Silicon Cast Iron Research Articles

Crystallization of Intermetallic Phases Fe2Si, Fe5Si3 for High Alloyed Cast Irons

This paper presents the results of laboratory tests related to high-alloy silicon cast iron (HSCI). These materials are corrosion-resistant and commonly used in cathodic protection systems as protective electrodes. Due to their high fragility, alloys with increased Si content are not suitable for producing elements exposed to dynamic loads. This paper analyzes the crystallization process of silicon alloys (with Si content between 23% and 25%) using thermal and derivation analysis methods. The tests also included an extended analysis of chemical composition. The metallographic tests included scanning electron microscopy with an EDS system, and the phase composition was determined using X-ray diffraction. As a result of the tests, the warp components were identified, the primary share of which are intermetallic phases of the Fe5Si3 type. Moreover, single silicon crystals were found. The test results allowed for clarification of the temperature range of the transition of the Fe2Si phase into the Fe5Si3 phase and the determination of characteristic points of the crystallization process (TSolidus i TLiquidus). Furthermore, bifilm-type inclusions were identified in the alloys. We also managed to present the silicon crystals and Fe5Si3 phases in a spatial layout via observation of the surfaces of contraction cavities using scanning electron microscopy.

THERMODYNAMIC ANALYSIS OF THE TECHNOLOGICAL OPERATION OF CAST IRON REFINING WITH A MIXTURE OF OXIDE COMPONENTS OF THE CaO-FeO-Na2CO3 SYSTEM

At present, at the metallurgical plants of Ukraine, a charge with an unstable chemical composition is used, which leads to significant fluctuations in temperature, the content of sulfur, silicon in cast iron and to a significant decrease in the technical and economic indicators of the further process of the production of iron-carbon semi-products. The application of standard technology of step-by-step multi-stage refining of cast iron from sulfur, silicon and phosphorus leads to an increasemelting cycle, a significant decrease in temperature, which reduces the technical and economic indicators of converter melting. Therefore, studies of the processes of one-stage removal of sulfur and silicon from liquid cast iron are relevant for the development of recommendations for reagents and technology of complex treatment of cast iron before steelmaking processing. The purpose of the work is to clarify the features of the physicochemical transformations occurring in the volume of liquid cast iron when the refining mixture of the CaO-FeO-Na2CO3 system is injected when the carrier gas is supplied in the jet. Information on the interaction of melt components with oxidation products formed in the zone of action of the gas jet was summarized, and the dependence of lgKp on temperature was constructed for possible reactions of chemical transformationsA thermodynamic analysis of the refining process was carried out due to the injection of the refining mixture of the CaO-FeO-Na2CO3 system using different carrier gases. It has been established that silicon removal processes mainly take place in the zone of direct impact of the gas-powder jet on the melt, and the silicon dioxin formed at the same time is effectively bound into dicalcium silicate. Removal of sulfur from the melt proceeds directly due to the interaction of elements of the melt with products formed in the zone of influence of the gas-powder jet on liquid cast iron and is based on desulfurization with soda in the presence of high concentrations of soda in the melt.

Efficient Technologies for Producing Cast Iron Billets and Products with Specified Properties and Microstructure

The article discusses the use of resonant-pulsating refining technology in order to improve the quality of cast iron products. This technology is used in the cast iron production and cast iron mold induction. It is relatively simple and easily fits into existing production. The effectiveness of this technology is at the world’s best indicator level. The chemical composition and smelting modes of cast iron influences significantly on the microstructure of gray cast iron. The determining factors are the content of silicon in cast iron, carbon, manganese, titanium and vanadium. The carbon content affects significantly taking into account its content above 3.8%, since this content increases the content of large, ripe forms of graphite in cast iron. Titanium and vanadium also influence significantly on the microstructure of cast iron. These two elements, even in small amounts, affect the size and shape of graphite greatly. It also affects the amount of ferrite, perlite and cementite in the structure of cast iron. Vanadium also affects greatly the service life of cast iron products.

The study on corrosion behavior and corrosion resistance of ultralow carbon high silicon iron-based alloy

The ultralow carbon high silicon iron-based alloy (sample A) with a single ferrite matrix was prepared. The corrosion performance difference and mechanism between it and conventional high silicon cast iron (sample B) were systematically studied using optical microscope, scanning electron microscope, electric corrosion equipment, electrochemical corrosion workshop and atomic force microscope. The results show that the corrosion rate of ultralow carbon iron-based alloys was significantly lower than that of high-silicon cast iron. For example, the static corrosion rate after 310 h, the corrosion rate of sample A was 0.2399 g/(m2 · h), and the corrosion rate of sample B was 1.5159 g/(m2 · h). The potential difference of the substrate was significantly reduced. That is, the ultralow carbon iron-based alloy exhibits better corrosion resistance, which is mainly attributed to the denser passivation film formed on its surface. The results of microhardness show that the hardness of Sample A was higher than that of Sample B.

