Efeito do envelhecimento em baixa temperatura nas propriedades de aços inoxidáveis lean duplex
Resumo
In this work, the mechanical and corrosion properties of two lean duplex steels
(LDSS) 2101 and 2404 aged at 475 °C for up to 2000 h were assessed, and the
obtained results were compared with the standard duplex stainless steel (DSS)
2205. The microstructural changes were analyzed by means of optical
microscopy (OM), X ray diffraction (XRD), measured by ferritescope and
transmission electron microscopy (TEM). The mechanical properties were
assessed based on Vickers microhardness measurements and Charpy impact
tests. The corrosion resistance was assessed by double loop electrochemical
potentiokinetic reactivation (DL-EPR), anodic polarization in 3.5% NaCl solution
and immersion tests in ferric chloride solution. The analysis by optical microscope
and X ray diffraction of the samples solution treated and aged for 2000 h of the
studied materials do not reveal microstructural change as a function of thermal aging. However, the measurements by ferritescope show a decrease in magnetic
permeability of the ferrite with the extension of aging time for 2000 h. TEM
analysis of the samples aged for 2000 h show that the formation of α’ phase
occurs in all materials. However, precipitation of G phase is much greater in the
AID 2205. Hardness measurements show that the hardening effect caused by
the formation of α’ phase is higher in DSS 2205. On the other hand, impact tests
show that the LDSS 2404 has the smaller impact toughness property of the
studied alloys as a function of thermal aging. DL-EPR results show that the LDSS
2101 has the greater degree of Cr depletion with aging for 2000 h. Anodic
polarization measurements of the materials studied show that the thermal aging
for 2000 h promotes a decrease in Epit, causing an increase in the density and
size of pits. Immersion tests in ferric chloride solution showed a higher corrosion
rate for the DSS 2205 as a function of aging time for 2000 h