Effect of Coiling Temperature on Microstructure and Mechanical Properties of a Nb-V Microalloyed Steel

Abstract

The effect of coiling temperature on the microstructure and mechanical properties of a Nb-V microalloyed steel was investigated. Controlled rolling followed by accelerated cooling and coiling was simulated by means of both, uniaxial compression, using a quenching and deformation dilatometer, and torsion. Specimens were reheated at 1250º for 5-10 min, then deformed at 1150°C, =0.3, and subsequently at 900°C, =0.4, followed by rapid cooling to a temperature between 450 and 700°C where coiling was simulated by holding the specimen for one hour at the selected temperature followed by a slow cooling to room temperature. Mechanical characterization was performed by means of hardness measurements and tensile tests, using tubular specimens machined from the torsion samples. It was found that decreasing the coiling temperature the ferrite-pearlite microstructure changed to ferrite-bainite, with a hardness peak reached for coiling at 600°C-650°C.

Effect of Controlling Nb Content and Cooling Rate on the Microstructure, Precipitation Phases, and Mechanical Properties of Rebar

“…Pan et al [16] showed that the microstructure of rebar consists of ferrite, pearlite, and bainite when the cooling rate is less than 5 • C•s −1 , and the microstructure changes to martensite and bainite when the cooling rate is 20 • C•s −1 . Olasolo et al [17] showed that when the transformation temperature was 600-650 • C, the content of ferrite and pearlite in the steel was the largest, and the hardness reached the peak. Zhang et al [18] showed that ferrite and pearlite exhibit different deformation behaviors during the deformation process.…”

Effect of Complex Strengthening on the Continuous Cooling Transformation Behavior of High-Strength Rebar

“…Therefore, it is important to improve the strength of steel for reinforced concrete and explore the new process of microalloyed high-strength reinforcing steel. In microalloyed hot-rolled steel, by optimizing the composition of trace alloying elements such as Ti, V, and Nb, combined with the controlled rolling and cooling process, the organization of microalloyed hot-rolled steel can be effectively improved, which ensures excellent strength and toughness [3][4][5][6]. The improvement in properties is mainly due to grain refinement and precipitation strengthening of precipitates (carbides, nitrides or carbonitrides) formed by microalloy elements at different process stages [7][8][9][10].…”