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How to deal with the low hardness of the nitrided layer in the nitriding process

Author:YiShengbai    Date:2020-05-24 22:46:44

Overview:


The chemical name of soft nitrogen is "nitrocarburizing", which is essentially low-temperature nitrocarburizing mainly based on nitriding. While nitrogen atoms infiltrating into steel, a small amount of carbon atoms are infiltrating. In comparison, the hardness of the infiltrated layer is lower than that of nitriding and brittleness, so it is called soft nitriding. As a work surface heat treatment process, it can improve the wear resistance, fatigue resistance, corrosion resistance and high temperature resistance of the workpiece, and is widely used in production. However, due to incorrect process or improper operation, defects such as low nitriding hardness, uneven hardness, and oxidation color on the surface are affected, which affects the life cycle of the workpiece. Therefore, it is very important to analyze the reasons, discuss methods and adjust the process.


Reasons for low hardness of nitriding layer:


The low hardness of the nitriding layer will reduce the wear resistance of the workpiece and reduce the service life of the workpiece. Analyzing the reasons we will find:


(1) The nitrogen content of the surface layer of the nitriding mold is low. This is because the furnace temperature is too high during nitriding or the ammonia decomposition rate in the first stage of nitriding is too high, that is, the nitrogen atmosphere in the furnace is too low.


(2) The hardness of the substrate is too low after heat treatment in advance.


(3) Poor sealing of nitriding furnace, air leakage or new nitriding tank.


Precaution:


1) Properly reduce the nitriding temperature, and correct the temperature control instrument frequently to maintain the appropriate nitriding temperature.


2) The workpiece should be heated slowly after it is installed in the furnace, and the ammonia decomposition rate should be appropriately reduced in the first stage of nitriding. Using Wuhan Huamin's nitriding atmosphere full-factor monitoring system to accurately reduce the ammonia cracking rate, hydrogen content and nitrogen potential in the original atmosphere.


3) The nitriding furnace should be sealed, and the leaked muffle tank should be replaced in time. The new nitriding tank should be pre-nitrided, and the whole process of monitoring through the system will make the ammonia decomposition rate in the furnace stable.



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