Mass fraction of carbides
The mass fraction of carbides indicates how much bound carbon is present in hard phases in the metal. It affects wear resistance and the microstructure.
Physical-Chemical Mechanism of Action
The mass fraction of carbides refers to the percentage of bound carbon in the form of hard phases like cementite in steel. These hard phases consist of carbon and iron, which have combined into solid crystals.
Metallurgical Relevance & Risks in Welding
A high mass fraction of carbides increases the wear resistance of the steel, as the hard phases offer strong resistance to mechanical stress. However, too high a carbon content (over 1.0 %) can lead to hot cracking and glass-hard microstructures, especially if cooling is too fast. This can be caused by a too short time t8/5 (< 5 s).
Workshop Practice & Instructions
To achieve an optimal mass fraction of carbides, pay attention to the correct cooling technique. Use a controlled cooling method like salt bath quenching or temperature profiles. For steels with high carbon content (e.g., HSS), ensure that the time t8/5 is between 10 and 20 seconds to obtain a balanced structure.