Influence of impressed current cathodic protection systems on chemical characteristics of underground water.

Despite well-known corrosion inhibition behavior of cathodic protection (CP) system, this process might be a potential hazard to surrounding ecosystem resulted mostly from continuous electrical current which is applied to the adjacent environment and metallic anode dissolution as well. In this research, deepwater CP wells at different locations of Golestan province, Iran, were taken into consideration to evaluate the impact of these protective systems on underground waters from viewpoint of chemical and physicochemical characteristics resulted from anode dissolution. For this purpose, concentration of metallic constituents of the anode as well as the amount of pH, total dissolved solids (TDS), electrical conductivity (EC), and total hardness were determined. On the basis of obtained results, the concentration of Mn, Cr, and Fe in CP well located nearby an industrial district (i.e., 0.087, 0.475, and 8.5mg/L, respectively) was higher than both WHO and USEPA standards. This fact can be resulted from the position where the well was dug as well as the CP anode dissolution within the deep CP water wells. PRACTITIONER POINTS: The impact of impressed current cathodic protection (ICCP) system on chemical and physicochemical characteristics of underground water has been evaluated. Anode dissolution of ICCP systems influences the water characteristics nearby the anodes. Despite low dissolution rate of high silicon cast iron anodes, their long-term utilization might be harmful for adjacent ecosystem. The amount of heavy metals in underground waters was demonstrated to be influenced by the employment of ICCP system. Both anode dissolution and the geological properties of the Earth`s crust surrounding the wellbore might be responsible for significant increase of heavy metals concentration.

Coarsening and dendritic instability of spheroidal graphite in high silicon cast iron under thermal cycling in the ferritic domain

High silicon ferritic spheroidal graphite cast irons have been developed for high temperature service, in particular under thermal cycling conditions. The theoretical maximum service temperature is defined as the upper limit of the two-phase ferrite+graphite domain, which increases with the alloy silicon content. While isothermal heat treatment close to this temperature showed little evolution of the graphite distribution, thermal cycling led to a significant coarsening of the graphite particles associated with dendritic overgrowth of the large graphite particles. This unexpected behaviour is here observed and described for the first time.

ABOUT THE CONDITIONS OF BLAST FURNACE SMELTING OF PIG IRON OF A CERTAIN QUALITY

The impact of operating conditions on the quality of pig iron has been investigated on a blast furnace with a volume of1500 m3at an average cost of pulverized coal up to160 kg/ ton of pig iron. It has been established that the influence on the content of silicon in cast iron by changing the slag regime has limited possibilities. In contrast to silicon, the change in the slag regime, primarily the basicity of the effective effect on the transition of sulfur to the slag. When designing optimum for specific conditions, the technology of blast-furnace smelting should take into account the difference in the behavior of silicon and sulfur when the heating of the furnace is changed, in particular, the content of sulfur in the pig iron varies faster than the content of silicon. The decrease in the temperature of the iron from 1500 to 1400oC was accompanied by an average decrease in the content of silicon from 0.89 to 0.47%, that is, approximately twice. The same decrease in temperature led to an increase in sulfur content in the metal, on average, from 0.013 to 0.042% or more than three times. Given this difference, depending on the possibilities of further processing of cast iron, it is necessary to establish such a thermal regime, which maintains the desired levels of sulfur and silicon content, providing a certain effect in the blast furnace process and further processing. The existence of a feedback between the intensity of the smelting and the content of silicon in the pig iron is established. The existence of pulsations of the average level of sulfur content in cast iron has been confirmed. An essential difference between our observations is an increase in the period of pulsations from 3-7 to 8-11. The reasons for increasing the period require further study.

