Slip and surface hardening process thereof

Abstract

The invention discloses a slip and a surface hardening process thereof, and belongs to the technical field of oil-gas exploration, development and drilling engineering equipment. The surface hardening process of the slip comprises the following steps: carrying out thermal refining on a slip base body blank; and after thermal refining is completed, the slip is subjected to ion nitriding treatment. The invention further discloses the slip. According to the surface hardening process of the slip, a brand-new ion nitriding process is adopted for one-time hardening forming, the size precision is enough, the slip can be put into application without finish machining, and therefore the problem that the carburizing treatment surface hardening yield of the cylindrical sharp tooth slip is extremely low is solved; and meanwhile, laser quenching and common ion nitriding tooth tip point ablation are avoided, the occurrence of a soft belt at the tooth tip part is greatly eliminated and weakened, and the hardness and uniformity of the tooth tip are guaranteed.

Description

Technical Field

[0001] This invention relates to the field of oil and gas exploration, development, and drilling equipment technology, specifically to a type of slip and its surface hardening process. Background Technology

[0002] The toothed cylindrical slip is made of alloy structural steel containing alloying elements such as chromium, nickel, and molybdenum, and is processed through surface hardening treatment. The structure of the toothed cylindrical slip is as follows: Figure 1 As shown. The pointed surface of the cannulated cylindrical slip is the main working surface. During operation, the pointed teeth of the cannulated cylindrical slip need to quickly engage with the workpiece to fix it in place and prevent slippage. The hardened surface properties of the cannulated cylindrical slip require wear resistance, corrosion resistance, high hardness, and resistance to breakage.

[0003] Currently, the industry mainly uses laser surface hardening, surface carburizing, surface gas nitriding, and conventional ion nitriding processes to harden the surface of the teeth of downhole tool slips in order to achieve a strong bite and wear resistance.

[0004] Laser hardening technology suffers from problems such as uneven surface hardness, surface oxidation, softening and burning of the cusps, and weak occlusion, often leading to slippage and failure during operation. Patent CN114395661A discloses a method for laser hardening the surface of a vibrator clip. While this patent employs methods such as enhanced detection and controlled laser intensity to minimize uneven hardening, the detection process is difficult, making it hard to avoid even minute deviations. Furthermore, manual grinding of the cusps is inefficient and yields poor results.

[0005] While carburizing heat treatment enables functional applications and provides a good, secure clamping fit, the high temperature and long processing time lead to severe deformation of the clamping jaws, making machining extremely difficult, resulting in a very low yield and poor product dimensional accuracy. Patent CN106435137B discloses a method and tooling for preventing clamping jaw deformation during carburizing heat treatment. While this patent can reduce deformation caused by workpiece compression, it cannot eliminate or reduce deformation caused by prolonged high temperatures during carburizing heat treatment, and it is not suitable for clamping jaws with high dimensional accuracy requirements and difficult machining processes, such as those with sharp teeth.

[0006] The conventional gas nitriding surface hardening process uses ammonia decomposition gas as the nitriding gas source. The structure of the nitriding layer compound is uncontrollable, and brittle structures of ε phase are inevitably produced. The resulting nitrided surface of the card is hard and has good occlusion, but the cusps are brittle and the cusp surface is very prone to cracking, chipping and failure, which in turn causes the occlusion to be weak and slippage to occur.

[0007] Ordinary ion nitriding processes and heating methods result in pitting erosion at sharp workpiece corners due to glow discharge overlap. Glow discharge overlap at the workpiece root and groove areas leads to high sputtering rates, low adhesion rates, and the formation of soft bands. Ordinary ion nitriding processes, such as... Figure 2 As shown ( Figure 2 The process comprises six stages: 1. Heating stage: glow discharge heating, arc heating rate ≤ 50℃ / h; 2. Holding stage: holding at 245℃-255℃ for 1.5h, glow discharge heating duty cycle 30%, ammonia decomposition temperature 560℃, flow rate 300ml / min, pressure 150Pa; 3. Heating stage: glow discharge heating, power supply duty cycle gradually adjusted to 65%-70%, heating rate ≤ 70℃ / h, ammonia decomposition temperature 560℃, flow rate gradually increased to... 1200ml / min; 4 is the holding stage: holding at 535℃-545℃ for 4 hours, ammonia decomposition temperature 580℃, flow rate 1200ml / min, pressure 300Pa, glow discharge heating duty cycle 70%; 5 is the holding stage: holding at 535℃-545℃ for 2 hours, ammonia decomposition temperature 680℃, flow rate 1000ml / min, pressure 200Pa, glow discharge heating duty cycle 70%; 6 is the unloading stage: workpiece temperature ≤150℃ before unloading. This toothed cylindrical jaw design requires essential tooth and root structures. Conventional ion nitriding processes relying on single glow discharge heating inevitably suffer from tooth tip ablation and the formation of a noticeable soft band at the tooth root, resulting in poor biting ability and slippage due to weak biting. Therefore, a surface hardening process for toothed cylindrical jaws is urgently needed to solve these problems. Summary of the Invention

[0008] The purpose of this invention is to provide a locking clip and its surface hardening process to solve the technical problem that the surface hardening treatment technology of the existing canine-type locking clips is immature, which makes the canines soften, burn, and become brittle, resulting in the locking clips not being able to bite firmly and easily slipping out, and often slipping and failing during operation.

