A composite surface modification method to improve the service performance of 42CrMo4 heavy-duty gears

Abstract

The present invention belongs to the technical field of metal component surface treatment, and specifically relates to a composite surface modification method for improving the service performance of 42CrMo4 heavy-duty gears. The method involves placing the quenched and tempered 42CrMo4 heavy-duty gears into a vacuum ion nitriding furnace for ion nitriding. After nitriding, a trace amount of air is introduced for oxidation at a temperature of 370°C to 430°C for a holding time of 1 to 4 hours. After oxidation, hydrogen is introduced for hydrogen sputtering at a temperature of 370°C to 430°C for a holding time of 1 to 4 hours. After sputtering, the gears are cooled to room temperature in the furnace to obtain a nitrided layer structure with minimal white layer. The beneficial effects of the present invention are as follows: through the composite treatment of ion nitriding, oxidation, and hydrogen sputtering, the white layer on the surface of the heavy-duty gears is reduced, the toughness of the nitrided layer is improved, and thus the premature failure of the gears under heavy-load impact service environments is avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of surface treatment of metal parts, and in particular relates to a composite surface modification method for improving the service performance of 42CrMo4 heavy-duty gears. Background Art

[0002] Ion nitriding is a clean, efficient, and pollution-free surface modification technology. Heavy-duty gears undergo ion nitriding, forming a nitrided layer consisting of a surface white layer and a subsurface diffusion layer. Due to the brittleness of the white layer, it is prone to localized cracking and even shedding when subjected to heavy loads, leading to premature failure of the heavy-duty gears. Currently, grinding is often used to thin the white layer in engineering projects. However, this method is challenging due to its high hardness, making it difficult to grind, and the difficulty in precisely controlling the amount of grinding.

[0003] The present invention adopts a composite treatment method of "ion nitriding + post-oxidation + hydrogen sputtering" to achieve the remarkable effect of thinning the surface white bright layer, improving the toughness of the nitriding layer, and improving the service performance of the gear without reducing the total thickness of the nitriding layer and slightly increasing it. Summary of the Invention

[0004] Based on the problems pointed out in the background technology section, the present invention provides a composite surface modification method for improving the service performance of 42CrMo4 heavy-duty gears. The specific method is: "ion nitriding + post-oxidation + hydrogen sputtering" composite surface modification method to solve the problem of early failure of gears under heavy-load impact conditions.

[0005] The technical solution adopted by the present invention based on the above-mentioned objectives is: a composite surface modification method for improving the service performance of 42CrMo4 heavy-duty gears, comprising the following steps:

[0006] (1) Place the 42CrMo4 heavy-duty gear that has been quenched and tempered on the workpiece table in the LDMC-8CL vacuum ion nitriding furnace and seal the furnace cover;

[0007] (2) Turn on the power supply, use a mechanical pump to evacuate the furnace for 0.5 h until the pressure inside the furnace is less than 25 Pa, fine-tune the voltage to 700 V and the current to 3 A to start a sparse arc, introduce hydrogen at a flow rate of 500 mL / min, adjust the voltage to 660 V and the current to 2.5 A to stabilize the arc in the ion nitriding furnace, and perform hydrogen sputtering for 0.5 h to clean impurities on the gear surface;

[0008] (3) After the sputtering is completed, nitrogen is introduced at a flow rate of 175 mL / min, and the hydrogen flow rate is adjusted to 525 mL / min. The temperature in the furnace is waited to rise to the set value of 470°C to 530°C, and the atmosphere pressure in the furnace is set to be maintained at 450 Pa to 550 Pa. The temperature is kept for 3 h to 8 h, and then the ion nitriding stage is entered;

[0009] (4) After nitriding is completed, turn off nitrogen and hydrogen, introduce air at a flow rate of 4L / min, wait until the temperature drops to the set value of 370℃~430℃, and the pressure reaches 300Pa~400Pa, keep warm for 1h~4h, and then carry out oxidation treatment;

[0010] (5) After the oxidation is completed, the oxygen is turned off and hydrogen is introduced at a flow rate of 500 mL / min. After the temperature reaches 370°C to 430°C, it is kept warm for 1h to 4h and then enters the hydrogen sputtering stage;

[0011] (6) Turn off the gas source, disconnect the power supply, wait for the gear to cool to room temperature along with the furnace, then open the gas valve to make the air pressure inside and outside the furnace the same;

[0012] (7) Open the furnace cover and take out the gear.

