HYDROGEN OCCLUSION BEHAVIOR DURING DELAYE D FRACTURE IN COLD DRAWN STEEL WIRE AND HEAT-TREATED STEEL BAR FOR PRESTRESSED CONCRETE

Stress-relieved steel wire for prestressed concrete (PC Wire), which i s produced with cold drawing, has a higher resistance to delayed fract ure than steel bar for prestressed concrete (PC Bar), which is produce d with heat treatment. However, the hydrogen occlusion behavior of PC Wire has not been investigated yet. To clarify this behavior, fracture surfaces were examined, the hydrogen occlusion content was measured b y using hydrogen thermal analysis, and hydrogen trapping sites were ob served by using secondary ion mass spectrometry. It is found that PC W ire occludes hydrogen released at 470 K which affects delayed fracture and at 620 K which does not affect delayed fracture. This shows that PC Wire decreases the ratio of hydrogen content at 470 K which affects delayed fracture. PC Wire has a higher critical hydrogen content at w hich delayed fracture occurs than PC Bar. Since PC Wire traps hydrogen along the direction of cold drawing, it does not create linear crack at delayed fracture. The hydrogen behavior of PC Wire thus increases t he resistance of PC Wire to delayed fracture.