016] Furthermore, in step 4, the cooling to a temperature is performed by water spray cooling.

[0017] Furthermore, in step 4, the cooling rate is not less than 200°C / min.

[0018] Furthermore, in step 4, the recrystallization temperature ranges from 600 to 650°C.

[0019] Furthermore, in step 5, the temperature before quenching is higher than the martensitic transformation temperature.

[0020] Furthermore, in step 3, the carburizing heating and insulation temperature is 920-960°C.

[0021] The present invention also provides a heavy-load component, which is prepared by the above-mentioned preparation method.

[0022] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0023] a) In the preparation method of the present invention, carburizing steel is first subjected to preforming treatment to obtain a part blank, and then the part blank is subjected to carburizing treatment, and then the carburized part blank is subjected to medium-temperature die forging and heat treatment to obtain a heavy-load carburized part; the preformed blank has a large carburizing surface area, which is fully utilized to enable the surface to fully and efficiently absorb the heat-diffused carbon element during the carburizing process, which can effectively avoid the problem of wasteful consumption of invalid carbon source atmosphere during the carburizing process, and the final die forging treatment is performed after carburizing, which can make the effective hardened layer depth after the die forging precision forming treatment thicker than the initial carburized layer by 1.1 to 1.7 times, which can significantly reduce the energy consumption of traditional carburizing heat treatment.

[0024] b) In the preparation method of the present invention, the cooling and medium-temperature die forging treatments carried out immediately after the carburizing furnace avoid the precipitation of carbon elements dissolved in austenite in the form of carbides, which can give full play to the solid solution strengthening effect of carbon elements in the final quenched martensite matrix, and greatly improve the strength of the carburized layer; the medium-temperature deformation carried out after carburizing introduces lattice defects such as storage dislocations, twins, and subgrain boundaries into the supercooled metastable austenite structure of the carburized layer. Such defects are inherited in the high-carbon martensite during the subsequent quenching phase transformation process, exist in the form of a large number of stored mobile dislocations, and interact with the carbon atoms in the martensite at the microscopic lattice, which further improves the strength of the carburized layer while ensuring sufficient plastic toughness of the carburized layer and avoiding the occurrence of quenching cracks.

[0025] c) In the preparation method of the present invention, by accurately controlling the height of the part blank in the forming direction, the height of the final part in the forming direction, the thickness of the carburized layer of the part blank and other parameters, it is possible to ensure that the carburized layer thickness of the final part that meets the requirements is obtained. The method of the present invention can be used for the preparation of parts that require a thick carburized layer, such as heavy-duty gears, shafts, and bearings.

[0026] d) Compared with the traditional method of first forming the parts - then carburizing - cooling - multiple high-temperature tempering - heating again for austenitization - quenching - deep cooling and low-temperature tempering, the preparation method of the present invention uses the same carburizing furnace time to obtain a deeper final carburized layer depth, which can significantly reduce energy consumption and improve production efficiency. At the same time, the shorter furnace time can avoid excessive grain growth and reduce the grade of network carbides to improve the comprehensive mechanical properties and wear resistance of the carburized layer; and significantly simplify the subsequent heat treatment process of carburizing heavy-loaded carburized parts, save energy consumption, and improve production efficiency.

[0027] e) In the preparation method of the present invention, due to the medium-temperature deformation applied to the overall part during the carburizing cooling process, not only the mechanical properties of the carburized layer can be significantly improved, but the mechanical properties of the carburized transition layer can also be improved synchronously, which is further manifested as an increase in the depth of the hardened layer; compared with traditional carburizing heat treatment with the same hardened layer depth, the preparation method provided by the present invention can effectively shorten the carburizing furnace time and save the energy consumption of carburizing heating and insulation.

[0028] f) The carburized parts of the present invention have fine and uniform grains, no coarse austenite grains, no continuously distributed network carbides, and the carburized layer has excellent comprehensive mechanical properties and wear resistance, for example, the maximum surface hardness reaches above HV770.

