Austempered Ductile Cast Iron Research Articles

Influence of Austempering Temperatures on the Microstructure and Mechanical Properties of Austempered Ductile Cast Iron

The influence of the austempering temperatures on the microstructure and mechanical properties of austempered ductile cast iron (ADI) was investigated. ADI is nodular graphite cast iron, which owing to higher strength and elongation, exceeds mechanical properties of conventional spheroidal graphite cast iron. Such a combination of properties is achieved by the heat treatment through austenitization, followed by austempering at different temperatures. The austenitization conditions were the same for all the samples: temperature 890 °C, duration 30 min, and quenching in a salt bath. The main focus of this research was on the influence of the austempering temperatures (270 °C, 300 °C, and 330 °C) on the microstructure evolution, elongation, toughness, and fatigue resistance of ADI modified by certain amounts of Ni, Cu, and Mo. The Vickers and Rockwell hardness decreased from 535.7 to 405.3 HV/1 (55.7 to 44.5 HRC) as the austempering temperature increased. Optical images showed the formation of graphite nodules and a matrix composed of ausferrite; the presence of these phases was confirmed by an XRD diffraction pattern. A fracture surface analysis revealed several types of the mechanisms: cleavage ductile, transgranular, and ductile dimple fracture. The stress-controlled mechanical fatigue experiments revealed that a 330 °C austempering temperature ensures the highest fatigue life of ADI.

The Effects of Austempering Temperature and Time on Mechanical Properties of Ductile Cast Iron Grade FCD450

The purpose of the study was to inspect microstructure, mechanical properties and impact toughness of ductile cast iron grade FCD450 produced by austempering process. The study focused on austempering parameter, which effected impact toughness of material at low temperature. The FCD450 was initially temperature austenized at 885°C (1625˚F) for 2 hours. Austempering was carried out at three different temperatures of 271°C (520˚F), 313°C (560˚F) and 357°C (675˚F). The austempering temperature were varied at 1.5, 2.5 and 3.5 hours. X-ray diffraction was showed that the austempered ductile cast iron (ADI) microstructure consists of austenite and ferrite. The results showed that when austempered at 357°C (675˚F) for 2.5 hours has highest hardness and impact energy at low temperature. The dimple ductile fracture of ADI fracture surfaces was revealed by scanning electron microscope (SEM).

Evaluation of Corrosion Behavior of Different Grades of Cast Iron Insodium Chloride Solutions

In this work, the corrosion behavior of different grades of cast iron in 3.5% and 5% of NaClsolution was evaluated. The samples used in this work are; Grey cast iron (GI), ductile cast iron(DI), austempered ductile cast iron (ADI), intercritically austempered cast iron (IADI) and Ni-Resist cast iron. The study was carried out using the Open- Circuit technique (OPC),Potentiodynamic polarization (PP), and electrochemical impedance spectroscopy (EIS)measurements and complemented by Scanning electron microscopy (SEM) and Energydispersive X-ray analysis (EDAX). The results obtained showed that the austempering heattreatment and nickel addition improves the corrosion resistance of cast iron. The order ofcorrosion resistance in NaCl solution is as follows: Ni-Resist > ADI > IADI > DI > GI.

Microstructural damage evaluation of ferritic-ausferritic spheroidal graphite cast iron

The goal of this work is to improve the understanding of the relation between the microstructural characteristics of Intercritical Austempered Ductile Cast Iron (IADI) and the damage micromechanisms observed during its tensile loading. The experimental methodology involves heat treatments to obtain IADI and the assessment of the damage mechanisms (sequence and occurrence) during step by step tensile testing. The damage evaluation was carried out by observing the surface of the tensile test specimen with optical and scanning electron microscopy. The results show that small cracks start forming soon after the yield stress is surpassed. The crack initiation is preferentially located at matrix-nodule interface. As loading increases, cracks also develop at the ferritic grain boundaries and the ausferritic/ferritic interfaces. Consequently, at higher strain values, a competition between the plastic deformation on internodular zones and crack propagation along ausferritic phase is observed. Finally, the final fracture is produced by the propagation of cracks across the internodular ligaments and through the ausferritic/ferritic interface that later coalesce into a single dominant crack leading to the material failure.

