Abstract
The torsional fatigue strength of newly developed case hardening steel, i.e., transformation-induced plasticity-aided martensitic steel subjected to vacuum carburizing followed by fine particle peening, was investigated for the fabrication of downsized precision gears with high torque capacity and wear resistance. The surface-hardened layer properties—i.e., high Vickers hardness, high compressive residual stress, and a large amount of retained austenite—considerably increased the torsional fatigue limits of vacuum-carburized and fine particle peened TM and JIS-SNCM420 steels, although the notch-sensitivity to fatigue was increased. The relation between torsional and rotational bending fatigue limits for the smooth specimens was found to be between the maximum principal stress and the minimum shear strain energy criterions. On the other hand, this relation for the notched specimens was represented through the maximum principal stress criterion.
Highlights
Several industrial precision gears are widely used as power transmitting gears, since can they carry larger loads and the dynamic load and the noise level experienced during the operation are minimal [1]
The relations between the torsional and rotational bending fatigue limits of smooth and notched specimens in TRIP-aided martensitic (TM) and SNCM420 steels subjected to vacuum carburization and subsequent fine particle peening shifted toward the maximum principal stress criterion, compared with the relations of heat-treated both steels, especially in the smooth specimens (Figure 9)
The surface-hardened layer properties and the depth of the crack initiation origin can be expected to be connected with the fatigue limits and the relation between the torsional and rotational bending fatigue limits in the smooth specimen of TM steel subjected to vacuum carburization and subsequent fine particle peening
Summary
Several industrial precision gears are widely used as power transmitting gears, since can they carry larger loads and the dynamic load and the noise level experienced during the operation are minimal [1]. As the precision gears undergo cyclic bending-torsion loadings [2,3,4,5], high rotational bending, torsional, and bending–torsional fatigue strengths are required. Two kinds of gear tooth damage can occur due to material fatigue under repeated loading-pitting and tooth breakage in the tooth root area [6]. Case hardenings such as gas-carburizing and surfacequenching provides improved contact and bending-torsional fatigue performance of steels with respect to through hardened gears [7] and other mechanical components. The effects of several variables—such as the specimen geometry, level of stress concentration factors, stress ratio, or the loading histories—on the fatigue performance must investigate. The demand for transmission precision gears with high torque capacity and high wear resistance has increased; in addition, the gears are being downsized to reduce energy consumption [8]
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