H. Yatabe et al., FORMATION OF HYDROGEN-ASSISTED INTERGRANULAR CRACKS IN HIGH-STRENGTH STEELS, Fatigue & fracture of engineering materials & structures, 18(3), 1995, pp. 377-384
The fracture behaviour of high strength steels under the influence of
hydrogen was studied, with special emphasis on the critical condition
for the formation of intergranular (IG) cracks. Mechanical tests were
carried out on cathodically charged specimens subjected to both a cons
tant load and a constant displacement under a variety of hydrogen-char
ging conditions. Experimental analyses show that a high local hydrogen
concentration plus a high stress intensity at a quasi-cleavage (QC) c
rack tip are required to initiate intergranular cracking. The conditio
n for continued intergranular crack propagation, leading to micro-void
coalescence (MVC), is determined by the combined effect of the speed
of crack propagation together with the rate of hydrogen diffusion. A q
uasi-cleavage crack triggers the onset of intergranular crack growth i
rrespective of the test control parameters, i.e. constant loading or c
onstant displacement conditions. A fracture map is proposed relating t
o the boundary conditions between QC, IG and MVC cracking, which will
assist further research.