Monday 5 December 2022

 *Programme subject to change 



Registration open


Welcome Address



Session 1: Oxidation Mechanisms, Properties, Morphology & Control


Keynote: Model-based assessment of the mechanical parameters for oxide scale fracture


Descaling processes can be based on the effect of mechanical stresses to remove the unwanted oxide scale independent of how these stresses are applied, e. g. in reverse bending. For a better adjustment of the parameters in the descaling process a (semi-) quantitative knowledge of the stress situation during the descaling process is required as well as knowledge on the oxide scale structure and on the parameters for fracture of the oxide. The latter has been a subject of research in high temperature materials science since the early work of U. R. Evans in the middle of the last century who came up with a first quantitative description of scale fracture as a function of scale thickness. Meanwhile there is a more profound understanding of mechanical scale failure based on a number of well-elaborated equations taking into account the relevant material parameters. These equations can be used for assessing and optimizing the parameters for the descaling process of oxides on steels. In the paper the different models and equations will be presented and evaluated together with experimental data from the literature and from own measurements. It will also be described how new oxide data can be measured with the respective laboratory equipment. Besides more complex approaches a pragmatic concept using data from metallographic investigations can provide a useful tool for assessing the mechanical parameters needed for scale removal, the   -c – concept. This approach will be described in some detail including data from the literature for different oxides but first of all with data on iron oxides. The approach offers a significant industrial potential for the adjustment of oxide descaling processes in steel industries.



Study of internal oxides formed during hot coil cooling and their evolution during pickling


Grain boundary oxides are formed during strip coil cooling of alloyed steels. The tertiary scale gets reduced due to the formation of alloy oxides in grain boundaries and bulk of the steel near surface. When pickled, the iron oxides are removed in the first seconds while after longer pickling times the grain boundaries are etched. We will show the results of experiments on both predicting the depth of internal oxides in coils and the determination of optimum pickling times to remove them before cold rolling.


  15:40 Refreshments, exhibition & networking

Oxidation of a dual phase steel during rapid alloy prototyping


The growth of oxide scale during high temperature processing routes such as reheating and rolling has a large influence on the surface quality of steels and can result in large quantities of metal loss during steelmaking. Within recent years, research focussed on rapid product development has resulted in the simulation of the integrated steelmaking route, allowing representative steel samples to be generated and processed on a laboratory-scale.  This study explores the effects of oxidation behaviour on a dual phase steel, DP800, using small-scale samples produced through Rapid Alloy Prototyping. In terms of oxidation, the limitations and opportunities of Rapid Alloy Prototyping are not yet fully understood. Experimental interrupted oxidation investigations have been conducted on both Rapid Alloy Prototyping and plant-generated samples to understand the scale growth evolution in DP800, with the intention of determining whether the laboratory route can be comparable and representative of processes taking place on an industrial scale, and to determine if Rapid Alloy Prototyping is suitable for oxidation studies.



Oxidation behaviour and oxide/metal interface characteristics in a low-carbon steel containing impurities


Residual elements have been added to a low carbon steel to simulate the scenario of scrap recycling during steel production. Five alloys were studied (in wt pct): Base, 0.15 Cu-0.15Ni- 0.03Sn, 0.30Cu-0.30Ni-0.06Sn, 0.60Cu-0.15Ni-0.06Sn, and 0.60Cu-0.30Ni-0.06Sn. The samples were oxidized in air at 1180°C for 3 hours using thermogravimetry analysis (TGA) to simulate reheating stage. Scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) were employed to characterize the oxides/metal interface. The effect of residual elements on oxidation rate and interface characteristics has been studied. TGA results showed that the oxidation rates increased and then decreased as the contents of residual elements increased under current experiment condition. FactStage software was used to predict the equilibrium phases at the interface, and agreements between the predication and experimental results were obtained.



Importance of roll oxide formation to improve hot rolling campaigns with high quality strip surface


S. Flament, Program Leader &  H. Uijtdebroeks, Activity manager, CRM Group, Liege, Belgium
Z. Koont, Program leader, ArcelorMittal Global R&D – Hamilton, Ont., Canada

The importance of the roll oxidation has already been observed in the 90’s when implementing the Rollscope in industrial rolling mills.  Roll oxidation is a complex process combining thermal, chemical and mechanical actuators. The formation of an adequate oxide layer strongly determine the performance of work rolls in a rolling stand with respect to roll friction and its degradation.

