Abstract: Surface and cross-sectional morphology, phase composition and hardness of domestic and imported electromagnetic workpieces with the same specifications and dimensions were tested and analyzed by using optical microscope, scanning electron microscope, X-ray diffractometer and microhardness tester, and the surface treatment processes of the two type workpieces were studied based on the Fe-N binary phase diagram. The results show that the matrix of both specimens is α pure iron, and the surface morphology and phase composition after surface treatment are basically the same. However, there is only a γ′-Fe bright compound layer above the diffusion layer of the domestic electromagnetic workpiece, with a thickness of 8-9 μm and a microhardness of 323 HV0.05. While there is a layer with a thickness of 12-13 μm between the bright compound layer and the diffusion layer of the imported electromagnetic workpieces, and the transition layer with a microhardness of 312 HV0.05 is the troostite structure formed after γ-Fe cooling. It can be inferred that domestic workpiece adopted a conventional low-temperature (below 590 ℃) nitriding process, while imported workpiece which has a deeper nitriding layer and a transition layer composed of troostite structure adopted a high-temperature ion nitriding process above 590 ℃.

Key words: α-Fe, electromagnetic pure iron, nitriding process, troostite, transition layer