Influence of Solution Treatment Temperature on the Microstructural Homogenization and Mechanical Behavior of Additively Manufactured Maraging Steel (18Ni300)
摘要
A conventional heat treatment may not be necessarily suitable for additive-manufactured maraging steel (18Ni300) owing to the heterogeneous microstructure developed during the process. The present study investigated the influence of two different solution treatment temperatures, 820°C (ST-820C: conventional) and 900°C (ST-900C: alternative), on the microstructure and mechanical properties of laser powder bed fusion (LPBF) processed 18Ni300. The investigation was conducted on specimens produced at two scan speeds (420 mm·s−1 [S420] and 850 mm·s−1 [S850]) with maximum relative density. The ST-820C resulted in partial homogenization owing to residual microsegregation, whereas ST-900C achieved complete homogenization and yielded a uniform lath martensitic structure. Although the S850 condition exhibited finer microstructures, the S420 samples showed marginally superior strength and ductility in the as-built condition, attributed to a lower retained austenite fraction. This contrasting difference decreased slightly after solution treatment because of an increase in martensitic block width and a decrease in retained austenite. Impact toughness was high in the as-built condition (56 J) and decreased after aging (STA-820C: 16 J; STA-900C: 12 J) because of brittle intermetallic precipitates. These findings demonstrate the essential need for heat treatment optimization in LPBF AM maraging steel to obtain a homogeneous microstructure and superior mechanical properties.