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

Jamwal R. S., Process Engineer, e-mail: ranbir.jamwal@thyssenkrupp.com
Norden M., Area Manager HDGL
Ehrhardt B., Director Quality and Development
Schönenberg R., Chief Technical Officer

Advanced High Strength Steels (AHSS) are considered as dominant future lightweighting material option for automobiles to meet the stringent fuel effi ciency and carbon emissions targets in the coming years. This paper illustrates the dominant role of AHSS in lightweighting of automobiles, the multiphase science behind the current generation of AHSS in production and future development moving into the third generation of high strength steels for the automotive industry. Challenges with respect to coating these high alloyed grades are discussed with corresponding solutions like using the “oxidation chamber” in continuous galvanizing lines is presented. The high alloying concepts incorporated for these steels pose a challenging issue of selective oxidation of the steel surface during annealing prior to galvanizing resulting in bare spots and poor Znadherence. Chemistry adjustments along with oxygen partial pressure of the annealing atmosphere are modification variables available to bring about a strong influence on the surface enrichments. However, in lieu of high Si/Al concepts for TRIP and other TRIP aided multiphase steels in development, the effectiveness of these methods is limited. Preoxidation using an oxidation chamber for surface conditioning prior to annealing proves to be a very effective tool when dealing with highly alloyed AHSS design concepts. It is suggested that for high Si chemistries with/without addition of Al, a closed-loop control of dew point control and preoxidation will be required to completely alleviate the issue poor coating. New concepts for higher strength and higher formable grades than the current traditional AHSS are evolving and resear chers along with steel makers are updating infrastructure and technical tools and pushing production capabilities to its limits in order to pursue and promote these next generation - third generation AHSS.

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