Heat treatment process of high-nitrogen stainless steel bearing

Abstract

The application relates to the technical field of heat treatment, and discloses a heat treatment process for high-nitrogen stainless steel bearings, which comprises the following steps: nitriding, cooling and heat treatment of the stainless steel bearings; the temperature for nitriding is 600-620 DEG C, and the time is 2-3 hours; the cooling process comprises three stages, in the first stage, the stainless steel bearings are cooled at a speed of 10-15 DEG C / h to 530-550 DEG C, in the second stage, the stainless steel bearings are cooled at a speed of 25-35 DEG C / h from 530-550 DEG C to 380-400 DEG C, and in the third stage, the stainless steel bearings are cooled at a speed of 50-55 DEG C / h from 380-400 DEG C to room temperature; the hardness of the high-nitrogen stainless steel bearings is improved by the technical scheme.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of heat treatment, in particular to a heat treatment process of high-nitrogen stainless steel bearing. BACKGROUND

[0002] In the industrial field, high-nitrogen stainless steel bearings are widely used in food processing, chemical industry, marine engineering and other harsh environments due to their corrosion resistance. However, traditional high-nitrogen stainless steel bearings are difficult to balance between hardness and corrosion resistance: when stainless steel materials have excellent corrosion resistance, their organizational structure characteristics limit the improvement of hardness, making it difficult to meet the needs of high-speed and high-load working conditions.

[0003] Traditional heat treatment processes face multiple challenges. For example, if the temperature is not properly controlled during the tempering process of martensitic stainless steel, chromium-depleted zones may be formed due to the precipitation of carbides, leading to the destruction of the passivation film and an increase in pitting sensitivity. In addition, the conventional quenching process is insufficient for the hardenability of large-sized parts, which easily leads to uneven organization and internal stress concentration, resulting in insufficient hardness of high-nitrogen stainless steel bearings. The problem that the heat treatment process cannot meet the high hardness requirement is particularly prominent in marine engineering, chemical equipment and other scenarios.

[0004] Therefore, it is crucial to develop a heat treatment process for high-nitrogen stainless steel bearings that improves hardness. SUMMARY

[0005] The present application proposes a heat treatment process for high-nitrogen stainless steel bearings, which solves the problem of poor hardness of high-nitrogen stainless steel bearings in the related art.

[0006] The technical solution of the present application is as follows:

[0007] The present application proposes a heat treatment process for high-nitrogen stainless steel bearings, which includes the following steps: nitriding, cooling, heat treatment of stainless steel bearings;

[0008] The temperature of nitriding is 600-620℃, and the time is 2-3h;

[0009] The cooling process includes three stages: in the first stage, the temperature is cooled to 530-550℃ at a rate of 10-15℃ / h; in the second stage, the temperature is cooled to 380-400℃ at a rate of 25-35℃ / h; in the third stage, the temperature is cooled to room temperature at a rate of 50-55℃ / h.

[0010] As a further technical solution, the stainless steel bearing is subjected to surface activation treatment before nitriding;

[0011] During the surface activation treatment, the catalyst is evenly applied to the stainless steel bearing.

[0012] As a further technical solution, the mass-volume ratio of the stainless steel bearing and the catalyst is 1g:3-5mL.

[0013] As a further technical solution, the raw material of the catalyst includes the following components by mass: ethanol 70-90 parts, activated carbon 7-8 parts, triethanolamine 12-16 parts, and rare earth oxide 2-5 parts.

[0014] The preparation method of the catalyst includes the following steps: uniformly mixing the raw material of the catalyst to obtain the catalyst.

[0015] In the heat treatment process of the high-nitrogen stainless steel bearing, the rare earth oxide can help to improve the nitriding speed and enhance the nitriding effect.

[0016] As a further technical solution, the rare earth oxide is a composite rare earth oxide.

[0017] The raw material of the composite rare earth oxide includes rare earth oxide, coupling agent, and n-octyl p-hydroxybenzoate.

[0018] As a further technical solution, the preparation method of the composite rare earth oxide includes the following steps:

[0019] A1, adding rare earth oxide into water, adding coupling agent, stirring, concentrating, and drying to obtain pretreated rare earth oxide;

[0020] A2, adding the pretreated rare earth oxide into dichloromethane, adding n-octyl p-hydroxybenzoate, stirring, concentrating, and drying to obtain composite rare earth oxide.

[0021] In the heat treatment process of the high-nitrogen stainless steel bearing, the coupling agent and n-octyl p-hydroxybenzoate composite rare earth oxide are used as the raw material of the catalyst to improve the corrosion resistance of the stainless steel bearing. The present application focuses on the poor dispersibility of rare earth oxide in ethanol solvent in the catalyst, so the coupling agent and n-octyl p-hydroxybenzoate composite rare earth oxide are used to improve the dispersibility of rare earth oxide, fully exert the nitriding effect of rare earth oxide, improve the nitriding effect, and thus improve the corrosion resistance of the stainless steel bearing.

