ISSN:
1662-9752
Source:
Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
SAE 8620 steel is typically used in the carburized condition for powertrain applicationsin the automotive industry, e.g. gears, roller bearings, camshafts. Such steels always containretained austenite to varying degrees in the as-hardened and also in the tempered microstructures.As well as retained austenite, heat treatment can produce residual stresses, which lead to distortion(size and shape). The intent of this study was to investigate the effect of heat treatment parameterson the amount of retained austenite, residual stress and distortion in carburized SAE 8620 steel.A specially designed specimen, the Navy C-ring, was used for this study. The steel was firstnormalized prior to machining the Navy C-ring specimens. The specimens were then heat treatedby carburizing at 927°C or 954°C (1700°F or 1750°F) at four levels of carbon potential (0.9, 1.0,1.1, 1.2) followed by oil quenching and tempering at either 149°C or 177°C (300°F or 350°F). Thedistortion of the C-ring was evaluated by dimensional measurements of the inner diameter, outerdiameter, gap width and thickness for size distortion, as well as flatness, cylindricity and roundnessfor shape distortion. X-ray diffraction (XRD) techniques were used to determine the residual stressand the amount of retained austenite. The amount of retained austenite was also measured byoptical metallography. The amount of retained austenite and the residual stress increased withincreasing carburizing temperature and carbon potential and decreased upon tempering. There wasnot a significant further reduction in the amount of retained austenite and residual stress when thetempering temperature was increased from 149°C to 177°C. Distortion was influenced by both theamount of retained austenite and the magnitude of the residual stress. With increasing retainedaustenite/residual stress, the distortion became more serious. Based on the distortion data for 3parameters (OD, gap width and flatness) for the quenched and tempered specimens, the amount ofretained austenite for minimum distortion was approximately 25%
Type of Medium:
Electronic Resource
URL:
http://www.tib-hannover.de/fulltexts/2011/0528/02/15/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.539-543.4464.pdf
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