Tensile behavior of normalized low carbon Nb-microalloyed steel in the presence of rare earth elements

In this study, attempts have been made to study the effects of RE on the tensile behavior of a low carbon Nb-microalloyed steel which confronts yield point phenomenon during its tensile test. The results of the tensile tests and microstructural examinations presented in this research showed that the upper and lower yield points increase by the RE addition which was mainly attributed to the indirect effects of RE on the Nb-precipitation manner and refinement of the microstructure. The results also demonstrated that the flow behavior (oscillation in stress level) during the Lüders strain zone is considerably different for the base and RE-added steels. It was found that the RE-added steel undergoes a uniform propagation of the Lüders bands while the base steel showed a distinct non-uninform Lüders strain with rough fluctuations of stress level within this area. This could be due to the uniformity in distribution of nanoprecipitates and solute, e.g. C, atoms in the RE-added steels. Moreover, It was observed that the Lüders strain increases in the presence of RE which could be probably attributed to the finer ferrite grains and the change in nanoprecipitation behavior caused by RE addition. A significant increase in total elongation of the RE-added steel was also observed.