| Duplex stainless steel(DSS) has combined excellent toughness and weldability of austenite steel with superior mechanical properties and corrosion resistance of ferrite steel.During the processing of heat treatment and welding,they must be performed carefully between 300℃and 1000℃in order to prevent harmful secondary phase precipitation.DSS are prone toσphase formation in isothermal aging treatment in the temperature range of 600℃～1000℃.σphase-notorious for its hardness and brittleness-could badly weaken mechanical properties of duplex stainless steel,while for which consists mainly of chromium-molybdenum precipitation,cause depletion of chromium and molybdenum at grain boundaries and weak pitting corrosion resistance follows.S31803 hot-rolled sheet was chosen as the study material,σphase precipitation during isothermal aging was studied under a series of aging treatments in 850℃,while the influence ofσphases on mechanical properties was made clear,and the pitting corrosion resistance of S31803 DSS was determined by anodic curves in aqueous contains NaCl or NaBr at different pitting conditions.The results showed thatσphase came out as long as aging for 5 min,while which got its peak point in 15min～30min.With prolonging of aging time,volume ofσphase and austenite increased markedly whereas volume of ferrite phase decreased a lot. Tensile properties and toughness of DSS lowered down significantly companied with hardness increased extremely.Toughness of DSS performed anisotropic role,and transverse impact energy absorption overweighed lengthways.Formation ofσphase resulted in Cr-Mo depletion in ambient regions,therefore initiation of localized corrosion tended to occur in the place,which meant pitting potential reduced with increasing aging time.Increasing temperature- impacted corrosion resistance-could accelerate medium movement speed,enhance metal surface energy,lower down passive film stability and make pitting corrosion rate faster,while which could also promote passive film forming,prevent base metal from dissolving.Anodic curves shifted negatively at earlier temperature period,while which shifted positively over 90℃.NaBr solution was used in this work to investigate pitting potential of DSS,the results indicated that which under 30℃NaBr solution approached that under 50℃NaCl solution.The summing up above meant that 50℃NaCl solution could instead of room-temperature NaBr one,so as to simplify experimental facilities.
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