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

Abstract

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...

Influence of Thermal Parameters Related to Destabilization Treatments on Erosive Wear Resistance and Microstructural Variation of White Cast Iron Containing 18% Cr. Application of Design of Experiments and Rietveld Structural Analysis

“…High-Cr hypoeutectic white cast irons are used in harsh environments that require high resistance to erosive wear [1]. Examples include the mining, cement and thermal power industries [2,3].…”

“…The first is that the matrix phase of their eutectic constituent is made up of austenite, while the second is that the carbides which form part of the said eutectic are of the (Fe,Cr) 7 C 3 type, also known as K 2 carbides. These carbides show hardness values ranging between 1500 and 1800 HV [1,4,5]. Austenite has high hardenability, allowing its partial transformation into martensite via air cooling [5].…”

Peculiarities of Alloying Effect on the Eutectic Cementite Behavior Under Hot Rolling

“…;Makarenko, K.V. 2010, Silman, G.I 1992, Dojka, M et al, 2018, Jiang et al, 2017, Bedolla-Jacuinde, A et al, 2005, Guo Erjun et al, 2009, Maja, M. E. et al, 2016, Liu et al, 2016, Bedolla-Jacuinde et al, 2015. One of the most effective means of the eutectic alloy product shape and microstructure transformation is hot plastic working in the process of which the eutectic net crushing occurs.…”

Influence of alloying elements and heat treatment on the mechanical properties of chromium cast iron

“…До настоящего времени за рубежом ведущими научными школами и учеными проводятся исследования комплексного влияния легирующих элементов и термообработки на структуру и эксплуатационные свой ства износостойких хромистых чугунов [1][2][3] с целью их дальнейшего применения в машинах и различном оборудовании . К примеру, целью научной работы [1] являлось улучшение механических свой ств существующего материала футеровки мельницы из высокохромистого белого чугуна (ВХБЧ) путем измельчения зерна . Было обнаружено, что добавление ниобия изменяет морфологию эвтектических карбидов от пластинчатой и стержнеобразной формы до изотропной .…”