Gas soft nitriding is a surface treatment method that uses a mixture of gases, such as N₂, CO₂, and NH₃, to form a compound layer composed of Fe–N–C phases on the surface of the workpiece. It is especially suitable for precision parts requiring minimal distortion, and allows for quick and safe processing. By utilizing carbon—which has a higher diffusion coefficient than nitrogen—the process achieves faster treatment speeds and improved cost efficiency compared to conventional gas nitriding.