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The impact of laser transformation hardening (LSH) and Laser surface melting (LSM) on an austempered ductile iron (ADI) alloy was investigated. Various laser fluences (J mm−2) were irradiated on the ADI specimens, obtained by different beam powers and scanning speeds to reach the optimum parameters to attain a surface with a good combination of high hardness and deep hardened depth, together with obtaining minimal distortion and crack-free surface. ADI surfaces were treated by means of high-power Nd:YAG laser in continuous wave mode. A detailed investigation of the obtained microstructure was characterized via optical and scanning electron microscopy attached to an EDX analyzer as well as X-ray diffraction analysis. Such a wide laser fluence range has a considerable effect on the achieved microstructure. A process parameter map was established which indicated that three different laser treatments were induced under such values of laser fluences: a laser transformation hardening, a partial laser melting, and a complete laser melting. The results revealed that to produce a hardened microstructure, specimens have to be operated within a very small range of laser fluence from 9.6 up to 29 J mm−2, achieving surface hardness values around 900 HV0.1 and depths of approximately 184–700 μm, respectively. Meanwhile, partial melting of the treated layer took place at a medium energy density range from 37 to 112 J mm−2, by a further increase in laser fluence (120–360 J mm−2), complete melting occurred which resulted in a deeper treated layer that reached 3.5 mm with an increase in microhardness value to almost 1100 HV0.1 at 360 J mm−2. The obtained microstructure in case of low laser fluence consisted of an austenite dendritic structure with undissolved graphite nodules, however, at medium and high laser fluence, the microstructure contains large cementite plates, iron-silicon carbides, a small area of ledeburite structure, and some retained austenite. The quantitative amounts of such phases directly depend on the applied laser fluence. Such phases were identified by means of EDX analysis.

The paper presents mathematical models and their implementation in C # language describing the phase transformations occurring in the process of austempered ductile iron (ADI) manufacture. The research includes two main stages: austenitization and isothermal holding at the bainitic range. The influence of free energy of austenite and ferrite on transformations was taken into account. Parameters of models were identified based on inverse analysis and experimental research. As part of the research, verification and validation of the developed models was carried out based on the results of experimental research. The tool developed and implemented enables the analysis of phase transformations occurring during heat treatment with isothermal holding of ductile iron with Ni addition. [ABSTRACT FROM AUTHOR]

Austempered ductile iron (ADI) is a hard-to-cut material used for a variety of purposes, including flanges in power plants, oil fields and railway sectors. This article aims to establish a correlation between the surface quality (Ra), the kerf angle (KTa), and the erosion rate and four critical process variables such as traverse speed (NS), abrasive flow rate (AFR), water jet pressure (WJP), and standoff distance (SoD). All of the inferences from the experiments were made using the RSM-CCD response surface methodology and the central composite design. An analysis of variance (ANOVA) was employed to identify which WJP factors had the greatest impact. WJP was shown to be the most influential parameter in the outcomes. The Ra and KTa both fell by 56.7 and 33% when the WJP reached a value of 360 MPa, whereas the MRR increased by 35.46 %. In order to fine-tune the abrasive water jet machining settings of the ADI sample, the desirable analysis is taken to optimize the parameter. Surface morphology and erosion processes of AWJM are studied using a scanning electron microscope and 3D surface roughness analysis. [ABSTRACT FROM AUTHOR]

