阅读说明：本技术 一种控制氮势的渗氮热处理方法 (Nitriding heat treatment method for controlling nitrogen potential ) 是由 雷丽芳 柳占雄 于 2019-11-30 设计创作，主要内容包括：本发明涉及一种控制氮势的渗氮热处理方法,该方法通过控制氮势,可以得到合金产品的不同级别的表面组织和不同厚度的白亮层,能够保证氮化产品质量,并且成本低。(The invention relates to a nitriding heat treatment method capable of controlling nitrogen potential, which can obtain surface tissues of different levels and white and bright layers with different thicknesses of alloy products by controlling the nitrogen potential, can ensure the quality of the nitrided products and has low cost.)

1. A nitriding heat treatment method for controlling nitrogen potential is characterized by comprising the following steps:

1) putting an alloy steel product to be nitrided into a nitriding furnace, wherein one end of a hydrogen probe of a control system with the hydrogen probe is inserted into the nitriding furnace, and the other end of the hydrogen probe is connected with a pressure sensor and the control system;

2) setting a nitrogen potential value in the nitriding furnace;

3) heating the temperature in the furnace to 520-530 ℃ of nitriding temperature;

4) introducing ammonia gas into the furnace, connecting cracking gas and nitriding;

5) measuring the hydrogen partial pressure of the atmosphere in the furnace, and transmitting a hydrogen partial pressure signal to a pressure sensor and a control system by a hydrogen probe to measure the nitrogen potential in the furnace;

6) the control system detects the nitrogen potential, when the nitrogen potential is higher than a set value, ammonia cracking gas is introduced into the furnace, and the nitrogen potential is reduced; when the nitrogen potential is lower than a set value, ammonia gas is introduced into the furnace, the nitrogen potential is improved, and the consistency of the surface structure and quality of the same product in different nitriding furnaces is ensured.

7) And detecting the values of pulse-shaped nitride, a white layer and porosity after the alloy steel workpiece is discharged from the furnace to obtain the relation between the alloy steel material and the set nitrogen potential, obtain the nitrogen potential values of different metal materials and different requirements, and accurately control the nitrogen potential in the nitriding process of various materials.

2. The method of claim 1, wherein: the nitrogen potential value in the step 2) is set according to the component requirement of the steel.

3. The method of claim 2, wherein: according to the components of steel, the nitrogen potential value of nitriding the high alloy steel is 2-4; the nitrogen potential value of medium alloy steel nitriding is 4-6.

Technical Field

The invention belongs to the technical field of heat treatment, and particularly relates to a nitriding heat treatment method for controlling nitrogen potential

Background

In general, gas nitriding is carried out by controlling the nitriding atmosphere by measuring the ammonia decomposition rate, and the nitriding quality of parts is not stable. The nitriding technology in the invention controls the nitrogen potential by directly, continuously and dynamically measuring the hydrogen partial pressure in the furnace through the hydrogen probe, and can effectively control the nitriding quality.

Nitriding is a chemical heat treatment process for enabling active nitrogen atoms to permeate into the surface of a workpiece at a certain temperature, and the nitriding treatment is used for improving the hardness and the wear resistance of the surface of a part and enabling the part to have good corrosion resistance. Gas nitriding (ordinary gas nitriding, vacuum nitriding), ion nitriding, nitrocarburizing are generally used. The drawbacks of gas carburization are long nitriding time (the nitriding process is divided into decomposition of ammonia, absorption of nitrogen atoms on the surface of a part and inward diffusion of nitrogen atoms from the surface), the drawbacks of ion nitriding are that the temperature observation is based on the experience of an operator (in the nitriding atmosphere lower than 1 atmosphere, the nitriding is carried out by glow discharge between the part and an anode, the temperature cannot be measured by a thermocouple), and the drawback of nitrocarburizing is that a carburized layer is too thin (the nitrocarburizing process is short in time, the time is prolonged, and the depth of the carburized layer is increased to a limited extent).

Disclosure of Invention

The invention aims to provide a nitriding heat treatment method capable of controlling nitrogen potential, which can obtain surface tissues of different levels and white and bright layers with different thicknesses of alloy products by controlling the nitrogen potential, can ensure the quality of the nitrided products and has low cost.

The technical scheme of the invention is as follows:

the nitriding heat treatment method for controlling the nitrogen potential comprises the following steps:

1) putting an alloy steel product to be nitrided into a nitriding furnace, wherein one end of a hydrogen probe of a control system with the hydrogen probe is inserted into the nitriding furnace, and the other end of the hydrogen probe is connected with a pressure sensor and the control system;

2) setting a nitrogen potential value in the nitriding furnace;

3) heating the temperature in the furnace to 520-530 ℃ of nitriding temperature;

4) introducing ammonia gas into the furnace, connecting cracking gas and nitriding;

5) measuring the hydrogen partial pressure of the atmosphere in the furnace, and transmitting a hydrogen partial pressure signal to a pressure sensor and a control system by a hydrogen probe to measure the nitrogen potential in the furnace;

6) the control system detects the nitrogen potential, when the nitrogen potential is higher than a set value, ammonia cracking gas is introduced into the furnace, and the nitrogen potential is reduced; when the nitrogen potential is lower than a set value, ammonia gas is introduced into the furnace, the nitrogen potential is improved, and the consistency of the surface structure and quality of the same product in different nitriding furnaces is ensured.