[0009] To achieve the above objectives, one embodiment of the present invention provides a surface hardening process for kaolin, comprising the following steps:

[0010] The card substrate blank is subjected to quenching and tempering treatment;

[0011] After the conditioning process, the Kava is subjected to ion nitriding.

[0012] Furthermore, the blank substrate is subjected to quenching and tempering treatment, including:

[0013] Quenching: The quenching temperature is 860℃-870℃, the holding time is 2h-2.5h, and water-based quenching medium is used for cooling after quenching.

[0014] After quenching, tempering is performed at a temperature of 615℃-625℃ for 2.5h-3h.

[0015] Furthermore, after the quenching and tempering treatment is completed, the kava is subjected to ion nitriding treatment, which includes a first heating, a first holding, a second heating, a second holding, a third heating, nitriding treatment, a fourth heating and diffusion treatment, and after the diffusion treatment is completed, it is taken out of the furnace and air-cooled.

[0016] Furthermore, the time difference between the completion of quenching and the start of tempering is less than 2 hours.

[0017] Furthermore, the ion nitriding treatment of the kava also includes pretreatment, which includes cleaning and deburring of the workpiece before it enters the furnace.

[0018] Furthermore, the heating process includes: maintaining a furnace pressure of 30Pa-50Pa and using electric heating wire to raise the temperature to 195℃-205℃ at a rate of ≤60℃ / h.

[0019] Furthermore, the secondary heating includes: using an internal furnace pressure of 100Pa-150Pa, employing electric heating wire as the primary heating method and pulse power supply as a secondary method, to raise the temperature to 315℃-325℃ at a heating rate of ≤60℃ / h.

[0020] Furthermore, the secondary insulation includes: maintaining the temperature at 315℃-325℃ for 0.3h-0.7h, and introducing a nitrogen-hydrogen mixture when the pressure inside the furnace is 190Pa-210Pa.

[0021] Furthermore, the three heating stages include: the furnace pressure is 290Pa-310Pa, the heating method is changed from electric heating wire to pulse power supply, the pulse power supply duty cycle is 60%-65%, and the temperature is increased to 520℃-530℃ at a heating rate of ≤70℃ / h.

[0022] Furthermore, the nitriding treatment includes: maintaining a furnace pressure of 290Pa-310Pa and a nitriding temperature of 520℃-530℃ for 3.5h-4.5h.

[0023] Furthermore, the four heating stages include: maintaining a furnace pressure of 190Pa-210Pa, using pulse power supply as the primary heating method and electric heating wire as the secondary method, with a pulse power supply duty cycle of 65%-75%, heating at a rate of ≤70℃ / h to 540℃-550℃, and adjusting the ratio of nitrogen and hydrogen.

[0024] Furthermore, the diffusion treatment includes: maintaining a furnace pressure of 130Pa-150Pa and a diffusion temperature of 540℃-550℃ for 0.5h-1.5h.

[0025] Based on the surface hardening process of the kata disclosed in this invention, this invention also discloses a kata comprising a material prepared by using a kata substrate as raw material and applying the above-mentioned surface hardening process.

[0026] Furthermore, the Kava matrix comprises the following chemical components in the indicated mass percentages:

[0027] C%: 0.28-0.33, Si%: 0.15-0.35, Mn%: 0.75-1.0, Cr%: 0.75-1.0, Ni%: 1.65-2.0, Mo%: 0.35-0.50, V%: 0.05-0.10, P%: ≤0.015, S%: ≤0.015, balance Fe.

[0028] In summary, the beneficial effects of the present invention are as follows:

[0029] 1. The surface hardening process of the present invention for the tooth clips adopts a novel ion nitriding process for one-time hardening and molding, with sufficient dimensional accuracy, eliminating the need for further finishing before application. This solves the problem of extremely low yield of surface hardening after carburizing of cylindrical tooth clips. At the same time, it avoids the ablation of tooth tips caused by laser quenching and ordinary ion nitriding, greatly eliminating and reducing the occurrence of soft bands at the tooth tips, ensuring the hardness and uniformity of the tooth tips. Furthermore, it achieves controllable microstructure of the nitriding layer compound, reduces the brittle phase of the surface compound by about 50%, and greatly reduces the brittleness of the nitrided tooth tip surface, significantly reducing the risk of chipping during tooth tip operation. It also shortens the nitriding process time by about 20%, saves energy and reduces consumption by about 20%, and correspondingly reduces pollutant emissions by about 20%.

