Dr. Johny Varghese

Incoming Fellow, affiliation:

12/2023-11/2025: Mechanical Engineering, University of Siegen

Additive Manufacturing of Maraging Steels and Influence of retained austenite on mechanical properties

Maraging steels have a very low carbon content and exhibit an outstanding combination of ultra-high strength, ductility, machinability, dimensional stability, and good fracture toughness. These alloys are being used extensively in die casting and tooling industries. Furthermore, there is potential for use as spring steel e.g., in food and automotive industry, where stiffness, high strength, and ductility are primary requirements. The production route of these steels is complex and, alternatively, additive manufacturing (AM) can be used as a cost-effective method to produce complex geometries with high precision, tailored microstructure, mechanical and corrosion properties within shortened lead times; though the control of porosity, inclusions and surface finish requires special attention.
Due to lack of carbon in the maraging steels, lath martensite produced during solidification is relatively soft and tough, which has a high ability to resist cracking during AM processing. The high level of strength is established through many uniformly distributed intermetallic nanoprecipitates by means of a subsequent aging treatment. Maraging steels may contain some retained austenite (RA) on solidification and reversion of austenite from martensite may happen during aging treatments; the control of both RA and reversed austenite are essential for attaining the pursued mechanical properties. In high Ni containing maraging steels, the RA content will be high as Ni is an austenite stabilizer and this RA can delay the crack propagation during deformation. But and increased RA content can have detrimental effects as well. Hence an optimum RA content in maraging steels can give the best mechanical properties.
Even though major research efforts in the scientific community have addressed the correlation between input parameters (particle size distribution, chemical composition, process parameters, strategies, etc.) and output parameters (mechanical properties, relative density, and microstructure), the effect of RA and reversed austenite and influence of heat treatment process is yet to be explored.
Major objectives:
• Generating a roadmap for tailoring mechanical properties of additive manufactured parts using commercially available maraging steel powders.
• Understanding the effect of process parameters and aging on RA content of the AM parts.
• Manufacturing of miniature specimens with superior mechanical and fatigue properties.