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Struck axle is a critical component of truck that bears the auto-body weight and load weight. Fatigue life safety is the primary consideration in the design process of axle. With the development of environmental protection concept of energy saving and emission reduction, lightweight design of vehicles becomes more and more urgent. It has been becoming a mainstream trend for design to ensure both safety and significantly reduce the weight of axle. Based on the basic truck axle structure design, revised designs with thickness-reduced were proposed to reduce the weight of truck axle .Both basic and modified design were modeled using Abaqus 3D software to calculate the stress and strain contours in the case of vertical load and axial torque, then fatigue life contours of models for each load case were calculated with the help of Brown-Miner biaxial fatigue theory. It was shown by the research that topology-optimization of truck axle, under a premise of qualified fatigue life and stiffness required by customers, can reduce the weight of two kinds of truck axles by 15.3% and 18.1% respectively.

To further improve the strength and toughness, the advanced thermomechanical controlled processing has been applied in the development of an ultralow C and high Nb bearing steel. In the present investigation, the effects of processing parameters, consisting of the coiling and starting temperatures in non-recrystallisation region, on the final microstructure and mechanical properties of this steel have been studied by tensile, Charpy impact tests, optical microscopy and transmission electron microscopy. Results indicate that the acicular ferrite dominated microstructure can be greatly refined in grain size with decreasing the starting temperature of finishing rolling. However, for high Nb steels, the too low starting temperature would promote the formation of high temperature transformation products and consequently make against the improvement of mechanical properties. In addition, the optimum temperature window of finishing rolling is found to be also related to alloying levels of austenite stabilising elements. At the high starting temperature of finishing rolling, the precipitation strength contribution increases with increasing coiling temperature. However, the increase in strain accumulation associated with low temperature processing greatly reduces the sensitivity of the precipitation strength contribution to coiling temperature.