High Chromium White Cast Iron Research Articles

Simulation for grinding balls production using sand mold-gravity casting

In this present work, the grinding balls from high chromium white cast iron (ASTM A-532) were produced by using sand mold-gravity casting. The simulation casting process was conducted before making these grinding balls by using SOLIDCast™ version 8.2.0. The gating system design and the pouring temperature of hot metal were investigated clearly to obtain grinding balls with no-defect. The sound casting of grinding balls was resulted by using the proper gating system with the addition of vent air on the top of each grinding ball’s mold. The dimension of vent air was reduced by the increasing of pouring temperature, thus it resulted on the increasing of the yield production of grinding balls.

Microstructure characterisation and mechanical properties of a functionally-graded NbC/high chromium white cast iron composite

A functionally graded NbC – high chromium white cast iron composite was successfully fabricated by centrifugal casting for high wear applications. The migration of primary NbC particles to the outer periphery, as predicted by Stokes' law, resulted in an extremely hard outer layer at the surface of a softer bulk material. Microstructural characterisation showed that both the volume fraction and the morphology of the carbides varies along the thickness of the specimen. At the outer surface, the NbC was present as primary carbides while Chinese-script NbC was found in the bulk of the material. Hardness, sliding wear and three-point bending tests confirmed that the outer layer was harder and more wear resistant than the rest of the material, which was correspondingly tougher. The study of the fracture surface of the specimens showed that there is a strong bond between NbC and the matrix such that delamination between the reinforcements and the matrix did not occur during fracture. If Chinese-script NbC can be reduced or prevented in the bulk material, further improvements to toughness could be achieved.

Microstructural evolution during austempering of a ASTM A-532 CLASS III type high chromium white cast iron undergoing abrasive wear

This paper studies the influence of variables such as holding temperatures and times during austempering of High Chromium White Cast Iron (HCWCI), with the following chemical composition: Cr 25 %, C 3 %, Si 0.47 %, Mn 0.74 % and Mo 1.02 %. The aim of the austempering was to modify the percentage of retained austenite and its correlation to abrasive wear resistance under different conditions.Microhardness tests, SEM-EDS and XRD were performed to determine mechanical properties, chemical composition, and type of carbides and microstructures present, respectively. The tests complied with the ASTM G-65 standard. Results showed that the best performance against abrasion was achieved for austempering at 450 ºC with holding time of 6 hours.

Nano-Scratching resistance of high-chromium white cast iron and its correlation with wear of cBN tool in machining

In this paper, a nano-scratch testing approach was used to measure and evaluate the abrasion wear resistance of high-chromium white cast irons in order to understand the wear mechanism in the interaction between the high-chromium white cast iron and the cBN cutting tool during the machining process. Scratch testing was performed on a nanoindentation instrument using a diamond indenter as the scratch tool. Linear multi-pass scratches in the same path were made on pre-worn surfaces of test materials. The correlation of the scratching resistance and tool wear measured from the machining is presented by the flank wear and maximum scratch depth. The appearance of the cutting edge on a cBN tool suggests that the abrasion wear is mainly related with a combined effect of the carbides and the matrix during machining the high-chromium white cast iron.

Tool wear and machining dynamics when turning high chromium white cast iron with pcBN tools

High chromium white cast irons (HCCI) with high hardness and abrasiveness owing to a particular combination of hard primary and eutectic carbides were used as workpiece materials for longitudinal turning with binderless cBN (bcBN) and high cBN (hcBN) tools. The materials with low and high Si content were used in as-cast and quenched states. Binderless cBN is prone to cratering and flank wear, while hcBN is more prone to significant cutting edge rounding. Atypical behavior was found when machining high-Si material where the increase in cutting forces was accompanied by suppression of vibrations. The observed formation of a tool protection layer (TPL) on the tool–chip interface was found to be responsible for the improved dynamic stability. Electron microscopy and EDX analysis revealed that the TPL consists of nanocrystalline Al2O3 with SiO2 inclusions, both present in the workpiece materials. The stability of TPL was found to depend on both workpiece and tool materials. The absence or removal of the layer resulted in the development of self-excited vibrations with a frequency of 380Hz, which affected the machined surface.

