Effect of niobium on the as-cast microstructure of hypereutectic high chromium cast iron

Xing, Zhi; Xing, Jiandong; Fu, Hanguang; Xiao, Bing

doi:10.1016/j.matlet.2007.06.084

Cited by 154 publications

(94 citation statements)

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“…Okada et al [39] suggested that titanium carbide formation (TiC) caused depletion of the carbon content in the solid/liquid interface, thus promoting the graphite formation of type D. Niobium, in surface addition, probably contributed to the structural changes of gray cast iron. According to the addition rate of niobium (1wt.% &3wt.%), the morphology of graphite gradually changes in the matrix of type B to type E passing through type D. In agreement with previous studies [40] , niobium, according to the addition process used in this work, can act in various ways. Since the carbide formation energy is much smaller than that of the sulfides, and due to its high affinity to carbon, niobium may first form carbides.…”

Section: Graphite Morphologysupporting

confidence: 90%

Niobium addition effect in molds at last cooling step on EN-GJL250 gray cast iron: Microstructural changes and electrochemical behavior

et al. 2018

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I t is well established that the variety of applications of cast iron is attributed to the presence of chemical elements in the solid solution as interstitial or substitutional form, such as so-called addition elements Ni, Cu, Ti, Cr, V and Nb [1][2][3][4] , and inoculation elements Al, Si, Ca, Sr, Mn, Zr, P, Sn and Ce [5][6][7] .In the foundry, additions are done by controlling the Abstract:The purpose of this study was to determine the impact of niobium addition as an inoculation element on the microstructure and electrochemical properties of EN-FGL250 gray cast iron. Niobium additions are in a powder form and have a 0.5 mm particle size at dfferent proportions of 1wt.% and 3wt.%. The addition was done during casting of the metal in the mold at the last cooling step of the melt cast iron. These additions have a significant impact on the phenomenon of solidification as the metal powder deposited in the sand molds creates new centers of germination and absorbs a lot of heat. The cooling rate directly affects the microstructure and electrochemical behavior. This is confirmed by SEM observations and electrochemical tests. Furthermore, the addition of niobium transforms the microstructure of gray cast iron from cellular structure into totally dendritic structure. As a consequence, the niobium addition affected the shape and size of graphite, thus considerably reducing the corrosion current density by increasing the polarization resistance R p . chemical composition of the melt rather than equivalent carbon, alloying elements and inoculation products. The minor additions of alloying elements for their affinities to carbon can be used to improve the mechanical properties of the cast iron mainly by the formation of M 7 C 3 , M 3 C and MC type carbides. Filipovic et al. [4] have shown that variable proportions of additions of niobium and vanadium to the hypoeutectic white cast iron containing 19% chromium modify its microstructure and affect its wear and hardness properties. Kesseri et al. [3] have also shown that the addition of niobium in chromium-rich cast irons improves the mechanical properties by the formation of MC-type niobium carbides. Similarly, the inoculation elements have a strong affinity to oxygen and sulfur [8][9][10][11] . Thus, oxides and sulphides of a homogeneous or heterogeneous nature formed in the melt give the graphite nucleation sites [12][13][14] . Some authors suggested that the Mn/S ratio affects the nucleation and morphology of graphite [15,16] . Other authors [17,18] indicated that the inoculations elements *M. O. Azzoug Male, born in 1979, Teacher (assistant master) at University of Sciences and Technology Houari Boumedienne Algiers, Algeria, also Ph.D student in Materials Science and Engineering. He is currently working on the development of a surface treatment process for gray cast irons directly in the manufacturing stage of parts without resorting to conventional (physical or chemical) surface treatments by metal deposition process or surface treatment. The influence of additions in ...

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Section: Graphite Morphologysupporting

confidence: 90%

Niobium addition effect in molds at last cooling step on EN-GJL250 gray cast iron: Microstructural changes and electrochemical behavior

et al. 2018

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“…The results obtained with this approach, which does not account for the GWT, have been experimentally validated in multiple cylindrical bar castings and in one production part. On the other hand, white cast iron (WCI) with high chromium (Cr) content was the focus of several experimental investigations due to its excellent performance under wear and abrasion conditions [36][37][38][39][40]. In particular, hardness, fracture toughness and wear resistance have been measured in hypoeutectic and hypereutectic WCIs with different Cr content [36,37].…”

Section: Introductionmentioning

confidence: 99%

Modeling and Simulation of the Gray-to-White Transition during Solidification of a Hypereutectic Gray Cast Iron: Application to a Stub-to-Carbon Connection Used in Smelting Processes

Urrutia

Celentano

Gunasegaram

2017

Metals

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This work reports on experimental and numerical results of the gray-to-white transition (GWT) during solidification of a hypereutectic gray cast iron (GCI) in a casting test using a stub-to-carbon (STC) connection assembly. Since in this process non-uniform cooling rates are produced, the mechanical properties are expected to spatially vary due to the development of different microstructures along the thimble. The twin aims of this work were to (1) experimentally validate the GWT prediction capabilities of the microstructural model proposed earlier by the authors in the rodding process of a hypereutectic GCI-STC, and (2) estimate, from the numerically obtained microstructure and ultimate tensile strength (UTS), the local hardness of the alloy after the numerical predictions of the microstructure were experimentally validated. To this end, the final microstructure at different points of the thimble and the hardness profile along its radial direction were measured for validation purposes. Moreover, this rodding process was simulated using an extension of a thermal microstructural model previously developed by the authors and the GWT was superimposed on that simulation. The computed results encompass cooling curves, the evolution of gray and white fractions, eutectic radii and densities and, in addition, the hardness profile. A detailed discussion of the experimental and numerical results is presented. Finally, the computed GWT was found to adequately reproduce the experimental data.

