The typical hardening treatments to ductile iron castings include quenching and tempering, carburizing quenching, high-frequency quenching and nitrocarburizing treatment. What are their differences, their advantages and disadvantages?
Ductile Iron Quenching and Tempering
The normal quenching and tempering process could increase the surface hardness of ductile iron castings to (Rockwell hardness) RC 30, moreover, it could improve the comprehensive mechanical properties to ductile irons too.
Ductile Iron Carburizing Quenching
If we heat the ductile iron castings in the carburizing furnace, the carbon content could be kept high, so the surface hardness could be increased to RC 50 - RC 55. So, its advantages are very high surface hardness and good abrasive resistance. The surface hardness could be kept in the depth of 2mm. This is the experience of our Dandong foundry.
The disadvantage will be low production rate, because the carburizing furnace is vacuum electric furnace, so it is not very large. Plus, the cost of heat treatment will be much higher than normal.
Ductile Iron High-Frequency Quenching
middle-frequency quenching, high-frequency quenching and flame quenching have the same character, the surface hardness could be increased to about RC 40, the hardness could be kept in the depth of 2 to 3mm, however, its abrasive resistance is normal.
The large gears need this treatment, because of the size problem. The advantages are comparatively low cost and no size limitation.
Ductile Iron Nitrocarburizing Treatment
Nitrocarburzing treatment does not need very high treatment temperature, so the deformation of the castings is very small, this is one advantage. Moreover, there is no oxide surface after treatment, which is another good point. The surface hardness could reach RC 50. However, the hardness can only be kept in 0.1 to 0.2mm depth., so too shallow hardness surface will cause poor abrasive performance. Our Dandong foundry can not do this treatment for now.