Cold heading process of toothed parts

Abstract

The present application relates to the cold heading process of toothed parts, and belongs to the technical field of part processing. The cold heading process of toothed parts disclosed by the present application comprises the following specific steps: raw material quenching, medium-temperature hot rolling, obtaining pretreatment material after tempering, cold heading treatment, low-temperature tempering and shallow cold treatment. Through the interaction of each step in the process, the pretreatment material with surface toughness and internal matrix with high strength is constructed, which provides strain force for the cold heading treatment and prevents cracking and springback phenomenon in the cold heading treatment process. In addition, the cold heading treatment is followed by low-temperature tempering to eliminate stress, and shallow cold treatment to further improve the mechanical strength of the material. Therefore, the toothed part obtained by the preparation process of the present application has high precision and excellent mechanical strength.

Description

Technical Field

[0001] This invention belongs to the field of parts processing technology, and relates to the cold heading process of toothed parts. Background Technology

[0002] Toothed parts refer to mechanical components with regular toothed structures on their edges or surfaces. The most common examples are gears and racks, which transmit power or change the form of motion through the meshing of teeth. Currently, toothed parts in China are mainly formed by hot forging. Hot forging is not only energy-intensive but also involves shrinkage during the cooling process, which affects the dimensional accuracy of the gears.

[0003] To address the problems arising from hot forging, existing technologies have proposed cold heading, a non-cutting metal pressure processing method. Cold heading utilizes the plastic deformation of metal under external force, and with the aid of a die, redistributes and transfers the metal volume to form the desired part. While cold heading reduces energy consumption and shrinkage, it often suffers from problems such as cracks during heading, large flash at the edges, dimensional instability after cold heading, springback leading to dimensional deviations, inconsistent product quality, and high die wear. In summary, this invention proposes a cold heading process for toothed parts, and based on existing technologies, provides corresponding technical solutions to the problems arising from the cold heading process. Summary of the Invention

[0004] This invention relates to the cold heading process of toothed parts, belonging to the field of parts processing technology. The specific steps of the cold heading process for toothed parts disclosed in this invention are: raw material quenching—medium-temperature hot rolling—tempering to obtain pretreated material—cold heading—low-temperature tempering—shallow cooling. Through the interaction of each step in the process, a pretreated material with surface toughness and high internal matrix strength is constructed, providing strain force for the cold heading process and preventing cracking and springback during cold heading. Furthermore, the cold heading process is followed by low-temperature tempering to relieve stress, and the shallow cooling further enhances the mechanical strength of the material. Therefore, the toothed parts obtained through the manufacturing process of this invention possess high precision and excellent mechanical strength.

[0005] The objective of this invention can be achieved through the following technical solution: a cold heading process for toothed parts, wherein the cold heading process for toothed parts includes the following steps: raw material quenching—medium-temperature hot rolling—tempering to obtain pretreated material—cold heading treatment—low-temperature tempering—shallow cooling treatment, wherein the thickness ratio between the hardened layer and the tough layer of the pretreated material is 1-1.3:1.5-2.

[0006] Furthermore, the raw material quenching specifically involves heating the gear steel and holding it at that temperature, then cooling it to room temperature with a quenching liquid. The heating temperature is 950-1000℃, the holding time is 60-90 minutes, and the quenching liquid is PAG quenching liquid.

[0007] Furthermore, the medium-temperature hot rolling specifically refers to the following: after quenching, the material is heated and then rolled in 4-6 passes, wherein the heating refers to heating to 480-600℃, and the cumulative rolling amount is 60-80%.

[0008] Furthermore, the tempering specifically involves heating the material that has undergone medium-temperature hot rolling to a temperature of 400-450°C and then cooling it to room temperature. The heating refers to heating to 400-450°C, and the cooling rate is 0.5-1°C / s.

[0009] Furthermore, the cold heading process specifically involves: placing the pretreated material into a cold heading machine and forming it with an upper mold; the cold heading speed is 5-15 mm / s; and the lubrication method of the cold heading machine is phosphating and saponification.

[0010] Furthermore, the low-temperature tempering specifically involves heating and holding the material after cold heading, followed by air cooling to room temperature. The heating refers to raising the temperature to 150-250℃, and the holding time is 30-60 minutes.

[0011] Furthermore, the shallow cooling treatment is as follows: the material that has been tempered at low temperature is cooled and kept at a certain temperature, and then restored to room temperature in air cooling. The cooling refers to dropping to -80~-60℃, and the holding time is 60-120 minutes.

