Preparation method of nitrogen-carbon composite hardened layer on surface of austenitic stainless steel and workpiece

Abstract

The invention discloses a preparation method of a nitrogen-carbon composite hardened layer on the surface of austenitic stainless steel and a workpiece, and belongs to the technical field of chemical heat treatment.The preparation method comprises the following steps that the austenitic stainless steel is subjected to solid solution heat treatment, and the workpiece is machined; the workpiece is loaded into a controlled atmosphere nitrocarburizing furnace, and air in the furnace is exhausted; continuously heating, and sequentially carrying out the following operations: injecting ammonia gas into the nitrocarburizing furnace; the nitriding surface of the workpiece is purified and activated; performing high-temperature activation on the surfaces of the workpiece and the sample; performing nitrogen-carbon low-temperature infiltration; according to the method, the problem of highly toxic pollution of a traditional liquid method and the limitation of overall treatment are overcome.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical heat treatment, and in particular relates to a method for preparing a nitrogen-carbon composite hardened layer on the surface of an austenitic stainless steel 1Cr18Ni9Ti material workpiece and the workpiece. Background Art

[0002] Austenitic stainless steel 1Cr18Ni9Ti, widely used in the aerospace industry, has an austenitic structure at room temperature and exhibits excellent toughness, ductility, weldability, corrosion resistance, and non-magnetic properties at both room and low temperatures. However, its low hardness and wear resistance, coupled with its inability to be strengthened by conventional solution heat treatment, limit its use. Therefore, there is an urgent need to create a high-hardness composite hardened layer on its surface to improve its surface wear resistance.

[0003] Creating a nitrogen-carbon composite hardened layer on the surface of this material is an effective way to improve its wear resistance. However, the conventional method for creating nitrogen-carbon composite hardened layers is a liquid process. This process produces cyanide and cyanate, and the resulting cyanide salt is highly toxic and harmful to the environment and human health. Furthermore, this liquid process can only create a hardened layer on the entire workpiece, not on a localized basis. Therefore, a safe and non-toxic method for creating nitrogen-carbon composite hardened layers is urgently needed. Summary of the Invention

[0004] The present invention provides a method for preparing a nitrogen-carbon composite hardened layer on the surface of austenitic stainless steel and a workpiece, which overcomes the highly toxic pollution problem and the limitation of overall treatment of the traditional liquid method. The process has the advantages of being safe and non-toxic. The hardness of the nitrogen-carbon composite hardened layer prepared on the surface of austenitic stainless steel 1Cr18Ni9Ti can reach above 1300HV.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a method for preparing a nitrogen-carbon composite hardened layer on the surface of austenitic stainless steel, comprising the following steps:

[0007] S1. subjecting austenitic stainless steel to solution heat treatment;

[0008] S2, machining workpieces with austenitic stainless steel after solution heat treatment;

[0009] S3, placing the workpiece into a nitrocarburizing furnace and exhausting the air in the furnace;

[0010] S4, starting to heat up, when the temperature of the nitrocarburizing furnace reaches the first target temperature, injecting ammonia into the nitrocarburizing furnace;

[0011] S5. Continue to raise the temperature. When the temperature of the nitrocarburizing furnace reaches the second target temperature, inject an activator into the nitrocarburizing furnace and keep the temperature to purify and activate the nitrided surface of the workpiece.

[0012] S6. Continue to raise the temperature. When the temperature of the nitrocarburizing furnace reaches a third target temperature, inject an activator into the nitrocarburizing furnace and maintain the temperature to perform high-temperature activation on the surfaces of the workpiece and the sample. The third target temperature is greater than the second target temperature and greater than the first target temperature.

[0013] S7, continue to raise the temperature. When the temperature inside the nitrocarburizing furnace reaches 490-530°C, introduce cracked ammonia and propane into the nitrocarburizing furnace, and adjust the ratio of ammonia, cracked ammonia and propane to make the nitrogen potential Kn 8-15. Keep the temperature and perform low-temperature nitrocarburizing.

[0014] S8. The workpiece completed in S7 is continued to be heated with the furnace. When the temperature in the nitrocarburizing furnace reaches 550-580°C, the ratio of ammonia, cracked ammonia and propane is adjusted to make the nitrogen potential Kn 2-5, and the workpiece is kept warm for high-temperature nitrocarburizing.

[0015] S9, the workpiece is cooled along with the furnace until it reaches room temperature and then taken out of the furnace, thereby obtaining a workpiece having a nitrogen-carbon composite hardened layer.

[0016] Furthermore, in S2, when processing a workpiece, the workpiece size is calculated according to the following formula:

[0017] D1=D-(0.2~0.4)d

[0018] D1: Size of the nitrogen-carbon composite hardened layer of the workpiece before preparation;

[0019] D: The size of the nitrogen-carbon composite hardened layer of the workpiece after preparation;

[0020] d: Depth of nitrogen-carbon composite hardened layer.

