Ludmila Kucerova
University of West Bohemia, Czech Republic
Title: Microstructure analysis of maraging steel X3NiCoMoTi 18-9-5 produced by additive manufacturing
Biography
Biography: Ludmila Kucerova
Abstract
Maraging steel X3NiCoMoTi 18-9-5 could be processed not only by conventional casting and heat treatment, but also by additive technology of laser direct melting. Input material for used selected laser melting (SLM) technology is metal powder. The powder used for additive manufacturing was analyzed to determine distribution of alloying elements within individual powder grains. Microstructure and mechanical properties of SLM build were determined in as-printed state and also after printing and subsequent heat treatment by either solution annealing or precipitation hardening. The microstructure in as-build state consisted of very fine cells of solid solution with thin films of retained austenite placed at the cell boundaries. An average tensile strength of 1050 MPa and total elongation of 8% was obtained in these samples. Solution annealing led to complete transformation of retained austenite to martensite and disappearance the original cellular microstructure. The resulting tensile strength was slightly below 1000 MPa, accompanied by total elongation of 9% and hardness of 328 HV 0.1. Precipitation hardening of as-built samples resulted in partial dissolution of the cells and an increased volume fraction of austenite. The ultimate tensile strength of hardened samples was nearly twice as high as in the as-built state reaching 1800 MPa. The microstructures and mechanical properties were compared with conventional maraging steel with the same chemical composition, sold under commercial name Vaco 180. In-situ observation of the straining of maraging steel in as-build condition was carried out, demonstrating the effect of metallurgical defects on failure initiation in additive manufactured steel.