Effects of the Voltage and Pressure on the Carburizing of Martensitic Stainless Steel in Pulsed DC Glow Discharge

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 H 2 gas dissociation rate tends to be significantly affected by the pressure parameter giving important support for the results obtained here.

An overview on plasma-assisted thermochemical treatments of martensitic stainless steels *

“…However, in 2012 Scheuer et al [30] evidenced that an adequate choice of electrical discharge and treatment parameters can lead to a significant increase in the LTPC AISI 420 MSS hardness, being reported an addition of about 2 times in surface hardness. After proving the treatment effectiveness, Scheuer et alcarried out it proper parameterization, evaluating the effects of gas mixture and gas flow rate [31], voltage and pressure [32], and of the carburizing temperature and time [33]. These results gave a new impetus to the subject, stimulating the accomplishment of complementary studies aiming to evaluate the corrosion [34] and wear [35][36][37] resistance of LTPC AISI 420 MSS.…”

Surface Hardening of Stainless Steel

“…Martensitic stainless steels can also be nitrocarburized or carburized [59][60][61][62]. Nitrocarburization of 420 martensitic stainless steel carried out at 450°C for4hcan achieve a surface hardening close to 1280 HV with a layer composed of nitrogen and Table 3.…”

“…Nitriding at lower temperatures avoids these precipitates in the layer. Figure 21 shows the hardness profile of the martensitic stainless steel after plasma hardening at 450°C for 4 h, with a maximum hardening potential of 800 HV and a hardening depth in the diffusion zone close to 0.040 mm [61].…”

“…When plasma nitriding is carried out at 400°C, hardening occurs by forming a nitrogen supersaturated layer of expanded martensite (α 0 N ) without nitrides precipitation, reaching 1130 Vickers. Hardness profile for a 450°C (4 h) plasma nitrided AISI 420 martensitic stainless steel [61].…”

“…Figure 21.Hardness profile for a 450°C (4 h) plasma nitrided AISI 420 martensitic stainless steel[61].…”