This paper examines how circular economy principles are understood and applied within the Swedish steel industry, situated within a broader European policy context. Drawing on qualitative interviews with industry and academic respondents, it explores drivers, barriers, and opportunities shaping the transition toward circular and low-emissions steelmaking. The findings show that while Sweden’s nearly fossil-free electricity mix, strong policy framework, and rising market demand create favorable conditions, progress remains constrained by high capital costs, technological immaturity, and limited availability of high-quality scrap. Respondents emphasise that economic feasibility and market acceptance currently outweigh policy ambition as determinants of change. Circularity is widely supported in principle but challenged in practice by material and infrastructural limitations. The paper concludes that Sweden’s structural advantages position it as a frontrunner and testbed for circular steel production, provided that coordinated action aligns technological innovation, market incentives, and regulatory frameworks.

The effect of tempering and auto-tempering on the microstructure–property relationship of two ultra-high strength press hardening steels (PHS1500 and PHS2000) was studied. Both steels were austenitized, oil quenched, and subsequently tempered at four different temperatures ranging from 180 °C to 300 °C. For auto-tempering, the steels underwent austenitization and quenching using a press equipped with planar tools and were subsequently ejected at varying cooling durations. The tensile properties, hardness, microstructure, and dislocation densities after heat treatment were characterized. The results showed that the effect of tempering temperature on tensile properties and microstructure features was more pronounced than the effect of tempering time for both steels. Tensile strength and hardness decreased slightly with increasing tempering temperature up to 200 °C. Above that temperature, there was a further decrease in tensile strength and hardness, which is suggested to be due to the formation and coarsening of carbides in the highly dislocated martensitic matrix. In contrast to the tensile strength and hardness, the yield strength increased with increasing tempering temperatures, which is most probably due to internal stress relaxation. Total elongation was increased with increasing tempering temperatures, except for the samples tempered at 250 °C and 300 °C. These samples experienced a reduction in elongation at fracture, which was more pronounced after tempering at 300 °C than at 250 °C. This was most likely attributed to the so-called tempered martensite embrittlement effect. Calculation of dislocation densities before and after tempering treatments confirmed dislocation annihilation and recovery of martensitic microstructure. 

Laser Powder Bed Fusion (LPBF) enables complex metal components for the space industry. However, as-built surface roughness affects material properties and is closely linked to design geometry. As computer-aided design tools struggle to model roughness accurately, this study explores Additive Manufacturing Design Artefacts (AMDAs) to investigate design-related roughness and its impact on fatigue performance. A space industry case study using AMDAs to replicate a 4 mm unsupported roof radius of a rocket engine component found fatigue performance reductions of 88% in horizontal builds and 65% in vertical builds compared to machined surfaces. Microstructural analysis confirmed the influence of roughness and grain structure on fatigue behaviour. Findings highlight how AMDAs provide design-specific insights and support engineers in investigating uncertainties.

This work investigates the quantitative effect of the hydrogen concentration of 100Cr6 bearing steel on the surface-initiated damage induced during lubricated rolling/sliding tribotesting. Hydrogen was introduced to the samples prior to tribotesting by electrochemical pre-charging, and hydrogen concentration was measured using thermal desorption analysis. The surface-initiated damage was quantified by optical profilometry and scanning electron microscopy. An upper limit for the critical hydrogen concentration was determined to be 1.4–2 wppm diffusible hydrogen. At this concentration, the area fraction covered by damage features was found to double compared to uncharged samples. As both charged and uncharged samples exhibited the same type of surface damage (early-stage micropitting), it was concluded that hydrogen did not change the wear mechanism but decreased the number of contact cycles necessary for the initiation of surface defects.

