Short-crack growth in corrosion fatigue for a high strength steel

Abstract

Fatigue crack growth tests of HY130 steel were conducted under either constant-load-range or constant-stress-intensity-range conditions, by using four-point-bend and compact-tension specimens with a crack of length 0.4–41 mm. The tests were conducted in 3.5% NaCl solution under either the freely corroding condition or with the specimen coupled to a sacrificial zinc anode.Crack growth rates for the zinc-coupled case were higher than those for the freely corroding case, for either the long crack or short crack specimen. The growth rates of short cracks were faster than those of long cracks for the same environment. The maximum amount of crack growth acceleration due to crack size effect was about a factor of two for these alloy-environment combinations. With increasing crack length, the rate for short cracks converges to that for long cracks. Since there was no crack-size effect in air, the additional enhancement in the rate of crack growth for short cracks must be chemical in nature.The upper limit of chemically short cracks (as delineated by the point of convergence of rates) was shorter for the freely corroding case than for the zinc-coupled case, and was longer for the higher stress intensity range, for both the constant-load-range and the constant-stress-intensity-range tests. The observed effect of crack size on crack growth rates is discussed in terms of the hydrogen embrittlement mechanisms.