A method for manufacturing a low-carbon alloy steel part

Abstract

The application relates to the technical field of bearings, in particular to a preparation method of a low-carbon alloy steel part, a preparation method of a low-carbon alloy steel part, which comprises the following steps: preparing a thin-wall stamping part of SCM415 material; performing chemical heat treatment on the thin-wall stamping part, and the heat treatment temperature is 830-860 DEG C; quenching the thin-wall stamping part after carbonitriding treatment by using quenching oil, and the oil temperature is controlled to be higher than 80 DEG C; performing tempering treatment on the quenched thin-wall stamping part, and the tempering temperature is 120 DEG C, and the time is 60 min; clamping the thin-wall stamping part after low-temperature tempering treatment and then performing tempering treatment, and then air cooling to obtain the low-carbon alloy steel part. After carbonitriding treatment, quenching and tempering treatment, the surface hardness of the obtained low-carbon alloy steel part reaches 670-810 HV1, the flatness is within 0.15 mm, and the microstructure is fine needle-shaped martensite and uniformly distributed point-shaped carbide / nitride, so that the technical indexes required by a flat thrust bearing are reached.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of bearings, in particular to a preparation method of a low-carbon alloy steel part. BACKGROUND

[0002] Flat thrust bearings are often used in automobile gearboxes, and bear large axial force and rotation speed during operation, so the bearings usually need to have high wear resistance and dimensional accuracy.

[0003] SCM415 material is a kind of low-carbon alloy steel, and the inner and outer rings of the thrust bearing adopt the material, which has excellent wear resistance after carbonitriding heat treatment, and is an ideal material for the shaft ring and the seat ring of the thrust bearing. After heat treatment, the microstructure is fine needle-shaped martensite and uniformly distributed point-shaped carbide / nitride, so that the material has very high strength and wear resistance. For the thrust bearing with a wall thickness of 0.8-1.5 mm and a diameter of 80-110 mm, it is difficult to achieve the technical index requirements of the hardness being higher than 670HV1, the microstructure being fine needle-shaped martensite and uniformly distributed point-shaped carbide / nitride, and the flatness being within 0.15 mm after heat treatment by using the general heat treatment method.

[0004] Therefore, it is of great significance for the use of the low-carbon alloy steel part to make the low-carbon alloy steel part formed by the SCM415 material after heat treatment meet the technical index requirements of the thrust bearing. SUMMARY

[0005] In order to meet the technical index requirements (the hardness being higher than 670HV1, the microstructure being fine needle-shaped martensite and uniformly distributed point-shaped carbide / nitride, and the flatness being within 0.15 mm after heat treatment) of the thrust bearing, the application provides a preparation method of a low-carbon alloy steel part.

[0006] The preparation method of the low-carbon alloy steel part adopts the following technical scheme:

[0007] The preparation method of the low-carbon alloy steel part comprises the following steps:

[0008] Part preparation: a thin-walled stamping part of SCM415 material;

[0009] Carbonitriding: the thin-walled stamping part is chemically heat-treated in a protective atmosphere environment, and the heat treatment temperature is 830-860 DEG C;

[0010] Quenching: the thin-walled stamping part after the carbonitriding treatment is quenched by using quenching oil, and the oil temperature is controlled to be higher than 80 DEG C;

[0011] Low-temperature tempering: the thin-walled stamping part after quenching is cleaned, and the cleaned thin-walled stamping part is subjected to tempering treatment, the tempering temperature is 120 DEG C, and the time is 60 min;

[0012] string clamp annealing: after low temperature annealing treatment, the thin-walled stamping part is clamped and then annealed, the annealing temperature is 240-260℃, the holding time is 180-240℃, and then air cooling to obtain a low-carbon alloy steel part.

[0013] By adopting the above technical scheme, after the thin-walled stamping part of SCM415 material is treated by carbonitriding combined with quenching and tempering, the temperature of each part of the thin-walled stamping part is reduced, thereby reducing the deformation amount of the thin-walled stamping part after heat treatment, the surface hardness of the obtained low-carbon alloy steel part reaches 670-810HV1, the flatness is within 0.15mm, and the microstructure is fine needle-shaped martensite and uniformly distributed point-shaped carbide / nitride, which meets the technical indexes required by the flat thrust bearing material.

