Open Access

Wiebke Hagedorn

• Human-induced climate change is progressing and threatens the basis of existence for human beings. The steel industry accounts for a significant proportion of the greenhouse gases emitted each year. One solution for its reduction is the Circular Economy in a broader sense. The strategies of narrowing, slowing, and closing resource flows are intended to increase material efficiency and reduce the environmental impact. Because the steel industry is a leading industry for closing resource flows by implementing recycling and recovery, the potential for improvement is low. In contrast, the so-called 10 Rs, which start at product level, have a large untapped environmental saving potential. To date, little is known about how these circularHuman-induced climate change is progressing and threatens the basis of existence for human beings. The steel industry accounts for a significant proportion of the greenhouse gases emitted each year. One solution for its reduction is the Circular Economy in a broader sense. The strategies of narrowing, slowing, and closing resource flows are intended to increase material efficiency and reduce the environmental impact. Because the steel industry is a leading industry for closing resource flows by implementing recycling and recovery, the potential for improvement is low. In contrast, the so-called 10 Rs, which start at product level, have a large untapped environmental saving potential. To date, little is known about how these circular interventions can be applied to steel products so that they are more material-efficient and environmentally sustainable and thus improved in terms of the Circular Economy. To close this gap, an assessment approach is required that quantifies the extent to which the implementation of circular interventions in steel products is in line with the Circular Economy. At the same time, it is essential to understand how the Circular Economy can be successfully applied to steel products. The aim of this dissertation is to develop an assessment approach for environmental sustainability and to generate knowledge about circular interventions for steel products. The inductive proceeding starts with investigating the mutual relationships between material, process, and product level by using the example of a U-bolt. The application of circular strategies to a machining knife is then analysed. An approach for assessing environmental sustainability is developed on the basis of the findings related to the methodology and steel specific characteristics of process chains. The proceeding is applied and validated to several steel products as part of a circular intervention. In addition to findings on the methodological proceeding, this dissertation also generates insights into how circular interventions can be successfully implemented on steel products. The first case study comprises the Life Cycle Assessment of an alloy development for a U-bolt. While the element-specific balancing of the changed composition at material level led to an increased environmental impact of the new alloy, the changed process chain and the now possible product design achieved an overall reduction in missions as well as energy and resource demand. The different conclusions emphasise the need for a lifecycle-wide assessment. Furthermore, relevant hotspots in the process chains of steel products (e.g. material production and heat treatment) become visible and the importance of material characteristics (cyclic strength) for product functionality and design. The second case study involves a Life Cycle Assessment and the application of mass-based indicators to analyse three circular interventions on a machining knife. These include axial ring rolling (narrowing), reworking a large machining knife into a smaller one (slowing) and recovering steel from the waste stream of grinding sludge (closing). All interventions showed an increase in material efficiency as well as a reduction in emissions and energy demand. In addition, the environmentally relevant influences of steel production, the energy mix and the auxiliary processes became clear. The study also shows that material efficiency as a mass-based indicator does not correlate with the results of the Life Cycle Assessment. Based on the findings, an approach for the environmental assessment of circular interventions on steel products was developed in this thesis. The integration of the Material Flow Analysis and mass-based indicators with the LCA eliminates its previously identified limitations of including product functionality, material quality, time, and dissipative losses. The system definition is fundamental for the definition of the conventional product system and the circular intervention. Then, the data collected on quantitative and qualitative aspects are incorporated into a material flow model of steel. This is followed on the one hand by the application of mass based indicators to quantify the parameters of the Circular Economy and on the other hand by the extension of the model to carry out a Life Cycle Assessment to analyse environmental sustainability. The application of the assessment approach to a further case study validates the procedure and the previous findings. The case study involves the production of hand tools from a machining knife. The results show that the circular intervention achieves only significant improvements regarding the resource and energy demand, provided that the increased functionality leads to a reduction in production volume. In summary, the dissertation shows how the integration of Life Cycle Assessment, Material Flow Analysis and mass-based indicators enables a holistic environmental assessment of circular interventions on steel products. The synergy of the methods, as the strengths of the individual approaches, overcome the individual limits. The integration of key characteristics of steel (e.g. steel production, heat treatment, grinding) and related parameters (e.g. material characteristics) enables the lifecycle-wide assessment of circular interventions, taking into account material quality, product functionality and lifetime. The case studies show that circular interventions in the steel sector can lead to improvements in material efficiency, emissions, and energy demand. To prevent the savings from being offset, the boundary conditions for the subsequent process design must be determined.…