Effect of Niobium and Vanadium Additions on the As-Cast Microstructure and Properties of Hypoeutectic Fe–Cr–C Alloy

Abstract

The effect of niobium and vanadium additions (0.5 mass% and 2 mass%) on the as-cast microstructure and properties of hypoeutectic white cast iron containing 19 mass% Cr and 2.9 mass% C, has been examined. NbC carbides present in the structure of tested Fe-Cr-CNb alloys, due to their characteristic morphology, show higher wear resistance and toughness than M7C3 carbides. Increasing amount of this type of carbides, caused by the increase of niobium in the alloy, contributes to the improvement of wear resistance and dynamic fracture toughness. The alloy containing 2% Nb gives the best compromise between wear resistance and fracture toughness. This alloy shows about 23% greater dynamic fracture toughness and about 25% greater abrasion wear resistance than the basic Fe-Cr-C alloy. Besides, the secondary carbides which precipitate in the matrix regions of the tested Fe-Cr-C-V white irons also influence the abrasion behaviour and fracture toughness. The alloy containing 0.5% V has approximately the same fracture toughness but lower wear resistance than alloy with 2% Nb.

Niobium Additions to a 15%Cr–3%C White Iron and Its Effects on the Microstructure and on Abrasive Wear Behavior

“…Note that the predicted and measured amounts of each phase are close, but a small difference was noticed since the real material does not solidify under equilibrium conditions as predicted by the software. The observed microstructure has been widely reported by several authors [12,[17][18][19][20][21][22][23] for niobium alloyed white irons. For these measurements, the matrix was considered to be fully austenitic; however, it is well known that some martensitic transformation follows the cooling down process after solidification.…”

“…To get primary vanadium carbides, at least vanadium amounts of 5% are necessary, other way vanadium only reinforces the M 7 C 3 carbide [14][15][16]. In the case of niobium, most works studying the effect of this carbide-forming element are limited to amounts of less than 3% [11,12,[17][18][19][20][21][22][23] but up to 5% have been also produced along with high amounts of Mo and W [24]. Niobium forms primary carbides in the liquid and are later enclosed by austenite upon solidification; the size and distribution of which depends on the solidification rate (thickness of the casting).…”

Microstructure and Abrasion Resistance of Fe-Cr-C and Fe-Cr-C-Nb Hardfacing Alloys Deposited by S-FCAW and Cold Solid Wires

“…These Nb carbides act as heterogeneous nuclei of the M 7 C 3 carbides. Filipovic et al [9,10], also observed the refinement effect of Nb in hypoeutectic white cast iron. The authors explained that besides heterogeneous nucleation, NbC limits austenitic primary dendrites growth due to a pin effect of the NbC in the matrix.…”

“…As these elements additions also affect the alloy hardenability, ferrite or martensite can form in the matrix along with austenite. Notably, the positive effects of Nb additions on the microstructure of both hypo and hypereutectic white cast irons for potential abrasive applications have been widely demonstrated [7][8][9][10][11][12].…”

Effect of Si Content on the Microstructure and Wear Resistance of High Chromium Cast Iron

“…7) Titanium and niobium were used to improve the wear resistance by forming the harder carbides. [8][9][10] Different from the titanium and niobium, silicon was rejected from forming carbides and mostly dissolved in the matrix. In the medium and high carbon high strength steel by applying quenching-portioning -tempering treatment (QPT), the addition of Si with high content (1.5-2.0 wt.%) was used to suppress the precipitation of cementites during portioning process and enhance the carbon partitioning from martens-…”