An analysis of induction hardening of ferritic ductile iron

Achievements of the induction hardening of ferritic ductile iron were investigated. Ductile iron is not advisable for use in induction hardening because of the small carbon content in the metal matrix of ferritic ductile iron. The carbon content in the metal matrix of ductile iron can be increased by additional preparation of metal matrix before final induction heat hardening. Wear resistance of the induction hardened ferritic ductile iron can increase as result of increased carbon content of the metal matrix and higher hardness after induction hardening. Some heat pretreatments for metal matrix preparation were applied before the induction hardening of ferritic ductile iron. The process parameters of the induction hardening heat pretreatment were analyzed and optimized. According to recommended elemental composition of ferritic ductile iron and required mechanical properties, the process parameters of the investigated induction heat pretreatment were optimized. The efficiency of pretreatment processes of induction hardening was analyzed. Applicability and manufacture ability of engineering components by proposed heat pretreatments were investigated. The limitations of the investigated heat pretreatment applications were estimated by the comparison of mechanical properties of heat-treated specimens.     

Austempering and austempered ductile iron microstructure in copper alloyed ductile iron

The variation in the austempered microstructure, the volume fraction of retained austenite, X_λ, the average carbon content of retained austenite, C_λ, their product X_λC_λ and the size of bainitic ferrite needles with austempering temperature for 0.6% Cu alloyed ductile iron have been investigated for three austempering temperatures of 270, 330, and 380 °C for 60 min at each temperature after austenitization at 850 °C for 120 min. The austempering temperature not only affects the morphology of bainitic ferrite but also that of retained austenite. There is an increase in the amount of retained austenite, its carbon content, and size of bainitic ferrite needles with the rise in austempering temperature. The influence of austempering time on the structure has been studied on the samples austempered at 330 °C. The increase in the austempering time increases the amount of retained austenite and its carbon content, which ultimately reaches a plateau.     

Polyurethane coating for ductile iron pipes

Polyurethane coating has been widely used in pipe protection because of its perfectly mechano-chemistry properties and convenient application. But, being a solvent coating, a thick coat can not be obtained by spraying once with a common polyurethane coating. Moreover, the common polyurethane coating cures slowly as a result of being a secondary hydroxy polyether polyol. Therefore, it does not meet the requirements of rapid current production nor is it suitable for spraying on the surface of du…     

一种球墨铸铁等温正火工艺

对一种球墨铸铁铸件进行了等温正火处理,分析了其不同等温正火工艺下的布氏硬度和显微组织。结果表明,等温温度一定时,随着正火加热温度的升高,硬度随之升高,当正火加热温度一定时,随着等温温度提高,硬度逐渐降低。加热温度为900 ℃、等温温度为650 ℃处理后球铁铸件的显微组织为大量珠光体（>85%）和少量铁素体,硬度较高（375~380 HB）;正火温度较低（850 ℃）、等温温度较高（700 ℃）时的显微组织为大量的游离铁素体（>60%）和少量珠光体,硬度较低（200~205 HB）。根据试验结果提出了一种较为合理的球墨铸铁等温正火工艺。     

Sponge iron in electric arc furnaces

When reducing iron ores at temperatures below their melting point, the end product will be a porous mass of more or less completely reduced iron; this product is called sponge iron.Sweden utilizes a greater tonnage of sponge iron than any other country at the present time. This report deals with Swedish experience and technique in the use of sponge iron in electric arc furnaces.     

Mathematical model for austenitization kinetics of ductile iron

A mathematical model was developed in the current study to understand the progress of austenitization process in ductile irons. The austenitization time required to produce homogeneous austenite in a two-phase region of austenite and graphite has been estimated in terms of (a) time required for transformation of matrix to austenite and (b) time required for dissolution of graphite in austenite to attain uniform carbon content, which remains in equilibrium with graphite. The time required been related to the structural parameters of cast ductile iron-like radius of graphite nodule, radius of austenite cell, volume fraction of graphite, volume fraction of ferrite in cast matrix, and diffusion constant. The model was used to determine the minimum austenitization time required to achieve homogeneous austenite in three commercial ductile irons when austenitized at a temperature of 900 °C. The results were compared with those obtained. The uniformity of the carbon content in austenite of ductile iron was verified indirectly by measuring microhardness.     

