阅读说明：本技术 气体氮碳共渗及后氧化工艺复合处理方法 (Composite treatment method for gas nitrocarburizing and post-oxidation process ) 是由 史文 胡俊豪 顾晓文 高新宇 祖武杰 赵桐 于 2019-12-06 设计创作，主要内容包括：本发明公开了一种气体氮碳共渗及后氧化复合处理方法,步骤如下：气体氮碳共渗处理,在工件表面依次生成扩散层和白亮层；第一段氧化工艺：通入水蒸气与氮气混合气体,氧化温度为430～450℃,氧化时间为25～35min；停止通入水蒸气,调节氮气流量,升温至第二段氧化温度；第二段氧化工艺：通入水蒸气与氮气混合气体,氧化温度为520～540℃,氧化时间为10～20min；冷却出炉,零件上油及烘干。本发明在氧化阶段利用二段阶梯式氧化方法,在白亮层表面形成两层氧化层：内层为致密氧化层,具有优异耐腐蚀性能、物理隔绝性；而表层为疏松氧化层,则具有更好的后道上油效果。发明工艺形成的氧化层可极大地提升零件的耐腐蚀性能。(The invention discloses a gas nitrocarburizing and post-oxidizing composite treatment method, which comprises the following steps: performing gas nitrocarburizing treatment, and sequentially generating a diffusion layer and a white bright layer on the surface of the workpiece; the first stage of oxidation process: introducing mixed gas of water vapor and nitrogen, wherein the oxidation temperature is 430-450 ℃, and the oxidation time is 25-35 min; stopping introducing the water vapor, regulating the flow of nitrogen, and heating to a second-stage oxidation temperature; and (3) a second-stage oxidation process: introducing mixed gas of water vapor and nitrogen, wherein the oxidation temperature is 520-540 ℃, and the oxidation time is 10-20 min; cooling and discharging, oiling and drying the parts. In the oxidation stage, a two-stage step oxidation method is utilized to form two oxide layers on the surface of a white bright layer: the inner layer is a compact oxide layer and has excellent corrosion resistance and physical isolation; and the surface layer is a loose oxide layer, so that the subsequent oiling effect is better. The oxidation layer formed by the process can greatly improve the corrosion resistance of the part.)

1. A composite treatment method for gas nitrocarburizing and post-oxidation process is characterized by comprising the following steps:

a. and (3) gas nitrocarburizing treatment:

performing gas nitrocarburizing treatment on the surface of a metal matrix of the workpiece, so as to sequentially generate a diffusion layer and a white and bright layer on the surface of the workpiece outwards;

b. the first stage of oxidation process:

b, placing the workpiece subjected to the gas nitrocarburizing treatment in the step a in an oxidizing atmosphere, introducing mixed gas of water vapor and nitrogen, controlling the oxidizing temperature to be 430-450 ℃ and the oxidizing time to be 25-35 min, and performing a first stage of oxidation process to generate Fe on the surface of a white bright layer of the workpiece ₃O ₄An oxide layer to form a dense oxide layer;

c. and (3) heating process:

after the preparation process of the compact oxide layer is finished in the step b, stopping introducing water vapor, adjusting the nitrogen flow, and heating to the target temperature of the second-stage oxidation process;

d. the second stage oxidation process:

continuously introducing mixed gas of water vapor and nitrogen, controlling the oxidation temperature to be 520-540 ℃ and the oxidation time to be 10-20 min, carrying out a second stage of oxidation process, and continuously generating Fe outside a compact oxide layer of the workpiece ₃O ₄An oxide layer, forming a loose oxide layer;

e. and d, after the preparation process of the loose oxide layer is finished in the step d, stopping introducing water vapor, cooling the workpiece, discharging the workpiece out of the furnace, taking the loose oxide layer as an oil coating surface layer of the part, and oiling and drying the part to obtain the part with the corrosion-resistant composite layer.

2. The combined treatment method of gas nitrocarburizing and post-oxidation process according to claim 1, characterized in that: in the step a, the nitriding temperature is controlled to be not lower than 560 ℃ when the gaseous nitrocarburizing treatment is carried outThe reaction time is at least 3h, and the gas is NH ₃、N ₂And CO ₂The mixed gas of (1).

