Striving for green steel

Steel underpins modern society but its production generates intensive carbon dioxide emissions. For its sustainable development, the steel industry requires technology and product upgrades, driven by innovation and cooperation.

The recent extreme weather, such as the heatwaves, that raged across the world this summer is a reminder of the severe consequences of human-induced global climate change. Reducing greenhouse gas emissions, typically CO₂, remains at the top of the agenda in response to the deepening climate crisis, and low-carbon materials and technological solutions are indispensable. Research and development on renewable energy sources to replace fossil fuels is crucial, as is the increased investment in the industrial chains for photovoltaics, battery vehicles, hydrogen energy and other frontier technologies. But, in the meantime, we cannot neglect the fact that iron and steel are still the fundamental materials for the modern world and emissions cuts in this sector are urgently required.

Credit: K7 Photography / Alamy Stock Photo

The iron and steel sector is the largest industrial emitter accounting for around 11% of global CO₂ emissions according to recent statistics¹. The major steel-producing countries and regions in the world, the top ranking being China, Europe, India, Japan, Russia and the United States, have made commitments and plans to decarbonize their steel industries in line with climate targets. As the largest steel producer and consumer, China has a crucial role. In a Comment in this issue of Nature Materials, Yue Zhang and colleagues discuss the ongoing reform of the steelmaking industry in China for achieving its “dual carbon” goals — for CO₂ to peak before 2030 and carbon neutrality before 2060 — as well as the driving factors of domestic policies and materials/technology development. Macroeconomic policies are clearly directed towards energy-saving upgrades, pollutant treatments, waste materials recycling, steel-sector restructuring and product capacity optimization. The key to realizing these goals, in practical terms, lies in the implementation of low-carbon technologies and product upgrades.

Low-carbon technologies primarily include the use of renewable energy sources, high-efficiency, low-carbon emission processing, and techniques related to carbon capture, utilization and storage (CCUS). Hydrogen metallurgy can play an important role in the deep decarbonization and reform of the steel industry, by leveraging hydrogen as both an effective reduction agent and a supply of clean energy. More broadly, materials science and technological progress have a great potential in facilitating the optimization of the entire steelmaking process and production, as well as renewable energy acquisition and CCUS innovation for more comprehensive carbon emissions reductions, as also discussed by Zhang and colleagues in their Comment.

The recycling of iron and steel is of particular importance for closing material loops, and enabling sustainability and emissions reductions, provided that the quality of the recycled steels can meet application demands, for example having strict control over elements such as carbon to achieve the desired properties. To this end, Gisele Azimi and colleagues report in an Article in this issue an electrorefining process that directly decarburizes molten iron to produce ultra-low-carbon steels and recovers silicon as a by-product, while requiring low energy input and no reagents. This process is applicable to molten iron containing any amount of carbon and is expected to be scalable and able to be integrated into secondary steel mills.

Based on well-developed manufacturing technologies, upgrading steel products to improve their performance and lifetime in applications can reduce the amount of materials needed, secondary processes and hence the emissions downstream. Also in this issue, Dianzhong Li and colleagues report in an Article that the extreme property variations of rare earth (RE) steels stem from the presence of oxygen-based inclusions. By keeping low levels of oxygen content in the steel melts and RE raw materials, stable and favourable effects of REs on mechanical properties can be achieved, with a 40-fold improvement in the tension–compression fatigue life and a 40% enhancement in the rolling contact fatigue life, with only parts-per-million-level RE addition.

In a Q&A, Gang Qian from a steel company based in China reflects on the demands on innovation in low-carbon technologies and advanced products needed to help the company cope with reducing its carbon footprint and to survive the reforms in the steel sector. Qian also highlights the importance of cooperation with downstream customers so that the products can be developed to fulfill the low-carbon requirements, as well as to satisfy the application needs in the clean energy sector.

In the implementation of technological innovations in the steel industry, efficiency, safety and cost must be taken into consideration. This, of course, cannot succeed without the mutual support of all of the different parties involved, from improving materials designs, to optimizing processes, to finding industrial solutions. Moreover, an encouraging market environment, with clear monitoring and evaluation standards under the guidance of national- and global-wide policies and regulations, can stimulate innovation adoption and restructuring in the steelmaking industry.