Secondary Phase Transformation
Solid-state microstructural change driven by thermal cycles or diffusion, precipitating new phases from a supersaturated matrix and largely governing mechanical properties.
Secondary phase transformation refers to the change in structure in already solidified weld metal or in the heat-affected zone when the material forms a new crystal structure during cooling or through subsequent heat treatment. Depending on the material and cooling rate, this can be good – then the structure becomes stronger and tougher – or bad, then it becomes hard and prone to cracking. You must therefore keep an eye on the cooling conditions and know which material can tolerate what. If you are unsure how your material behaves during welding, the only help is a look at the data sheet or consultation with the person who created the welding procedure specification.