[0013] The beneficial effect of the present invention is: through the "ion nitriding + post-oxidation + hydrogen sputtering" composite surface modification method, that is, after the ion nitriding is completed, a trace amount of air is introduced into the furnace, oxidation is carried out, and then hydrogen is introduced and sputtering is carried out, so as to obtain a nitrided layer structure with little white bright layer and an effective hardened layer of the required thickness.

[0014] The method of the present invention not only effectively thins the white bright layer on the gear surface, but also ensures the thickness of the effective hardened layer, thereby ensuring good service performance of the gear. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a cross-sectional microhardness analysis diagram of 42CrMo4 heavy-duty gears after conventional ion nitriding and treatment with different oxidation and sputtering times (corresponding to Examples 1-2 and 1-5);

[0016] Figure 2 This is the surface indentation morphology of 42CrMo4 heavy-duty gear after ion nitriding treatment at 500℃ for 5h;

[0017] Figure 3 This is the surface indentation morphology of a 42CrMo4 heavy-duty gear after ion nitriding at 500°C for 5 hours, oxidation at 400°C for 1 hour, and hydrogen sputtering at 400°C for 1 hour (i.e., Example 1);

[0018] Figure 4 This is the surface indentation morphology of a 42CrMo4 heavy-duty gear after ion nitriding at 500°C for 5 hours, oxidation at 400°C for 2 hours, and hydrogen sputtering at 400°C for 1 hour (i.e., Example 2);

[0019] Figure 5 This is the surface indentation morphology of a 42CrMo4 heavy-duty gear after ion nitriding at 500°C for 5 hours, oxidation at 400°C for 4 hours, and hydrogen sputtering at 400°C for 1 hour (i.e., Example 3);

[0020] Figure 6 This is the surface indentation morphology of a 42CrMo4 heavy-duty gear after ion nitriding at 500°C for 5 hours, oxidation at 400°C for 2 hours, and hydrogen sputtering at 400°C for 2 hours (i.e., Example 4);

[0021] Figure 7 This is a surface indentation morphology of a 42CrMo4 heavy-duty gear after ion nitriding at 500°C for 5 hours, oxidation at 400°C for 2 hours, and hydrogen sputtering at 400°C for 4 hours (i.e., Example 5). DETAILED DESCRIPTION

[0022] The present invention will now be further described with reference to specific examples. The following examples are intended to illustrate the present invention rather than to further limit the present invention.

[0023] Example 1

[0024] (1) After quenching and tempering, the 42CrMo4 heavy-duty gear is placed on the workpiece table in the LDMC-8CL vacuum ion nitriding furnace and the furnace cover is sealed.

[0025] (2) Turn on the power supply, use a mechanical pump to evacuate the furnace for 0.5 h until the pressure inside the furnace is less than 25 Pa, fine-tune the voltage to 650 V and the current to 2 A to start a sparse arc, introduce hydrogen at a flow rate of 500 mL / min, adjust the voltage to 660 V and the current to 2.5 A to stabilize the arc in the ion nitriding furnace, perform hydrogen sputtering for 0.5 h to clean impurities on the gear surface.

[0026] (3) After sputtering is completed, nitrogen gas is introduced at a flow rate of 175 mL / min, and the hydrogen flow rate is set to 525 mL / min. After the temperature in the furnace rises to the set temperature of 500°C, it is kept warm for 5 hours and then enters the ion nitriding stage.

[0027] (4) After nitriding is completed, nitrogen and hydrogen are turned off, and air with a flow rate of 4L / min is introduced. After the temperature reaches the set value of 400℃ and the pressure reaches 300Pa, it is kept warm for 1h and then enters the oxidation treatment stage.

[0028] (5) After the oxidation is completed, the oxygen is turned off and hydrogen is introduced at a flow rate of 500 mL / min. After the temperature reaches 400°C, it is kept warm for 1 hour and then enters the hydrogen sputtering stage.

[0029] (6) Turn off the gas source, disconnect the power supply, wait for the gear to cool to room temperature along with the furnace, open the gas valve to make the air pressure inside and outside the furnace consistent.

[0030] (7) Hardness and toughness analysis were performed using a HXD-1000TMC Vickers hardness tester.

[0031] Example 2

[0032] (1) After quenching and tempering, the 42CrMo4 heavy-duty gear is placed on the workpiece table in the LDMC-8CL vacuum ion nitriding furnace and the furnace cover is sealed.

[0033] (2) Turn on the power supply, use a mechanical pump to evacuate the furnace for 0.5 h until the pressure inside the furnace is less than 25 Pa, fine-tune the voltage to 650 V and the current to 2 A to start a sparse arc, introduce hydrogen at a flow rate of 500 mL / min, adjust the voltage to 660 V and the current to 2.5 A to stabilize the arc in the ion nitriding furnace, perform hydrogen sputtering for 0.5 h to clean impurities on the gear surface.

