Corrosion Fatigue Crack Propagation Behavior of a C-Mn-Cb Steel

Abstract

The fatigue crack propagation properties of a C-Mn-Cb plate steel (SA633 Grade C) in a 3.5 percent NaCl solution have been evaluated for loading frequencies of 10, 1.0, and 0.1 Hertz. To reveal the influence of test specimen orientation and steel cleanliness, both a conventional sulfur level and a low sulfur-calcium treated plate were examined in the three major testing orientations. In addition to other basic testing of the plates, the elastic-plastic fracture toughness properties were also established. The fatigue crack growth rates at 0.1 Hz of both steels were increased by factors of 2–5 over air data, depending on the ΔK level and specimen orientation; some increase was also noted at 1.0 Hz. The acceleration due to the salt water environment was a result of a hydrogen embrittlement mechanism which resulted in bursts of faceted, cleavage-like, transgranular fracture of ferrite grains in this ferrite-pearlite steel. At higher ΔK levels, the calcium treated steel showed slower growth rates than the conventional sulfur level steel for all testing conditions. It was found that higher oxygen contents of a salt water solution could lead to corrosion product wedging at low ΔK levels, which could retard crack growth.