Austempered ductile iron (ADI) is composed of an ausferritic matrix with graphite nodules and has a wide range of applications because of its high mechanical strength, fatigue resistance, and wear resistance compared to other cast irons. The amount and size of the nodules can be controlled by the chemical composition and austenitizing temperature. As the nodules have lower stiffness than the matrix and can act as stress concentrators, they influence crack propagation. However, the crack propagation mechanism in ADI is not yet fully understood. In this study, we describe a numerical investigation of crack propagation in ADIs subjected to cyclic loading. The numerical model used to calculate the stress intensity factors in the material under the given conditions is built with the aid of Abaqus commercial finite element code. The crack propagation routine, which is based on the Paris law, is implemented in Python. The results of the simulation show that the presence of a nodule generates a shear load on the crack tip. Consequently, even under uniaxial tensile loading, the presence of the nodule yields a non-zero stress intensity factor in mode II, resulting in a deviation in the crack propagation path. This is the primary factor responsible for changing the crack propagation direction towards the nodule. Modifying the parameters, for example, increasing the nodule size or decreasing the distance between the nodule and crack tip, can intensify this effect. In simulations comparing two different ADIs with the same graphite fraction area, the crack in the material with more nodules reaches another nodule in a shorter propagation time (or shorter number of cycles). This suggests that the high fatigue resistance observed in ADIs may be correlated with the number of nodules intercepted by a crack and the additional energy required to nucleate new cracks. In summary, these findings contribute to a better understanding of crack propagation in ADIs, provide insights into the relationship between the presence of nodules and the fatigue resistance of these materials, and support studies that associate the increased fatigue resistance with a higher number of graphite nodules. These results can also help justify the enhanced fatigue resistance of ADIs when compared to other cast irons. [ABSTRACT FROM AUTHOR]

This study focused on the development of austempered ductile iron (ADI) with desirable combination of mechanical properties for crankshaft applications by the combined effect of vanadium (V) alloying and an optimized heat treatment process. The produced unalloyed GGG60, 0.15% V-alloyed GGG60 (V-15), and 0.30% V-alloyed GGG60 samples were subjected to austenitizing at 900 °C for 1 h and subsequent austempering processes at 250, 300, and 350 °C for 15, 30, 60, 90, and 180 min. As a result of these austempering processes, different bainitic structures were obtained, which led to the formation of diverse combinations of mechanical properties. The mechanical properties of the austempered samples were tested comprehensively, and the results were correlated with their microstructures and the stability of the retained austenite phases. From the microstructural observations, the V-alloyed samples exhibited a finer microstructure and a more acicular ferrite phase than unalloyed samples. The V addition delayed the coarsening of the acicular ferrite structures and considerably contributed to the improvement of the mechanical properties of GGG60. Moreover, the X-ray diffraction results revealed that the retained austenite volume and the carbon enrichment of austenite phases in ADI samples were remarkably affected by the addition of vanadium. The increase in volume fraction of retained austenite and its carbon content provided favorable ductility and toughness to V-15, as confirmed by the elongation and impact test results. Consequently, the dual-phase ausferrite microstructure of V-15 that was austempered at 300 °C for 60 min exhibited high strength with substantial ductility and toughness for crankshaft applications. [ABSTRACT FROM AUTHOR]

The effects of strain-induced austenite transformation on the microstructure evolution and phase transformation characteristics have been investigated in an austempered ductile iron during various processing routes (heat and thermomechanical treatments). The thermomechanical treatment is performed using a Gleeble 3800 thermomechanical simulator coupled with dilatometry. The deformation-induced microstructure evolution and phase transformation during the austempering process have been characterized using optical microscopy, scanning electron microscopy, and X-ray diffraction techniques. The variations in retained austenite percentage (%) and its carbon content for different austempering times are analyzed to study the strain-induced transformation of austenite. It has been observed that the thermomechanical treatment significantly influences the phase transformation kinetics during the austempering process. The thermomechanical treatment produced a martensite-free ausferritic microstructure with a high-volume fraction of carbon enriched retained austenite for all austempering times compared to the conventional heat treatment. [ABSTRACT FROM AUTHOR]

The present study was performed to investigate the influences of short-time austenitization on mechanical properties and transformation-induced plasticity (TRIP) in austempered ductile iron. For this purpose, Cu–Ni–Mo-alloyed ductile iron (DI) were poured into sand molds and subsequently the DI samples were austenitized at 850 °C for the duration of 15–30–60 min followed by holding in a salt bath at an austempering temperature of 260 °C for 90 min. Characterization studies were carried out with dilatometer, image analyses software, tensile test, hardness test, XRD analysis, optical and scanning electron microscopies. Findings revealed that as the austenitization time increased, carbon content of austenite (total of high carbon and blocky) and bainitic ferrite cell size enhanced, and phase volume fractions of transformation products of austenite changed. Within this context, changes in the mechanical properties were discussed. Optimum combination of strength and ductility and maximum TRIP effect were determined in the shortest (15 min)-austenitized sample. Accordingly, it was determined 15 min austenitization led to progression in the mechanical properties as 146 MPa and 2.8 % increment in the tensile strength and total elongation respectively, compared to 45 min austenitized sample. [ABSTRACT FROM AUTHOR]

