Abstract: Laser directed energy deposition has shown its advantage in developing intragranular austenite-dominated duplex stainless steels in-situ for exceptional performances. However, how this intragranular austenite-dominated phase balance is formed remains unclear. In order to reveal the novel nucleation and growth mechanism of intragranular austenite, both interdendritic and interphase elemental distributions are investigated. It is found that the supersaturation-induced driving force for interdendritic austenite nucleation reaches 822 J/mol, dominating the austenite nucleation. Instead of the well-accepted para-equilibrium diffusion-controlled growth, intragranular austenite growth is a Cr-dragged nitrogen diffusion-controlled process at the rational boundary and a mixed-mode controlled process at the irrational boundary. The extensive nucleation and dragged growth promote the novel fine intragranular austenite-dominated phase balance.

Key words: Laser deposition, Stainless steel, Segregation, Austenite transformation