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.     

Machinability of alloyed austempered ductile iron

Austempered ductile iron (ADI) has found enormous applications in recent years due to its high strength and hardness, coupled with substantial ductility and toughness. The high strength and hardness of ADI have caused many researchers and engineers to doubt the machinability of this material. Many investigations have adopted tool life, tool wear rate, cutting forces, and surface finish produced on a job as general criteria for evaluating the machinability of ADI. In the present investigation, an attempt has been made to evaluate the machinability of ADI alloyed with nickel by calculating the machinability index based on material removal rate and unit power consumed at various cutting speeds and feeds. The results thus obtained are presented in this paper.     

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.     

Thermomechanical treatment of austempered ductile iron

The production of lightweight ferrous castings with increased strength properties became unavoidable hter aluminum and magnesium castings. The relatively new ferrous casting alloy ADI offers promising strength prospects, and the thermo-mechanical treatment of ductile iron may suggest a new fluence of thermomechanical treatment,either by ausforming just after quenching and before the onset of austempering reaction or by cold rolling after of this work, ausforming of ADI up to 25％ reduction in height during a rolling operation was found to add a mechanical processing component compared to the conventional ADI heat treatment, thus increasing the rate ics of ausferrite formation was studied using both metallographic as well as XRD-techniques. The effect of ausforming on strength was quite dramatic (up to 70％ and 50％ increase in the yield and ultimate strength respectively). A mechanism involving both a refined microstructural scale and an elevated dislocation density was suggested. Nickel eformation is necessary to alleviate the deleterious effect of alloy segregation on ductility.luence of cold rolling (CR) on the mechanical properties and structural characteristics ofADI wasinvestigated. The variation in properties was related to the amount of retained austenite nsformation. In the course of tensile deformation of ADI, transformation induced plasticity (TRIP) takes place, indicated by the increase of the instantaneous value of strain-hardening exponent with o partial transformation of γr to martensite under the CR strain. Such strain-induced transformation resulted in higher amounts of mechanically generated therefore increased, while ductility and impact toughness decreased with increasing CR reduction.     

Corrosion behavior of boro-tempered ductile iron

In this study, the effect of boro-tempering heat treatment on the microstructure and corrosion behavior of unalloyed ductile iron was investigated. The corrosion characteristics of ductile iron have been determined by current-potential curves. To determine the corrosion rates, the anodic and cathodic Tafel regions extrapolating to corrosion potentials were used. The inhibitor efficiency was calculated from i _corr values. Optical microscope and X-ray diffraction (XRD) were used to examine the microstructure of polished and etched specimens. Thicknesses of the boride layers formed on samples were measured by an optical micrometer attached to the optical microscope. Results show that boro-tempering heat treatment can be successfully applied to ductile iron. The corrosion potential has shifted to more positive values in the boronized samples. The boride layer has behaved like an anodic inhibitor. The boronizing time has affected the corrosion rate. The increase in boronizing time has made the coating thicker, which has increased the corrosion resistance of the material. The best inhibition and the lowest corrosion rate have been performed on the sample which was boronized for 5 hours after cooling in furnace. The tempering at higher temperatures leads to an increase in the corrosion resistance of the materials tested here.     

