Detection of Hydrogen Evolution during Tensile Deformation and Fracture in Carbon Steel

Abstract

Hydrogen evolution behavior during tensile deformation and fracture in hydrogen-charged and uncharged carbon steels was investigated using a hydrogen microprint technique (HMT). A tensile testing machine equipped with a mass spectrometer placed in an ultrahigh vacuum (UHV) chamber was used to detect hydrogen evolution during the tensile test. In the uncharged specimens, the HMT revealed that silver particles, which represented the emission sites of hydrogen, were clearly observed when the applied strain increased. The accumulation of the silver particles along the slip lines was observed at the surface of the highly deformed specimens adjacent to the fracture zone. This indicated that hydrogen atoms primarily dissolved in the specimen were transported by mobile dislocations. In the hydrogen-charged specimen, a large number of silver particles were distributed almost uniformly in the matrix even in the undeformed state; however, the preferential distribution of the silver particles on the slip lines was not clearly identified, probably due to the low fracture strain, which resulted from the hydrogen embrittlement. In all the specimens, HMT showed that silver particles were not visible directly on the Al₂O₃ inclusions after the deformation. Mass spectrometry analysis in the UHV tensile test revealed that evolution of hydrogen gas increased significantly when the specimens were strained to a level that corresponded to maximum stress.