Influence of furfuryl moulding sand on flake graphite formation in surface layer of ductile iron castings

The influence of the use of moulding sand with furan resin, prepared both with fresh sand and reclaimed matrix, on the formation of a flake graphite formation at the surface layer of ductile iron castings has been investigated. A series of experimental heats of ductile iron cast in moulds made of moulding sand characterised by different levels of surface active elements (sulphur, oxygen) were performed. The effect of the wall thickness and the initial temperature of the metal in the mould cavity on the formation of flake graphite in the surface layer of the casting is shown in the paper. Investigations carried out by means of scanning electron microscopy (energy dispersive X-ray spectroscopy and wavelength dispersive X-ray spectroscopy) showed concentration of gradient profiles of surface active elements in the castings surface layer, which are responsible for their quality. Finally, it has been shown that there exists a significant effect of the quality of the sand on the formation of the flake graphite layer and the surface characteristics of ductile iron castings.     

Structural and operating aspects of rapid solidification of surface layer of spheroidal graphite iron castings

The relationship between the surface layer microstructure of iron castings after gas tungsten arc weld (GTAW) surfacing and their service properties (friction wear resistance and microhardness) has been investigated. A structural analysis of the fused (remelted) zone, in particular evaluation of the interphase spacing in the cementite eutectic λ_av, is presented. Relationships between the GTAW process parameters, microstructure and microhardness of the fused zone have been developed and are presented. Formulae relating hardness to λ_αv and relating friction wear rate to λ_av and hardness are presented. IJCMR/426     

Linear contraction of ductile iron castings

The effect of casting design on the linear contraction of ductile iron castings produced in clay- and silicate-bonded sand moulds has been studied. The designs included free and restrained square bar castings.

Free contraction of very thin sections of ductile iron in sand moulds was found to approach 1.35%. As sections increased to 25 mm thick, the contraction decreased linearly to 1.08% in silicate-bonded sand moulds, but to 0.90% in clay-bonded sand moulds.

For test pieces with end flanges which stimulated various degrees of constraint as would be experienced in a shaped casting, the contraction was found to be sensitive to the third power of the relative cooling time of the flange and the cast section. In conditions of high constraint, contraction could fall as low as 0.55%.

The data from this study represent a first attempt to provide a designer and toolmaker with realistic contraction allowances for shaped castings.     

Analysis of ductile iron production on steel scrap base

The cast iron production (melting) process is commonly based on pig iron. However, economic and ecological factors necessitate that the melting process is more often based on steel scrap (with no pig iron at all). This kind of cast iron is called synthetic cast iron. This approach may, however, cause a decrease in the quality of the alloys obtained, particularly when ductile iron (DI) is produced. The following article presents an analysis of the product and some aspects of ductile iron produced exclusively on a base of steel scrap. The experiments and the charging materials are described. The results of the chemical analysis of the produced DI, the carburisation efficiency and microstructure of the obtained material are presented as well. The results of cast iron melted on a pig iron base are presented for comparison. A quantitative microstructure analysis is also presented.     

Performance of heavy ductile iron castings for windmills

The main objective of the present paper is to review the specific characteristics and performance obtaining conditions of heavy ductile iron (DI) castings, typically applied in windmills industry, such as hubs and rotor housings. The requirements for high impact properties in DI at low temperatures are part of the EN- GJS-400-18U-LT (SRN 1563) commonly referred to as GGG 40.3 (DIN 1693). Peaditic influence factor (Px) andantinodularising action factor (K1) were found to have an important influence on the structure and mechanical properties, as did Mn and P content, rare earth (RE) addition and inoculation power. The presence of high purity pig iron in the charge is extremely beneficial, not only to control the complex factors Px and K1, but also to improve the 'metallurgical quality' of the iron melt. A correlation of C and Si limits with section modulus is very important to limit graphite nodule flotation. Chunky and surface-degenerated graphite are the most controlled graphite morphologies in windmills castings. The paper concluded on the optimum iron chemistry and melting procedure, Mg-alloys and inoculants peculiar systems, as well as on the practical solutions to limit graphite degeneration and to ensure castings of the highest integrity, typically for this field.     

Microstructural characteristics of the surface layer in high-pressure die castings

A thin layer of distinct microstructure, commonly called the surface layer, is often present near the surface of high-pressure die cast (HPDC) components. Although the surface layer formation has been previously investigated, its salient microstructural features in recent studies are significantly different. Therefore, this research aims to gain a better understanding of the surface layer’s microstructural characteristics and the surface layer formation. Microstructural analysis was performed on complex-geometry, industrial-part Al-11Si-2Cu-1Fe (ADC12) and Zn-4Al (Zamak3) HPDC specimens and Al-5Mg-2Si-0.7Mn U-shaped HPDC specimens. The characterized microstructural features suggest that the surface layer starts to form during die filling and becomes stagnant at the die wall. When the inner material moves past the surface layer, primary crystals in the inner material migrate away from the surface layer, resulting in a region adjacent to the surface layer containing only solute-enriched liquid. The solute-enriched liquid in this region subsequently solidifies into the surface-layer edge.     