[0021] Furthermore, when preparing a local hardened layer on the workpiece, the copper or tin layer is plated to protect the area where the hardened layer is not required, and only the surface of the target part is hardened. After the hardening is completed, the copper or tin layer is removed.

[0022] Furthermore, in S7, the ratio of ammonia, cracked ammonia and propane is adjusted to (55-65): (20-35): (10-20); in S8, the ratio of ammonia, cracked ammonia and propane is adjusted to (25-35): (50-65): (10-15).

[0023] Furthermore, the S2 also includes processing the target sample with austenitic stainless steel after solution heat treatment, and in S3-S9, the sample is processed in the same way as the target workpiece; after S9 is completed, the sample is dissected and sampled, and the hardened layer depth and nitriding surface hardness of the sample are tested.

[0024] Furthermore, in said S4, when injecting ammonia into the nitrocarburizing furnace, the circulation fan and the exhaust gas burner of the nitrocarburizing furnace are turned on.

[0025] Furthermore, in S5 and S6, the holding time is 10-20 minutes; in S7, the holding time is 30-60 minutes; and in S8, the holding time is 30-90 minutes.

[0026] Furthermore, the first target temperature is 300-340°C, the second target temperature is 350-380°C, and the third target temperature is 390-420°C.

[0027] Furthermore, in S3, the air in the nitrocarburizing furnace is exhausted by filling the furnace with argon.

[0028] In a second aspect, the present invention provides a stainless steel workpiece having a nitrogen-carbon composite hardened layer, wherein the nitrogen-carbon composite hardened layer is prepared by the above-mentioned method for preparing the nitrogen-carbon composite hardened layer on the surface of austenitic stainless steel.

[0029] Compared with the prior art, the present invention has at least the following beneficial technical effects:

[0030] The preparation method of the nitrogen-carbon composite hardening layer provided by the present invention completely avoids the production of highly toxic substances such as cyanide (CN-) and cyanate (OCN-) during the process of preparing the nitrogen-carbon composite hardening layer on the surface of austenitic stainless steel, eliminates the harm to the human body and the environment, and fundamentally solves the defects of the traditional liquid method for preparing the nitrogen-carbon composite hardening layer.

[0031] The nitrogen-carbon composite hardened layer prepared on the surface of 1Cr18Ni9Ti austenitic stainless steel using the method of the present invention is infiltrated at low temperatures under high nitrogen potential conditions. After the nitrogen atoms penetrate the stainless steel, they densely accumulate in the outermost area of ​​the stainless steel, forming a hardened layer with a relatively high hardness on the workpiece surface. Combined with high-temperature diffusion under low nitrogen potential, it drives the nitrogen atoms to migrate deeper, increasing the depth of the hardened layer. The prepared hardened layer can reach a hardness of over 1300 HV, far higher than that of the base material. This greatly improves the wear resistance of the workpiece surface, effectively overcoming the core shortcomings of the 1Cr18Ni9Ti material itself: low hardness and insufficient wear resistance. It extends the service life of key components and expands the application range of this material in applications requiring high wear resistance.

[0032] The method of the present invention can protect the parts of the workpiece that do not need to be hardened by plating a copper layer or a tin layer, and only harden the surface of the remaining parts. After the hardening is completed, the copper layer or the tin layer can be removed, thereby realizing the preparation of a nitrogen-carbon composite hardened layer on a specific part (local) of the workpiece, meeting the needs of selective strengthening of complex workpieces. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A flow chart of a method for preparing a nitrogen-carbon composite hardened layer on the surface of austenitic stainless steel provided by the present invention;

[0034] Figure 2 is the first workpiece dimension drawing;

[0035] Figure 3 This is the depth detection diagram of the composite hardened layer of the first workpiece;

[0036] Figure 4 This is the second workpiece dimension drawing;

[0037] Figure 5 This is the depth detection diagram of the composite hardened layer of the second workpiece;

[0038] Figure 6 This is the dimension drawing of the third workpiece;

[0039] Figure 7 This is the depth detection diagram of the composite hardened layer of the third workpiece;

[0040] Figure 8 This is the fourth workpiece dimension drawing;

[0041] Figure 9 Depth detection diagram of the composite hardened layer of the fourth workpiece

[0042] In the accompanying drawings: 1, first workpiece; 2, second workpiece; 3, third workpiece; 4, fourth workpiece. DETAILED DESCRIPTION

[0043] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0044] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0045] It should be noted that when an element is referred to as being "disposed on" another element, it may be directly on the other element or there may be another element centered thereon. When an element is considered to be "connected" to another element, it may be directly connected to the other element or there may be another element centered thereon at the same time. The terms "upper", "lower", "front", "back", "left", "right", "top", "bottom", "inside", "outside", etc. used herein indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0047] The present invention provides a safe, efficient, and high-performance solution for surface strengthening of austenitic stainless steel, which realizes the preparation of ultra-high hardness (≥1300HV) nitrogen-carbon composite hardened layer on the surface of materials such as 1Cr18Ni9Ti, significantly improving its wear resistance and applicability.