[0034] (3) After sputtering is completed, nitrogen gas is introduced at a flow rate of 175 mL / min, and the hydrogen flow rate is set to 525 mL / min. After the temperature in the furnace rises to the set temperature of 500°C, it is kept warm for 5 hours and then enters the ion nitriding stage.

[0035] (4) After nitriding is completed, nitrogen and hydrogen are turned off, and air with a flow rate of 4L / min is introduced. After the temperature reaches the set value of 400℃ and the pressure reaches 300Pa, it is kept warm for 2h and enters the oxidation treatment stage.

[0036] (5) After the oxidation is completed, the oxygen is turned off and hydrogen is introduced at a flow rate of 500 mL / min. After the temperature reaches 400°C, it is kept warm for 1 hour and then enters the hydrogen sputtering stage.

[0037] (6) Turn off the gas source, disconnect the power supply, wait for the gear to cool to room temperature along with the furnace, open the gas valve to make the air pressure inside and outside the furnace consistent.

[0038] (7) Hardness and toughness analysis were performed using a HXD-1000TMC Vickers hardness tester.

[0039] Example 3

[0040] (1) After quenching and tempering, the 42CrMo4 heavy-duty gear is placed on the workpiece table in the LDMC-8CL vacuum ion nitriding furnace and the furnace cover is sealed.

[0041] (2) Turn on the power supply, use a mechanical pump to evacuate the furnace for 0.5 h until the pressure inside the furnace is less than 25 Pa, fine-tune the voltage to 650 V and the current to 2 A to start a sparse arc, introduce hydrogen at a flow rate of 500 mL / min, adjust the voltage to 660 V and the current to 2.5 A to stabilize the arc in the ion nitriding furnace, perform hydrogen sputtering for 0.5 h to clean impurities on the gear surface.

[0042] (3) After sputtering is completed, nitrogen gas is introduced at a flow rate of 175 mL / min, and the hydrogen flow rate is set to 525 mL / min. After the temperature in the furnace rises to the set temperature of 500°C, it is kept warm for 5 hours and then enters the ion nitriding stage.

[0043] (4) After nitriding is completed, nitrogen and hydrogen are turned off, and air with a flow rate of 4L / min is introduced. After the temperature reaches the set value of 400℃ and the pressure reaches 300Pa, it is kept warm for 4 hours and then enters the oxidation treatment stage.

[0044] (5) After the oxidation is completed, the oxygen is turned off and hydrogen is introduced at a flow rate of 500 mL / min. After the temperature reaches 400°C, it is kept warm for 1 hour and then enters the hydrogen sputtering stage.

[0045] (6) Turn off the gas source, disconnect the power supply, wait for the gear to cool to room temperature along with the furnace, open the gas valve to make the air pressure inside and outside the furnace consistent.

[0046] (7) Hardness and toughness analysis were performed using a HXD-1000TMC Vickers hardness tester.

[0047] Example 4

[0048] (1) After quenching and tempering, the 42CrMo4 heavy-duty gear is placed on the workpiece table in the LDMC-8CL vacuum ion nitriding furnace and the furnace cover is sealed.

[0049] (2) Turn on the power supply, use a mechanical pump to evacuate the furnace for 0.5 h until the pressure inside the furnace is less than 25 Pa, fine-tune the voltage to 650 V and the current to 2 A to start a sparse arc, introduce hydrogen at a flow rate of 500 mL / min, adjust the voltage to 660 V and the current to 2.5 A to stabilize the arc in the ion nitriding furnace, perform hydrogen sputtering for 0.5 h to clean impurities on the gear surface.

[0050] (3) After sputtering is completed, nitrogen gas is introduced at a flow rate of 175 mL / min, and the hydrogen flow rate is set to 525 mL / min. After the temperature in the furnace rises to the set temperature of 500°C, it is kept warm for 5 hours and then enters the ion nitriding stage.

[0051] (4) After nitriding is completed, nitrogen and hydrogen are turned off, and air with a flow rate of 4L / min is introduced. After the temperature reaches the set value of 400℃ and the pressure reaches 300Pa, it is kept warm for 2h and enters the oxidation treatment stage.

[0052] (5) After the oxidation is completed, the oxygen is turned off and hydrogen is introduced at a flow rate of 500 mL / min. After the temperature reaches 400°C, it is kept warm for 2 hours and then enters the hydrogen sputtering stage.

