Cryogenic properties of additive manufactured austenitic stainless steels for space applications

Sammanfattning: The mechanical properties of three austenitic stainless steel alloys, namely 21-6-9, 316L and a modifed 316, fabricated via laser powder bed fusion, have been studied. From the results previously obtained through tensile tests at room and cryogenic temperatures, their strength and ductility were compared against similar conventionally processed materials. The three alloys exhibited a higher or similar strength than their conventional counterparts at both temperatures. In the case of ductility, the additive manufactured 316L was the only alloy that outperformed a conventional 316L at room temperature. At cryogenic temperature, the ductility of the three alloys was either similar or lower. Also, their plastic behavior throughout di˙erent stages of deformation was characterized from their microstructure evolution. At room temperature, a two stage, monotonically descending strain hardening rate was observed, similar to FCC medium stacking fault energy materials. At cryogenic temperatures, four stages of strain hardening rates were observed, caused by a martensite transformation induced by plastic deformation, as it happens in TRIP steels.