In this study, the effect of the austempering times on the microstructures and mechanical properties of dual-matrix structure austempered ductile iron (DMS-ADI) was investigated. With this aim, unalloyed as-cast ductile iron tensile samples were austenitized at 810 °C for 30 min to intercritical austenitizing followed by austempering at 350°C for various austempering times (45 min to 180 min). Experimental results showed that dual-matrix structures consisting of proeutectoid ferrite + ausferrite were obtained in austempered ductile iron from intercritical austenitizing temperatures. It was determined that as the austempering time increased, the ausferritic structure became considerably clear and its volume fraction was almost constant (45–47%) after 90 min of austempering time. The yield and tensile strength of the samples decreased and the total elongation and breaking energy increased with increasing austempering times, but after the 120-min austempering time, both the total elongation and breaking energy of the samples decreased. It was established that the austempering times had no significant effect on the morphology of ausferrite. The best mechanical properties were obtained between 70- and 130-minute austempering times that can be defined as the processing window. In addition, it was determined that the DMS-ADI had similar austempering kinetics with the ADI. [ABSTRACT FROM AUTHOR]

A transmission electron microscope was used to study the morphology of austenite and ferrite in austempered ductile iron obtained through conventional and two-step austempering process. In this investigation, two compositions of ductile iron with carbon equivalent 4.3% (alloy 1) and 3.1% (alloy 2) were selected. Both alloys were austenitized for 60 min at 900 °C. In conventional treatment, after austenitization, specimens were quenched into salt bath at 400 °C and austempered for 120 min. In two-step process, first specimens were quenched into salt bath at 250 °C and then temperature was raised to 400 °C and specimen was austempered for 120 min. The TEM study showed lamellar arrangement of ferrite and austenite in both the austempering processes. The width of the ferrite and austenite lamina was found to be smaller in specimen austempered by two-step process than by conventional austempering process. [ABSTRACT FROM AUTHOR]

In the present research, the orthogonal experiment was carried out to investigate the influence of different austempering process parameters (i.e. austenitizing temperature and time, and austempering temperature and time) on microstructure and mechanical properties of LZQT500-7 ductile iron dense bars with 172 mm in diameter which were produced by horizontal continuous casting (HCC). The results show that the major factors influencing the hardness of austempered ductile iron (ADI) are austenitizing temperature and austempering temperature. The fraction of retained austenite increases as the austenitizing and austempering temperatures increase. When austenitizing temperature is low, acicular ferrite and retained austenite can be efficiently obtained by appropriately extending the austenitizing time. The proper austmepering time could ensure enough stability of retained austenite and prevent high carbon austenite decomposition. The optimal mechanical properties of ADI can be achieved with the following process parameters: austenitizing temperature and time are 866 °C and 135 min, and austempering temperature and time are 279 °C and 135 min, respectively. The microstructure of ADI under the optimal austempering process consists of fine acicular ferrite and a small amount of retained austenite, and the hardness, tensile strength, yield strength, elongation and impact toughness of the bars are HBW 476, 1670 MPa, 1428 MPa, 2.93% and 25.7 J, respectively.

Austempered ductile iron (ADI) parts have a unique combination of high strength and toughness with excellent design flexibility and low cost. These excellent properties are directly related to its microstructure called "ausferrite" that is the result of austempering heat treatment applied to ductile irons. Alloying elements increase ADI austemperability and change speeds of austempering reactions. Thus, they can affect ADI resultant microstructure and mechanical properties. In this paper, the effects of alloying elements on ADI mechanical properties, microstructural changes, two-stage austempering reactions, processing windows, austemperability, and other aspects are reviewed.

