VHCF, Tribology Characteristics and UNSM Effects of Bainite and Martensite Spring Steels

It has been reported that the duplex bainite microstructure obtained by austempering (AT) shows higher strength, ductility and impact toughness than quench and tempered (QT) martensite structure in SAE9254 spring steel. However, there seems to be no research on the very high cycle fatigue (VHCF) and...

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Bibliographic Details
Published inMetals (Basel ) Vol. 12; no. 6; p. 901
Main Authors Suh, Min Soo, Nahm, Seung Hoon, Suh, Chang Min, Pyun, Young Sik
Format Journal Article
LanguageEnglish
Published Basel MDPI AG 01.06.2022
Subjects
Austempering
Bainite
Crack propagation
Durability
Electron backscatter diffraction
Engineering
Fatigue cracks
Fatigue limit
Fracture mechanics
Heat treating
High cycle fatigue
Impact strength
Inclusions
Industrial applications
Martensite
Mechanical properties
Metal fatigue
Microstructure
Nanocrystals
Quantitative analysis
Research methodology
spring steel
Spring steels
Steel
Stress concentration
Tensile strength
Tribology
very high cycle fatigue
Weight reduction
Japan
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Summary:It has been reported that the duplex bainite microstructure obtained by austempering (AT) shows higher strength, ductility and impact toughness than quench and tempered (QT) martensite structure in SAE9254 spring steel. However, there seems to be no research on the very high cycle fatigue (VHCF) and tribology characteristics of bainite structure for durability design of next generation spring steel from the perspective of engineering and industrial applications. This is a follow-up study that quantitatively analyzed the mechanical properties, microstructural deformation characteristics, and impact toughness of bainite and martensite using EBSD (Electron Backscatter Diffraction) and SEM (Scanning Electron Microscope) analyses. In this study, VHCF, HCF, tribology characteristics and UNSM (ultrasonic nanocrystal surface modification) effects under duplex bainite and single martensite microstructures were quantitatively studied and analyzed by fracture mechanics from the engineering and industrial point of view to improve durability and weight reduction in spring steels. The bainite AT and martensite QT specimens showed a 56% and 33% increase in fatigue limit for as received AR specimens. Fisheye cracks in duplex bainite AT specimens are similar to ‘facet internal cracks’ that initiated in the absence of inclusions. Generally fisheye crack fracture mode is preferred in VHCF, but fisheye crack was not found in the QT and the AR specimens at all. The UNSM-treated specimens showed fatigue limits that were about 33~50% higher than the untreated specimens.
ISSN:2075-4701
2075-4701
DOI:10.3390/met12060901