The Development of High Strength Galvanized Steels for Automotive Applications

Results of a continuing program to develop a family of Cb-microalloyed high strength galvanized steels are described here. Laboratory and production data indicate that “in-line” annealed fully recrystallized sheet products having yield strengths ranging from 40 ksi (276 MPa) to 60 ksi (414 MPa) can be produced on selected galvanizing lines. Statistical analyses of production data for these steels indicate that the variation in mechanical properties from coil to coil is quite small. Sheet products having yield strengths ranging from 70 ksi (483 MPa) to 140 ksi (965 MPa) with limited ductility are over produced by recovery annealing. Pre-annealing followed by galvanizing is currently being used for such products. However, laboratory work shows that “in-line” recovery annealing should be successful for these products. Limited production of “in-line” recovery annealed 120 ksi (828 MPa) min. yield strength product supports these studies.

Hot rolled high strength galvanized steels are also being produced. These steels range in yield strength from 40 ksi (276 MPa) to over 80 ksi (552 MPa). Limited laboratory and production data indicate that galvanizing can cause either aging or simultaneous aging and softening depending on the annealing temperature. However, the effect upon tensile properties is minimal.

The future for high strength galvanized steels looks bright because of the continuing emphasis on weight reduction and corrosion protection by the major automobile producers. Continuing development and production efforts are expanding the variety of the various H. S. galvanized steel products aimed at meeting automotive demands.