Dynamic Recrystallization Behavior of Vanadium Microalloyed Cryogenic Fine Grain Structural Steel Pipe at High Strain Rate

Abstract

Dynamic recrystallization (DRX) behavior of a vanadium microalloyed steel pipe was systematically investigated at temperatures range of 850–1,200 °C and a strain rate of 5 s−1 on a Gleeble-3800 thermo-simulation machine. Constitutive equation was obtained by characteristic points of DRX which derived from the strain hardening rate and stress curves. DRX kinetics model was established for determining the recrystallization volume fraction (X). Effect of dynamic precipitation of V(C, N) imposed on DRX at temperatures from 850–1,000 °C was analyzed. Results show that true stress-strain curves exhibited no clearly defined stress peaks with typical dynamic recovery behavior. X increased from 43.9 % to 100 % with increasing deformation temperature, which was in reasonable agreement with the observation of microstructure. Moreover, the calculation pinning force of V(C, N) precipitates was weaker than the recrystallization driving force, revealing that V(C, N) precipitates could effectively retard rather than prevent the progress of DRX.

Effect of vanadium on microstructure and mechanical properties of Fe–1.8Ni–0.5Mo–2Cu–0.45C PM steel

“…It is obvious that VN exhibited higher thermodynamic stability than VC, which could be dissolved below 1000°C. The situation for V(C,N) solution in austenite is more complex, but it can be assumed that V(C,N) has a higher solution temperature than VC, and is close to the solution temperature of VN, which starts to dissolve at above 1000°C depending on the contents of vanadium and nitrogen [27,28]. This again explained that there were still some in situ synthesised V(C,N) presented in the outer layer of the iron particle for the sintered specimens with V addition.…”