Using differential scanning calorimetry to characterize the precipitation and dissolution of V(CN) and VC particles duri
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Downloaded from https://www.cambridge.org/core. Tufts Univ, on 01 Jul 2018 at 23:26:07, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/jmr.2018.189
Using differential scanning calorimetry to characterize the precipitation and dissolution of V(CN) and VC particles during continuous casting and reheating process Mujun Long,a) Tao Liu, Huabiao Chen, Dengfu Chen,b) Huamei Duan, Helin Fan, Kai Tan, and Wenjie He Laboratory of Metallurgy and Materials, College of Materials Science and Engineering, Chongqing University, Chongqing 400044, People’s Republic of China (Received 19 January 2018; accepted 25 May 2018)
In this work, differential scanning calorimetry (DSC) was used to characterize and analyze the precipitation/dissolution kinetics of second phase particles during the cooling/reheating process in a vanadium microalloyed steel. The results indicated that three obvious exothermic peaks were detected on the cooling DSC curve. Furthermore, three corresponding endothermic peaks were also detected on the heating DSC curve. Combined with thermodynamic calculation and transmission electron microscopy analysis, these three exothermic peaks along cooling DSC curve were defined as the precipitation reaction of V(CN), the reaction of austenite transformation into ferrite and the precipitation reaction of VC, respectively. Meanwhile, three corresponding reverse reactions for cooling were also defined along the reheating DSC curve. The linear regression result revealed that the precipitation activation energies for V(CN) and VC were identified as 311.2 kJ/mol and 167.6 kJ/mol, respectively. The dissolution activation energies for VC and V(CN) were identified as 255.4 kJ/mol and 592.6 kJ/mol, respectively.
I. INTRODUCTION
The weathering steels such as YQ450NQR1 (Panzhihua, China) are widely used to manufacture rails, railway wheels, etc., and generally, they have lower strength and ductility compared with martensitic steels.1 Currently, the most common way to obtain an excellent combination in high strength and well ductility is adding the microalloying elements into steels.2–4 The alloying elements of interest are typically niobium, vanadium, and titanium. These elements are frequently added into steels in individual or federated way and then precipitate the nanometer-sized carbides, nitrides, or carbonitrides in the austenite or ferrite phase during cooling.5–8 However, the addition of these alloying elements will lead generally a deterioration in hot ductility of C–Mn steels.9,10 The hot cracking risk for microalloyed steels is associated with the loss of hot ductility in continuous casting, thus the hot ductility loss of microalloyed casting slabs has been received much attention.11,12 The survey result found that hot ductility deterioration of casting slab usually occurred in the temperature range of 700–1000 °C, and this deterioration is generally associated with the precipitation of nitrides and carbonitrides in the sensitive temperature range.13,14 T
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