高性能球墨铸铁在汽车底盘轻量化中的应用

介绍了高性能球墨铸铁的发展现状及优异性能,并结合汽车轻量化需求,分析了等温淬火球墨铸铁材料在汽车底盘上的应用趋势,最后介绍了等温淬火球墨铸铁在实际生产中的应用。     

Wear resistance properties of austempered ductile iron

A detailed review of wear resistance properties of austempered ductile iron (ADI) was undertaken to examine the potential applications of this material for wear parts, as an alternative to steels, alloyed and white irons, bronzes, and other competitive materials. Two modes of wear were studied: adhesive (frictional) dry sliding and abrasive wear. In the rotating dry sliding tests, wear behavior of the base material (a stationary block) was considered in relationship to countersurface (steel shaft) wear. In this wear mode, the wear rate of ADI was only one-fourth that of pearlitic ductile iron (DI) grade 100-70-03; the wear rates of aluminum bronze and leaded-tin bronze, respectively, were 3.7 and 3.3 times greater than that of ADI. Only quenched DI with a fully martensitic matrix slightly outperformed ADI. No significant difference was observed in the wear of steel shafts running against ADI and quenched DI. The excellent wear performance of ADI and its countersurface, combined with their relatively low friction coefficient, indicate potential for dry sliding wear applications. In the abrasive wear mode, the wear rate of ADI was comparable to that of alloyed hardened AISI 4340 steel, and approximately one-half that of hardened medium-carbon AISI 1050 steel and of white and alloyed cast irons. The excellent wear resistance of ADI may be attributed to the strain-affected transformation of high-carbon austenite to martensite that takes place in the surface layer during the wear tests.     

Graphite degeneration in surface layer of ductile iron castings

Abstract

In the furan resin moulding technique sulphur in P-toluenesulphonic acid (PTSA), usually used as the hardener, has been identified as an important factor causing graphite degeneration at the metal/mould interface, especially at lower graphite nodularity levels. The greatest surface layer thickness and the lowest graphite nodularity, and shape factors, were obtained with irons solidified in moulds coated with an S bearing material. Uncoated moulds provided better results, but employing a MgO type coating effectively neutralised the sulphur migrating from the mould. In the present solidification conditions, the application of an active mould coating also influenced the graphite phase characteristics in the entire section of the casting, up to its centre. Negative effects were observed using an S bearing coating and positive effects from an MgO based coating.     

Correlative thermal methodology for castability simulation of ductile iron in ADI production

The present paper investigates the simulation analysis of simultaneous mold filling and solidification of ductile iron casting in a permanent mold by virtue of its thermal characteristics. Thermal analysis was performed to determine the solidification behavior and nature of alloy of the melt during its solidification. It revealed the variation in the nature of alloy due to the variations in eutectic freezing and carbon equivalent of the melt. The obtained thermal parameters from the thermal analysis were further used for the casting simulation of the melt. The simulation results show a progressive solidification behavior of the casting. There is a significant decrease in the overall heat transfer coefficient with time during the solidification process. The simulation results were further verified experimentally. The experimental results show porosity defects at the top section of the casting. Two distinct zones (center and outer) were observed on the produced samples based on the average graphite nodule counts and average graphite nodule size.     

Development of thermal simulation system for heavy section ductile iron solidification

A new reliable thermal simulation system for studying solidification of heavy section ductile iron has been developed using computer feedback control and artificial intelligent methods. Results of idle test indicate that the temperature in the system responses exactly to the inputted control data and the temperature control error is less than ± 0.5 %. It is convenient to simulate solidification of heavy section ductile iron using this new system. Results of thermal simulation experiments show that the differences in nodularity and number of graphite nodule per unit area in the thermal simulation specimen and the actual heavy section block is less than 5 % and 10 %, respectively.     

A study on controlled cooling process for making bainitic ductile iron

In the present research, TTT curve of bainitic ductile iron under the condition of controlled cooling was generated. The cooling rate of grinding ball and its temperature distribution were also measured at the same time. It can be concluded that the bainitic zone of TTT curve is separated from the pearlitic zone. As compared to the water-quenching condition, more even cooling rate and temperature distribution can be achieved in the controlled cooling process. The controlled cooling can keep away from pearlitic zone in the high temperature cooling stage and produce similar results to the process of traditional isothermal cooling with a low cooling rate in the low temperature cooling stage.