12th International Conference on Zinc & Zinc Alloy Coated Steel Sheet - GALVATECH Highlight Symposium 2022Hybrid conference

This talk will be focused on key mechanisms responsible for Liquid Metal Embrittlement of Zn coated AHSS, making use of some of the key results that were presented during the Galvatech’2021 remote conference.
The four required conditions that must be met for LME to occur will be discussed: the presence of a liquid phase in contact with the solid, the presence of high energy grains boundaries at the solid surface for the GB complexion reaction to occur (giving a liquid like mechanical behaviour to the wetted GB), the presence of an applied tensile stress to trigger the GB opening, and the required deformation rate allowing GB to open before the Fe-Zn reaction can occur.
The role of steel chemistry will be discussed through the way it can decrease the Fe-Zn mutual solubilities and promote LME.
Possible differences between LME assessment through either Gleeble testing either spot welding will be highlighted.

Best Paper Winner Jean-Michel Mataigne, ArcelorMittal Global R&D, will present highlights from his Galvatech 2021 paper "Comparative Assessment of GI And GA Coated AHSS LME Sensitivity During Spot Welding". Selected highlights from other Galvatech 2021 automotive applications papers will also be summarized.

Each session will start with the 20 minute lecture, followed by a 20 minute panel discussion. This will be followed by 10 minutes of general discussion and a short break before beginning the next session.

Hot-dip galvanized (GI) and galvanneal (GA)-coated third generation steels have been developed and commercialized at minimum tensile strength levels at both 780 and 980 MPa. This GalvaTech Highlights presentation will discuss lessons learned in manufacturability and the importance of cultivating “Third Generation” properties outside of simple strength x elongation (MPa*%). A review of the other papers offered in the 2021 Galvatech Technical Areatitled “Challenges in Galvanizing Advanced High Strength Steels” revealed similar interesting insights into manufacturability and practical aspects of comprehensive material design. New findings, success stories, and challenges will be discussed.

Best Paper Winner Matthew M. McCosby, U.S. Steel Corp., will present highlights from his Galvatech 2021 paper "U. S. Steel 3rd Generation Steel: Customer-Friendly Chemistry, Properties, and Manufacturability Enabled by Unique Processing". Selected highlights from other Galvatech 2021 papers on recent advances in AHSS galvanizability will also be summarized.

Each session will start with the 20 minute lecture, followed by a 20 minute panel discussion. This will be followed by 10 minutes of general discussion and a short break before beginning the next session.

The high volume application of PHS material in state of the art Body-in-White concepts is driven by high variety of possibilities to adapt the properties of PHS parts perfectly to the needs. This is true not only in respect to the strength (500 up to 2000 MPa) - even locally - crash-performance and high weight reduction target, but also regarding surface properties. PHS part production controls final coating- and base materials formation and properties. The intermetallic coating formation due to press hardening is very complex on the one hand, but surprisingly robust on the other hand. Thus reasonable process windows are provided. New developments are targeting to extend application possibilities as well as to increase cost-effectiveness.
One example of unexpected robustness was outlined in the awarded paper. The risk of so-called 2’nd order micro cracking during part production of galvanized PHS parts at hot forming temperatures less than 750°C is very limited. The depth of the micro cracks does not exceed a few multiples of 10 µm due the micro crack formation mechanism resp. available amount of Zn atoms generated by cracking of the solidified ZnFe-coating in an oxygen depleted surrounding atmosphere. Micro cracking of galvanized PHS was the most discussed topic in session 3.
One paper was focusing on modifications of the AlSi coating composition by adding Mg and Zn to improve specific coating and surface properties like corrosion creepage and/or paint appearance. A further topic was the formation of the surface oxide on press hardened galvanized steel sheets including the effect of shot blasting. Avoiding of surface conditioning, like slight shot blasting, for galvanized PHS parts by specific in-line surface treatments is a very challenging but also very beneficial development goal. Another topic of interest is the modification of surface emissivity to increase heating rates in the furnace and/or to compensate different heating rates, as a consequence of different sheet thicknesses (TWB, TRB). This can be achieved by using GI or GA for galvanized coatings or also by darkening of the coating surface by in-line or off-line surface treatments as shown in one paper. For a very high strength level, hydrogen embrittlement is also an important issue as shown by the paper from VW in the automotive session. Reduction of coating thickness is in consideration for several reasons like improvement of bending resp. crash properties, especially for very high strength PHS material (> 1800 MPa). Surface decarbonisation treatment, is a further approach to increase bendability. Improvement of productivity of part production by development of countermeasures to minimize coating build up on PHS furnace rolls, preferable in cooperation with equipment suppliers, is a hot topic too.
To sum up there are enough questions to be answered, mechanism to be well-understood and other future development issues in respect to PHS coatings. Let us go for them.

Best Paper Winner Josef Faderl , voestalpine Stahl GmbH, will present highlights from his Galvatech 2021 paper "Avoiding Zinc Induced Cracking In Hot Forming". Highlights from other Galvatech 2021 papers on zinc-coated press hardened steel advances will also be summarized.