[0012] Furthermore, the elemental composition of the gear steel is: C 0.13-0.15%, Cr 3.3-3.6%, Ni 6-9.6%, Co 13-15%, Mo 1.2-1.6%, V 0.08-0.12%, Si 0.03-0.05%, Al 0.02-0.04%, with the remainder being Fe.

[0013] The beneficial effects of this invention are as follows: The specific steps of the cold heading process for toothed parts disclosed in this invention are: raw material quenching—medium-temperature hot rolling—tempering to obtain pretreated material—cold heading treatment—low-temperature tempering—shallow cooling treatment. Through the interaction of each step in the process, a surface toughness is constructed, and the internal matrix has a high-strength pretreated material, which provides strain force for cold heading treatment and prevents cracking and springback during the cold heading process. Among them, a uniform strip-shaped martensite matrix is ​​obtained through quenching, while medium-temperature hot rolling ensures that the strip-shaped martensite does not decompose in large quantities, and at the same time increases the content of surface austenite, thereby improving surface toughness. In addition, the M2C carbide is refined during the tempering process, which further improves the toughness of the steel. Therefore, the toothed parts have the best performance when the thickness ratio of the hardened layer to the toughness layer constructed by the pretreated material is 1.3:1.5. Cold heading followed by low-temperature tempering to relieve stress, and shallow cooling further enhance the mechanical strength of the material. Therefore, the toothed parts obtained through the manufacturing process of this invention possess high precision and excellent mechanical strength. Detailed Implementation

[0014] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features and effects of the present invention, in conjunction with embodiments, is provided below.

[0015] Example 1: Cold heading process of toothed parts, the cold heading process of toothed parts includes the following steps: raw material quenching - medium temperature hot rolling - tempering to obtain pretreated material - cold heading treatment - low temperature tempering - shallow cooling treatment.

[0016] The raw material quenching process specifically involves heating the gear steel and holding it at that temperature, then cooling it to room temperature with a quenching liquid. The heating temperature is 950°C, the holding time is 60 minutes, and the quenching liquid is PAG quenching liquid.

[0017] The medium-temperature hot rolling specifically refers to the following: after quenching, the material is heated and then rolled in 4 passes, wherein the heating refers to heating to 480°C, and the cumulative rolling amount is 60%.

[0018] The tempering process specifically involves heating the material that has undergone medium-temperature hot rolling to 400°C and then cooling it to room temperature. The heating process is described as heating to 400°C and the cooling rate is 0.5°C / s.

[0019] The cold heading process specifically involves: placing the pretreated material into a cold heading machine and forming it with an upper mold; the cold heading speed is 5 mm / s; and the lubrication method of the cold heading machine is phosphating and saponification.

[0020] The low-temperature tempering specifically involves heating and holding the cold-forged material at 150°C, followed by air cooling to room temperature. The holding time is 30 minutes.

[0021] The shallow cooling process is as follows: the material that has been tempered at low temperature is cooled and kept at a certain temperature, and then restored to room temperature in air cooling. The cooling refers to dropping to -80°C, and the holding time is 60 minutes.

[0022] The elemental composition of the gear steel is: C 0.13%, Cr 3.3%, Ni 6%, Co 13%, Mo 1.2%, V 0.08%, Si 0.03%, Al 0.02%, with the remainder being Fe.

[0023] Example 2: Cold heading process for toothed parts, the cold heading process for toothed parts includes the following steps: raw material quenching—medium-temperature hot rolling—tempering to obtain pretreated material—cold heading treatment—low-temperature tempering—shallow cooling treatment.

[0024] The raw material quenching process specifically involves heating the gear steel and holding it at that temperature, then cooling it to room temperature using a quenching liquid. The heating temperature is 980°C, the holding time is 75 minutes, and the quenching liquid is PAG quenching liquid.

[0025] The medium-temperature hot rolling specifically refers to the following: after quenching, the material is heated and then rolled in 5 passes, wherein the heating refers to heating to 540°C, and the cumulative rolling amount is 70%.

[0026] The tempering process specifically involves heating the material that has undergone medium-temperature hot rolling to a temperature of 425°C and then cooling it to room temperature. The heating process is described as heating to 425°C and the cooling rate is 0.8°C / s.

[0027] The cold heading process specifically involves: the pre-treated material being placed into a cold heading machine and formed by an upper mold; the cold heading speed is 10 mm / s; and the lubrication method of the cold heading machine is phosphating and saponification.

