Hypereutectic High Chromium Cast Iron Research Articles

Abnormal erosion–slurry velocity relationship of high chromium cast iron with high carbon concentrations

Abstract It is usually expected that the damage to materials by sand-containing water slurry erosion is enhanced as the slurry velocity increases. However, a recent study on high chromium cast iron (HCCI) showed abnormal decreases in erosion of hypereutectic HCCIs having high carbon concentrations (e.g., 6 wt.%C) as the velocity of water–sand slurry increased from 2.5 m/s to 5 m/s. For HCCIs having lower carbon concentrations (hypoeutectic), the trend was reversed. In order to explain the abnormal erosion behavior of the hypereutectic HCCIs, microstructure, erosion–corrosion resistance, mechanical and electrochemical properties of the HCCIs under study were characterized and evaluated. It was demonstrated that the observed abnormal erosion–slurry velocity relationship was attributed to the competition between mechanical attack (erosion) and electrochemical attack (corrosion). At low slurry velocities, corrosion played an important role in erosion–corrosion, while at higher slurry velocities the mechanical attack/erosion became dominant.

Effect of Ti addition on morphology and size of primary M7C3 type carbide in hypereutectic high chromium cast iron

Effect of Ti addition on the morphology and size of primary M7C3 type carbide in hypereutectic high chromium cast iron was investigated. The results indicated that the carbide is refined gradually, and its morphology becomes more equiaxed as titanium addition increases, but rather slowly when Ti addition exceeds 0·95%. The qualitative measurement result indicated that value shape factor K increases clearly first and then changes little, and the average equivalent diameter D changes against K exactly. Furthermore, by TEM analysis and Brammit’s theory calculation, the results also indicated that there are orientation relationships of TiC||M7C3 and [011]TiC||[0001]M7C3 between M7C3 type carbide and TiC, and the lattice misfit δ between TiC and M7C3 is 1·32%, explaining that TiC may provide the effective substrate plane for M7C3 nucleation to ameliorate morphology and size of primary M7C3 type carbide.

Microstructure and properties of semisolid hypereutectic high chromium cast iron prepared by slope cooling body method

To improve the toughness of hypereutectic high chromium cast iron, the morphology of the primary carbides were improved by the slope cooling body method, a semisolid forming process. The semisolid specimens were prepared under different forming techniques, and the microstructure, impact toughness and wear resistance were studied. The results indicate that the morphology of primary carbide is improved, impact toughness initially increases then remains constant as the semisolid forming temperature increases, impact toughness was improved, but wear resistance was reduced.

Effect of TiC Particle Additions on Structure and Properties of Hypereutectic High Chromium Cast Iron

The present work studies the effects of titanium carbide (TiC) particle additions on the microstructure and mechanical properties of hypereutectic high chromium cast iron containing about 20%Cr and 4.0%C by the optical microscopy (OM), the transmission electron microscopy (TEM), the X-ray diffraction (XRD) analysis, the digital image analysis system, impact tester, and hardness tester. The carbides of high chromium cast iron are refined gradually and the shape of the primary M7C3-type carbides became more isotropic with the increase of TiC particles. When the addition of TiC particles exceeds 1.0 wt.%, the change of microstructure is not obvious. The hardness of high chromium cast iron has a slight increase and impact toughness has a obvious increase with the increase of TiC additions. However, when the addition of TiC particles exceeds 1.0 wt.%, the impact toughness has no obvious change.

Effects of titanium addition on microstructure and wear resistance of hypereutectic high chromium cast iron Fe–25wt.%Cr–4wt.%C

A finer microstructure generally helps to increase the wear resistance of materials. It was reported that Ti could act as an inoculant to generate fine microstructure for white cast iron, one of widely used in industrial materials. To confirm this, we investigated influences of Ti addition (up to 6 wt.%) on microstructure of a hypereutectic high chromium cast iron (Fe–25wt.%Cr–4wt.%C). Ingot samples were prepared using an arc furnace by melting pieces of the cast iron with titanium powder. Microstructures of the samples were examined by optical microscopy, scanning electron microscopy, energy dispersive X-ray spectrometry and X-ray diffraction. It was demonstrated that the added titanium did not act as an inoculant to reduce the size of coarse primary carbides. Instead, as the titanium amount was increased, the cast iron changed from a hypereutectic microstructure to a hypoeutectic one due to the depletion of carbon that was consumed by Ti to form titanium carbides. When 2 wt.% Ti was added, the finest microstructure was achieved, which corresponded to the eutectic structure with mixed chromium carbides and titanium carbides. The eutectic structure exhibited the highest wear resistance and hardness due to the refined microstructure as well as the fact that an amount of chromium carbides were replaced by Ti carbides, which are harder than the former.

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

The effect of cerium element on the as-cast microstructure of a hypereutectic high chromium cast iron (HCCI) containing 4.0 wt.% C and 20.0 wt.% Cr was studied by means of optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS). The results indicate that the primary M 7C 3 carbides are refined and spheroidized with the addition of suitable amount of cerium. Ce 2O 2S is found in the primary carbide. The mechanism of Cerium modification on microstructure of the alloy is also discussed.

Effect of titanium on the morphology of primary M 7C 3 carbides in hypereutectic high chromium white iron

This paper studies the effect of titanium concentration on the morphology of primary M 7C 3 carbides in hypereutectic high chromium white cast iron by means of the optical microscopy (OM), the scanning electron microscopy (SEM), the X-ray diffraction (XRD), the energy dispersive X-ray spectrometry (EDS) and Leica image analyzer. Theoretical calculation shows that solute Ti atoms can react with carbon and form TiC particles under certain conditions in the melt of hypereutectic high chromium cast iron. The experimental results show that the morphology of primary M 7C 3 carbides can be improved by adding a suitable amount of Ti. This improvement correlated with the emergence of TiC particles. These particles can act as the substrates for heterogeneous nucleation of primary M 7C 3 carbides, which results in significant refinement of the final grain size.

Investigation of Microstructure and Impact Toughness of Semisolid Hypereutectic High Chromium Cast Iron Prepared by Slope Cooling Body Method

Investigation of Microstructure and Impact Toughness of Semisolid Hypereutectic High Chromium Cast Iron Prepared by Slope Cooling Body Method