灰铸铁件表层石墨的球化

在铸型表面涂刷特种合金涂料，浇注普通灰铸铁成分４９铁水，可得到表层为球墨铸铁、其余主体为灰口铸铁冶金结合的球灰复合材料，表面球化层可达６ｍｍ以上。     

Characterization of the austemperability of partially austenitized ductile iron

This study focuses on the characterization of the hardenability and the austemperability of partially austenitized ductile iron melts alloyed with small amounts of Cu, Ni and Mn.     

物理模拟大断面球墨铸铁中异常石墨形态的观测

使用自行研制的大断面铸件冷却模拟装置,研究了不同共晶时间球墨铸铁样品的石墨形态及相关的力学性能。验证了这一装置对于厚大断面球铁铸件研究的有效性。随着共晶时间的延长,铸件的石墨形态逐渐偏离球形,向异常化趋势发展,石墨颗粒的圆整度随之降低。异常石墨的形态表现出相互联结的立体网络状。     

表层石墨球化的灰铸铁件外表层片状石墨的防止

利用含有稀土的涂料实现了表层石墨球化的灰铸铁件,其组织形态由外到内依次为球化区、过渡区和灰铸铁本体。生产中发现,在某些条件下,已经实现了表层石墨球化的灰铸铁件的外表层又出现片状石墨。为防止这种现象发生,进行了研究。     

激光扫描速度对球墨铸铁热轧辊表面铁基合金化层组织性能的影响

采用激光合金化技术在球墨铸铁QT600-3表面制备铁基合金化层,采用扫描电镜(SEM)、X射线衍射(XRD)、Raman光谱仪、显微硬度计和高温摩擦磨损试验等方法研究了不同激光扫描速度对铁基合金化层物相、微观结构、力学性能、常温和高温摩擦学性能的影响。研究结果表明,铁基合金化层与基体冶金结合良好、显微硬度高(高达830 HV0.1)、高温摩擦因数低至0.28、高温磨损率低至2.41×10^-6 g·N^-1·m^-1。合金化层显微组织为奥氏体树枝晶+共晶碳化物,且随着扫描速度增加,组织逐渐细化,合金化层平均厚度减小,裂纹率升高,显微硬度先增加后减小,高温耐磨性能逐渐提高。铁基合金化层的高温磨损机制以磨粒磨损为主,同时还存在着疲劳磨损和氧化磨损。     

球墨铸铁轧辊表面镍基激光合金化层及其磨损性能

采用激光合金化技术在球墨铸铁QT600-3表面制备镍基合金强化层,通过XRD、SEM和摩擦磨损试验等研究了不同激光扫描速率对合金化层物相、微观结构、力学性能、常温和高温摩擦学性能的影响,并使用Raman光谱仪对磨痕进行分析。结果表明:Ni合金化层与基体冶金结合好、显微硬度高(高达720 HV0.1)、高温摩擦因数低至0.305、高温磨损率低至7.55×10^-6 g·N^-1·m^-1。随着扫描速率的增加,显微组织更加致密,显微硬度先升高后降低,700 ℃耐磨性能提高,但合金化层裂纹率增加。高温摩擦磨损过程中,合金化层的磨损机制以磨粒磨损为主,同时还存在疲劳磨损和氧化磨损。同时,扫描速率的增加可细化晶粒和提高显微硬度。而Ni合金化层表面在高温摩擦过程中形成的氧化产物和碳化物在高温下会对提高其耐磨性能产生积极作用。     

Evaluation of ductile iron casting material quality using ultrasonic testing

The study presents the influence of pouring delay time on the decay of spheroidisation effect and magnesium content in the alloy, as well as the influence of magnesium content on the shape and number of graphite precipitations in bar samples. For one particular set of production conditions, it was observed that 17 min after completing the spheroidisation and modification process, the magnesium content had decreased from 0.07% to 0.04%. This resulted in a decrease in the graphite precipitation shape index S_s from 0.081 to 0.067, as well as a decrease in the average number of graphite precipitations N_A from 568 to 305 mm⁻².     

Foundry technology and its applications of ductile iron castings produced by water-cooled copper alloy mold

The high efficiency mechanized foundry technology of castings produced by using water-cooled copper alloy permanent mold has been systematically studied. Through the researching a Cu-Cr-Mg alloy with high conductivity and good combined mechanical properties used for making permanent mold was developed, and the basic design principles of the water-cooled permanent mold along with the control-range of relevant foundry processing parameters were also established.A cast production line equipped with water-cooled copper alloy mold was designed and fabricated for production of ductile iron automobile gear castings. This production line can consistently make automobile gear castings in QT500-15 and QT600-5 (Chinese Standard) grades of ductile iron with up to 95 % casting success rate.     

