Metastable phase solidification in electron beam welding of dissimilar stainless steels

Electron beam welds between dissimilar stainless steels with different solidification modes were studied with a view to elucidating the role of nucleation, cooling rate and direction of dendrite growth on the tendency towards metastable phase solidification. The results are compared with the solidification behaviour of levitation melted samples. It is demonstrated that with careful design, stainless steels which normally solidify as ferrite can be induced into metastable austenitic solidification by removing the barrier to the nucleation of austenite. This is achieved in practice by allowing stable dendrites of austenite to continue growth into the liquid which normally solidifies to ferrite; it is found that the direction of growth of the dendrites has to be carefully controlled.