[0014] In a specific embodiment, the protective atmosphere is a mixed gas of methanol, propane and ammonia in a volume ratio of 85:10:5.

[0015] By adopting the above technical scheme, the protective atmosphere can protect the thin-walled stamping part from oxidation and decarburization, and the heat treatment is completed in a reducing atmosphere, so that a bright surface without oxidation and decarburization can be obtained, the surface quality is improved, and the pickling, shot blasting or sand blasting process is omitted, thereby improving the operation efficiency and significantly reducing the production cost.

[0016] Propane combustion produces carbon dioxide and water, which can achieve good oxidation-free effect, but it cannot prevent decarburization; methanol produces a reducing mixed gas containing carbon monoxide, relatives and methane after high-temperature cracking or cracking, realizing oxidation-free and decarburization heating of the part during heat treatment, considering that the carbon potential of the cracking product is relatively low, other substances need to be added for supplementation; ammonia gas is decomposed into nitrogen and hydrogen after heating, and the two do not react with the heated part, which can save a large amount of pure hydrogen with high price. Through the synergistic effect of the above three protective gases, the oxidation and decarburization phenomena during chemical heat treatment of the part are ensured, and the surface quality and processing efficiency of the part are improved.

[0017] In a specific embodiment, during the carbonitriding, the chemical heat treatment of the thin-walled stamping part is divided into two stages, specifically: a strong penetration holding stage, the carbon potential is controlled to be 0.9%; a diffusion holding stage, the carbon potential is controlled to be 0.8%.

[0018] By adopting the technical scheme, the carbon potential of the atmosphere in the carbonitriding process is controlled to obtain the required carbon concentration on the surface of the steel piece and the carbon distribution from the surface to the inside. At a certain temperature, the carburizing capacity (carbon potential) of the carburizing gas is determined by the gas components (such as the proportion of carbon monoxide, carbon dioxide, water vapor, oxygen, etc.) contained therein. Usually, the content of a certain component (such as water vapor, carbon dioxide, oxygen) is measured to provide a signal to the control instrument, and the gas composition is adjusted in time to change the carbon potential in the furnace.

[0019] In a specific implementable embodiment, the chemical heat treatment time (T) is selected according to the product hardened layer depth requirement during the carbonitriding, T (min) = 450 x hardened layer depth (mm).

[0020] By adopting the technical scheme, the static load capacity of the general bearing depends on the depth of the hardened layer, and insufficient depth of the hardened layer will cause damage to the bearing core. When the hardness of the surface hardened layer of the bearing is lower than 660 HV, the static load capacity of the bearing decreases with the decrease of the hardness of the bearing surface. Therefore, the surface hardness of the hardened layer of the general bearing is higher than 660 HV, and the hardness gradually decreases to 510 HV with the increase of the depth of the hardened layer, and then rapidly decreases to the hardness of the core material; by controlling the time during the chemical heat treatment, products with different requirements can be obtained, and the product diversity is improved.

[0021] In a specific implementable embodiment, the thin-walled stamping piece is horizontally placed in the mesh belt furnace for chemical heat treatment during the carbonitriding.

[0022] By adopting the technical scheme, the mesh belt furnace runs more stably, the surface of the part after heat treatment in the mesh belt furnace is smoother, the hardness is more uniform, and the deformation is small; continuous production can be realized, the process parameters are easy to control, the sealing performance is good, the energy consumption of the controllable atmosphere is controllable, various preparation atmospheres or dripping atmospheres can be applied, carbonitriding can be realized, mass production and processing of parts can be realized, the production scale with high efficiency is realized, the whole process degree control is realized, and the automation precision is high.

[0023] In a specific implementable embodiment, the thin-walled stamping piece adopts graded quenching oil during quenching, and the maximum cooling speed is 75-90 ℃ / s.

[0024] By adopting the technical scheme, the workpiece heated after the step quenching time is firstly cooled in a medium slightly higher than the martensite transformation temperature, and then is rapidly transferred to oil to cool to room temperature before the austenite starts to decompose, so that the austenite is transformed into martensite organization, the cooling medium used in the process is called step quenching oil; the step quenching oil is prepared from high-oxidation-resistance and heat-stable base oil, generally has high flash point and viscosity, and contains an antioxidant, so that it has a long service life in a harsh working environment, and is mainly applied to large-diameter, thin-walled and complex-shaped bearings requiring small deformation, so that satisfactory hardenability and hardenability can be obtained, and cracking and deformation can be prevented.

