Bending fatigue behavior of vacuum carburized AISI 8620 steel

Book · Sat Dec 30 23:00:00 EST 1995

OSTI ID:389725

Evanson, K; Krauss, G; Medlin, D ^[1]; Patel, M J ^[2]

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1. Colorado School of Mines, Golden, CO (United States)
2. Cummins Engine Co., Columbus, IN (United States)

The bending fatigue performance of aircraft-quality AISI 8620 steel was evaluated after vacuum carburizing. Case depths of 0.45 mm (0.018 in.) and 1.30 mm (0.051 in.) were produced by carburizing in propane atmospheres, and both sets of specimens were subjected to a cold-stabilizing treatment at {minus}73 C ({minus}100 F) before tempering. Bending fatigue specimens were characterized by light metallography to determine microstructure and prior austenitic grain size, x-ray analysis for residual stress and retained austenite measurements, and scanning electron microscopy to evaluate fatigue crack initiation, propagation, and overload. The case microstructure of the specimens with the deeper case contained 10--20{micro}m diameter carbides at the prior austenitic grain boundaries, and had a fatigue endurance limit of 1,230 MPa (180 ksi). The shallow-case specimens had case microstructures with 1--2{micro}m diameter spherodized carbides decorating the austenitic grain boundaries, and had an endurance limit of 1,370 MPa (200 ksi). The high endurance limits resulting from both carburizing processes are attributed to the lack of surface intergranular oxidation and to high residual compressive surface stresses, in excess of 900 MPa (130 ksi), which are attributed primarily to the cold-stabilization treatment.

• OSTI ID: 389725
• Report Number(s): CONF-951222--; ISBN 0-87170-561-3
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
AUSTENITE
BENDING
CARBURIZATION
CHEMICAL COMPOSITION
CRACK PROPAGATION
CRACKS
EXPERIMENTAL DATA
FATIGUE
GRAIN BOUNDARIES
GRAIN SIZE
HEAT TREATMENTS
MICROHARDNESS
MICROSTRUCTURE
OPTICAL MICROSCOPY
PROPANE
RESIDUAL STRESSES
S-N DIAGRAM
SCANNING ELECTRON MICROSCOPY
STEELS
TEMPERING