[0029] Other features and advantages of the present invention will be described in the following description, and part of them will become obvious from the description, or will be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the contents particularly pointed out in the written description and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0031] Figure 1 It is a schematic diagram of the preparation method of the present invention;

[0032] Figure 2 This is the cross-sectional hardness gradient distribution diagram of the hardened layer of the part blank and the hardened layer of the final formed part in Example 1. DETAILED DESCRIPTION

[0033] Preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of the present invention and are used to explain the principles of the present invention together with the embodiments of the present invention.

[0034] In the existing technology, for the carburized layer above 3mm, the traditional surface carburizing heat treatment usually requires a very long diffusion time in the furnace, has low production efficiency, and generates huge energy consumption. In addition, the existing carburizing and subsequent heat treatment process technology requires high-temperature austenitization treatment above 900°C. The strengthening factors introduced by the previous forging deformation process have been basically eliminated, and the long-term carburizing and heat preservation result in coarse austenite grains, further limiting the room for improvement of the hardness and strength of the carburized layer.

[0035] The present invention provides a medium temperature forming preparation method for a heavy-load carburized part, comprising:

[0036] Step 1: Carburizing steel is preformed by hot pressure processing to obtain a part blank;

[0037] Step 2: Process the part blank to remove the surface decarburized layer;

[0038] Step 3: Carburizing the part blank;

[0039] Step 4: Cool the carburized part blank to a temperature below the recrystallization temperature;

[0040] Step 5: Below the recrystallization temperature, a medium-temperature die forging method is used to obtain heavy-load carburized parts, which are then quenched and cooled, and deep-cooled and tempered.

[0041] The preparation method of the present invention is as follows Figure 1 shown.

[0042] Specifically, in the above step 1, the hot pressure processing method can be extrusion, forging and rolling, etc.; the formed parts can be shafts, gears and circular rings, etc.; the total alloy component content of heavy-duty carburizing steel is not less than 4wt%, and the alloy elements include Cr, Ni, Mn, Si, W, Mo, Ti, etc.

[0043] Specifically, the height H of the part blank in the forming direction in the above step 1 and the height h of the final part in the forming direction in step 5 meet the following relationship:

[0044]

[0045] Among them, H is the height of the part blank in the forming direction, h is the height of the final part in the forming direction, T is the carburized layer depth of the part blank in step 3, t is the effective hardened layer depth of the final part, and the effective hardened layer depth takes the microhardness HV500 as the critical value, and the value range of H / h is 1.1~2.

[0046] Considering that too large a value of H / h will cause forging cracks, and too small a value will result in an insignificant thickening effect of the carburized layer, the value of H / h is controlled within the range of 1.1 to 2.

[0047] Specifically, in the above step 2, the processing may be turning, milling, grinding, etc.; the surface decarburization layer is generally within a depth of 0.6 mm.

[0048] Specifically, in the above step 1, if the holding temperature of the hot press processing is too high, it will cause serious decarburization on the surface and a thick decarburization layer; if the holding temperature is too low, it will make it difficult to form the blank parts and prone to forging cracks. Therefore, the holding temperature of the hot press processing is controlled to be 1000-1200°C, such as 1050°C, 1100°C, 1150°C.

[0049] It should be noted that, for a part blank with a carburized layer thickness of less than 2 mm, even with a larger forging ratio, such as H / h=2, a final carburized layer thickness of more than 3.5 mm cannot be achieved, and the requirement for high wear resistance of heavy-loaded parts cannot be met. Therefore, the present invention requires that the carburized layer depth of the part blank be controlled to be more than 2 mm.

[0050] Specifically, in the above step 3, considering that the carburizing heating and holding temperature of the carburizing treatment is too high, it will lead to coarse austenite grains and easy to form mixed crystals; too low temperature will lead to insufficient carburizing rate. Therefore, the carburizing heating and holding temperature is controlled to be 920-960°C, such as 930°C, 940°C, 950°C.

