2013 Volume 54 Issue 4 Pages 603-608
The homogeneous microstructure, precise texture, and weldability of pre-hardened AISI P21 plastic mold steel are ideal for mirror-finished plastic mold cores and cavities. This study applies a nitriding heat treatment and oxynitriding to AISI P21 plastic mold steel, using various processing parameters to determine the influence that nitriding treatment has on the surface characteristics. Regarding the prepared specimen, an optical microscope was used to analyze the microstructure and thickness of the nitride layer, X-ray diffraction (XRD) was performed to examine the structure, a 3D surface profile meter was employed to analyze the surface morphology and roughness, and polarization corrosion was conducted to assess the corrosion resistance. A Rockwell C test was also applied to examine the hardness. The results show that applying nitriding treatment to AISI P21 plastic mold steel can effectively improve the surface hardness, and the addition of an oxynitride surface layer increases the corrosion resistance. The nitrogen element under the surface layer, which although relatively hard is brittle, produces ferrous nitrides such as Fe3N and Fe4N that maintain the precise shape of the plastic mold and extend its service life.