Delayed cracking of low-nickel austenitic stainless steel studied with constant load tensile testing

Delayed cracking in unstable low-Ni austenitic stainless steel 204Cu was studied by constant load tensile testing. The developed testing arrangement enabled a systematical examination on the effect of applied stress, strain-induced alpha'-martensite and internal hydrogen content on time to fracture. Volume fraction of strain-induced alpha'-martensite was shown to affect cracking kinetics, except at a very high stress level. Hydrogen content had a marked effect on time to fracture, also at the highest applied stress level. When hydrogen content was reduced by annealing, delayed cracking kinetics and susceptibility were suppressed, and cracking required a considerably higher stress level. The apparent critical hydrogen content, below which delayed cracking was not observed, was about 0.85 wppm. According to scanning electron microscope and electron backscattering diffraction examination, fracture mechanism in the constant load test specimens was mainly transgranular quasi-cleavage, and cracking propagated along alpha'-martensite.