Low-temperature Plasma Assisted Thermochemical Treatments of AISI 420 Steel: Comparative Study of Obtained Layers

Abstract

Formation of metastable C-, N-, or even Formation of metastable C-, N-, or even C/N-expanded phases can be observed for typical non-equilibrium conditions attained at the plasma assisted thermochemical treatments when temperatures relatively low are used. In present work, kinetics data are considered in a comparative study comprising low-temperature plasma assisted carburizing, nitriding and nitrocarburizing of AISI 420 martensitic stainless steel samples treated at 350, 400, and 450 °C, aiming to put in evidence the main metallurgical differences of the obtained layers. Microstructural characterization and hardness measurement results for untreated and treated sample surfaces show significant difference for the carburized layer growth in relation to that verified for the nitrided and nitrocarburized layers. While the carburized layer is constituted of a thin outer layer and a deep diffusion layer, just the opposite was observed for the other two treatments, id est., formation of thicker outer layers and thinner diffusion layers. Finally, carbide-/nitride-precipitation-free layers were supposedly obtained for samples carburized, nitrided, and nitrocarburized at 350 °C temperature.

Growth Kinetics and Some Mechanical Properties of Plasma Paste Borided Layers Produced on Nimonic 80A-Alloy

“…When compared to the conventional thermo-chemical boriding processes, plasma-assisted boriding has many advantages: shorter duration of process, lower temperature of process, relatively low gas consumption, lower activation energy for the formation of the boride layers, and reduction in emission of pollutants and toxic wastes [ 1 , 2 ]. Plasma-assisted boriding has become an interesting technique for producing the borided layers on various materials such as: steels [ 1 , 2 , 3 , 4 , 5 , 6 , 7 ], titanium alloys [ 8 , 9 , 10 , 11 , 12 , 13 ], nickel alloys [ 14 , 15 ], molybdenum alloys [ 16 ] and cobalt alloys [ 17 ].…”

The “Expanded” Phases in the Low-Temperature Treated Stainless Steels: A Review

“…Since the formation of Cr nitrides and carbides is related to diffusion phenomena, both treatment temperature and time are the process parameters which must be carefully controlled in order to avoid the formation of these precipitates. For martensitic stainless steels, the limit temperature for avoiding Cr nitride/carbide precipitation is considered to be ~350 • C for nitriding [10,79], ~400 • C for nitrocarburizing [79,80], and ~450 • C for carburizing [79,81], with a treatment duration of up to 8 h. When a treatment temperature of 400 • C was employed for AISI 420 martensitic stainless steel, 4 h was reported to be the threshold for sensitization, i.e., the precipitation of Cr compounds, for nitriding treatments [64,78], 6 h for nitrocarburizing [80], and more than 36 h for carburizing [82].…”

Improvement of mechanical properties and corrosion resistance of 316L and 304 stainless steel by low temperature plasma cementation

“…The field of surface engineering is the process commonly used to design the surface of this type of material in order to improve its surface hardness and wear resistance. Thus, to improve the surface properties, diffusion and thermochemical techniques are used, such as carburizing [8][9][10][11], nitrocarburizing [11][12][13], nitriding [13][14][15] and ion implantation [16].…”