Analysis of cavity evolution in 9%Cr heat-resistant steel welded joint during creep

Abstract

This paper reports the cavity damage in one 9%Cr steel (T92) welded joints during creep. The creep test was conducted at 973 K with applied stress of 90 MPa. The welded specimen ultimately fractured at the fine-grained heat affected zones (FGHAZ) after creep 1560 h. The metallographic results show that within 40% creep life fraction, the quantities of creep cavity in FGHAZ are relatively few. Beyond this range, the cavity number density, cavity area fraction and average cavity area of the FGHAZ progressively increase with the creep time, while the cavity spacing gradually decreases. The coalescence of creep cavities happened at the late stage of the creep life, resulting in the formation of micro-crack. The adjacent cavities linking with a central cavity to form a micro-/macro-crack as different from adjacent cavities growing into each other. The cavity number density can be correlated with the creep life of the T92 welds by using the fitting damage model, while the conventional A-parameter measurement is not suitable for assessing the creep life in the present case.