Secondary crystallization
Secondary crystallization is the process where new crystals form in an already solid metal. This can be triggered by temperature changes or changes in the chemical environment.
Physikalisch-chemischer Wirkmechanismus
Secondary crystallization happens when a metal, in a solid state, forms new crystals under certain conditions. This can be caused by a temperature drop or by chemical reactions like precipitation of compounds. The new crystals can change the existing structure, either by fitting into the current crystal structure or by forming new phases.
Metallurgical Relevance & Welding Risks
In welding, secondary crystallization can cause problems, for example grain coarsening and reduced toughness. This can especially happen with metals that have a high carbon or other alloy content. Cooling too fast can make new crystals grow irregularly and contaminate the metal.
Werkstattpraxis & Handlungsanweisungen
To minimize secondary crystallization, it's important to cool in a controlled way. This can be done with cooling water or special cooling media. The cooling rate should be set so the metal cools slowly and evenly. For metals that crystallize easily, like high-carbon steel, continuous cooling works best.