[0030] 2. This invention is applicable to the surface hardening of the teeth of downhole tools, surface equipment, and similar workpieces with high dimensional accuracy requirements for well conditions such as high temperature, high pressure, and corrosive environments; this invention has broad application prospects in the fields of drilling exploration and development of downhole tools and surface equipment.

[0031] 3. In the ion nitriding process of the surface hardening process of the present invention, the initial heating is entirely assisted by electric heating wire, which avoids the burning and softening of the canine matrix caused by the sudden current ablation of the canine cusp in the arc cleaning process of conventional ion nitriding. At the same time, resistance wire is added to assist heating throughout the process to suppress and weaken the intensity and amplitude of the cusp discharge current, thereby alleviating and reducing the overheating of the glow overlap area and reducing and avoiding the appearance of the surface hardening soft band area.

[0032] 4. The use of resistance wire-assisted heating in the ion nitriding process of this invention greatly improves the uniformity of furnace temperature, which greatly overcomes the low uniformity of furnace temperature in ion nitriding furnaces. In particular, it greatly improves the constant temperature at the sharp teeth of the workpiece, making the hardness and depth of the nitriding layer of the workpiece more uniform.

[0033] 5. In the ion nitriding treatment of this invention, a nitrogen-hydrogen mixture is used as the nitriding atmosphere. The nitrogen-hydrogen ratio is adjusted according to different process stages to achieve controllable compound phases in the nitrided layer, suppressing and reducing the ε-brittle phase by about 50%, which greatly reduces the surface brittleness of the nitrided layer. At the same time, the diffusion period and the surface denitrification process are combined into one, and the temperature is increased to further reduce the brittle ε-phase, shorten the process cycle, save process time and cost, and make the hardness gradient of the nitrided layer more gradual, which is conducive to improving the overall wear resistance of the workpiece and increasing the service life of the workpiece.

[0034] 6. The hardness of the card substrate of the present invention is 360HB-400HB after tempering and quenching at 620℃. The matrix structure is uniform tempered sorbite with a grain size of 8-9. After tempering and quenching, the hardness of the matrix does not decrease when nitriding at 580℃ for a long time. It has high nitrided matrix hardness and strength.

[0035] 7. Compared to carburizing heat treatment, the surface hardening process of the locator of this invention features a lower temperature and shorter processing time. The outer diameter deformation of the toothed cylindrical locator is ≤0.05mm, fully meeting the usage requirements without the need for subsequent finishing. Compared to laser quenching surface hardening, the ion nitriding process of this invention adds resistance wire auxiliary heating throughout the process, suppressing and weakening the intensity and amplitude of the sharp-corner discharge current, thereby alleviating and reducing overheating in the glow overlap area, reducing and avoiding the soft band area of ​​surface hardening, and maintaining a constant temperature at the sharp teeth of the workpiece. This results in a more uniform hardness and depth of the overall nitrided layer, with no ablation at the sharp teeth, and a more uniform surface hardened layer without obvious soft spots. Compared to gas nitriding, this invention uses a nitrogen-hydrogen mixture as the nitriding atmosphere. The nitrogen-hydrogen ratio is adjusted according to different proportions at different process stages, achieving controllable compound phases in the nitrided layer, suppressing and reducing the ε-brittle phase by about 50%, and greatly reducing the surface brittleness of the nitrided layer.

[0036] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention will be apparent from the effects described in the description and the accompanying drawings. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the canine-shaped slip in this invention;

[0038] Figure 2 This is a curve diagram of an existing common ion nitriding process;

[0039] Figure 3 This is a process curve diagram of the conditioning and tempering treatment of the kava matrix in this invention;

[0040] Figure 4 This is a schematic diagram of the tempered blank of the canine-shaped card slot matrix in this invention;

[0041] Figure 5 This is a graph showing the ion nitriding process of the kava of the present invention. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] This invention provides a surface hardening process for kaolin, comprising the following steps:

[0044] Step (1): The blank substrate of the card is subjected to quenching and tempering treatment, such as... Figure 3 As shown ( Figure 3 The process includes six stages: 1) quenching heating stage; 2) quenching holding stage: holding at 860℃-870℃ for 2-2.5 hours; 3) quenching cooling stage: rapid cooling to room temperature; 4) tempering heating stage; 5) tempering holding stage: holding at 615℃-625℃ for 2.5-3 hours; 6) tempering cooling stage: rapid cooling to room temperature. Specifically, it includes the following steps:

[0045] Step (101): Quenching: Steel toothed cylindrical chuck base blank (such as...) Figure 4 (As shown) The steel cone-shaped chuck blank is heated to 860℃-870℃ in a high-temperature heating furnace and held at 860℃-870℃ for 2h-2.5h to fully complete the austenitization transformation of the internal structure. After the complete austenitization transformation, the steel cone-shaped chuck blank is transferred to rapid quenching oil for rapid cooling to quickly cool the temperature of the steel cone-shaped chuck blank to room temperature, so that the internal structure of the steel cone-shaped chuck blank is maximized to transform from austenite to martensite.

