Gradient-distribution high-nitrogen-concentration carbonitriding process and part

Abstract

The invention discloses a carbonitriding process with high nitrogen concentration in gradient distribution and a part. According to the method, the carbon potential and the nitrogen potential in the co-permeation stage are precisely controlled, so that the nitrogen atom concentration higher than 0.5% is formed on the surface of the part, the specified nitrogen atom diffusion depth is reached, the gradient of the carbon and nitrogen contents of different depths of a part permeation layer is stable, the quality difference of parts of different heat numbers is greatly reduced, and the contact fatigue strength of a transmission part can be greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of thermal processing of transmission parts, and in particular relates to a carbonitriding process and parts with a high nitrogen concentration and a gradient distribution. Background Art

[0002] Carbonitriding is a common surface thermal processing method that can significantly improve the hardness, wear resistance and corrosion resistance of transmission parts. In the traditional carbonitriding process, the actual amount of each medium introduced cannot be accurately measured and controlled in real time, which makes the carbon and nitrogen content gradient of the parts' carburized layer unstable at different depths, or only controls the carbon potential, which cannot meet the requirements of nitrogen atom diffusion depth and diffusion concentration, resulting in low contact fatigue strength of transmission parts that do not meet actual requirements. Summary of the invention

[0003] In order to solve the above-mentioned problems existing in the existing technology, the present invention provides a high nitrogen concentration carbonitriding process and parts with a gradient distribution, so that the amount and proportion of each medium introduced into the parts during the co-diffusion stage can be precisely controlled, thereby stabilizing the carbon-nitrogen content gradient at different depths of the part's diffusion layer and greatly reducing the quality differences of parts from different batches.

[0004] The present invention is achieved through the following technical solutions:

[0005] A high nitrogen concentration carbonitriding process with gradient distribution, the specific process method is as follows:

[0006] The parts are carbonitrided at a temperature range of 840-860°C. In the first stage, the carbon potential is controlled at 0.06-0.70%, the nitrogen potential is 0.50-0.60%, and the co-diffusion time is 40 minutes; in the second stage, the carbon potential is controlled at 1.00-1.10%, the nitrogen potential is 0.45-0.55%, and the co-diffusion time is 150-190 minutes; in the third stage, the carbon potential is controlled at 0.90-1.05%, the nitrogen potential is 0.45-0.55%, and the co-diffusion time is 120-140 minutes.

[0007] Furthermore, the carbonitriding medium is ammonia, methanol, nitrogen and propane.

[0008] Furthermore, the medium flow is precisely controlled: in the first, second and third stages, the methanol flow is 2-4 L / h, and the nitrogen flow is 2.2-4.4 m 3 / h, propane flow rate is 0-0.6m 3 / h; the ammonia flow rate in the first stage is 0, and the ammonia flow rate in the second stage is 0.20-0.30m 3 / h, the ammonia flow rate in the third stage is 0.15-0.25m 3 / h.

[0009] Furthermore, in each stage, methanol and nitrogen are introduced at a ratio of 1:1.1.

[0010] Furthermore, the medium flow, carbon potential and nitrogen potential are controlled by a high-precision mass flow meter, an ammonia analyzer and a hydrogen analyzer.

[0011] Furthermore, the carbonitriding equipment is a multi-purpose furnace with controlled atmosphere.

[0012] The present invention also protects parts treated by the carbonitriding process with a high nitrogen concentration in a gradient distribution, wherein a uniform diffusion layer with a high carbon and nitrogen content in a gradient distribution is formed from the surface to the core of the parts.

[0013] Furthermore, a nitrogen atom concentration higher than 0.5% is formed on the surface of the component, and a diffusion layer depth is not less than 0.45 mm.

[0014] Furthermore, the surface of the part is 0<depth≤0.05mm, the nitrogen atom concentration is 0.5-0.75%, and the carbon atom concentration is 0.70-0.95%; the sub-surface is 0.05<depth≤0.10mm, the nitrogen atom concentration is 0.35-0.60%, and the carbon atom concentration is 0.70%-0.95%; the shallow surface is 0.10<depth≤0.45mm, the nitrogen atom concentration is 0-0.20% (excluding 0), and the carbon atom concentration is 0.25-0.50%.

[0015] The beneficial effects achieved by the present invention are as follows:

[0016] (1) The present invention controls the carbon potential and nitrogen potential of the system by precisely controlling the medium introduced into the furnace during the co-diffusion stage, thereby obtaining parts with a stable carbon and nitrogen content gradient at different depths of the diffusion layer, and the quality difference of parts from different batches is greatly reduced.

[0017] (2) The temperature of the co-penetration stage of the process of the present invention is low, which reduces the deformation of the parts during heat treatment, thereby greatly reducing the energy consumption and cost of the subsequent finishing process (especially the fine grinding process).