The role of microstructure in high stress abrasion of white cast irons

The abrasion wear resistance of white cast irons can be controlled primarily by adjusting the size, size distribution, and volume fraction of the carbide phase. The main physical property of white cast irons correlating with abrasion resistance is hardness. This study concentrates on the evaluation of hardened and stress relieved, normalized, self-hardened, and as-cast states of high chromium white cast irons in high stress abrasion. The correct size and orientation of the carbides were found to be crucial for the wear resistance of white cast irons in high stress abrasive conditions. The different annealing procedures affected the formation of the carbide structure and its distribution, as well as the microstructure of the matrix. The austenite-to-martensite ratio together with a beneficial carbide structure was found to have a strong effect on the abrasion wear resistance of WCI specimens.

Correlation between the Meyer's law parameters and the wear resistance of chromium white cast irons

This work studies plastic behaviour and its influence on the abrasive wear resistance of a group of high chromium white cast irons. The irons were poured in metallic moulds and heat treated. The studied alloys have 3% C, 12% Cr, as well as 0.6% and 2.4% Si. The plastic characteristics are evaluated through the parameters obtained from Meyer's test: the strain hardening capacity (n) and the constant of penetration resistance (k).The influence of silicon content and applied heat treatments on Meyer's test parameters was determined. The heat treated samples showed values between n=2.3 and n=2.5. These values confirm a hardening capacity greater than the cast specimens. The high silicon alloy specimens show greater n-values than the low silicon alloy ones. This tendency is remarked when the complete treatments (austenitizing, cooling and holding) are applied. Correlation between n, k and the relative abrasive wear show good values for (k), but too much dispersion for the Meyer's Index (n).

The Althoff-Radtke Test Adapted for High Chromium Cast Iron

Abstract The paper presents results of the possibility of adapting the Althoff-Radtke test for High Chromium Cast Iron. The Althoff-Radtke test is a clump attempt used for steel. The Althoff-Radtke test has four different lengths of clamp which qualifies it as a test to quantitatively take into account different kinds of shrinkage ΔL. The length of the slot of the cracked corner and the length of each staple (50 - 350 mm) are the parameters tendency to cast cracks. Castings of white cast iron have a high tendency to hot cracking due to the large range of solidification temperatures, unfavorable kinetics parameters of shrinkage, and especially a lack of expansion before shrinkage. Shrinkage of high chromium white cast iron is similar to the shrinkage of cast steel, and is approximately 2%. Therefore it is important to test susceptibility to hot cracks. Research was carried out under industrial conditions. Four melts were performed, one of the initial chemical composition and the other three modified by different amounts of Fe-Ti, respectively, 0.25%, 0.5% and 0.75% Fe-Ti. The propensity for hot cracking was based on the observation of the dark surface in the corner of the sample. The study shows that the Althoff-Radtke test can be adapted to determine the tendency for hot cracking of high chromium cast iron. It should however be noted that the test results cannot be compared with those for other alloys.

Effects of heat treatment and counterface on the wear behaviour of Cr21 cast iron

The unlubricated sliding wear test of high chromium white cast irons (HCCIs) was conducted using a pin-on-disc configuration under different heat treatments and different hardnesses of the counterface. With the increase of counterface hardness (20 HRC–47 HRC–54 HRC), the mass loss of the sample first increases then decreases. When the counterface hardness is 20 HRC, adhesion wear mainly takes place between the high chromium cast iron and the surface of 1045 steel. When the hardness is 47 or 54 HRC, first HCCI’ matrix wear takes place, then carbide bump flakes under alternating stress. The mass loss of the counterface decreases with the increase of hardness for the same sample. The mass loss of quenching, once tempering and twice tempering sample decreases gradually for the same counterface hardness, but fluctuation of the samples’ surface increased. The disc material is always softer than the pin material and results in a severe wear regime operation.

Formation mechanism of bimetal composite layer between LCS and HCCI

A low carbon steel (LCS)/high chromium white cast iron (HCCI) bimetal wear plate about 20 mm in thickness was prepared by liquid-liquid bimetal composite casting technology to substitute for the welding wear plate. A clear and distinguishable composite layer between the LCS and the HCCI was detected with SEM, and the composition and phase were analyzed through EDS and XRD. The composite layer was composed of three sublayers from the LCS to the HCCI: pearlite transition layer, composite layer, and HCCI transition layer. The Vickers hardness from the pearlite transition layer to the HCCI transition layer was 360 HV to 855 HV. The austenite grows as dendrites between the composite layer and the HCCI transition layer under constitutional undercooling. A large amount of C and Cr, and a small amount of Si and Mn dissolve in the matrix. Granular Cr7C3 is uniformly distributed. Due to the solute redistribution at the solid-liquid interface, the primary austenite grows from planar to cellular and finally to the distinct dendrite crystals. The dendrite crystals have an obvious growth direction perpendicular to the composite layer.

