Decrease of solidification cracking susceptibility on fully austenitic weld metal with a large amount of Phosphorus using application of Rare Earth Monophosphide

- Development of method to prevent solidification crack in austenitic weld metal with a large amount of Phosphorus -

Abstract

It was clarified that the promotion of the crystallization of rare earth monophosphide during welding solidification by increasing Nd content was effective to decrease the solidification cracking susceptibility of fully austenitic weld metal with a large amount of Phosphorus. The decrease of solidification cracking susceptibility by increasing Nd content in Fe-18%Cr-15%Ni-0.1%P weld metal was confirmed using transverse varestraint testing and restraint weld cracking test. Also, NdP crystallization during GTA welding solidification on 0.5%Nd weld metal was confirmed by in-situ observation using synchrotron radiation. In order to solve the mechanism of the decrease of solidification cracking susceptibility by the crystallization of rare earth monophosphide, a numerical model to predict the behavior of microsegregation during welding solidification was developed with notable features considering the competition of the crystallization between NdP and M₂₃C₆ eutectic phases and the coupling with modified thermodynamic database. It was found that the decrease of solidification cracking susceptibility on fully austenitic weld metal with 0.1% Phosphorus by increasing Nd content caused by the restraint of the increase of Phosphorus amount in liquid phase by NdP crystallization.