Abstract
Studies are made on stress relief embrittlement of duplicated weld HAZ for 50 kgf/mm2 HTS. Degree of stress relief embrittlement expressed by Δ∇Ts is a function of weld thermal cycle cooling rate, and results showed that the highest notch toughness of stress-relieved weld HAZ was achieved in microstructure containing slight polygonal ferrite. That sort of microstructure can be obtained with thermal cycles cooling time of around 30 seconds from 800°C to 500°C for steels investigated, which shows the effectiveness for obtaining the safety of welded joints and the efficiency of welding fabrication by using comparatively high heat input of around Cf cooling time in SH-CCT diagram.
Furthermore, grain boundary fracture was little found for both as duplicated and duplicated and stress-relieved HAZ, showing the significance of niobium and vanadium nitride and carbide coherent precipitation for stress relief embrittlement in weld HAZ, as it occurs transgranular cleavage fracture easily.
