| Duplex stainless steel (DSS) is composed of ferrite and austenite phase, whichhas been widely used in ocean and petroleum chemical industry owning to itsexcellent mechanical properties and corrosion resistance. In general, DSS has goodcorrosion resistance, but it will happen to localized corrosion under certain conditions.Compared to single-phase stainless steel, the localized corrosion of DSS is morecomplicated, mainly in alloy elements distribution in the two phases and theprecipitations (carbide, nitride, σ, et al.) produced by heat treatment and weldingthermal cycle. Currently, Low-nickel duplex stainless steel is one of the importantdirections of duplex stainless steel, the main characteristic of which is low nickel andmolybdenum. In order to accelerate the popularization and application of this newtype steel, we should pay more attention to the related research of its corrosionresistance.In this article, the mechanic property and localized corrosion resistance ofLow-nickel duplex stainless steel LDX2101were studied by hardness, tensile tests,electrochemical tests and slow strain rate tests (SSRT), which included the effects ofheat treatment(annealing at high temperature and aging at tip temperature for differenttime). The microstructure evolution of LDX2101after the corresponding heattreatment was analyzed by optical microscope (OPM), scanning electron microscopy(SEM) combined with energy spectrometer (SEM+EDS) and X-ray diffraction(XRD), and then explored the the relationship between its microstructure andmechanical properties, localized corrosion resistance. In addition, the effects ofchanges in element content on the microstructure and properties of LDX2101wereresearched by comparison with SAF2205which contains higher Ni and Mo).The results showed that: in comparison with SAF2205, although LDX2101hadlower Ni and Mo contents, it still had well mechanical properties and low stresscorrosion sensitivity in3.5%NaCl solution at the room temperature, but its pittingresistance decreased.LDX2101had excellent structure stability and without obvious precipitations atthe solution treatment temperature of950℃~1100℃. The same as SAF2205, with theincrease of solution temperature, the tensile properties and hardness of LDX2101changed little. At the strain rate of5×10-6S-1, with the increase of solution temperature, the stress corrosion cracking resistance of LDX2101changed little, butits pitting corrosion resistance changed a lot. At the solution treatment temperature950℃, a small amount of σ precipitate phase of SAF2205led to the poor stresscorrosion cracking resistance and pitting corrosion resistance, but at the othertemperature, its corrosion resistance changed little. Comprehensive analysis showedthat LDX2101and SAF2205which annealed at1050℃had excellent mechanicalproperties and corrosion resistance.In comparison with SAF2205aged at the nose temperature850℃for differenttime (0.5h,1h,2h,4h,8h,24h), due to the changes in element content, only a smallamount of Cr2N precipitation phase was found in LDX2101specimens aged at thenose temperature700℃for the same time. And with the increase of aging time, theamount of Cr2N precipitation phase and microhardness increased slowly. The same asSAF2205, with the increase of aging time, the pitting corrosion resistance ofLDX2101decreased gradually. While the stress corrosion cracking resistance ofLDX2101changed intricately, and when the LDX2101was aged at700℃for4h, thestress corrosion cracking resistance of it was poorer. In addition, a large number ofcorrosion products and secondary cracks were not found on the fracture surface ofLDX2101after aging treatment. |
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