[0048] Reference Figure 1 A method for preparing a nitrogen-carbon composite hardened layer on the surface of austenitic stainless steel comprises the following steps:

[0049] S1 pre-treatment

[0050] Before preparing the nitrogen-carbon composite hardened layer, austenitic stainless steel 1Cr18Ni9Ti (hereinafter referred to as austenitic stainless steel) is subjected to solid solution heat treatment.

[0051] The solution heat treatment process is: 1050±15℃, air cooling.

[0052] S2 workpiece size determination

[0053] The austenitic stainless steel that has completed the S1 solution heat treatment is processed into the required workpieces and specimens. In order to ensure the final size requirements of the nitrogen-carbon composite hardened layer of the workpiece, the size of the nitrogen-carbon composite hardened layer is calculated according to the following formula when processing the workpiece:

[0054] D1= D-(0.2~0.4)d (1)

[0055] D1: Size of the nitrogen-carbon composite hardened layer of the workpiece before preparation;

[0056] D: The size of the nitrogen-carbon composite hardened layer of the workpiece after preparation;

[0057] d: Depth of nitrogen-carbon composite hardened layer.

[0058] S3 Surface Cleaning

[0059] Soak the workpiece and specimen processed by S1 in industrial alcohol to clean the surface stains, and then soak them in clean industrial alcohol for 10 to 20 minutes.

[0060] S4 exhaust

[0061] The workpieces and samples processed by S3 are placed in a controlled atmosphere nitrocarburizing furnace. First, 2-3 volumes of argon are filled into the furnace to exhaust the air in the furnace to prevent the surface of the workpiece from being oxidized by the air during the heating process.

[0062] S5 injects ammonia gas

[0063] After completing S4, the temperature begins to rise. When the temperature of the nitrocarburizing furnace rises to 300-340°C, ammonia is injected into the nitrocarburizing furnace, and the circulating fan and exhaust gas burner of the nitrocarburizing furnace are turned on to form an ammonia atmosphere in the nitrocarburizing furnace to ensure the rapid arrival of nitrogen potential when preparing the nitrogen-carbon composite hardened layer.

[0064] S6 Low Temperature Surface Activation

[0065] After completing S5, continue to heat up. When the temperature of the nitrocarburizing furnace rises to 350-380℃, inject 5-10ml of activator tetrachloroethylene into the nitrocarburizing furnace and maintain this temperature for 10-20 minutes to purify and activate the nitrided surface of the workpiece.

[0066] S7 high temperature surface activation

[0067] After completing S6, continue to raise the temperature. When the nitrocarburizing furnace temperature reaches 390-420°C, inject 10-20ml of tetrachloroethylene into the nitrocarburizing furnace and maintain this temperature for 10-20 minutes to activate the workpiece and sample surface. A large amount of tetrachloroethylene and a higher temperature can further activate the workpiece and act as a catalyst to promote nitrocarburization.

[0068] Low temperature infiltration of S8 nitrogen-carbon composite hardened layer

[0069] After completing S7, continue to heat up. When the temperature inside the nitrocarburizing furnace reaches 490-530°C, introduce cracked ammonia and propane into the nitrocarburizing furnace, and adjust the ratio of ammonia, cracked ammonia and propane to (55-65): (20-35): (10-20). By adjusting the ratio of ammonia and cracked ammonia, the nitrogen potential Kn is controlled to 8-15. Under this high nitrogen potential condition, nitrogen and carbon penetrate quickly, and the hardened layer obtained has high hardness. The holding time is 0.5-1h, and low-temperature penetration is performed.

[0070] S9 nitrogen-carbon composite hardened layer high temperature infiltration

[0071] The workpiece and sample of S8 are continued to be heated with the furnace. When the temperature in the nitrocarburizing furnace reaches 550-580℃, the ratio of ammonia, cracked ammonia and propane is adjusted to (25-35): (45-65): (10-20) so that the nitrogen potential Kn is 2-5, the holding time is 0.5-1.5h, and high-temperature infiltration is carried out.

[0072] S10 Cooling

[0073] Turn on the cooling fan in the furnace and cool the completed S9 workpiece in the nitrocarburizing furnace until it reaches room temperature before taking it out of the furnace.

[0074] S11 depth and hardness testing

[0075] After the S10 specimen was dissected and prepared, it was polished and then corroded with nitric acid. A 100x microscope was used for depth inspection. The depth of the nitrogen-carbon composite hardened layer was about 20-42μm. A metallographic microhardness tester with a load of 200g was used to test the hardness of the nitrided surface of the specimen, which was ≥1300HV. 0.2 .

[0076] S12 size detection

[0077] The workpiece size is detected using a micrometer, and the dimensional variation in the diameter direction is 4-16μm.

[0078] Example 1

[0079] S1 pre-treatment

[0080] Before preparing the nitrogen-carbon composite hardened layer, the austenitic stainless steel 1Cr18Ni9Ti is subjected to solid solution heat treatment.

