Strengthening of Sintered Austenitic Stainless Steels through Low-Temperature Carburization

The tensile strength and hardness of pressed-and-sintered 316L and 304L are generally poor due to the low sintered density and austenitic structure. To improve these properties, low-temperature carburization (LTC) was applied to these materials. In contrast to fully dense parts, for which LTC can increase the surface hardness with only limited depth, carbon can effectively diffuse into the center of pressed-and-sintered specimens through interconnected pores and harden all pore surfaces inside the compact. For sintered 316L with a density of 6.71 © 10 3 kg/m 3 , the hardness increased from 25 to 75 HRB (from HV70 to HV137) and the tensile strength increased from 295 to 520MPa after LTC, while the corrosion resistance remained almost the same because no chromium carbide formed. The hardness and tensile strength of sintered 304L were also improved after LTC. For sintered 304L with a density of 6.70 © 10 3 kg/m 3 , the hardness increased from 27 to 74 HRB (from HV72 to HV135), and the tensile strength increased from 291 to 519MPa. The bulk hardness and tensile strength of the high-density part were lower than those with a low density, since less carbon could diffuse into the center and fewer carburized regions formed. [doi:10.2320/matertrans.M2011150]