The effect of fretting and environment on fatigue crack initiation and early propagation in a quenched and tempered 4130
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Two metallic surfaces in intimate contact and subjected to a small a m o u n t of relative motion (faying) often suffer large amounts of material loss due to a p h e n o m e n o n known as fretting corrosion. In the absence of an aggressive environment such as air metal loss still occurs and the p h e n o m e n o n is known simply as fretting or cyclic wear. This wear process often results in a significant reduction in fatigue resistance for a large n u m b e r of metals and alloys. The mechanisms leading to fatigue crack initiation have recently been reviewed by a committee of the National Materials Advisory Board ~with the conclusion that there have been few basic studies of fretting induced fatigue and that the existing literature is contradictory. For example, most studies of fretting fatigue have concentrated on the phenomenology of fatigue failures with little emphasis on the micromechanics of the process. Theories which have been advanced include adhesive wear theories where individual cold or w a r m welded j unctions rupture during sliding at some location away from the original interface. 2 s However, it has been difficult to apply them to the fatigue situation since they do not address the problem of early crack propagation into the material. Similarly, abrasive or corrosive wear models have been emphasized as primary causes of fretting induced fatigue since typical fretting products are too small to cause severe abrasion. 6 More recently, a delamination theory for wear has been developed which considers that dislocation interactions initiate voids and cracks parallel to the worn surface. Support for the role of subsurface cracks has also been advanced by other workers 7-~~including studies in our laboratories on spheroidized 4130 steels)1-1s The results presented herein extend these studies on the basic mechanics of fretting damage to fretting D. J. GAUL is Research Scientist, Owens Corning Fiberglas, Granville, OH 43023. D. J. DUQUETTE is Professor of Metallurgical Engineering, Materials Engineering Department, Rensselaer Polytechnic Institute, Troy, NY 12181. Manuscript submitted November 15, 1979.
fatigue induced crack initiation in quenched and tempered 4130 steels. EXPERIMENTAL PROCEDURE Fretting fatigue experiments were conducted on a commercial heat of 4130 steel after a quench and temper heat treatment. The steel was received in the spheroidized (normalized) condition and was austenitized at 1223 K for 20 min followed by quenching into r o o m temperature water. Specimens were subsequently tempered at 723 K. This heat treatment resulted in a yield strength of 800 MPa, ultimate tensile strength of 2485 MPa and an elongation to failure of 12.7 pct. Specimen blanks with gage sections of 89 x 2.7 m m were cut from sheets of 156 x 32 x 2.7 m m prior to heat treatment. Fretting pads of 5 x 5 x 2.7 m m were cut from identical sheets and received the same heat treatment. Specimen surfaces were ground to 600 grit SiC paper prior to testing with residual scratches parallel to the rolling direction and te
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