[0046] Step (102): Tempering: After quenching, transfer the steel toothed cylindrical chuck base blank into a tempering furnace and heat it to 615℃-625℃ within a maximum of 2 hours. Hold it at 615℃-625℃ for 2.5h-3h. After holding, quickly transfer the steel toothed cylindrical chuck base blank into a cooling water tank to cool to room temperature. Using room temperature water for rapid cooling can better improve the impact toughness of the steel toothed cylindrical chuck base blank, thereby reducing the breakage of the teeth when the chuck is engaged.

[0047] The purpose of the quenching and tempering process is to obtain a uniform and dense tempered sorbite structure, which ensures the mechanical properties of the core and facilitates the formation of a uniform nitriding layer in the subsequent nitriding process, thereby reducing the brittleness of the nitrided layer formed in the subsequent nitriding process.

[0048] Step (2): After the conditioning treatment is completed, the Kava is subjected to ion nitriding treatment;

[0049] The reason for using ion nitriding is that the toothed cylindrical slip of this invention needs to quickly engage with the workpiece to fix it in place without breaking. Therefore, the surface properties of the toothed cylindrical slip must be wear-resistant, corrosion-resistant, and have high hardness to prevent breakage. The nitriding process should minimize the content of the brittle ε phase in the brittle compound layer on the surface. Moreover, the length of the workpiece is not large, so there is no problem of excessive temperature difference between the upper and lower parts of the nitrided surface. Therefore, ion nitriding is more suitable for surface hardening treatment.

[0050] like Figure 5 As shown ( Figure 5 The process includes 9 stages: Stage 1 is the heating stage, where electric heating wire assists in heating to 200℃ at a rate ≤60℃; Stage 2 is the holding stage, where electric heating wire assists in holding at 195℃-205℃ for 0.5 hours; Stage 3 is the heating stage, where glow discharge heating is activated, pulse power supply duty cycle is 20%, and heating rate is ≤60℃; Stage 4 is the holding stage, where the temperature is held at 315℃-325℃ for 0.5 hours at a pressure of 200 Pa, with a nitrogen-hydrogen mixture (nitrogen:hydrogen = 2:8) and pulse power supply duty cycle of 30%; Stage 5 is the heating stage, where the heating rate is <70℃ / h, the mixed gas flow rate gradually increases, and the pulse power supply duty cycle is 60%- 65%; 6 is the nitriding stage: nitriding at 520℃-530℃ for 4 hours, pressure 300Pa, nitrogen-hydrogen mixture, nitrogen:hydrogen = 2:8, pulse power supply duty cycle 60%-65%; 7 is the heating stage: pressure 200Pa, nitrogen-hydrogen mixture, nitrogen:hydrogen = 1:9, pulse power supply duty cycle 70%; 8 is the diffusion denitrification stage: diffusion denitrification at 540℃-550℃ for 1 hour, pressure 130-150Pa, nitrogen-hydrogen mixture, nitrogen:hydrogen = 1:9, pulse power supply duty cycle 70%; 9 is the furnace exit stage: workpiece ≤100℃ exits the furnace. Specifically, ion nitriding treatment includes the following steps:

[0051] Step (201): Preparation before nitriding: Ultrasonic cleaning of the workpiece before it enters the furnace, strict degreasing, wet sandblasting to remove burrs, and avoid point ablation during glow discharge heating.

[0052] Step (202): First heating: The furnace is evacuated to 30Pa-50Pa, and the heating is done entirely by electric heating wire without turning on the traditional power glow discharge heating. The temperature is raised to 195℃-205℃ at a rate of ≤60℃.

[0053] Objective: To minimize the arc-scraping process, reduce the large pulse current during arc-scraping, avoid and minimize point ablation of sharp corners of the workpiece, and shorten the heating time;

[0054] Step (203): First heat preservation: keep the temperature at 195℃-205℃ for 0.4h-0.6h to achieve uniform temperature of the canine surface. The heating method is entirely based on electric heating wire to ensure uniform temperature of the canine cusp and prevent canine cusp ablation.

