Effect of Normalizing on Semi Float Axle Shaft Performance - Case Study

The primary function of axle shaft in semi float rear axle is to transmit the power to wheels. These shafts would experience the torsional load along with bending load as well. Hence shaft metallurgical structure at case & core would become very important. The objective of this study is to understand the importance of normalizing heat treatment process carried out at post forging treatment. Bench test Performance study conducted by comparing the normalized shaft Vs nonnormalized shaft. Ultimate torsion test, torsional impact test & shaft side impact test conducted on both the shafts. The ultimate torsion test result shows JAEL of normalized shaft is 5106Nm & non normalized shaft is 4718Nm. The drop is 7.6%. The torsional impact test shows peak torque of normalizing shaft is 9384Nm & non normalizing shaft is 8386Nm. The drop is 10.6%. The side impact test shows impact energy of normalized shaft is 2903 Jouls & non normalized shaft is 2321Joule. The drop is 20%. The fractography shows ductile fracture in normalized shafts & nonnormalized shaft shows brittle. This is evident by complete fracture (breakage) in non- normalized shaft & bend in (not broken) normalized shaft. Micro structural comparison shows the grain size in normalized shaft is finer but non- normalized shafts are coarser. During the impact test, the fracture occurs by sudden heavy load applied on part surface, causes the tremendous shock load in the shaft. As a result microcracks generates at multiple points & propagates through the grain boundary. This phenomenon reduces fracture toughness characteristics & hastens the dislocation movements. Normalized shaft having finer grain size, shows sufficient ductility before final fracture but non normalized shaft do shows brittle nature due to coarser grain size. Relatively non normalized shaft shows lesser ability to absorb impact energy, JAEL torque & peak torque. The coarser grain size is easing the fracture in non- normalized shaft.