To evaluate delayed fracture properties of martensitic bolt steels containing Cr, Mo, and V, the relationship between critical content for delayed fracture [Hc] and environmentally absorbed content [H_E] in diffusible hydrogen have been investigated. The critical value [Hc] and the environmental value [H_E] were determined by accelerated delayed fracture tests under constant applied load using specimens with uniformly distributed hydrogen and by cyclic corrosion tests in 5% NaCl aqueous solution as an environmental condition, respectively. The diffusible hydrogen was detected by hydrogen thermal desorption analysis after respective tests.
On the other hand, the delayed fracture resistance was defined as fracture ratio [F] of bolts exposed in the seaside testing site.
Based on the result that ( [H_C] [H_E])/[H_C] increases monotonically with a decrease in fracture ratio [F], it is proposed that the parameter ([H_C]/[H_E] )/[H_C] would be a quantitative indication showing delayed fracture susceptibility of high strength steels in service environment.