[0055] Objective: To reduce the deformation of tooth tips during heating, and to remove oil stains from the workpiece surface to reduce the intensity of arcing when the pulse power supply is turned on, so as to avoid burning the tooth tips by glow discharge arc when the pulse power supply is turned on.

[0056] Step (204): Secondary heating: Heating is mainly done by electric heating wire. At this time, the power supply is turned on for glow discharge heating. The duty cycle of the pulse power supply is ≤20%. A suitable amount of nitrogen-hydrogen mixture is introduced. The ratio of nitrogen to hydrogen is 2:8. The pressure inside the furnace is gradually increased to 100Pa-150Pa. The heating rate is controlled to ≤60℃ / h. The temperature is raised to 315℃-325℃.

[0057] Step (205): Secondary heat preservation: Keep the temperature at 315℃-325℃ for 0.3h-0.7h, with heating mainly by electric heating wire, pulse power supply duty cycle of about 30%, and gradually increase the pressure inside the furnace to about 200Pa. Introduce an appropriate amount of nitrogen-hydrogen mixed gas, nitrogen:hydrogen = 2:8, and keep the furnace pressure stable.

[0058] Objective: To further homogenize the temperature of the cusps and other areas, reduce deformation and the intensity of subsequent temperature rise, and reduce cusp overheating;

[0059] Step (206): Three heating cycles: The heating method gradually shifts from electric heating wire to pulse power supply, with the pulse power supply duty cycle at 60%-65%. The temperature is gradually increased to 520℃-530℃ at a heating rate of ≤70℃ / h. The nitrogen-hydrogen mixture has a nitrogen:hydrogen ratio of 2:8, and the flow rate is gradually increased. The furnace pressure is gradually adjusted to 290Pa-310Pa.

[0060] Step (207): Nitriding treatment: Heating is mainly done by pulse power supply and supplemented by electric heating wire. The duty cycle of the pulse power supply is 60%-65%. The nitriding temperature is 520℃-530℃ and the temperature is maintained for 3.5h-4.5h. The pressure inside the furnace is 290Pa-310Pa. A nitrogen-hydrogen mixture is introduced with a nitrogen:hydrogen ratio of 2:8 and an appropriate flow rate to maintain a stable furnace pressure.

[0061] Step (208): Four heating cycles: Heating is mainly done by pulse power supply and supplemented by electric heating wire. The duty cycle of the pulse power supply is 65%-75%. The heating rate is ≤70℃ / h, and the temperature is gradually increased to 540℃-550℃. The pressure inside the furnace is gradually adjusted to 190Pa-210Pa. The ratio of nitrogen to hydrogen in the nitrogen-hydrogen mixture is gradually adjusted from 2:8 to 1:9.

[0062] Step (209): Diffusion treatment: Heating is mainly done by pulse power supply and supplemented by electric heating wire. The duty cycle of the pulse power supply is 65%-75%. The diffusion temperature is maintained at 540℃-550℃ for 0.5h-1.5h. The pressure inside the furnace is reduced to about 130Pa-150Pa. The ratio of nitrogen to hydrogen in the nitrogen-hydrogen mixture is 1:9. The flow rate is appropriate to maintain a stable furnace pressure.

[0063] Step (209): Cooling and unloading from the furnace: Turn off all heating power supplies and atmosphere valves, and allow the workpiece to cool in the furnace until it reaches ≤100℃ before unloading and air cooling.

[0064] This invention employs a novel ion nitriding process, completely replacing the traditional glow discharge heating method with resistance band heating in the initial nitriding stage. Stepped insulation is added to make the surface temperature of the tooth tips more uniform, further reducing the current intensity after activating glow discharge heating with a pulse power supply, thus minimizing overheating and burn-off of the tooth tips. Resistance band auxiliary heating is activated throughout the nitriding process, resulting in better overall temperature uniformity of the workpiece. The glow discharge heating current intensity of the pulse power supply is reduced, significantly decreasing burn-off and overheating of the tooth tips. A nitrogen-hydrogen mixture is used instead of the traditional ammonia decomposition gas as the nitriding gas source, enabling controllable phase composition of the nitriding layer compound and reducing the content of the brittle ε phase. High-temperature diffusion is added in the final stage of the process to further reduce the brittle ε phase content, further reducing the brittleness of the tooth tip surface and thus improving the design life of the clips.

[0065] The present invention also provides a kava, comprising a material prepared by using a kava substrate as raw material and applying the above-described surface hardening process.

[0066] The Kava matrix comprises the following chemical components in the indicated mass percentages:

[0067] C%: 0.28-0.33, Si%: 0.15-0.35, Mn%: 0.75-1.0, Cr%: 0.75-1.0, Ni%: 1.65-2.0, Mo%: 0.35-0.50, V%: 0.05-0.10, P%: ≤0.015, S%: ≤0.015, balance Fe.