Within the RFCS European project “Mastering Rolls II”, new developments like a full non-destructive roll oxide thickness measurement by XRF and roll pre-oxidation have been further assessed. This paper will give a complete overview on the complex phenomenon of roll oxidation and its benefits for the hot strip mills.


The impact of oxidised powder particles on the microstructure and mechanical properties of Ti-6Al-4V processed by laser powder bed fusion


In selective laser melting (SLM) heat diffusing from the melt pool promotes the growth of surface oxide layers on powder particles surrounding the built part, and material ejected from the melt pool oxidises rapidly before landing on the powder bed, creating local variability in the oxygen content of any used powder. Although large particles are removed when recycling, smaller oxidised particles (the size of the specified powder for the machine) and oxide residue (<10 µm) are not removed and become incorporated into subsequent builds on powder reuse. This paper considers the effect these oxidised particles may have on part integrity and how they affect mechanical failure. In this research, grade 23 Ti-6Al-4 V metal powder was artificially oxidised to produce a range of interference colours that correspond to specific oxide thicknesses. Powder characterisation established the oxygen wt% of each coloured powder. Yellow and blue powder were chosen for further investigation as in the context of this study, they represent low (0.4 wt%) and high (0.7 wt%) oxygen levels respectively. Tensile builds were produced using SLM with a known feedstock layer, part way up the build, formed of a blend of oxidised and virgin particles. Tensile tests were performed for each build to evaluate the failure modes. Microscopy techniques were used to examine the material near the fractured region, including chemical composition and semi-quantification of the oxygen levels, allowing any microstructural and chemical changes to be investigated. It was shown that the region doped with oxidised particles negatively affected the mechanical properties of the final build, as they produce mechanical (oxide films/residue) and chemical flaws (interstitial elements). Unless these particles can be removed from recycled feedstock their effects will limit the reuse of powder, especially in safety critical industries, significantly increasing the costs of components produced by this route.


  18:15-19:45 Drinks & canapés
Tuesday 6 December

 *Programme subject to change 

Tuesday 6 December 2022


Session 2: Oxide Removal & Conditioning


Keynote: Optimisation of hydraulic descaling and effect on heat transfer


Hydraulic descaling is widely used to remove oxide layer from hot steel. The study of quality of water jets generated by high pressure flat fan nozzles is presented as well as effect of wear during long time usage or under extreme conditions. Optimization of nozzle setup as well as alternative descaling systems are presented and the effect on quality of descaling is shown with focus on maximum impact, overlap, and energy saving. As the water jets hit the hot product, intensive, but in most cases unwanted, cooling occurs. The effect of optimum configuration on heat losses is also presented as well as rapid increase of cooling during low descaling speeds. In often cases the descaled surface is not perfectly clean. The cause of uneven cooling during heat treatment is discussed and it is shown that it can be caused by residual scales.



Micro-indentation study of stresses and cracks in the oxide layer during descaling


During high pressure descaling, the local fast very fast cooling creates stresses in the oxide through time-dependent differential contraction. This results in cracks first through the oxide layer, next at the metal scale interface and finally the oxide layer is peeled-off.
In this study we analyze the transformation of the oxide layer by these constraints. For that micro-indentations are carried out, both at room temperature and at the process temperatures. Simulating the experiments by FEM including Cohesive Zone Modelling give insight into crack location and lengths. It also gives fracture stresses criterion which aimed to be used in a future global modeling of hydraulic descaling.
The experimental work consists of oxidizing carbon steel samples and next indenting them out at 25°C, 600, 700 and 800°C with a Berkovich indenter using Alemnis HTM800 inside a SEM.
For all tests done at 25°C, circular and corner cracks are visible in surface. FIB cross-sections show delamination. At 600°C/700°C, only part of the indentations develops cracks, probably depending on local defects. At 800°C, over the brittle to ductile transition, no cracks, whatever the indentation conditions were found. In these tests, the transition temperature depends on strain rate: high speed hardens oxide. This agrees to other mechanical tests on scale found in literature.
As a conclusion to have an effective descaling, the oxide layer should be cooled down below the transition temperature before the underlying metal starts to contract. Fracture stress criteria that were determined here will implemented in future thermo-mechanical FE simulations of descaling.



