The Effects of Nb and V Microalloying on Hardenability and Age Hardening in Ultrathin Cast Strip Steels Produced by the Castrip~? Process

摘要

The effects of niobium and vanadium on the hardenability and response to age hardening heat treatments of ultra-thin cast strip (UCS) steels produced via the unique regime of rapid solidification, large austenite grain size, and inclusion engineering by the CASTRIP~? process were investigated. Continuous cooling transformation diagrams were constructed for C-Mn, 0.04%Nb, 0.04%V and 0.04%Nb-0.04%V containing UCS steels. Niobium sharply suppressed polygonal ferrite formation, shifting the ferrite C-curve to the right, which promoted the formation of bainite and acicular ferrite at slower cooling rates in comparison to the plain C UCS steel. The vanadium addition, however, did not increase the hardenability. This agreed with plant processing experience in which microalloying with niobium produced microstructural hardening while vanadium did not. Niobium and vanadium were also retained in solid solution, which allowed subsequent strengthening via age hardening heat treatment during downstream processing. The effects of Nb and V on hardenability and age hardening of commercially produced UCS steels will be discussed.