[0028] The low-temperature tempering specifically involves heating and holding the cold-forged material at that temperature, followed by air cooling to room temperature. The heating refers to raising the temperature to 200°C, and the holding time is 45 minutes.

[0029] The shallow cooling process is as follows: the material that has been tempered at low temperature is cooled and kept at a certain temperature, and then restored to room temperature in air cooling. The cooling refers to dropping to -70°C, and the holding time is 90 minutes.

[0030] The elemental composition of the gear steel is: C 0.14%, Cr 3.45%, Ni 7.6%, Co 14%, Mo 1.4%, V 0.1%, Si 0.04%, Al 0.03%, with the remainder being Fe.

[0031] Example 3: Cold heading process for toothed parts, the cold heading process for toothed parts includes the following steps: raw material quenching—medium-temperature hot rolling—tempering to obtain pretreated material—cold heading treatment—low-temperature tempering—shallow cooling treatment.

[0032] The raw material quenching process specifically involves heating the gear steel and holding it at that temperature, then cooling it to room temperature with a quenching liquid. The heating temperature is 1000℃, the holding time is 90 minutes, and the quenching liquid is PAG quenching liquid.

[0033] The medium-temperature hot rolling process specifically involves: after quenching, the material is heated and then rolled in 6 passes, where the heating refers to heating to 600°C, and the cumulative rolling amount is 80%.

[0034] The tempering process specifically involves heating the material that has undergone medium-temperature hot rolling to 450°C and then cooling it to room temperature. The heating rate is 1°C / s.

[0035] The cold heading process specifically involves: placing the pretreated material into a cold heading machine and forming it with an upper mold; the cold heading speed is 15 mm / s; and the lubrication method of the cold heading machine is phosphating and saponification.

[0036] The low-temperature tempering specifically involves heating and holding the material after cold heading, followed by air cooling to room temperature. The heating refers to raising the temperature to 250°C, and the holding time is 60 minutes.

[0037] The shallow cooling process is as follows: the material that has been tempered at low temperature is cooled and kept at a certain temperature, and then restored to room temperature in air cooling. The cooling refers to dropping to -60°C, and the holding time is 120 minutes.

[0038] The elemental composition of the gear steel is: C 0.15%, Cr 3.6%, Ni 9.6%, Co 15%, Mo 1.6%, V 0.12%, Si 0.05%, Al 0.04%, with the remainder being Fe.

[0039] Comparative Example 1: Based on Example 2, the heating temperature during the raw material quenching process was adjusted to 1200℃, while other conditions remained the same as in Example 2.

[0040] Comparative Example 2: Based on Example 2, the heating temperature during the medium-temperature hot rolling process was adjusted to 650°C, while other conditions remained the same as in Example 2.

[0041] Comparative Example 3: Based on Example 2, the heating temperature during the medium-temperature hot rolling process was adjusted to 400°C, while other conditions remained the same as in Example 2.

[0042] Comparative Example 4: Based on Example 2, the cumulative deformation during the medium-temperature hot rolling process was adjusted to 90%, while other conditions remained the same as in Example 2.

[0043] Comparative Example 5: Based on Example 2, the cumulative deformation during the medium-temperature hot rolling process was adjusted to 50%, while other conditions remained the same as in Example 2.

[0044] Comparative Example 6: Based on Example 2, the cold heading process of the toothed part includes the following steps: raw material quenching - tempering to obtain pretreated material - cold heading treatment - low temperature tempering - shallow cooling treatment.

[0045] The raw material quenching process specifically involves heating the gear steel and holding it at that temperature, then cooling it to room temperature using a quenching liquid. The heating temperature is 980°C, the holding time is 75 minutes, and the quenching liquid is PAG quenching liquid.

[0046] The tempering process specifically involves heating the quenched material to 425°C and then cooling it to room temperature. The heating rate is 0.8°C / s.

[0047] The cold heading process specifically involves: the pre-treated material being placed into a cold heading machine and formed by an upper mold; the cold heading speed is 10 mm / s; and the lubrication method of the cold heading machine is phosphating and saponification.

[0048] The low-temperature tempering specifically involves heating and holding the cold-forged material at that temperature, followed by air cooling to room temperature. The heating refers to raising the temperature to 200°C, and the holding time is 45 minutes.

[0049] The shallow cooling process is as follows: the material that has been tempered at low temperature is cooled and kept at a certain temperature, and then restored to room temperature in air cooling. The cooling refers to dropping to -70°C, and the holding time is 90 minutes.