MICROSEGREGATION OF SILICON IN CAST IRON

The literature presents contradictory data on the microsegregation of silicon in cast iron. Authors of the previous works have investigated silicon microsegregation in dendritic cell consisting both of primary austenite and eutectic austenite that grows on the primary austenite dendrites. Since the silicon content in austenite affects the temperature and completeness of the phase transitions during cooling and heat treatment, the absence of data on silicon microsegregation do not allow to predict the microstructure of cast iron in the as-cast condition and after heat treatment. The silicon microsegregation in gray cast iron with composition Fe + 3.11 % С + 1.6 % Si + 0.4 % M n by the energy dispersive X-ray spectroscopy and calculation of the nonequilibrium solidification in the Thermo-Calc software were investigated. The silicon microsegregation in the primary austenite is not observed. The silicon content in the primary austenite was ≈2 % that is higher than silicon content in the eutectic austenite ≈1.5 %. Due to the calculations results the microsegregation of silicon in primary austenite are negligible. By calculation the non-equilibrium solidification of ternary alloys Fe – Si – C [Fe + 1.5 % Si + X % C], at X = 1.5; 2.8; 3.7 it was shown that the only primary austenite solidified at 1.5 % С and microsegregation of silicon are positive (Si content in the center of the dendritic cells is lower than on its boundaries). For the alloy with 2.8 % С, the microsegregation of Si in the primary austenite is also positive, however the silicon content in the eutectic austenite, growing on the primary austenite during the austenite-graphite eutectic formation, will be lower and the “rim effect” (maximum Si content at the boundary between primary and eutectic austenite) should appears. At the 3.7 % of C in alloys the primary dendrites amount should be limited, so the major part of the dendritic cell should consist of the eutectic austenite, the Si content in which should be decreasing during the solidification. In this case the so-called negative microsegregation should occur.

Evaluation of microstructure and electrochemical behavior of dual-layer NiCrAlY/mullite plasma sprayed coating on high silicon cast iron alloy

Abstract Protective single-layer mullite and dual-layer NiCrAlY/mullite coatings were deposited on high silicon cast iron by plasma spraying process. The microstructure analysis showed that NiCrAlY layer with a thickness of 90±19 µm as bond coat and the nano-structured mullite layer with a thickness of 163±23 µm as a top coat formed homogeneously on the surface of high silicon cast iron. The X-ray diffraction (XRD) results indicate amorphous phases as a result of rapid cooling of molten particles. The microhardness of mullite layer in dual-layer NiCrAlY/mullite coating was significantly higher than bond coat and substrate. In addition, the corrosion behavior of the samples was comparatively studied using electrochemical tests. Polarization and EIS results showed that the uncoated sample has not suitable corrosion resistance in 3.5% NaCl solution due to the formation of micro-galvanic cells between graphite flakes and metal. However, its corrosion resistance was improved by the surface modification process. In the case of the coated samples, the dual-layer NiCrAlY/mullite coated sample exhibited better corrosion resistance due to the existence of a dense corrosion resistance bond coat and stronger bonding strength. Finally, the corrosion mechanisms for the mullite single-layer, NiCrAlY/mullite dual-layer, and uncoated samples were proposed.

Physicochemical Properties of Silicon Cast Iron

Abstract The article presents results of pitting corrosion studies of selected silicon cast irons. The range of studies included low, medium and high silicon cast iron. The amount of alloying addition (Si) in examined cast irons was between 5 to 25 %. Experimental melts of silicon cast irons [1-3] were conducted in Department of Foundry of Silesian University of Technology in Gliwice and pitting corrosion resistance tests were performed in Faculty of Biomedical Engineering in Department of Biomaterials and Medical Devices Engineering of Silesian University of Technology in Zabrze. In tests of corrosion resistance the potentiostat VoltaLab PGP201 was used. Results obtained in those research complement the knowledge about the corrosion resistance of iron alloys with carbon containing Si alloying addition above 17 % [4-6]. Obtained results were supplemented with metallographic examinations using scanning electron microscopy. The analysis of chemical composition for cast irons using Leco spectrometer was done and the content of alloying element (silicon) was also determined using the gravimetric method in the laboratory of the Institute of Welding in Gliwice. The compounds of microstructure were identify by X-ray diffraction.

As cast high silicon ductile irons with optimised mechanical properties and remarkable fatigue properties

The present work shows a comparative study regarding the mechanical properties of 25 as cast ferritic ductile iron alloys, nine of them with silicon contents higher than 3·00% and carbon contents lower than 3·60%. In a first step, different carbon equivalent values have been used in order to analyse the effect of this parameter on the mechanical properties. After this comparative analysis, the composition ranges C = 3·30–3·40 wt-% and Si = 3·75–3·80 wt-% have been selected as the most proper ones to optimise the tensile and impact properties among the high silicon ductile iron alloys. Finally, a second study was carried out to compare the tensile and fatigue properties of the optimised high silicon alloy with the corresponding ones obtained from an EN GJS 400-18-LT grade alloy with low silicon content. Although the room temperature impact values obtained from the high silicon ductile iron are lower than 6 J cm−2, the measured fatigue limit of this alloy (358 MPa) is clearly higher than the one obtained from the low silicon cast iron (170 MPa). A discussion about the benefits and advantages of the high silicon alloy is included.

