Effect of Vanadium on the Phase Transformation Behavior of Ti–Mo Microalloyed Ultra‐High Strength Steel

Abstract

Vanadium is a vital microalloying element in the precipitation hardening of hot‐rolled high strength steel. Its effects on the continuous cooling phase transformation behavior, microstructure, and properties of Ti–Mo and Ti–Mo–V microalloyed ultra‐high strength steels are studied by the thermal simulator, scanning electron microscopy (SEM), high‐resolution transmission electron microscopy (HRTEM), energy dispersive spectrometer (EDS), and electron backscatter diffractometer (EBSD). The dynamic continuous cooling transformation curves are obtained which show that vanadium can restrain the ferrite‐pearlite and bainite transformation, refine the microstructure, and harden the steel matrix. It is also found that the strain‐induced precipitation of nano‐sized (Ti, Mo) C and (Ti, V, Mo) C particles, with NaCl type structure, exists in Ti–Mo and Ti–Mo–V steel, respectively, as identified by the HRTEM and EDS. And the lattice constants of (Ti, Mo) C and (Ti, V, Mo) C are 0.432 and 0.430 nm, respectively. The higher hardness of Ti–Mo–V steel is attributed to the grain refinement and precipitation hardening by the nano‐sized (Ti, Mo, V) C particles.

Effect of Vanadium and Rare Earth on the Structure, Phase Transformation Kinetics and Mechanical Properties of Carbide-Free Bainitic Steel Containing Silicon

“…It has been confirmed in various studies [23,24,28] that with an increasing vanadium content, the rate of perlite transformation slows and the steel hardness increases by increasing the vanadium content. Vanadium in solution seems to affect the mobility of the carbon atoms [10,[25][26][27][28][29][30]. Using Thermo-Calc software we performed the thermodynamic analysis, showing that the type of stable carbides in the matrix changes from cementite to M6C and M7C3 carbides.…”

“…However, because of the formation of carbide in the sample containing cerium and lanthanum in the bainite transformation, the carbon content of the parent phase has decreased, and as a result, its thermodynamic stability has decreased and martensitic transformation occurred at higher temperatures than the vanadium containing sample. It has been confirmed in various studies [23,24,28] that with an increasing vanadium content, the rate of perlite transformation slows and the steel hardness increases by increasing the vanadium content. Vanadium in solution seems to affect the mobility of the carbon atoms [10,[25][26][27][28][29][30].…”

“…The formation of these carbides is due to the uphill diffusion o elements such as cerium and molybdenum [31]. Therefore, the formation kinetics of these It has been confirmed in various studies [23,24,28] that with an increasing vanadium content, the rate of perlite transformation slows and the steel hardness increases by increasing the vanadium content. Vanadium in solution seems to affect the mobility of the carbon atoms [10,[25][26][27][28][29][30].…”

Effect of V on the Precipitation Behavior of Ti−Mo Microalloyed High-Strength Steel

“…Recently, the literature [ 10 , 11 , 12 , 13 , 14 , 15 , 16 ] reported that adding Nb or V to Ti−Mo steel could further optimize microstructures and improve mechanical properties. Cai et al [ 10 ] improved the yield strength of ultra-low carbon Ti−Mo steel to 680 MPa by adding Nb.…”

“…Meanwhile, the addition of Nb could also refine ferrite grains and inhibit bainitic transformation, thus improving the mechanical properties of hot-rolled ferritic steel. Compared to Nb, V could also inhibit bainitic transformation and has a stronger ability for precipitation strengthening [ 14 ]. Zhang et al [ 15 ] reported that Ti−Mo−V composite microalloying could improve the yield strength of ferritic steel to 900 MPa due to the contribution of nano-sized (Ti, Mo, V)C particles.…”