Correlating shrinkage microporosity with the mechanical properties of sand-cast superduplex stainless steel using a numerical/experimental approach

• Tensile tests on miniaturised specimens from a sand cast plate allowed the Niyama threshold evaluation.
• The mechanical and deformative material response can be well correlated to the Niyama value.
• The purely thermal Niyama parameter can be used to predict the sand cast material behaviour.
• The knowledge of the microporosity value does not play a key role anymore.

In this work, the Niyama criterion for the prediction of shrinkage microporosity in a superduplex stainless steel (ASTM A890 Gr. 5A) end-risered plate produced by sand-casting is adopted. To validate numerical results obtained using the commercial software MAGMASoft, experimental castings were produced, and both the shrinkage microporosity and its effect on the material behaviour was evaluated. Metallographic techniques were used to quantify the microporosity and evaluate its distribution; the effect of the shrinkage microporosity on the sand cast material was measured through tensile tests on miniaturised specimens extracted along the longitudinal direction of the plate.Image analyses allowed estimation of the threshold Niyama value for microporosity in the investigated material. An analogous threshold for the Niyama parameter was determined from the mechanical data arising from tensile tests in which specific microporosity levels (and Niyama values) were identified that corresponded to minimum required levels of yield stress, UTS and elongation after fracture as specified by the ASTM standard. Mechanical data were found to be well correlated to the Niyama value, thus allowing to effectively use the purely thermal parameter Niyama to predict the sand cast material behaviour.

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