Effect of heat treatment on the microstructure and mechanical properties of 18Ni 300 maraging steel manufactured by wire + arc additive manufacturing

A thin-walled structure was manufactured by wire + arc additive manufacturing using 18Ni 300 maraging steel, and the heat treatment process had been investigated. The microstructure of as-deposited sample was martensite, ferrite and nano-precipitated phases. Differently, more nano-precipitated phases and reverted austenite existed in the direct aging (AT) sample. However, only lath martensite and nano-precipitated phases existed in the solution + aging (SAT) sample. The as-deposited and AT samples performed a high strength with well plastic. The primary strengthening mechanism for this great improvement of tensile strength arose by the formation of nano-precipitated phases, which was known as the Orowan strengthening mechanism. The well plastic of as-deposited and AT samples was attributed to dual phase net basket sub-structures, which were beneficial to improve the length of crack propagation and the ability of cooperative deformation. And the reverted austenite was also main factor for the well plastic of the AT samples.