Effects of stress relief tempering on microstructure and tensile/impact behavior of quenched and partitioned commercial spring steel

Effects of stress relief tempering on microstructure and tensile/impact behavior of quenched and partitioned commercial spring steel

The primary aim of the present study was to investigate the impacts of tempering (at 200–300 °C) on microstructure and mechanical properties of commercial spring steel of 60Si2CrV grade under “Quenching and Partitioning” heat treatment. Three different heat treatment routes were applied: (a) oil que...

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Bibliographic Details
Published in:Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 745; pp. 307 - 318
Main Authors: Zurnadzhy, V.I., Efremenko, V.G., Wu, K.M., Azarkhov, A.Yu, Chabak, Yu.G., Greshta, V.L., Isayev, O.B., Pomazkov, M.V.
Format: Journal Article
Language:English
Published: Lausanne Elsevier B.V 04-02-2019
Elsevier BV
Subjects:
Austenite
Bainite
Carbon content
Cemented carbides
Cementite
Dilatometry
Dimpling
Electron microscopy
Fracture toughness
Heat treating
Heat treatment
Impact strength
Martensitic transformations
Mechanical properties
Microstructure
Middle-carbon steel
Oil quenching
Partitioning
Phase transformation
Quenching and tempering
Quenching-partitioning-tempering
Retained austenite
Slopes
Spring steels
Tempered martensite
Tempering
Tensile/impact testing
Ultimate tensile strength
Tensile/impact testing
Phase transformation
Middle-carbon steel
Electron microscopy
Quenching-partitioning-tempering
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Summary:The primary aim of the present study was to investigate the impacts of tempering (at 200–300 °C) on microstructure and mechanical properties of commercial spring steel of 60Si2CrV grade under “Quenching and Partitioning” heat treatment. Three different heat treatment routes were applied: (a) oil quenching and tempering at 300 °C (Q-T), (b) bath quenching at 160 °C followed by partitioning at 300 °C for 300 s (Q-P), and (c) the same Q-P treatment followed by tempering at 200 °C, 250 °C, and 300 °C for 90 min (Q-P-T), and it was found that due to the formation of tempered martensite/carbide-free bainite/retained austenite (16 vol%) structure, Q-P treatment significantly improved the tensile/impact behavior of spring steel as compared to the Q-T treatment. Moreover, stress relief tempering at 200–300 °C caused a two-fold increase in ductility (up to 9%) and manifested improved ultimate tensile strength (2022–2065 MPa) and U-notched impact toughness (64–64 J/cm2) in comparison to Q-P treatment. Further, tempering at 200–250 °C resulted in the impact fracture of steel in combination of quasi-cleavage facets with dimpled ruptured profile; tempering at 250–300 °C led to the partial transformation of retained austenite into bainite accompanied with increase in carbon content in austenite; tempering at 300 °C caused 30% decrease in impact toughness of spring steel as compared to Q-P treatment due to the formation of cementite carbide precipitation. In addition, the structural properties of spring steel in different tempering stages were analyzed using SEM, TEM, XRD, dilatometric and magnetometric measurements.
ISSN:0921-5093
1873-4936
DOI:10.1016/j.msea.2018.12.106