[0068] The slip matrix of the present invention has a hardness of 360HB-400HB at 620℃ after tempering, and the matrix structure is uniform tempered sorbite with a grain size of grade 8-9. Moreover, the hardness of the matrix does not decrease after tempering and nitriding at a temperature below 580℃ for a long time. It has high nitrided matrix hardness and strength, which fully meets the requirement of avoiding the crushing and breakage of the nitrided surface of the canine slip under the large load clamping force.

[0069] Example 1

[0070] This embodiment uses 30CrNi2MoV steel, and the material composition is as follows:

[0071] C%: 0.31, Si%: 0.28, Mn%: 0.90, Cr%: 0.95, Ni%: 1.86, Mo%: 0.45, V%: 0.08, P%: 0.009, S%: 0.010, balance Fe.

[0072] (1) The processing flow is as follows:

[0073] Hot-rolled bar stock—turning—quenching and tempering—turning—stress relief—turning—ultrasonic testing—clamping—milling—stress relief—finish milling—nitriding—wire cutting—warehousing;

[0074] (2) Tempering process: After being heated to 860°C and held for 2.5 hours in the high-temperature furnace of the controlled atmosphere box-type multi-purpose furnace production line, it is cooled to room temperature using water-based quenching medium. After cleaning the surface oil, it is quickly transferred to the resistance tempering furnace of the controlled atmosphere box-type multi-purpose furnace production line and heated to 620°C and held for 3 hours, and then cooled to room temperature by water.

[0075] After tempering, the hardness of the toothed cylindrical chuck matrix blank is 385HB;

[0076] (3) After the toothed cylindrical cladding blank is precision milled into the final tooth shape, it is subjected to ion nitriding treatment in the effective heating zone: φ920mm×1600mm bell-type pre-vacuum ion nitriding furnace.

[0077] Ion nitriding process:

[0078] (301) Preparation before nitriding: Ultrasonic cleaning of workpieces before entering the furnace, strict degreasing, wet sandblasting to remove burrs, to avoid point ablation during glow discharge heating.

[0079] To reduce deformation during the kava nitriding process, the furnace is charged vertically.

[0080] (302) First preheating: The furnace is evacuated to 30Pa and heated entirely by electric heating wire at a rate of 60℃ / h to 200℃.

[0081] (303) First stage of heat preservation: The surface of the canine is heated to 200℃ for 0.5 hours, and the heating method is completely adopted to make the canine tip uniformly heated;

[0082] (304) Second stage of heating: Heating is mainly done by electric heating wire. At this time, glow discharge heating is turned on, pulse power duty cycle is 20%, and an appropriate amount of nitrogen-hydrogen mixture is introduced. Nitrogen:hydrogen = 2:8. The pressure inside the furnace is gradually increased to 200Pa, and the temperature is increased to 320℃ at a heating rate of 60℃ / h.

[0083] (305) Second stage heat preservation: the surface of the canine is heated to 320℃ for 0.5 hours. The heating is mainly by electric heating wire, the pulse power supply duty cycle is 30%, and a nitrogen-hydrogen mixture is introduced. The ratio of nitrogen to hydrogen is 2:8. The pressure inside the furnace is 200Pa and the atmosphere flow rate is 700ml / min.

[0084] (306) Third stage of heating: The heating gradually shifts from electric heating wire to pulse power supply heating, gradually increasing the proportion of pulse power supply heating, with a pulse power supply duty cycle of 65%, and a heating rate of 70℃ / h, gradually increasing the temperature to 525℃. The ratio of nitrogen to hydrogen in the nitrogen-hydrogen mixture is 2:8, the flow rate is gradually increased to 1000ml / min, and the pressure inside the furnace is increased to 300Pa.

[0085] (307) Nitriding period: Heating is mainly done by pulse power supply and supplemented by electric heating wire. The duty cycle of pulse power supply is 65%. The nitriding temperature is 525℃ and held for 4 hours. The pressure inside the furnace is gradually adjusted to 300Pa. The ratio of nitrogen to hydrogen in the nitrogen-hydrogen mixture is 2:8 and the flow rate is 1000ml / min.

[0086] (308) Fourth stage of heating: Heating is mainly done by pulse power supply and supplemented by electric heating wire. The duty cycle of the pulse power supply is 70%. The temperature is gradually increased to 545℃ at a heating rate of 70℃ / h. The pressure inside the furnace is gradually adjusted to 200Pa. The ratio of nitrogen to hydrogen in the nitrogen-hydrogen mixture is gradually adjusted from 2:8 to 1:9. The flow rate is 1100ml / min.

