Phosphorus grain flank embrittlement
Phosphorus grain flank embrittlement raises the ductile-to-brittle transition temperature by weakening grain boundary cohesion. This can lead to weld areas more prone to cracking.
Physico-chemical mechanism of action
Phosphorus, which exists as an interstitial dissolved element in the metal, can cause a local increase in the ductile-to-brittle transition temperature. This happens by weakening grain boundary cohesion, meaning the material becomes more brittle at these locations.
Metallurgical relevance & risks in welding
Phosphorus grain boundary embrittlement can lead to more crack-prone weld regions. This occurs when the material at grain boundaries becomes too brittle and easily cracks under mechanical stress. This increases the risk of hot cracking and reduces the toughness of the weld.
Workshop practice & instructions
To minimize phosphorus grain boundary embrittlement, it is important to control the melting process carefully. This includes setting the correct melting temperature and time as well as proper cooling of the material. For high-phosphorus steels, special attention should be paid to slow and controlled cooling to lower the ductile-to-brittle transition temperature and increase weld toughness.