The influence of crack length on SCC crack growth behavior of high-strength steel under dynamic loading conditions.

Abstract

The influences of crack length on stress corrosion cracking (SCC) crack growth of a 523K tempered high·strength steel, SCM435H (ΔB=1 770 MPa) immersed in 3.5 % NaCl solution were investigated under dynamic loading conditions : static SCC under a sustained load, dynamic SCC under a sustained load with high frequency vibratory stresses superimposed, and cyclic SCC under 10w frequency variation. Threshold values of static and dynamic SCC of short crack, whose crack length from notch root, l, ranged from 1.52 mm to 2.81 mm, were smaller than those of long crack (l= 6.86-9.78 mm). Dissolution of fracture surface was more prevalent in short crack than in long crack, and a decrease in threshold values of short crack is considered to be caused by increased hydrogen uptake at the crack tip associated with accelerated dissolution of fracture surfaces compared to long crack. Crack growth rates of short crack (1l6.5 mm) at the plateau region were also accelerated compared to those of long crack (l>6.5 mm). Static SCC crack growth rates of long crack were accelerated and the threshold value was lowered by deaeration of the solution. However, the deaeration had no influence on crack growth rates of static SCC of short crack. In the case of cyclic SCC at R=0.1, no influence of crack length (1>1.18 mm) on crack growth rates was observed. But at R =0.5, crack growth rates of short crack were accelerated compared to those of long crack.