Ultrafine grained steels and the n coefficient of strain hardening

Though many efforts have been made to obtain ultrafine grained steels, the industrial production level has not yet been reached due to the plastic instability during forming. The present work shows, using three examples, that high strength low alloy steels produced by advanced thermomechanical controlled rolling are in fact ultrafine grained steels with grain sizes below 5 mu m, establishing also a connection between the coefficient of strain hardening, mechanical strength and admissible thickness tolerances in steel sheets, in order to use these materials in cold work forming (bending and drawing). A minimum value of coefficient n must be reached in order to assure commercial use of the steel sheet.