[0022] As a further technical solution, in step A1, the mass-volume ratio of the rare earth oxide and water is 1g:10-12mL.

[0023] As a further technical solution, in step A2, the mass-volume ratio of the pretreated rare earth oxide and dichloromethane is 1g:10-12mL.

[0024] As a further technical solution, the mass ratio of the rare earth oxide, coupling agent, and n-octyl p-hydroxybenzoate is 25:3:4-5.

[0025] In the heat treatment process of the high-nitrogen stainless steel bearing of the present invention, when the mass ratio of rare earth oxide, coupling agent and n-octyl p-hydroxybenzoate is 25:3:4~5, the corrosion resistance of the high-nitrogen stainless steel bearing of the present invention is further improved.

[0026] In the heat treatment process of the high-nitrogen stainless steel bearing of the present invention, the mass ratio of rare earth oxide, coupling agent and n-octyl p-hydroxybenzoate can be 25:3:4, 25:3:4.1, 25:3:4.2, 25:3:4.3, 25:3:4.4, 25:3:4.5, 25:3:4.6, 25:3:4.7, 25:3:4.8, 25:3:4.9, or 25:3:5, preferably 25:3:4.

[0027] As a further technical solution, the coupling agent includes one of KH-550 coupling agent and KH-560 coupling agent, preferably KH-550 coupling agent.

[0028] As a further technical solution, in step A1, the stirring speed is 300~400 rpm, the time is 1~2 hours, and the temperature is 30~40℃;

[0029] In step A2, the stirring speed is 300~400 rpm, the time is 4~5 h, and the temperature is 20~30℃.

[0030] As a further technical solution, the raw materials of the composite rare earth oxide include one or two of yttrium oxide and cerium oxide.

[0031] As a further technical solution, during nitriding, the raw material used for the nitriding agent includes the following components in parts by weight:

[0032] Ethanol 70-90 parts, triethanolamine 20-30 parts, citrate 15-25 parts;

[0033] During the heat treatment, the stainless steel bearing is heated to 1030~1050℃, held at that temperature, cooled, and tempered.

[0034] The tempering temperature is 150~190℃, and the time is 2~3h.

[0035] As a further technical solution, the heat treatment is carried out for 2 to 3 hours.

[0036] In the heat treatment process of the high-nitrogen stainless steel bearing of the present invention, the holding time can be any time among 2h, 2.2h, 2.4h, 2.6h, 2.8h, and 3h.

[0037] As a further technical solution, the preparation method of the nitriding agent includes the following steps: mixing the raw materials of the nitriding agent evenly to obtain the nitriding agent.

[0038] As a further technical solution, the stainless steel bearing is made of 9Cr18Mo.

[0039] The working principle and beneficial effects of this invention are as follows:

[0040] Unlike traditional methods that rely on simple cooling after nitriding of high-nitrogen stainless steel bearings and fail to guarantee hardness, this invention employs a three-stage cooling process to improve the hardness of high-nitrogen stainless steel bearings. In the first stage, the temperature is lowered to 530-550℃ at a rate of 10-15℃ / h. This process allows for sufficient diffusion and arrangement of atoms within the stainless steel, forming a uniform and ordered microstructure, thus initially improving the bearing's hardness. In the second stage, the temperature is lowered from 530-550℃ to 380-400℃ at a rate of 25-35℃ / h. This change in cooling rate promotes the formation of a dense and refined structure within the stainless steel. The increased grain boundaries in this refined structure hinder dislocation movement, further enhancing the bearing's hardness. In the third stage, the temperature is rapidly cooled from 380-400℃ to room temperature at a rate of 50-55℃ / h. This rapid cooling generates a large number of dislocations within the internal structure, forming entanglements that significantly hinder dislocation movement, greatly increasing hardness while simultaneously suppressing structural softening and maintaining stable hardness. Therefore, this invention improves the hardness of high-nitrogen stainless steel bearings through the combined regulation of multiple cooling stages. Detailed Implementation

[0041] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0042] Example 1

[0043] A heat treatment process for a high-nitrogen stainless steel bearing includes the following steps: after cleaning and drying a stainless steel bearing sample made of 9Cr18Mo, a nitriding agent is evenly applied to the surface of the sample with a coating thickness of 0.5mm. Nitriding agent is added dropwise at 620℃ at a flow rate of 6mL / s for 3 hours, followed by cooling. The stainless steel bearing is then heated to 1050℃, held for 2 hours, cooled, and then tempered at 190℃ for 2 hours to obtain a high-nitrogen stainless steel bearing.

