Effect of Strain Rate on the Hot Ductility Behavior of a Continuously Cast Ti–Nb Microalloyed Steel

Abstract

During the continuous casting process, alloys may be more susceptible to crack initiation under some conditions due to lower ductility. A Ti–Nb microalloyed steel is subjected to in situ melted hot tensile tests to evaluate its hot ductility behavior. The ductility is examined at different strain rates and temperatures. The samples are heated with an induction coil to the melting temperature in a vacuum atmosphere. Afterward, they are cooled to the desired test temperatures. Hot tensile tests are conducted by a thermomechanical simulator with strain rates varying from 10−5 to 10−2 s−1. The results show a ductility minimum around 800 °C for the standard strain rate of 10−3 s−1 and a significant influence of the changes in strain rate in the behavior of the alloy for all the tested temperatures. The fracture surfaces are compared for 700, 800, and 900 °C at 10−4, 10−3, and 10−2 s−1, as well as the microstructure. Computer simulations are done for the determination of the transformation temperatures, Scheil–Gulliver solidification simulation, and analysis of the precipitation kinetics during the tests. The results from simulations are discussed in comparison with the ones seen experimentally.

Effect of Reheating Temperatures on Hot Ductility and Precipitation Behavior of Low‐Carbon Steels

“…Analyzing the effect of strain rate on the hot ductility of Ti–Nb‐microalloyed steel, Gontijo et al concluded that at higher strain rates, ductility improves due to the time in which the sample spends at a high temperature allowing for deformation‐induced ferrite film to occur. [ 14 ] Besides controlling alloying elements, increasing the strain rate can improve the hot ductility.…”

“…[2][3][4][5] A single trough usually depicts hot ductility curves of low-carbon steels at around 873-1173 K. [3,[6][7][8][9][10][11][12][13] High-temperature ductility is maintained due to the absence of ferrite film at the austenite grain boundaries (PAGBs) and annihilation of dislocations accompanied by simultaneous dynamic recrystallization. [14] The lowtemperature ductility is maintained due to the deformation of thick ferrite films surrounding the PAGB. During the tensile test, the deformation reduces the strain concentration between the ferrite/austenite interface.…”

Modeling the hot deformation behavior of micro-alloyed steel in the single and two-phase fields

“…In this temperature range, it has been reported that the material becomes brittle during deformation, leading to surface crack initiation [3][4][5]. Various factors, for instance, the presence of proeutectoid ferrite film, precipitates, and microstructural modification during hot deformation influence the ductility behavior [2,3].…”

“…Continuous casting process is largely used to produce slabs of steels . Sometimes, slabs can present superficial cracks due to the thermomechanical stresses that arise during the continuous casting process, especially between 700 °C and 1000 °C [1,2]. Steels undergo plastic deformation in the temperature range of 700 °C-1000 °C after solidification [2,3].…”

“…Sometimes, slabs can present superficial cracks due to the thermomechanical stresses that arise during the continuous casting process, especially between 700 °C and 1000 °C [1,2]. Steels undergo plastic deformation in the temperature range of 700 °C-1000 °C after solidification [2,3]. In this temperature range, it has been reported that the material becomes brittle during deformation, leading to surface crack initiation [3][4][5].…”