[0081] Solution heat treatment process: 1050±15℃, air cooling;

[0082] S2 workpiece size determination

[0083] The workpiece processed in this embodiment is a first workpiece 1, which is simply referred to as the workpiece in this embodiment.

[0084] The austenitic stainless steel that has completed the solution heat treatment is processed into the required workpieces and specimens. The workpiece size is as follows: Figure 2 As shown, it is a hollow cylinder. The workpiece is prepared with a nitrogen-carbon composite hardened layer as a whole. The hardened layer thickness is 20 to 30 μm. According to formula 1, the dimensions of each part of the workpiece are calculated as follows:

[0085] Workpiece outer diameter: The drawing requires the final size to be 80.42-0.005. To ensure the final size of the workpiece, the processing size before preparing the composite hardened layer should be 80.42-0.025×0.2=80.415mm, that is, before preparing the composite hardened layer, the workpiece outer diameter should be controlled between 80.410 and 80.415mm.

[0086] Inner diameter of workpiece: The drawing requires the final size of the workpiece to be 72.36+0.004. To ensure the final size of the workpiece, the processing size before preparing the composite hardened layer should be 72.36-0.025×0.2=72.355mm, that is, before preparing the composite hardened layer, the inner diameter of the workpiece should be controlled between 72.355 and 72.359mm.

[0087] Workpiece thickness: The drawing requires the final size of the workpiece to be 5.3±0.002. To ensure the final size of the workpiece, the processing size before preparing the composite hardened layer should be 5.3-0.025×0.2=5.295mm, that is, before preparing the composite hardened layer, the workpiece thickness should be controlled between 5.293 and 5.297mm.

[0088] S3 Surface Cleaning

[0089] Soak the workpiece and specimen processed by S1 in industrial alcohol to clean the surface stains, and then soak them in clean industrial alcohol for 10 to 20 minutes.

[0090] S4 exhaust

[0091] The workpiece and sample processed by S3 are placed in a controlled atmosphere nitrocarburizing furnace. First, 2 volumes of argon gas are filled into the furnace to exhaust the air in the furnace to prevent the surface of the workpiece from being oxidized by the air during the heating process.

[0092] S5 injects ammonia gas

[0093] After completing S4, the temperature begins to rise. When the furnace temperature rises to 300°C, ammonia is injected into the nitrocarburizing furnace, and the equipment circulation fan and exhaust gas burner are turned on to form an ammonia atmosphere in the nitrocarburizing furnace to ensure the rapid arrival of nitrogen potential when preparing the nitrogen-carbon composite hardened layer.

[0094] S6 Low Temperature Surface Activation

[0095] After completing S5, continue to heat up. When the furnace temperature reaches 350°C, inject 5ml of tetrachloroethylene into the furnace and maintain this temperature for 10 minutes to purify and activate the nitrided surface of the workpiece.

[0096] S7 high temperature surface activation

[0097] After completing S6, continue to heat up. When the furnace temperature reaches 420°C, inject 10 ml of tetrachloroethylene into the furnace and maintain this temperature for 10 minutes to activate the surface at high temperature.

[0098] Low temperature infiltration of S8 nitrogen-carbon composite hardened layer

[0099] After completing S7, continue to heat up. When the temperature in the furnace reaches 490°C, introduce cracked ammonia and propane into the nitrocarburizing furnace, and adjust the ratio of ammonia, cracked ammonia and propane to 65:25:10, so that the nitrogen potential Kn is 15, and the holding time is 0.5h for low-temperature infiltration.

[0100] S9 nitrogen-carbon composite hardened layer high temperature infiltration

[0101] The workpiece and sample of S8 will be completed and continue to heat up with the furnace. When the temperature in the nitrocarburizing furnace reaches 550℃, adjust the ratio of ammonia, cracked ammonia and propane to 25:65:10, make the nitrogen potential Kn to 2, hold the temperature for 1h, and then carry out high-temperature infiltration.

[0102] S10 Cooling

[0103] Turn on the cooling fan in the furnace and cool the completed S9 workpiece in the nitrocarburizing furnace until it reaches room temperature before taking it out of the furnace.

[0104] S11 depth and hardness testing

[0105] After the S10 sample was dissected and prepared, it was polished and etched with nitric acid alcohol. A 100x microscope was used for depth inspection. The inspection results are as follows: Figure 3 As shown, the depth of the nitrogen-carbon composite hardened layer is 24-25 μm; the hardness of the nitrided surface of the sample is 1350 HV when the metallographic microhardness tester with a load of 200 grams is used. 0.2 .

[0106] S12 size detection

[0107] The workpiece size was detected using a micrometer. The outer diameter, inner diameter and thickness of the workpiece all met the requirements, and the dimensional change was approximately 5 μm.

[0108] Example 2

[0109] S1 pre-treatment

[0110] Before preparing the nitrogen-carbon composite hardened layer, the austenitic stainless steel 1Cr18Ni9Ti is subjected to solid solution heat treatment.

