Abstract
A ring which was part of high-pressure equipment, made from medium carbon 4.5% Cr tool steel with a tensile strength of 2100 MPa was fractured after short-term operation in water. The equipment was used for synthesizing a hard substance, and the ring was anodically polarized at 3 V during the operation. The anodic polarization of the failed ring was attributed to the 6 V DC current applied to the equipment for supplying reaction heat. The surface of the failed ring in water became the anode of the 3 V cell. Delayed fracture tests in water were conducted using bent-beam specimens without notches to investigate the effects of anodic polarization on fracture susceptibility. We confirmed that the fracture time under 3 V was shorter than that at natural potential, showing good agreement with the actual fracture time of the ring. Therefore, we recommended that the surface of the ring be protected from water with a plastic film to prevent the occurence of delayed fracture due to anodic polarization.
