Effect of Normalizing Heat Treatment on Material and Mechanical Properties of High Strength Steel Tube for Lift axle of Commercial Vehicles

Lift axles of heavy commercial vehicles are deployed to handle increased payload. These axles of Commercial vehicles are made of low alloy carbon steel materials. Lift axles are designed in hollow condition for weight reduction opportunity. Two types of tube materials are used for the manufacturing of lift axles. These are either Cold Drawn Seamless (CDS) tubes or Hot Finished Seamless (HFS) tube material. The vanadium micro-alloyed steel grade, 20MnV6 is an excellent choice for the manufacturing of lift axles. The 20MnV6 has favorable mechanical properties for lift axles and also offers good weldability. However, lift axles made of 20MnV6 when manufactured in hot-finished condition, shows significant scatter in terms of durability performance. This requires further heat treatment of 20MnV6 to be deployed for reducing the scatter in the material properties to reduce scatter in durability performance and thus increasing the reliability of the lift axles. This study was undertaken to develop the heat treatment process for the 20MnV6 lift Axle material to reduce scatter of mechanical properties, improve impact strength, and establish the uniformity of metallurgical characteristics. In the study, detailed normalizing heat treatment cycle was developed and the effect of normalizing cycle on monotonic mechanical properties, impact properties and cyclic properties were evaluated using rotating bending fatigue test. The data from study will help in optimization of designs for further light-weighting and performance improvement of lift axle tube.