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“…Grain refinement is the only strengthening method that also improves the fracture strength of iron. Many researchers (Zhang et al, 2014;Zhi et al, 2008aZhi et al, , 2008b have attempted to improve the mechanical properties of HCWCI through grain refinement, especially in hypereutectic HCWCI. However, their work focused more on improving the wear resistance by increasing the hardness.…”

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confidence: 99%

“…The formation of the first precipitated NbC reduces the carbon available to form primary M 7 C 3 carbides and as a result the volume fraction and the size of the primary M 7 C 3 carbides decreases (Zhi et al, 2008b). The concentration of Nb in the matrix and M 7 C 3 is very low as this element tends to partition into NbC in the Fe-Cr-Cr (Zhi et al, 2008b;Hannes and Gates, 1997;Coelho et al, 2003;Baik and Loper, 1998). This results in niobium enrichment at the grain boundaries of the carbides during solidification until NbC precipitates due to solubility of Nb at the grain boundaries being exceeded.…”

mentioning

confidence: 99%

“…This results in niobium enrichment at the grain boundaries of the carbides during solidification until NbC precipitates due to solubility of Nb at the grain boundaries being exceeded. The precipitated NbC impedes the preferential directional growth of the M 7 C 3 carbides and result in finer, isotropic carbides (Fiset et al, 1993;Zhi et al, 2008b). Figure 4 shows the microstructural analysis of the HCWCI after heat treatment.…”

mentioning

confidence: 99%

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Effect of niobium on the solidification structure and properties of hypoeutectic high-chromium white cast irons

Maja

Maruma

Mampuru

et al. 2016

J. South. Afr. Inst. Min. Metall.

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For the past few years Mintek has been involved in a project in which a number of alloys have been identified for grinding media applications. The high-chromium white cast iron (HCWCI) alloys were among the alloys researched for this application. The knowledge acquired from the grinding ball media research has now been extended to mill liners, which have traditionally been made of manganese-, chromium-and chrome-molybdenum steels. The replacement of worn mill liners costs the mining industry a significant amount of money and this has led to a need for continuous research to prolong the life of the liners. During milling operations, liner wear has an adverse effect on the capacity of the mill, the energy efficiency and milling efficiency and finally leads to relining, to replace worn liners.The mill efficiency depends on the charge motion, which in turn is largely influenced by the liner profiles and performance. The choice of a liner requires a holistic approach that examines the compatibility with the mill conditions, the mechanical performance and the cost-effectiveness. The operating conditions in a fine grinding mill require that the liner should be made of highly wearresistant material with some fracture strength such as (HCWCI).HCWCI contains a minimum of 2%C with a chromium content ranging from 15% to 35%. The term 'white cast iron' refers to the appearance of a white fractured surface in the material after damage, due to the presence of white cementite. This material has been proven to be effective for applications in aggressive environments where wear and erosion resistance are required. The high wear resistance of HCWCI is attributed to the microstructural constituents such as hard primary and/or eutectic carbides of M 7 C 3 (where M is iron, chromium and other strong carbide formers) and a relatively ductile ferrous matrix (Bedolla-Jacuinde et al., 2005Adler and Dogan, 1999;Dogan, Hawk and Laird, 1997;Stevenson and Hutchings, 1995;Radzikowska, 2004). Austenitizing at a temperature above 1100°C leads to the precipitation M 7 C 3 carbides while below 1100°C the precipitation of both M 7 C 3 and M 23 C 6 carbides, which are rich in alloying elements, occurs (Kootsookos and Gates, 2008). The precipitation of secondary carbides lowers the alloy content in the dendritic austenite and thus raises the martensite start temperature, hence the formation of martensite upon cooling (Cetinkaya, 2006).The hardness of M 7 C 3 is in the range of 1200 HV (Stevenson and Hutchings, 1995), which may vary with the composition and the ferrous matrix binds the hard M 7 C 3 carbides and provides the material with certain fracture strength that is vital for handling high impact forces (Bedolla-Jacuinde et al., 2005; Effect of niobium on the solidification structure and properties of hypoeutectic high-chromium white cast irons by M.E. Maja* † , M.G. Maruma*, L.A. Mampuru* and S.J. Moema*The most commonly used high-chromium white cast iron (HCWCI) is the hypoeutectic white cast iron that contains 2-3.5 wt.% C and 10-30% Cr. T...

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Effect of niobium on the as-cast microstructure of hypereutectic high chromium cast iron

Cited by 154 publications

References 8 publications

Niobium addition effect in molds at last cooling step on EN-GJL250 gray cast iron: Microstructural changes and electrochemical behavior

Niobium addition effect in molds at last cooling step on EN-GJL250 gray cast iron: Microstructural changes and electrochemical behavior

Modeling and Simulation of the Gray-to-White Transition during Solidification of a Hypereutectic Gray Cast Iron: Application to a Stub-to-Carbon Connection Used in Smelting Processes

Effect of niobium on the solidification structure and properties of hypoeutectic high-chromium white cast irons

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