Article

Metallurgical and Materials Transactions A

, Volume 43, Issue 12, pp 4571-4586

Precipitation of Nb in Ferrite After Austenite Conditioning. Part II: Strengthening Contribution in High-Strength Low-Alloy (HSLA) Steels

  • M. A. AltunaAffiliated withMaterials Department, CEITGrupo WEC
  • , Amaia Iza-MendiaAffiliated withThermomechanical Treatments Group, Materials Department, CEIT and Tecnun (University of Navarra) Email author 
  • , I. GutiérrezAffiliated withThermomechanical Treatments Group, Materials Department, CEIT and Tecnun (University of Navarra)

Abstract

Often, Nb contributes to the strength of a microalloyed steel beyond the expected level because of the grain size strengthening resulting from thermomechanical processing. Two different mechanisms are behind this phenomenon, and both of them have to do with the amount of Nb remaining in solution after hot rolling. The first of them is the increase of the hardenability of the steel as a result of Nb, and the second one is the fine precipitation of NbC in ferrite. Three Nb microalloyed steels were thermomechanically processed in the laboratory and coiled at different temperatures to investigate the effect of Nb content on the tensile properties. The extra strength was linearly related to the Nb remaining in solution after the hot working. The maximum contribution from Nb was reached for a coiling temperature of 873 K (600 °C).