Resource efficient NANO-steels through in-situ and simultaneous studies of the precipitation and phase transformation kinetics.
Researchers: Chrysoula Ioannidou, Zaloa Arechabaleta Guenechea, Arjan Rijkenberg, Ad van Well and Erik Offerman
Steel consumption and CO2-emissions can be reduced simultaneously with NANO-steels that have been developed for lightweight automotive applications and high-rise buildings for fire-resistance. The drawback of NANO-steels is that they rely on considerable micro-alloying additions, including Niobium, Vanadium, and Molybdenum that form the essential nanometer-sized precipitates. Moreover, Niobium is considered to be a critical raw material for the EU, because the supply risk is high. The challenge is to design and produce NANO-steels that are more resource-efficient by a factor of 2 or more and that contain less or no critical raw materials, while at the same time maintain or improve their excellent mechanical properties. For this challenge we need to: 1) disentangle the effects of different micro-alloying additions on the nano-precipitation kinetics, 2) disentangle precipitation kinetics and the solid-state phase transformation kinetics, and 3) unravel the indirect effects of Manganese, Chromium, and Molybdenum on the nano-precipitation kinetics via the solid-state phase transformation. The novelty of our approach lies in a balanced combination of model alloys, heat-treatments, neutron scattering techniques, atom probe tomography, and simulation methods. Unique will be the combination of small-angle neutron scattering and neutron diffraction to study, simultaneously and in-situ, the interaction between the precipitation kinetics and phase transformation kinetics. This is possible thanks to the development of the Larmor instrument at ISIS (see http://www.isis.stfc.ac.uk/instruments/Larmor/). The overall result will be fundamental insight into the role of individual chemical elements on the precipitation and phase transformation kinetics, which is deemed essential for the development of NANO-steels with reduced amounts of alloying elements without compromising properties.
This project is performed in close collaboration with:
The project is supported by STW, M2i, Tata Steel, Nedschroef, and VDL Weweler
The role of silicon in strip steels
Researchers: Monika Krugla, Dave Hanlon, Jilt Sietsma and Erik Offerman
Advanced High Strength and Ultra High Strength Steels (AHSS and UHSS) are increasingly employed in automotive applications due to their attractive balance of strength and ductility. The balance of properties is attributed to complex microstructures comprising mixtures of phases. Alloying strategies that incorporate significant silicon (Si) additions proliferate. Most of these strategies aim to utilise Si to retard the formation of cementite and in turn to keep carbon free for partitioning to metastable austenite during a range of phase transformation phenomena. Since each phase has unique properties they affect the deformation behaviour differently. Researchers claim that the key to optimising performance is achieving a homogeneous dispersion of phases on micro- and mesoscale. In many cases, for steels produced as strip, the microstructure exhibits heterogeneity in the form of interchanging bands of softer and harder phases. The often cited root cause of this is micro-chemical segregation formed due to the casting and rolling processes. As a result strip comprises lamella with varying compositions and therefore local variations in the critical transformation temperatures. While the thermodynamic parameters are well known and the influence of alloying elements thereupon already explored, the kinetics of this process are still under investigation. Another complication arises from the fact that commercial steels are invariably multicomponent alloys. Therefore, it is difficult to decouple the effects of individual elements on microstructural banding and the resulting mechanical properties. The aim of this study will be to determine the effects of Si on microstructural evolution and properties across a range of contemporary and future AHSS strip substrates. It is hoped, that by judicial selection of the substrates to be studied, that more light can be shed on the roles of the individual microstructural mechanisms that take place during processing.
This project is performed in close collaboration with Tata Steel
Sustainable Rare-Earth Metal Cycles
From waste to high-value alloys.
Researchers: Chenna Borra, Yongxiang Yang, Thijs Vlugt and Erik Offerman
The increasing popularity of hybrid and electric cars, wind turbines and compact fluorescent lamps is causing an unprecedented increase in the demand for rare earth metals (REM), which is expected to grow faster than primary supply. Recycling of REM from pre-consumer scrap and “urban mines” is a strategic necessity. However, as recently pointed out in the United Nations Environmental Program report Recycling Rates of Metals (2011), less than 1% of the rare earths are currently being recycled, mainly due to inefficient collection, technological problems and lack of incentives. One of the challenges is to solve the ‘balance problem’: there is an oversupply of light REM (e.g. La and Ce) and a limited supply of heavy REM. This makes recycling of light REM economically less attractive at this moment. The balance problem is the result of the composition of the rare earth ores consisting of all 17 rare earth elements, which are mined together. The project aims at an efficient recycling method for a particular waste stream of light REM, and using the recycled REM as alloying elements in high-value alloys for light-weight automotive applications. In other words, the project aims to combine rare earth recycling technologies and metals processing technology to turn waste containing light REM into high-value alloys.
This project is performed in collaboration with VITO.