The use of austempered ductile iron (ADI) is rapidly increasing in many engineering applications such as automotive due to its unique and promising characteristics, for example; high strength to weight ratio, high wear and corrosion resistance, high yield stress, and high toughness. However, other properties such as low thermal conductivity undesirably affects ADI machinability and accelerate cutting tool failure. Additionally, other issues associated with cutting ADI are the high cutting temperature, high pressure and dynamic loads, and tendency of chip to adhere to cutting tool face. To overcome such issues, a proper coolant should be applied. However, flood coolant has sufficient effects in reducing the generated cutting heat, further alternatives are still required to decease its environmental and health impacts. Minimum quantity lubrication (MQL) serves as the best alternative to flood cooling from an environmental perspective as it minimizes the amount of cutting fluid; however, its heat capacity is lower than the traditional flood coolant. To improve the cooling and lubricating efficiency of MQL, aluminum oxide (Al2O3) gamma nanoparticles are used in this work and its effect on the tool wear behavior during cutting of ADI is investigated. The combination of MQL-nanofluid at cutting speed of 120 m/min and feed rate of 0.2 mm/rev showed the best tool life, while test 3 which has been performed at cutting speed of 240 m/min and feed rate of 0.2 mm/rev using classical MQL provided the worst flank wear value. [ABSTRACT FROM AUTHOR]

The effect of austempering parameters on impact energy of non-alloyed cast iron with nodular graphite was examined. The analysis involved the austenitizing temperature in the range of 830-950 °C for the time of 60 min and the austempering temperature in the range of 300-400 °C for the time of 8, 16, 32 and 64 min. The value of the impact energy KV was determined. It has been found that the austenitizing temperature and austempering conditions affect the impact energy of ADI. The conducted analytical studies helped to develop a method for the selection of heat treatment parameters to obtain the ausferritic ductile iron with appropriate impact energy KV. The applied machine learning methods included support vector machine, decision trees, artificial neural networks and the method of variational component analysis. [ABSTRACT FROM AUTHOR]

The three-step austempering heat treatment of ductile iron parts in this paper is simulated by employing a coupled thermo-mechanical-metallurgical model. The thermo-mechanical formulation is solved in the macroscale using the finite element method to predict the evolution of temperatures and deformations in the whole part. The metallurgical model deals with phase transformations that occur during the heat treatment, which are analyzed in the microscale. For each phase transformation the microstructure features such as type, distribution, and shape and size of phases are considered employing representative volume elements. The performance of the proposed model is tested by simulating experimental heat treatments reported in the literature. By means of comparison with experimental results, the model proved to be able to predict correctly the evolutions of temperature and dimensional changes, the minimum austenitization and austempering times, and the final phase fractions. It is concluded that this model could be a useful computational tool in the design of austempered ductile iron parts as well as the austempering heat treatment process. [ABSTRACT FROM AUTHOR]

Alloyed Ductile iron, austenitized at 840 °C for 30 min in a special sealed austempering furnace, was austempered for 30 min in molten salt mixture at 4 trial temperatures of 300 °C, 320 °C, 340 °C and 360 °C. Tensile strength, yield strength, percentage elongation and impact energy were evaluated for the as-cast and austempered samples. Microstructures were investigated using microscopy, coupled with analyzing software and a scanning electron microscopy. The specific wear of samples was tested using pin-on-disc wear testing machine. X-ray diffraction was performed to calculate the amount of retained austenite present in the ausferrite matrix. As-cast microstructure consists of ferrite and pearlite, whereas austempered ductile iron (ADI) contains a mixture of acicular ferrite and carbon enriched austenite, called “ausferrite”. Hardness and strength decreased, whereas ductility and impact strength improved with an increase in the austempering temperature. XRD analysis revealed that the increase in austempering temperature increased the retained austenite content. A decrease in wear resistance with austempering temperature was observed. Modified Quality Index (MQI) values were envisaged, incorporating tensile strength, elongation and wear resistance. MQI for samples austempered at 340 °C and 360 °C showed a better combination of properties. About an 8% reduction in energy consumption was gained when the heat treatment parameters were optimized.

