Coherent precipitate
Coherent precipitation is a seamless phase transformation during welding, leading to improved toughness and higher strength.
Physical-Chemical Mechanism of Action
In coherent precipitation, the new crystal lattice merges seamlessly into the base lattice of the metal. This occurs without the formation of local stress fields, allowing a continuous microstructure.
Metallurgical Relevance & Risks in Welding
Coherent precipitation improves toughness and strength level of the weld. It prevents cracks and hot cracking because no stress fields that could lead to fracture are formed. However, an incomplete or faulty process can lead to a lack of coherent precipitation, which in turn leads to porosity and reduced mechanical properties.
Workshop Practice & Action Guidelines
To ensure coherent precipitation, it is important to precisely control welding parameters such as temperature and time. Too rapid cooling can lead to a lack of coherent precipitation, while too slow cooling results in grain coarsening and thus reduced mechanical properties. For steels with high carbon content, controlling cooling rate is particularly important.