Abstract
Duplex stainless steels have a large number of industrial applications and may replace high cost materials, especially in chloride-containing environments like seawater in off-shore platforms due to their high mechanical properties and good corrosion resistance. The influence of the ferrite content on the performance of duplex stainless steels in these corrosive environments is not well known. For the present paper, new superduplex stainless steels with ferrite between 30 and 60% were developed and their microstructure and corrosion resistance were evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests in NaCl 3.5% (wt %) at 26°C and 78°C. The results obtained at 26°C showed that the pitting potential (Epitt) is little affected by the ferrite content, but for the materials with higher ferrite it was possible to observe an increase in the repassivation potential with a decrease in the corrosion potential and passive currents due to the presence of more resistive passive films. Tests performed at 78°C indicated a high decrease in the Epitt for all the samples, independently of the ferrite percentage, although maintaining superiority in higher ferrite content. Alloys with a 55% ferrite phase content, i.e. less dependent of Ni element, present a superior performance of corrosion resistance.
Highlights
Austenitic-ferritic stainless steels are wellknown to have good corrosion resistance in a large number of environments and may replace standard austenitic stainless steels in some industrial applications due to their high mechanical properties and good stress-corrosion cracking resistance.[1,2,3]Duplex stainless steels have been developed in response to the demand for more resistant materials in the chemical, petrochemical and oil industries.[4,5] New duplex grades with higher levels of Cr, Mo and N have been developed, as they present better localized corrosion resistance and mechanical properties
Superduplex ASTM A995M-Gr.5A/EN 10283-Mat#1. 4469(GX2CrNiMo26-7-4) stainless steels with six distinct ferrite contents were prepared in an electrical induction furnace
For the stainless steels studied in this work, the pitting resistance equivalent (PREn = %Cr + 3.3%Mo + 16%N ≥ 40) indicates they are all classified as superduplex stainless steels
Summary
Austenitic-ferritic (duplex) stainless steels are wellknown to have good corrosion resistance in a large number of environments and may replace standard austenitic stainless steels in some industrial applications due to their high mechanical properties and good stress-corrosion cracking resistance.[1,2,3]. Duplex stainless steels have been developed in response to the demand for more resistant materials in the chemical, petrochemical and oil industries.[4,5] New duplex grades with higher levels of Cr, Mo and N have been developed, as they present better localized corrosion resistance and mechanical properties. These materials have been increasingly used in aggressive environments, seawater in petrochemical plants and oil and gas production systems. The present study investigates the effect of ferrite content on the microstructure and corrosion resistance (in a sodium chloride medium) of the ASTM A995M Gr.5A superduplex stainless steel with ferrite ranging between 30 and 60%
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