Short-Term Formation Kinetics of the Continuous Galvanizing Inhibition Layer on Mn-Containing Steels

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1 Seminar MATLS 702 Short-Term Formation Kinetics of the Continuous Galvanizing Inhibition Layer on Mn-Containing Steels By Samaneh Alibeigi Supervisor Dr. J.R. McDermid September 25, 2012

2 Galvanizing and Inhibition Layer Zinc coating steel Zinc Coating Steel Interfacial Layer Zn Al Zn Al Zn Fe Al Al Zn Zn Minor Addition ( wt%) of Aluminum to the Zinc Bath Fe steel Zinc Pot (Zn - Al) Fe-Al interfacial layer Interfacial Layer of Fe-Al Intermetallic Phase(s) No Fe-Zn Intermetallic Compounds Ductile and Adhesive Coating 2

3 Continuous Hot-Dip Galvanizing Furnace (Annealing) Zinc Pot (Dipping) Schematic of continuous hot-dip galvanizing process. [E.A. Silva (2007)] 3

4 [Fine et al., 1979, Kubaschewski et al., 1977] Mn Selective Oxidation The presence of Mn is essential for obtaining the desired mechanical properties, but leads to the formation of surface MnO during annealing. 4

5 t MnO (nm) Aluminothermic Reduction 3MnO 2Al Al O 3Mn ( Bath) 2 3 ( Bath) -50 Δt(MnO) t (MnO) t (MnO) initial final Al 2 O reaction time (s) Change in MnO layer thickness vs. reaction time. 5 * R. Khondker et al., Mater.ials Science & Engineering A, 463 (2007) 157 ** R. Kavitha and J. McDermid, Surface & Coatings Technology (Accepted)

6 Research Objectives The objectives of the present research were to investigate the interfacial layer formation as a function of bath Al content, substrate Mn content and reaction time (i.e. sum of dipping time and solidification time), including the effect of the MnO layer arising from the selective oxidation. 6

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8 Compositions of Experimental Steels (wt.%) Alloy Name C Mn Mo Si Nb Al 0.2Mn Mn Mn Mn Alloy Name Annealing Parameters PAT [ C] N 2 [vol.%] H 2 [vol.%] Dew Point [ºC] po 2 [atm] 0.2Mn E Mn E Mn E Mn E-25 Dipping Parameters Bath Temperature [ºC] Bath Dissolved Al Content [wt%] Dipping Time [s] , /0.7/1/1.5/ 2/2.5/4/6 8

9 Schematic Figure of Steel Panel Dimensions and Spot Cooler Position 200 mm Quench Spot A helium jet spot cooler with a flow rate of 500L/min was used to rapidly solidify the zinc coating and arrest the interfacial reaction. The actual reaction time was calculated by summing the dipping and solidification times. 120 mm 9

10 Experimental Apparatus McMaster Galvanizing Simulator Load steel panel / Cooling Infrared Furnace Helium jet spot cooler Zinc Pot 10

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12 XPS Depth Profiles of Annealed Samples Measured Binding Energy (ev) Fe 2p/2 Mn 2p3/2 Mn 2p1/2 O 1s State (Compound) MnO, Fe (metallic) 12 [Franzen et al., J. Solid State Chem., 18 (1976) 363.] [Foord et al., Philos. Mag. A, 49 (1984) 657.]

13 AES Mapping of Steels Surfaces Prior to Dipping 1.4Mn 2.5Mn 3.0Mn 13

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15 ICP Analysis- Al Uptake of the Interfacial Layer Zinc Coating Steel Fe-Al Inhibition Layer ICP Image Analysis 15

16 ICP Analysis- Al Uptake of the Interfacial Layer 2s reaction time 4s reaction time 7s reaction time 16

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18 SEM Analysis of Interfacial Layer 0.2Mn Steel 0.2Al 1µm 1µm 2.1s 7.6s 0.3Al 1µm 1µm s 7.6s

19 SEM Analysis of Interfacial Layer 2.5Mn Steel 0.2Al 1µm 1µm 2.2s 7.7s 0.3Al 1µm 1µm s 7.7s

20 Summary Significant Mn segregation to the surface in the form of MnO during annealing was observed for the wt.%mn steels. Mn enrichment occurred primarily along the grain boundaries and adjacent areas. In addition, oxide nodules with areas of metallic iron between them were observed. The Al uptake increased with increasing reaction time for all experimental steels. However, for 0.3Al bath, a significant increase in Al uptake was observed for 2.5Mn and 3.0Mn steels at higher reaction times that can be explained by aluminothermic reduction and defective-microstructure subsurface (due to the formation of MnO). Finer and more compact interfacial layer morphology was observed for 0.3Al bath due to the higher nucleation rate at higher Al bath content. This, also, can explain the lower Al uptake for 0.2Mn and 1.4Mn steels at 0.3Al bath. S. Alibeigi, R. Kavitha, R.J. Meguerian and J.R. McDermid, Investigation of Reactive Wetting of High Mn Steels during Continuous Hot Dip Galvanizing, Acta Materialia, 59 (2011)

21 Acknowledgments Supervisory Committee Member: Dr. Joe McDermid, Dr. Ken Coley, Dr. Joey Kish John Thomson, Mariana Budiman, Ray Fullerton, Chris Butcher, Dr. Steve Koprich, John Rodda, Doug Culley, Fred Pearson, Julia Huang, Mark MacKenzie U.S. Steel Canada, Xstrata Zinc, the Natural Science and Engineering Research Council of Canada (NSERC) and the members of the McMaster Steel Research Centre for their financial support USSC for provision of experimental materials (IF and CMn) and the AUAF program of MTL-CANMET for fabrication of the two high Mn steels. Li Sun (ArcelorMittal Dofasco) for the XPS analysis Shihong Xu (ACSES, University of Alberta) for the Auger analysis 21

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