[0044] The preparation method of the penetration enhancer includes the following steps: mixing 90 parts by weight of ethanol, 8 parts by weight of activated carbon, 16 parts by weight of triethanolamine and 5 parts by weight of cerium oxide to obtain the penetration enhancer;

[0045] The preparation method of the nitriding agent includes the following steps: mixing 90 parts by weight of ethanol, 30 parts by weight of triethanolamine and 25 parts by weight of citrate to obtain the nitriding agent;

[0046] The cooling process after nitriding and before heating consists of three stages: the first stage involves cooling to 550°C at a rate of 15°C / h; the second stage involves cooling from 550°C to 400°C at a rate of 35°C / h; and the third stage involves cooling from 400°C to room temperature at a rate of 55°C / h.

[0047] Example 2

[0048] A heat treatment process for a high-nitrogen stainless steel bearing includes the following steps: After cleaning and drying a stainless steel bearing sample made of 9Cr18Mo, a nitriding agent is evenly applied to the surface of the sample with a coating thickness of 0.5mm. Nitriding agent is added dropwise at 600℃ at a flow rate of 5mL / s for 2 hours. After cooling, the stainless steel bearing is heated to 1030℃ and held for 2 hours. After cooling, it is tempered at 150℃ for 3 hours to obtain a high-nitrogen stainless steel bearing.

[0049] The preparation method of the penetration enhancer includes the following steps: 70 parts by weight of ethanol, 7 parts by weight of activated carbon, 12 parts by weight of triethanolamine and 2 parts by weight of yttrium oxide are mixed evenly to obtain the penetration enhancer;

[0050] The preparation method of the nitriding agent includes the following steps: mixing 70 parts by weight of ethanol, 20 parts by weight of triethanolamine and 15 parts by weight of citrate to obtain the nitriding agent;

[0051] The cooling process after nitriding and before heating consists of three stages: the first stage involves cooling to 530°C at a rate of 10°C / h; the second stage involves cooling from 530°C to 380°C at a rate of 25°C / h; and the third stage involves cooling from 380°C to room temperature at a rate of 50°C / h.

[0052] Example 3

[0053] The difference between this embodiment and Embodiment 2 is that the cooling process after nitriding and before heating in this embodiment includes three stages: the first stage is to cool to 530°C at a rate of 15°C / h; the second stage is to cool from 530°C to 380°C at a rate of 35°C / h; and the third stage is to cool from 380°C to room temperature at a rate of 55°C / h.

[0054] Example 4

[0055] The only difference between this embodiment and Embodiment 2 is that in this embodiment, yttrium oxide is replaced with an equal mass of composite yttrium oxide;

[0056] The preparation method of composite yttrium oxide includes the following steps:

[0057] A1. Add yttrium oxide to water (the mass-volume ratio of yttrium oxide to water is 1g:12mL), add KH-550 coupling agent, stir at 400rpm for 1h at 40℃, concentrate, and dry to obtain pretreated yttrium oxide.

[0058] A2. Add pretreated yttrium oxide to dichloromethane (the mass-volume ratio of pretreated yttrium oxide to dichloromethane is 1 g: 12 mL), add n-octyl p-hydroxybenzoate (the mass ratio of yttrium oxide, KH-550 coupling agent, and n-octyl p-hydroxybenzoate is 25:3:5), stir at 400 rpm for 4 h at 30 °C, concentrate, and dry to obtain composite yttrium oxide.

[0059] Example 5

[0060] The only difference between this embodiment and Embodiment 2 is that in this embodiment, yttrium oxide is replaced with an equal mass of composite yttrium oxide;

[0061] The preparation method of composite yttrium oxide includes the following steps:

[0062] A1. Add yttrium oxide to water (the mass-volume ratio of rare earth yttrium oxide to water is 1g:10mL), add KH-550 coupling agent, stir at 300rpm for 2h at 30℃, concentrate, and dry to obtain pretreated yttrium oxide.

[0063] A2. Add pretreated yttrium oxide to dichloromethane (the mass-volume ratio of pretreated yttrium oxide to dichloromethane is 1 g: 10 mL), add n-octyl p-hydroxybenzoate (the mass ratio of yttrium oxide, KH-550 coupling agent, and n-octyl p-hydroxybenzoate is 25:3:4), stir at 300 rpm for 5 h at 20 °C, concentrate, and dry to obtain composite yttrium oxide.

[0064] Comparative Examples 1-8

[0065] The only difference between Comparative Examples 1-8 and Example 2 is that the cooling rates after nitriding and before heating in Comparative Examples 1-8 are different from those in Example 2. The cooling rates after nitriding and before heating in Comparative Examples 1-8 are shown in Table 1.

