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This article has investigated a 60 mm Ca‐treated Q550 steel used for high‐heat input welding. The results have shown that the Ca‐type inclusions account for 70% of the inclusions in the steel which are mainly CaAlMg type, Ca–Al type, and a small amount of CaS type while the non‐Ca‐type inclusions are mainly FeCO. After undergoing the welding thermal cycle, the number of Ca‐containing inclusions above 2 μm in size is decreased while the number of non‐Ca‐containing inclusions below 1 μm (mainly FeO) is increased significantly. However, the total area of inclusions is decreased. It has been found out that the CaAlSO‐type inclusions undergo "diffusion" of O element to the surroundings during the thermal cycle, forming a ring‐shaped oxygen‐rich zone and carbon‐rich zone which promotes the nucleation of acicular ferrite. In contrast, the CaAlMgSO‐type inclusions undergo "decomposition" during the thermal cycle which forms a group of inclusions with different sizes and types, promoting nucleation of multioriented acicular ferrite. [ABSTRACT FROM AUTHOR]

AH36 marine steel processed through high heat‐input welding is subjected to microstructural characterization, hydrogen permeation test, internal friction test, and slow strain rate tensile test to reveal its hydrogen diffusion and hydrogen embrittlement failure behaviors. Compared with the base metal, the coarse‐grained heat‐affected zone (CGHAZ) exhibits a significantly coarsened microstructure and decreased hydrogen trap density, resulting in a high hydrogen diffusion coefficient and short hydrogen permeation time. The presence of hydrogen yields a hydrogen‐induced Snoek internal friction peak and promotes the movement of the Snoek–Kê–Köster internal friction peak to the low‐temperature region. In addition, B and Kê peaks, which are not found in the base metal, appear in the CGHAZ. With increasing hydrogen content, the plastic loss and brittle fracture of the AH36 marine steel become increasingly significant, and the hydrogen embrittlement sensitivity of the heat‐affected zone increases compared with that of the base metal. The discontinuous yield phenomenon gradually disappears under slow strain rate tension owing to the weak pinning effect of the Cottrell atmosphere on mobile dislocations. [ABSTRACT FROM AUTHOR]

Herein, the microstructure evolutions and mechanical properties of lean duplex stainless steel 2101 (LDX2101) are evaluated at different temperatures and a strain rate of 1 s−1. The experimental results show that the ratio of ferrite to austenite (α/γ) is increased between 950 and 1250 °C in total, but a turning temperature range occurs at 1000–1050 °C due to dissolution of the Cr2N precipitates along the phase boundaries. In LDX2101, high number density of Cr2N precipitates exist below 1000 °C and above 1100 °C, respectively. The morphologies of Cr2N precipitates change from massive to acicular with increasing temperatures. In addition, the excess strain is concentrated in α, and therefore strain is difficult to transfer to the adjacent γ. The aforementioned factors may lead to greater stress concentration along the phase boundaries (α/γ) and grain boundaries or grains (α), which causes edge cracking and surface cracking. With increase in deformation temperatures, the reduction of area increases and tensile strength decreases, but a turning temperature range occurs at 1000–1050 °C. The optimum hot deformation zone is in the temperature range of 1000–1100 °C by considering the precipitation temperature range of Cr2N precipitates. The formation mechanisms of Cr2N precipitates at different annealing temperatures are investigated. [ABSTRACT FROM AUTHOR]