[0050] The elemental composition of the gear steel is: C 0.14%, Cr 3.45%, Ni 7.6%, Co 14%, Mo 1.4%, V 0.1%, Si 0.04%, Al 0.03%, with the remainder being Fe.

[0051] Comparative Example 7: Based on Example 2, the cold heading process of the toothed part includes the following steps: raw material quenching - medium-temperature hot rolling - cold heading treatment - low-temperature tempering - shallow cooling treatment.

[0052] The raw material quenching process specifically involves heating the gear steel and holding it at that temperature, then cooling it to room temperature using a quenching liquid. The heating temperature is 980°C, the holding time is 75 minutes, and the quenching liquid is PAG quenching liquid.

[0053] The medium-temperature hot rolling specifically refers to the following: after quenching, the material is heated and then rolled in 5 passes, wherein the heating refers to heating to 540°C, and the cumulative rolling amount is 70%.

[0054] The cold heading process specifically involves: the material after medium-temperature hot rolling is placed into a cold heading machine and formed by an upper die; the cold heading speed is 10 mm / s; and the lubrication method of the cold heading machine is phosphating and saponification.

[0055] The low-temperature tempering specifically involves heating and holding the cold-forged material at that temperature, followed by air cooling to room temperature. The heating refers to raising the temperature to 200°C, and the holding time is 45 minutes.

[0056] The shallow cooling process is as follows: the material that has been tempered at low temperature is cooled and kept at a certain temperature, and then restored to room temperature in air cooling. The cooling refers to dropping to -70°C, and the holding time is 90 minutes.

[0057] The elemental composition of the gear steel is: C 0.14%, Cr 3.45%, Ni 7.6%, Co 14%, Mo 1.4%, V 0.1%, Si 0.04%, Al 0.03%, with the remainder being Fe.

[0058] Comparative Example 8: Based on Example 2, the temperature rise during the tempering process before cold heading was adjusted to 500°C, while other conditions remained the same as in Example 2.

[0059] Comparative Example 9: Based on Example 2, the temperature rise during the tempering process before cold heading was adjusted to 350°C, while other conditions remained the same as in Example 2.

[0060] Comparative Example 10: Based on Example 2, the cold heading rate during the cold heading process was adjusted to 20 mm / s, while other conditions remained the same as in Example 2.

[0061] Performance testing: The toothed parts prepared in Examples 1-3 and Comparative Examples 1-10 were used as samples. The surface of the samples was observed for cracks and the results were statistically analyzed. The samples were comprehensively measured using a gear testing instrument and the accuracy grade was determined according to GB / T 10095 (ISO1328). The pretreated materials of Examples 1-3 and Comparative Examples 1-10 before cold heading were used as samples. The microstructure and thickness of the hardened layer of the samples were observed using an optical microscope and a GeminiSEM 300 scanning electron microscope. The microhardness was tested using an HVS-1000A Vickers hardness tester (specifically, measurements were taken every 0.3 mm along the depth direction of the cross section, and the average value was taken for the same depth, with a load of 0.98 N and a holding time of 10 s) to determine the thickness ratio between the hardened layer and the tough layer.

[0062] The test results are shown in Table 1.

[0063] Table 1 Test Results: Example 1 No cracks 5 1:1.5 Example 2 No cracks 4 1.3:1.5 Example 3 No cracks 5 1.3:2 Comparative Example 1 Cracks account for 6.5% of the total area. 6 1.5:1.2 Comparative Example 2 No cracks 7 1:2 Comparative Example 3 The crack area accounts for 2.7%. 6 1.3:1 Comparative Example 4 No cracks 7 1.1:2 Comparative Example 5 The crack area accounts for 1.3%. 6 1.5:1.2 Comparative Example 6 Cracks accounted for 6.9% of the total area. 6 2:1 Comparative Example 7 Crack area accounts for 5.1% 6 2.2:1.3 Comparative Example 8 No cracks 7 1.5:2.6 Comparative Example 9 The crack area accounts for 0.5%. 6 1.8:1.1 Comparative Example 10 The crack area accounts for 3.5%. 7 1.3:1.5 Note: The smaller the level, the higher the precision.

