Tertiary cementite
Tertiary cementite is the finest cementite that precipitates from ferrite at low temperatures and preferentially deposits at grain boundaries. It occurs when the carbon content of the melt is too high.
Physical-Chemical Mechanism of Action
Tertiary cementite forms through rapid cooling of the weld pool after welding. If the carbon content in the melt is too high, it crystallizes quickly and finely at the grain boundaries of the ferrite.
Metallurgical Relevance & Welding Risks
Tertiary cementite can increase the hardness and toughness of the weld, leading to crack-sensitive microstructures. It can also cause stress buildup and corrosion issues if not handled properly.
Workshop Practice & Action Guidelines
To avoid tertiary cementite, the weld pool should be well protected to minimize carbon loss. Cooling steps should be controlled to ensure uniform grain size and a stable microstructure.