Decomposition state
The decomposition state is the process by which unstable phases in a metal transform into more stable equilibrium phases. This reduces hardness and brings the material closer to its thermodynamic ground state.
Physical-Chemical Mechanism of Action
In the decomposed state, metals undergo various phase transformations where unstable crystal structures are transformed into stable ones. This process is often triggered by thermal or mechanical stress and leads to a reduction in hardness and improvement in toughness of the material.
Metallurgical Relevance & Welding Risks
The decomposed state is crucial for the quality of weld seams. An insufficient decomposed state can lead to high stress buildup and hot cracking, while excessive decomposition can make the material too soft and impair its mechanical properties. It is important to ensure proper cooling duration and temperature to achieve the optimal decomposed state.
Workshop Practice & Action Guidelines
To optimize the decomposed state, the metal should be cooled in a protected environment after welding. The cooling duration and temperature should be adjusted according to material and application. For high-carbon steel, a cool furnace or slow cooling process is recommended to reduce hardness and avoid cracking.