Evaluation method of sensitivity of hydrogen embrittlement for high strength bolts

In this study, high strength bolts of 1100 MPa and 1300 MPa grades were charged with hydrogen to measure the sensitivity of hydrogen embrittlement (HE). Different levels of stress conditions based on various tensile stress and strain rates were applied. The bolts were then examined to see whether cracks were formed on the screw threads. The tensile stress and strain rate condition producing the most number of cracks on the screw thread of the bolt was decided as the most suitable test condition for the measurement of sensitivity of HE. For 1100 MPa grade high strength bolts, the most cracks were observed at the tensile stress ratio of 0.85 (load of 80 kN) and strain rate of 1.6×10E−5/s, while for 1300 MPa grades, the most cracks were observed at tensile stress ratio 0.87 (load of 100 kN) and strain rate of 1.6×10E−5/s. No cracks were found on the screw threads of bolt when the strain rate was increased over 8.3×10E−4/s.