[0051] Specifically, in the above step 3, the carburizing process includes two stages: intensive carburizing and diffusion. The carbon potential in the intensive carburizing stage is not less than 1.0, and the carbon potential in the diffusion stage is not less than 0.8. The depth of the carburized layer takes the carbon content of 0.5wt% as the critical value, and the depth of the carburized layer is greater than 2mm.

[0052] Specifically, the above step 4 is executed immediately after step 3 is completed, and step 5 is executed immediately after step 4 is completed, that is, the blank of the part in step 3 is immediately cooled to a temperature below the recrystallization temperature after being taken out of the furnace, and a medium-temperature die forging method is adopted to obtain a heavy-load carburized part. The medium-temperature deformation after carburizing introduces lattice defects such as storage dislocations, twins, and subgrain boundaries in the supercooled metastable austenite structure of the carburized layer. Such defects are inherited in the high-carbon martensite during the subsequent quenching phase transformation process, and exist in the form of a large number of stored mobile dislocations, and interact with the carbon atoms in the martensite at the microscopic lattice, which further improves the strength of the carburized layer while ensuring sufficient plastic toughness of the carburized layer and avoiding the occurrence of quenching cracks.

[0053] Specifically, in the above step 4, the cooling to a temperature is water spray cooling, the cooling rate is not less than 200°C / min, and the recrystallization temperature ranges from 600 to 650°C.

[0054] Specifically, in the above step 5, the die forging process is completed in 2 to 4 steps, and the temperature before quenching is higher than the martensitic transformation temperature, which is in the range of 100 to 300°C.

[0055] Specifically, in the above step 5, if the quenching treatment is left for too long, the residual austenite in the high carbon area of ​​the surface will be stabilized at room temperature and will no longer undergo deep transformation, thereby reducing the final surface hardness. Therefore, the cryogenic treatment is controlled to be carried out within 12 hours after quenching.

[0056] Specifically, in the above step 5, if the temperature of the cryogenic treatment is too high and the time is too short, the residual austenite transformation will be incomplete, resulting in insufficient hardness of the final surface layer; if the temperature is too low and the time is too long, the stress of the quenched martensite structure will be too large, and internal microcracks will easily appear, which will deteriorate the wear resistance of the surface layer and even cause the surface layer to crack and the parts to be scrapped. Therefore, the temperature of the cryogenic treatment is controlled not to be higher than -60°C and not lower than -120°C, and the cryogenic treatment time is not less than 6 hours and not more than 24 hours. For example, the temperature of the cryogenic treatment is -70 to -110°C, such as -80°C, -90°C, and -100°C, and the time of the cryogenic treatment is 6 to 24 hours, such as 8h, 10h, 12h, 14h, 16h, 18h, 20h, and 22h.

[0057] Specifically, in the above step 5, the holding temperature of the low-temperature tempering treatment is controlled to be 170°C to 200°C (for example, 180°C, 190°C, 200°C), and the holding time of the low-temperature tempering is more than 2 hours, for example, 2 to 8 hours (for example, 4h, 5h, 6h, 7h, 8h).

[0058] Specifically, the preparation method of the present invention further comprises:

[0059] Step 6: The medium temperature formed carburized parts obtained above are finely ground to achieve the target size.

[0060] Specifically, in the above step 6, the surface removal depth of the fine grinding process is less than 0.2 mm.

[0061] The present invention also provides a heavy-load carburized part, which is prepared by adopting the above-mentioned preparation method.

[0062] Specifically, the effective hardened layer depth of the heavy-load carburized part of the present invention is 2.3 to 7 mm.

[0063] Specifically, the carburized layer of the heavy-load carburized parts of the present invention has fine and uniform grains, no coarse austenite grains, no continuously distributed network carbides, and excellent comprehensive mechanical properties and wear resistance of the carburized layer, for example, the maximum surface hardness reaches above HV770.

