Abstract
Abstract In the present work, the influence of the pulse voltage and pressure on the treatment glow discharge characteristics and consequently on the surface properties obtained for low temperature plasma carburized AISI 420 martensitic stainless steel was investigated. Two distinct sets of samples were carburized at 450 °C, for 8 h, one aiming to study the applied pulse voltage effects, which was varied for 500, 600 and 700 V, at a fixed pressure of 400 Pa, and the other aiming to study the pressure effects, which was varied for 200, 400, and 800 Pa, at a fixed pulse voltage of 700 V. Treated samples were characterized by means of confocal laser scanning microscopy (CLSM), X-ray diffraction (XRD) analysis, microhardness and roughness measurements. The glow discharge (plasma) was characterized by optical emission spectroscopy (OES) and current measurements. Results show that the edge effect, surface roughness, hardness and outer layer growth kinetics are dependent on the studied plasma parameters. OES analyses showed that the pulse voltage parameter does not promote significant changes on the plasma chemistry, but confirmed that the molecular H2 gas dissociation rate tends to be significantly affected by the pressure parameter giving important support for the results obtained here.
Highlights
Two typical microstructures of the applied pulse voltage and pressure treatment series are presented in Figure 1a, b, one obtained at 500 V / 400 Pa and the other at 800 Pa / 700 V, just the lower voltage and the higher pressure studied here, respectively
The white-aspect layer occurrence suggests carbon diffusing and enriching in interstitial solid solution the surface martensitic structure, promoting the formation of the termed ‘outer layer’, according to the terminology previously used in ref[41]
A study strengthened by an optical emission spectroscopy approach for low-temperature plasma carburizing was performed aiming to evaluate the influence of the treatment pressure and applied pulse voltage on the glow-discharge characteristics, and on surface properties of the treated AISI 420 martensitic stainless steel
Summary
Martensitic stainless steels (MSSs) are widely used in different industrial fields comprising the manufacturing of surgical instruments[1,2,3], forming tools[3,4,5], hydraulic system elements[3,5,6], structural and machine parts[3,5,7], dairy and food apparatus[1,4,7], petrochemical[8], and mining industry[9] components They present wide application field due to their relatively high mechanical strength and moderate corrosion resistance[10].
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