The use of modern casting materials allows the achievement of higher product quality indices. The conducted experimental studies of new materials allow obtaining alloys with high performance properties while maintaining low production costs. Studies have shown that in certain areas of applications, the expensive to manufacture austempered ductile iron (ADI) can be replaced with ausferritic ductile iron or bainitic nodular cast iron with carbides, obtained without the heat treatment of castings. The dissemination of experimental results is possible through the use of information technologies and building applications that automatically compare the properties of materials, as the machine learning tools in comparative analysis of the properties of materials, in particular ADI and nodular cast iron with carbides. [ABSTRACT FROM AUTHOR]

Austempered ductile iron is a heat treated form of as-cast ductile iron. The heat treatment process-austempering, was developed with the intent of improving the strength and toughness of ferrous alloys. It offers a range of mechanical properties superior to those of other cast iron, and shows excellent economic competitiveness with steels and aluminum alloys. The main aim is to analyze the mechanical properties and microstructural characteristics of as-cast ductile iron austenitized at 900 °C for 90 min and afterward austempered over a range of temperatures to obtain distinctive microstructures. The samples were austempered for durations of 60, 90 and 180 min at each austempering temperature of 340, 360, 380, and 400 °C. The influence of these austempering temperatures and times on the microstructure and tensile properties were investigated at room temperature. [ABSTRACT FROM AUTHOR]

The paper presents the possibility of application of ductile iron of isothermal transformation (ADI) for responsible parts of vehicles and machines. For the selected smelting proposed a variant of the heat treatment, in order to obtain the final stage cast according to PN-EN ISO 1564. Austenitizing ADI hardening effect on the carbon content in the austenite versus temperature heating.Ductile iron of matrix ferritic tempered with isothermal transformation in at temperature tpi = 400 and 300 0C in the time interval τpi = 7.5 ÷ 240 min. The samples austenitized gradually. Research in this area will continue. [ABSTRACT FROM AUTHOR]

Dry machining is being recognized as ecological machining due to its less environmental impact and manufacturing cost. However, the choice of dry machining is mainly influenced by the workpiece material properties, machining operation and cutting conditions. The recent emergence of austempered ductile iron (ADI) can be considered a significant economic advantage to the increasing industrial demand for cost- and weight-efficient materials. However, due to its microstructure-induced inherent properties, ADI is considered hard-to-machine material. Thus, the dry drilling of ADI is investigated in this paper. The ADI material used in the present study is produced using an innovative process route for near net shape casting production. Drilling experiments are conducted on a DMU80P Deckel Maho five-axis machining centre using PVD-coated carbide tools under dry cutting environment. The dry drilling of ADI under different cutting conditions is evaluated in terms of specific cutting force and tool wear analysis. The influence of cutting conditions on chip morphology and surface roughness is also investigated. The experimental results revealed that the combination of the low feed rate and higher cutting speed leads to the higher mechanical and thermal loads on the tool's cutting edge, resulting in higher specific cutting force values. This behaviour is further supported by the chip morphology analysis, which revealed the formation of segmented chips at higher cutting speed with segment spacing increase with an increase in feed rate. Depending upon the cutting parameters, different modes of tool failures including crater wear, flank wear, chipping, breakage and built-up edge were observed. Surface roughness analysis revealed the influence of tool wear and chip morphology on the machined surface finish. [ABSTRACT FROM AUTHOR]

