Papers by Keyword: High Chromium Cast Iron

Abstract: Welded arc welding repair welding technology was used to repair the casting defects of high chromium cast iron ball mill liners. Select the same high-chromium cast iron as the casting. The diameter of the electrode is 4mm and the welding current is 150-160A. After welding, the castings were found to have no cracks by surface non-destructive testing. The macro-hardness was comparable to that of the matrix material, and the microstructure showed that the fused surface was a good metallurgical bond.

Abstract: The effects of destabilisation and tempering heat treatments on hardness and corrosion behavior in 28 wt.%Cr-2.6 wt.%C cast irons with up to 6 wt.%Mo addition were studied. The irons were destabilised at 1025 °C for 4 h and air cooled. Tempering was carried out at 450 °C for 4 h. Phase identification and microstructure were investigated by X-ray diffraction (XRD), light microscope (LM), scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). Vickers macro-hardness was measured. A potentiodynamic technique was used to indicate aqueous corrosion resistance. The results revealed that the as-cast microstructure of 28 wt.%Cr iron consisted of primary austenite dendrites with eutectic M₇C₃ carbides. In the irons with 6 wt.%Mo addition, eutectic carbides including M₇C₃, M₂₃C₆ and M₆C were found. After destabilisation, the microstructure contained secondary carbide precipitates within an essentially martensitic matrix. Vickers macro-hardness of the as-cast and destabilised irons increased from 500 HV30 and 736 HV30 in the 28 wt.%Cr iron up to 570 HV30 and 870 HV30 in the iron with 6 wt.%Mo addition. Tempering slightly increased the macro-hardness. The as-cast 28 wt.%Cr iron had the lowest values for critical current density and passive current density. The destabilised + tempered treatment gave the lowest corrosion resistance.

Abstract: The paper presents the result of studies of composite powders produced by self-propagating high temperature synthesis (SHS) in the reaction mixtures of titanium, carbon and high chrome cast iron, and electron-beam coatings based on them. It was found that the morphology and dispersion of titanium carbide particles in the SHS-product were determined by cast iron powder content in the reaction mixtures. The effect of content of the SHS powders on the characteristics of electron-beam coatings, including abrasive wear resistance of facing coatings was shown.

Abstract: This work focuses on the oxidation behavior of 2.4wt.%C-30wt.%Cr-3.75wt.%V cast iron in air at 1000 °C for 1-48 h with weight gain measurements taken at different times. The oxidized surfaces and cross sections were characterized by XRD, OM, SEM and EDS. It was found that the as-cast microstructure consisted of a ferritic matrix and M₇C₃ carbide. The surface oxide scale consisted of multi-oxides and the grain size of the oxides increased with increasing holding times. XRD and SEM-EDS results revealed that the multi-oxide layer can be Cr₂O₃, (Fe,Cr,V)₂O₃ and SiO₂. After about 48 h, a continuous SiO₂ inner-layer was observed and the oxide scale tended to swell, contained pores, and became detached from the surface because of its poor adherence.

Abstract: The effect of carbide orientation on the dry sliding wear behaviour of high chromium cast iron was studied by pin-on-disc type wear tests at room temperature. The carbide anisotropy was achieved by thermomechanical treatments at temperatures of 950 and 1150 °C. By cladding with low carbon steel, the brittle high chromium cast iron was hot compressed severely with crack free. The thermomechanical treatments not only change the carbide orientation, but also increase the volume fraction of carbides. Due to the long axis of carbide rods is parallel to the wear surface, the high chromium cast iron treated at 1150 °C has a superior wear resistance than the as-cast one, in which the long axis of carbides is perpendicular to the wear surface. For the high chromium cast iron treated at 950 °C, high volume fraction of carbide pits accelerates the wear rate significantly even though it has a similar carbide orientation as the sample treated at 1150 °C. The observations on wear tracks reveal that the ferrous matrix can be protected better from abrasion when the high chromium cast iron was treated at 1150 °C.

Abstract: Effects of destabilisation heat treatment on microstructure, hardness and corrosion resistance of 18wt.%Cr and 25wt.%Cr irons have been investigated. The as-cast samples were heat-treated by destabilisation at 1000°C for 4 hour and then air cooling. The microstructure was investigated by light microscopy and scanning electron microscopy. The results show that the as-cast microstructure in 18wt.%Cr iron consists of pearlite, formed by decomposition of primary dendritic austenite, plus eutectic structure. In the 25wt.%Cr iron with lower hardness, the microstructure consists of primary dendritic austenite plus eutectic structure. The austenite had partly transformed to martensite, especially at areas adjacent to eutectic carbides. After destabilisation, the microstructure of both irons consists of eutectic and secondary carbides in a martensite matrix giving increased hardness. It was found that corrosion resistance of the irons was improved after destabilisation. The 25wt.%Cr showed superior corrosion resistance than the 18wt.%Cr iron due to greater residual Cr in the matrix to encourage passivity.

Abstract: High chromium cast iron and stainless steel bimetal were fabricated by liquid-solid composite casting .The interface diffusion behavior and microstructure evolution of high chromium cast iron were studied. The results indicated that interface element diffusion behavior between stainless steel and high chromium cast iron was obviously existed. Under experimental conditions, there were many refined grainy-shaped carbides precipitation in stainless steel near interface, located at austenite grain boundary and intragranular austenite. As for high chromium cast iron, the morphology of the carbides varied from the interface to the specimen edge. The rod shaped carbides approached to composite interface were finer and become coarser rod-like or blade-like with increased distance from the composite interface. The reasons for elements diffusion and microstructure change were associated with alloys contents and temperature field.

Abstract: The corrosion property of high chromium cast iron was test under different phosphoric acid medium concentration. On the base of experimental data, the binary equation model of corrosion weight loss (W) versus phosphoric acid concentration and corrosion time (c, t) was built using multiple regression analysis, which can predict corrosion property of high chromium cast iron effectively. The prediction results show that the corrosion weight loss rises lineally with increasing corrosion time, and the corrosion rate rises quadratically with increasing phosphoric acid concentration. The corrosion failure mechanism is that chromium composite carbides (M7C3) stand out of matrixes surface after the matrixes composed of martensite and austenite are corroded firstly, then the M7C3 carbides drop out of matrixes when the matrixes can not wrap M7C3 carbides, resulting gradual corrosion of high chromium cast iron. The prediction values have sufficiently mined the basic domain knowledge of corrosion process of high chromium cast iron under phosphoric acid medium. Therefore, a new way of predicting corrosion property according to corrosion conditions was provided by the authors.

Abstract: In this paper, a type of high-deposition-rate, low-dilution-rate and wide-welding-bead flux-cored strip which is easy to realize automatic surfacing was designed. Considering the working condition of high temperature and abrasive wear in the iron and steel industry, a kind of high-chromium iron surfacing flux-cored strip was designed. The effect of alloy elements on the microstructure and property abrasive wear resistance of deposited metal was investigated. The abrasion and heat resistant plate deposited by the flux-cored strip was carried out on raw material transport system in steel enterprises. The service life was significantly improved and the examination and repair time is reduced.

Abstract: Effect of RE and V on microstructure and mechanical properties of high chromium cast iron were investigated by optical microscopy, scanning electron microscopy, X-ray diffraction, impact test and wear test. The results show that proper modification using RE combined with V makes the alloy present a more refined and homogenous austenite matrix, and makes the morphology of carbide changing from thick lath to thin lath, and rosette-like. Modification can also increase hardness, wear resistance and impact toughness of high chromium cast iron.