[0025] In a specific implementable embodiment, when the string clamp is tempered, the thin-walled stamping part is clamped by a thick-walled clamp, and the clamping force is greater than 6 KN.

[0026] In a specific implementable embodiment, when the part is prepared, the method further comprises cleaning the thin-walled stamping part by using a vacuum hydrocarbon solvent.

[0027] By adopting the technical scheme, the cleaning treatment can remove cutting oil and iron filings and other dirt remaining on the surface of the thin-walled stamping part, so that the surface of the thin-walled stamping part reaches a certain cleanliness, and the surface hardness of the part after quenching has no soft spots and the appearance has no color spots.

[0028] In a specific implementable embodiment, when the part is prepared, the chemical composition of the SCM415 material is: C: 0.13-0.18wt%, Mn: 0.6-0.9wt%, Si: 0.15-0.35wt%, Ni≤0.25wt%, S≤0.03wt%, P≤0.03wt%, Cr: 0.9-1.2wt%, Mo: 0.15-0.25wt%.

[0029] By adopting the technical scheme, the SCM415 material contains low carbon content, C needs to form a large amount of carbides with the alloy, heat treatment forms high-carbon martensite, the content of which is controlled to be 0.13-0.18wt%; and Cr is selected as the main strengthening element, when the content of Cr is high to a certain extent, Cr can form dense oxides with oxygen, which can block the further occurrence of corrosion, thereby good corrosion resistance is generated, and the content thereof is preferably 0.9-1.2wt%; Mo can refine the structure and improve the toughness of the material, and the content thereof is preferably 0.15-0.25wt%; the addition of Si can improve the resistance to temper softening, so as to ensure sufficient heat resistance, and can also improve the bearing contact fatigue life in a contaminated lubricating environment, and excessive addition amount will bring defects such as pores, and the content thereof is preferably 0.15-0.35wt%; the addition of Mn can reduce the brittle phase of S element in the material, and can effectively ensure the carbonitriding and the quench hardenability of the core part, and the content thereof is preferably 0.6-0.9wt%; the addition of Ni can improve the toughness of the material, but excessive content of Ni will lead to a decrease in wear resistance, and the content thereof is controlled to be ≤0.25wt%. The SCM415 material has excellent wear resistance and corrosion resistance.

[0030] In a specific implementation scheme, the chemical composition of the SCM415 material further includes W: 0.3-0.5wt%.

[0031] By adopting the technical scheme, the addition of W can form WC particles with C in the material, which greatly improves the wear resistance of the material, and therefore a small amount of W can significantly improve the performance of the material, and excessive addition of W will easily form decarburized phases, which will greatly increase the brittleness of the material, and therefore the preferred addition amount of W is 0.3-0.5wt%.

[0032] In summary, the present application includes at least one of the following beneficial technical effects:

[0033] 1. The present application sets the heating temperature, carbon potential, ammonia flow, time and string clamping tempering and shaping temperature and time during the preparation process of the low-carbon alloy steel part, realizes the heat treatment of the thin-walled (0.8-1.5mm) and large-diameter (80-110mm) SCM415 material, so that the hardness of the material is greater than 670HV1, and the flatness is less than 0.15mm; and the heat-treated material has fine needle-shaped martensite and uniformly distributed point-shaped carbides / nitrides, so that the material has extremely high strength and wear resistance, and meets the technical indexes required by the flat thrust bearing;

[0034] 2. The protection atmosphere of the present application is a mixed gas of methanol, propane and ammonia, which ensures that there is no oxidation and decarburization phenomenon in the chemical heat treatment of the part, and improves the surface quality and treatment efficiency of the part;

[0035] 3. The chemical composition of the SCM415 material of the application includes a proper amount of W element, which can form WC particles with C in the material, greatly improving the wear resistance of the material. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 is a flow chart of the preparation method of the low-carbon alloy steel part of the application.

[0037] Figure 2 is a 5-fold metallographic photograph of the low-carbon alloy steel part of Example 1 of the application. DETAILED DESCRIPTION

[0038] The following is illustrated by examples and accompanying drawings. Figures 1-2 The application is further described in detail.

