MICROSTRUCTURAL CHANGE OF LOW CARBON AND LOW-ALLOY STEELS CAUSED BY HYDROGEN-INDUCED FATIGUE-CRACK GROWTH

摘要

The effect of external high-pressure H_2 gas on fatigue-crack growth behavior has been examined using low carbon ferritic-pearlitic and low-alloy tempered lath martensitic steels. The presence of hydrogen accelerates the crack-growth rate by ≈13-18 times compared to the uncharged state and shifts the fracture surface morphology from ductile striations to a mixture of "flat" and "quasi-cleavage" features for both steels. The common feature found in the microstructure immediately beneath the hydrogen-induced fracture surfaces is enhanced plasticity in terms of refined dislocation cell structures and refined sub-grains.