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Article
Author(s)
Zhang Yongqing1,2, Jose M. Rodriguez-Ibabe3, Beatriz Lopez3, Felipe Bastos4 and Marcelo Rebellato4
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DOI:10.17265/2159-5275/2022.03.002
Affiliation(s)
1. China Iron & Steel Research Institute Group, No. 76 Xueyuan Nanlu, Haidian, Beijing 100081, China
2. CITIC Metal Co., Ltd, Room 1901 Capital Mansion, Beijing 100004, China
3. Ceit Research Institute P. M. Lardizabal 15, Donostia San Sebastian 20018, Spain
4. CBMM, Av. Brg. Faria Lima, 4285, São Paulo-SP 04538-133, Brazil
ABSTRACT
In this paper, CCT (continuous cooling transformation) diagrams are determined for Nb-containing reinforcing bars with different Nb, Mn additions, and initial austenite grain sizes by simulating industrial conditions via dilatometry tests. It was found that coarse austenite grain size, high Mn content and Nb remaining in solution all increase hardenability of Nb-containing rebars, namely lower Ar3 for acicular phase transformation products, which leads to continuous yielding during tensile deformation when the volume fraction of acicular ferrite or bainite microstructure reaches a certain volume fraction. By coupling with actual cooling rates for different size rebars, it can be explained why bainitic structure is prone to form in the center of rebars, especially for small size rebars. In order to achieve required ferrite-pearlite microstructure, cooling strategy is optimized for industrial production.
KEYWORDS
Nb microalloying, hardenability, CCT diagram, continuous yielding.
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