Nitrogen Bubble Formation in Steel.

The behavior of nitrogen during solidification of iron melts (high purity iron and 0. 1C - 0. 4Si - 0. 5Mn) is characterized by the maximum possible amount present after solidification (limiting saturation value, LSV) and the amount responsible for cavity formation (limiting porosity value, LPV). With increasing heat extraction rate (0 to 1000 cal/g. min), LSV increases from solubility in delta iron to solubility in molten iron, which suggests a diffusion controlled process at the solid/liquid interface. The LPV at intermediate heat extraction rates is 60 to 80 ppm nitrogen in Fe - 0. 4Si alloys and a multiple of this value in unalloyed steel castings.