The effect of solution annealing temperature ranging from 950 to 1 200℃ on the microstructure and corrosion performance of duplex stainless steel(DSS)2204 were investigated.The proportion of the ferrite phase increased while the austenite phase decreased and the ferrite stabilizing elements diluted in the ferrite phase with the increase of annealing temperature.The critical pitting temperature(CPT)of specimens annealed at 1 000℃ was higher than those annealed at 950 ℃,whereas further increasing the annealing temperature to 1 200 ℃ decreased the CPT.The pitting initiation sites were observed in the austenite phase,at the boundary of ferrite/austenite phase and inside the ferrite phase for specimens annealed at 950,1 000℃ and exceeding 1 100℃,respectively.The evolution trend of the CPT and the pit initiation site were analyzed by the pitting resistance equivalent number.
The corrosion behaviors of pure titanium and its weldment welded by tungsten inert gas(TIG) welding in simulated desulfurized flue gas condensates in thermal power plant chimney were investigated using potentiodynamic polarization,electrochemical impedance spectroscopy(EIS) and immersion tests.The effects of heat input and shielding gases on the corrosion behavior of the welded titanium were also studied.Grain coarsening and Widmansta¨tten structure were found in both the fusion zone and the heat-affected zone.The welded titanium exhibited active–passive behavior in the simulated condensates.Both the polarization curves and EIS measurements confirmed that TIG welding process with different parameters had few effects on the corrosion behavior.It was proved that the microstructure changes were not the key material factors affecting the corrosion behavior of pure titanium under the test conditions,while the oxide film had remarkable effect on improving the corrosion resistance.
Two kinds of 90Cu10 Ni tubes with different service lives(more than 3 years and only 1 year,respectively)under identical working conditions were studied by an immersion test in a 3.5 wt% NaCl solution and the electron backscattered diffraction(EBSD) technique.The morphology after immersion showed severer corrosion attack at the grain boundaries of the tube with shorter service life compared with the tube with longer service life.The grain boundary characterization distributions(GBCDs) of the two tubes obtained by EBSD revealed more Σ3 boundaries and twins,and larger random boundary meshes in the tube with longer service life.A short immersion test in a modified Livingston's solution was conducted to evaluate the tendency to corrosion attack of different types of the grain boundaries.SEM and AFM were used to characterize the corrosion morphologies of the boundaries.A strong correlation between varying depths of corrosion grooves and types of the grain boundaries was obtained.The influence of deviation angle of low Σ boundaries on corrosion resistance of the grain boundaries was also discussed.It is concluded that a special ‘‘grain boundary engineering''(GBE) treatment has been performed on the tube with longer service life.It is proposed that the optimized GBCD is responsible for the better service performance of the tube.