This work investigates the machining characteristics of Austempered Ductile Iron (ADI) using Electrical Discharge Machining (EDM) process with copper as an electrode. Experiments have been carried out to analyze the effect of each parameter on the machining characteristics, and to predict the optimal choice for each EDM parameters such as peak current, pulse on time, pulse off time and tool geometry. Three different specimens were austenised at 900° C for 90min and then austempered in a salt bath at 360° C, 380° C, and 400° C for 120min. Experiments have been designed as per Taguchi's L18 orthogonal array. Analysis of variance (ANOVA) is used to find the level of significance of machining parameters. Machining responses such as the metal removal rate (MRR), Tool wear rate (TWR), surface roughness (SR) and taper angle (DVEE) for entrance – exit of the tool was studied while machining the Austempered Ductile Iron (ADI) with copper as an electrode. Discharge current, Pulse on time and Austempering temperature are found most influential parameters on each performance measure. Tool geometry is found the least influential parameters. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: Using especially designed and constructed isothermal calorimeter, the austempering of Cu–Ni ductile iron was carried out at temperatures of T pi =270, 350, 390 and 430°C, simultaneously with the measurement of accompanying thermal effects. The values of enthalpy changes ΔH show the correct and expected trend, varying from 45J/g at T pi =430°C to 70J/g at T pi =270°C. The changes of enthalpy were observed to increase with decreasing temperature of the isothermal transformation during austempering. The results of the present work did not allow revealing the influence of alloying elements, i.e. Cu and Ni, on the heat of isothermal transformation. The discrepancies between the results of the actual measurements and the results quoted in other papers were discussed in terms of DSC measurements. [Copyright &y& Elsevier]

In the current study, an unalloyed ductile iron containing 3.50 C wt.%, 2.63 Si wt.%, 0.318 Mn wt.%, and 0.047 Mg wt.% was intercritically austenitized (partially austenitized) in two-phase regions (α + γ) at different temperatures for 20 min and then was quenched into salt bath held at austempering temperature of 365 °C for various times to obtain different ausferrite plus proeutectoid ferrite volume fractions. Fine and coarse dual matrix structures (DMS) were obtained from two different starting conditions. Some specimens were also conventionally austempered from 900 °C for comparison. The results showed that a structure having proeutectoid ferrite plus ausferrite (bainitic ferrite + high-carbon austenite (retained or stabilized austenite)) has been developed. Both of the specimens with ~75% ausferrite volume fraction (coarse structure) and the specimen with ~82% ausferrite volume fraction (fine structure) exhibited the best combination of high strength and ductility compared to the pearlitic grades, but their ductility is slightly lower than the ferritic grades. These materials also satisfy the requirements for the strength of the quenched and tempered grades and their ductility is superior to this grade. The correlation between the strain-hardening rates of the various austempered ductile iron (ADI) with DMS and conventionally heat-treated ADI microstructures as a function of strain was conducted by inspection of the respective tensile curves. For this purpose, the Crussard-Jaoul (C-J) analysis was employed. The test results also indicate that strain-hardening behavior of ADI with dual matrix is influenced by the variations in the volume fractions of the phases, and their morphologies, the degree of ausferrite connectivity and the interaction intensities between the carbon atoms and the dislocations in the matrix. The ADI with DMS generally exhibited low strain-hardening rates compared to the conventionally ADI. [ABSTRACT FROM AUTHOR]

In the present study, during austempering, microstructure formations in the ferritic ductile irons austempered from intercritical temperature ranges have been investigated. For this purpose a ferritic ductile iron was intercritically austenitised (partially austenitised) at intercritical temperature ranges and then austempered in a salt bath held at austempering temperature of 365°C for various times. Following austempering from various intercritical annealing temperatures, microstructure variation graphics were created to illustrate the transformation of products quantitatively as a function of austempering time. Metallographic measurements showed that during austempering, the total volume fraction of the transformed phases from the original austenite formed at intercritical austenitization temperature is approximately equal to the volume fraction of original austenite for all austempering times. Within each of the austempered specimen from intercritical temperature ranges, in addition to proeutectoid and bainitic ferrite, the new ferrite (epitaxial ferrite) introduced into the structure. The new ferrite volume fraction increased with increasing intercritical austenitizing temperature but transforming percentage of new ferrite from the original austenite present at intercritical austenitizing temperature increased with decreasing intercritical austenitizing temperature. Increasing the austempering time causes new ferrite, bainitic ferrite and high C austenite to displace martensite. Some specimens were also conventionally austempered from 900°C for comparison. The new ferrite was absent in the conventionally austempered samples. [ABSTRACT FROM AUTHOR]

