2008•Ironmaking & Steelmaking Processes Products and ApplicationsRequires access
Effect of Isothermal Heat Treatment on Microstructure and Mechanical Properties of a Medium-Carbon Ultra High Strength Spring Steel
Dong Han
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Abstract
The effect of isothermal heat treatment on microstructure and mechanical properties of a medium-carbon ultra high strength spring steel(U) was studied.The results show that a carbide-free bainite/martensite duplex microstructure could be obtained by austempering at 325-375 ℃.The austenitizing temperature before austempering has obvious influence on both the microstructure and mechanical properties of bainite/martensite duplex microstructure of steel U.With increasing austenitizing temperature from 875 ℃ to 930 ℃,the strength of steel U increases,while its toughness decreases markedly.Bainite/martensite duplex microstructure with good combination strength and toughness was obtained by austempering at 325 ℃ for 120 s after austenitizing for 30 min at 875 ℃ followed by tempering at 300 ℃ for 2 h.The fracture toughness of specimens was 83 MPa·m1/2,1.5 times higher than that of single tempered martensite with same strength level.