[0064] Compared with the prior art, in the preparation method of the present invention, carburizing steel is first preformed to obtain a part blank, the part blank is then carburized, and then the carburized part blank is subjected to medium-temperature die forging and heat treatment to obtain a heavy-load carburized part; the preformed blank has a large carburizing surface area, which makes the surface fully and efficiently absorb the heat-diffused carbon elements in the carburizing process, which can effectively avoid the waste of invalid carbon source atmosphere in the carburizing process, and the final die forging treatment is performed after carburizing, which can make the effective hardened layer depth after die forging precision forming treatment 1.1 to 1.7 times thicker than the initial carburized layer, which can significantly reduce the energy consumption of traditional carburizing heat treatment.

[0065] In the preparation method of the present invention, the cooling and medium-temperature die forging treatments carried out immediately after the carburizing furnace avoid the precipitation of carbon elements dissolved in austenite in the form of carbides, which can give full play to the solid solution strengthening effect of carbon elements in the final quenched martensite matrix, and greatly improve the strength of the carburized layer; the medium-temperature deformation carried out after carburizing introduces lattice defects such as storage dislocations, twins, and subgrain boundaries in the supercooled metastable austenite structure of the carburized layer. Such defects are inherited in the high-carbon martensite during the subsequent quenching phase transformation process, exist in the form of a large number of stored mobile dislocations, and interact with the carbon atoms in the martensite at the microscopic lattice, which further improves the strength of the carburized layer while ensuring sufficient plastic toughness of the carburized layer and avoiding the occurrence of quenching cracks.

[0066] In the preparation method of the present invention, by accurately controlling parameters such as the height of the part blank in the forming direction, the height of the final part in the forming direction, and the carburized layer thickness of the part blank, it is possible to ensure that the carburized layer thickness of the final part meets the requirements.

[0067] Compared with the traditional method of first forming parts - then carburizing - cooling - multiple high-temperature tempering - heating again for austenitization - quenching - deep cooling and low-temperature tempering, the preparation method of the present invention uses the same carburizing furnace time to obtain a deeper final carburized layer depth, which can significantly reduce energy consumption and improve production efficiency. At the same time, the shorter furnace time can avoid excessive grain growth and reduce the grade of network carbides to improve the comprehensive mechanical properties and wear resistance of the carburized layer; and it significantly simplifies the subsequent heat treatment process of carburizing heavy-loaded carburized parts, saves energy consumption and improves production efficiency.

[0068] In the preparation method of the present invention, due to the medium-temperature deformation applied to the overall parts during the carburizing cooling process, not only the mechanical properties of the carburized layer can be significantly improved, but the mechanical properties of the carburized transition layer can also be improved synchronously, which is further manifested as an increase in the depth of the hardened layer; compared with traditional carburizing heat treatment with the same hardened layer depth, the preparation method provided by the present invention can effectively shorten the carburizing furnace time and save the energy consumption of carburizing heating and insulation.

[0069] The carburized parts of the present invention have fine and uniform grains, no coarse austenite grains, no continuously distributed network carbides, and the carburized layer has excellent comprehensive mechanical properties and wear resistance, for example, the maximum surface hardness reaches above HV770.

[0070] The advantages of the process of the present invention are demonstrated below with specific examples and comparative examples.

[0071] Example 1

[0072] This embodiment provides a medium temperature forming preparation method for a heavy-duty carburized part and a heavy-duty carburized part. This embodiment is implemented on a large-module gear, and its alloy element content is: Cr: 2wt%; Ni: 4wt%; W: 0.8wt%; Mo: 0.3wt%. The gear module is 45, the number of teeth is 13, the height is 200mm, and the final effective hardened layer depth is required to be 3.5mm.

