A steam treatment process for iron-based powder metallurgy parts

Abstract

A steam treatment process for iron-based powder metallurgy parts, step: parts to be treated are loaded into a steam treatment furnace, and nitrogen atmosphere is passed through for protection; after being warmed up to low-temperature infiltration temperature, heat preservation is performed, water vapor is passed through for steam treatment, vacuum treatment is performed at regular intervals during heat preservation, relative atmospheric vacuum is required to be lower than 10kPa, and water vapor is passed through again for steam treatment, and cycle number is ≥1 time; after being warmed up to steam treatment layer formation temperature, heat preservation is performed, vacuum treatment is performed at regular intervals during heat preservation, relative atmospheric vacuum is required to be lower than 10kPa, and water vapor is passed through again for steam treatment, and cycle number is ≥1 time; nitrogen is passed through again after steam treatment ends, and it is taken out to be cooled. The present invention has simple process, easy operation, and under the premise of maintaining cost advantage, greatly improves the preparation efficiency of steam treatment process, and the surface steam treatment layer of parts after treatment is dense and uniform, effectively improves the wear resistance and air tightness of parts.

Description

Technical Field

[0001] The invention belongs to the technical field of surface protection of iron-based powder metallurgy parts and relates to a steam treatment process for iron-based powder metallurgy parts. Background Art

[0002] The upgrade of industries such as automobile engines, gearboxes and air-conditioning compressors has continuously increased the requirements for wear resistance and air tightness of iron-based powder metallurgy parts. The existing steam treatment process has low preparation efficiency, and the parts are prone to wear and frequent leakage, which can no longer meet the needs of existing industries. How to achieve the improvement of the performance of iron-based steam-treated parts under low-cost conditions has become a problem that needs to be solved urgently.

[0003] The steam treatment process is a chemical reaction between superheated steam and the iron substrate, which is expressed by the following formula:

[0004] 3Fe+4H2O==Fe3O4+4H2

[0005] Among them, the generation of Fe3O4 is a key factor affecting the hardness, wear resistance and air tightness of iron-based powder metallurgy parts, while temperature, atmosphere (water vapor, hydrogen ratio) and furnace load can greatly affect the progress of the steam treatment process. It can be observed from the chemical equation that the consumption and generation ratio of water vapor and hydrogen is 1:1. When the hydrogen in the steam treatment furnace accumulates to a certain concentration, the reaction kinetics will be slowed down, greatly affecting the preparation efficiency. The existing steam treatment process is to directly and continuously introduce water vapor into the furnace at a specific temperature for oxidation reaction, and directly discharge the gas in the furnace through a bypass. The ratio of water vapor and hydrogen in the furnace is not controllable, and it can be seen from the actual production process that this exhaust method cannot effectively discharge the hydrogen in the furnace, and the steam treatment reaction rate will gradually decrease over time. In addition, the inability of hydrogen to be discharged from the furnace smoothly will also cause defects in the steam treatment layer, resulting in a decrease in film quality.

[0006] Therefore, it is necessary to develop a new steam treatment process for iron-based powder metallurgy parts to meet the requirements of high preparation effect, wear resistance and good air tightness. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a steam treatment process for iron-based powder metallurgy parts with simple operation and high efficiency. The steam treatment layer on the surface of the treated parts is uniform and dense, which effectively improves the wear resistance and air tightness of the parts.

[0008] The technical solution adopted by the present invention to solve the above technical problems is: a steam treatment process for iron-based powder metallurgy parts, characterized by comprising the following steps:

[0009] 1) Place the parts to be treated into the steam treatment furnace and introduce nitrogen atmosphere for protection;

[0010] 2) After heating to the low-temperature infiltration temperature, keep the temperature, and at the same time, introduce water vapor for steam treatment. During the insulation process, vacuum treatment is carried out at regular intervals, and the vacuum degree relative to atmospheric pressure is required to be lower than -10kPa. Water vapor is introduced again for steam treatment. The number of cycles is ≥1;

[0011] 3) Then, the temperature is raised to the temperature at which the steam treatment layer is formed and then kept warm. During the warming process, vacuum treatment is performed at regular intervals, and the vacuum degree relative to atmospheric pressure is required to be lower than -10kPa. Water vapor is then introduced again for steam treatment. The number of cycles is ≥1;

[0012] 4) After the steam treatment is completed, nitrogen is introduced again and the container is taken out after cooling.

[0013] Furthermore, the low-temperature infiltration temperature of step 2) is 480-530°C.

[0014] Furthermore, the steam treatment layer formation temperature in step 3) is 530-600°C.

[0015] Furthermore, depending on the usage requirements of the parts, step 2) or step 3) can be implemented separately.

[0016] Finally, the interval time of the vacuum treatment in step 2) and step 3) is 10 to 60 minutes.

