Phases and defects upon the solidification of nitrogen-alloyed stainless steels

Abstract

One of the technological problems in alloying molten steels with nitrogen is the precipitation of nitrogen into the gas phase upon the solidification of steels and the formation of nitrogen bubbles and porosity in steel ingots with the result that potentials of nitrogen as an alloying element are used incompletely. The formation of bubbles and pores in nitrogen-alloyed stainless steels occurs heterogeneously and is limited by the desorption rate of nitrogen from the molten-metal surface into bubbles. For this reason, it is convenient to determine the critical nitrogen concentration in steels as the concentration at which in the process of equilibrium solidification the content of nitrogen in the residual liquid phase at all temperatures of semisolid state does not exceed its solubility in the residual liquid at a given pressure. Hereafter, this concentration should be refined experimentally for concrete conditions of solidification. To calculate the nitrogen concentration in the arising phases, a Thermo-Calc software can be employed.