Low temperature plasma carburising of austenitic stainless steels for improved wear and corrosion resistance

Abstract

A novel plasma surface engineering process has been developed for engineering the surfaces of austenitic stainless steels to achieve combined improvements in wear and corrosion resistance. The process employs carbon as the major alloying species in the glow discharge of a plasma, facilitating the diffusion of carbon into the surfaces of various austenitic stainless steels and forming a precipitate free layer supersaturated with carbon at relatively low temperatures. This low temperature plasma surface alloying process produces a surface engineered layer several tens of micrometres thick, which has a high hardness together with excellent wear and corrosion resistance. The present paper describes various aspects of the novel process, concerning processing, structures, properties, and applications to engineering components.

Results of Characterization Tests of the Surfaces of a Commercially Carburized Austenitic Stainless Steel

“…Some inclusions and *-ferrite phase particles that were embraced by the Kolsterised layer became more sensitive to acid etching. Generally, many of these observations are similar to those reported by other researchers for stainless steel carburized by a plasma process conducted at temperatures between 300 and 600 o C [4,5].…”

“…Nevertheless, plastic deformation and martensite may occur during cooling from the Kolsterising  temperature. A phase similar to α'-martensite has been reported in the surface layer of 316 austenitic steel carburized in a methane gas plasma at 400-600 o C [4], but was not detected in other work conducted under the same conditions by the same authors on 316 and 304 steels [5].…”

“…The observed expansion of the lattice is due to absorption of carbon in supersaturated solid solution. Published data [5] relating lattice parameter to dissolved carbon concentration for 316 stainless steel carburized with up to 2.5 wt%C at 450-500 o C shows a linear function, a = 0.3597 + 0.0054C, where C is wt% carbon. In the present work, the average a value measured for the expanded austenite at the surface is 0.3688nm, which corresponds to a carbon concentration of 1.68 wt% in solid solution in the austenite.…”

Low temperature plasma carburizing of AISI 316L austenitic stainless steel and AISI F51 duplex stainless steel

“…During plasma processing the passive layer is removed by sputtering prior to the nitriding step without any damage to the part's surface. Based on the nitrogen expanded austenite concept, low temperature carburizing has been studied for austenitic and other stainless steels types [Sun, 1999], . [Ceschini, 2008], [Souza, 2009].…”

Novel Low-temperature Solid-carburizing Using C60 Fullerene for Austenitic Stainless Steel SUS316L

“…Recently, new carburizing techniques, including the socalled low-temperature gas or plasma-carburizing techniques, have been developed which make it possible to avoid the Cr depletion problem for austenitic stainless steels. [1][2][3][4][5][6][7][8][9][10][11] The carburizing process is done at around 450-500°C which is in the temperature range below the nose of the time-temperature-transformation (TTT) diagram. 12) In the temperature range, interstitial atoms such as C and N can diffuse in the parent lattice but the diffusion of substitutional atoms such as Cr is impeded, thus suppressing the formation of Cr carbides.…”