[0017] Compared with the prior art, the advantages of the present invention are:

[0018] (1) Compared with the existing steam treatment process, the steam treatment coating prepared by the steam treatment process of the present invention has a dense surface, uniform film thickness, and exhibits a large compressive stress. At the same time, it has a low friction coefficient (the oil lubrication friction coefficient is about 0.11) and wear rate, which can effectively improve the wear resistance and fatigue resistance of the steam treatment layer and extend the life of such parts;

[0019] (2) The steam treatment process of the present invention can discharge the generated hydrogen in a timely manner, so as to promote the reaction to proceed in a positive direction. Compared with the traditional steam treatment process, the preparation efficiency is higher and the quality of the steam treatment layer is comprehensively improved;

[0020] (3) The steam treatment process of the present invention is simple to operate and can be upgraded by simply modifying existing equipment. It is suitable for mass production and can form a standardized process with strong executability.

[0021] The process of the present invention is simple and easy to operate. While maintaining cost advantages, it greatly improves the preparation efficiency of the steam treatment process. The steam treatment layer on the surface of the treated parts is dense and uniform, effectively improving the wear resistance and air tightness of the parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A flow chart of the steam treatment process provided by the present invention;

[0023] Figure 2 This is a surface morphology of the steam-treated layer obtained in Example 1 of the present invention;

[0024] Figure 3 This is a cross-sectional metallographic image of the steam-treated layer obtained in Example 1 of the present invention;

[0025] Figure 4 This is an XRD stress test result spectrum of the steam-treated layer prepared in Example 1 of the present invention;

[0026] Figure 5 This is a friction coefficient curve of the steam treatment layer prepared in Example 1 of the present invention under oil lubrication conditions;

[0027] Figure 6 The wear scar morphology of the steam-treated layer prepared in Example 1 of the present invention under oil lubrication conditions;

[0028] Figure 7 This is a cross-sectional metallographic image of the steam treatment layer prepared in Example 2 of the present invention.

[0029] Figure 8 This is a surface morphology of the steam-treated layer obtained in Comparative Example 1 of the present invention;

[0030] Figure 9 This is a cross-sectional metallographic image of the steam-treated layer obtained in Comparative Example 1 of the present invention;

[0031] Figure 10 This is the XRD stress test result spectrum of the steam-treated layer prepared in Comparative Example 1 of the present invention;

[0032] Figure 11 This is the friction coefficient curve of the steam treatment layer prepared in Comparative Example 1 of the present invention under oil lubrication conditions;

[0033] Figure 12 This is the wear scar morphology of the steam-treated layer prepared in Comparative Example 1 of the present invention under oil lubrication conditions;

[0034] Figure 13 This is a cross-sectional metallographic image of the steam-treated layer obtained in Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0035] The present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

[0036] The steam treatment process of the present invention is as follows Figure 1 shown.

[0037] Example 1:

[0038] (1) Load the parts to be processed into the furnace and introduce nitrogen atmosphere for protection;

[0039] (2) After heating to 500°C and maintaining the temperature, steam is introduced for steam treatment. During the heat preservation process, vacuum treatment is performed every 30 minutes, and the vacuum degree relative to atmospheric pressure is required to be lower than -15kPa. Steam is introduced again for steam treatment. The number of cycles is 2, for a total of one and a half hours;

[0040] (3) The temperature was raised to 560°C and then kept warm. During the holding process, vacuum treatment was performed every 30 minutes. The vacuum degree relative to atmospheric pressure was required to be less than -15 kPa. Water vapor was introduced again for steam treatment. The cycle was repeated twice for a total of one and a half hours.

[0041] (4) After the steam treatment process is completed, nitrogen is introduced again and the steam is taken out after cooling.

[0042] The surface morphology of the steam-treated layer is as follows: Figure 2 As shown, the cross-sectional metallographic structure of the steam-treated layer is as follows: Figure 3 As shown, the steam-treated layer exhibits a compressive stress of 400-700 MPa ( Figure 4 ), the friction coefficient curve under oil lubrication conditions (10N load, 50mm / s speed) is as follows Figure 5 As shown, it is about 0.11, and the wear scar morphology is as follows Figure 6 shown.

[0043] Example 2:

[0044] (1) Load the parts to be processed into the furnace and introduce nitrogen atmosphere for protection;

[0045] (2) After heating to 520°C and holding the temperature, steam is introduced for steam treatment. During the holding process, vacuum treatment is performed every 20 minutes, and the vacuum degree relative to atmospheric pressure is required to be lower than -10 kPa. Steam is introduced again for steam treatment. The number of cycles is 3, and the total treatment time is one and a half hours.

[0046] (3) After heating to 590°C again, vacuum treatment is performed every 40 minutes during the heat preservation process, requiring the vacuum degree relative to atmospheric pressure to be lower than -10 kPa, and water vapor is introduced again for steam treatment. The cycle number is 2 times, and the treatment time is 2 hours and 20 minutes in total.

[0047] (4) After the steam treatment process is completed, nitrogen is introduced again and the steam is taken out after cooling.

[0048] The cross-sectional metallographic structure of the steam treatment layer is as follows: Figure 7 shown.

