臺灣博碩士論文加值系統

The effect of sigma phase on the mechanical property and stress
corrosion cracking (SCC) resistance of 2205 duplex stainless
steel(DSS 2205) was investigated. The changes of pitting and
intergranular corrosion as a function of sigma phase were also
studied.DSS 2205 were aged at 800℃ up to 20 hours for the
precipitation of various amount of sigma phase. The content of
sigma phase was measured using image analysis of the etched
surface of DSS 2205.The results of image analysis showed that
the s phase content reached saturation level about 40% after
being aged at 800℃for 20h. Both hardness and tensile strength
increased while elongation decreased with increasing s phase
content.The oxalic acid etch test showed that the precipitation
of sigma phase result in the dual and ditch structure in s phase
contained DSS 2205. The experimental results of potentiodynamic
polarization test in 26wt% sodium chloride showed that the
passive region was decreased increasing the aging time at 800℃
The region will increase by aging more than 10 hours. This is
due to the self healing effect of Cr diffusion. Pits were found
in s phase containing DSS 2205 after cyclic polarization test.
Slow strain rate test (SSRT) was conducted to evaluate the of
stress corrosion cracking resistance of 2205 DSS containing
various amount of s phase. The experimental results indicated
that the presence of s phase caused a decrease in ductility of
2205 DSS either in air or in 5M MgCl2 solution. The brittle
feature of sigma phase was found to participate the SCC
processes of 2205 DSS in MgCl2 solution.The susceptibility to
SCC increased with increasing s phase content and solution
temperature. Microscopic examination revealed that sigma phase
was responsible for the cracking processes in MgCl2 solution