Effects of composition and strain rate on hot ductility of Cr-Mo-alloy steel in the two-phase region

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 degrees 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.

Automated summary

The effects of Nb, B, Mo, and V on the hot ductility of 25CrMo alloy steel were studied through hot tensile tests, revealing that the addition of different elements can either improve or deteriorate hot ductility. The influences of ferrite transformation and precipitates on hot ductility were also observed.