ThyssenKrupp Steel Europe AG (Dortmund, Germany):

Norden M., Dr. Eng., Senior Engineer, martin.norden@thyssenkrupp.com
Blumenau M., Dr. Eng., Head of Continuous Annealing Line
Zaum A., Dr. Eng., Senior Vice President

ThyssenKrupp Steel Europe AG (Duisburg, Germany):

Peters K. J., Dr. Eng., Head of Process Technology

ThyssenKrupp Steel USA LLC (Calvert/Alabama, USA):

Schönenberg R., Vice President, Operations

The modern automobile requires the utilization of Advanced High Strength Steels (AHSS) for cold and hot stamping. Thyssen-Krupp Steel Europe is a key player in galvanizing regarding the use of pre-oxidation in radiant tube furnaces. This contribution is aimed at showing that pre-oxidation and dew point control are key technologies for the hot dip galvanizing AHSS. The present work aims at demonstrating how continuous annealing has to be controlled to hot dip galvanize and galvanneal Al- and Si-alloyed TRIP-aided AHSSs with superior surface quality utilizing HDGLs with all-RTF. Based on the results of presented investigations, galvanizing of a Si (1.5% mass content)-TRIP-aided steel becomes possible by utilizing preoxidation and thus controlling surface chemistry. Overall sub-surface structure is the key factor to ensure good adhesion results of the GI coating. Regarding the impact of pre-oxidation on the GA coating of Al (1.6% mass content)-TRIP-aided steel, it can be concluded that external segregated oxides of the alloying elements hamper the galvannealing kinetics of AHSS. To overcome the hampered galvannealing  properties it is useful to utilize pre-oxidation for the purpose of surface conditioning during annealing. By increasing the surface reactivity of AHSS by utilizing pre-oxidation, the coating structure can be altered positively. For controlling the surface chemistry of AHSS pre-oxidation has proven to be a very effective tool. Recent results show that even the hot-dip galvanizing of high-Mn alloyed TWIP steels seems to be possible, if an appropriate pre-oxidation treatment is performed. Furthermore, dew point control and pre-oxidation have to be incorporated in a closed-loop process to ensure high-quality coatings of present and future AHSS. To conclude, understanding how surface chemistry and sub-surface structure are controlled by annealing condition is the key to develop next-generation technologies for the hot dip galvanizing and galvannealing of AHSS.

1. Gomez, M.; Isaac, G.-C.; Haezebrouck, D.-M.; DeArdo, A.-J.: ISIJ Intern. 49 (2009) No. 2, S. 302/11. 
2. Heller, T.; Deinzer, G.-H.; Steinbeck, G.: Reducing time to market for new steel by defining a material approval process, Proc., Int. Conf. on Steels in Cars and Trucks (SCT 2008), Wiesbaden, Germany, 1–5 June 2008, p. 503/9.
3. Bellhouse, E.-M.; McDermid, J.-R.: Met. Mat. Trans. A 41A (2010) No. 6, p. 1539/53.
4. Staudte, J.; Mataigne, J.-M.; Loison, D.; Del Frade, F.: Galvanizability of high Mn grade versus mixed Mn-Al and Mn-Si grades, Proc. Galvatech 11 Conference, Genoa, Italy, 21–24 June 2011.
5. Sohn, I.-R.; Chin, K.-G.: Selective Oxidation and Its influence on Surface Quality of TWIP steel, Proc. 1st Int. Conf. on High Manganese Steels, Seoul, South Korea, 15–18 May 2011.
6. Alibeigi, S.; Kavitha, R.; Meguerian, R. J.; McDermid, J. R.: Acta Mat. 59 (2011) No. 9, p. 3537/49.
7. Zhong, N.; Zhang, K.; Li, J.; Hu, W. B.: steel res. int. 82 (2010) No. 3, p. 180/86.
8. Bleck, W.; Beste, D.: Surface conditioning of high-strength steels by gas-metal reactions prior to hot-dip galvanising, Proc. Galvatech 04 Conference, Chicago, USA, 4–7 April 2004, p. 349/61.
9. Leuschner, R.; Zeizinger, S.: Controlled oxidation of advanced high-strength steels in hot-dip galvanizing lines, Proc. ATS 2006 Conference, Paris, France, 14–15 Dec 2006, p. 236/37.
10. Norden, M.: Heterogene Glühgas/Metall-Reak tionen in der Schmelztauchveredelung höherfester Mehrphasenstähle, RWTH Aachen, ISBN 978-3-8322-9652- 0, Shaker Verlag Aachen, 2010.
11. Blumenau, M.; Gusek, C.; Norden, M.; Schönenberg, R.: Industrial use of pre-oxidation during continuous hot-dip coating of high alloyed steels, Proc., AISTech 2012 Conference, Atlanta, USA, 7–10 May 2012.
12. Schuhmacher, B.; Heller, T.; Steinhorst, M.; Warnecke, W.: Recent development of high strength steels with zinc or zinc alloy coating in Europe, Proc. Galvatech 07 Conference, Osaka, Japan, 18–22 Nov 2007, p. 397/402.
13. Norden, M.; Macherey, M.; Friedel, F.; Peters, M.: Influence of thin zinc-melt oxide films on galvanizing of IF and Advanced High Strength Steels. Proc. Galvatech 11 Conference, Genoa, Italy, 21–24 June 2011. 
14. Norden, M.; Blumenau, M.; Schönenberg, R.; Peters, K.-J.: Changes and Challenges of of using preoxidation in hot dip galvanizing of AHSS, Proc. Galvatech 11 Conference, Genua, Italy, 21–24 June 2011.
15. Blumenau, M.; Norden, M.; Friedel, F.; Peters, K.: steel res. int. 81 (2010) No. 12, p. 1125/36.
16. Suzuki, Y.; Yamashita, T.; Sugimoto, Y.; Fujita, S.; Yamaguchi, S.: ISIJ Internat. 49 (2009) No. 4, p. 564/73.
17. Bellhouse, E.-M.; McDermid, J.-R.: Effect of oxygen partial pressure during annealing on the selective oxidation and gal vanizing of a 1,5% Al TRIP-assisted steel, Proc. Materials Science and Technology (MS&T), Pittsburgh, USA, 25–29 Oct 2009, p. 913/24.
18. Blumenau, M.: Schmelztauchveredelung von hochmanganlegiertem TWIP-Stahl unter Berücksichtigung der wasserstoffinduzierten Rissbildung nach Umformen, ISBN 978-3-8322-9541-7, Universität des Saarlandes, Dissertation, Shaker Verlag, Aachen, 2010.
19. Blumenau, M., Norden, M., Friedel, F., Peters, K.- J.: Surface Coatings Techn. 206 (2011) No. 2-3, p. 559/67.