Effective design of new austenitic cast steels for ultra-high temperature automotive exhaust components through combined CALPHAD and experimental approaches

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• 作者：Y.H. Zhang^a ; M. Li^b ; L.A. Godlewski^b ; J.W. Zindel^b ; Q. Feng^a ; ^c ; ^{qfeng@skl.ustb.edu.cn}
• 关键词：Austenitic cast steel ; CALPHAD ; Carbonitride ; Ferrite ; Tensile property
• 刊名：Materials Science and Engineering: A
• 出版年：2017
• 出版时间：23 January 2017
• 年：2017
• 卷：683
• 期：Complete
• 页码：195-206
• 全文大小：2102 K
• 卷排序：683

文摘

Designing engines with higher power densities to comply with ever increasing emissions and fuel economy regulations requires the development of cost-effective alloys with superior properties than existing high-performance alloys. A new class of Nb-bearing austenitic heat-resistant cast steels showed promise to withstand exhaust gas temperatures of as high as 1000 °C. This paper describes the development of this new class of alloys using combined CALPHAD (CALculation of PHAse Diagrams) and experimental approaches to investigate the effect of C and N additions on the microstructure and tensile properties. Composition ranges were first established based on CALPHAD predictions to achieve the desired phases, and then four alloys of varying N/C ratios were cast and experimentally characterized to determine quantitatively the microstructure and mechanical properties. Microstructural characterization revealed that the NbC/Nb(C,N) phase transformed from “Chinese-script”, a mixed flake-blocky morphology to faceted-blocky morphology as the N/C ratio increased. The area fractions of the different phases were quantified and agreed favorably with the calculated results. Alloys with the “Chinese-script” NbC/Nb(C,N) showed favorable tensile properties at room temperature and 1000 °C. Excessive δ-ferrite diminished the tensile resistance at 1000 °C, while limited quantity of (Cr, Fe)23C6 did not show adverse effects.