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

Abstract

In this work an austenitic AISI 316L and a duplex AISI F51 (EN 1.4462) stainless steel were DC-Plasma carburized at 480 o C, using CH 4 as carbon carrier gas. For the austenitic AISI 316L stainless steel, low temperature plasma carburizing induced a strong carbon supersaturation in the austenitic lattice and the formation of carbon expanded austenite (g C ) without any precipitation of carbides. The hardness of the carburized AISI 316L steel reached a maximum of 1000 HV due to ~13 at% carbon supersaturation and expansion of the FCC lattice. For the duplex stainless steel AISI F51, the austenitic grains transformed to carbon expanded austenite (g C ), the ferritic grains transformed to carbon expanded ferrite (a C ) and M 23 C 6 type carbides precipitated in the nitrided case. Hardness of the carburized case of the F51 duplex steel reached 1600 HV due to the combined effects of austenite and ferrite lattice expansion with a fine and dispersed precipitation of M 23 C 6 carbides.Keywords: Plasma carburizing, austenitic stainless steel, duplex stainless steel, expanded austenite, expanded ferrite. Resumo

Study of the Thermochemical Surface Treatment Effect on the Phase Precipitation and Degradation Behaviour of DSS and SDSS

“…On the other hand, DSS sample does not show oxides when compared with slight oxides that appeared in the surface of SDSS sample as shown in Figure 4a, b. Internal oxidation is typical in gas carburizing processes due to the penetration of oxygen, where the atmosphere contain partial pressures of CO, CO 2 and H 2 O leading to some internal oxidation of the samples [24,25]. However, in plasma carburizing, such an issue can be discarded, and no intragranular oxidation is observed as expected.…”

“…However, the presence of the chi-phase in the core of the SDSS C + TT, and not on the surface, leads to the fact that the relatively low distribution of carbides in this sample does not harm it from the corrosion properties point of view. Usually carbides and nitrides are responsible for the decrease in corrosion resistance in such processes at low temperatures [13,25,41]. Herein, due to the extremely low amount of nitrogen, the small dark phases were identified mainly as carbides.…”

“…Regarding the plasma carburizing at lower temperatures, carbon presents lower diffusivity, and consequently, low solubility in the ferrite phase (0.0025%) [48]. Therefore, the adsorbed carbon atoms on the surface do not have enough mobility to diffuse into the substrate, a saturation of the carbon Usually carbides and nitrides are responsible for the decrease in corrosion resistance in such processes at low temperatures [13,25,41]. Herein, due to the extremely low amount of nitrogen, the small dark phases were identified mainly as carbides.…”

Wear resistance of AISI 304 stainless steel submitted to low temperature plasma carburizing

“…This technique has been used in A316 austenitic steels and the high mechanical and corrosion performance is due to the formation of an expanded austenitic microstructure, also known as the carbon S phase. The hardening mechanism is based on supersaturation of carbon into the austenitic structure, expanding the FCC cell and producing high levels of residual stress (Gallo et al, 2012;Pinedo and Tschiptschin, 2013;Sousa et al, 2013).…”

Aços inoxidáveis duplex: uma breve visão

“…A microestrutura mista faz com que esse aço apresente uma combinação favorável das propriedades dos aços inoxidáveis ferríticos e austeníticos, conferindo-lhes uma elevada resistência à corrosão sob tensão, se comparados com os aços inoxidáveis austeníticos e uma maior ductilidade, quando comparados aos aços inoxidáveis ferríticos. A sua tenacidade situa-se entre a dos aços inoxidáveis austeníticos e ferríticos, além de apresentar uma elevada tensão de escoamento que permite a fabricação de componentes com paredes finas e alta resistência mecânica, possibilitando, assim, a redução da quantidade de material (PINEDO;TSCHIPTSCHIN, 2013;SILVA, 2008).…”