[0053] (6) Turn off the gas source, disconnect the power supply, wait for the gear to cool to room temperature along with the furnace, open the gas valve to make the air pressure inside and outside the furnace consistent.

[0054] (7) Hardness and toughness analysis were performed using a HXD-1000TMC Vickers hardness tester.

[0055] Example 5

[0056] (1) After quenching and tempering, the 42CrMo4 heavy-duty gear is placed on the workpiece table in the LDMC-8CL vacuum ion nitriding furnace and the furnace cover is sealed.

[0057] (2) Turn on the power supply, use a mechanical pump to evacuate the furnace for 0.5 h until the pressure inside the furnace is less than 25 Pa, fine-tune the voltage to 650 V and the current to 2 A to start a sparse arc, introduce hydrogen at a flow rate of 500 mL / min, adjust the voltage to 660 V and the current to 2.5 A to stabilize the arc in the ion nitriding furnace, perform hydrogen sputtering for 0.5 h to clean impurities on the gear surface.

[0058] (3) After sputtering is completed, nitrogen gas is introduced at a flow rate of 175 mL / min, and the hydrogen flow rate is set to 525 mL / min. After the temperature in the furnace rises to the set temperature of 500°C, it is kept warm for 5 hours and then enters the ion nitriding stage.

[0059] (4) After nitriding is completed, nitrogen and hydrogen are turned off, and air with a flow rate of 4L / min is introduced. After the temperature reaches the set value of 400℃ and the pressure reaches 300Pa, it is kept warm for 2h and enters the oxidation treatment stage.

[0060] (5) After the oxidation is completed, the oxygen is turned off and hydrogen is introduced at a flow rate of 500 mL / min. After the temperature reaches 400°C, it is kept warm for 4 hours and then enters the hydrogen sputtering stage.

[0061] (6) Turn off the gas source, disconnect the power supply, wait for the gear to cool to room temperature along with the furnace, open the gas valve to make the air pressure inside and outside the furnace consistent.

[0062] (7) Hardness and toughness analysis were performed using a HXD-1000TMC Vickers hardness tester.

[0063] Comparative Example 1

[0064] (1) After quenching and tempering, the 42CrMo4 heavy-duty gear is placed on the workpiece table in the LDMC-8CL vacuum ion nitriding furnace and the furnace cover is sealed.

[0065] (2) Turn on the power supply, use a mechanical pump to evacuate the furnace for 0.5 h until the pressure inside the furnace is less than 25 Pa, fine-tune the voltage to 650 V and the current to 2 A to start a sparse arc, introduce hydrogen at a flow rate of 500 mL / min, adjust the voltage to 660 V and the current to 2.5 A to stabilize the arc in the ion nitriding furnace, perform hydrogen sputtering for 0.5 h to clean impurities on the gear surface.

[0066] (3) After sputtering is completed, nitrogen gas is introduced at a flow rate of 175 mL / min, and the hydrogen flow rate is set to 525 mL / min. After the temperature in the furnace rises to the set value of 500°C, it is kept warm for 5 hours and then enters the ion nitriding stage.

[0067] (4) After nitriding is completed, nitrogen and hydrogen are turned off, and air with a flow rate of 4L / min is introduced. After the temperature reaches the set value of 400℃ and the pressure reaches 300Pa, it is kept warm for 1h and then enters the oxidation treatment stage.

[0068] (5) Turn off the gas source, disconnect the power supply, wait for the gear to cool to room temperature along with the furnace, open the gas valve to make the air pressure inside and outside the furnace consistent.

[0069] (6) Hardness and toughness analysis were performed using a HXD-1000TMC Vickers hardness tester.

[0070] Comparative Example 2

[0071] (1) After quenching and tempering, the 42CrMo4 heavy-duty gear is placed on the workpiece table in the LDMC-8CL vacuum ion nitriding furnace and the furnace cover is sealed.

[0072] (2) Turn on the power supply, use a mechanical pump to evacuate the furnace for 0.5 h until the pressure inside the furnace is less than 25 Pa, fine-tune the voltage to 650 V and the current to 2 A to start a sparse arc, introduce hydrogen at a flow rate of 500 mL / min, adjust the voltage to 660 V and the current to 2.5 A to stabilize the arc in the ion nitriding furnace, perform hydrogen sputtering for 0.5 h to clean impurities on the gear surface.

[0073] (3) After sputtering is completed, nitrogen gas is introduced at a flow rate of 175 mL / min, and the hydrogen flow rate is set to 525 mL / min. After the temperature in the furnace rises to the set temperature of 500°C, it is kept warm for 5 hours and then enters the ion nitriding stage.

