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In the present study, the welding thermal cycle of magnesium-treated EH36 steel was simulated by a thermal simulation experiment machine. The effects of welding heat input on the microstructure and low temperature toughness of the welded joint were studied, and the mechanism of acicular ferrite nucleation induced by MgAl 2 O 4 inclusion was revealed. The results showed that, when the welding heat input of 150 kJ/cm, 250 kJ/cm and 350 kJ/cm was utilized, the microstructure of heat affected zone in the experimental EH36 steel consisted of grain boundary ferrite, acicular ferrite, granular bainite, and a small amount of pearlite, but the volume fraction and grain size of each independent microstructure were different. With the increase of welding heat input, the content of acicular ferrite and granular bainite decreased, the content of grain boundary ferrite increased, and the average grain size increased, whereas the low temperature toughness of the experimental EH36 steel welded joint reduced from 174 to 67 J. Furthermore, MgAl 2 O 4 inclusions can induce acicular ferrite nucleation, whereas the nucleation mechanism is a combination of low lattice mismatch and low interfacial energy. [ABSTRACT FROM AUTHOR]

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]

Herein, the effects of quenching, lamellarizing, and tempering (QLT) on reversed austenite and cryogenic toughness of 9Ni steels were investigated in terms of microstructure characterization, internal friction tests, and low temperature impact tests. The results showed that QLT treatment not only refined the grain effectively, but also promoted the formation of reversed austenite, thus obtaining excellent ultra-cryogenic toughness. Furthermore, QLT treatment promoted the redistribution of C, Mn, and Ni elements, so that more stable austenite was retained to room temperature. The phase transformation peak in the internal friction peak confirmed that QLT treatment effectively promoted the formation of reversed austenite, while the Snoek–Kê–Köster peak showed a strong interaction between carbon atoms and dislocations. Due to the synergistic effect of fine grain toughening and TRIP effect, the 9Ni steel treated by QLT appeared more excellent ultra-cryogenic toughness.Please check and confirm the corresponding author mail id is correctly identified.The corresponding author mail id is correct. [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]

The hot deformation behavior and dynamic recrystallization (DRX) of Fe-15Mn-15Al-5Ni-1C low-density steel in the as-cast state was investigated via hot compression experiments over temperature and strain rate ranges of 925 to 1150 °C and 0.01 to 10 s−1, respectively. A constitutive equation and a critical DRX model of the Fe-15Mn-15Al-5Ni-1C low-density steel were also constructed. The results showed that higher strain rates resulted in significant work hardening and subsequent rapid softening of the Fe-15Mn-15Al-5Ni-1C low-density steel, while lower strain rates resulted in predominantly steady-state flow behavior. The activation energy of deformation for the Fe-15Mn-15Al-5Ni-1C low-density steel was Q = 540 kJ mol−1 and the stress index was n = 4. The hot deformation mechanism was solute dragging and dislocation climbing, which was controlled by the strain rate. Increasing the deformation temperature or strain rate reduced the critical stress value σc of the DRX of the Fe-15Mn-15Al-5Ni-1C low-density steel and contributed to the DRX of austenite and δ-ferrite. The Fe-15Mn-15Al-5Ni-1C low-density steel after the hot compression deformation was mainly composed of austenite, ferrite, and κ carbide phases. [ABSTRACT FROM AUTHOR]

Abstract Oxide-dispersion strengthened (ODS) ferritic steels containing a high density of nanoscale oxides are good candidates for structural applications in future fusion power reactors. In this research, to study the effects of zirconium (Zr) addition on the thermal stability of the microstructure and tensile properties of ODS steels, two kinds of 15Cr-ODS ferritic steels with nominal compositions (wt.%) of Fe-15Cr-2W- 0.3Y 2 O 3 and Fe-15Cr-2W-0.3Zr-0.3Y 2 O 3 were produced by the mechanical alloying (MA) of premixed powders and then consolidated by hot isostatic pressing (HIP) techniques. Elevated-temperature annealing in the range of 1150 °C–1350 °C on the coarsening kinetics of nanoscale oxides and microstructural evolution with and without Zr were systematically investigated by means of transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) techniques. Results showed that Zr addition could improve the coarsening resistance of the nanoscale oxides and grains during annealing treatment due to the formation of stable nm-scale trigonal-phase Y 4 Zr 3 O 12 oxides. Tensile tests on the annealed-ODS steels showed that the ultimate tensile strength and yield strength of 15Cr-Zr-ODS steel were higher than those of 15Cr-ODS steel. It was considered that the excellent thermal stability and tensile properties of 15Cr-Zr-ODS steel were related with the refined microstructure. [ABSTRACT FROM AUTHOR]