| Abstract |
| This study was conducted to investigate the effect of aging treatment from 300 ℃ to 420 ℃ on the mechanical properties of the pressure tube material at 310 ℃, which is outlet temperature pressure tube in CANDU reactor. The short range ordering (SRO) phenomenon during aging process is confirmed by differential scanning calorimetry (DSC), TEM, and slow strain rate tensile test. As-received and aged pressure tube materials exhibit a sudden stress drop in stress at 50 MPa or less when subjected to tensile strain at a strain rate as low as 1 × 10-6/s at 310 ℃. This is an evidence of destruction of SRO formed in the initial and the aged state. The yield and tensile strengths decreased by 4-11% by aging treatment at 300-420 ℃ for 3,000 hours. Through the DSC analysis, the quadruple-melted pressure tube materials showed an exothermic reaction at around 410 and 590 ℃ in the heating process. This is due to SRO reaction, and the activation energy for the exothermic reaction at around 590 ℃ is obtained as Q = 90 kJ / mole. This reaction seems to be related to the formation of SRO between Zr and O (oxygen) which is dominated by grain boundary diffusion of oxygen in α-Zr. The effects of strain rate and short range ordering (SRO) were discussed in detail.
(Received May 16, 2018; Accepted June 8, 2018) |
|
|
| Key Words |
| Zr-2.5%Nb, differential scanning calorimetry (DSC), short range ordering (SRO), aging, tensile property |
|
|
 |
|
