Effects of Cr Reduction on High-Temperature Strength of High-Ni Austenitic Cast Steels Used for High-Performance Turbo-chargers

Since greater high-temperature strength is required for maintaining high-performance turbo-chargers at higher exhaust gas temperatures, e.g ., 1323 K (1050 °C), high-Ni (20 wt pct) austenitic steel (ASTM HK40 steel) is presented as an excellent turbo-charger candidate material. To enhance the streng...

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Published in:Metallurgical and materials transactions. A, Physical metallurgy and materials science Physical metallurgy and materials science, 2018-10, Vol.49 (10), p.4604-4614
Main Authors: Yoo, Jisung, Choi, Won-Mi, Sohn, Seok Su, Lee, Byeong-Joo, Kim, Gi-Yong, Oh, Yong-Jun, Lee, Sunghak
Format: Article
Language:English
Subjects:
Alloying elements
Austenitic stainless steels
Carbides
Characterization and Evaluation of Materials
Chemistry and Materials Science
Chromium
Exhaust gases
Heat resistant steels
High temperature
Materials Science
Materials selection
Mechanical properties
Metallic Materials
Nanotechnology
Room temperature
Steel
Structural Materials
Surfaces and Interfaces
Thin Films
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Summary:Since greater high-temperature strength is required for maintaining high-performance turbo-chargers at higher exhaust gas temperatures, e.g ., 1323 K (1050 °C), high-Ni (20 wt pct) austenitic steel (ASTM HK40 steel) is presented as an excellent turbo-charger candidate material. To enhance the strength, three types of austenitic cast steel were fabricated in this study by controlling the Cr content in HK40 steel, and high-temperature strength improvement was achieved by detailed microstructural evolution including carbide formation and matrix strengthening. Room temperature and high-temperature strengths were expected to be proportional to the carbide volume fraction, but revealed an opposite trend because the steel containing more Cr (having more carbides) revealed lower strength than the steel containing less Cr (having fewer carbides). This result was associated mainly with the M 7 C 3 to M 23 C 6 decomposition occurring at high temperatures in the less-Cr-steel that beneficially strengthened the austenite matrix and reduced the hardness difference between the carbide and matrix, consequently improving the high-temperature strength. In considering the alloying prices (14 pct cost saving of alloying elements) as well as the high-temperature strength, the steel containing less Cr is promising for new high-performance turbo-charger applications.
ISSN:1073-5623
1543-1940
DOI:10.1007/s11661-018-4783-0