7) And detecting the values of pulse-shaped nitride, a white layer and porosity after the alloy steel workpiece is discharged from the furnace to obtain the relationship between various alloy steel materials and the set nitrogen potential, obtain the nitrogen potential values of different metal materials and different requirements, accurately control the nitrogen potential of various materials in the nitriding process, and ensure the product quality.

The nitrogen potential value in the step 2) is set according to the component requirement of the steel.

According to the components of steel, the nitrogen potential value of nitriding the high alloy steel is 2-4; the nitrogen potential value of medium alloy steel nitriding is 4-6.

The nitriding layer tissue comprises vein-like nitride, brittleness, porosity and a white layer, particularly the loose white layer and the white layer have close relation with the nitrogen potential in the furnace, tissues of different levels and the white layers with different thicknesses can be obtained by controlling the nitrogen potential, the nitrogen potential is controlled by the ammonia decomposition rate for common gas nitriding, the method is a rough method, the artificial factor is large, and the control precision is not high. The method of the invention adopts a control system with a hydrogen probe, which can not only continuously and dynamically detect the nitrogen potential in the furnace in real time, but also automatically adjust the nitrogen potential through PID control after comparing with a set value. Through setting for reasonable nitrogen potential, realized the intelligent control of nitriding process, solved the unstable problem of nitrogenize tissue, guaranteed the uniformity of the same part nitrogenize hardness and the degree of depth of different heats, can guarantee to organize qualified, reduction in production cost.

The method adopts the control system with the hydrogen probe to control the nitrogen potential in the furnace, has high precision, reduces the consumed ammonia gas amount, accelerates the nitriding speed and has low production cost.

Detailed Description

According to the components of steel, the nitrogen potential value of nitriding the high alloy steel is 2-4; the nitrogen potential value of medium alloy steel nitriding is 4-6.

This example measures the nitrogen potential of medium and low carbon steel.

The nitrogen potential control method comprises the following steps:

1) putting an alloy steel product to be nitrided into a nitriding furnace, and inserting one end of a hydrogen probe with a hydrogen probe control system into the nitriding furnace;

2) setting a nitrogen potential value in the nitriding furnace;

3) heating the temperature in the furnace to 520-530 ℃ of nitriding temperature;

4) introducing ammonia gas into the furnace, and introducing pyrolysis gas to start nitriding;

5) the hydrogen partial pressure of the atmosphere in the furnace is measured, and then the hydrogen partial pressure signal is transmitted to a pressure sensor at the other end of the hydrogen probe outside the furnace, so that the hydrogen partial pressure in the furnace can be directly read out, and the nitrogen potential in the furnace can be known.

6) If the nitrogen potential is higher than the set value, introducing ammonia cracking gas into the furnace to reduce the nitrogen potential; when the nitrogen potential is lower than a set value, introducing ammonia gas into the furnace to improve the nitrogen potential; the adjusting process is automatically completed by a control system, and the consistency of the surface structure and the quality of the same product in different nitriding furnaces can be ensured.

7) By accumulating data, the relation between various alloy steel materials and the set nitrogen potential can be accurately mastered, the nitrogen potential values of different materials and different requirements can be obtained, the nitrogen potential of various materials in the nitriding process can be accurately controlled, and the product quality is ensured;

test of nitrogen potential kn

A. Test No.)

The first section kn is 6 hours, the second section kn is 4 hours, the second section kn is 5 hours, the nitriding material is 40Cr, 30CrNi2MoVA, 32Cr2MoVA, 42CrMo and 40CrNiMoA, the nitriding temperature is 530 ℃, and the test results are shown in table 1.

TABLE 1

B. Test No. two

The first section kn is 8 hours for 15 hours, the second section kn is 6 hours for 5 hours, nitriding materials are 40Cr, 42CrMo and 30CrNi2MoVA, the nitriding temperature is 530 ℃, and test results are shown in Table 2.

TABLE 2

C. Experiment three

The first section kn is 4 hours for 15 hours, the second section kn is 6 hours for 5 hours, the nitriding material is 30CrNi2MoVA or 40CrNiMoA, the nitriding temperature is 520 ℃, and the test results are shown in Table 3.

TABLE 3

And (3) analyzing test results:

comparing the results of the nitrided structures in tables 1, 2 and 3, it can be seen that:

1. the nitrogen potential Kn is high, the white bright layer is deep, the Kn is low, and the white bright layer is shallow;

2. the larger Kn is used firstly, and then the smaller Kn value is used for sectional control, so that the nitriding layer is seriously loosened; the small Kn is firstly used, and then the section control of a large Kn value is used, so that the porosity of the nitriding layer is improved.

In conclusion, the reduction of the nitrogen potential kn is beneficial to reducing the thickness of the white layer, but the nitriding time is increased; the nitrogen potential Kn value is set according to big principle segmentation setting after little earlier when setting for, can reduce the white layer, improves the layer of nitriding loose, recommends to choose 4 ~ 6 to medium and low alloy steel Kn to satisfy different nitrogenize tissue requirements.