[0111] Solution heat treatment process: 1050±15℃, air cooling;

[0112] S2 workpiece size determination

[0113] The workpiece processed in this embodiment is a second workpiece 2, which is simply referred to as the workpiece in this embodiment.

[0114] The austenitic stainless steel that has completed the solution heat treatment is processed into the required workpieces and specimens. The workpiece size is as follows: Figure 4 As shown in the figure, a disk with multiple through holes is prepared on the workpiece as a whole with a nitrogen-carbon composite hardened layer. The thickness of the hardened layer is 25 to 35 μm. The dimensions of each part of the workpiece are calculated according to formula 1:

[0115] The drawing requires that the final outer diameter of the workpiece be 104.78-0.008. To ensure the final size of the workpiece, the processing size before preparing the composite hardened layer should be the workpiece outer diameter: 104.78-0.03×0.3=104.771mm, that is, before preparing the composite hardened layer, the outer diameter of the workpiece should be controlled between 104.762 and 104.771mm.

[0116] The drawing requires that the final size of the workpiece's small hole diameter is 8-0.05. To ensure the final size of the workpiece, the processing size before preparing the composite hardened layer should be: small hole diameter: 8-0.03×0.3=7.991mm, that is, before preparing the composite hardened layer, the workpiece's small hole diameter should be controlled between 7.991 and 8.041mm.

[0117] The drawing requires that the final size of the workpiece hole diameter is 8-0.05. In order to ensure the final size of the workpiece, the processing size of the workpiece before preparing the composite hardened layer should be: 3.3-0.005. The workpiece thickness is: 3.3-0.03×0.3=3.291mm, that is, before preparing the composite hardened layer, the workpiece thickness should be controlled between 3.281 and 3.291mm.

[0118] S3 Surface Cleaning

[0119] Soak the workpiece and specimen processed by S1 in industrial alcohol to clean the surface stains, and then soak them in clean industrial alcohol for 15 minutes.

[0120] S4 exhaust

[0121] The workpiece and sample processed by S3 are placed in a controlled atmosphere nitrocarburizing furnace. First, 2 volumes of argon gas are filled into the furnace to exhaust the air in the furnace to prevent the surface of the workpiece from being oxidized by the air during the heating process.

[0122] S5 injects ammonia gas

[0123] After completing S4, the temperature begins to rise. When the furnace temperature rises to 320°C, ammonia is injected into the nitrocarburizing furnace, and the equipment circulation fan and exhaust gas burner are turned on to form an ammonia atmosphere in the nitrocarburizing furnace to ensure the rapid arrival of nitrogen potential when preparing the nitrogen-carbon composite hardened layer.

[0124] S6 Low Temperature Surface Activation

[0125] After completing S5, continue to heat up. When the furnace temperature reaches 365°C, inject 8ml of tetrachloroethylene into the furnace and maintain this temperature for 15 minutes to purify and activate the nitrided surface of the workpiece.

[0126] S7 high temperature surface activation

[0127] After completing S6, continue to heat up. When the furnace temperature reaches 405°C, inject 10 ml of tetrachloroethylene into the furnace and maintain this temperature for 10 minutes to activate the surface at high temperature.

[0128] Low temperature infiltration of S8 nitrogen-carbon composite hardened layer

[0129] After completing S7, continue to heat up. When the temperature in the furnace reaches 500°C, introduce cracked ammonia and propane into the nitrocarburizing furnace, and adjust the ratio of ammonia, cracked ammonia and propane to 60:22:20, so that the nitrogen potential Kn is 12, and the holding time is 1h for low-temperature infiltration.

[0130] S9 nitrogen-carbon composite hardened layer high temperature infiltration

[0131] The workpiece and sample of S8 will be completed and continue to heat up with the furnace. When the temperature in the nitrocarburizing furnace reaches 580℃, adjust the ratio of ammonia, cracked ammonia and propane to 30:55:15, make the nitrogen potential Kn to 3, hold the temperature for 1h, and then carry out high-temperature infiltration.

[0132] S10 Cooling

[0133] Turn on the cooling fan in the furnace and cool the completed S9 workpiece in the nitrocarburizing furnace until it reaches room temperature before taking it out of the furnace.

[0134] S11 depth and hardness testing

[0135] After the S10 sample was dissected and prepared, it was polished and etched with nitric acid alcohol. A 100x microscope was used for depth inspection. The inspection results are as follows: Figure 5 As shown, the depth of the nitrogen-carbon composite hardened layer is 28-32μm; the hardness of the nitrided surface of the sample is 1380HV when the metallographic microhardness tester with a load of 200 grams is used. 0.2 . S12 size detection

[0136] The workpiece size was detected using a micrometer. The outer diameter, inner diameter and thickness of the workpiece all met the requirements, and the dimensional change was approximately 9μm.

[0137] Example 3

[0138] S1 pre-treatment

[0139] Before preparing the nitrogen-carbon composite hardened layer, the austenitic stainless steel 1Cr18Ni9Ti is subjected to solid solution heat treatment.