Effect of austempering parameters on microstructure and mechanical properties of heavy section Machinable Austempered Ductile Cast Iron (MADI)

The first important limitation of ADI usage in industries is the machinability of the parts. Machinable Austempered Ductile Cast Iron (MADI) is a novel kind of ADI with improved properties such as better machinability compared to ADI and similar to as cast ductile iron. Furthermore, MADI has a higher strength than ductile iron at the same hardness value. The present work aimed to investigate into the impact of the austempering time and temperature on microstructure and mechanical properties of ductile iron samples prepared from Y-block with 75 mm thickness. In order to achieve the microstructure of the continuous matrix of equiaxed ferrite with islands of austenite, samples were partially austenitized (intercritical austenitization) at 850 °C for 2 hours. The austempering process was carried out at 350 °C and 390 °C for 1, 2, 3, 4 hours. The result of this study indicated that austempering at 390 °C, results in lower strength and hardness and higher ductility and toughness compared to austempering at 350 °C. It was also noticed that the minimum hardness was achieved by austempering at 390 °C for 2 hours.

Corrosion behavior of ductile and austempered ductile cast iron in 0.01M and 0.05M NaCl Environments.

In this investigation, the corrosion performance of ductile iron (DI) and austempered ductile cast iron (ADI) used in the production of engine sleeve was considered. The significant concentration of sodium chloride (0.01 M and 0.05 M) was utilized to analyse corrosion behaviour of both alloyed materials in the two environments. The microstructural images of the two distinct materials in each condition were resolved and diverse stages developed are mainly (carbides and the martensitic stage). Additionally, in Comparism with the DI and ADI not subjected to any condition, the consumption rate of DI was higher than that of ADI. The SEM was used to affirm the uniqueness of each phase. The two imperative components, for example, Cl- and Fe were assessed by SEM-EDS examination. The samples subjected to these conditions were appeared to have comparable corrosion attack. The nearness of delamination of oxide layers and oxidation was essential to each sample attempted under the 0.05 NaCl. As a result of silicon content, the DI indicates more oxidation at the surface accessible to the conditions. Thus, releases an impression of being the materials with the most raised corrosion resistance as a result of more broad scope of passive layers.

Processing of Nanostructured Austempered Ductile Cast Iron (ADI) by a Novel Method

Austempered ductile cast iron (ADI) has emerged as a major engineering material in recent years. It has a unique microstructure consisting of bainitic ferrite and high carbon austenite. In this investigation, nanostructured austempered ductile cast iron (ADI) consisting of bainitic ferrite and high carbon austenite was developed by applying a unique process consisting of austenitization and simultaneous high temperature plastic deformation at the same austenitizing temperature followed by austempering. It was theorized by these authors that further refinement of this of ADI in the nanoscale region could possibly further enhance the mechanical properties of ADI and nanostructured ADI can be potentially a useful structured material. The influence of plastic deformation, single step and two-step austempering process on the resultant microstructure and mechanical properties of nanostructured ADI has been examined. Test results indicate that the application of high temperature plastic defor

Chemical composition of chosen phase constituents in austempered ductile cast iron

Abstract A procedure a for multi-step characterization of microstructural features observed in austempered ductile cast iron (ADI), was proposed based on the results of microscopic examinations, a local X-ray microanalysis and EBSD-based crystallographic evaluation. The polyphase complex microregions having an increased content of alloying elements such as Mo, Cr, Mn in comparison with that estimated for the alloy's matrix, were observed in the examined material. As a first step, a classification of microregions was performed based on their morphology and specific distribution in the alloy's microstructure. Subsequently, by using established criteria for the selection of microanalysis data for a further microregions discrimination, several groups of particles characterized by a particular ratio of the alloying elements, were distinguished. The particles were classified based on the specific range of the carbide stabilizers concentration revealed, then were ascribed in situ to two types of carbides identified by means of EBSD analysis. Furthermore, the effect of heat treatment conditions on the evolution of the chemical composition of the microregions was examined experimentally and discussed.

