Thermomechanical processing is a metallurgical operation to produce high-strength steel bars (rebars), through combining plastic deformation with thermal processes like heat treatment, water quenching, heating, and cooling at various rates into a single process. Ribbed reinforcing steel bars (rebars) are used for the reinforcement of concrete structures. Tempcore is a unique process to produce high-yield-strength rebars from mild steel without addition of a high weight percentage of costly alloying elements. The strength of rebar originates from the formation of a surface layer consisting of quenched and tempered martensite that surrounds a core composed of ferrite and pearlite. The economic advantages of this process are significant in comparison to those processes requiring alloying elements or further metal working to improve the mechanical properties. However, when there is a limitation in the water-cooling capacity, the required volume fraction of the martensite layer can’t be accomplished particularly when rolling bigger diameters of 32 mm - 40 mm at a higher rolling speed to maintain high productivity. Accordingly, a small addition of microalloying elements vanadium or niobium could be used in combination with Tempcore process to obtain high-strength steel rebars. In this contribution, 0.06 weight percentage of vanadium is added to the Tempcore treated rebars to satisfy ASTM A 706 Standard of Rebar Grade 80 PSI [550 MPa]. In order to decrease the trials in the steel plant floor, thermodynamics equilibrium calculations are predicted by Thermo-Calc, CCT, TTT diagrams are calculated by JMat Pro and the kinetics evolution of the vanadium carbonitrides precipitates are predicted by the computational database Mat Calc. High yield strength and tensile strength are obtained due to the effect of fine dispersions of nanometer-scale vanadium carbonitrides precipitates inspected by transmission electron microscope.
KeywordsTempcoreMicro-Alloyed SteelPrecipitation HardeningThermodynamics of EquilibriumKinetics of Formation
Park, C.S., Yi, H.J., Kim, Y.-T., Han, S., Lee, T. and Moon, Y.H. (2019) Tempcore Process Simulator to Analyze Microstructural Evolution of Quenched and Tempered Rebar. Applied Sciences, 9, 2938. https://doi.org/10.3390/app9142938
Nikolaou, J. and Papadimitriou, G. (2004) Microstructures and Mechanical Properties after Heating of Reinforcing 500 MPa Class Weldable Steels Produced by Various Processes (Tempcore, Microalloyed with Vanadium and Work-Hardened). Construction and Building Materials, 18, 243-254. https://doi.org/10.1016/j.conbuildmat.2004.01.001
DiMatteo, A., Vannucci, M. and Colla, V. (2015) A Finite Element Method for the Prediction of Thermal, Metallurgical, and Mechanical Behavior of Rebars in the TempCore Process. Steel Research International, 87, 276-287. https://doi.org/10.1002/srin.201500029
Sankar, I.B., Rao, K.M. and Krishna, A.G. (2009) Prediction of Heat Transfer Coefficient of Steel Bars Subjected to Tempcore Process Using Nonlinear Modeling. The International Journal of Advanced Manufacturing Technology, 47, 1159-1166. https://doi.org/10.1007/s00170-009-2240-3
Bandyopadhyay, K., Lee, J., Shim, J.-H., Hwang, B. and Lee, M.-G. (2019) Modeling and Experiment on Microstructure Evolutions and Mechanical Properties in Grade 600 MPa Reinforcing Steel Rebar Subjected to TempCore Process. Materials Science and Engineering: A, 745, 39-52. https://doi.org/10.1016/j.msea.2018.12.079
Khalifa, H., Megahed, G., El-Bitar, T. and Taha, M. (2020) Development of Direct Hot-Rolled Ultralow-Carbon Pre-Peritectic Ferrite-Bainite Dual-Phase Steel for a Compact Slab Production Plant. Journal of Materials Engineering and Performance, 30, 5773-5786. https://doi.org/10.1007/s11665-021-05789-y
Khalifa, H., Megahed, G., El-Bitar, T. and Taha, M. (2020) Development of Tailored Structure and Tensile Properties of Thermomechanical Treated Micro Alloyed Low Carbon Dual Phase Steel. Materials Sciences and Applications, 11, 851-866. https://doi.org/10.4236/msa.2020.1112056
Wen, H., Topping, T.D., Isheim, D., Seidman, D.N. and Lavernia, E.J. (2013) Strengthening Mechanisms in a High-Strength Bulk Nanostructured Cu-Zn-Al Alloy Processed via Cryomilling and Spark Plasma Sintering. Acta Materialia, 61, 2769-2782. https://doi.org/10.1016/j.actamat.2012.09.036
Liu, J., Yu, H., Zhou, T., Song, C. and Zhang, K. (2014) Effect of Double Quenching and Tempering Heat Treatment on the Microstructure and Mechanical Properties of a Novel 5Cr Steel Processed by Electro-Slag Casting. Materials Science and Engineering: A, 619, 212-220. https://doi.org/10.1016/j.msea.2014.09.063
Bikmukhametov, I., Beladi, H., Wang, J., Hodgson, P.D. and Timokhina, I. (2019) The Effect of Strain on Interphase Precipitation Characteristics in a Ti-Mo Steel. Acta Materialia, 170, 75. https://doi.org/10.1016/j.actamat.2019.03.022
