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Fatigue cracking of near-eutectoid steel in corrosive environments

University of British Columbia

The fatigue crack propagation behavior of near-eutectoid steel (AISI 1070) was investigated in both pearlitic and fully spheroidized microstructures. Experiments were conducted on single edge notched specimens. Constant amplitude sinusoidal loading was applied at high frequency (-97 Hz) with R ratio of 0.5. Testing conditions were primarily under plane strain and good mixing between the crack tip solution and bulk solution was maintained. Experiments were conducted at ambient temperature and surface crack growth was measured optically. Attention was directed towards the effects of environment, heat treatment and cathodic protection. Environments were: desiccated air, distilled water, 3.5% NaCl solution, and buffered 3.5% NaCl solution (pH=10.5). Experiments in the NaCl solutions were conducted with and without cathodic protection. The results indicate that crack propagation is slower in the fully spheroidized microstructure. Formation of corrosion products in the crack caused crack growth retardation. The minimum crack propagation rate was observed in the spheroidized microstructure in 3.5% NaCl solution cathodically polarized to -1.0 VSCE- Corrosion products induced a crack closure effect, and reduced the effective crack tip cyclic stress intensity factor (AKefj) to a lower level. Crack fractography was examined using scanning electron microscopy (SEM). Fatigue striations were not readily visible in stage-II fatigue crack propagation. The overload region (stage-Ill) showed crystallographic cleavage-like facets and river lines.

Thesis/Dissertation

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2009-03-10

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http://hdl.handle.net/2429/5866

Materials Engineering

University of British Columbia

UBCV

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