[0039] Example

[0040] Example 1

[0041] The material of this example is a thrust bearing of SCM415, with an outer diameter of φ95mm, a wall thickness of 1.0mm, a surface hardness requirement of 670-810HV1, and a flatness requirement of within 0.15mm; the metallographic structure is fine needle-shaped martensite and uniformly distributed point-shaped carbide / nitride.

[0042] The example of the application discloses a preparation method of a low-carbon alloy steel part, comprising the following steps:

[0043] S1, part preparation: preparing a thin-walled stamping part of SCM415, and the chemical composition of the SCM415 material is (JIS G4085-2008): C: 0.13-0.18wt%, Mn: 0.6-0.9wt%, Si: 0.15-0.35wt%, Ni≤0.25wt%, S≤0.03wt%, P≤0.03wt%, Cr: 0.9-1.2wt%, Mo: 0.15-0.25wt%, W: 0.3-0.5wt%; using a vacuum hydrocarbon solvent to clean the thin-walled stamping part to remove surface residual dirt;

[0044] S2, carbonitriding: placing the thin-walled stamping part uniformly and horizontally into a high-temperature mesh belt furnace for chemical heat treatment, with a temperature of 860℃, a furnace atmosphere of methanol, propane and ammonia in a volume ratio of 85:10:5, a methanol flow rate of 1700ml / min, a propane flow rate of 200ml / min, and an ammonia flow rate of 100ml / min; one-zone strong penetration for 50min, with a carbon potential controlled at 0.9%Cp; two-zone diffusion for 45min, with a carbon potential controlled at 0.8%Cp;

[0045] S3, quenching: the carbonitrided thin-walled stamping part is put into an oil tank for quenching, a fractional quenching oil of model EO-1 of Nanjing Zhounian New Product Technology Research Institute is adopted, the maximum cooling speed is 90 ℃ / s, the oil temperature is controlled at 100 ℃; the quenching oil is stirred at a low speed of 150 r / min, and a closed cooling tower is adopted for quenching cooling; the hot quenching oil is extracted from the bottom of the quenching oil tank, cooled through the closed cooling tower, and returned from the upper part of the quenching oil tank, so that the temperature of the oil tank is ensured within the set range, the thin-walled stamping part is uniformly cooled, and deformation is reduced;

[0046] S4, low-temperature tempering: the thin-walled stamping part after quenching is cleaned by using a vacuum carbon hydrogen solvent to remove residual oil stains on the surface; the cleaned thin-walled stamping part is tempered by using a box-type protective atmosphere tempering furnace, the tempering temperature is 120 ℃, and the time is 60 min, so that the part retains a part of residual stress;

[0047] S5, string clamp tempering: the thin-walled stamping part after low-temperature tempering is clamped by using a thick-wall clamp, the clamping force is 8 KN, and then the thin-walled stamping part is tempered in a tempering furnace to eliminate stress and reshape the thin-walled stamping part, the tempering temperature is 245 ℃, the holding time is 180 min, and the low-carbon alloy steel part is obtained after the tempering furnace is taken out and cooled in air.

[0048] Example 2

[0049] The material of the example is a thrust bearing of SCM415, the outer diameter is φ80 mm, the wall thickness is 0.8 mm, the surface hardness requirement is 670-810 HV1, and the flatness requirement is within 0.15 mm; the metallographic structure is fine needle-shaped martensite and uniformly distributed point-shaped carbide / nitride.

[0050] The example of the application discloses a preparation method of a low-carbon alloy steel part, which comprises the following steps:

[0051] S1, part preparation: a thin-walled stamping part of SCM415 is prepared, and the chemical composition of the SCM415 material is (JISG4085-2008): C: 0.13-0.18wt%, Mn: 0.6-0.9wt%, Si: 0.15-0.35wt%, Ni≤0.25wt%, S≤0.03wt%, P≤0.03wt%, Cr: 0.9-1.2wt%, Mo: 0.15-0.25wt%, and W: 0.3-0.5wt%; a vacuum carbon hydrogen solvent is used to clean the thin-walled stamping part to remove surface residual dirt;

[0052] S2, carbonitriding: the thin-walled stamping parts are uniformly and horizontally placed into a high-temperature mesh belt furnace for chemical heat treatment, the temperature is 845℃, the atmosphere in the furnace is: methanol, propane and ammonia gas in a volume ratio of 85:10:5, the methanol flow is 1700ml / min, the propane flow is 200ml / min, and the ammonia gas flow is 100ml / min; the first zone is strongly penetrated and kept for 40min, the carbon potential is controlled to be 0.9%Cp; the second zone is diffused and kept for 40min, the carbon potential is controlled to be 0.8%Cp;