Influence of intercritical austempering on the microstructure and mechanical properties of austempered ductile cast iron (ADI)

The focus of this investigation was to examine the influence of intercritical austempering process on the microstructure and mechanical properties of low-alloyed austempered ductile cast iron (ADI). The investigation also examined the influence of intercritical austempering process on the plane strain fracture toughness of the material. The effect of both austenitization and austempering temperature on the microstructure and mechanical properties was examined. The microstructural analysis was carried out using optical microscopy, scanning electron microscopy and X-ray diffraction. The test results indicate that by intercritical austempering it is possible to produce proeutectoid ferrite in the matrix microstructure. Lower austenitizing temperature produces more proeutectoid ferrite in the matrix. Furthermore, the yield, tensile strength and the fracture toughness of the ADI decreases with decrease in austenitizing temperature. A considerable increase in ductility was observed in the samples with higher proeutectoid ferrite content. The fracture surfaces of the ADI samples revealed that dimple ductile fracture produced higher fracture toughness of 60±5MPa√m in this intercritically austempered ADI.

Effect of Ti as a trace element on mechanical properties and microstructural evolution in direct austempered ductile cast iron

Abstract In this study, the effect of Ti as a trace element on acicular ferrite formation in direct austempered ductile cast irons was investigated. A step-block shape sample was used and the melt was poured into a sand mold at about 1450 °C. After cooling in the mold, the melt was hot knocked out at approx. 900 °C and then medium cooling to 350 °C was applied to the step-block shape sample. Afterwards, isothermal treatment was conducted in a commercial furnace at this temperature for 1 h, and then the sample was air-cooled down to room temperature. It was found that Ti as a trace element has an important effect on the nucleation of beneficial phases such as acicular ferrite in ductile irons which can result in increasing of mechanical properties. The microstructural examination confirmed that Ti actually acts as nucleation site for acicular ferrite. Moreover, the results show that in direct austempered ductile cast iron samples contain 0.25 wt.-% Ti, an increase from 820 to 950 MPa in tensile strength properties can be seen. Furthermore, the impact test results show that with an increase of tensile strength, the impact toughness does not decrease, but rather remains constant.

Improvement in Abrasion Wear Resistance and Microstructural Changes with Deep Cryogenic Treatment of Austempered Ductile Cast Iron (ADI)

The application of a deep cryogenic treatment during the heat-treatment processes for different types of steels has demonstrated a significant influence on their mechanical and tribological properties. A great deal of research was conducted on steels, as well as on other kinds of materials, such as hard metal, gray cast iron, aluminum, aluminum alloys, etc., but not on austempered ductile iron (ADI). In this research the influence of a deep cryogenic treatment on the microstructure and abrasive wear resistance of austempered ductile iron was investigated. The ductile cast iron was austempered at the upper ausferritic temperature, deep cryogenically treated, and afterwards tempered at two different temperatures. The abrasion wear resistance was tested using the standard ASTM G65 method. The microstructure was characterized using optical microscopy, field-emission scanning electron microscopy, electron back-scattered diffraction, and X-ray diffraction in order to define the microstructural changes that influenced the properties of the ADI. The obtained results show that the deep cryogenic treatment, in combination with different tempering temperatures, affects the matrix microstructure of the austempered ductile iron, which leads to an increase in both the abrasion wear resistance and the hardness.

Properties investigation of austempered ductile iron

This work concerns microstructural and mechanical properties of an austempered ductile cast iron (ADI). The ductile iron material was produced by the sand mould casting technique. Afterwards, austempering heat treatment was applied to the specimens at two different temperatures of 250°C and 350°C. Austempered Ductile Irons (ADIs) were produced successfully by different two-stage heat treatments, to obtain favorable microstructure and hardness. The microstructure and hardness obtained by such variable heat treatments were compared. The austempering temperature and time were found to be decisive parameters in obtaining a desired ADI microstructure.

