Effect of Titanium on Microstructure and Mechanical Behaviour of Additively Manufactured 1.2709 Maraging Steel

The effect of titanium on the microstructure and properties of additively manufactured 1.2709 maraging steel is thoroughly studied in this work. For this purpose, a standardized alloy with 0.84wt. % Ti and a model alloy with 0.02wt. % of Ti were prepared by laser powder bed fusion. The microstructures and mechanical behaviour (tensile properties and hardness) of the alloys are described and compared here. It is shown that in contrast to the standardized alloy, the model alloy cracks along grain boundaries in a brittle manner. The effect of Ti is further completed by investigations of (i) an alloy with an addition of 0.7wt. % Ti prepared by laser powder bed fusion and (ii) a low-Ti alloy produced by conventional casting. It is unambiguously shown that the cracking is primarily caused by the interplay of steep temperature changes during laser powder bed fusion of the steel powder and of the low Ti content in the model alloy causing the absence of retained austenite at grain boundaries. Additionally, the tendency of grain boundaries to crack during additive manufacturing is shown to depend on the grain boundary character.