Vacuum Carburizing of Small Diesel Engine Fuel Injection Needle Valve Body

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The material is 18Cr2Ni4WA steel

The technical requirements are: the depth of the carburized layer in the valve body and seat surface is 0.75~0.85mm, the mass fraction of carbon is 0.70%~0.85%, the hardness of the carburized layer is ≥58HRC, and the injection hole is also required to be carburized.

The structure size of the injection needle valve body is shown in Figure 1, and the carburizing process curve is shown in Figure 2. The carburizing temperature is 970 ° C, the infiltration and expansion ratio is 2: 1, that is, carburizing 10min, diffusion 5min, carburizing time is 15 pulse cycles, that is, 15X 15min=225min. Furnace pressure: initial vacuum degree is 10.64Pa, The higher the vacuum degree, the less residual air in the furnace tank, which is beneficial to improve the carbon potential of the furnace gas. The vacuum degree in the carburizing period is 4X10⁴Pa. If the vacuum degree is low, the carbon potential in the furnace will be high, which is beneficial to increase the infiltration rate, but may make the carbon concentration of the carburized layer too high. The vacuum degree in the diffusion period is 13~20Pa, and the carbon potential of the furnace gas is low.

Figure 1 Shape of Diesel Engine Needle Valve Body

Fig.2 Pulse vacuum carburizing process curve of 18Cr2Ni4WA steel fuel injection needle valve body

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