Plasma nitriding of HP13Cr supermartensitic stainless steel

Supermartensitic stainless steels (SMSS) are commonly employed in the oil exploitation industry and present a good balance between the necessary physical and chemical properties and financial costs. Certain applications, such as in extreme corrosive and abrasive environments, demand improvements in the surface properties of these steels. In the present work, HP13Cr SMSS with a fully martensitic microstructure were plasma nitrided in the 350-450 degrees C range. The high diffusivity and low solubility of nitrogen in the martensitic structure allowed the production of thick layers (16-61 pin) containing epsilon-Fe2-3N, gamma'-Fe4N and expanded phase (alpha(N)) in all the temperatures. In addition, anisotropic sputtering rate and N-diffusion were observed for different grain orientations. Mechanical properties were measured by instrumented indentation, appropriately corrected from roughness effects on the results. Hardness profiles increased from 3.8 GPa (bulk) to similar to 14 GPa (near surface region) in all the working temperatures, whereas the elastic modulus was 230 GPa, presenting no statistically significant differences with respect to the bulk value. Nanoscratch tests revealed a hardened-ductile like behavior of these nitride layers. The surface tribo-mechanical behavior was correlated with elastic-plastic responses of the precipitatecontaining texturized layers. Results are interpreted in light of the effectiveness of plasma nitriding to modify the surface properties of SMSS. (C) 2015 Elsevier B.V. All rights reserved.