Effects of processing on the transverse fatigue properties of low-sulfur AISI 4140 steel |
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Authors: | Sunniva R Collins and Gary M Michal |
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Affiliation: | (1) Department of Materials Science and Engineering, Case Western Reserve University, 44106-7204 Cleveland, OH |
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Abstract: | The effects of inclusions due to steelmaking processes on the fatigue life of AISI 4140 have been investigated. The test matrix
consisted of three commercially produced heats of AISI 4140 of comparable cleanliness: one was conventionally cast (CC), and
two were inert gas-shielded/ bottom-poured (IGS). One of the IGS heats was calcium-treated to explore the effects of inclusion
shape control (IGS/SC). All heats were hot-rolled and reduced over 95 pct to produce bar stock of 127 to 152 mm (5 to 6 in.)
in diameter. Transverse axial specimens conforming to ASTM E466 were machined, quenched, and tempered to approximately 40
HRC, and they were fatigue tested in tension-tension cycling (R = 0.1). Test results and statistical analyses of the stress-life data show that the IGS grade has several times the fatigue
strength of the CC grade at 107 cycles. Lower-limit fatigue strengths calculated at a 99.9 pct probability were 518.5 MPa (75.2 ksi) for IGSvs 55.6 MPa (8.1 ksi) for the CC grade. The IGS/SC grade had the best performance at all stress and life levels. The results
obtained indicate that fatigue performance can be improved by choosing a processing method that reduces the incidence of exogenous
oxides and by controlling the shape of the sulfides. |
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