This study investigates the impact of hydrogen gas on the tensile and low cycle fatigue (LCF) properties of two high strength steels by means of the hollow specimen method. The steels studied have ultimate tensile strengths in the range of 530 to 650 MPa, and ferritic-pearlitic and bainitic microstructures, respectively. The behaviour of these steels was evaluated in a pressurized environment containing either inert gas (Ar) or hydrogen (H2) at room temperature and a pressure of 200 bar. The findings of this work indicate that hydrogen has a detrimental effect on the ductility and reduction in area, while the other tensile properties remain unaffected for both steels. Hydrogen uptake due to the interaction between H2 and steel during mechanical testing was measured. The fractographic analysis revealed presence of brittle fracture and embrittlement despite that the tensile properties of the steels were not affected. In contrast, the fatigue life of both steels was severely affected by H2 compared to Ar environment when tested at high strain amplitudes. The fractographic inspection of the LCF tested specimens indicated differences in crack propagation behaviour between Ar and H2 environment. Specimens tested in H2 indicated faster crack growth and widely spread striations. Finally, this work concludes that the bainitic steel exhibits slightly better mechanical performance than the ferritic-pearlitic steel in pressurized hydrogen gas for the respective testing conditions. 

As hydrogen reduces the fatigue life of 100Cr6 bearing steel significantly, extensive research on the interaction of hydrogen with 100Cr6 is necessary. This study investigated the influence of rolling/sliding tribotesting performed on a micro-pitting-rig on the hydrogen absorption and trapping behaviour of 100Cr6 bearing steel. Thermal desorption mass spectrometry was used to compare the hydrogen desorption spectra of 100Cr6 samples after tribological tests and static heated oil-immersion tests to untested reference samples. The approach was chosen to further understand the influence of both microstructural deformation as well as steel-oil contact on the hydrogen absorption and trapping behaviour of 100Cr6. The tribological test showed a stable friction behaviour and mild wear which was dominated by local plastic deformation of surface asperities. Despite the mild wear, a change in de-trapping temperatures was found for tribotested samples compared to oil-immersed and untested reference samples. This finding indicates that even mild tribotesting conditions alter the hydrogen trapping behaviour of 100Cr6 bearing steel.

Additive manufacturing is known for producing complex metal components, particularly with materials like 316L stainless steel. However, ensuring the quality and microstructural consistency of such components remains a challenge, as traditional testing methods are often destructive and time-intensive. Data driven models that are used for non-destructive evaluation are often difficult to interpret. This study explores the use ultrasound measurements combined with a multivariate statistical technique (partial least squares), to estimate the material properties of steel samples and examining the relationships between ultrasound signals at various frequencies and material properties such as porosity, grain size, and hardness. This aims to enhance the interpretability of ultrasound testing for additive manufacturing. Our findings indicate that ultrasound backscatter can be effectively linked to key material properties.

Additive manufacturing (AM) using powder bed fusion is becoming a mature technology that offers great possibilities and design freedom for manufacturing of near net shape components. However, for many gas turbine and aerospace applications, machining is still required, which motivates further research on the machinability and work piece integrity of additive-manufactured superalloys. In this work, turning tests have been performed on components made with both Powder Bed Fusion for Laser Beam (PBF-LB) and Electron Beam (PBF-EB) in as-built and heat-treated conditions. The two AM processes and the respective heat-treatments have generated different microstructural features that have a great impact on both the tool wear and the work piece surface integrity. The results show that the PBF-EB components have relatively lower geometrical accuracy, a rough surface topography, a coarse microstructure with hard precipitates and low residual stresses after printing. Turning of the PBF-EB material results in high cutting tool wear, which induces moderate tensile surface stresses that are balanced by deep compressive stresses and a superficial deformed surface that is greater for the heat-treated material. In comparison, the PBF-LB components have a higher geometrical accuracy, a relatively smooth topography and a fine microstructure, but with high tensile stresses after printing. Machining of PBF-LB material resulted in higher tool wear for the heat-treated material, increase of 49%, and significantly higher tensile surface stresses followed by shallower compressive stresses below the surface compared to the PBF-EB materials, but with no superficially deformed surface. It is further observed an 87% higher tool wear for PBF-EB in as-built condition and 43% in the heat-treated condition compared to the PBF-LB material. These results show that the selection of cutting tools and cutting settings are critical, which requires the development of suitable machining parameters that are designed for the microstructure of the material.