전기동력학 기술을 이용한 시설재배지 토양의 염류제거 효과연구

To verify that the electrokinetic remediation is effective for decreasing salinity of fields of the plastic-film house, field tests for physical property, chemical property, and crop productivity of soils have been conducted. The abridged result of those tests is as follows. In the EK treatment, the electrokinetic remediation has been treated at the constant voltage (about 0.8 V ) for fields of the farm household. At this time, an alternating current (AC) 220 V of the farm household was transformed a direct current. The HSCI (High Silicon Cast Iron) that the length of the stick for a cation is 20cm, and the Fe Plate for an anion have been spread out on the ground. As the PVC pipe that is 10 cm in diameter was laid in the bottom of soils, cations descend on the cathode were discharged together. For soil physical properties according to the EK treatment, the destruction effect of soil aggregate was large, and the infiltration rate of water was increased. However, variations of bulk density and porosity were not considerable. Meanwhile, in chemical properties of soils, principal ions of such as EC, -N, , and were better rapidly reduced in the EK treated control plot than in the untreated control plot. And properties such as pH, and had a small impact on the EK. For cropping season of crop cultivation according to the EK treatment, decreasing rates of chemical properties of soils were as follows; -N 78.3% > 72.3% > EC 71.6% 71.5% > 36.8%. As results of comparing the experimental plot that EK was treated before crop cultivation with it that EK was treated during crop cultivation, the decreasing effect of chemical properties was higher in the case that EK was treated during crop cultivation. After the EK treatment, treatment effects were distinct for -N and EC that a decrease of nutrients is clear. However, because the lasting effect of decreasing salinity were not distinct for the single EK treatment, fertilization for soil testing was desirable carrying on testing for chemical properties of soils after EK treatments more than two times. In the growth of cabbages according to the EK treatment, the rate of yield increase was 225.5% for the primary treatment, 181.0% for the secondary treatment, and 124.2% for third treatment compared with the untreated control plot. The yield was increased by a factor of 130.0% for the hot pepper at the primary treatment (Apr. 2011), 248.1% for the lettuce at the secondary treatment (Nov.2011), and 125.4% for the young radish at the third treatment (Jul. 2012). In conclusion, the effect of yield increase was accepted officially for all announced crops.

Removal characteristics of salts of greenhouse in field test by in situ electrokinetic process

The addition of excessive fertilizer to the soil in greenhouse makes salts accumulate in the soil, such as nitrate, sulfate, sodium and so on. As a result, productivity of crops in greenhouse decreases and the quality of crops is also deteriorated. In this study, electrokinetic (EK) technique in a field was applied to remove the salts from the soil in a greenhouse for growing chrysanthemum. EK experiments were carried out for 2 ridges with dimensions of 3m in length and 2m in width. Initial electrical conductivity (EC) of the soil was extremely high (20–60dS/m), but it varied too much with positions due to the heterogeneity of the soil. Electrode modules implanted in each furrow were composed of 4 anodes and 3 cathodes. High Silicon Cast Iron (HSCI) rod and Fe plate were used for anode and cathode material, respectively. In this study, we introduced the EK systems which equipped electrodes, data acquisition system, water supplying to the soil, and EOF drain system in greenhouse. In order to check the process during EK experiments, we monitored total current, total voltage, the current of each electrode, and the temperature of soil with variable positions. After applying a constant voltage (∼0.8V/cm) to the soil for 2months, EC change, pH change, moisture, and salts concentrations such as Na+, K+, Cl−, NO3−, and so on were investigated with different positions. Experimental results showed that in situ EK technique reduced the concentration of main salts such as sodium, nitrate, and chloride to 90% effectively. However, other salts such as sulfate, magnesium, and calcium were not removed from the soil effectively. The effects of in situ EK technique on the removal of salts from the soil of greenhouse were discussed.

Effects of Aluminizing on the High Temperature Oxidation Behavior of High Silicon Cast Iron

In this study, the aluminizing of high silicon cast iron by hot-dipping in pure Al melt was performed and their high temperature oxidation behaviour was tested at 750 °C for virous exposure time. After high temperature oxidation tests, the microstructure analysis of all samples were investigated by means of metallographical examination, scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectrometer (EDS) and X-ray diffractometry (XRD).The results showed that the coating layers consisted of three layer, in the sequence of Al, Fe-Al and Si-rich layers from external topcoat to substrate. Nodules graphite had a blocking effect to retard the outward diffusion of Fe atoms and impeded the growth of Fe2Al5 in C-axis. Eventually, the cast iron substrate was oxidized directly by oxygen penetration via the greater cracks and pores to form Fe oxide nodules after 750 °C oxidation for 48h.