Effect of TiBAl inoculation and heat treatment on microstructure and mechanical properties of hypereutectic high chromium white cast iron

Hypereutectic high chromium white cast iron alloys were produced with TiBAl (1–3 wt.%) inoculants. The heat treatments were applied to the samples as 1000 °C for 1 and 2 h. The microstructures of the samples were investigated by SEM. The chemical concentrations of matrix and carbides were determined by EDS and XRD to detect the type of carbides and matrix. The surface hardness of the samples was detected as HRC. The images of the fracture surfaces of the samples were examined by SEM. The toughness of the samples was evaluated by using charpy V-notch samples to detect the relationship between inoculation, carbide size and fracture toughness.

Mejoramiento de la resistencia al desgaste abrasivo de la fundición al alto cromo ASTM A-532 a través de ciclos de tratamiento térmico

Las fundiciones blancas de hierro al alto cromo son muy usadas en la minería y en la perforación de pozos petroleros, debido a su alta resistencia al desgaste, sin embargo, debido a que en el estado de colada su microestructura es austenítica, es necesario someterlas a un adecuado ciclo de tratamiento térmico. Este trabajo estudia los efectos de los diferentes medios de enfriamiento después de un tratamiento de desestabilización de la microestructura y, por ende, el efecto del grado de endurecimiento sobre el comportamiento a la abrasión de una fundición blanca al alto cromo hipoeutéctica. Los resultados muestran que a pesar de que el enfriamiento al aire, seguido por inmersión en CO2, puede reducir eficazmente la austenita retenida, esto no es suficiente para transformarla completamente en martensita. El bajo porcentaje de austenita retenida incrementa la dureza del material, pero disminuye la resistencia a la abrasión de las fundiciones al alto cromo. La mejor combinación de dureza y resistencia al desgaste se encontró en las muestras enfriadas al aire, debido al porcentaje de austenita retenida y a una moderada precipitación de carburos de cromo.

Effect of Niobium on the Microstructure of High Chromium White Cast Iron

ABSTRACTEquipment wear is caused by the disintegration of material due to the contact between the machines components and the ore, resulting in stress to the surface of the material. Wear causes loss of efficiency, vibration, misalignment and, in severe cases, cracks that may lead to fracture and damage to the equipment. In mining, wear is caused by operational problems in which generate high costs. Some researchers studied white cast iron alloys with high chromium and the addition of niobium for wear plates manufacturing and therefore, plates to protect structural parts of the equipment have been developed. This study presents the characterization of the microstructure of two alloys of white cast iron with high chromium containing 3.8 wt.% C and 27.1 wt.% Cr and the addition of 0.9 wt.% Nb (alloy 1) and 1.6 wt.% Nb (alloy 2), respectively. Samples of the two alloys were subjected to metallographic tests, microhardness and abrasion type rubber wheel tests, according to the ASTM: G65-91 standard. Complexes carbides have been identified in both alloys. The results of microhardness and wear resistance tests were correlated and identified the effect of niobium addition. The findings suggest that the addition of niobium in these alloys contributes to the formation of NbC and increase of Cr in the matrix; consequently increase in the hardenability of the material. The wear resistance of alloy 2 was 47.95% higher than alloy 1 in abrasion type rubber wheel tests. It demonstrates that the increase of niobium in the alloy has contributed to improve wear resistance due to the substantial change in the microstructure and distribution of NbC carbides.

Grain refinement of 25 wt% high-chromium white cast iron by addition of vanadium

Grain refinement of 25 wt% high-chromium white cast iron by addition of vanadium

Tool Wear and Vibrations Generated When Turning High-chromium White Cast Iron with pCBN Tools

Dynamic behavior and stability of system ‘tool-workpiece’ when machining HCCI with pCBN tools are determined by the processes which occur in cutting zone. The cutting process is characterized by formation of tool protection layer (TPL) on the chip contact area but its stability depends on the workpiece material composition, tool material and cutting conditions. The higher content of Si in the HCCI promotes the TPL formation and its stability. The presence and stability of TPL, besides the cutting edge protection, provides the system with additional damping resulting in the suppression of vibrations. A low Si content and low cutting speed leads to increase of cutting forces that in turn causes the self-generated vibration occurrence.

