Effect of Niobium Micro-alloyed on Microstructures and Mechanical Properties of Q500MPa Hot-Rolled H-beam Steel
HUANG Zhang1, DU Chuanzhi2, FANG Jinlin2, YU Hao1, LI Shuying1, SONG Chenghao3, DUAN Xiaoni1
1 School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China 2 Technology Center, Laiwu Branch of Shandong Iron and Steel Co., Ltd., Laiwu 271104, China 3 School of Mechanical Engineering, Dongguan University of Technology, Dongguan 523808, China
Abstract: The effect of Nb on the microstructures and properties of H-beam steel was investigated by nanoindentation test,, EBSD and transmission electron microscope. The results show that yield strength and low temperature impact energy at -20 ℃ reaches 552 MPa and 102 J of H-beam steel containing 0.025wt% Nb, which are 17.7% and 20.0% higher than those without Nb, respectively, under the same rolling and coo-ling condition. In addition, grain size is refined from 5 μm to 4 μm. The interface energy between matrix and (Nb1-xVx)C formed in ferrite matrix is smaller than that between NbC and matrix by thermodynamic calculation, which promote the precipitation of Nb composite precipitates. And the average size of nano-precipitates in ferrite matrix decreases from 16.3 nm to 11.46 nm, and the volume fraction of which increases from 0.053% to 0.108%, as a result of precipitation strengthening increasing from 55 MPa to 102 MPa. The hardness of ferrite matrix increases from 247HV to 279HV, and the contribution of precipitation strengthening after adding Nb is 18 MPa, which is greater than that of fine grain strengthening.
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