Carburizing carbonitriding combined heat treatment process

Advantages of carburizing carbonitriding combined heat treatment process

Carburizing-carbonitriding composite heat treatment process has the advantages of low treatment temperature, rapid carburizing speed and so on. It can effectively restrain the structural defects easily produced in single carburizing and single carbonitriding. The concentration gradient and hardness gradient of carburizing layer are gentle, the bonding strength between carburizing layer and matrix is high, the surface residual stress is high, and the comprehensive mechanical properties are good. 

Application characteristics of carburizing carbonitriding combined heat treatment process

For parts with low carbon content, few alloying elements and more than 1.0 mm carburized layer, carburizing-carbonitriding composite heat treatment is usually used in heavy load, medium impact, medium and high speed conditions. Carburizing at high temperature and high carbon potential in the early stage can obtain sufficient carbon concentration on the surface of the carburized layer and carbonitriding diffusion in the later stage, which can not only thicken the carburized layer and smooth the carbon concentration gradient, but also inhibit the appearance of massive and reticulated carbides. Because the carbonitriding is carried out during the diffusion period, the speed of Carbonitriding is greatly increased. The low carbon potential and ammonia inflow can effectively inhibit and black microstructure.

Composite heat treatment makes the surface and subsurface layers have very high hardness, which improves the strength, hardness and residual compressive stress of the area, and inhibits the fatigue crack initiation and propagation, thus improving the fatigue strength. The eutectoid layer of composite treatment is generally between 0.25 mm and 0.35 mm. The gentle concentration and hardness gradient slow down the formation of low energy multi-impact crack and bending eccentric crack. The following figure shows the surface structure of 20# plunger produced by our company for a famous mechanical company after carburizing-carbonitriding combined heat treatment.