Thermally Induced Phase Transformation
The change of a material's atomic lattice due to temperature changes to minimize free enthalpy. This leads to different phases and properties.
Physicochemical mechanism of action
Thermally induced phase transformations change the atomic lattice of a material due to temperature changes. These changes occur to minimize the free enthalpy of the material. For example, during the transformation from α-crystal structure to β-crystal structure or when grain size changes occur.
Metallurgical relevance & risks in welding
These phase transformations can lead to various problems, such as the formation of cracks or distortions in the weld. For instance, rapid cooling after welding can result in glass-hard martensite, which leads to hot cracks. Too slow cooling can cause grain coarsening and thus a loss of toughness.
Workshop practice & instructions
To control thermally induced phase transformations, it is important to precisely regulate the cooling position and rate. For steels with high carbon content, slow cooling (e.g., in an oven) should be applied to prevent cracks. For other materials, rapid cooling may be necessary to achieve certain properties. It is important to consider the specific conditions for the respective material system.