[0140] Solution heat treatment process: 1050±15℃, air cooling;

[0141] S2 workpiece size determination

[0142] The workpiece processed in this embodiment is a third workpiece 3, which is simply referred to as the workpiece in this embodiment.

[0143] The austenitic stainless steel that has completed the solution heat treatment is processed into the required workpieces and specimens. The workpiece size is as follows: Figure 6 As shown, the workpiece is prepared with a nitrogen-carbon composite hardened layer as a whole, and the thickness of the hardened layer is 30 to 40 μm. The dimensions of each part of the workpiece are calculated according to formula 1:

[0144] The drawing requires that the final size of the workpiece's spherical outer diameter is 16.26-0.015. To ensure the final size of the workpiece, the processing size before preparing the composite hardened layer should be: workpiece outer diameter: 16.26-0.035×0.4=16.246mm, that is, before preparing the composite hardened layer, the workpiece outer diameter should be controlled between 16.231 and 16.246mm.

[0145] S3 Surface Cleaning

[0146] Soak the workpiece and specimen processed by S1 in industrial alcohol to clean the surface stains, and then soak them in clean industrial alcohol for 20 minutes.

[0147] S4 exhaust

[0148] The workpiece and sample processed by S3 are placed in a controlled atmosphere nitrocarburizing furnace. First, 2 volumes of argon gas are filled into the furnace to exhaust the air in the furnace to prevent the surface of the workpiece from being oxidized by the air during the heating process.

[0149] S5 injects ammonia gas

[0150] After completing S4, the temperature begins to rise. When the furnace temperature rises to 340°C, ammonia is injected into the nitrocarburizing furnace, and the equipment circulation fan and exhaust gas burner are turned on to form an ammonia atmosphere in the nitrocarburizing furnace to ensure the rapid arrival of nitrogen potential when preparing the nitrogen-carbon composite hardened layer.

[0151] S6 Low Temperature Surface Activation

[0152] After completing S5, continue to heat up. When the furnace temperature reaches 380°C, inject 10ml of tetrachloroethylene into the furnace and maintain this temperature for 20 minutes to purify and activate the nitrided surface of the workpiece.

[0153] S7 high temperature surface activation

[0154] After completing S6, the temperature was continued to rise. When the furnace temperature reached 390°C, 20 ml of tetrachloroethylene was injected into the furnace and maintained at this temperature for 20 minutes to activate the surface at high temperature.

[0155] Low temperature infiltration of S8 nitrogen-carbon composite hardened layer

[0156] After completing S7, continue to heat up. When the temperature in the furnace reaches 530°C, introduce cracked ammonia and propane into the nitrocarburizing furnace, and adjust the ratio of ammonia, cracked ammonia and propane to 55:30:15, so that the nitrogen potential Kn is 10, and the holding time is 1.5h for low-temperature infiltration.

[0157] S9 nitrogen-carbon composite hardened layer high temperature infiltration

[0158] The workpiece and sample of S8 will be completed and continue to heat up with the furnace. When the temperature in the nitrocarburizing furnace reaches 550℃, adjust the ratio of ammonia, cracked ammonia and propane to 35:50:15, make the nitrogen potential Kn to 5, hold the temperature for 1.5h, and then carry out high-temperature infiltration.

[0159] S10 Cooling

[0160] Turn on the cooling fan in the furnace and cool the completed S9 workpiece in the nitrocarburizing furnace until it reaches room temperature before taking it out of the furnace.

[0161] S11 depth and hardness testing

[0162] After the S10 sample was dissected and prepared, it was polished and etched with nitric acid alcohol. A 100x microscope was used for depth inspection. The inspection results are as follows: Figure 7 As shown, the depth of the nitrogen-carbon composite hardened layer is 40-42 μm; the hardness of the nitrided surface of the sample is 1375 HV when the metallographic microhardness tester with a load of 200 grams is used. 0.2 .

[0163] S12 size detection

[0164] The workpiece size was detected using a micrometer. The outer diameter, inner diameter and thickness of the workpiece all met the requirements, and the dimensional change was approximately 12μm.

[0165] Example 4

[0166] S1 pre-treatment

[0167] Before preparing the nitrogen-carbon composite hardened layer, the austenitic stainless steel 1Cr18Ni9Ti is subjected to solid solution heat treatment.

[0168] Solution heat treatment process: 1050±15℃, air cooling;

[0169] S2 workpiece size determination

[0170] The workpiece processed in this embodiment is a fourth workpiece 4, which is simply referred to as the workpiece in this embodiment.

[0171] The austenitic stainless steel that has completed the solution heat treatment is processed into the required workpieces and specimens. The workpiece size is as follows: Figure 8 As shown, the workpiece is prepared with a nitrogen-carbon composite hardened layer as a whole, and the thickness of the hardened layer is 30 to 40 μm. The dimensions of each part of the workpiece are calculated according to formula 1:

[0172] The drawing requires that the final size of the workpiece spherical diameter is 17.475+0.013. In order to ensure the final size of the workpiece, the processing size before preparing the composite hardened layer should be: workpiece outer diameter: 17.475-0.03×0.4=17.463mm, that is, before preparing the composite hardened layer, the workpiece outer diameter should be controlled between 17.463 and 17.476mm.

