| 316L stainless steel has been used to make nuclear grade cladding tube due to its excellent mechanical properties,formability, corrosion resistance and high-density.The operating environment of nuclear grade cladding tube is extremely wicked,so it has strict requirements on the mechanical properties and corrosion resistance of the applied material. In order to provide experimental and theoretical basis for making reasonable production process of nuclear grade cladding tube,this dissertation used tensile test studied the influence of carbon content and degree of cold deformation on the mechanical properties of316L at ambient temperature and350℃; used Thermo-Calc thermodynamic software, SEM, TEM and Phase analysis technology studied the precipitation behavior of316L after aging at770℃; and used electrochemical and chemical immersion method studied the influence of carbon content and degree of cold deformation on the resistance to intergranular corrosion and pitting corrosion after sensitized at770℃.The tensile test results indicated that the tensile strength of316L at ambient temperature as well as350℃were increased rapidly with increase of cold deformation, however, the ductility of them were just the reverse. And with the increase of C content, the tensile strength of316L at both ambient temperature and350℃were also increased, but the ductility of them were irregular. TEM observation showed that the dislocation configuration, when at low degree of cold deformation, was mainly Parallel dislocation, while after25%deformation it changed to slip bands and dislocation cells.The Swift regression result of the true stress-strain curve of316L showed that the strain hardening exponent was decreased with increase of cold deformation, and when after25%deformation the work hardening ability was even almost lost.As seen from the research of precipitate phases, the precipitate phases of316L containing0.02%C after aging at770℃were σ,χ and M23C6, and the intermetallic phase (σ and χ) is the main part of them. The precipitation was found to occur first on grain boundaries, then in the intragranular.The precipitation of Intergranular was mainly σ and χ, and the morphology of them were bulk and spindle respectively while the intragranular precipitation was mainly χ, and the morphology of them were Irregular large block, tetragonum, rhabditiform and parallelogram. The precipitate phases of316L containing0.0018%C after aging at770℃were σ and χ.The precipitation of intermetallic phase decreased with the increase of C content.The precipitation of316L could be promoted by cold deformation, and the effect of it increased with aging time.The results of the intergranular corrosion of316L studied by electrochemical potentiokinetic reactivation (EPR) showed that the degree of sensitization (DOS) of316L increased with increase of sensitization time. Under the same sensitization time, the DOS of316L increased with the increase of cold deformation, whereas decreased with the increase of C content.The SEM and EDS analysis showed that, the sensitization of the alloy at770℃was caused by the intermetallic phase at grain boundary.The result of the65%HNO3method used for evaluating the intergranular corrosion Resistance of undeformed316L sensitized at770℃was consistent with that of the EPR method.Pitting corrosion resistance test carried out by electrochemical method showed that the pitting corrosion resistance decreased with the increase of sensitization time and cold deformation.The FeCl3chemical immersion method results were in accord with the electrochemical method.Furthermore,the chemical immersion method result showed that the influence of C on pitting corrosion resistance was irregular.The SEM observation showed that,the pitting corrosion of316L was mainly occurred around the intermetallic phases as well as in the non-metallic inclusion which was rich in Al、 Ti、Mg and O. |
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