Nitriding treatment of seamless steel pipe
2022-02-09 16:01:58 COMMENT：0 HITS：
According to the basic principle and process characteristics of nitriding treatment of seamless steel pipe, the process parameters include nitriding degree, nitriding time and ammonia decomposition rate. The main points are summarized as follows.
【1】 Nitriding temperature
When the nitriding temperature is 500 ° C, it has the highest surface hardness. If it exceeds this temperature, the hardness will decrease. The reason is that the accumulation of nitrides below 500 ° C is not significant and the smoke dispersion is large. At the same time, considering the relationship between nitriding temperature and hardness, nitriding layer depth, seamless steel pipe deformation and many other factors, the nitriding temperature is usually controlled at 480 ~ 560 ° C. The relationship between nitriding and hardness is shown in Figure 8-2.
【2】 Nitriding time
After nitriding for a certain time, the surface hardness reaches the maximum value, and the hardness decreases slightly after prolonging the time. For example, the higher the nitriding temperature, the shorter the time to reach the maximum value, and the lower the hardness; The depth of k-layer increases with time. Figure 8-3 shows the relationship between the hardness and depth of gas ft layer of 38CrMoAl nitrided steel and temperature and time.
【3】 Decomposition rate of ammonia
The decomposition rate of ammonia is the percentage of hydrogen and nitrogen produced by ammonia decomposition in the volume of furnace gas. High decomposition results in high hydrogen concentration in the furnace, making nitrogen atoms in a standstill state, that is, preventing the infiltration of nitrogen atoms; On the contrary, the low decomposition rate will reduce the number of active nitrogen atoms in contact with the surface of seamless steel pipe, and increase the brittleness.
The decomposition rate is related to the pressure in the furnace, the flow rate of ammonia, the shape 2 on the surface of seamless steel pipe and the presence or absence of catalyst. Therefore, the decomposition rate should be controlled within the most appropriate s range Generally speaking, the decomposition rate of ammonia is controlled at about 18% - 45%. The ammonia decomposition rate can be adjusted by ammonia flow and pressure in the furnace > 1.
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