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

In this work an austenitic AISI 316L and a duplex AISI F51 (EN 1.4462) stainless steel were DC-Plasma carburized at 480 degrees C, using CH4 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 (gamma(C)) without any precipitation of carbides. The hardness of the carburized AISI 316L steel reached a maximum of 1000 HV due to similar 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 (gamma(C)), the ferritic grains transformed to carbon expanded ferrite (alpha(C)) and M23C6 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 M23C6 carbides.