1997 Volume 83 Issue 10 Pages 659-664
An increase in the torsional strength of automotive shafts has been a subject of particular interest. Induction hardening can afford a medium-carbon steel shaft desirable torsional strength. When case hardness exceeded a certain level, the fracture mode of some test-pieces changed from mode III to mode I with intergranular fracture. The purpose of this study is to establish a method of increasing strength of shaft steels to mode I fracture. The effects of carbon, silicon and molybdenum on torsional strength in mode I fracture were investigated.
The strength in mode I fracture of induction hardened steel decreased with increasing carbon content. The precipitation of fine cementite in the prior austenite grain boundary was recognized. The amount of cementite in the grain boundary was increased by increasing carbon content. The reduction of the strength with increasing carbon content was due to two causes: large amount of grain boundary cementite and high hardness. The magnitude of effect of grain boundary cementite on strength was almost the same as the effect of hardness.
The strength in mode I fracture was increased by increasing silicon or molybdenum contents. This was because the size of grain boundary cementite was refined by the addition of silicon or molybdenum.