[0018] (3) The present invention forms a uniform diffusion layer with a high carbon-nitrogen content from the surface to the core of the part, and the surface forms a nitrogen atom concentration higher than 0.5% and reaches a specified nitrogen atom diffusion depth, thereby greatly improving the contact fatigue strength of the part. It can greatly improve the contact fatigue strength of the transmission part, achieve lightweight, high precision, high stability and high durability, and reduce energy consumption during installation and use.

[0019] (4) The process of the present invention reduces the amount of methanol, ammonia, nitrogen, propane, etc. introduced into the furnace through precise control, while also reducing waste gas emissions, thereby achieving a green production process that saves energy and reduces emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the device of the present invention.

[0021] Figure 2 It is a schematic diagram of the process curve of the present invention.

[0022] Figure 3 This is the metallographic structure diagram of the carburized layer of the parts processed by the patented process of this invention.

[0023] Figure 4 The surface layer of the parts processed by the patented process of this invention is non-horse tissue.

[0024] Figure 5 This is the gradient map for detecting the hardened layer of the parts processed by the patented process of this invention.

[0025] Figure 6 The carbon and nitrogen content requirements and test results of parts processed by the patented process of this invention.

[0026] Figure 7 is the carbon and nitrogen content of the carbonitriding diffusion layer of the present invention. DETAILED DESCRIPTION

[0027] The present invention is further described below in conjunction with specific embodiments, but the present invention is not limited to these specific embodiments. Those skilled in the art should recognize that the present invention covers all possible alternatives, improvements and equivalents within the scope of the claims.

[0028] The specific implementation of the present invention is based on a fully automated box-type controlled atmosphere multi-purpose furnace production line with good working conditions. The temperature uniformity SUS of the multi-purpose furnace equipment at 850℃ and 930℃ does not exceed ±5℃, and the furnace temperature system accuracy SAT is ≤2.2℃ using the detection method. Figure 1As shown, the multi-purpose furnace includes a front furnace door 1, an antechamber 2, antechamber dead zone 3, a smoke exhaust pipe 4, a zero pressure surface 5, a middle door hole 6, a middle furnace door 7, a heating chamber 8, an entrance 1 9 and an entrance 2 10. The oxygen probe of the multi-purpose furnace equipment enters the heating chamber through the sealed pipe seat from the back wall so that it can fully contact the furnace gas. The probe air supply is equipped with a special diaphragm air pump, including necessary solenoid valves, filters, flow meters, etc. The multi-purpose furnace equipment is also equipped with a CO analyzer to detect the CO content. The multi-purpose furnace equipment must also be equipped with a trace ammonia content analyzer and a hydrogen content analyzer. Through the above customized equipment, the following can be achieved: real-time monitoring, automatic control and traceability of process Cp and Np; the medium flow (nitrogen, methanol, propane, ammonia) is automatically regulated by an automatic flow controller, and the equipment can realize real-time monitoring and traceability of the medium flow; through the combination of software and hardware, the production line can achieve full automatic control. Based on theoretical analysis and actual batch processing verification, the present invention finally selects the best medium inlet 1 9 and inlet 2 10 to optimize the uniformity of the atmosphere in the furnace during the production process, and finally achieves uniform and consistent quality of the products in the same furnace. Based on theoretical analysis and actual large-scale experimental verification, the present invention adopts the method of full furnace loading. If the parts are not full of the furnace, they need to be matched with scrap to make the furnace loading reach full.

[0029] The carbonitriding process parameter curve of high nitrogen concentration with gradient distribution that can be used for batch processing in a specific embodiment of the present invention is as follows: Figure 2 The horizontal axis of the process curve represents time (unit: minutes), and the vertical axis represents temperature (unit: °C). The co-penetration process is mainly divided into six stages:

[0030] The AB segment represents the preparation stage for parts to enter the furnace;

[0031] The BC section represents the temperature rise section. In this stage, the co-penetration temperature reaches 840-860°C, the methanol flow rate is controlled at 2-4L / h, and the nitrogen flow rate is 2.2-4.4m 3 / h, propane flow rate is 0-0.6m 3 / h, methanol and nitrogen are introduced in a ratio of 1:1.1, so that the carbon potential is 0.06-0.70%, and the nitrogen potential is 0.50-0.60%. The co-penetration time in this stage is 40 minutes, which is set according to the heating capacity of the parts and equipment;

[0032] The CD section represents the strong permeation section, the temperature reaches 840-860℃, the methanol flow rate is controlled at 2-4L / h, and the nitrogen flow rate is 2.2-4.4m 3 / h, ammonia flow rate is 0.20-0.30m 3 / h, methanol and nitrogen are introduced in a ratio of 1:1.1, so that the carbon potential is 1.00-1.10%, the nitrogen potential is 0.45-0.55%, and the co-penetration time of this stage is 150-190min, which is set according to the depth of the hardened layer of the part;

