Kd. Chang et al., Effects of heat-treatment process of a novel bainite/martensite dual-phasehigh strength steel on its susceptibility to hydrogen embrittlement, ISIJ INT, 41(11), 2001, pp. 1397-1401
The susceptibility to hydrogen embrittlement of a bainite/martensite dual-p
hase high strength steel with different morphologies obtained by the conven
tional or thermomechanical heat-treatment has been investigated by means of
electrolytic hydrogen charging in this paper. The results show that the fi
ner the microstructure, the lower the sensitivity of steel to hydrogen embr
ittlement is. The fractographic analysis suggests that the fracture mode of
the hydrogen-charged specimens is a mixture of quasicleavage and dimple fo
r both treating processes. The quasicleavage facet of the thermomechanical
treated specimens is smaller than that of the conventional heated ones. The
observation of the fracture profile specimen shows that the crack propagat
es preferentially along bainite/martensite laths boundary, suggesting that
the fracture mode is predominantly lath boundary separation. In addition, t
he fractographic analysis indicates that the rhombic Ti(N,C) inclusion is t
he predominant type of inclusions on the fracture surface of the hydrogen-c
harged specimens of thermomechanical heat-treatment. The separation between
Ti(N,C) inclusions and matrixes is a brittle fracture with small facets, w
hich indicates that inclusions such as Ti(N,Q are harmful to hydrogen embri
ttlement.