[0049] Example 3:

[0050] (1) Load the parts to be processed into the furnace and introduce nitrogen atmosphere for protection;

[0051] (2) After the temperature is raised to 480°C, steam is introduced for steam treatment. During the heat preservation process, vacuum treatment is performed every 20 minutes, and the vacuum degree relative to atmospheric pressure is required to be lower than -10 kPa. Steam treatment is then introduced again for steam treatment. The number of cycles is 2, and the total treatment time is one hour and 40 minutes.

[0052] (3) After heating to 540°C again, vacuum treatment is performed every 30 minutes during the heat preservation process. The vacuum degree relative to atmospheric pressure is required to be lower than -10 kPa, and water vapor is introduced again for steam treatment. The cycle number is 1, and the treatment is performed for a total of one hour.

[0053] (4) After the steam treatment process is completed, nitrogen is introduced again and the steam is taken out after cooling.

[0054] Comparative Example 1:

[0055] (1) Load the parts to be processed into the furnace and introduce nitrogen atmosphere for protection;

[0056] (2) Heating to 500°C and then maintaining the temperature, introducing steam for a total of one and a half hours;

[0057] (3) Heat up to 560°C again and keep warm for a total of one and a half hours;

[0058] (4) After the steam treatment process is completed, nitrogen is introduced again and the steam is taken out after cooling.

[0059] The surface morphology of the steam-treated layer is as follows: Figure 8 As shown, the cross-sectional metallographic structure of the steam-treated layer is as follows: Figure 9 As shown, the steam-treated layer exhibits a tensile stress of 300 to 500 MPa ( Figure 10 ), the friction coefficient curve under oil lubrication conditions (10N load, 50mm / s speed) is as follows Figure 11 As shown, it is about 0.125, and the wear scar morphology is as follows Figure 12 shown.

[0060] Comparative Example 2:

[0061] (1) Load the parts to be processed into the furnace and introduce nitrogen atmosphere for protection;

[0062] (2) Heating to 520°C and then maintaining the temperature, introducing water vapor for steam treatment for a total of one and a half hours;

[0063] (3) heating to 590°C again and then maintaining the temperature for a total of three and a half hours;

[0064] (4) After the steam treatment process is completed, nitrogen is introduced again and the steam is taken out after cooling.

[0065] The cross-sectional metallographic structure of the steam treatment layer is as follows: Figure 13 shown.

[0066] from Figures 2 to 13 The experimental data show that:

[0067] (1) The steam-treated coating prepared in Example 1 of the present invention has a dense surface, uniform film thickness, and exhibits a large compressive stress. It also has a low friction coefficient (the oil-lubricated friction coefficient is approximately 0.11) and a low wear rate. The steam treatment process of the present invention can promptly discharge the generated hydrogen, promoting the continuous forward reaction. Compared with the traditional steam treatment process, the preparation efficiency is higher, and the quality of the steam-treated layer is comprehensively improved.

[0068] (2) By comparing the results of Example 1 with those of Comparative Example 1, it can be found that the preparation efficiency of the traditional steam treatment process is low, there are more pores on the surface, and it exhibits greater tensile stress and poor wear resistance.

[0069] (3) By comparing the results of Example 2 with those of Comparative Example 2, it can be found that the new steam treatment process can significantly shorten the steam treatment time and improve production efficiency.

[0070] In summary, the steam treatment process of the present invention boasts high production efficiency, exceeding 30% compared to conventional processes. The resulting steam-treated parts have a uniform, dense coating, effectively improving their airtightness. Furthermore, the resulting steam-treated layer exhibits significant compressive stress, effectively enhancing its wear and fatigue resistance, thereby extending the life of such parts. Furthermore, the steam treatment process of the present invention is simple, enabling upgrades to existing equipment through simple modifications, making it suitable for mass production.

[0071] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A steam treatment process for iron-based powder metallurgy parts, characterized in that The following steps are involved: 1) Load the parts to be treated into the steam treatment furnace and introduce nitrogen atmosphere for protection; 2) After heating to the low-temperature infiltration temperature, keep the temperature and introduce water vapor for steam treatment. During the insulation process, vacuum treatment is carried out at regular intervals. The vacuum degree relative to atmospheric pressure is required to be lower than -10 kPa. Water vapor is introduced again for steam treatment. The number of cycles is ≥1; The low-temperature infiltration temperature is 480-530°C; 3) Then, the temperature is raised to the temperature at which the steam treatment layer is formed and then kept warm. During the warming process, vacuum treatment is performed at regular intervals, with the vacuum degree relative to atmospheric pressure being required to be lower than -10 kPa, and water vapor is introduced again for steam treatment. The number of cycles shall be ≥ 1; The steam treatment layer is formed at a temperature of 530-600°C; 4) After the steam treatment is completed, introduce nitrogen again and take it out after cooling.

2. The steam treatment process according to claim 1, characterized in that: The interval time of the vacuum treatment in step 2) and step 3) is 10 to 60 minutes.

3. The steam treatment process according to claim 1, characterized in that: Depending on the usage requirements of the parts, implement step 2) or step 3) separately.

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