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Influence of Composition on the Solidification, Microstructure and Mechanical Properties of HP-Nb Austenitic Stainless Steels.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Influence of Composition on the Solidification, Microstructure and Mechanical Properties of HP-Nb Austenitic Stainless Steels./
作者:	Orzolek, Sean Michael.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2021,
面頁冊數:	150 p.
附註:	Source: Dissertations Abstracts International, Volume: 83-01, Section: B.
Contained By:	Dissertations Abstracts International83-01B.
標題:	Materials science. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28316519
ISBN:	9798516063138

Influence of Composition on the Solidification, Microstructure and Mechanical Properties of HP-Nb Austenitic Stainless Steels.
Orzolek, Sean Michael.

Influence of Composition on the Solidification, Microstructure and Mechanical Properties of HP-Nb Austenitic Stainless Steels. - Ann Arbor : ProQuest Dissertations & Theses, 2021 - 150 p.

Source: Dissertations Abstracts International, Volume: 83-01, Section: B.

Thesis (Ph.D.)--Lehigh University, 2021.

This item must not be sold to any third party vendors.

HP-Nb austenitic stainless steels (25Cr-35Ni-Nb) are commonly used in high temperature applications above 850°C. The HP-Nb alloys are used in the as-cast condition and exhibit good creep properties due to chromium and niobium eutectic carbide strengthening. The size, morphology and distribution of these carbides are controlled by the nominal composition and solidification conditions, which give rise to differences in microstructure and mechanical properties. Previous studies have identified that the eutectic carbides form continuous networks along grain boundaries and interdendritic regions, coinciding with insufficient room temperature tensile properties and low ductility. As a consequence, HP-Nb alloys experience cracking during welding and fabrication in the base metal and heat affected zone, associated with the lack of ductility needed to withstand the residual stress from the weld thermocycle. Although previous work has provided qualitative relations between composition, microstructure and properties, quantitative relationships are needed to reliably develop HP-Nb alloys with acceptable properties. Therefore, the objective of this study is to improve the understanding of the solidification of HP-Nb alloys through the development of a quantitative model. A systematic matrix of 12 alloys was characterized via quantitative image analysis, differential thermal analysis, electron microprobe analysis and tensile testing. A quantitative solute redistribution model was developed using solidification equations and a novel, experimentally derived γ-C-Cr-Nb, pseudo quaternary liquidus projection. Linear regression was used to develop empirical equations, quantifying the relationships between the composition, microstructure and mechanical properties of HP-Nb alloys. The quantitative solidification model was validated for three experimental alloys and two industrial alloys, with good agreement between the measured and predicted percent total eutectic. The linear regression models were found to be statistically significant (p<0.05) and exhibited excellent correlation to experimental data. Solidification modeling revealed that the volume percent of chromium carbides are primarily controlled by carbon additions while niobium carbides are primarily controlled by the niobium concentration. Fractographic analysis revealed that fracture of HP-Nb primarily occurs through chromium-rich M7C3 carbides and is impeded by the niobium-rich MC carbides. The regression equations indicate that the minimum ambient temperature tensile properties can be met with a niobium concentration of 1.3 wt.%, independent of chromium and carbon additions and would therefore be resistant to cracking during welding and fabrication. The results of this work show the novel development and application of a pseudo quaternary liquidus projection as well as the quantitative relationships between composition and the tensile properties.

ISBN: 9798516063138Subjects--Topical Terms:

543314
Materials science.
Subjects--Index Terms:

Chromium carbide

Influence of Composition on the Solidification, Microstructure and Mechanical Properties of HP-Nb Austenitic Stainless Steels.
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500 $a Source: Dissertations Abstracts International, Volume: 83-01, Section: B.
500 $a Advisor: DuPont, John N.
502 $a Thesis (Ph.D.)--Lehigh University, 2021.
506 $a This item must not be sold to any third party vendors.
520 $a HP-Nb austenitic stainless steels (25Cr-35Ni-Nb) are commonly used in high temperature applications above 850°C. The HP-Nb alloys are used in the as-cast condition and exhibit good creep properties due to chromium and niobium eutectic carbide strengthening. The size, morphology and distribution of these carbides are controlled by the nominal composition and solidification conditions, which give rise to differences in microstructure and mechanical properties. Previous studies have identified that the eutectic carbides form continuous networks along grain boundaries and interdendritic regions, coinciding with insufficient room temperature tensile properties and low ductility. As a consequence, HP-Nb alloys experience cracking during welding and fabrication in the base metal and heat affected zone, associated with the lack of ductility needed to withstand the residual stress from the weld thermocycle. Although previous work has provided qualitative relations between composition, microstructure and properties, quantitative relationships are needed to reliably develop HP-Nb alloys with acceptable properties. Therefore, the objective of this study is to improve the understanding of the solidification of HP-Nb alloys through the development of a quantitative model. A systematic matrix of 12 alloys was characterized via quantitative image analysis, differential thermal analysis, electron microprobe analysis and tensile testing. A quantitative solute redistribution model was developed using solidification equations and a novel, experimentally derived γ-C-Cr-Nb, pseudo quaternary liquidus projection. Linear regression was used to develop empirical equations, quantifying the relationships between the composition, microstructure and mechanical properties of HP-Nb alloys. The quantitative solidification model was validated for three experimental alloys and two industrial alloys, with good agreement between the measured and predicted percent total eutectic. The linear regression models were found to be statistically significant (p<0.05) and exhibited excellent correlation to experimental data. Solidification modeling revealed that the volume percent of chromium carbides are primarily controlled by carbon additions while niobium carbides are primarily controlled by the niobium concentration. Fractographic analysis revealed that fracture of HP-Nb primarily occurs through chromium-rich M7C3 carbides and is impeded by the niobium-rich MC carbides. The regression equations indicate that the minimum ambient temperature tensile properties can be met with a niobium concentration of 1.3 wt.%, independent of chromium and carbon additions and would therefore be resistant to cracking during welding and fabrication. The results of this work show the novel development and application of a pseudo quaternary liquidus projection as well as the quantitative relationships between composition and the tensile properties.
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653 $a Heat resistant
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653 $a Niobium carbide
653 $a Psuedo-quaternary
653 $a Solidification
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