[0053] S3, quenching: the thin-walled stamping parts after carbonitriding are placed into an oil tank for quenching, a step quenching oil with a maximum cooling speed of 75℃ / s is used, the oil temperature is controlled to be 90℃, the quenching oil is stirred at a low speed of 150r / min, and a closed cooling tower is used for quenching cooling, the hot quenching oil is extracted from the bottom of the quenching oil tank, cooled through the closed cooling tower, and returned to the upper part of the quenching oil tank, so that the temperature of the oil tank is ensured to be in a set range, the thin-walled stamping parts are uniformly cooled, and deformation is reduced;

[0054] S4, low-temperature tempering: the thin-walled stamping parts after quenching are cleaned by using a vacuum carbon hydrogen solvent, and residual oil stains on the surface are removed; the cleaned thin-walled stamping parts are tempered by using a box-type protective atmosphere tempering furnace, the tempering temperature is 120℃, the time is 60min, and a part of residual stress of the parts is reserved;

[0055] S5, string clamp tempering: the thin-walled stamping parts after low-temperature tempering are clamped by using a thick-wall clamp, the clamping force is 8KN, and the thin-walled stamping parts are tempered in a tempering furnace, stress is eliminated, and the thin-walled stamping parts are shaped, the tempering temperature is 260℃, the holding time is 180min, and the low-carbon alloy steel parts are obtained after the thin-walled stamping parts are cooled in air after being taken out of the furnace.

[0056] Example 3

[0057] The material of this example is a thrust bearing of SCM415, the outer diameter is φ108mm, the wall thickness is 1.5mm, the surface hardness requirement is 670-810HV1, the flatness requirement is within 0.15mm, the metallographic structure is fine needle-shaped martensite and uniformly distributed point-shaped carbide / nitride.

[0058] The example of the application discloses a preparation method of a low-carbon alloy steel part, which comprises the following steps:

[0059] S1, part preparation: prepare a thin-walled stamping part of SCM415, and the chemical composition of SCM415 material is (JIS G4085-2008): C: 0.13-0.18wt%, Mn: 0.6-0.9wt%, Si: 0.15-0.35wt%, Ni≤0.25wt%, S≤0.03wt%, P≤0.03wt%, Cr: 0.9-1.2wt%, Mo: 0.15-0.25wt%, W: 0.3-0.5wt%; the thin-walled stamping part is cleaned by vacuum carbon hydrogen solvent to remove surface residual dirt;

[0060] S2, carbonitriding: the thin-walled stamping part is uniformly placed horizontally in a high-temperature mesh belt furnace for chemical heat treatment, the temperature is 830℃, the furnace atmosphere is: methanol, propane and ammonia gas in a volume ratio of 85:10:5, the methanol flow is 1700ml / min, the propane flow is 200ml / min, and the ammonia gas flow is 100ml / min; the first zone is strongly penetrated for 60min, and the carbon potential is controlled to be 0.9%Cp; the second zone is diffused for 60min, and the carbon potential is controlled to be 0.8%Cp;

[0061] S3, quenching: the carbonitrided thin-walled stamping part is placed in an oil tank for quenching, a Nanjing Zhounian New Product Technology Institute type EO-2 graded quenching oil is used, the maximum cooling speed is 75℃ / s graded quenching oil, the oil temperature is controlled at 90℃; the quenching oil is stirred at a low speed of 150r / min, and a closed cooling tower is used for quenching cooling, the hot quenching oil is extracted from the bottom of the quenching oil tank, cooled through the closed cooling tower, and returned from the upper part of the quenching oil tank, so that the oil tank temperature is ensured within the set range, the thin-walled stamping part is cooled uniformly, and the deformation is reduced;

[0062] S4, low-temperature tempering: the above-mentioned quenched thin-walled stamping part is cleaned by vacuum carbon hydrogen solvent to remove the residual oil dirt on the surface; the cleaned thin-walled stamping part is tempered by a box-type protective atmosphere tempering furnace, the tempering temperature is 120℃, and the time is 60min, so that the part retains a part of residual stress;

[0063] S5, string clamp tempering: the above-mentioned low-temperature tempered thin-walled stamping part is clamped by a thick-walled clamp, the clamping force is 8KN, and then the part is tempered in a tempering furnace to eliminate stress and reshape the thin-walled stamping part, the tempering temperature is 240℃, the holding time is 240min, and the part is cooled in air after being taken out of the furnace to obtain a low-carbon alloy steel part.