3. The combined treatment method of gas nitrocarburizing and post-oxidation process according to claim 1, characterized in that: in the step b, when the first-stage oxidation process is carried out, the oxidation temperature is controlled to be 440-450 ℃, the oxidation time is 25-30 min, the introduced gas is a mixed gas of steam and nitrogen, the flow rate is determined according to the actual hearth volume, the steam flow rate is controlled to be 1.5-2.5L/h per cubic meter of the hearth volume, and the nitrogen flow rate is 1-1.5 m per cubic meter of the hearth volume ³/h。

4. The combined treatment method of gas nitrocarburizing and post-oxidation process according to claim 3, characterized in that: in the step b, when the first-stage oxidation process is carried out, the flow rate of the water vapor is controlled to be 1.8-2.5L/h per cubic meter of the volume of the hearth, and the flow rate of the nitrogen is controlled to be 1.2-1.5 m per cubic meter of the volume of the hearth ³/h。

5. The combined treatment method of gas nitrocarburizing and post-oxidation process according to claim 1, characterized in that: in the step c, during the temperature rise process, the flow of nitrogen is adjusted to be 3-5 m per cubic meter of hearth volume ³/h。

6. The combined treatment method of gas nitrocarburizing and post-oxidation process according to claim 5, characterized in that: in the step c, during the temperature rise process, the flow of nitrogen is adjusted to be 4-5 m per cubic meter of hearth volume ³/h。

7. The combined treatment method of gas nitrocarburizing and post-oxidation process according to claim 1, characterized in that: in the step d, when the second-stage oxidation process is carried out, the oxidation temperature is controlled to be 530-540 ℃, the oxidation time is 10-15 min, the introduced gas is a mixed gas of water vapor and nitrogen, the flow rate is determined according to the actual furnace volume, and the flow rate of the water vapor is controlled to be every dayThe volume of the square meter hearth is 1.5-2.5L/h, and the nitrogen flow is 1-1.5 m per cubic meter hearth ³/h。

8. The combined treatment method of gas nitrocarburizing and post-oxidation process according to claim 7, characterized in that: in the step d, when the second-stage oxidation process is carried out, the flow rate of the water vapor is controlled to be 1.8-2.5L/h per cubic meter of the volume of the hearth, and the flow rate of the nitrogen is controlled to be 1.2-1.5 m per cubic meter of the volume of the hearth ³/h。

9. The combined treatment method of gas nitrocarburizing and post-oxidation process according to claim 1, characterized in that: in the step e, after the preparation process of the loose oxide layer is completed, stopping water vapor introduction in the cooling process, and regulating the nitrogen flow to be 3-5 m per cubic meter of hearth volume ³Cooling the workpiece to 80-180 ℃ along with the furnace, and discharging; and then in the oiling process, the oil immersion time is 3-8 min, the drying time is 2-5 min, and the drying temperature is 60-120 ℃.

10. The combined treatment method of gas nitrocarburizing and post-oxidation process according to claim 1, characterized in that: in the step e, after the preparation process of the loose oxide layer is completed, the flow rate of nitrogen is adjusted to be 4-5 m per cubic meter of hearth volume ³Cooling the workpiece to 120-180 ℃ along with the furnace, and discharging; and then in the oiling process, the oil immersion time is not less than 6-8 min, the drying time is 3-5 min, and the drying temperature is 100-120 ℃.

Technical Field

The invention relates to a metal material surface modification process method, in particular to a metal material surface composite treatment process method for gas nitrocarburizing, which is applied to the technical field of metal material heat treatment.

Background

The composite treatment process of gas nitrocarburizing and post-oxidation is a novel surface modification process developed by a QPQ salt bath composite treatment process, not only can greatly improve the hardness, the wear resistance and the corrosion resistance of parts, but also overcomes a series of environmental protection problems of severe process environment, difficult treatment of waste salt and wastewater and the like during the QPQ salt bath treatment. Firstly, sequentially forming a diffusion layer and a white layer on the surface of a metal matrix through gas nitrocarburizing treatment so as to improve the hardness and the wear resistance of parts; then, carrying out steam oxidation treatment on the part to generate a layer of Fe with the thickness of 1-3 mu m on the surface of the white bright layer ₃O ₄And oxidizing the layer. Fe ₃O ₄Has high chemical stability and can obviously improve the corrosion resistance of parts.