Correlating the Vibration Modal Analysis Parameters to the Material Impact Toughness for Austempered Ductile Iron

Abstract Modal analysis is used in identifying the dynamic parameters of the mechanical components in different industrial applications. A growing research interest focuses on the use of modal testing as an alternative to the destructive testing methods used to predict the mechanical properties of components. This paper investigates the ability of modal analysis technique to predict the impact toughness of metallic parts. The sensitivity of the modal parameters to the change of the material impact toughness is investigated for austempered ductile cast iron (ADI), heat treated at different holding times. Modal testing is applied on four groups of specimens before and after heat treatment, after which the Charpy v-notched impact test is conducted on the same specimens to obtain the toughness value at each austempering holding time. The analysis of results from both tests reveals the potential of modal analysis in predicting the impact toughness values for the tested material.

An investigation on the stability of austenite in Austempered Ductile Cast Iron (ADI)

Austempered Ductile Cast Iron (ADI) has emerged as an important commercial engineering material in recent years because of excellent properties such as high strength with good ductility as well as good fatigue strength and fracture toughness together with excellent wear resistance. These properties are as a result of a microstructure composed primarily of acicular ferrite (α) and high carbon austenite (γHC). The role of the austenite in ADI is a topic that has been discussed extensively in the literature. Several investigators in the past have reported that the austenite in ADI is both thermally and mechanically stable; while others have reported it is neither thermally nor mechanically stable. Moreover, it is not clear whether the austenite formed at lower austempering (or bainitic) temperatures is more mechanically and thermally stable than that produced in the upper austempering (or bainitic) ranges.In this investigation, a comprehensive study was carried out to examine both the thermal and mechanical stability of austenite in the upper and lower austempering (or bainitic) temperature ranges. Compact tension and cylindrical tensile specimens were prepared and austempered at five different temperatures ranging from lower to upper bainitic temperatures. A select number of samples were then cryogenically treated to examine the thermal stability of the high carbon austenite. In order to examine the mechanical stability of austenite the microstructure and mechanical properties of these materials were evaluated as a function of austempering temperature, cryogenic treatment, and mechanical testing. The results of this study show that the austenite formed at lower austempering temperatures (260 and 288°C) was neither thermally nor mechanically stable; while the austenite formed in the upper bainitic temperature range (371–399°C) was partially stable under both thermal and mechanical conditions. Both stress- and strain-induced austenite-to-martensite transformations were observed in the ADI samples during mechanical tests. The test results also showed that cryogenic treatment can improve the mechanical properties without compromising the fracture resistance of the ADI. This is hypothesized to be due to a threshold level for the amount of austenite transformed to martensite; below this level, the amount transformed is not sufficient to produce an observable change in the fracture toughness.

Improvement of Abrasion Wear Resistance of Ductile Iron by Two-Step Austempering

Abrasion wear rates of conventional and two-step austempered ductile cast iron (ADI) were investigated. Conventional austempering and two-step austempering processes were carried out at 280, 300, and 320°C. Microstructures revealed that higher austemperig temperature resulted in coarser ausferrite and higher volume fractions of blocky retained austenite. The ausferrite in two-step austempered ADI was slightly coarser comparing to the coventional ADI since the temperature was raised by 30°C during austempering. Two-body abrasion wear rates of ADIs were studied using a Suga abrasion wear tester. It was found wear rates of the two-step ADI become significantly lower than those of the conventional ADI, especially when the austempering was carried out at low temperature, i.e. 280°C. Such behavior was due to the strong influence of high carbon concentration in retained austenite eventhough the ausferrite matrix was coarser.

