극초임계압 화력발전소용 마르텐사이트계 10Cr 내열강 열영향부의 용접후열처리 균열 감수성

In this study, the post-weld heat treatment (PWHT) cracking susceptibility in the heat affected zone (HAZ) of martensitic 10Cr steel was evaluated. The specimens taken from the 10Cr steel were thermally cycled using a Gleeble to simulate HAZ 1 (δ-ferrite) and HAZ 2 (single phase, γ). HAZ 2 had martensite and some M23C6-type carbides were present. On the other hand, HAZ 1 had martensite and the carbides were completely dissolved. In addition, δ-ferrite is observed in HAZ 1. The simulated HAZ specimens were stress rupture tested at a temperature range of 688-788 ℃ under stress of 150-450 MPa (21, 750-65, 250 psi). After the stress rupture test, a stress rupture parameter (SRP) was obtained using the rupture strength and ductility. In this way, the PWHT cracking susceptibility was evaluated through the SRP. Both HAZ 1 and HAZ 2 tended to increase rupture strength with decreasing PWHT temperature, but with a decrease in ductility. Also, it was noteworthy that the HAZ 1 had a lower PWHT cracking susceptibility than the HAZ 2 due to its higher rupture strength, despite its lower ductility. Because the precipitation strengthening occurs due to reprecipitation of MC-type carbide during PWHT. (Received May 3, 2019; Accepted May 28, 2019)