Each session will start with the 20 minute lecture, followed by a 20 minute panel discussion. This will be followed by 10 minutes of general discussion and a short break before beginning the next session.

ArcelorMittal Group is the first steelmaker to industrialize in 2016 the vacuum deposition technology called "Jet Vapour Deposition (JVD)", for the continuous deposition of zinc coatings on steel coils. Compared to conventional deposition processes such as Electro-Galvanizing (EG) and Hot-Dip Galvanizing (HDG), this technology has the potential to produce coated steels with coating configurations adapted to customer needs (single-sided, double-sided coatings with differential thicknesses of zinc on each side of the steel coils …), and this, with high levels of productivity. This technology allows also to coat steel grades with very high mechanical resistance properties (Advanced High Strength Steels - AHSS), without the major constraints of conventional processes. Indeed, on one hand, JVD technology doesn’t lead to hydrogen pick up in steel, thus making steel insensitive to delayed fracture, which is the major drawback of EG process for AHSS. On the other hand, this technology overcomes the problems of zinc wettability and so of coatability issues encountered on some AHSS with HDG process, due to the presence of oxidizable elements. After 6 years of industrial production, this industrialization can be considered today as a success. Indeed, a total of more than 600,000 tons was produced at the end of 2021, and forecasts indicate that annual volumes should grow, allowing the industrial line to reach its maximum capacity. To achieve this success, numerous preliminary studies and developments were necessary to make the JVD technology compatible with the industrial constraints of a high-speed deposition line (up to 200 m/min at the moment): continuous operation over several weeks, management of formats and types of steel, management of coating thicknesses… An overview of these developments will be presented during the lecture.

Best Paper Winner Daniel Chaleix of ArcelorMittal (current presenting author at GALVATECH Highlight will be Sergio Pace), will present highlights from his Galvatech 2021 paper "JET VAPOUR DEPOSITION: A TECHNICAL ECONOMIC ALTERNATIVE TO ELECTRO-GALVANIZING FOR ZN COATINGS OF FUTURE STEELS". Selected highlights from other Galvatech 2021 papers on recent advances in PVD, electrogalvanized coatings and non-automotive applications will also be summarized.

Each session will start with the 20 minute lecture, followed by a 20 minute panel discussion. This will be followed by 10 minutes of general discussion and a short break before beginning the next session.

The Galvatech 2021 session entitled “Furnace pre-treatments for Hot Dip Galvanizing lines” contained 14 excellent contributions from renowned experts in the field of galvanising and furnace control.
The continuing demand for new and stronger advanced high-strength and ultra-high strength steels, imposes challenges to combine desired substrate properties with stringent requirements on coating and surface quality. These new A/UHSS grades require more complex annealing cycles with increasingly lower thermal tolerances. This complexity entails a need for increased cooling rates and top temperatures, as well as the capability for intermediate cooling and reheating for quench & partitioning processes.
For the successful production of challenging A/UHSS grades, a well-balanced and controlled process starting from upstream processing down to continuous hot-dip galvanizing is crucial. Knowing the variations in the incoming product and anticipating accordingly with adjustments in furnace settings is good practice. For example, variations in emissivity along the coil length and width can affect the heating rate during the annealing cycle, potentially resulting in undesired inhomogeneities in mechanical properties and other product inconsistencies.
The new A/UHSS steels are harder to galvanize due to an increased alloy content, for which a tighter atmosphere control is required, with often an oxidation step or dew point control. External selective oxidation can – apart from resulting in a poor galvanized surface – also result in build-up on furnace rolls, which may lead to defects on the steel strip. Roll coatings can prevent or minimize this oxide pick-up. Furthermore, the challenging product mix for many galvanizing lines nowadays demands flexibility in terms of coil width and gauge and temperature cycle. This comes with the necessity for increased flexibility to adapt furnace settings accordingly, which may impact lifetime expectancy of the equipment and maintenance schedules.
In the presentation results will be given from flash oxidation in an annealing simulator, in which the growing Fe-oxide layer is being monitored by an in-situ RGB camera. This will be followed by selected highlights from the session, addressing some of the challenges mentioned above.

Best Paper Winner Marga Zuijderwijk, Tata Steel Europe Research and Development, will present highlights from her Galvatech 2021 paper "Evaluation of Iron-Oxide Layers During Flash Pre-Oxidation in an Annealing Simulator". Selected highlights from other Galvatech 2021 papers on furnace pretreatment advances will also be summarized.

Each session will start with the 20 minute lecture, followed by a 20 minute panel discussion. This will be followed by 10 minutes of general discussion and a short break before beginning the next session.

