Effect of Austenite Grain Size on Torsional Strength of Notched Specimens of Induction Hardened Steel for Automotive Shafts

An increase in the torsional strength of automotive shafts has been a subject of particular interest. The purpose of this study is to establish a method of increasing strength of shaft steels to mode fracture. The effect of austenite grain size on torsional strength in mode fracture is investigated. The torsional strength in mode fracture improves according to the grain refining of the austenite grain. A ductility fracture is observed partially in the fine grained steel though the initiation site of fracture presents the intergranular fracture in all aspects in the coarse grained steel. The amount of P of the grain boundary segregation decreases by the grain refining as a result of investigating the grain boundary properties by AES. The improvement of strength by the grain refining is possibly guessed that the following effect superimposed it above. The amount of the grain boundary segregation must decrease along with an increase of the area of the grain boundary. The ratio of the low energy grain boundary must increase. It must accompany an increase of the ratio of the low energy grain boundary and the amount of the grain boundary segregation must decrease.