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AISI 430 is a non-stabilized ferritic stainless steel grade with carbon content lower than 0.12%.After hot and cold rolling this material is annealed. The slow cooling after soaking at temperatures between 900 o C and 1000 o C promotes the formation of a high quantity of carbides and nitrides, while the rapid cooling partially suppresses the formation of these precipitates, but introduces martensite in the microstructure. Intergranular martensite can also be produced in the weld metal and in the heat affected zone (HAZ) of welds of nonstabilized ferritic stainless steels. In this work, several heat treatments between 900 o C and 1000 o C, with different cooling rates, were performed in a commercial sheet of AISI 430 grade. Also, an autogenous welding was produced with GTAW process, and post weld heat treatment at 700°C was carried out. The different microstructures produced were analyzed by optical and scanning electron microscopy (SEM). The degree of sensitization was measured by double loop electrochemical potentiodynamic tests (DL-EPR). The pitting corrosion resistance was evaluated by cyclic polarization tests in 3.5%NaCl solution. Hardness and toughness tests were also performed in selected heat treatment conditions. The results indicate that the slow cooling results in a higher degree of sensitization than observed in the material rapid cooled from the annealing temperature. The ferritic martensitic structure produced by water cooling has higher pitting potential and lower degree of sensitization, but is brittle at room temperature. A subsequent tempering treatment between 600 and 800 o C can increase the toughness, but the corrosion resistance may decrease due to carbides precipitation.The heat affected zone of AISI 430 welds contains intergranular martensite, which is brittle and susceptible to corrosion attack. Post weld heat treatment at 700 o C decomposed the martensite into ferrite and carbides and improved the corrosion resistance.Key-words: ferritic stainless steels, microstructure, DL-EPR test. ________________________________________________________________________________ INTRODUCTIONAISI 430 steel is one of the most popular ferritic stainless steels. Although more modern ferritic stainless steels have been developed, the production of AISI 430 is still elevated due to its low cost and good corrosion properties.The influence of heat treatments on microstructure, corrosion resistance and mechanical properties of stainless steels is a key issue. Depending on the final heat treatment, the mechanical properties and corrosion properties may vary significantly. Frequently, the best heat treatment for corrosion resistance is not the best for the desired mechanical properties.On the other hand, welding always produces important changes on the microstructure of weld metal and heat affected zone (HAZ) which affects corrosion resistance and mechanical properties. In the case of ferritic stainless steels, the main change produced in fusion welding processes is the pronounced grain growth in the weld...

Superduplex stainless steels (SDSS) are frequently employed in the petrochemical industries where is required high mechanical strength, toughness, and corrosion resistance. However, these properties can be affected by deleterious phases formation due thermomechanical processes applied in the field during pipes and vessels construction. This work propose the nondestructive microstructural characterization of deleterious phases precipitated in SDSS isothermally treated in 800 and 850ºC using portable double loop electrochemical polarization reactivation tests (DL-EPR). The results obtained in this nondestructive test are quite close to those obtained by conventional test, and can be correlated with the amount of deleterious phases precipitated. It can be concluded that the microstructural degradation of superduplex stainless steel can be evaluated by portable DL-EPR test with slow sweep rates, using a special cell and a proper electrolyte at room temperature.