Mechanical properties of duplex layer formed on AISI 403 stainless steel by chromizing and boronizing treatment

In order to improve the high temperature performance of AISI 403 martensitic stainless steel, duplex surface treatment which combines the methods of pack cementation chromizing and boronizing was carried out. Specimens were chromized at 1100 °C for 2 h and were subsequently boronized in a solid medium consisting of EKabor-III powders at 950 °C for 9 h. The characteristics of the duplex treated specimens were evaluated by a scanning electron microscopy, X-ray diffraction (XRD), glow discharge optical emission spectroscopy and Micro-Vickers hardness testing. The chromizing for 2 h had created a Cr diffusion layer of approximately 130 μm thickness. Subsequent boronizing on the Cr diffused layer induced formation of duplex layer of approximately 50 μm thickness with a largely improved surface microhardness up to approximately 2300 Hv. The cross-sectional microstructure of duplex treated specimen consisted of a duplex layer, a transition region between duplex layer and Cr diffusion layer, a Cr diffusion layer and matrix in series. XRD analysis revealed that the various phases of FeB, Fe2B and CrB are present in the duplex layer. The wear volume of duplex treated specimen after a wear test at 500 °C, comparing the duplex treated specimen with the specimen treated only by boronizing, was reduced by a factor of 1.5. In addition, the duplex treated specimen showed a much-improved high temperature oxidation resistance, which could be attributed to the high Cr content (≈20 at.%).