Cheaper, greener steel for the automotive industry

Automakers today use a special type of steel (called Advanced High-Strength Steel, or AHSS) in components critical to driver and passenger safety, such as safety cages and bumpers. These parts of the car are designed to absorb collision forces so that less impact is transferred to occupants.

Researchers in Finland have developed not only a new composition for this type of steel but also a new manufacturing process that produces a stronger steel while also making it cheaper and more environmentally friendly. Their findings are published in the journal Materials & Design.

“We wanted to know: can we make steels that are two or three times stronger than current formulations, so we can reduce the amount of steel required and lower the overall weight of a vehicle?”  says Roohallah Aliabad, a researcher at the Microstructure and Mechanisms research group (Centre for Advanced Steels Research) at the University of Oulu. “A byproduct of this research is reducing greenhouse gas emissions. When you reduce the weight of cars, you are indirectly contributing to that goal.”

Aliabad and his colleagues are investigating compositions and processing routes that use manganese as an alloying element. Manganese is significantly less expensive than chromium and nickel, which are traditionally used in steel alloys. The team found that, by tailoring the microstructure of their steel, they could create an ultra strong, non-uniform microstructure (controlled heterogeneity) that contains two types of austenite, a form of iron.

Their findings show that a mixture of low-alloy blocky austenite (characterized by block-like grains) and high-alloy lamellar austenite (which exists as thin films or plates) produces stronger steel while requiring less manganese. They also discovered that the steel does not need to be held at high temperatures for as long as is typical in conventional processing, which reduces energy consumption during production.

To understand these effects, the researchers used a variety of different techniques, including electron microscopy, atom probe tomography, and X-ray diffraction – the latter which was done at the Canadian Light Source at the University of Saskatchewan). These methods allowed them to observe in real time how the metal’s microstructure evolved during heating and how those changes influenced its mechanical properties.

“It was great to be able to watch this happening live (at the CLS),” says Aliabad. “It’s exciting to see how such a small increase in temperature can have such a huge effect on a steel’s ductility.” Ductility is the ability of a material – especially steel – to stretch or bend without breaking.

As an example, the team identified 730 °C as the optimal heating temperature for achieving the best strength-to-weight ratio when the steel was heated slowly. According to Aliabad, this finding could be applied directly in existing industrial steel processing lines without requiring new equipment. “People working in industry could heat the steel to this temperature range and achieve optimal mechanical properties with only a few minutes of annealing time.”

This research was supported by funding from the Jane and Aatos Erkko (J&AE) and the Tiina and Antti Herlin (TAH) Foundations.

--

Aliabad, Roohallah Surki, Saeed Sadeghpour, Pentti Karjalainen, Markus Riihimäki, Alexander Dahlström, Sonia Guehairia, Tao Zhou et al. "Decoding the role of pre-existing austenite in transformation pathways during slow heating of cold-rolled medium-Mn steel for process design." Materials & Design (2026): 115582. https://doi.org/10.1016/j.matdes.2026.115582