Residual stresses, distortion and surface roughness produced by grinding thin wall ductile iron plates

This work deals with grinding effects on thin wall ductile iron plates. Residual stresses, shape distortion and surface roughness were measured on thin wall plates of different nodule count, ferritised and afterwards dry ground under several grinding conditions. In all cases, tensile residual stresses are maximum at the surface, and their profile decreases with depth until becoming compressive. No phase transformations can be observed at depths of up to 30 μm below surface, although plastic deformation is visible through nodules and grains enlargement. Distortion increases when the depth of cut and nodule count increase and the workspeed decreases. The mean stresses of the profile tensile zone also increase when the nodule count increases. Surface roughness improves slightly as nodule count increases and workspeed decreases. This tendency is more noticeable when depth of cut decreases. The arithmetic mean roughness (Ra) values obtained were always below 0.8 μm.     

Application of 3-D numerical simulation software SRIFCAST to produce ductile iron castings

1. IntroductionSince the 1960's, there have been 3 progressive periodsfor modeling and simulation of the technological processof castings. In 1988, 3-D temperature fields were calculatedsuccessfully during the solidification process of steelcastings in many countries [1-4]. In 1995, 3-D velocityfields calculations of metal flow in mold filling were alsoachieved by advanced researchers [5-8]. From 1990 untilnow, the new task has been to model and simulate themicrostructure and morphology of cr…     

Shrinkage evaluation in ductile iron as influenced by mould media and inoculant type

Abstract

The present work was undertaken in hypereutectic ductile irons, to simultaneously study cooling curves, specimen contraction curves, microstructures and shrinkage tendencies as a function of inoculant selection and mould rigidity. Specific equipment was developed for simultaneous recording of cooling and contraction curves. The highest level of both concentrated and total shrinkage was recorded on the green sand mould system, where a much higher level of the initial eutectic expansion was observed, as compared to furan resin moulds. It was found that the Ca,Ce,S,O–FeSi inoculation gives the highest nodule count and a unique wide distribution of nodules sizes (large and small size nodules, in a peculiar ratio), as well as lower tendency to shrinkage formation. Also, the strongest graphitising effect before the start of eutectic solidification and more prolonged graphitising throughout the end of eutectic freezing characterise were observed with this complex inoculant system in addition to its peculiar action on minimising the shrinkage tendency of ductile irons.     

QT-500球墨铸铁表面激光熔覆镍基合金的组织与性能

利用DL-T5000型二氧化碳激光器在QT-500球墨铸铁表面熔覆镍基合金,分析了激光熔覆层的显微组织,测试了其显微硬度及磨损性能。结果表明:所制得熔覆层组织致密、无裂纹,与基体形成了良好的冶金结合。从熔覆层表面到基体热影响区,组织依次为大量的树枝晶、等轴晶、树枝晶。熔覆层的硬度较基体提高了5倍,熔覆层的总磨损率大约为基体的1/6。熔覆层耐磨性能增强的主要原因是镍基合金与涂层元素镍、铬等固溶强化和碳化物等析出相的强化作用。     

Effect of thermomechanical processing parameters on phase transformation and hardness of dual matrix ductile iron

The microstructural changes and hardness exhibited by ductile iron with dual matrix structure (DMS) are investigated. In particular, DMS microstructures are obtained by continuous cooling in the (ferrite+austenite) region followed by quenching to transform the austenite into martensite or by austempering at 375°C, to transform the austenite into ausferrite. Additionally, two deformation steps are applied in the austenite region. The structure was produced in a thermomechanical simulator equipped with a dilatometry system. The dilatometry is used to monitor the structure development throughout the thermomechanical processes. The structure was investigated using light optical microscopy and scanning electron microscopy. The influence of introducing ferrite to the microstructure and the deformation magnitude on the structure development and hardness properties are explored.     

Low temperature impact strength of heavy section ductile iron castings：effects of microstructure and chemical composition

A foundry research project has been recently initiated at RTIT in order to better understand the fabrication of as-cast heavy section DI parts meeting high impact energy requirements at low temperatures.The experimental castings have the following dimensions 180 mm x 180 mm x 190 mm.The achieved as-cast Charpy impact strengths were as follows:17 J (RT),16 J (-20℃) and 11 J (-40℃).The foundry process,the chemical composition and the microstructure of this experimental casting are compared to the ones of various examples in order to show the detrimental effects of residual elements,microshrinkage and microcarbide on the impact properties.Finally,quality index empirical models (based on casting chemical compositions) are used to analyse the impact tests results.This paper illustrates that an adequate nodule count can contribute to reducing the detrimental effects of the residual elements and microsegregation.