[0064] A comprehensive analysis of the data in Table 1 shows that the toothed parts prepared in Examples 1-3 have no surface cracks, an accuracy grade of 4 or 5, and a thickness ratio of the hardened layer to the tough layer of 1-1.3:1.5-2, with Example 2 exhibiting the highest accuracy. In Comparative Example 1, increasing the quenching temperature coarsens the martensite structure, increasing its brittleness. This resulted in cracking even with a constant cold heading rate. Furthermore, the large amount of coarsened martensite hindered the precipitation of austenite, reducing toughness and further increasing the proportion of crack area. Correspondingly, the thickness ratio of the hardened layer to the tough layer also increased. Since the generation of numerous cracks provides space for the shrinkage or expansion of the part itself, the accuracy decreased. In Comparative Examples 2-3, the medium-temperature hot rolling temperature was increased or decreased. When the temperature was increased, the thickness of the tough layer increased. Although it possessed good toughness and no cracks, during the cold heading process, the large proportion of the tough layer thickness hindered the transmission of dispersed force to the internal hardened layer, causing springback and significantly reducing accuracy. When the temperature was decreased, the thickness of the hardened layer increased. Insufficient toughness leads to cracking, resulting in decreased precision. Comparative Examples 4-5, by increasing or decreasing the deformation during medium-temperature hot rolling, similarly affect the thickness ratio of the hardened layer to the toughened layer, causing cracking and a decrease in precision. Comparative Examples 6-7, by removing medium-temperature hot rolling or tempering from the process, result in a decrease in the toughened layer thickness, leading to cracking and a decrease in precision. Comparative Examples 8-9, by increasing or decreasing the tempering temperature, affect the thickness of the toughened layer due to the increase or decrease in austenite and the refinement of M2C carbides, resulting in either a decrease or increase in the toughened layer thickness, causing cracking and a decrease in precision. Comparative Example 10, by increasing the cold heading rate during the cold heading process, creates a large impact force exceeding the strain range of the toughened layer, causing the material to crack. In summary, the medium-temperature hot rolling step and its temperature, deformation, and the tempering step and its temperature all affect the thickness ratio of the hardened layer to the toughened layer. Furthermore, it can be observed that the toothed part exhibits optimal performance when the thickness ratio of the hardened layer to the toughened layer is 1.3:1.5.

[0065] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A cold heading process for toothed parts, characterized in that, The cold heading process of the toothed part includes the following steps: raw material quenching—medium-temperature hot rolling—tempering to obtain pretreated material—cold heading treatment—low-temperature tempering—shallow cooling treatment, wherein the thickness ratio between the hardened layer and the tough layer of the pretreated material is 1-1.3:1.5-2.

2. The cold heading process for toothed parts according to claim 1, characterized in that, The quenching of the raw material specifically involves heating the gear steel and holding it at that temperature, then cooling it to room temperature with a quenching liquid. The heating temperature is 950-1000℃, the holding time is 60-90 minutes, and the quenching liquid is PAG quenching liquid.

3. The cold heading process for toothed parts according to claim 1, characterized in that, The medium-temperature hot rolling process specifically involves: after quenching, the material is heated and then rolled in 4-6 passes, where the temperature rises to 480-600℃ and the cumulative rolling amount is 60-80%.

4. The cold heading process for toothed parts according to claim 1, characterized in that, The tempering process specifically involves heating the material that has undergone medium-temperature hot rolling to a temperature of 400-450°C and then cooling it to room temperature. The heating process refers to heating the material to 400-450°C and the cooling rate is 0.5-1°C / s.

5. The cold heading process for toothed parts according to claim 1, characterized in that, The cold heading process specifically involves: placing the pretreated material into a cold heading machine and forming it with an upper mold; the cold heading speed is 5-15 mm / s; and the lubrication method of the cold heading machine is phosphating and saponification.

6. The cold heading process for toothed parts according to claim 1, characterized in that, The low-temperature tempering specifically involves heating and holding the cold-forged material at a temperature of 150-250°C, followed by air cooling to room temperature. The heating refers to raising the temperature to 150-250°C, and the holding time is 30-60 minutes.

7. The cold heading process for toothed parts according to claim 1, characterized in that, The shallow cooling process is as follows: the material that has been tempered at low temperature is cooled and kept at a certain temperature, and then restored to room temperature in air cooling. The cooling refers to dropping to -80~-60℃, and the holding time is 60-120 minutes.

8. The cold heading process for toothed parts according to claim 2, characterized in that, The elemental composition of the gear steel is: C 0.13-0.15%, Cr 3.3-3.6%, Ni 6-9.6%, Co 13-15%, Mo 1.2-1.6%, V 0.08-0.12%, Si 0.03-0.05%, Al 0.02-0.04%, with the remainder being Fe.