Effect of V and N Precipitation on Acicular Ferrite Formation in Sulfur-Lean Vanadium Steels

Abstract

This article deals with the mechanical properties achieved in two S-lean laboratory-cast V steels with two different N content levels, as compared with commercial acicular ferrite steel. The designed heat treatments ensure an almost homogeneous microstructure consisting of acicular ferrite for N-rich and commercial steels and consisting of bainite for the N-lean steel. The results presented in this work demonstrate that, in the absence of sulfide inclusions, acicular ferrite is nucleated on V(C,N) precipitates. The mechanical tests indicate that N-rich acicular ferrite steel achieves the same toughness values as N-lean bainitic steel but with a substantial improvement in strength properties. The S-lean steels present better toughness properties than commercial acicular ferrite steel, which is consistent with the detrimental effect of inclusions on toughness.

Effect of Thermomechanical Treatment on Acicular Ferrite Formation in Ti–Ca Deoxidized Low Carbon Steel

“…There have been many reported inclusion types effective for AF nucleation, such as Al-Mg-Zr-O, Ti-Al-Mn-O-S, Ti-Al-O-N, Ti-Mn-Al-Si-O-S-N, Mn-S-V-C-N, etc. [2][3][4][5][6]. Some comprehensive reviews were made on the influence of inclusion composition on AF formation potency [7][8][9], in which Ti-and Mn-containing complex inclusions were described as particularly effective nucleating sites.…”

Effect of composition and isothermal holding temperature on the precipitation hardening in Vanadium-microalloyed steels

“…Vanadium microalloyed high strength low alloy (HSLA) steels are widely being used for construction, line pipe, pressure vessel, automobile, naval and defense applications [1,2]. VN or V(C,N) precipitates contribute to ferrite grain refinement either by retarding the recrystallization of hot-deformed austenite or by acting as the heterogeneous nucleation sites for intragranular ferrite formation [1,[3][4][5][6][7][8][9][10]. Although, the prime objective of V addition is to achieve precipitation strengthening from the fine VC or V(C,N) precipitates [1,[3][4][5][6]11].…”

“…Increase in both C and N levels in steel cannot be an effective way of strengthening as that can impart brittleness and hamper the weldability and formability. Therefore, either the steel can be richer in C or richer in N. Effect of C addition and N addition on the precipitation strengthening of V-microalloyed steels has been studied separately and both are found to be beneficial [1,3,[7][8][9][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]. However, the effect of two different alloying strategies, i.e.…”

On the determining role of acicular ferrite in V-N microalloyed steel in increasing strength-toughness combination

“…But during thermo-mechanically controlled processing (TMCP) of advanced medium and heavy steel plates, deformation and cooling are rarely uniform across the thickness, because of which unfavorable microstructures such as coarse granular bainite and Widmanstatten ferrite are obtained at small reduction and low cooling rate in the center of the steel plate, and toughness is severely deteriorated [1,11]. Acicular ferrite is of considerable practical significance in the case of plates because it is characterized by relatively high strength and toughness [12]. In the early 1970s, acicular ferrite was preferred in highstrength low-alloy steel plates [13].…”

“…The mechanism of inclusion stimulated nucleation is summarized as follows [18,24]: (1) solute depletion from austenite in the vicinity of non-metallic inclusion; (2) good lattice matching [24][25][26]. In the absence of sulfide inclusions, acicular ferrite is capable of nucleating on V(C,N) precipitates in V-N microalloying low S steel [12,[27][28]. Ferrite exhibits Baker-Nutting orientation relationship with respect to small vanadium nitride (VN), and (001) VN [24,[29][30].…”