Effects of tramp elements on recycled steel

Researchers: Khalifa Maissara and Ida Kero

The main goal of this project is to identify and develop methods to improve steel recycling and minimize the reliance on primary iron, by optimizing steel processing.

Steel is one of the most recycled commodities in the world. However, most of what is today termed recycling constitutes downcycling – i.e., that the recycled products exhibit significantly poorer quality than the original products. As an example, it is not possible to make new cars out of old, scrapped cars because of quality constraints. Many of the automotive materials are so-called advanced high strength steels (AHSS), which are among the most challenging steel grades to base on scrap. The main goal of this project is to identify and develop methods to avoid downcycling of AHSS and reduce the reliance on primary iron for their production.

The long-term strategies for steel recycling should aim to reduce the diversity and complexity of steel alloys (grades) in use and in production, so that fewer alloying additives need to be added in the first place. It may be possible to decrease the number of alloying elements in steel, as well as their concentration by improved control of the steel microstructures by optimized thermomechanical processing (TMP). The idea of producing many different grades by differentiated processing of the same chemical composition is sometimes referred to as unialloying. This would require new approaches to alloy design where the focus is on microstructure development, using TMP rather than alloying additives.

Sustainability aspects

The current production of iron and steel is based on the blast furnace process and has many negative effects on the environment. It is recognized as one of the most difficult industries to decarbonize (hard-to-abate sector). Secondary steel production, based on steel scrap, is recognized by the world steel association as one of few strategies compatible with a (near-) zero-emission pathway. Recycling can reduce industrial emissions, pollution, as well as energy consumption, and land area use. As such, this project directly supports the UN SDG’s 8, 9, 11, 12, and 15.

Other societal and financial motivations for increasing recycling improved resilience, reduced supply chain risks and increased ability to retain and make use of the critical and strategic raw materials often included in steel as alloying elements.