1MPa水素ガスパイプライン用炭素鋼STPG 370 (0.19 C-0.21 Si-0.56 Mn, mass%) の引張特性に及ぼす水素と予ひずみの影響

The effects of hydrogen and pre-strain on tensile properties of JIS-STPG 370 carbon steel pipe for hydrogen pipelines were investigated. In order to pre-charge hydrogen, the specimens were immersed in a 20 mass% aqueous solution of ammonium thiocyanate at 313 K for 48 h. The hydrogen content increased with increasing the pre-strain. The reduction of area of hydrogen-charged specimens decreased with pre-strain. Although pearlite cracks were formed both in the uncharged and hydrogen-charged specimens, the initiation of pearlite cracks occurred at the lower true strain in the hydrogen-charged specimen. Furthermore, the pearlite cracks grew in the direction perpendicular to the loading axis in the hydrogen-charged specimen. The experimental evidences are shown to explain the mechanism of the initiation and growth of pearlite cracks in the hydrogen-charged specimen by the hydrogen enhanced localized plasticity model rather than the lattice decohesion model.