[0173] S3 Surface Cleaning

[0174] Soak the workpiece and specimen processed by S1 in industrial alcohol to clean the surface stains, and then soak them in clean industrial alcohol for 20 minutes.

[0175] S4 exhaust

[0176] The workpiece and sample processed by S3 are placed in a controlled atmosphere nitrocarburizing furnace. First, 2 volumes of argon gas are filled into the furnace to exhaust the air in the furnace to prevent the surface of the workpiece from being oxidized by the air during the heating process.

[0177] S5 injects ammonia gas

[0178] After completing S4, the temperature begins to rise. When the furnace temperature rises to 360°C, ammonia is injected into the nitrocarburizing furnace, and the equipment circulation fan and exhaust gas burner are turned on to form an ammonia atmosphere in the nitrocarburizing furnace to ensure that the nitrogen potential reaches quickly when preparing the nitrogen-carbon composite hardened layer.

[0179] S6 Low Temperature Surface Activation

[0180] After completing S5, continue to heat up. When the furnace temperature reaches 380°C, inject 10ml of tetrachloroethylene into the furnace and maintain this temperature for 20 minutes to purify and activate the nitrided surface of the workpiece.

[0181] S7 high temperature surface activation

[0182] After completing S6, the temperature was continued to rise. When the furnace temperature reached 410°C, 20 ml of tetrachloroethylene was injected into the furnace and maintained at this temperature for 20 minutes to activate the surface at high temperature.

[0183] Low temperature infiltration of S8 nitrogen-carbon composite hardened layer

[0184] After completing S7, continue to heat up. When the temperature in the furnace reaches 530°C, introduce cracked ammonia and propane into the nitrocarburizing furnace, and adjust the ratio of ammonia, cracked ammonia and propane to 55:35:10, so that the nitrogen potential Kn is 8, and the holding time is 1 hour for low-temperature infiltration.

[0185] S9 nitrogen-carbon composite hardened layer high temperature infiltration

[0186] The workpiece and sample of S8 will be completed and continue to heat up with the furnace. When the temperature in the nitrocarburizing furnace reaches 550℃, adjust the ratio of ammonia, cracked ammonia and propane to 35:50:15, make the nitrogen potential Kn to 5, hold the temperature for 1h, and then carry out high-temperature infiltration.

[0187] S10 Cooling

[0188] Turn on the cooling fan in the furnace and cool the completed S9 workpiece in the nitrocarburizing furnace until it reaches room temperature before taking it out of the furnace.

[0189] S11 depth and hardness testing

[0190] After the S10 sample was dissected and prepared, it was polished and etched with nitric acid alcohol. A 100x microscope was used for depth inspection. The inspection results are as follows: Figure 9 As shown, the depth of the nitrogen-carbon composite hardened layer is 29-30 μm; the hardness of the nitrided surface of the sample is 1375 HV when the metallographic microhardness tester with a load of 200 grams is used. 0.2 .

[0191] S12 size detection

[0192] The workpiece size was detected using a micrometer. The outer diameter, inner diameter and thickness of the workpiece all met the requirements, and the dimensional change was approximately 12μm.

[0193] In one embodiment of the present invention, a stainless steel workpiece is further provided, wherein the stainless steel workpiece has a nitrogen-carbon composite hardened layer, and the nitrogen-carbon composite hardened layer is prepared by the above-mentioned method for preparing the nitrogen-carbon composite hardened layer on the surface of austenitic stainless steel.

[0194] The term "consisting of" when describing a combination should include the identified elements, ingredients, components, or steps as well as other elements, ingredients, components, or steps that do not materially affect the basic novel characteristic of the combination. The use of the terms "comprising" or "including" to describe a combination of elements, ingredients, components, or steps herein also contemplates embodiments consisting essentially of these elements, ingredients, components, or steps. The use of the term "may" herein is intended to indicate that any of the attributes described as "may" be optional.

[0195] Multiple elements, ingredients, parts or steps can be provided by a single integrated element, ingredient, part or step. Alternatively, a single integrated element, ingredient, part or step can be divided into separate multiple elements, ingredients, parts or steps. The disclosure of "a" or "an" to describe an element, ingredient, part or step is not intended to exclude other elements, ingredients, parts or steps.

[0196] It should be understood that the above description is for illustrative purposes only and is not intended to be limiting. Many embodiments and many applications beyond the examples provided will be apparent to those skilled in the art upon reading the above description. Therefore, the scope of the present teachings should not be determined with reference to the above description, but rather with reference to the preceding claims and the full scope of equivalents to which such claims are entitled. For the purpose of completeness, all articles and references, including disclosures of patent applications and publications, are incorporated herein by reference. The omission of any aspect of the subject matter disclosed herein from the preceding claims is not a disclaimer of such subject matter, nor should it be considered that the applicants did not consider such subject matter to be part of the disclosed inventive subject matter.

