One of the most direct, effective ways to improve the fuel efficiency of vehicles – and thereby lower greenhouse gas emissions – is to reduce its weight. However, this can come at the cost of vehicle safety.

For example, every 10% reduction in total vehicle weight achieves an average fuel economy improvement of 4.9%; however, a decrease of 100kg in the weight of a car can also cause a 3%-4.5% increase in safety risk.

One way forward is to develop new materials that are lighter and stronger than those they replace. Responding to the needs of vehicle manufacturers, steel makers around the world are developing new advanced high-strength steels (AHSSs) that are both lighter and stronger than conventional steel, offering improved fuel efficiency without compromising safety.

According to an environmental case study reported by the World Steel Association, the use of every 1kg of AHSSs in a five-passenger family car could achieve a total lifecycle saving of 8kg greenhouse gas, which corresponds to a 5.7% reduction in emissions over the life of the vehicle.

In their paper ‘Thermomechanical processing of advanced high strength steels’, University of Wollongong (UoW) researchers Professor Zhengyi Jiang and Dr Jingwei Zhao provide a comprehensive review of the first, second and third generations of AHSSs and also of Nano Hiten steels, another type of high-performance steel used in the automotive industry.

Thermomechanical processing is a metallurgical process that combines mechanical processes (such as forging or rolling) with thermal processes (heat treatment, water quenching, heating and cooling at various rates) into a single process.

Professor Jiang, from UOW’s School of Mechanical, Materials, Mechatronics and Biomedical Engineering, says AHSSs are complex and sophisticated materials, with microstructures that are controlled by precise thermomechanical processing technologies.

“AHSSs are regarded as the most promising materials for vehicles in the 21st century due to the unique combination of excellent performance and competitive cost,” says Professor Jiang. “The unique metallurgical properties and processing methods of AHSSs will enable the automotive industry to meet requirements for safety, efficiency, emissions, manufacturability, durability and quality at relatively low cost.”

Professor Jiang adds that research into the thermomechanical processing of AHSSs in the laboratory was essential for the optimal design of processing conditions by precise control of temperature, strain, strain rate, heat treatment and cooling parameters: “As each type of AHSS has a unique application in vehicles, specified thermomechanical processing technologies should be developed to produce high-quality AHSS products where they might be best employed to meet mechanical property demands for the automotive parts.”

Professor Jiang’s research group is equipped with powerful facilities for the research on steel processing and manufacturing, including Hille 100 rolling mill, rolls cross and shifting system, accelerated ultrafast water-cooling systems and lubricant emulsification machine, and has been conducting research in this area for more than 27 years.

Professor Jiang and Dr Zhao’s research was funded by an Australian Research Council (ARC) Discover Projects grant, ARC Future Fellowships grants, and by the Baosteel-Australia Joint Research and Development Centre Research and Development Fund.