Phosphorus Block Segregation
Phosphorus macrosegregation is an uneven distribution of phosphorus during solidification, leading to local phosphide eutectics and low toughness.
Physikochemical mechanism of action
Phosphorus diffuses during melting and cooling of steel. With uneven distribution, it forms phosphide eutectics where phosphorus crystallizes in the copper phases. This changes the microstructure and affects the mechanical properties of the material.
Metallurgical relevance & risks in welding
Phosphorus segregation can lead to increased toughness and reduced ductility. Local phosphide eutectics can cause cracks and hot cracking, especially when the material is under stress or at high temperatures. This impairs the mechanical strength of the weld and can lead to fractures.
Workshop practice & instructions
To minimize phosphorus segregation, the steel should be well pre-treated. This includes uniform cooling and the use of welding materials with low phosphorus content. When selecting the welding process, care should be taken that it does not adversely affect the microstructure. Controlled cooling and careful material selection can reduce the effects of phosphorus segregation.