Claims

1. A method for preparing a nitrogen-carbon composite hardened layer on the surface of austenitic stainless steel, characterized in that: The following steps are involved: S1. subjecting austenitic stainless steel to solution heat treatment; S2, machining workpieces with austenitic stainless steel after solution heat treatment; S3, placing the workpiece into a nitrocarburizing furnace and exhausting the air in the furnace; S4, starting to heat up, when the temperature of the nitrocarburizing furnace reaches the first target temperature, injecting ammonia into the nitrocarburizing furnace; S5. Continue to raise the temperature. When the temperature of the nitrocarburizing furnace reaches the second target temperature, inject an activator into the nitrocarburizing furnace and keep the temperature to purify and activate the nitrided surface of the workpiece. S6. Continue to raise the temperature. When the temperature of the nitrocarburizing furnace reaches a third target temperature, inject an activator into the nitrocarburizing furnace and maintain the temperature to perform high-temperature activation on the surfaces of the workpiece and the sample. The third target temperature is greater than the second target temperature and greater than the first target temperature. S7, continue to raise the temperature. When the temperature inside the nitrocarburizing furnace reaches 490-530°C, introduce cracked ammonia and propane into the nitrocarburizing furnace, and adjust the ratio of ammonia, cracked ammonia and propane to make the nitrogen potential Kn 8-15. Keep the temperature and perform low-temperature nitrocarburizing. S8. The workpiece completed in S7 is continued to be heated with the furnace. When the temperature in the nitrocarburizing furnace reaches 550-580°C, the ratio of ammonia, cracked ammonia and propane is adjusted to make the nitrogen potential Kn 2-5, and the workpiece is kept warm for high-temperature nitrocarburizing. S9, the workpiece is cooled along with the furnace until it reaches room temperature and then taken out of the furnace, thereby obtaining a workpiece having a nitrogen-carbon composite hardened layer.

2. The method for preparing a nitrogen-carbon composite hardened layer on the surface of austenitic stainless steel according to claim 1, characterized in that: In S2, when processing a workpiece, the workpiece size is calculated according to the following formula: D1=D-(0.2~0.4)d D1: Size of the nitrogen-carbon composite hardened layer of the workpiece before preparation; D: The size of the nitrogen-carbon composite hardened layer of the workpiece after preparation; d: Depth of nitrogen-carbon composite hardened layer.

3. The method for preparing a nitrogen-carbon composite hardened layer on the surface of austenitic stainless steel according to claim 1, characterized in that: When preparing a local hardened layer on a workpiece, the copper or tin layer is plated to protect the area where the hardened layer is not required, and only the surface of the target part is hardened. After the hardening is completed, the copper or tin layer is removed.

4. The method for preparing a nitrogen-carbon composite hardened layer on the surface of austenitic stainless steel according to claim 1, characterized in that: In the step S7, the ratio of ammonia, cracked ammonia and propane is adjusted to (55-65): (20-35): (10-20); in the step S8, the ratio of ammonia, cracked ammonia and propane is adjusted to (25-35): (50-65): (10-15).

5. The method for preparing a nitrogen-carbon composite hardened layer on the surface of austenitic stainless steel according to claim 1, characterized in that: Said S2 also includes processing the target sample with austenitic stainless steel after solid solution heat treatment, and in S3-S9, the sample is subjected to the same treatment as the target workpiece; after S9 is completed, the sample is dissected and sampled, and the hardened layer depth and nitrided surface hardness of the sample are detected.

6. The method for preparing a nitrogen-carbon composite hardened layer on the surface of austenitic stainless steel according to claim 1, characterized in that: In the above-mentioned S4, when ammonia is injected into the nitrocarburizing furnace, the circulation fan and the exhaust gas burner of the nitrocarburizing furnace are turned on.

7. The method for preparing a nitrogen-carbon composite hardened layer on the surface of austenitic stainless steel according to claim 1, characterized in that: In S5 and S6, the holding time is 10-20 minutes; in S7, the holding time is 30-60 minutes; and in S8, the holding time is 30-90 minutes.

8. The method for preparing a nitrogen-carbon composite hardened layer on the surface of austenitic stainless steel according to claim 1, characterized in that: The first target temperature is 300-340°C, the second target temperature is 350-380°C, and the third target temperature is 390-420°C.

9. The method for preparing a nitrogen-carbon composite hardened layer on the surface of austenitic stainless steel according to claim 1, characterized in that: In S3, the air in the nitrocarburizing furnace is exhausted by filling the furnace with argon.

10. A stainless steel workpiece, characterized in that: The stainless steel workpiece has a nitrogen-carbon composite hardened layer, and the nitrogen-carbon composite hardened layer is prepared by the method for preparing a nitrogen-carbon composite hardened layer on the surface of austenitic stainless steel according to any one of claims 1 to 9.

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