Nitriding treatment of seamless steel pipe
Posted by zora li on December 7th, 2022
Precautions for nitriding treatment of seamless pipe include:
1) Nitriding temperature
When the nitriding temperature is 500°C, the surface strength is high, and the strength decreases beyond this temperature. The reason is that the agglomeration of nitrogen-containing compounds is not obvious below 500 ° C, and the dispersion is large. In addition, the relationship between the nitriding temperature and strength, the depth of the nitriding layer, and the deformation of the seamless steel pipe is fully considered, and the nitriding temperature is generally controlled at 480-560°C.
2) Nitriding time
After nitriding for a certain period of time, the surface strength gradually increases, and the strength decreases slightly after increasing the time. For example, the higher the nitriding temperature and the longer the time, the lower the strength value.
3) Ammonia decomposition rate
The ammonia decomposition rate is the percentage of hydrogen and nitrogen in the furnace gas volume caused by ammonia dissolution. The decomposition rate is high, and the hydrogen concentration in the furnace is high, so that the nitrogen atoms are in a stagnant state, that is, the penetration of nitrogen atoms is hindered; and vice versa. The decomposition rate is related to factors such as the working pressure in the furnace, the total flow rate of ammonia gas, the surface state of the seamless steel pipe, and whether there is a metal catalyst, so the decomposition rate should be controlled.
According to the requirements of the depth and strength of the nitriding layer, the nitriding treatment of seamless steel pipes is divided into three types
One-time nitriding process, high surface hardness of about HV1000~1200, small deformation, low brittleness, simple process, convenient handling, but long process cycle, high cost, and shallow permeable layer. seamed steel pipe;
Compared with the first-level nitriding process, the surface hardness is slightly different (HV850~1000), the deformation is slightly increased, but the infiltration speed is fast, and it is mostly used for deep nitriding and large-scale seamless steel pipes.
The three-stage nitriding process has a fast nitriding speed, but its hardness, brittleness, and deformation are worse than that of isothermal nitriding.
Nitriding treatment refers to the chemical heat treatment process in which nitrogen atoms penetrate into the surface of steel pipes in a certain medium at a certain temperature. The common ones are liquid nitriding, gas nitriding and ion nitriding. The purpose is to improve the surface hardness and wear resistance of the steel pipe. Improve fatigue strength, corrosion resistance, etc.