The gas nitrocarburizing and post-oxidizing composite treatment process has been widely applied to the surface modification treatment of steel parts due to the characteristics of simple and convenient operation, no pollution, low treatment temperature and the like. However, in the oxidation production work of enterprises, a one-stage oxidation process is generally adopted: and generating an oxide layer with moderate thickness on the surface of the workpiece at a certain oxidation temperature and time. The oxidation temperature and the oxidation time are adjusted to easily meet the requirements of the thickness of the oxidation layer, but the overall corrosion resistance of the part is lower. This is because, in the case of a single-stage oxidation process, if a lower oxidation temperature (e.g., 440 ℃) is adopted, the surface oxide layer is very dense and has good physical isolation, but the subsequent oiling effect is very unfavorable, and a longer oxidation time is required for forming an oxide layer with a target thickness; if a higher oxidation temperature (such as 530 ℃) is adopted, the oxidation layer can generate great looseness, although great promotion effect is achieved on the subsequent oiling effect, the corrosion rate can be rapidly increased once the corrosion medium penetrates through the oil layer; and the moderate oxidation temperature (such as 500 ℃) is adopted, and the oxidation layer is not compact enough, and the loosening degree is not enough to promote the oiling effect.

Therefore, under the circumstances, a novel oxidation process needs to be developed, the growth rule of the oxide layer tissue is organically combined with the oxygen on the surface of the part and the subsequent oiling process, the requirement of the corrosion resistance of the oxide layer can be met, the subsequent oiling effect can be promoted, the overall corrosion resistance of the part is improved, and the technical problem to be solved urgently is solved.

Disclosure of Invention

In order to solve the problems in the prior art, the invention aims to provide a composite treatment method for a gas nitrocarburizing and post-oxidation process, which utilizes a two-stage oxidation method to improve the corrosion resistance of steel parts, performs the composite treatment of gas nitrocarburizing and post-oxidation to prepare a corrosion-resistant composite layer, and obviously improves the corrosion resistance of the steel parts.

In order to achieve the purpose, the invention adopts the following technical scheme:

a composite treatment method for gas nitrocarburizing and post-oxidation process comprises the following steps:

a. and (3) gas nitrocarburizing treatment:

performing gas nitrocarburizing treatment on the surface of a metal matrix of the workpiece, so as to sequentially generate a diffusion layer and a white and bright layer on the surface of the workpiece outwards; the gas nitrocarburizing treatment aims at generating a white bright layer and a diffusion layer with certain thickness on the surface of a workpiece, improving the hardness of the part, and determining process parameters according to the actual product requirements;

b. the first stage of oxidation process:

b, placing the workpiece subjected to the gas nitrocarburizing treatment in the step a in an oxidizing atmosphere, introducing mixed gas of water vapor and nitrogen, controlling the oxidizing temperature to be 430-450 ℃ and the oxidizing time to be 25-35 min, and performing a first stage of oxidation process to generate Fe on the surface of a white bright layer of the workpiece ₃O ₄An oxide layer to form a dense oxide layer;

c. and (3) heating process:

after the preparation process of the compact oxide layer is finished in the step b, stopping introducing water vapor, adjusting the nitrogen flow, and heating to the target temperature of the second-stage oxidation process;

d. the second stage oxidation process:

continuously introducing mixed gas of water vapor and nitrogen gas, and controllingThe oxidation temperature is 520-540 ℃, the oxidation time is 10-20 min, the second stage oxidation process is carried out, and Fe is generated outside the compact oxidation layer of the workpiece ₃O ₄An oxide layer, forming a loose oxide layer;

e. and d, after the preparation process of the loose oxide layer is finished in the step d, stopping introducing water vapor, cooling the workpiece, discharging the workpiece out of the furnace, taking the loose oxide layer as an oil coating surface layer of the part, and oiling and drying the part to obtain the part with the corrosion-resistant composite layer.

As a preferred technical scheme of the invention, when the gaseous nitrocarburizing treatment is carried out, the nitriding temperature is controlled to be not lower than 560 ℃, the nitriding time is controlled to be at least 3h, and the gas is NH ₃、N ₂And CO ₂The mixed gas of (1).