[0073] The preparation method is as follows:

[0074] Step 1: Use high temperature die forging method to extrude the cylindrical steel billet into a gear blank state with a height of 300 mm;

[0075] Step 2: Grind to remove the oxide scale and decarburized layer on the surface of the gear blank, with a grinding depth of 0.3 mm;

[0076] Step 3: Carburizing the ground gear blank at high temperature to obtain a carburized layer with a depth of 2.7 mm;

[0077] Step 4: Cool the high-temperature carburized blank to below 650°C;

[0078] Step 5: The gear blank after being heated is subjected to die forging and precision forming. The height of the part after two forming passes is 200mm. The temperature of the gear parts after forging is greater than 200℃, and then water-cooling quenching is performed; then deep cooling is performed within 3 hours, the deep cooling temperature is -80℃, and the deep cooling holding time is 6 hours; then low-temperature tempering is performed at 180℃, and the tempering time is 6 hours;

[0079] Step 6: The gear parts after die forging are finely ground, with a surface grinding removal depth of 0.1mm to obtain the final finished parts.

[0080] In this embodiment, the size of the final finished part has a tolerance within 0.3 mm.

[0081] In this embodiment, the effective hardened layer depth of the gear part finally formed is 3.5mm. The carburizing process in step 3 includes two stages: strong carburizing and diffusion. The carbon potential in the strong carburizing stage is 1.1, and the carbon potential in the diffusion stage is 0.85. The carburizing temperature is 930℃, and the total carburizing time in the furnace is 32h. In step 4, the cooling is water spray cooling, and the cooling rate is 250℃ / min.

[0082] The carburized layer of the final finished part of this embodiment has no coarse austenite grains and no continuously distributed network carbides. The grade is level 2, the highest surface hardness reaches HV770, and the gradient distribution of cross-sectional hardness is as follows: Figure 2 As shown in the figure, it can be seen that the effective hardened layer depth can be significantly improved through precision die forging.

[0083] Example 2

[0084] This embodiment provides a medium temperature forming preparation method for a heavy-load carburized part and a heavy-load carburized part. This embodiment is implemented on a large-diameter bearing outer support ring, and its alloy element content is: Cr: 2wt%; Ni: 4wt%; Mn: 0.4wt%. The outer circle diameter of the outer support ring is 3.5m, the inner circle diameter is 3.0m, the wall thickness is 25mm, the height is 300mm, and the final effective hardened layer depth is required to be 3.8mm.

[0085] The preparation method is as follows:

[0086] Step 1: Using a high temperature upsetting rolling method, the cylindrical steel billet is formed into a ring blank state with a height of 600 mm;

[0087] Step 2: Use rough turning to remove the oxide scale and decarburized layer on the surface of the ring blank, with a grinding depth of 0.5 mm;

[0088] Step 3: Carburizing the ground ring blank at high temperature to obtain a carburized layer with a depth of 2.4 mm;

[0089] Step 4: Cool the high-temperature carburized blank to below 650°C;

[0090] Step 5: The carburized blank is precision forged, and the height of the part after three forming steps is 300mm; the temperature of the parts after forging is greater than 250℃, and then water-cooled quenching is performed; then deep cooling is performed within 3 hours, the deep cooling temperature is -100℃, and the deep cooling holding time is 8 hours; then low-temperature tempering is performed at 170℃, and the tempering time is 8 hours;

[0091] Step 6: The die-forged parts are finely ground, with a surface grinding removal depth of 0.1 mm to obtain the final finished parts.

[0092] In this embodiment, the size of the final finished part has a tolerance within 0.3 mm.

[0093] In this embodiment, the effective hardened layer depth of the final formed part is 3.8mm. The carburizing process in step 3 includes two stages: strong carburizing and diffusion. The carbon potential in the strong carburizing stage is 1.2, and the carbon potential in the diffusion stage is 0.85. The carburizing temperature is 930℃, and the total carburizing furnace time is 25h. In step 4, the cooling is water spray cooling, and the cooling rate is 230℃ / min.