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

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

Wear resistance of high chromium white cast iron for coal grinding rolls

Las fundiciones blancas al alto cromo utilizadas en componentes demolinos de carbon son materiales que presentan diferentes resistencias al desgaste,dependiendo del tratamiento termico usado en su fabricacion. Las propiedades mecanicas,microestructurales y tribologicas de la aleacion con 22% de cromo y 3% de carbono (II DASTM A532-10) y su infl uencia en la resistencia al desgaste fueron investigadas. Para lacaracterizacion de la aleacion fueron realizados diversos ensayos, utilizando los siguientesequipos de laboratorio: durometro, microdurometro, microscopio optico, microscopioelectronico de barrido, difraccion de rayos X, espectrofotometro de emision optica, yequipo para ensayo de desgaste abrasivo de acuerdo con la norma ASTM G65-04 (2010).Los resultados encontrados mostraron que la resistencia al desgaste incrementa cuandola matriz tiene una baja fraccion volumetrica de austenita retenida y una alta fraccion decarburos secundarios. Tambien indican que no es necesario usar largos tiempos durante ladesestabilizacion en la aleacion II D para obtener una optima resistencia al desgaste, cuandola aleacion fue previamente recocida. Estos resultados indican que la industria puede usartiempos cortos durante la desestabilizacion de los rodillos de molinos de carbon.

Fabrication of plain carbon steel/high chromium white cast iron bimetal by a liquid–solid composite casting process

High-chromium white cast iron (HCWCI) is one of the most widely used engineering materials in the mining and cement industries. However, in some components, such as the pulverizer plates of ash mills, the poor machinability of HCWCI creates difficulties. The bimetal casting technique is a suitable method for improving the machinability of HCWCI by joining an easily machined layer of plain carbon steel (PCS) to its hard part. In this study, the possibility of PCS/HCWCI bimetal casting was investigated using sand casting. The investigation was conducted by optical and electron microscopy and non-destructive, impact toughness, and tensile tests. The hardness and chemical composition profiles on both sides of the interface were plotted in this study. The results indicated that a conventional and low-cost casting technique could be a reliable method for producing PCS/HCWCI bimetal. The interfacial microstructure comprised two distinct layers: a very fine, partially spheroidized pearlite layer and a coarse full pearlite layer. Moreover, characterization of the microstructure revealed that the interface was free of defects.

Effect of PCBN tool grade and cutting type on hard turning of high-chromium white cast iron

The turning of mechanical construction and bearing steels is widely carried out using PCBN and oxide ceramic tools, even when materials have high hardness (40 to 60 HRC), reached after quenching and tempering heat treatment. However, mechanical components submitted to severe abrasive loads show, in addition to matrix hardness, the presence of a high-volume fraction of hard particles in the microstructure. Turning materials with a high content of hard particles in the microstructure will result in high rates of abrasive wear or damage to the cutting edges of the tool. Information regarding the turning of materials characterized by a high-volume fraction of carbides in the microstructure is limited in literature. The objective of this study was to determine the performance of two grades of PCBN tools (high CBN and low CBN content with an added ceramic phase) in the turning of high-chromium white cast iron applying continuous and interrupted cutting. Evaluations of tools’ life, wear mechanisms at the tool cutting edges, roughness, and microstructure remaining on the turned surface were carried out. The results show that the grades with low CBN content and the addition of a ceramic phase, the tool life was three times longer than that of the grades with high CBN content. The most interesting result obtained concerns the microstructural modifications in a narrow subsurface layer of the turned material. Carbide fragmentation and alignment in the direction of the cutting shear plane were identified, which may potentiate the use of the material.

Analysis of heat transport and thickness of bimetal composition layer between low-alloy steel and high-chromium white cast iron

Two-liquid bimetal casting technique was worthy of being widely used in wear-resistant materials. Research on the fusion mechanism at the bimetal composite layer can lay the theoretic foundation for the extension of the dissimilar ferroalloy composition material. Two-liquid bimetal between the low-alloy steel and high-chromium white cast was prepared by controlling the pouring temperature, and the composite layer microstructure and composition distribution were studied. In accordance with the detected results, two-liquid bimetal casting technique can be assured, and the various casting technique parameters have an obvious effect on the composite layer microstructure. To maintain the casting technique stability, the freezing time and element diffusion of the low-alloy steel were evaluated and analysed.