In the past ten years, the on-the-spot application of the separator to more than two thousand factories and mines in China shows that, the initial permeability method has been successfully applied to identifying the kinds of steel and iron, sorting the mixed steel and iron material and identifying the state of the heat treatment. The separator can also be used to nondestructive determining the carbon content of structural steel, the precision can be ± 0.02%. The single-valued or linear relationship between the displayed value on the separator and hardness of the structural steel such as 45, 40Cr and 65Mn etc. has been acquired, and the international difficult problem of the "N" shape relation between the above mentioned two sides has been successfully solved. The precision of hardness testing with the separator can be ±1HRC or ±10HB, and the precision of carburized layer thickness testing can be ±0.05 mm. The defects such as cracks on the surface and interior cracks which are 20 mm deep below the surface can be tested with coil, and the defects such as cracks which are 100 mm deep below the surface can be tested with probe. The separating speed can be 1500 parts per hour.