Keyhole Compact Tension Specimen Fatigue of Selected High-Strength Steels in Seawater

Abstract

Fatigue experiments have been performed in flowing natural seawater on nine different steels with yield stress in the range 370 to 990 MPa (54 to 143 ksi) employing keyhole compact tension specimens. All experiments were at a frequency of 1.0 Hz and R = 0.5. Corrosion state was either freely corroding (FC) or cathodically polarized (CP) to ∼1.10 V saturated calomel electrode (SCE). Limited experiments were also performed in air. Seven of the steels represent relatively new technology where strengthening involves either (1) precipitation hardening, (2) microalloying and quenching and tempering, (3) control rolling, or (4) thermomechanical control processing (TMCP). The results are represented in a ΔK(ρ)-1/2 versus cycles to initiation format and are evaluated with regard to the effects of environment and cathodic polarization. Endurance limit (CP tests only) was related to tensile strength and fracture behavior.

Microbe-Enhanced Environmental Fatigue Crack Propagation in HY130 Steel

“…[23][24] SENT specimens for experiments in moist air, sterile NaCl, and the SRB in Postgate C were notched similarly (with a root radius [] of 0.25 mm and by grinding without additional polishing), and subjected to a constant ∆K of 20.8 MPa√m (calculated as if the blunt notch was a crack of the same length) at a frequency of 1 Hz and R of 0.1. (6) After a period of no measurable crack formation, FCI progressed from the notch, as indicated by electrical potentials measured during cyclic loading.…”

“…It is well known that, compared to fatigue in moist air, sterile NaCl degrades the FCI resistance of C-Mn and alloy steels. [23][24] This environmental effect is severe for electrode potentials near free corrosion (-600 mV SCE to -750 mV SCE ) and is mitigated by applied cathodic potentials near -1,000 mV SCE . 25 The detrimental effect of sterile NaCl at -600 mV SCE and the beneficial effect of applied cathodic polarization are reflected in Figure 6.…”