Perspectives on coated advanced high strength steels for automotive applications

Abstract

Advanced High Strength Steels (AHSS) is the fastest growing segment of sheet products in the automotive
industry. Coated (galvanized or galvannealed) AHSS are the most important of this class of steels. AHSS
includes various families of steels, major among them being dual-phase, multi-phase or complex-phase, TRIP
and martensitic steels. Recently, Twin Induced Plasticity (TWIP) and Quenching and Partitioning (QP) steels
are also becoming popular. Finally, press-hardened steels (PHS) are increasingly becoming a material of
choice for many automotive manufacturers. In addition to tensile and yield strength properties, many of these
steels are also required to possess other functionalities such as total and uniform elongation, sheared-edge
stretch- flangeability, bendability and weldabilty. To achieve the combination of properties, most of these steels
contain significant amounts of various alloying elements. Presence of both the alloying elements as well as the
complex microstructures poses a challenge for coatability. These multi-faceted aspects of coated AHSS and
their metallurgical challenges will be discussed in this paper. Mechanisms to explain coating behavior will be
included as appropriate. Finally, new coatings for improved functionalities and future breakthrough products
for automotive applications will also be briefly discussed.