As a preferred technical scheme, when the first-stage oxidation technological process is carried out, the oxidation temperature is controlled to be 440-450 ℃, the oxidation time is 25-30 min, the introduced gas is a mixed gas of steam and nitrogen, the flow rate is determined according to the actual hearth volume, the steam flow rate is controlled to be 1.5-2.5L/h per cubic meter of the hearth volume, and the nitrogen flow rate is 1-1.5 m per cubic meter of the hearth volume ³H is used as the reference value. As a further preferable technical scheme, when the first-stage oxidation process is carried out, the flow rate of water vapor is controlled to be 1.8-2.5L/h per cubic meter of hearth volume, and the flow rate of nitrogen is controlled to be 1.2-1.5 m per cubic meter of hearth volume ³/h。

As the preferable technical scheme of the invention, during the temperature rise process, the nitrogen flow is adjusted to be 3-5 m per cubic meter of hearth volume ³H is used as the reference value. As a further preferable technical scheme of the invention, during the temperature rise process, the nitrogen flow is adjusted to be 4-5 m per cubic meter of hearth volume ³/h。

As a preferred technical scheme, when the second-stage oxidation process is carried out, the oxidation temperature is controlled to be 530-540 ℃, the oxidation time is 10-15 min, the introduced gas is a mixed gas of steam and nitrogen, the flow rate is determined according to the actual hearth volume, the steam flow rate is controlled to be 1.5-2.5L/h per cubic meter of the hearth volume, and the nitrogen flow rate is 1-1.5 m per cubic meter of the hearth volume ³H is used as the reference value. As a further preferable technical scheme, when the second-stage oxidation process is carried out, the flow rate of water vapor is controlled to be 1.8-2.5L/h per cubic meter of hearth volume, and the flow rate of nitrogen is controlled to be 1.2-1.5 m per cubic meter of hearth volume ³/h。

As the preferable technical scheme of the invention, after the preparation process of the loose oxide layer is finished, the water vapor is stopped to be introduced in the cooling process, and the nitrogen flow is regulated to be 3-5 m per cubic meter of the hearth volume ³Cooling the workpiece to 80-180 ℃ along with the furnace, and discharging; and then in the oiling process, the oil immersion time is 3-8 min, the drying time is 2-5 min, and the drying temperature is 60-120 ℃. As a further preferable technical scheme of the invention, after the preparation process of the loose oxide layer is completed, the flow of nitrogen is adjusted to be 4-5 m per cubic meter of hearth volume ³Cooling the workpiece to 120-180 ℃ along with the furnace, and discharging; and then in the oiling process, the oil immersion time is not less than 6-8 min, the drying time is 3-5 min, and the drying temperature is 100-120 ℃.

Compared with the prior art, the invention has the following obvious and prominent substantive characteristics and remarkable advantages:

1. after gas nitrocarburizing, the method adopts a two-stage step type steam oxidation process, and firstly adopts a low oxidation temperature to form a compact oxide layer on the surface of a white bright layer; then, carrying out second-stage oxidation treatment at a higher temperature, and continuously generating a loose oxidation layer on the surface; the oxide layer with a compact inner layer has excellent corrosion resistance and physical isolation, and protects a matrix from being corroded; the oxide layer with loose surface layer can effectively promote the penetration of the anti-rust oil, fully play the anti-rust function of the anti-rust oil and further improve the corrosion resistance of the parts;

2. according to the method, the growth rule of the oxide layer structure is organically combined with the oxygen on the surface of the part and the subsequent oiling process, so that the requirement on the corrosion resistance of the oxide layer can be met, the subsequent oiling effect can be promoted, and the overall corrosion resistance of the part is improved;

3. the method has the advantages of simple process, obvious effect, easy realization and low cost.

Drawings

FIG. 1 is a photograph of a metallographic structure of an oxide layer prepared by a method according to an embodiment of the present invention.

FIG. 2 is a scanning electron microscope photograph of the surface of the oxidized layer after the first stage oxidation prepared by the method of the embodiment of the invention.

FIG. 3 is a scanning electron micrograph of the surface of the oxidized layer after the second stage of oxidation according to one embodiment of the present invention.

FIG. 4 is a comparison graph of salt spray corrosion experimental results of a part sample prepared by a method in an embodiment of the invention and a sample prepared by a conventional one-stage oxidation process.

Detailed Description

The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: