Heat treatment optimisation of 18 % Ni maraging steel produced by DED-ARC for enhancing mechanical properties

This article deals with the Directed Energy Deposition using Wire and Arc (DED-ARC) for maraging steel cladding. A technology for cladding using Gas Metal Arc Welding (GMAW) has been developed that enables the perfect deposition of maraging steel. The material characterisation was carried out in different material states: in the as-built, solution annealed and aged. The research included visual examinations, optical microscopy, Scanning Electron Microscopy / Energy-dispersive X-ray spectroscopy (SEM/EDS), fractography, hardness testing, tensile testing and impact toughness testing. The as-deposited state exhibited a microstructure with very long crystal grains and microsegregations orientated the direction of the heat sink, consisting of lath martensite. Consequently, a subsequent heat treatment is absolutely necessary in order to obtain a uniform fine-grained microstructure. Two different solution annealing processes were analysed, which allowed us to select the most suitable process for the first step of heat treatment followed by aging. A response surface methodology was used to optimise the aging conditions. The results show that additively manufactured maraging steel reaches a tensile strength of 1947 MPa, a hardness of 657 HV5 and a Charpy impact toughness of 11 J at peak aging condition, which is comparable to conventionally manufactured maraging steel.