Oxygen depletion in front of the finishing stands


The hot rolling of some high strength steel grades is a main concern for the hot strip mill to assure a high surface quality.  In the RFCS Infire project new (oxygen depletion, micro dimples) and existing (lubrication, skin cooling) roll bite actuators have been studied on a DP800HpF grade and Strenx700MC grade.  The most promising actuator was oxygen depletion just in front of the first rolling stand.  During these first trials oxygen depletion was obtained on the CRM hot rolling pilot line by installing a tunnel with nitrogen between the reheating furnace and the rolling stand.  Installing a tunnel is however not possible in industry as it would be damaged by ski head ends, cobbles and/or threading refusals.  As already a reduction of oxygen to 10% would have a significant impact a more robust way to apply the nitrogen has been studied during the last years on the continuous hot rolling pilot line.  The principle is to apply nitrogen by a flat jet spray nozzle only directly at the exit of the reheating furnace and by this have a strong influence on the start of tertiary oxidation.  In this presentation the results will be discussed. 


  10:15 Refreshments, exhibition & networking

Session 3: Oxide Scale Behaviour, Modelling, Coating, Characterisation & Detection


Using models to address scale issues


Most of the work done by an expert in oxidation and surface defects is metallographic analysis, in depth process analysis and laboratory furnace experiments. But numerical simulations bring additional understandings of the phenomena occurring on the hot surface. These can be a help finding solutions. 

In this presentation, I illustrate a few practical situations where using computations gave clues about the management of the hot metal surface: scale amount and surface defects during hot rolling.  



Combining experimental and numerical modelling approaches for predicting short-time high-temperature surface oxidation behaviour of iron alloys


High-temperature oxidation occurs at various stages during the steelmaking process. Due to oxidizing in high temperatures and harsh atmospheres, it is practically impossible to observe the compositional changes in the steel surface and the formed oxide scales in-situ during steel production. Therefore, a coupled thermodynamic-kinetic numerical model is developed that predicts the composition profile of the steel alloy's constituents due to external oxidation for linear and parabolic growth. The model is applied to the high-temperature oxidation of Fe-Mn alloys. The kinetic parameters that serve as an input for the model are determined via oxidizing experiments with a Thermogravimetric Analysis (TGA) for different Mn contents (below 10 wt %). The mechanism of oxidation was determined by characterizing the oxidized samples with SEM-EDS and in-situ-XRD. The effect of different parameters such as temperature, oxygen partial pressure, and flow rate on the oxidation rate was studied and shows that the Mn depletion zone is strongly dependent on the oxidation rate. Also, some data analytics approaches for the determination of the kinetic parameters besides experiments are discussed. These serve as the input for the numerical model and high-temperature oxidation of steel during steelmaking could be simulated.


  12:30 Lunch, exhibition & networking

Oxidation behaviour of CrSi coatings deposited by magnetron sputtering technique


Materials like stainless steel exposed at higher temperatures result in a reduction of corrosion resistance, therefore necessitating protective coatings on them to improve their oxidation resistance at elevated temperatures. 

In this work, the compact and uniform CrSi (with different content of silicon) coatings were deposited on stainless steel alloy samples by a close filed unbalanced magnetron sputtering technique. The coatings on the samples were oxidised in air at 550, 700 °C and 800 °C for varied times. Mass changes after oxidation were measured to evaluate the susceptibility of the coating or scale to spallation. Characterisation of the coating before and after oxidation was evaluated through systematic analyses of surfaces and cross-sections using different techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The capability of the protective behaviour of the CrSi coatings was verified by the phase constituent change. 

The dense Cr2O3 oxide layer on CrSi coatings can significantly improve the oxidation resistance, and their weight gains are reduced. A small amount of Si in the chromium coating demonstrates a better performance as a large amount of silicon leads to the embrittlement of the coating.  



Leveraging infrared video imaging for in-line assessment of oxide descaler functionality and characterisation


Infrared video imaging of a moving steel strip following laminar cooling was used to assess and quantify the effectiveness of the strip mill descalers. Anomalous temperature values (i.e., cold spots) were observed on the strip surface. Finite element temperature modeling of the strip determined that the temperature anomalies are not associated with actual thermal variations and are likely due to localized variations in surface emissivity.  Post processing of the infrared images was used to determine the location and area fraction of these temperature anomalies. The transverse spacing of the  cold spots correlated with descaler positioning across the strip. The variation in location and area fraction of the temperature anomalies along the length of an individual strip indicate that the oxides in localized regions are exhibiting enhanced resistance to the descaling operation. 


  14:20 Roundtable discussion and Q&A
  14:50 Close of conferencce