(1) Austenitic stainless steels have higher hardness, YS & UTS than ferritic stainless steels. However, (2) in case of DSS, ferrite has higher hardness and YS, UTS than austenite. Why this ? In one case, are we looking into carbon% and in other case, are we looking into slip systems ?
First, be sure that the Dual-phase stainless steel has contributions from only ferrite and austenite, not other phases. Secondly, bear in mind that, Ferritic Stainless steel might not have same chemical composition as and likely not in chemical equilibrium with ferritic phase of such dual-phase stainless steel. Microscale mechanical properties may vary substantially from Macroscale, you know!
And high TS of ASS compared to FSS might be due to martensitic transformation- are you sure that occurs as unhindered as ASS in gamma-phase of F-A-DSS? The phases that are more difficult to deform are going to have higher hardness and strength, unless fracture occurs. It is likely that, while embedded in Austenitic matrix, ferritic phases deform and fracture at a much higher stress compared to FSS, and ferrite-austenite microscopic GB binding strength might play some role here.
consider strength vs phase content of FA-DSS. If the strength rises more than linear sum midways, you can see for yourself the mutual strengthening effect.
Hope this helps
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