Martensitic Stainless Steel with precipitation hardening and high mechanical strength for Additive Manufacturing.

The combination of Additive Manufacturing (AM) design freedom and a new generation of high-performance metal powders offers a great opportunity to achieve an industrial leap regarding performance, weight reduction, decarbonization, cost, ... To support those challenges, Aubert & Duval is evaluating the AM powder version of MLX®19 grade that has originally been developed for forged mechanical parts.

The MLX®19 grade is a precipitation hardening stainless steel combining ultra-high tensile strength and good corrosion resistance. This stainless steel has been designed for severe service conditions with targeted properties similar to 300M performance required for structural aerospace components: ultimate tensile strength (UTS) range between 1800 and 1950 MPa, toughness (KIC) from 50 to 80 MPa.m^1/2.

In this study, MLX®19 powder produced by gas atomization was processed by Laser Powder Bed Fusion (LPBF). AM processes result in specific non-equilibrium microstructures leading to original properties when compared to conventional processes such as forging. This works highlights the process-microstructure-performance parameters that have been optimized to improve mechanical properties. Thermal analysis, DRX measurement and SEM observations were performed to optimize heat treatments and understand their effect on hardening phases precipitation and mechanical properties. Based on the acquired knowledge, future work for the alloy development is discussed.