This content is not included in
your SAE MOBILUS subscription, or you are not logged in.
Strengthening of Surface Induction Hardened Parts for Automotive Shafts Subject to Torsional Load
Annotation ability available
Sector:
Language:
English
Abstract
The purpose of this study is twofold: to clarify the factors governing the torsional strength of surface induction hardened parts and, to present a method for strengthening automotive shaft parts for their weight reduction. The torsional strength against Mode III fracture can be expresssed by a new indicator, “equivalent hardness” defined as an average hardness weighted with the radius squared. If the equivalent hardness is continuously increased, the fracture mode change from Mode III to Mode I. The torsional strength against Mode I fracture is governed by grain boundary strength. Accordingly, the key-points in increasing the torsional strength of surface induction hardened parts are to raise the equivalent hardness and increase the grain boundary strength of the steel. By application of this method, the torsional strength of steel can be raised by 50%, which, in turn, enables about a 25% weight reduction for shaft parts.
Over recent years, product and material engineers have pursued automotive component mass reduction by increasing material strength. An increase in the torsional strength of shafting has been a subject of particular interest. As the main function of a shaft is the transmission of torque, the main property required of them is high torsional strength. Shafts are normally manufactured by induction hardening a medium-carbon streel. Although many have reported on the bending strength of induction hardened parts (1, 2, 3 and 4), only a few have reported on the static strength and the strength of parts under repeated stress in connection with the torsional strength of induction hardened parts (5, 6). Therefore, the factors governing the torsional strength of surface induction hardened parts are not clear.
The purpose of this research is to clarify the factors governing the torsional strength of induction hardened parts and to devise a method for strengthening automotive shafts in order to reduce their mass. As static torsional strength is the most important property of automotive shafts, our research focused on the static torsional strength of surface induction hardened parts. Since induction hardened parts normally have a hardness distribution from surface to center, torsional strength is thought to be determined by a combination of hardness distribution and stress distribution. Therefore, we first investigated the effect of hardness distribution on the torsional strength of induction hardened parts. We then examined, from the viewpoint of grain boundary strength, the factors governing the torsional strength related to Mode I fracture which is often encountered in strengthening steels.
Recommended Content
Topic
Citation
Ochi, T. and Koyasu, Y., "Strengthening of Surface Induction Hardened Parts for Automotive Shafts Subject to Torsional Load," SAE Technical Paper 940786, 1994, https://doi.org/10.4271/940786.Also In
References
- Natsume Y. “Static Bending Strength and Correlation between Static Strength and Endurance Limit of Induction Hardened Steel” J. Soc. Materi. Sci. Japan 26 1977 361 366
- Nemerguth B. F. et al “Predicting the Fatigue Life of an Induction-Hardened Machine Component Using Its Material Properties” HEAT TREATMENT '79 Birmingham The Metals Society 1979 194 201
- Egami N. et al “Bending Strength of Some Surface Hardened Steels” J. Japan Soc. Heat Treat. 25 1985 3 129 135
- Yonetani S. et al “Effect of Residual stress on Fatigue Strength of Induction Hardened Specimens of a Medium Carbon Steel” Tetsu-to-Hagane 75 1989 1362 1369
- Naito T. et al “Torsional Fatigue Strength of Induction Hardened Steels” J. Soc. Materi. Sci. Japan 32 1983 1132 1136
- Hisamatu S. et al “Study on the Proper Case Depth of Induction Hardened Parts” Isuzu Tech. J. 67 1982 9 13