[0066] Table 1 Cooling rates after nitriding and before heating in Comparative Examples 1-8

[0067]

[0068] Experimental Example 1

[0069] The high-nitrogen stainless steel bearings prepared in Examples 1-3 and Comparative Examples 1-8 were tested for hardness according to the method specified in GB / T 230.1-2018 "Metallic materials Rockwell hardness test - Part 1: Test method". The test results are shown in Table 2.

[0070] Table 2 Hardness Test Results

[0071]

[0072] As shown in Table 2, the hardness of the high-nitrogen stainless steel bearings obtained in Examples 1-3 of this invention reached above 62 HRC. Therefore, this invention improves the hardness of the stainless steel bearings by designing the cooling rate after nitriding and before heating. In the first stage, the temperature is cooled to 530-550℃ at a rate of 10-15℃ / h. In the second stage, the temperature is cooled to 380-400℃ at a rate of 25-35℃ / h. In the third stage, the temperature is cooled to room temperature at a rate of 50-55℃ / h.

[0073] Experiment Example 2

[0074] The high-nitrogen stainless steel bearings prepared in Examples 2 and 4-5 were tested for corrosion resistance according to the method specified in GB / T 10125-2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test". The test method was a neutral salt spray test with a sodium chloride mass concentration of 5% and a spray pressure of 70 kPa. The test results are shown in Table 3.

[0075] Table 3 Corrosion Resistance Test Results

[0076]

[0077] As shown in Table 3, the high-nitrogen stainless steel bearings prepared in Examples 4-5 of this invention showed a corrosion time of over 195 hours in the neutral salt spray test. Therefore, the use of coupling agent and n-octyl p-hydroxybenzoate composite rare earth oxide in this invention improves the corrosion resistance of stainless steel bearings.

[0078] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A heat treatment process for high-nitrogen stainless steel bearings, characterized in that, The process includes the following steps: nitriding, cooling, and heat treatment of the stainless steel bearing; The nitriding temperature is 600~620℃, and the time is 2~3h; The cooling process includes three stages: in the first stage, the temperature is cooled to 530-550°C at a rate of 10-15°C / h; in the second stage, the temperature is cooled from 530-550°C to 380-400°C at a rate of 25-35°C / h; and in the third stage, the temperature is cooled from 380-400°C to room temperature at a rate of 50-55°C / h. The stainless steel bearing underwent surface activation treatment before nitriding. During the surface activation treatment, the permeation catalyst is evenly applied to the stainless steel bearing; The raw materials of the penetration enhancer include the following components in parts by weight: 70-90 parts ethanol, 7-8 parts activated carbon, 12-16 parts triethanolamine, and 2-5 parts rare earth oxides. The rare earth oxide is a composite rare earth oxide; The raw materials for the composite rare earth oxide include rare earth oxides, coupling agents, and n-octyl p-hydroxybenzoate.

2. The heat treatment process for a high-nitrogen stainless steel bearing according to claim 1, characterized in that, The preparation method of the penetration enhancer includes the following steps: mixing the raw materials of the penetration enhancer evenly to obtain the penetration enhancer.

3. The heat treatment process for a high-nitrogen stainless steel bearing according to claim 1, characterized in that, The preparation method of the composite rare earth oxide includes the following steps: A1. Add rare earth oxides to water, add coupling agent, stir, concentrate, and dry to obtain pretreated rare earth oxides. A2. Add the pretreated rare earth oxide to dichloromethane, add n-octyl p-hydroxybenzoate, stir, concentrate, and dry to obtain composite rare earth oxide.

4. The heat treatment process for a high-nitrogen stainless steel bearing according to claim 1, characterized in that, The mass ratio of the rare earth oxide, coupling agent, and n-octyl p-hydroxybenzoate is 25:3:4~5.

5. The heat treatment process for a high-nitrogen stainless steel bearing according to claim 3, characterized in that, In step A1, the stirring speed is 300~400 rpm, the time is 1~2 hours, and the temperature is 30~40℃; In step A2, the stirring speed is 300~400 rpm, the time is 4~5 h, and the temperature is 20~30℃.

6. The heat treatment process for a high-nitrogen stainless steel bearing according to claim 1, characterized in that, The raw materials for the composite rare earth oxides include one or both of yttrium oxide and cerium oxide.

7. The heat treatment process for a high-nitrogen stainless steel bearing according to claim 1, characterized in that, During nitriding, the raw materials used in the nitriding agent include the following components in parts by weight: Ethanol 70-90 parts, triethanolamine 20-30 parts, citrate 15-25 parts; During the heat treatment, the stainless steel bearing is heated to 1030~1050℃, held at that temperature, cooled, and tempered. The tempering temperature is 150~190℃, and the time is 2~3h.

8. The heat treatment process for a high-nitrogen stainless steel bearing according to claim 1, characterized in that, The stainless steel bearing is made of 9Cr18Mo.

Images