Cyclic wear behavior (fretting) of a tempered martensite steel
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transformation of the room temperature oxide, •-Fe203, to a-Fe203 occurs at ~285 ~ 9 A direct method of measurement, one that was employed in this study, was touse a constantan (Cu-Ni alloy) fretting pad against a steel specimen to create an iron-constantan thermocouple junction at the fretted surface. In a previous study the measured temperature rise was ~ 18 ~ above ambient temperature for a spheroidized steel) ~ EXPERIMENTAL PROCEDURES Fretting corrosion experiments were performed on 4130 steel in the quenched and tempered heat treatment. Specifically, sheet specimens of 2.7 mm thickness were annealed at 1223 K for 20 rain, quenched in room temperature water, and subsequently tempered for 1 h at 723 K. The microstructure of the heat treated alloy was martensitic. Both the specimen and the pads were polished to 600 grit emery paper. Fretting of the alloy surface was accomplished by cyclically stressing the sheet specimens in a closed loop servohydraulic fatigue test frame. Fretting pads, which were also 4130 steel heat treated identically to the specimens, were attached to a frame fixed to the specimen grips, and normal forces were applied through a colinear arrangement of disk springs which could be mechanically compressed. The length of the spring arrangement was calibrated to measure applied forces normal to the specimen surfaces. The magnitude of slip of the pad and the specimen surface was controlled by the location of the pad on the gage length of the specimen and the range of applied stresses. Thus cyclic elastic deformation in the gage length of the specimen induced relative slip between the specimen and the "fixed" fretting pad. A schematic diagram of the fretting frame is shown in Fig. 1. The specimens were cyclically stressed in tensiontension with a peak stress of 517 MPa (62.5 pct of the yield strength and below the endurance limit of a specimen fatigued without fretting) and a minimum of 5 MPa. In order to monitor temperature changes during fretting the martensitic steel fretting pads were replaced
ISSN 0360-2133/80/0911-1581500.75/0 METALLURGICAL TRANSACTIONS A 9 1980 AMERICAN SOCIETY FOR METALS AND VOLUME 11A, SEPTEMBER 1980--1581 THE METALLURGICAL SOCIETY OF AIME
slightly due to the "plowing" of fretting debris. A comparison of this signal with the cyclic load signal indicated that, when elastic strain in the frame paralleled the load signal, no relative motion occurred between the pad and the specimen. Alternatively, either constant elastic strain in the fixture, or a change of slope of the strain vs time signal indicated sliding of the interfaces. The sliding rate between the specimen and pad was examined utilizing an unique laser light measuring system. In this system, diffraction gratings with a line spacing of 1.9 # m were attached to the specimen and to the fretting pad. A hole was drilled through the pad perpendicular to the direction of relative slip. One grating was attached to the pad covering the hole. The second grating was attached to the specimen, but also covered the hole behind
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