• Proceedings of the KSME Conference
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• 2005.11a
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• pp.142.2-142.2
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• 2005

• Journal of the Korean Society for Heat Treatment
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• v.19 no.1
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• pp.30-36
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• 2006

Fretting fatigue behavior of SCM420 steel commonly used in the automotive industry for structural applications was investigated in this study. In addition, the effect of bridge pad on the fretting fatigue test was evaluated from different pad materials and following conclusions were drawn. Simple fatigue limit of SCM 420 steel was determined to be 350 MPa while this value was 225 MPa and 285.5 MPa with SCM420H and with SM45C pad, respectively. Reduction in fatigue limit was, thus found to be 35.7% and 17.9% with SCM 420H pad and SM45C pad, respectively. Results of fracture surface observation revealed that typical striation pattern of fatigue failure existed as well as dimpled and cleavage frature appearance was found in final fractured region. From the EDS compositional analysis, test sample and pad part all had high signals for oxygen and iron, suggesting that worn particles might be iron oxide, although exact chemical composition has to be confirmed. Considerable reduction in fatigue life was apparent in SCM 420 steel under fretting fatigue against simple fatigue. Such reduced fatigue life by fretting damage should be considered as an important factor not only in the viewpoint of repairing but also inevitably in the design stage of structural components.

• Tribology and Lubricants
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• v.36 no.1
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• pp.18-26
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• 2020

The effects of the carburizing process on the sliding wear behavior of SCM420H steel have been investigated. In particular, the effects of grain boundary corrosion observed in the surface layer after gas carburizing and the effects of hardness of the carburized cases after heat-treatment on the sliding wear properties were examined. Pin specimens carburized by two methods (gas carburizing and vacuum carburizing) were tempered at two temperatures of 180℃ and 400℃ after oil-quenching, respectively. Sliding wear tests were carried out against heattreated SKH51 steel at several sliding speeds using a pin-on-disc type test machine. As results, it can be found that there is no difference in the wear behavior between the pins carburized using two methods. This implies that the grain boundary corrosion that formed in the surface layer after gas carburizing has no effect on the sliding wear behavior of carburized SCM420H steels. Additionally, there is no significant difference in the wear behavior between carburized pins tempered at 400℃ and at 180℃ after oil-quenching, regardless of the carburizing method. This is because carburized pins tempered at 400℃ have a troostite structure, which exhibits higher tribochemical reactivity even though its hardness is lower than that of martensite structure. In this respect, it can be considered that good wear resistance of carburized cases is maintained at least until the effective case depth.

• Journal of the Korean Society for Heat Treatment
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• v.28 no.6
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• pp.300-309
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• 2015

The aim of the present study was to predict the variations in microstructure and deformation occurring during gas carburizing and quenching processes of a SCM420H planetary gear in a real production environment using the finite element method (FEM). The motivation for the present study came from the fact that previous FEM simulations have a limitation of the application to the real heat treatment process because they were performed with material properties provided by commercial programs and heat transfer coefficients (HTC) measured from laboratory conditions. Therefore, for the present simulation, many experimentally measured material properties were employed; phase transformation kinetics, thermal expansion coefficients, heat capacity, heat conductivity and HTC. Particularly, the HTCs were obtained by converting the cooling curves measured with a STS304 gear without phase transformations using an oil bath with an agitator in a real heat treatment factory. The FEM simulation was successfully conducted using the aforementioned material properties and HTC, and then the predicted results were well verified with experimental data, such as the cooling rate, microstructure, hardness profile and distortion.