[0064] Comparative example

[0065] Comparative example 1

[0066] The materials used in this comparative example are the same as those in Example 1, except that this comparative example discloses a method for preparing a low-carbon alloy steel part, including the following steps:

[0067] S1. Part Preparation: Prepare thin-walled stamped parts of grade SCM415, with the chemical composition of SCM415 material as follows (JISG4085-2008): C: 0.13-0.18wt%, Mn: 0.6-0.9wt%, Si: 0.15-0.35wt%, Ni≤0.25wt%, S≤0.03wt%, P≤0.03wt%, Cr: 0.9-1.2wt%, Mo: 0.15-0.25wt%, W: 0.3-0.5wt%. Clean the thin-walled stamped parts with a vacuum hydrocarbon solvent to remove residual dirt from the surface.

[0068] S2, Carbonitriding: Thin-walled stamped parts are uniformly and horizontally placed in a high-temperature mesh belt furnace for chemical heat treatment at 870℃. The furnace atmosphere consists of methanol, propane, and ammonia in a volume ratio of 80:10:10, with methanol flow rate of 1600 ml / min, propane flow rate of 200 ml / min, and ammonia flow rate of 200 ml / min. The first zone is held for strong carbonitriding for 50 min, and the second zone for diffusion for 45 min.

[0069] S3, Quenching: The carbonitrided thin-walled stamped parts are placed in an oil tank for quenching. The Nanjing Zhoulian New Product Technology Research Institute uses graded quenching oil of model EO-5, with a maximum cooling rate of 108℃ / s and an oil temperature controlled at 120℃. The quenching oil is stirred at a low speed of 150r / min and quenched by circulating it in a closed cooling tower. The hot quenching oil is drawn from the bottom of the quenching oil tank, cooled by the closed cooling tower, and then returned from the top of the quenching oil tank to ensure that the oil tank temperature is within the set range, ensuring uniform cooling of the thin-walled stamped parts and reducing deformation.

[0070] S4, Low-temperature tempering: The above-mentioned quenched thin-walled stamping parts are cleaned with vacuum hydrocarbon solvent to remove residual oil stains on their surface; the cleaned thin-walled stamping parts are tempered in a box-type protective atmosphere tempering furnace at a tempering temperature of 120℃ for 60 minutes to retain some residual stress in the parts.

[0071] S5, Clamping Tempering: The thin-walled stamping parts that have undergone low-temperature tempering are clamped with thick-walled clamps with a clamping force of 8KN, and then tempered in a tempering furnace to relieve stress and shape the thin-walled stamping parts. The tempering temperature is 235℃ and the holding time is 150min. After tempering, the parts are cooled in air to obtain low-carbon alloy steel parts.

[0072] Comparative Example 2

[0073] The materials used in this comparative example are the same as those in Example 2, except that this comparative example discloses a method for preparing a low-carbon alloy steel part, including the following steps:

[0074] S1. Part Preparation: Prepare thin-walled stamped parts of grade SCM415, with the chemical composition of SCM415 material as follows (JISG4085-2008): C: 0.13-0.18wt%, Mn: 0.6-0.9wt%, Si: 0.15-0.35wt%, Ni≤0.25wt%, S≤0.03wt%, P≤0.03wt%, Cr: 0.9-1.2wt%, Mo: 0.15-0.25wt%, W: 0.3-0.5wt%. Clean the thin-walled stamped parts with a vacuum hydrocarbon solvent to remove residual dirt from the surface.

[0075] S2, Carbonitriding: Thin-walled stamped parts are uniformly and horizontally placed in a high-temperature mesh belt furnace for chemical heat treatment at 845℃. The furnace atmosphere consists of methanol, propane, and ammonia in a volume ratio of 85:10:5, with methanol flow rate of 1700 ml / min, propane flow rate of 200 ml / min, and ammonia flow rate of 100 ml / min. The first zone is held at high temperature for 40 minutes with strong carbonitriding, and the carbon potential is controlled at 0.9% Cp. The second zone is held at high temperature for 40 minutes with diffusion, and the carbon potential is controlled at 0.8% Cp.

