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Abstract

In this study, ODS ferritic stainless steels were fabricated using a commercial alloy powder, and their microstructures and mechanical properties were studied to develop the advanced structural materials for high temperature service applications. Mechanical alloying and uniaxial hot pressing processes were employed to produce the ODS ferritic stainless steels. It was revealed that oxide particles in the ODS stainless steels were composed of Y-Si-O, Y-Ti-Si-O, and Y-Hf-Si-O complex oxides were observed depending on minor alloying elements, Ti and Hf. The ODS ferritic stainless steel with a Hf addition presented ultra-fine grains with uniform distributions of fine complex oxide particles which located in grains and on the grain boundaries. These favorable microstructures led to superior tensile properties than commercial stainless steel and ODS ferritic steel with Ti addition at elevated temperature.

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Authors and Affiliations

Sanghoon Noh
Suk Hoon Kang
Tae Kyu Kim
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Abstract

Thermal/cold spray deposition were used for additive manufacture of oxide dispersion strengthened (ODS) steel layers. Mechanically alloyed F/M ODS steel powders (Fe(bal.)-10Cr-1Mo-0.25Ti-0.35Y2O3 in wt.%) were sprayed by a high velocity oxygen fuel (HVOF) and cold spray methods. HVOF, as a thermal method, was used for manufacturing a 1 mm-thick ODS steel layer with a ~95% density. The source to objective distance (SOD) and feeding rate were controlled to achieve sound manufacturing. Y2Ti2O7 nano-particles were preserved in the HVOF sprayed layer; however, unexpected Cr2O3 phases were frequently observed at the boundary area of the powders. A cold spray was used for manufacturing the Cr2O3-free layer and showed great feasibility. The density and yield of the cold spray were roughly 80% and 45%, respectively. The softening of ODS powders before the cold spray was conducted using a tube furnace of up to 1200°C. Microstructural characteristics of the cold sprayed layer were investigated by electron back-scattered diffraction (EBSD), the uniformity of deformation amount inside powders was observed.

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Authors and Affiliations

Suk Hoon Kang
Chang-Kyu Rhee
Sanghoon Noh
Tae Kyu Kim
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Abstract

Ferrtic/martensitic and ODS steels were fabricated by the mechanical alloying process, and their microstructures and mechanical properties were investigated. The 9Cr-1W and 9Cr-1W-0.3Ti-0.35Y2O3 (in wt.%) steels were prepared by the same fabrication process such as mechanical alloying, hot isostatic pressing, and hot rolling processes. A microstructural observation of these steels indicated that the Ti and Y2O3 additions to 9Cr-1W steel were significantly effective to refine the grain size and form nano-sized Y-Ti-O oxide particles. As a result, the tensile strengths at room and elevated temperatures were considerably enhanced. Considerable improvement of the creep resistances at 700°C was also evaluated. It is thus concluded that 9Cr-1W ODS steel with Ti and Y2O3 additions would be very effective in improving the mechanical properties especially at elevated temperatures.

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Authors and Affiliations

Ga Eon Kim
Tae Kyu Kim
Sanghoon Noh
ORCID: ORCID
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Abstract

In this study, to investigate effects of rhenium addition on the microstructures and mechanical properties, 15Cr-1Mo ODS ferritic steels with rhenium additions were fabricated by the mechanical alloying, hot isostatic pressing, and hot rolling processes. Unremarkable differences on grain morphologies and nano-oxide distributions were estimated in the microstructure observations. However, the ODS ferritic steels with 0.5 wt.% rhenium showed higher tensile and creep strengths at elevated temperature than that without rhenium. It was found that rhenium is very effective to improve the mechanical properties.

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Authors and Affiliations

Sanghoon Noh
ORCID: ORCID
Suk Hoon Kang
Tae Kyu Kim

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