Abstract
Abstract The hot tensile tests were conducted in this study to investigate the effects of Nb, B, Mo, and V on hot ductility of 25CrMo alloy steel in a temperature range of 650–850°C with strain rates of 0.005 and 0.5 s−1. Besides, the influences of ferrite transformation and precipitates on hot ductility were also investigated by the use of SEM and TEM. Thermo-Calc and J Mat Pro were used for calculating equilibrium precipitates and CCT curves, respectively. The results indicated that the hot ductility is deteriorated with the addition of 0.04% Nb due to Nb(C,N) particles and ferrite transformation. The addition of B inhibits ferrite transformation and improves hot ductility. The hot ductility is improved with increasing strain rate from 0.005 to 0.5 s−1 due to the nucleation and growth behavior of ferrite. The fast strain rate promotes nucleation of ferrite; however, the ferrite has no sufficient time to grow up. The addition of Mo inhibits ferrite transformation and improves hot ductility. The addition of 0.12% V has no obvious effect on ferrite transformation. The hot ductility has deteriorated a little with the addition of 0.12% V due to the solution V that increases stress during hot deformation.
Highlights
25CrMo steel is used for the axle of a high-speed train
The area reduction of the tested steels is all above 60% in the temperature range of 650–850°C
The results show that the hot ductility has deteriorated with the addition of 0.04% Nb
Summary
V and Mo affect phase transformation and carbide precipitation, which will influence hot ductility [17,18,19]. The hot ductility can be improved with a fast strain rate [4]. The intergranular ferrite has less time to grow up, and the second particles at grain boundary have no sufficient time to precipitate with a fast strain rate; the hot ductility is much better than that of low strain rate. The intergranular crack has more time to nucleate and grow up with a low strain rate and deteriorate hot ductility. The present work aims to study the effects of Nb, B, Mo, V, and strain rate on hot ductility of 25CrMo alloy steel. The relation among precipitates, phase transformation, and the hot ductility of 25CrMo steel was discussed
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