The process and parameters of well type nitriding furnace are mainly determined according to the requirements of nitriding depth and surface hardness of parts. There are three common nitriding processes: isothermal nitriding, two-stage nitriding and three-stage nitriding. Its main process parameters (temperature, time, ammonia decomposition rate), functions, characteristics and applications are as follows. The well type carburizing furnace manufacturer will introduce it to you

Isothermal nitriding method (general nitriding method)

Isothermal nitriding temperature is generally 500~510 ℃, holding time is 48~100h, and the depth of nitriding layer can reach 0 45 ～ 0.60mm, the surface hardness is above 900HV, and the nitriding layer is brittle.

1. Process content and function

a. In the early stage, the ammonia decomposition rate is controlled at the low limit, so that the nitride with large dispersion can be rapidly formed on the surface to obtain a high hardness surface layer.

b. In the later stage, the ammonia decomposition rate increases, which makes the surface nitrogen atoms diffuse to the inner layer and increases the thickness of the infiltration layer.

c. In order to reduce the brittleness of the nitrided layer, 2h diffusion treatment can be carried out before the end of nitriding to reduce the surface nitrogen concentration. At this time, the ammonia decomposition rate can be controlled above 70%.

d. For parts with strict deformation requirements, the furnace shall be cooled to 180-200 ℃ after nitriding. Generally, it can be cooled to below 450 ℃ for quick cooling.

2. Features and Applications

a. Low nitriding temperature, small part deformation, high hardness surface layer can be obtained, which is easy to operate, but the nitriding layer is shallow, and the production cycle is long.

b. The surface is easy to produce nitrogen rich embrittlement layer, and sometimes there is loose layer.

c. It is applicable to parts with strict deformation requirements and high hardness requirements for nitriding layer.

Two-stage nitriding

Two stage nitriding is carried out at 510 ℃ first, and then at 530~540 ℃. The holding time of the two stages is equal or the later stage is slightly longer, and the nitriding time is about 1/3 less than that of isothermal nitriding. The surface hardness is low, 30~50HV.

1. Process content and function

a. The decomposition rate of primary nitriding is low, so that the surface can form nitride with fine particles and high dispersion, and obtain higher surface hardness.

b. The temperature and ammonia decomposition rate of two-stage nitriding increase, which accelerates the diffusion of nitrogen, increases the depth of nitriding layer, shortens the production cycle, flattens the hardness gradient, and also thins the brittle white bright layer.

2. Features and Applications

a. On the premise of ensuring high surface hardness, the production cycle can be shortened, and a deeper nitriding layer can be obtained at the same time.

b. It is applicable to parts with deep nitriding layer, hard surface and simple structure.

Three-stage nitriding

The three-stage nitriding is 510 ℃ nitriding, and then it is heated to 550~560 ℃ nitriding, and then it is reduced to 520~530 ℃ nitriding. The holding time is about 1/3 each, and the nitriding speed is faster. The surface hardness is similar to that of the two-stage nitriding, but the deformation is slightly larger.

1. Content and function

a. In the first stage, under the condition of low nitriding temperature and low nitrogen decomposition rate, the nitrogen concentration in the outer layer is saturated.

b. The increase of temperature in the second stage increases the decomposition rate of ammonia and the diffusion rate of nitrogen atoms to the interior.

c. The third stage continues nitriding to make the nitrogen concentration of the surface layer reach the concentration without making the surface hardness too low.

2 Features and Application

Well type furnace has short nitriding time and deep nitriding layer, but the process is complex and difficult to control. The allowable deviation of nitriding temperature is ± 10 ℃, and the nitriding time is generally determined by the depth of nitriding layer measured on the furnace sample. The pre heat treatment before nitriding usually adopts quenching and tempering treatment, and normalizing treatment is allowed for general parts.