Electron microstructure and mechanical properties of silicon and aluminium ductile irons

Samples of unalloyed silicon and aluminium spheroidal graphite cast iron have been studied in the austempered condition. Austempering times of up 3 h at 400°C for Al SG and 1 h at 350°C for Si SG gives a typical ADI microstructure consising of carbide-free banitic ferrite and stable, high carbon enriched, retained austenite. This has an attractive combination of elongation and strength. For longer austempering times transition carbides are precipitated in the bainitic ferrite, η-carbide in the upper bainitic range, i.e.400°C for Al SG and 350°C for Si SG, and ϵ-carbide in the lower bainite range. Increasing amounts of transition carbide reduce the ductility and produce a mixed model of fracture. For longer austempring times X-carbide is precipitated at the ferrite/austenite boundaries leading to a more brittle fracture mode.

Microstructure and Properties of Electrodischarge Machined Surfaces

Ten materials with a wide range of microstructures and properties have been electrodischarge machined using copper and graphite electrodes with three pulse energies, and their machining rates, roughness, microstructure, micro hardness, cracking behaviour, and - for the white cast iron - dry sliding wear behaviour deternlined. Materials that are difficult to machine by conventional means (e.g. metal matrix composites, white cast iron, and high silicon cast iron) could be readily processed. Machining rates were approximately a linear function of the square root of pulse energy. A similar topography, which was difficult to quantify, was observed on all the materials. Surface roughness of the tool steel was a function of cube root of pulse energy. Hard surface layers occurred on the ferrous materials, but in some non-ferrous materials softening occurred. Extensive cracking occurred only in steels and cast irons containing a high concentration of chrOlnium. Electrodischarge machining increased the wear resistance of white cast iron fivefold.

Crystal-structure changes during tempering of hardened high-strength cast irons with nodular graphite

1. The martensite of high-strength cast iron is decomposed by a two-phase mechanism in the first stage of tempering (up to 100°C); the second stage of martensite decomposition occurs at 100–300°C and has the same character as that of high-carbon steel. 2. The decomposition of residual austenite occurs in two stages: The austenite is decomposed with the segregation of α-phase crystals and the carbon enrichment of intact austenite segments in the first stage (100–400°C); the decomposition is completed in the second stage (400–550°C) with the segregation of carbide from the carbon-enriched residual austenite. 3. Decomposition of residual austenite during tempering begins at 100°C in silicon cast iron, and at 200°C in manganese cast iron.

On the Rapid Cooled Structure of High Silicon Cast Iron

On the Rapid Cooled Structure of High Silicon Cast Iron

LiTaO<SUB>3</SUB>単結晶のラッピング特性

LiTa03 single crystals were lapped and basic data were obtained relating to practical machining for opto-electronic elements and crystal filters. Moreover, the skin structure of the lapped surfaces and the chip-built-mechanism in lapping were considerd, based upon the examination by using oblique sectioning, electron diffraction etc. Stock removal rate, surface roughness, depth of damaged layer and depth of breakage at the periphery on the X-face of crystal are 1. 68 μm·m-1/kg·cm-2, 1. 3 μmRmax, 12 μm and 50 μm, respectively, in using # 1000 green silicon carbide abrasives and cast iron lap. These amounts are found to have a tendency to change in proportion to the average size of abrasives. Fracture inside the lapped surface advances along the cleavage surfaces and minute chips release easily from the bulk with cleavage.

Determination of silicon in cast iron by 14 MeV neutron activation

Silicon in cast iron was analyzed by 14 MeV neutron activation—high-resolution γ-ray spectrometry. Silicon was detected as28Al, the product of the28Si(n, p)28Al reaction. Interference of56Mn was separated using a Ge(Li) detector and a biased amplifying system. The 1. 81 MeV gamma-radiation of56Mn, which is the product of the56Fe(n, p)56Mn reaction of the matrix of cast iron, was used as an internal standard and for correction of the self-absorption of the 1. 78 MeV gamma-radiation of28Al by the sample. The interferences of aluminum, phosphorus and manganese could be neglected according to the results calculated from their nuclear properties and contents in the cast iron of this experiment.