[0087] (309) Diffusion + Surface denitrification: Heating is mainly done by pulse power supply and supplemented by electric heating wire. The pulse power supply duty cycle is 70%. The temperature is kept at 545℃ for 1 hour. The pressure inside the furnace is gradually reduced to 140Pa. The ratio of nitrogen to hydrogen in the nitrogen-hydrogen mixture is 1:9 and the flow rate is 1100ml / min.

[0088] (310) Cooling and unloading from the furnace: Turn off all heating power supplies and all atmosphere valves, and cool the workpiece surface temperature to 90°C with the furnace before unloading and air cooling to room temperature.

[0089] Testing and Inspection

[0090] The test results of the canine-shaped Kavalve after nitriding are as follows:

[0091] After nitriding, the surface hardness of the nitrided parts at both ends of the tooth-shaped clip is 745HV, the hardened layer depth is 0.33mm, the surface hardness of the nitrided parts of the upper, middle and lower parts of the specimen is relatively consistent with the depth of the nitrided layer, the nitrided layer is loose grade 1, the nitride grade in the nitrided layer is grade 1, the surface brittleness of the nitrided layer is grade 1, the outer diameter of the tooth-shaped clip expands by 0.05mm, and there is no obvious overheating phenomenon at the tooth of the clip.

[0092] Comparative Example 1

[0093] The material composition and other process flow are the same as in Example 1, except that in the first preheating stage (302), the electric heating wire auxiliary heating and the pulse power supply glow heating are turned on at the same time. The duty cycle of the glow heating pulse power supply is 15%. The subsequent process flow and control parameters are the same as in Example 1.

[0094] The test results of the canine-shaped Kavalve after nitriding are as follows:

[0095] After nitriding, the surface hardness of the nitrided ends of the canine-shaped clip was 752 HV, and the hardened layer depth was 0.33 mm. The surface hardness of the upper, middle, and lower parts of the specimen was consistent with the nitrided layer depth. The nitrided layer was grade 1 in terms of porosity, grade 1 in terms of nitride content, and grade 1 in terms of surface brittleness. The outer diameter of the canine-shaped clip increased by 0.05 mm. There was significant localized overheating at the canine teeth of the clip. Although the duty cycle of the glow discharge heating pulse power supply was adjusted to a very small value during the heating process, compared with Example 1, the test results still showed significant arcing at the canine teeth, which should be the reason for the significant localized overheating at the canine teeth.

[0096] Comparative Example 2

[0097] The material composition and other process flow are the same as in Example 1, except that in the third stage of heating (306), the heating is still mainly done by electric heating wire, the pulse power supply duty cycle is 30%, and the subsequent process flow and control parameters are the same as in Example 1.

[0098] The test results of the canine-shaped Kavalve after nitriding are as follows:

[0099] After nitriding, the surface hardness of the nitrided parts at both ends of the tooth-shaped clip is 748HV, the hardened layer depth is 0.32mm, the surface hardness of the upper, middle and lower parts of the specimen is consistent with the nitrided layer depth, the nitrided layer is loose grade 1, the nitride grade in the nitrided layer is grade 1, the surface brittleness of the nitrided layer is grade 1, and the outer diameter of the tooth-shaped clip expands by 0.05mm.

[0100] Compared to Example 1, the cusps of the card show almost no signs of overheating, and the color of the cusps is more silvery-gray than in Example 1. However, the temperature rise is significantly lower and slower, affecting production efficiency.

[0101] Comparative Example 3

[0102] The material composition and other process flow are the same as in Example 1. In the fourth stage of (308), the heating is mainly done by pulse power supply heating and supplemented by electric heating wire heating. The pulse power supply duty cycle is 70%, and the temperature is gradually increased to 560°C at a heating rate of 70°C / h. Other parameters are the same as in Example 1.

[0103] (309) Diffusion + surface denitrification: Heating is mainly done by pulse power supply and supplemented by electric heating wire. The pulse power supply duty cycle is 70%. The temperature is kept at 560℃ for 1 hour. The pressure inside the furnace is gradually reduced to 140Pa. The ratio of nitrogen to hydrogen in the nitrogen-hydrogen mixture is 1:9 and the flow rate is 1100ml / min.

[0104] The test results of the canine-shaped Kavalve after nitriding are as follows:

[0105] After nitriding, the surface hardness of the nitrided parts at both ends of the tooth-shaped clip is 760HV, the hardened layer depth is 0.36mm, the surface hardness of the upper, middle and lower parts of the specimen is consistent with the nitrided layer depth, the nitrided layer is loose grade 1, the nitride grade in the nitrided layer is grade 2, the surface brittleness of the nitrided layer is grade 1, and the outer diameter of the tooth-shaped clip expands by 0.06mm.

