Abstract
Duplex stainless steels are high strength and corrosion resistant steels extensively used in the petrochemical and chemical industries. The aging at 475 °C for long periods of time provokes embrittlement and deterioration of corrosion resistance. However, short duration aging at 475 °C may be used as heat treatment to improve mechanical resistance with small decrease in the other properties. In this work the flow stress curves of lean duplex UNS S32304 and duplex UNS S32205 steels were modeled with Hollomon’s equation and work hardening exponents (n) were determined. The analyses were conducted in specimens annealed and heat treated at 475 °C for short periods of time. The aging at 475 °C for 4 hours, 8 hours and 12 hours promoted significant hardening with small decrease of ductility. The work hardening exponents of both steels were compared, being higher in the duplex steel than in the lean duplex grade.
Highlights
The use of austenitic-ferritic stainless steels has been increasing inside industry environment, replacing traditional austenitic grades for a number of components
The ferrite contents measured by quantitative metallography in 10 fields were (59.3 ± 4.0)% in the lean duplex, and (58.5 ± 3.0)% in the duplex steel
Observing that the Cr contents are similar in both steels, the more pronounced hardening of duplex steel may be attributed to the influence of Mo on the intensity and kinetics of α’ precipitation
Summary
The use of austenitic-ferritic stainless steels has been increasing inside industry environment, replacing traditional austenitic grades for a number of components. The success of this subclass of stainless steels is due to its excellent combination of corrosion resistance, mechanical resistance and toughness. The reason is because the long term aging in the 350‐550 °C may provoke the precipitation of very fine Cr‐rich particles formed by spinodal decomposition mechanism from the ferrite phase (δ). It is worth noting that in the literature α’ is used to designate the bcc magnetic martensite which appears in many austenitic and duplex stainless steels subjected to cold deformation[6,7,8,9]. In this work the effects of short duration heat treatments on the tensile mechanical properties of UNS S32304 and UNS S32205 steels were investigated
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