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Abstract: An optimized thermomechanical treatment (TMT) applied to austenitic alloy 800H (Fe–21Cr–32Ni) had shown significant improvements in corrosion resistance and basic mechanical properties. This study examined its effect on radiation resistance by irradiating both the solution-annealed (SA) and TMT samples at 500°C for 3dpa. Microstructural characterization using transmission electron microscopy revealed that the radiation-induced Frank loops, voids, and γ′-Ni3(Ti,Al) precipitates had similar sizes between the SA and TMT samples. The amounts of radiation-induced defects and more significantly γ′ precipitates, however, were reduced in the TMT samples. These reductions would approximately reduce by 40.9% the radiation hardening compared to the SA samples. This study indicates that optimized-TMT is an economical approach for effective overall property improvements. [Copyright &y& Elsevier]

Abstract: Ferritic–martensitic (F–M) steels with 9wt.%Cr are important structural materials for use in advanced nuclear reactors. Alloying composition adjustment, guided by computational thermodynamics, and thermomechanical treatment (TMT) were employed to develop high strength 9Cr F–M steels. Samples of four heats with controlled compositions were subjected to normalization and tempering (N&T) and TMT, respectively. Their mechanical properties were assessed by Vickers hardness and tensile testing. Ta-alloying showed significant strengthening effect. The TMT samples showed strength superior to the N&T samples with similar ductility. All the samples showed greater strength than NF616, which was either comparable to or greater than the literature data of the PM2000 oxide-dispersion-strengthened (ODS) steel at temperatures up to 650°C without noticeable reduction in ductility. A variety of microstructural analyses together with computational thermodynamics provided rational interpretations on the strength enhancement. Creep tests are being initiated because the increased yield strength of the TMT samples is not able to deduce their long-term creep behavior. [Copyright &y& Elsevier]

Abstract: RAFM steels are one of the candidate structural materials for fusion reactors, in which tantalum (Ta) and tungsten (W) are alloyed to replace niobium (Nb) and molybdenum (Mo) in conventional FM steels, respectively. This paper, using three RAFM heats, presents the effects of Ta and the primary austenite stabilizer carbon (C) on microstructure and strength. Thermomechanical treatment (TMT) was also applied to the heats, leading to significant increases in strength, attributable to the TMT-refined sub-grains and precipitates. The Ta-alloying favored the formation of (V,Ta)(N,C) and (Ta,V)C and exhibited greater strength. Fractographs also revealed the beneficial effects of TMT and Ta-alloying. However, extra C content, favoring a larger amount of M23C6 precipitates, did not show strengthening effect. [Copyright &y& Elsevier]

Abstract: The microstructural evolution, specifically of grain boundaries, precipitates, and dislocations in thermomechanically processed (TMP) Alloy 800H samples was characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), electron backscattered diffraction (EBSD), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The TMP not only significantly increased the fraction of low-Σ coincidence site lattice boundaries, but also introduced nanoscale precipitates in the matrix and altered the distribution of dislocations. Statistical analysis indicates that the morphology and distribution of grain boundary precipitates were dependent on grain boundary types. The microstructure optimization played a synergistic effect on the significantly increased strength with comparable ductility and enhanced intergranular corrosion resistance and creep-fatigue life compared to the as-received samples. [Copyright &y& Elsevier]

As a candidate material for advanced nuclear reactors, a ferritic-martensitic (FM) steel Grade 92 in the standard normalized and tempered (NT) condition was subjected to two types of thermomechanical treatments (TMTs) with one having a lower level of deformation (T5A) and the other having a higher level of deformation (T5B). The testing results of the three conditions indicated that the TMTs significantly improved yield strength, creep resistance, fracture toughness, and sodium corrosion resistance compared with the NT condition. T5A excelled at creep resistance while T5B at sodium corrosion resistance. Microstructural characterization of the three conditions supports the varied enhancements in the properties. This study suggests that an appropriate TMT can be developed and applied to FM steels to better meet specific application requirements. [ABSTRACT FROM AUTHOR]

As a candidate material for advanced nuclear reactors, a ferritic-martensitic (FM) steel Grade 92 in the standard normalized and tempered (NT) condition was subjected to two types of thermomechanical treatments (TMTs) with one having a lower level of deformation (T5A) and the other having a higher level of deformation (T5B). The testing results of the three conditions indicated that the TMTs significantly improved yield strength, creep resistance, fracture toughness, and sodium corrosion resistance compared with the NT condition. T5A excelled at creep resistance while T5B at sodium corrosion resistance. Microstructural characterization of the three conditions supports the varied enhancements in the properties. This study suggests that an appropriate TMT can be developed and applied to FM steels to better meet specific application requirements. [ABSTRACT FROM AUTHOR]