[0106] Compared with Example 1, the test results of increasing the diffusion temperature to 560°C show that as the nitriding temperature increases, the hardened layer depth of the nitrided layer increases significantly, which is beneficial to improving wear resistance. However, the nitride grade deteriorates, increasing the brittleness of the canines, and the overall deformation of the clips increases.

[0107] Repeated experiments revealed that the higher the diffusion temperature (≤580℃), the lower the content of the brittle ε phase, and the better the brittleness reduction effect. However, when the diffusion temperature is >580℃, the porosity of the nitrided layer increases, the nitride level in the nitrided layer deteriorates, and the surface brittleness of the nitrided layer worsens.

[0108] In summary, the surface hardening process of the slip of the present invention has the advantages of low temperature and short process time of ion nitriding process. The outer diameter deformation of the toothed cylindrical slip is ≤0.05mm, which fully meets the requirements of use and does not require subsequent finishing.

[0109] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A surface hardening process for a clapper, characterized in that, Includes the following steps: The card substrate blank is subjected to quenching and tempering treatment; After the conditioning process, the Kava is subjected to ion nitriding.

2. The surface hardening process of a kaolin as described in claim 1, characterized in that, The heat treatment of the kava substrate blank includes: Quenching: The quenching temperature is 860℃-870℃, the holding time is 2h-2.5h, and water-based quenching medium is used for cooling after quenching. After quenching, tempering is performed at a temperature of 615℃-625℃ for 2.5h-3h.

3. The surface hardening process of a kaolin as described in claim 1, characterized in that, After the conditioning treatment is completed, the kava is subjected to ion nitriding treatment, which includes a first heating, a first holding, a second heating, a second holding, a third heating, a nitriding treatment, a fourth heating and a diffusion treatment. After the diffusion treatment is completed, the kava is removed from the furnace and air-cooled.

4. The surface hardening process of a kaolin as described in claim 2, characterized in that: The time difference between the completion of quenching and the start of tempering is less than 2 hours.

5. The surface hardening process of a chalcoat as described in claim 3, characterized in that: The ion nitriding treatment of the kalo also includes pretreatment, which includes cleaning and deburring of the workpiece before it enters the furnace.

6. The surface hardening process of a kaolin as described in claim 3, characterized in that, The first heating step includes: the furnace pressure is 30Pa-50Pa, and the temperature is raised to 195℃-205℃ by heating with electric heating wire at a heating rate of ≤60℃ / h.

7. The surface hardening process of a clapper as described in claim 3, characterized in that, The secondary heating includes: heating the furnace at a pressure of 100Pa-150Pa, using electric heating wire as the main method and pulse power supply as the auxiliary method, to raise the temperature to 315℃-325℃ at a heating rate of ≤60℃ / h.

8. The surface hardening process of a kaolin as described in claim 3, characterized in that, The secondary heat preservation includes: maintaining a temperature of 315℃-325℃ for 0.3h-0.7h, and introducing a nitrogen-hydrogen mixture when the pressure inside the furnace is 190Pa-210Pa.

9. The surface hardening process of a chalcoat as described in claim 3, characterized in that, The three heating stages include: furnace pressure of 290Pa-310Pa, switching from electric heating wire as the main heating method to pulse power supply as the main heating method, with a pulse power supply duty cycle of 60%-65%, and heating to 520℃-530℃ at a heating rate of ≤70℃ / h.

10. The surface hardening process of a kaolin as described in claim 3, characterized in that, The nitriding treatment includes: maintaining a furnace pressure of 290Pa-310Pa and a nitriding temperature of 520℃-530℃ for 3.5h-4.5h.

11. The surface hardening process of a kalouse as described in claim 3, characterized in that, The four heating cycles include: maintaining a furnace pressure of 190Pa-210Pa, using pulse power supply as the primary heating method and electric heating wire as the secondary method, with a pulse power supply duty cycle of 65%-75%, heating at a rate of ≤70℃ / h to 540℃-550℃, and adjusting the ratio of nitrogen and hydrogen.

12. The surface hardening process of a kaolin as described in claim 3, characterized in that, The diffusion treatment includes: maintaining a furnace pressure of 130Pa-150Pa and a diffusion temperature of 540℃-550℃ for 0.5h-1.5h.

13. A type of kava, characterized in that: This includes materials prepared using a kava matrix as raw material and applying a kava surface hardening process as described in any one of claims 1-12.

14. A kava as described in claim 13, characterized in that, The Kava matrix comprises the following chemical components in the indicated mass percentages: C%: 0.28-0.33, Si%: 0.15-0.35, Mn%: 0.75-1.0, Cr%: 0.75-1.0, Ni%: 1.65-2.0, Mo%: 0.35-0.50, V%: 0.05-0.10, P%: ≤0.015, S%: ≤0.015, balance Fe.

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