Abstract
Hot tensile tests were conducted in this study to investigate the effect of strain rate (10−3 and 10 s−1) and vanadium content (0.029 and 0.047 wt.%) on the hot ductility of low-carbon microalloyed steels. The results indicate that a hot ductility trough appears at a low strain rate (10−3 s−1) because of the sufficient time for ferrite transformation and the growth of second particles, but it disappears at a high strain rate (10 s−1). The hot ductility is improved with the increase in strain rate at 700 °C or higher temperatures. In addition, with the increase in vanadium content, the large amounts of precipitate and increased ferrite transformation result in poor hot ductility of steels fractured at a low temperature range (600~900 °C). However, when the steel is fractured at a high temperature range (1000~1200 °C), more vanadium in the solid solution in the austenite inhibits the growth of parental austenite grains and results in grain refinement strengthening, slightly improving the hot ductility.
Highlights
Microalloyed steels with superior mechanical properties have received much attention due to how the reheating treatment after part formation can be cut out from the entire production process, saving significant costs and energy
The hot ductility behavior of four plain carbon steels containing different V contents has been investigated by Mohamed [5]; this revealed that raising the V content from 0.009 to 0.1% was found to deteriorate the ductility because the ductility trough became wider and deeper as the V content increased due to the increased amount of VN precipitate in the steel
It is obvious that the hot ductility curve at a low strain rate (10−3 s−1) contains two ductility troughs located in the temperature ranges of 600~800 ◦C and 1100~1200 ◦C, whereas it does not show the ductility trough when samples were fractured at a high strain rate (10 s−1), and it increases with the increase in fracture temperature
Summary
Microalloyed steels with superior mechanical properties have received much attention due to how the reheating treatment after part formation can be cut out from the entire production process, saving significant costs and energy. Lee et al [6] studied the hot ductility of a medium-carbon steel that contained V and demonstrated that V (C, N) particles precipitated at the austenite grain boundary and deteriorated the hot ductility when in a temperature range of 800~950 ◦C. The influence of strain rate on the hot ductility of a V-containing steel slab was investigated by Großeiber et al [13] at strain rates of 3 × 10−4 s−1 to 0.3 s−1 They claimed that the hot ductility improved with the increase in strain rate and the fracture mode changed from intergranular to transgranular. In the present study, the effects of V content and strain rate at a wider strain rate range on the hot ductility and fracture mechanism of V-microalloyed steels were investigated, aiming to provide a theoretical reference for optimizing the parameters of the practical industrial production process
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