ICF100866OR/Yoru Wada Fracture toughness characterization of hydrogen embrittled Cr-Mo steel Yoru WADA and Yasuhiko TANAKA1) 1)Muroran Research laboratory, The Japan steel Works,ltd 4-Chatsu machi Muroran city, Hokkaido, 051-8505 JAPAN ABSTRACT Since pressure vessels for petroleum use are operated at high temperature high pressure hydrogen gas, it is a special concern whether a crack at a stressed region grow by internal hydrogen embrittement (I.H.E.) mechanism during shutdown low to temperature ambience. In this study, fracture mechanics tests were conducted to clarify how hydrogen assisted crack of 2.25Cr-1Mo steels grows under I.H.E. condition. Hydrogen was pre-charged inside of the steel by high pressure, high temperature hydrogen autoclave and tests were conducted at room temperature air ambience. As a result, for the majority of steels tested, the stress intensity factor at hydrogen crack growths by I.H.E. mechanism were very low at initiation (=KIH∼30MPa·m1/2)) and grows faster if an active, rising load was applied. The old 60's made generation steel, which has higher temper embrittlment susceptibility, exhibited a higher crack velocity and resulted in fast fracture (KIC-H) during rising loading. On the contrary, if a load was applied for a static, fixed crack mouth displacement manner (i.e. falling load condition), the crack velocity significantly decreased and finally stopped to give a higher threshold stress intensity factor (=Kth) except for higher strength steel. Higher strength steel (; Enhanced 2.25Cr-1Mo grade material) tended to continue to propagate despite under fixed displacement condition and falls on to a very low Kth. KEYWORDS I.H.E., Hydrogen charging, 2.25Cr-1Mo steel,KIH, KIC-H, Kth INTRODUCTION In the pressure vessel with overlay or attachment of stainless steel inside of the wall, a high stress may be arised at discontinuous and complex structure area due to thermal expansion mismatch between stainless steel
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