| Abstract: | Continuous annealed low-carbon low-aluminium steel grades with good aging resistance and bake-hardenability were investigated. Taking into account the amounts of solute carbon and nitrogen in supersaturated ferrite it was tried to optimize the steel composition. Aging sensitivity depends mainly on solute nitrogen though the contribution to aging of solute carbon cannot be neglected. A reduced nitrogen aging requires a low nitrogen content (20 ppm) as well as Al/N ratios not lower than 5 and carbon contents higher than 0,025%. Both, low amounts of solute carbon and decrease of ferrite grain sizes of steels coiled at 650°C increase the effect of bake hardening. In comparison with aged steels the yield strength of overaged steels is conservative after baking. Bake-hardenable steels with good aging resistance are obtained in the carbon range 0,025 to 0,030%. Optimization according to the r?-value is not achieved in this range. |