[0076] S3, Quenching: The carbonitrided thin-walled stamped parts are placed in an oil tank for quenching. The Nanjing Zhoulian New Product Technology Research Institute uses EO-2 graded quenching oil with a maximum cooling rate of 75℃ / s and the oil temperature is controlled at 90℃. The quenching oil is stirred at a low speed of 150r / min and quenched by circulating it in a closed cooling tower. The hot quenching oil is drawn from the bottom of the quenching oil tank, cooled by the closed cooling tower, and then returned from the top of the quenching oil tank to ensure that the oil tank temperature is within the set range, ensuring uniform cooling of the thin-walled stamped parts and reducing deformation.

[0077] S4, Low-temperature tempering: The above-mentioned quenched thin-walled stamping parts are cleaned with vacuum hydrocarbon solvent to remove residual oil stains on their surface; the cleaned thin-walled stamping parts are tempered in a box-type protective atmosphere tempering furnace at a tempering temperature of 120℃ for 120 minutes. After tempering, they are cooled in air to obtain low-carbon alloy steel parts.

[0078] Comparative Example 3

[0079] The materials used in this comparative example are the same as those in Example 3, except that this comparative example discloses a method for preparing a low-carbon alloy steel part, including the following steps:

[0080] S1, part preparation: a thin-walled stamping part of SCM415 is prepared, and the chemical composition of SCM415 material is (JIS G4085-2008): C: 0.13-0.18wt%, Mn: 0.6-0.9wt%, Si: 0.15-0.35wt%, Ni≤0.25wt%, S≤0.03wt%, P≤0.03wt%, Cr: 0.9-1.2wt%, Mo: 0.15-0.25wt%, W: 0.3-0.5wt%; the thin-walled stamping part is cleaned by vacuum carbon hydrogen solvent to remove surface residual dirt;

[0081] S2, carbonitriding: the thin-walled stamping part is uniformly and horizontally placed into a high-temperature mesh belt furnace for chemical heat treatment, the temperature is 820℃, the furnace atmosphere is: methanol, propane and ammonia in a volume ratio of 80:5:15, the methanol flow is 1600ml / min, the propane flow is 100ml / min, and the ammonia flow is 300ml / min; the first zone is strongly penetrated for 60min; the second zone is diffused for 60min;

[0082] S3, quenching cooling: the thin-walled stamping part after carbonitriding is placed into an oil tank for quenching, a graded quenching oil of Nanjing Zhounian New Product Technology Research Institute is used, the maximum cooling speed is 70℃ / s graded quenching oil, the oil temperature is controlled at 120℃; the quenching oil is stirred at a low speed of 150r / min, and closed cooling tower circulation is used for quenching cooling, the hot quenching oil is extracted from the bottom of the quenching oil tank, cooled through the closed cooling tower, and returned from the upper part of the quenching oil tank, so that the oil tank temperature is ensured within the set range, the thin-walled stamping part is cooled uniformly, and the deformation is reduced;

[0083] S4, low-temperature tempering: the thin-walled stamping part after quenching is cleaned by vacuum carbon hydrogen solvent to remove the residual oil dirt on the surface; the cleaned thin-walled stamping part is tempered by a box-type protective atmosphere tempering furnace, the tempering temperature is 120℃, and the time is 60min, so that the part retains a part of residual stress;

[0084] S5, string clamp tempering: the thin-walled stamping part after low-temperature tempering is clamped by a thick-wall clamp, the clamping force is 8KN, and then the part is tempered in a tempering furnace to eliminate stress and reshape the thin-walled stamping part, the tempering temperature is 240℃, the holding time is 250min, and the part is cooled in air after being taken out of the furnace to obtain a low-carbon alloy steel part.

[0085] Performance detection

[0086] 1. The hardness of the low-carbon alloy steel parts prepared in each example and each comparative example is tested by JJG148-2006 "Standard Vickers Hardness Block Test Procedure", and the test results are recorded in Table 1.

