Influence of Annealing Temperature on Deformation Behavior of 329LA Lean Duplex Stainless Steel

- Jan 09, 2017-

Duplex stainless steels (DSSs) exhibit excellent combination of corrosion resistance and mechanical properties, which has enabled their development as structural components in chemical and pulp industries as well as on/offshore applications. DSSs contain two phases, ferrite and austenite, the equilibrium fractions of which depend on annealing temperature.

The chemical composition of 329LA stainless steel is listed Fe-0.17N-0.02C-20.5Cr-2.0Ni-1.8Mn-0.7Cu-0.6Mo-0.5Si (wt%)

The effect of annealing temperature on deformation behavior of a329LA lean duplex stainless steel was investigated.
1. As the annealing temperature increases, the percentage of ferrite increases and austenite is enriched with austenite stabilizing elements. Accordingly, the stability of austenite upon quenching and deformation is significantly improved.
2. In the alloy with less stable austenite, more α′-martensite forms during quenching, which enhances the strength and strain hardening rate.
3. Deformation-induced martensitic transformation (DIMT) is the main deformation mechanism at room temperature regardless of the annealing temperature between 950 and 1150 °C, while specimen annealed at 1200 °C shows almost no DIMT.
4. The stability of austenite decelerates the nucleation and growth of deformation-induced martensite. Thus, the strain hardening rate starts to increase and reaches the peak more slowly for the alloy annealed at higher temperature; moreover, its maximum strain hardening rate was lower.
5. During the deformation, blocky martensite forms directly from austenite, not via hexagonally indexed deformation band. This is because the driving force for martensite transformation is relatively higher for the present alloy in comparison with the alloy which experiences hexagonally indexed deformation band.