[0094] The carburized layer of the final finished part of this embodiment has no coarse austenite grains and no continuously distributed network carbides, and the grade is level 2, and the maximum surface hardness reaches HV780.

[0095] The inventor has conducted a lot of research during the research process, and now uses some solutions with poor performance as comparative examples.

[0096] Comparative Example 1

[0097] This comparative example provides a method for preparing a carburized part and a carburized part, and the implementation objects and technical requirements are the same as those of Example 1. The preparation method is as follows:

[0098] Step 1: Using a high temperature die forging method, the cylindrical steel billet is extruded into a gear shape with a height of 200 mm;

[0099] Step 2: Use grinding to remove the oxide scale and decarburized layer on the surface of the formed gear, with a grinding depth of 0.3mm;

[0100] Step 3: Carburizing the ground gear blank at high temperature to obtain a carburized layer with a depth of 3.5 mm;

[0101] Step 4: Quench the carburized parts and then deep cool them within 3 hours at a temperature of -80°C and a holding time of 6 hours; then perform low-temperature tempering at 180°C for 6 hours;

[0102] Step 5: The gear parts after die forging are finely ground, with a surface grinding removal depth of 0.2 mm to obtain the final finished parts.

[0103] In this comparative example, the hardened layer depth of the final formed part is 3.5 mm. The carburizing process in step 3 includes two stages: strong carburizing and diffusion. The carbon potential in the strong carburizing stage is 1.1, and the carbon potential in the diffusion stage is 0.85. The carburizing temperature is 930°C, and the total carburizing furnace time is 86 hours.

[0104] In this comparative example, the carburized layer of the final molded part has a mixed crystal structure and a continuously distributed network of carbides, which is graded as Grade 3. The highest surface hardness is HV680.

[0105] It can be seen that compared with Example 1, the carburizing time in the furnace of the conventional heat treatment method described in this comparative example is 2.7 times that of Example 1, the energy consumption is huge, the production efficiency is low, and mixed crystals and continuous network carbides are easily formed in the carburized layer, which deteriorates the mechanical properties of the carburized layer. The maximum hardness of the surface is insufficient to resist more severe service loads.

[0106] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing heavy-load carburized parts by medium-temperature forming, characterized in that: The preparation method comprises: Step 1: Carburizing steel is preformed by hot pressure processing to obtain a part blank; Step 2: Process the part blank to remove the surface decarburized layer; Step 3: Carburizing the part blank; Step 4: Cool the carburized part blank to a temperature below the recrystallization temperature; Step 5: Below the recrystallization temperature, a medium-temperature die forging method is used to obtain heavy-load carburized parts, which are then quenched and cooled, and deep-cooled and tempered.

2. The preparation method according to claim 1, characterized in that: The height H of the part blank in the forming direction in step 1 and the height h of the final part in the forming direction in step 5 meet the following relationship: Wherein, T is the carburized layer depth of the part blank in step 3, and t is the effective hardened layer depth of the final part.

3. The preparation method according to claim 2, characterized in that: The value of H / h ranges from 1.1 to 2.

4. The preparation method according to claim 1, characterized in that: Step 4 is executed immediately after step 3 is completed, and step 5 is executed immediately after step 4 is completed.

5. The preparation method according to claim 1, characterized in that: In step 4, cooling to a temperature is performed by water spray cooling.

6. The preparation method according to claim 1, characterized in that: In the step 4, the cooling rate is not less than 200°C / min.

7. The preparation method according to claim 1, characterized in that: In step 4, the recrystallization temperature ranges from 600 to 650°C.

8. The preparation method according to claim 1, characterized in that: In the step 5, the temperature before quenching is higher than the martensitic transformation temperature.

9. The preparation method according to any one of claims 1 to 8, characterized in that: In step 3, the carburizing heating and insulation temperature is 920-960°C.

10. A heavy-load carburized part, characterized in that: The preparation method is described in any one of claims 1 to 9.

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