Khalifa, H., Megahed, G.M., El-Bitar, T. and Taha, M.A. (2020) Development of Tailored Structure and Tensile Properties of Thermomechanical Treated Micro Alloyed Low Carbon Dual Phase Steel. Materials Sciences and Applications, 11, 851-866. https://doi.org/10.4236/msa.2020.1112056
Zhou, T., Babu, R.P., Odqvist, J., Yu, H. and Hedstrom, P. (2018) Quantitative Electron Microscopy and Physically Based Modelling of Cu Precipitation in Precipitation-Hardening Martensitic Stainless Steel 15-5 PH. Materials & Design, 143, 141-149. https://doi.org/10.1016/j.matdes.2018.01.049
Scott, C., Allain, S., Faral, M. and Guelton, N. (2006) The Development of a New Fe-Mn-C Austenitic Steel for Automotive Applications. Metallurgical Research & Technology, 103, 293-302. https://doi.org/10.1051/metal:2006142
Radis, R. and Kozeschnik, E. (2010) Kinetics of AlN Precipitation in Microalloyed Steel. Modelling and Simulation in Materials Science and Engineering, 18, Article ID: 055003. https://doi.org/10.1088/0965-0393/18/5/055003
Miyamoto, G., Hori, R., Poorganji, B. and Furuhara, T. (2011) Interphase Precipitation of VC and Resultant Hardening in V-Added Medium Carbon Steels. ISIJ International, 51, 1733-1739. https://doi.org/10.2355/isijinternational.51.1733
Donga, H., Chen, H., Khorasgani, A., Zhang, B., Zhang, Y., Wang, Z., Zhou, X., Wan, W., Wang, H., Li, T., Yang, Z. and Zwaag, S. (2022) Revealing the Influence of Mo Addition on Interphase Precipitation in Ti-Bearing Low Carbon Steels. Acta Materialia, 223, Article ID: 117475. https://doi.org/10.1016/j.actamat.2021.117475
Maugis, P. and Goune, M. (2005) Kinetics of Vanadium Carbonitride Precipitation in Steel: A Computer Model. Acta Materialia, 53, 3359-3367. https://doi.org/10.1016/j.actamat.2005.03.036
Zhou, J., Hu, C., Hu, F., Hou, T., Yin, C., Zhu, X. and Wu, K. (2022) Insight into the Effect of Nb Microalloying on the Microstructure-Property Relationship of a Novel Wire Rod. Journal of Materials Research and Technology, 16, 276-289. https://doi.org/10.1016/j.jmrt.2021.11.144
Parusov, V.V., Sychkov, A.B., Derevyanchenko, I.V., et al. (2004) High-Carbon Wire Rod Made of Steel Microalloyed with Vanadium. Metallurgist, 48, 618-625. https://doi.org/10.1007/s11015-005-0037-7
Yang, Y., Zhang, X.F., Li, Y.M. and Huang, Z.Y. (2020) Isothermal Precipitation Behavior of Vanadium Carbonitride in V-, N-Added Low-Carbon Steel. Steel Research International, 91, Article ID: 2000086. https://doi.org/10.1002/srin.202000086
Bu, F.Z., Wang, X.M., Chen, L., Yang, S.W., Shang, C.J. and Misra, R.D.K. (2015) Influence of Cooling Rate on the Precipitation Behavior in Ti-Nb-Mo Microalloyed Steels during Continuous Cooling and Relationship to Strength. Materials Characterization, 102, 146-155. https://doi.org/10.1016/j.matchar.2015.03.005
Clark, S., Janik, V., Rijkenberg, A. and Sridhar, S. (2016) Analysis of the Extent of Interphase Precipitation in V-HSLA Steels through In-Situ Characterization of the γ/α Transformation. Materials Characterization, 115, 83-89. https://doi.org/10.1016/j.matchar.2016.03.021
Chen, C.Y., Yen, H.W., Kao, F.H., Li, W.C., Huang, C.Y., Yang, J.R. and Wang, S.H. (2009) Precipitation Hardening of High-Strength Low-Alloy Steels by Nanometer-Sized Carbides. Materials Science and Engineering: A, 499, 162-166. https://doi.org/10.1016/j.msea.2007.11.110
Zhang, Y.J., Miyamoto, G., Shinbo, K., Furuhara, T., Ohmura, T., Suzuki, T. and Tsuzaki, K. (2015) Effects of Transformation Temperature on VC Interphase Precipitation and Resultant Hardness in Low-Carbon Steels. Acta Materialia, 84, 375-384. https://doi.org/10.1016/j.actamat.2014.10.049
Khalifa, H., Megahed, G., Hamouda, R. and Taha, M. (2016) Experimental Investigation and Simulation of Structure and Tensile Properties of Tempcore Treated Rebar. Material Processing Technology, 230, 244-253. https://doi.org/10.1016/j.jmatprotec.2015.11.023
ASTM E112-13 (2013) Standard Test Methods for Determining Average Grain Size, ASTM International, West Conshohocken. http://www.astm.org/cgi-bin/resolver.cgi?E112
ASTM E8/E8M-16ae1 (2016) Standard Test Methods for Tension Testing of Metallic Materials. ASTM International, West Conshohocken. https://www.astm.org/standards/e8
Seok, M.Y., Choi, I.C., Moon, J., Kim, S., Ramamurty, U. and Jang, J.L. (2014) Estimation of the Hall-Petch Strengthening Coefficient of Steels through Nanoindentation. Scripta Materialia, 87, 49-52. https://doi.org/10.1016/j.scriptamat.2014.05.004
Sonderegger, B. and Kozeschnik, E. (2010) Interfacial Energy of Diffuse Phase Boundaries, in the Generalized Broken-Bond Approach. Metallurgical and Materials Transactions A, 41, 3262-3269. https://doi.org/10.1007/s11661-010-0370-8