Plasma nitriding of 90CrMoV8 tool steel for the enhancement of hardness and corrosion resistance

Abstract

is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. The aim of the study is to apply a plasma nitriding process to the 90CrMoV8 steel commonly employed in wood machining, and to determine its efficiency to improve both mechanical and electrochemical properties of the surface. Treatments were performed at a constant N 2 :H 2 gas mixture and by varying the temperature and process duration. The structural and morphological properties of nitrided layers were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) coupled with EDS microanalyses. Surface hardening and hardness profiles were evaluated by micro hardness measurements. To simulate the wood machining conditions, electrochemical tests were carried out with an oak wood electrolyte with the purpose of understanding the effects of the nitriding treatment on the corrosion resistance of the tool in operation. X-ray diffraction analyses revealed the presence of both γ′ (Fe 4 N) and ε (Fe 2-3 N) nitrides with a predominance of the ε phase. Moreover, α-Fe (110), γ′ and ε diffraction peaks were shifted to lower angles suggesting the development of compressive stresses in the post nitrided steel. As a result, it was shown that nitriding allowed a significant hardening of steel with hardness values higher than 1200 HV. The diffusion layers were always composed of an outer compound layer and a hardened bulk layer which thickness was half of the total diffusion layer one. No white layer was observed. Similarly, no traces of chromium nitrides were detected. The temperature seemed to be a parameter more influent than the process duration on the morphological properties of the nitrided layer, while it had no real influence on their crystallinity. Finally, the optimal nitriding conditions to obtain a thick and hard diffusion layer are 500°C for 10 h. On the other hand, to verify the effect of these parameters on the corrosion resistance, potentiodynamic polarization tests were carried out in an original "wood juice" electrolyte. After corrosion, surface was then observed at the SEM scale. Electrochemical study indicated that the untreated steel behaved as a passive material. Although the very noble character of steel was somewhat mitigated and the corrosion propensity increased for nitrided steels, the passive-like nature of the modified surface was preserved. For the same optimized parameters as those deduced from the mechanical characterization (500°C, 10 h), surface presented, in addition to a huge surface hardening, a high corrosion resistance.

Surface hardening of age-hardenable Cu–Ti dilute alloys by plasma nitriding

“…as polished by a diamond slurry) was (0.02 ± 0.01) μm. This indicates that plasma nitriding altered the roughness of Cu-Ti alloy surface, as it does for conventional steel surfaces [5][6][7]. Fig.…”

“…Plasma nitriding, a high-temperature surface chemical treatment, is one of the most widely used surface modification techniques for enhancing the surface properties such as the hardness, wear, and corrosion resistance of alloys based on iron and steel [5][6][7], titanium [8,9], aluminum [10], and magnesium-based alloys [11]. Plasma nitriding forms a nitrided zone such as a nitrided layer and/or precipitates on the material surface through the reaction of nitrogen ions with nitrogen-friendly elements in the materials.…”

Wood machining with a focus on French research in the last 50 years

“…Stellite tipping is one of the oldest methods and is very efficient for sawing high-density siliceous tropical woods (Chardin 1962). Nitriding steel gives promising results (Beer 1998;Nouveau et al 2011). Thin coating with a hard material (Cr x N y type) using physical vapour deposition also gives promising results (Nouveau 2001;Nouveau et al 2001).…”

Estudo da resistência ao desgaste da camada zeta de pressão de risers flexíveis submetida a tratamento criogênico e nitretação a plasma

“…[54], o qual constata um perfil de microdureza semelhante, no aço 90CrMoV8, associado à concentração N na amostra.…”

“…Este perfil é proveniente da difusão de N a partir da superfície até o núcleo do material, sendo produtos deste processo a saturação de N na matriz, precipitação de nitretos, redistribuição do carbono e alterações do contorno de grão [17]. Geralmente, amostras nitretadas apresentam este comportamento de maior dureza na região mais próxima à superfície, na região da camada branca e zona de difusão, e um decaimento até uma dureza semelhante à do material não nitretado (CR) [52][53][54][55][56]. Porém, foi observado que as amostras nitretadas apresentaram um valor de dureza abaixo daquele encontrado no material CR, em uma profundidade de aproximadamente 400 µm.…”