[0087] 2. Repeat a plurality of examples and comparative examples, and measure the flatness qualification rate of the low-carbon alloy steel parts prepared, specifically, place one end face of the low-carbon alloy steel part on a platform, and the end face is a positioning reference, measure the flatness of the upper end face, if the maximum value of the measurement is lower than the flatness tolerance, it is qualified; measure the flatness of the other end face according to the above method, calculate the qualification rate, and record the test results in Table 1.

[0088] 3. Take the low-carbon alloy steel part obtained in Example 1, take a metallographic sample according to GB / T9441-2009 and polish, and take a micrograph (magnification is 5 times) using an optical microscope, and the micrograph is as follows Figure 1 .

[0089] Table 1 Performance test data table of Examples 1-3 and Comparative Examples 1-3

[0090]

[0091] According to Table 1, combined with Examples 1, 3 and Comparative Examples 1, 3, it can be seen that by setting the heating temperature, carbon potential, ammonia flow, time and string clamping tempering temperature time and other parameters in the preparation method, the heat treatment of SCM415 material with thin wall (0.8-1.5mm) and large diameter (80-110mm) is realized, so that the hardness reaches more than 670HV1, and the qualification rate of the flatness of 0.15mm is improved.

[0092] According to Table 1, combined with Example 2 and Comparative Example 2, it can be seen that by first low-temperature tempering and then string clamping tempering of the thin-wall stamping part after quenching and cooling, the hardness and flatness qualification rate of the low-carbon alloy steel part obtained are better than those of the low-carbon alloy steel part after low-temperature tempering; After low-temperature tempering, a part of residual stress is retained in the thin-wall stamping part, and after re-tempering, the residual stress of the thin-wall stamping part is eliminated, and the part is shaped at the same time, so that the low-carbon alloy steel part obtained has smaller deformation, higher hardness and higher flatness qualification rate.

[0093] According to Table 1 and combined with Figure 1 , by setting the heating temperature, carbon potential, ammonia flow, time and string clamping tempering temperature time and other parameters in the low-deformation preparation method of the low-carbon alloy steel part and combining with the specific preparation process, a material with fine needle-shaped martensite and uniformly distributed point-shaped carbide / nitride is obtained, which has extremely high strength and wear resistance. Such material meets the technical index requirements of flat thrust bearing.

[0094] The embodiments are only illustrative of the present application, and are not intended to limit the present application, and those skilled in the art can make modifications to the embodiments without creative contribution after reading the specification, but as long as the modifications are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A method for preparing low-carbon alloy steel parts, characterized in that: Includes the following steps: Part preparation: Thin-walled stamped parts made of SCM415 material, wherein the wall thickness of the thin-walled stamped parts is 0.8-1.5mm and the diameter is 80-110mm. The chemical composition of the SCM415 material is C: 0.13-0.18wt%, Mn: 0.6-0.9wt%, Si: 0.15-0.35wt%, Ni≤0.25wt%, S≤0.03wt%, P≤0.03wt%, Cr: 0.9-1.2wt%, Mo: 0.15-0.25wt%, and the SCM415 material also includes W: 0.3-0.5wt%. The thin-walled stamped parts are cleaned using a vacuum hydrocarbon solvent. Carbonitriding: Thin-walled stamped parts are chemically heat-treated in a protective atmosphere, wherein the protective atmosphere is a mixture of methanol, propane and ammonia in a volume ratio of 85:10:5, and the heat treatment temperature is 830-860℃. The chemical heat treatment is divided into two stages: a strong infiltration and heat preservation stage in zone one with the carbon potential controlled at 0.9%, and a diffusion and heat preservation stage in zone two with the carbon potential controlled at 0.8%. Quenching: The thin-walled stamped parts after carbonitriding are quenched with graded quenching oil, and the oil temperature is controlled above 80℃. The maximum cooling rate of the graded quenching oil is 75-90℃ / s. Low-temperature tempering: The quenched thin-walled stamping parts are cleaned, and then tempered at 120℃ for 60 minutes. Clamping and tempering: The thin-walled stamping parts after low-temperature tempering are clamped using thick-walled clamps with a clamping force of more than 6KN, and then tempered at a temperature of 240-260℃ for 180-240min. After that, they are air-cooled to obtain low-carbon alloy steel parts.

2. The method for preparing low-carbon alloy steel parts according to claim 1, characterized in that: During the carbonitriding process, the thin-walled stamped parts are placed horizontally in a mesh belt furnace for chemical heat treatment.

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