Carbon peak, carbon neutrality is a profound industrial revolution, but also a very challenging scientific and technological revolution, will bring far-reaching social changes to China's economic and social system. As the highest carbon emitting industry in China's manufacturing industry, the steel industry will emit 1.86 billion tons of CO2 in 2021, accounting for 16% of the country, and the steel industry is facing great pressure to be carbon neutral.

 "Under the background of 'double carbon', recycled steel raw materials will become the main raw materials for China's steel industry production, and the use of recycled steel raw materials to organize production is an important path to achieve carbon neutrality in the steel industry." Therefore, it is imperative to make high-quality use of it."

The future is here, and carbon neutrality is imminent

Steel is an important basic structural material, and the rapid development of the steel industry has strongly supported the national economy, social development and national defense construction. 

 These pressures come from: First, the total steel production capacity is large. Economic and social development needs to promote steel production capacity continues to hit new highs, and China's crude steel production in 2020 will be 1.065 billion tons, accounting for 56.8% of the world. Second, the blast-converter long process is dominant, and the ratio of electric furnace steel is low, and the ratio of electric furnace steel in China is about 11.6% in 2018, and the world average is about 29% (excluding China is 47%). Third, coal-based energy structure. In 2020, the proportion of coal in China's primary energy is as high as 58%, of which the proportion of coal in the energy structure of the steel industry is 83%. Fourth, the industry concentration is not high. In 2022, the total output of China's top 10 steel production enterprises (CR10) is 434 million tons, accounting for 42.8% of the national steel production, an increase of 1.36 percentage points over 2021.

At the same time, the market level has also put forward an urgent demand for ecological steel materials. In China, in August 2022, BMW Group and Hesteel Group signed the "Memorandum of Cooperation on Building Green Mild steel iron Supply chain", starting from mid-2023, Hesteel needs to reduce CO2 emissions in the production process of automotive steel by 10%-30%; From 2026 onwards, CO2 emissions in the production of automotive steel will be gradually reduced by 95% based on processes such as green electricity and electric furnaces. In November 2022, BBAC and Baosteel signed the "Memorandum of Cooperation on Building a Green Steel Supply Chain", and Baosteel will gradually provide automotive steel with significantly reduced carbon emission intensity by 2023; From 2026, with the help of the hydrogen-based shaft furnace-electric furnace technology path, Baosteel will gradually reduce the carbon emission intensity of automotive steel by 50%-80%, and then further provide green steel with a carbon reduction of 95%. In February 2023, the European Parliament passed the EU Carbon Border Adjustment Mechanism (CBAM), and the EU will impose carbon tariffs on products in five areas, including steel, from 2026.

"These events show that it is urgent for the steel industry to become carbon neutral. To achieve carbon neutrality in the steel industry, to remove 1.86 billion tons of CO2, is a very complex matter, requiring comprehensive technological innovation in many areas of the steel industry to achieve, is a difficult task."  At the same time, he stressed that the realization of carbon neutrality is of great significance to the steel industry, and the process of achieving carbon neutrality goals is the process of comprehensively improving the technological innovation ability of the steel industry, the process of significantly improving the comprehensive competitiveness, and the process of achieving progress from a steel country to a steel power.

Solve the industry's "headache" residual elements to achieve high-quality utilization of recycled steel raw materials

High-end products such as automotive steel used to be produced using a long process, which was not possible in the face of the need to significantly reduce carbon emissions throughout the life cycle. In the three carbon reduction paths of raw material structure adjustment, energy structure optimization, and simple and efficient process, it is relatively easy to adjust the raw material structure.

"For this reason, the use of recycled steel raw materials with excellent low-carbon properties to produce low-carbon high-end products has become an imminent technical choice." To achieve high-quality utilization of recycled steel raw materials, the problem of residual elements must be solved." 

The residual elements mainly come from two sources. One is the initial smelting process is not completely removed, born with some elements; The other type is the elements added in the subsequent processing in order to adjust the performance of the organization, which become residual elements in the process of secondary or multiple uses. At present, there are about 19 kinds of these residual elements, such as Cu, Ni, Cr, Mo, etc., which are easy to lead to segregation segregation, low thermoplasticity, copper brittleness and other problems, and worsen material properties and processability.

He admitted that the high-quality utilization of recycled steel raw materials is a world-class problem. In 2020, the German Science Foundation and the Ministry of Education of China launched the "Steel Cycle - Steel Cycle for Carbon Neutrality" cooperation project to carry out basic and applied basic research on the high-quality utilization of recycled steel raw materials; In 2021, the British Foundation set up a research institute to carry out research on the efficient recycling of steel resources, with the aim of providing cutting-edge scientific support for the high-quality utilization of steel resources in the UK and the carbon neutrality of the steel industry.

 He believes that at the raw material level, it is necessary to strengthen the classification management of raw materials and improve the technical content of intelligent sorting of scrap steel as much as possible. "Moving from grading and analysis based on shape, size and so on to classification from a chemical composition perspective is definitely the future." He pointed out.

At the smelting level, the corresponding residual elements (including copper, surface zinc, tin, lead, etc.) should be removed as far as possible to achieve clean smelting. "Especially when a lot of scrap steel is used and the electric furnace process is used, the problem of high nitrogen content will be generated, which is fatal to the production of materials such as automotive steel." How to solve this problem is also a global technical challenge." 

At the same time, at the level of continuous casting, the thermodynamic database of residual elements was established, the mechanism of action of residual elements was defined, and the harmless integration technology of residual elements was formed. At the level of preparation and processing, the influence mechanism of residual elements on product quality during preparation and processing was revealed, and harmless processing technology was formed through component design and process optimization.

At the product end, it is also necessary to study the influence law and mechanism of residual element occurrence on material service performance, such as the influence on formability, fatigue performance, hydrogen-induced delayed cracking and welding performance, etc., and then develop residual element regulation technology to improve material service performance.

"By solving these problems, we can basically produce qualified products that meet quality standards."  For example, by using the technical characteristics of rapid solidification and direct rolling, the problems of segregation and segregation of residual elements can be solved, and the tolerance limit can be increased. Make full use of the near final shape characteristics and some residual elements on the material strength, corrosion resistance of the beneficial effect, to develop high performance steel materials.

 "Only if the relevant basic scientific problems and key technical problems are solved, the future use of scrap will be broader, and the scrap industry can develop well."