[0074] (4) After nitriding is completed, nitrogen and hydrogen are turned off, and air with a flow rate of 4L / min is introduced. After the temperature reaches the set value of 400℃ and the pressure reaches 300Pa, it is kept warm for 2h and enters the oxidation treatment stage.

[0075] (5) Turn off the gas source, disconnect the power supply, wait for the gear to cool to room temperature along with the furnace, open the gas valve to make the air pressure inside and outside the furnace consistent.

[0076] (6) Hardness and toughness analysis were performed using a HXD-1000TMC Vickers hardness tester.

[0077] Table 1 Comparative analysis of the carburized layer characteristics of 42CrMo4 heavy-duty gears after ion nitriding and composite treatment

[0078]

[0079] As can be seen from Table 1, the thickness of the white bright layer of the gear treated only with ion nitriding is 9.41 μm. The thickness of the white bright layer of the gear treated with ion nitriding + oxidation + hydrogen sputtering (Examples 1-5) gradually decreases with the increase of oxidation time and sputtering time. When the oxidation time is 2 hours and the sputtering time is 4 hours, the white bright layer disappears.

[0080] from Figure 1 As shown in Table 1, the surface hardness and effective hardened layer thickness of the gears (Examples 1-5) treated with ion nitriding + oxidation + hydrogen sputtering are improved compared with those treated with ion nitriding alone, ion nitriding + oxidation alone, and the surface hardness is as high as 825HV. 0.05 ;The maximum effective hardened layer thickness is 378μm.

[0081] contrast Figure 2 、 3 , 4, 5, 6, and 7, it can be clearly seen that after conventional ion nitriding treatment, obvious gear surface damage occurred around the indentation on the gear surface. However, with the increase of oxidation time and sputtering time, the degree of indentation damage on the gear surface gradually decreased. After oxidation at 400°C for 2h and hydrogen sputtering for 4h, no obvious indentation damage was observed around the gear surface, indicating that the toughness was significantly improved.

[0082] With the above-described preferred embodiments of the present invention as a guide, and with reference to the above description, relevant personnel are fully capable of making various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the contents of the specification and must be determined according to the scope of the claims.

Claims

1. A composite surface modification method for improving the service performance of 42CrMo4 heavy-duty gears, characterized in that: The specific steps of the method are as follows: (1) Place the 42CrMo4 gear after quenching and tempering on the workpiece table in the vacuum ion nitriding furnace and seal the furnace cover; turn on the power, use a mechanical pump to evacuate the vacuum, adjust the voltage and current to start the ignition, and introduce hydrogen for hydrogen sputtering to clean the gear surface; (2) After sputtering, nitrogen is introduced, the ratio of nitrogen and hydrogen is adjusted, and the atmosphere pressure in the furnace is set to be maintained at 450Pa~550Pa. After reaching the temperature of 470℃~530℃, the temperature is kept constant for ion nitriding; (3) After nitriding is completed, nitrogen and hydrogen are turned off and air is introduced for oxidation treatment, wherein the oxidation temperature is 370℃~430℃ and the holding time is 1h~4h; (4) After the oxidation is completed, the oxygen is turned off and hydrogen is introduced. After the temperature reaches 370℃~430℃, it is kept warm and hydrogen sputtering treatment is carried out for 1h~4h; (5) After hydrogen sputtering treatment, wait for the gear to cool to room temperature in the furnace and then take it out.

2. The composite surface modification method for improving the service performance of 42CrMo4 heavy-duty gears according to claim 1, characterized in that: In step (1), the vacuum is evacuated to a pressure less than 25 Pa; the operating voltage is 650V-700V; the operating current is 2A-3A; the hydrogen flow rate is 500mL / min; and the sputtering time is 0.5h.

3. The composite surface modification method for improving the service performance of 42CrMo4 heavy-duty gears according to claim 1, characterized in that: In step (2), the volume ratio of nitrogen to hydrogen is 1:3, the total flow rate of nitrogen and hydrogen is 700 mL / min, and the ion nitriding holding time is 3 h to 8 h.

4. The composite surface modification method for improving the service performance of 42CrMo4 heavy-duty gears according to claim 1, characterized in that: In step (3), the atmosphere pressure in the furnace is set to 300 Pa to 400 Pa, and the air flow rate is set to 4 L / min; in step (4), the hydrogen flow rate is set to 500 mL / min.

5. The composite surface modification method for improving the service performance of 42CrMo4 heavy-duty gears according to claim 1, characterized in that: The oxidation treatment temperature is 400° C., and the oxidation time is 2 hours; the hydrogen sputtering temperature is 400° C., and the hydrogen sputtering time is 2 hours.

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