Columbium and Vanadium-Nitrogen High Strength Cold-Rolled Steels

High-strength cold-rolled steels that are both formable and weldable can be produced based on either the columbium or vanadium-nitrogen strengthening systems. The critical aspects of chemistry and processing were determined for these steels in a laboratory program, and the results were used in planning a mill trial. It was found that a high-strength, formable product was favored by factors that produced a high hot band yield strength, large amounts of cold reduction, and annealing at low temperatures just into the range where full recrystallization occurs.

In the mill trial, 80,000-90,000 psi yield strength hot bands, relatively high cold reductions (50 and 65%), and controlled batch annealing between 1180-1225°F were used to produce 60,000 psi minimum yield strength fully recrystallized product. Very good property uniformity was achieved in the 0.042 in and 0.050 in thick product with longitudinal yield strengths averaging 63,300 psi with a standard deviation of 1880 psi. The formability of these steels generally matched that of high-strength hot-rolled steels of equivalent strength. It was also determined that sulfide inclusion shape control will be necessary to achieve the full formability potential of these steels.