The Woodruff School

SUMMARY

Duplex stainless steel (DSS) is a dual-phase material with approximately equal volume amount of austenite and ferrite. It has both great mechanical properties (good ductility and high tensile/fatigue strength) and excellent corrosion resistance due to the mixture of the two phases. However, stress corrosion cracking (SCC) of DSSs is a big concern for the application of DSSs. In this study, the SCC susceptibility of DSS 2205 is studied in acidified sodium chloride and caustic white liquor (WL) solutions. The cyclic stress effect on SCC of DSS 2205 in the above environments is also investigated. SCC of DSS 2205 in acidified sodium chloride solution is investigated. Potentiodynamic polarization tests at different pH values are performed to find out the pH value that gives active-passive polarization behavior of the material. Series of slow strain rate tests (SSRTs) at different applied potential values (within the theoretical SCC potential range) and at different strain rates are conducted to reveal the optimum applied potential value and the strain rate for SCC to happen. Low temperature static and cyclic creep tests are performed in air to reveal the strain accumulation effect of cyclic stresses. Test results show that cyclic loading could accumulate extra amount of strain in DSS 2205 compared to static loading, even at room temperature. Cyclic SSRTs are performed under the conditions that SCC occurs in sodium chloride and WL solutions. Preliminary test results show that cyclic stress facilitate crack initiations in DSS 2205, but work-hardening of the material will retard crack initiations induced by cyclic stresses.

SUBJECT:	Ph.D. Dissertation Defense

BY:	Di Yang

TIME:	Friday, September 30, 2011, 1:15 p.m.

PLACE:	IPST Building, 521

TITLE:	Cyclic Stress Effect on Stress Corrosion Cracking of Duplex Stainless Steel in Chloride and Caustic Solutions

COMMITTEE:	Dr. Preet M. Singh, Co-Chair (MSE) Dr. Richard W. Neu, Co-Chair (ME) Dr. W. Steven Johnson (MSE) Dr. Naresh Thadhani (MSE) Dr. Hamid Garmestani (MSE)

SUMMARY Duplex stainless steel (DSS) is a dual-phase material with approximately equal volume amount of austenite and ferrite. It has both great mechanical properties (good ductility and high tensile/fatigue strength) and excellent corrosion resistance due to the mixture of the two phases. However, stress corrosion cracking (SCC) of DSSs is a big concern for the application of DSSs. In this study, the SCC susceptibility of DSS 2205 is studied in acidified sodium chloride and caustic white liquor (WL) solutions. The cyclic stress effect on SCC of DSS 2205 in the above environments is also investigated. SCC of DSS 2205 in acidified sodium chloride solution is investigated. Potentiodynamic polarization tests at different pH values are performed to find out the pH value that gives active-passive polarization behavior of the material. Series of slow strain rate tests (SSRTs) at different applied potential values (within the theoretical SCC potential range) and at different strain rates are conducted to reveal the optimum applied potential value and the strain rate for SCC to happen. Low temperature static and cyclic creep tests are performed in air to reveal the strain accumulation effect of cyclic stresses. Test results show that cyclic loading could accumulate extra amount of strain in DSS 2205 compared to static loading, even at room temperature. Cyclic SSRTs are performed under the conditions that SCC occurs in sodium chloride and WL solutions. Preliminary test results show that cyclic stress facilitate crack initiations in DSS 2205, but work-hardening of the material will retard crack initiations induced by cyclic stresses.