Loss of Coherency Precipitation
The transition from a lattice-matched to a lattice-incoherent precipitate phase during progressive particle growth lowers the hardness generated by lattice distortion.
Physical-chemical mechanism of action
During the welding process, lattice-matched precipitate phases initially form, which align with the crystal lattice of the metal. With increasing particle growth, this phase can transform into a lattice-incoherent precipitate, where the lattice is no longer perfectly aligned.
Metallurgical relevance & risks in welding
Loss-of-coherence precipitation leads to a reduction in hardness and strength level of the weld. This can lead to an increased occurrence of cracks and coarsening of the structure, which impairs mechanical stability.
Workshop practice & instructions
To avoid loss-of-coherence precipitates, it is important to carefully control welding parameters such as temperature and time. For high-hardness steels, rapid cooling (short t8/5 time) can help minimize lattice distortion. For low-hardness steels, slow cooling (long t8/5 time) is advisable to keep the precipitate phases lattice-matched.