Zinc and zinc alloyed coated steel are widely used in the automotive and construction industries. Although these materials provide good corrosion protection under atmospheric weathering conditions it is important to monitor the corrosion rate in-situ and in real time for various applications. Different monitoring techniques have been developed during the last decades. The presentation will first review the progress in monitoring atmospheric corrosion for zinc and zinc alloyed coated steel. Example of use of corrosion sensors based on either electrical resistance or electrochemical measurements will be given under various exposure conditions (e.g. cyclic corrosion tests, exposure at atmospheric field station, mobile exposure on vehicle). From the results, it is possible to better understand the atmospheric corrosion of zinc in particular the effect of different climatic parameters such as chloride deposition, temperature and relative humidity. It is also shown that the galvanic sensor may also be used to evaluate the current demand at cut edges of galvanized steel. These sensors should also allow the design of reliable and realistic corrosion tests for different industrial applications and provide a better understanding of the atmospheric corrosion of zinc.

Best Paper Winner Dominique Thierry, French Corrosion Institute, will present highlights from his Galvatech 2021 paper "Recent Advance in Corrosion Monitoring of Atmospheric Corrosion of Galvanised Steel and Zinc Alloyed Coated Steel". Selected highlights from other Galvatech 2021 papers on advances in our understanding of corrosion and hydrogen embrittlement will also be summarized.

Each session will start with the 20 minute lecture, followed by a 20 minute panel discussion. This will be followed by 10 minutes of general discussion and a short break before beginning the next session.

Under certain conditions of oxygen shortage and high temperatures as could occur after coiling a hot-rolled strip, alloying elements can diffuse and oxidise preferably along grain boundaries, causing a depletion zone of solute alloying elements in the surface near region. When oxides are present along grain boundaries, pickling can alter surface topography by selective dissolution of these oxides on the µm-scale (µ-topography).
In this lecture I would like to introduce you into the principles of grain boundary oxidation in hot strip and its influence on the subsequent processes.
This grain boundary oxidation in hot rolled state leads to surprisingly visible effects on the µ-topography before galvanising. This altered topography and the depletion of alloying elements influence diffusion properties during intercritical annealing prior to hot-dip galvanising, leading to a reduced surface segregation of alloying elements. Surfaces with altered µ-topography show lower surface segregation of alloying elements, can build more dense inhibition layers during hot-dip galvanising with the same annealing conditions, and exhibit improved coating adhesion. This effect could be helpful to enhance galvanisability of future challenging steel grades.
Furthermore, I will give a short overview of the topic “Developments in On-Line Coated Steel Measurements & Coating Analysis”. In this thematic field, I will present a selection of exciting findings on the topics of coating characterisation, surface inspection systems with deep learning and interesting analytical methods in a short overview.

Best Paper Winner Nils Köpper, Salzgitter Mannesmann Forschung GmbH, will present highlights from his Galvatech 2021 paper "ON GRAIN BOUNDARY TOPOGRAPHY AND SURFACE REACTIVITY DURING HOT-DIP GALVANISING
". Selected highlights from other Galvatech 2021 papers on advances in our understanding of coating analysis and on-line measurements will also be summarized.

Each session will start with the 20 minute lecture, followed by a 20 minute panel discussion. This will be followed by 10 minutes of general discussion and a short break before beginning the next session.

In order to make sure the reliability/accuracy of the snout pyrometer (multiwavelength) for various steel grades (e.g. DP600, DP780 and DP980 etc.) and to monitor the deterioration of the pyrometer due to Zn dust buildup or other causes, predictive models were developed for #5CGL, ArcelorMittal Dofasco. Two approaches (a regression method based on rapid cool wedge-pyrometer readings, and a Zn bath thermal balance method based on Zn pot thermocouples readings) were developed and compared. Based on model evaluation, the snout pyrometer generally provides a reliable measurement, including for DP grades.

Best Paper Winner Weimin Zhong, ArcelorMittal Dofasco, will present highlights from his Galvatech 2021 paper "Snout Temperature Predictive Model and Zn Pot Thermal Balance". Selected highlights from other Galvatech 2021 papers on advances in bath management, pot hardware and coating formation will also be summarized.

Each session will start with the 20 minute lecture, followed by a 20 minute panel discussion. This will be followed by 10 minutes of general discussion and a short break before beginning the next session.

The solution of the Navier Stokes equation is analyzed and discussed for low speed and heavy coatings. The question of return flow to the bath due to wiping in relation with line speed and coating weight is addressed. Special attention is dedicated to the edge effect that is related to a non uniform return flow. From the analysis, the max coating weight that can be reached industrially on wide and smooth strip is proposed in relation with the line speed.
Then will be presented a quick review of key results from the the paper presented in the wiping session of the June 2021 Conference.
Finally, a list of the pending question on air knives and coating uniformity as well as future challenges will be proposed to the audience for debate

Best Paper Winner Michel Dubois, recently retired from John Cockerill, will present highlights from his Galvatech 2021 papers “Production Of Heavy Coating At Low Line Speed” and “Pot Roll Geometry and Crossbow Correction” Selected highlights from other Galvatech 2021 papers on advances in coating control will also be summarized.

Each session will start with the 20 minute lecture, followed by a 20 minutes panel discussion. This will be followed by 10 minutes of general discussion and a short break before beginning the next session.