[0033] The DE section represents the diffusion section, the temperature reaches 840-860°C, the methanol flow rate is controlled at 2-4L / h, and the nitrogen flow rate is 2.2-4.4m 3 / h, ammonia flow rate is 0.15-0.25m 3 / h, methanol and nitrogen are introduced in a ratio of 1:1.1, so that the carbon potential is 0.90-1.05%, and the nitrogen potential is 0.45-0.55%. The co-penetration time of this stage is 120-140min, which is set according to the depth of the hardened layer of the part;

[0034] The EF section represents the quenching stage of the parts. The quenching medium is high-temperature oil, and the oil temperature is 110-130°C. The stirring parameters are set according to the part material and the core hardness requirements. Specifically, fast stirring for 10 minutes and slow stirring for 15 minutes, with speeds of 1200rpm and 800rpm respectively;

[0035] The FG segment represents the low-temperature tempering stage. According to the surface hardness and organizational requirements of the parts, the tempering temperature is 150-170°C and the time is not less than 120 minutes.

[0036] The hardness and metallographic examination of the parts after the process of the present invention are in accordance with the relevant international and national standards. The metallographic structure diagram of the infiltration layer of the parts of the test example is as follows: Figure 3 As shown, the retained austenite on the surface of the part is 52% (X-ray diffractometer test results); non-horse tissue is shown Figure 4 ; Hardening layer gradient see Figure 5 ; The C and N contents at different depths from the surface to the core of the part are tested by the peeling method, such as Figure 6 , Figure 7 .

[0037] It can be seen from the test results that the retained austenite content of the parts of the present invention can reach 35-70%, and the subsurface hardness is not less than 680HV0.5, and the hardness gradient is smooth. The carbon and nitrogen content of the parts is distributed in a gradient, and the nitrogen atom concentration is 0.5-0.75% and the carbon atom concentration is 0.70-0.95% on the surface of the parts 0<depth≤0.05mm; the nitrogen atom concentration is 0.35-0.60% and the carbon atom concentration is 0.70%-0.95% on the subsurface 0.05<depth≤0.10mm; the nitrogen atom concentration is 0-0.20% (excluding 0) and the carbon atom concentration is 0.25-0.50% on the shallow surface 0.10<depth≤0.45mm.

[0038] In summary, the surface of the part of the present invention forms a nitrogen atom concentration higher than 0.5% and reaches a specified nitrogen atom diffusion depth, thereby greatly improving the contact fatigue strength of the part.

Claims

1. A high nitrogen concentration carbonitriding process with gradient distribution, characterized in that: The specific process is as follows: The parts are carbonitrided at a temperature range of 840-860°C. In the first stage, the carbon potential is controlled at 0.06-0.70%, the nitrogen potential is 0.50-0.60%, and the co-diffusion time is 40 minutes; in the second stage, the carbon potential is controlled at 1.00-1.10%, the nitrogen potential is 0.45-0.55%, and the co-diffusion time is 150-190 minutes; in the third stage, the carbon potential is controlled at 0.90-1.05%, the nitrogen potential is 0.45-0.55%, and the co-diffusion time is 120-140 minutes.

2. The carbonitriding process according to claim 1, characterized in that: The carbonitriding medium is ammonia, methanol, nitrogen and propane.

3. The carbonitriding process according to claim 1, characterized in that: The medium flow is precisely controlled: in the first, second and third stages, the methanol flow is 2-4 L / h, and the nitrogen flow is 2.2-4.4 m / h. 3 / h, propane flow rate is 0-0.6m 3 / h; the ammonia flow rate in the first stage is 0, and the ammonia flow rate in the second stage is 0.20-0.30m 3 / h, the ammonia flow rate in the third stage is 0.15-0.25m 3 / h.

4. The carbonitriding process according to claim 3, characterized in that: In each stage, methanol and nitrogen were introduced in a ratio of 1:1.

1.

5. The carbonitriding process according to claim 1, characterized in that: The medium flow, carbon potential and nitrogen potential are controlled by a high-precision mass flow meter, an ammonia analyzer and a hydrogen analyzer.

6. The carbonitriding process according to claim 1, characterized in that: The carbonitriding equipment is a multi-purpose furnace with controlled atmosphere.

7. A part treated by carbonitriding according to any one of claims 1 to 6, characterized in that: A uniform diffusion layer with high carbon and nitrogen content and gradient distribution is formed from the surface to the core of the component.

8. The component according to claim 7, characterized in that A nitrogen atomic concentration higher than 0.5% is formed on the surface of the part, and a diffusion layer depth is not less than 0.45 mm.

9. The component according to claim 8, characterized in that The surface of the part has a nitrogen atom concentration of 0.5-0.75% and a carbon atom concentration of 0.70-0.95% at a depth of 0.05 < ≤ 0.05 mm; the sub-surface has a nitrogen atom concentration of 0.35-0.60% and a carbon atom concentration of 0.70%-0.95% at a depth of 0.05 < ≤ 0.10 mm; Shallow surface 0.10<depth≤0.45mm, nitrogen atom concentration is 0-0.20% (excluding 0), and carbon atom concentration is 0.25-0.50%.

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