抄録
The high pressure reactors are sometimes autofrettaged to have the life elongated which is based on the highly compressive residual stress near the bore surface. In this study, to evaluate the material degradation based on the autofrettaged strain, the effect of autofrettage on the fracture toughness behavior was investigated using the 3.5% Ni-Cr-Mo-V steels.
(1) When the prestrain increases, the fracture toughness decreases, especially in the higher yield strength steel. The decrease of the fracture toughness of the material was observed in the prestrain range larger than 5 percent for the about 1000MPa yield strength steel and than 2 percent for the about 1150 MPa yield strength steel.
(2) The material resistance to ductile fracture, that is, tearing modulus TJ decreases in the same prestrain ranges as those of the fracture toughness.
(3) However, the autofrettaged material taken out of the actual pressure reactor shows no decrease of the fracture toughness and the tearing modulus which is caused by the small amount of the prestrain, less than about 1 percent even in the 100 percent autofrettaged reactors.
