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On the Use of LPBF 300 Grade Maraging Steel (Fe-18%Ni) for Aluminum Alloy Die Casting

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The appearance and growth of cracks in casting dies from the accumulated thermo-mechanical stress from thousands of cycles of high pressure die casting is a recurring challenge. The use of additive manufacturing (AM) to realize die inserts with conformal cooling has been implemented as a solution to help improve cooling efficiency during casting. However, despite this, premature tool failure still sometimes occurs. The presentation will showcase a methodology deployed to identify both the design and build parameters that can increase the tool life of AM inserts, more notably a 300 grade maraging steel processed via laser powder bed fusion (LPBF). A range of sample types were printed during multiple campaigns. Geometric coupons with different surface inclinations and conformal channel designs were printed to study the effect of process parameters on geometric fidelity, surface topography, and depowdering. Mechanical testing coupons were printed to identify the response to aging with/without a prior solution heat treatment step and correlate performance back to microstructure (grain size, austenite content). It was demonstrated - via a carefully constructed correlation between hardness, high temperature Charpy impact energy, mean grain size and percentage of reverted austenite – that a solution treatment step was not required to achieve a good balance of hardness and toughness. Conformal channels retained a near-circular final geometry, although depowering of these channels did present a challenge at times.

Learning Objectives:

  • Optimize their maraging steel heat treatment strategies based on the hardness and toughness combinations of values obtained with and without a solution heat treatment precursor step.
  • Re-evaluate the design of conformal cooling channels to minimize any distortion and fused powder overhang inside of the channel(s).
  • Correlate the microstructure of overaged maraging steel with the mechanical properties best suited for die casting applications, with and without a solution heat treatment precursor step.