WAM Super Duplex Stainless Steel Shows Promising Fatigue Life

Super Duplex Stainless Steel Shows Promising Fatigue life and Crack Growth resistance for Tough Applications

Wire Additively Manufactured Super Duplex Stainless Steel Shows Promise for Tough Applications.

Imagine building super strong structures using a large-scale metal 3D printer. That's the potential of Wire Additive Manufacturing (WAM®), a technique for creating metal objects layer by layer.

AML3D's CTO, Andy Sales, and his peers Aditya Khanna from The School of Mechanical & Mining Engineering at The University of Queensland with James Hughes, Ling Yin and Andrei Kotousov, from The School of Electrical and Mechanical Engineering at The University of Adelaide, have been investigating how well this unique type of steel - Super Duplex Stainless Steel (SDSS) - performs under stress (fatigue) when manufactured using WAM®.

An example of a Super Duplex Stainless Steel casting that can be metal 3D printed using WAM.
An example of a Super Duplex Stainless Steel casting that can be metal 3D printed using WAM.

The good news? The results are promising!

The study investigated the fatigue properties of Super Duplex Stainless Steel (SDSS) manufactured using the Wire-arc Additive Manufacturing (WAM®) method. The Fatigue Crack Growth (FCG) rates were measured in two directions: longitudinal and transverse to the deposition direction.

The key findings are:

  • Fatigue properties are almost identical, or Isotropic, in both directions when expressed in terms of the effective stress intensity factor range.
  • Crack tip opening loads are sensitive to the choice of parameters used in the evaluation method. The study defines a new method for better consistency.
  • The difference in crack tip opening loads between the two directions can be attributed to any residual stresses induced by the WAM® process (there are techniques to reduce the residual stresses). If a component is overloaded in service, this difference can affect its fatigue life.
  • The rate at which a crack grows under fatigue load is affected by crack closure, and if residual stresses are present.
  • To prolong the fatigue life of a load-bearing SDSS component, one can account for a longitudinal deposition direction in the component design, leveraging the materials deposition direction that has the most extended fatigue life when under cyclic stress.

Cracking the Code on Fatigue

The study focused on Fatigue Crack Growth (FCG), tiny cracks that grow over time under stress. Researchers measured these cracks in two directions: along the printing lines (longitudinally) and across them (transverse). The findings showed that regardless of the direction, the fatigue resistance of the SDSS was very similar when considering a specific factor called the "effective stress intensity factor." This suggests that crack closure mechanisms, where tiny cracks close up slightly under pressure, are important when considering the design of SDSS components.

The study also highlighted the influence of the manufacturing process itself. Residual stresses, induced by the rapid cooling during WAM, were identified as a likely cause for the small differences in crack growth behaviour between the two printing directions.

Fatigue crack growth rates for different load ratios; for (a) crack propagating longitudinally to the deposition direction and (b) crack propagating transversely to the deposition direction. Figure 7. from article.
Fatigue crack growth rates for different load ratios; for (a) crack propagating longitudinally to the deposition direction and (b) crack propagating transversely to the deposition direction. Figure 7. from article.

Building a Stronger Future

While more research is needed to confirm these findings using different printing parameters, this study paves the way for using WAM®-fabricated SDSS components and parts for fatigue-loaded applications. This super steel's potential for strength, fatigue durability, and adaptability to complex designs makes it an exciting prospect for the future of construction, engineering, and various industries such as marine and offshore.

 

Talk to AML3D

If you would like to learn more about AML3D's Wire Additive Manufacturing technology and producing large-scale SDSS parts with ARCEMY®, contact us today.

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About AML3D

AML3D Limited, a publicly listed technology company founded in 2014, utilises new technologies to pioneer and lead metal additive manufacturing globally. Disrupting the traditional manufacturing space, AML3D has developed and patented a Wire Additive Manufacturing (WAM®) process that metal 3D prints commercial, large-scale parts for Aerospace, Defence, Maritime, Manufacturing, Mining and Oil & Gas. AML3D provides parts contract manufacturing from its Technology Centre in Adelaide, Australia, and is the OEM of ARCEMY®, an industrial metal 3D printing system that combines IIoT and Industry 4.0 to enable manufacturers to become globally competitive.