| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 1579226 | Materials Science and Engineering: A | 2011 | 10 Pages |
Development of new, advanced high and ultra-high strength bainitic steels requires the selection of the optimum balance of bainite promoting elements allowing the production of the desired bainitic microstructure over a wide range of cooling rates. The addition of boron or a combined addition of boron and niobium is well known to retard strongly the polygonal ferrite formation but very little knowledge has been acquired on the bainitic transformation. Therefore, the purpose of this study is to investigate the influence of boron and boron plus niobium on the bainite transformation kinetics, microstructural evolution and mechanical properties in a low carbon steel (Fe–0.05C–1.49Mn–0.30Si). Isothermal and continuous cooling transformation diagrams were determined and followed by a detailed quantitative characterisation of the bainite microstructure and morphology using complementary advanced metallographic techniques (FEG-SEM-EBSD, SIMS and TEM). The relationship between microstructure and hardness has been evaluated. Finally, results of SIMS and TEM analyses coupled with microstructural investigations enable to propose a mechanism to explain the effect of the synergy between boron and niobium on the bainitic transformation and the resultant microstructure.
Research highlights► B retards slightly the bainite transformation kinetics. ► Combined addition of B + Nb delayed dramatically bainite transformation kinetics. ► B refines the microstructure and promotes lath morphology of bainite. ► Larger packets of laths and longer laths are observed in the B + Nb steel. ► More free boron/finer borocarbide precipitates on γ grain boundaries in B + Nb steel.