Fe-0.4C-2.3Si강의 기계적 성질에 미치는 오스템퍼링 열처리 조건의 영향

The effect of heat treatment on mechanical properties of 0.4C-2.3Si(wt%) steel with bainitic ferrite matrix were investigated. This steel has been synthesized intergrating concepts from TRIP(Transformation Induced Plasticity) steel & Austempered Ductile Cast Iron(ADI) technology. The low alloy medium carbon (0.4 %C) steel with high silicon (2.3 %Si) was initially annealed for 60 min at , and respectively in the intercritical region and then subsequently austempered at various temperatures at , and for 30 min in a salt bath. The mechanical properties were measured by using a tensile test. A detailed study of the microstructure of this steel after heat treatment was carried out by means of electron back scattering diffraction (EBSD) technic. In this study, a new low alloy steel with high strength (780~1,050MPa) and exceptionally high ductility (20~40%) was obtained.

Effects of Austempering Heat Treatment Conditions on Fracture Toughness of Austempered Ductile Cast Iron

Effects of Austempering Heat Treatment Conditions on Fracture Toughness of Austempered Ductile Cast Iron

Comparison of the Mechanical Properties of Austempered Ductile Cast Iron (ADI) Processed by Conventional and Step-Down Austempering Process

An investigation was carried out to examine the influence of step-down austempering process on the mechanical properties of austempered ductile cast iron (ADI). Compact tension and cylindrical tensile specimens were prepared from nodular cast iron as per ASTM standards and were subjected to two different austempering heat treatments; that is, conventional and step-down austempering in the upper bainitic temperature range. The specimens were austempered at four different temperatures; that is, 343, 357, 371, and 385°C. The influence of these austempering processes on the microstructure and the mechanical properties of the material was examined at room temperature and ambient atmosphere. The influence of these austempering processes on the plane strain fracture toughness of the material was also investigated. The present test results indicate no significant difference in the mechanical properties and fracture toughness in ADI processed by conventional as well as step-down austempering process at the same austempering temperature. However, the step-down austempering process has the advantage of lower processing cost compared to the conventional austempering process, without compromising any of the mechanical properties.

Effects of austempering conditions on the microstructures and mechanical properties in Fe-0.9%C-2.3%Si-0.3%Mn steel

In this study, the effect of the microstructure and mechanical properties of austempered high-carbon (0.9 %C) high-silicon (2.3 %Si) cast steel were investigated. The specimens were austenitised for 60 min. at 900 °C, and austempered at 260 °C, 320 °C, and 380 °C for periods of time ranging from 30 min to 240 min. After receiving this heat treatment, the mechanical properties were measured using both a tensile test and hardness test. To analyze the microstructure, an optical microscope was used and an X-ray diffraction (XRD) analysis was carried out. In this study, high carbon high silicon cast steel without graphite and with higher tensile strength (1300 MPa to 2200 MPa) and elongation (∼25 %), when compared to austempered ductile cast iron (ADI), was developed. When the austempering temperature was at 260 °C, the microstructures were low ausferrite, but at 380 °C, an upper ausferrite structure was formed. As the austempering temperature increased from 260 to 380 °C, the ultimate tensile strength and hardness decreased, but the elongation and retained austenite volume fraction increased. In addition, the microstructures were coarser.

Comparison of low cycle fatigue of ductile cast irons with different matrix alloyed with nickel

Total strain controlled tests have been performed on cylindrical specimens of austempered ductile cast iron (ADI) and ductile cast iron with the ferritic matrix, both alloyed with 2.75% Ni, with the aim to compare cyclic plasticity and the fatigue life at temperatures 23 °C and–45 °C. Microstructure and its features are documented using light microscope (image analysis) and neutron diffraction. In ADI the measurement of retained austenite by neutron diffraction before and after fatigue tests is used to discuss the cyclic stress-strain response. Cyclic hardening/softening curves, cyclic stress-strain curves and fatigue life curves were obtained for both temperatures and materials. Cyclic stress-strain curve obtained at–45 °C is shifted to higher stress amplitudes relative to room temperature curve. The fatigue life curves at both temperatures can be well approximated by the Manson-Coffin and Basquin laws. The Manson-Coffin curves are identical for both materials and temperatures while the Basquin curve is shifted to longer fatigue life for ADI. The surface relief developed during fatigue was studied using SEM. Fatigue cracks initiated preferably from persistent slip markings at the interface of graphite nodule.