火SUS304J1HTBの内圧クリープ損傷

抄録

Internal pressure creep tests were conducted on boiler tube of KA-SUS304J1HTB under stress of 60 to 80 MPa at 750°C, and the creep test results were compared with those of uniaxial tensile creep test. Increase in outer diameter of tubular specimens was recognized at about 0.4 of creep life ratio, independent of stress condition, and acceleration creep stage was clearly observed. Creep rupture elongation of 5 to 8% of internal creep test was smaller than those of uniaxial tensile creep test in the range of 17 to 43%. Many cracks were observed on the cross section near the fracture part. Number density of cracks was highest in the area close to outer surface, and it decreased to about half in the area close to inner surface of the tube. Voids and cracks were mainly observed at the interface between sigma phase and γ-matrix. Large misorientation of austenite matrix phase was observed in the vicinity of sigma-phase, and many dislocations were also observed in the same area. It has been concluded that formation of void and crack was enhanced by non-uniform local deformation at the interface between sigma phase and γ-matrix due to difference in deformability of them.