Unlocking the effect of residual elements via the NANOengineering of Sustainable MARTensitic steels

Informazioni relative al progetto

NANO-S-MART

ID dell’accordo di sovvenzione: 101178431

DOI

10.3030/101178431

Data della firma CE 1 Ottobre 2024

Data di avvio 1 Novembre 2024

Data di completamento 31 Ottobre 2028

Finanziato da

• Digital, Industry and Space

Costo totale

€ 3 079 420,00

Contributo UE

€ 3 079 420,00

Coordinato da

ASOCIACION CENTRO TECNOLOGICO CEIT
Spain

Periodic Reporting for period 1 - NANO-S-MART (Unlocking the effect of residual elements via the NANOengineering of Sustainable MARTensitic steels)

Periodo di rendicontazione: 2024-11-01 al 2026-04-30

Sintesi del contesto e degli obiettivi generali del progetto

The European steel industry is at a critical juncture, facing intense global market conditions while working to meet ambitious climate change commitments. As the most energy-consuming manufacturing sector in Europe, iron and steel production is responsible for 5.7% of the total greenhouse gas emissions in the EU. To help meet global climate goals like the Paris Agreement and the European Green Deal, which aim for net-zero emissions by 2050, steel companies such as ArcelorMittal are committed to transitioning toward cleaner production methods. This involves moving away from traditional processes (Blast Furnace/Basic Oxygen Furnace, BF/BOF) toward technologies based on electric furnaces (EAF) and greater use of recycled steel scrap, significantly reducing emissions. While increased scrap use supports decarbonization and circular economy principles, it also introduces higher levels of residual elements (e.g. Cu, Sn, As, Sb, P), which can significantly affect processability and mechanical performance. The NANO-S-MART project was launched to address this challenge, focusing specifically on high-performance martensitic steels. These special steels are vital to EU competitiveness across strategic sectors, including construction, automotive, energy, and defense. In this context, the overall objective of the NANO-S-MART project is to systematically assess the impact of increased residual element levels and processing conditions on a C-Mn-Si-B reference martensitic steel across multiple length scales (macro-, micro- and nano-scale). To reach these goals, the project is structured around six specific objectives (SO):
• SO1: Quantify the impact of residual elements on tensile properties and damage resistance under critical processing conditions (wave 1) and define optimized alloy compositions (wave 2).
• SO2: Assess the influence of residual elements on hot processability, including hot ductility, hot working, and phase transformation behaviour.
• SO3: Investigate damage mechanisms at micro- and nano-scale, including crack initiation and propagation, and the role of residual elements around critical microstructural features (IMFs).
• SO4: Analyze nanoscale segregation and precipitation phenomena in relation to processing conditions and element interactions.
• SO5: Develop predictive models using ab initio calculations, machine learning, and diffusion simulations to describe thermodynamic and kinetic effects of residual elements.
• SO6: Define guidelines for the nano-engineering of martensitic steels to accommodate higher residual levels while meeting stringent performance requirements.
The expected impact of this project is profound both environmentally and economically. Increasing scrap usage by 10% in the European martensitic steel market (~4 Mt) could reduce CO2 emissions by approximately 600,000 tonnes per year, corresponding to an estimated €60 million in annual savings under current carbon pricing. Furthermore, NANO-S-MART supports EU circular economy objectives by enabling greater internal recycling of steel scrap, reducing dependence on exports and strengthening raw material security.

Lavoro eseguito dall’inizio del progetto fino alla fine del periodo coperto dalla relazione e principali risultati finora ottenuti

To translate its objectives into practice, the NANO-S-MART project has conducted extensive scientific and technical activities, bridging industrial processing (macro and micro-scale) with nano-scale analysis. The project successfully the ranking of the impact of individual residual elements on high-performance steel behaviour for wave 1 materials. This stage included tensile and Charpy impact tests performed under Direct Quenching (DQ) and Re-Austenitization and Quenching (RAQ) conditions, supported by a comprehensive literature review. This work established a baseline ranking of the detrimental effects of five residual elements under representative processing conditions. Similarly, the industrial feasibility of casting and hot-rolling high residual level steels was extensively mapped. To simulate casting, hot tensile tests were executed across representative bending/unbending operation conditions. Furthermore, torsion and bending tests were carried out to evaluate susceptibility to micro-cracking and structural embrittlement during the rolling process.
To see exactly where material failure originates, the project transitioned to microscopic mechanical tracking. Over 5,000 nanoindentation measurements were performed to map local strength variations. To better link these measurements to real mechanical behavior, micropillars were fabricated using Focused Ion Beam (FIB) within a Scanning Electron Microscope (SEM) and subsequently compressed, covering 240 pillars across 24 distinct material conditions.
For understanding how impurities segregate, mapping of the materials nanoscale structure is required. For this purpose, EBSD characterization was completed for all materials, followed by Atom Probe Tomography (APT). Results revealed homogeneous carbon distribution and strong phosphorus segregation at critical defects. To support these findings, ab initio simulations have been developed to model impurity segregation at grain boundaries. Initial results quantified copper segregation, with ongoing work extending to phase transformations and carbon-impurity interactions.
Finally, a Life Cycle Assessment (LCA) is being carried out through the definition of a ‘Cradle-to-Gate’ environmental framework. Production routes in BOF and EAF plants have been mapped, enabling correlations between operational practices and contamination levels, and supporting the development of guidelines for low-CO2 steel production.

Progressi oltre lo stato dell’arte e potenziale impatto previsto (incluso l’impatto socioeconomico e le implicazioni sociali più ampie del progetto fino ad ora)

The NANO-S-MART project aims to deliver advances beyond the current state of the art by addressing key scientific and technological gaps in the understanding of residual elements in high-performance martensitic steels.
Existing literature shows that research on residual elements is largely fragmented and incomplete. Most studies have focused on phosphorus and on low-strength ferritic steels, with only limited investigations into other residual elements such as Cu, Sn, Sb, and As. Furthermore, systematic studies on high-strength martensitic steels (1200-1500 MPa) are largely missing. At the current stage of the project, significant progress has already been achieved on the wave 1 materials, where the impact of individual residual elements is being analyzed.
The project has already gone beyond the state of the art by establishing a first systematic and quantitative ranking of the impact of five key residual elements (Cu, Sn, As, Sb, P) on tensile properties and toughness in high-strength martensitic steels under representative industrial processing routes (DQ and RAQ). In parallel, and complementing the mechanical property evaluation, the project has also assessed industrial processability at the macro-scale. Hot tensile, torsion, and bending tests were conducted to evaluate susceptibility to micro-cracking and structural embrittlement during casting and hot rolling operations.
Substantial progress has also been achieved at the microscale. Nanoindentation mapping and micro-mechanical testing have enabled the identification of local strength variations. Ongoing analyses are providing insight into impacted microstructural features (IMFs) governing damage initiation and propagation, an area that remains poorly understood in the literature.
At the nanoscale, the project’s objectives remain ahead of the current state of the art, but results are not yet fully available at this stage. Ongoing work focuses on applying Atom Probe Tomography (APT) to quantify segregation of residual elements at specific microstructural features and on establishing direct correlations between local chemistry and mechanical behaviour. In parallel, modelling activities based on ab initio calculations and machine learning are underway to describe thermodynamic and kinetic effects of residual elements and their interactions. These activities are expected to deliver key breakthroughs in the next phase of the project.