Abstract: This study presents the results of machining tests carried out to determine the effect of microstructure and mechanical properties of austempered ductile irons (ADIs) on cutting forces and surface roughness. Specimens were prepared under different austempering times with the addition of Cu and Ni at various contents. Six different specimen groups were austenised at 900°C for 90min and then austempered in molten salt at 370°C for 60, 90, 180 and 200min. The results were evaluated after machining tests which were carried out in accordance with ISO 3685. Austempering heat treatment resulted in considerable improvement on the surface quality when compared to as-cast specimens while the changes in cutting forces remained at about 20% level for different specimens. In terms of both criterion, the best result was obtained from 60min austempered and 0.7% Ni and 0.7% Cu added specimens. [Copyright &y& Elsevier]

Abstract: Sol–gel organic–inorganic hybrid coatings are being increasingly used to protect metal surfaces. The presence of non-hydrolysable groups in their structure can lead to the formation of coatings with properties intermediate between glasses and organic polymers. Crack-free, homogeneous and adherent hybrid silica sol–gel coatings around 1 μm thick were obtained by dip-coating on glass and Austempered Ductile Iron (ADI). Homogeneous multilayer coatings up to 4 μm were obtained on glass substrates, but not on ADI substrates since coating cracked after the densification of a second layer. The hardness of the coating on ADI substrates was slightly higher than that of as received ADI. Preliminary electrochemical impedance polarization spectroscopy (EIS), potentiodynamic polarization and polarization resistance tests in NaCl solution have shown an improvement of corrosion resistance of ADI. [Copyright &y& Elsevier]

Impact properties of standard American Society for Testing Materials (ASTM) grades of austempered ductile iron (ADI) were evaluated at subzero temperatures in unnotched and V-notched conditions and compared with ferritic and pearlitic grades of ductile irons (DIs). It was determined that there is a decrease in impact toughness for all ADI grades when there is a decrease in content of retained austenite and a decrease in test temperature, from room temperature (RT) to −60 °C. However, the difference in impact toughness values was not so noticeable for low retained austenite containing grade 5 ADI at both room and subzero temperatures as it was for ADI grade 1. Furthermore, the difference in impact toughness values of V-notched specimens of ADI grades 1 and 5 tested at −40 °C was minimal. The impact behaviors of ADI grade 5 and ferritic DI were found to be more stable than those of ADI grades 1, 2, 3, and 4 and pearlitic DI when the testing temperature was decreased. The impact toughness of ferritic DI was higher than that of ADI grades 1 and 2 at both −40 °C and −60 °C. The impact properties of ADI grades 4 and 5 were found to be higher than that of pearlitic DI at both −40 °C and −60 °C. The scanning electron microscopy (SEM) study of fracture surfaces revealed mixed ductile and quasicleavage rupture morphology types in all ADI samples tested at both −40 °C and −60 °C. With decreasing content of retained austenite and ductility, the number of quasicleavage facets increased from ADI grade 1–5. It was also found that fracture morphology of ADI did not experience significant changes when the testing temperature decreased. Evaluation of the bending angle was used to support impact-testing data. Designers and users of ADI castings may use the data developed in this research as a reference. [ABSTRACT FROM AUTHOR]

Austempered ductile irons exhibit an interesting combination of properties such as low cost, elevated strength, fatigue and wear resistance. In the present contribution, the influence of shot-peening on the dry-sliding wear behavior of as-cast and austempered ductile irons was evaluated. Specimens from a casting with an initial ferritic-pearlitic matrix were submitted to austempering at 320 °C for 60 min after which an ausferritic microstructure with 40 HRC and approximately 30% retained austenite was obtained. The wear and friction behaviors were assessed by applying ball-on-disc tests using a hard metal (WC) counter-body on as-cast and austempered materials before and after shot-peening and after removal of the rough surface layer created by the shot-peening process. The microstructure of the tested materials was evaluated by X-ray diffraction, optical and scanning electron microscopy. After shot-peening, the austempered samples experienced an elevated increase in surface hardness because of the formation of strain-induced martensite, but a reduction in wear resistance caused by the increase in surface roughness. By removing 20 μm from the surface of the shot-peened samples, it was possible to reduce roughness while preserving the hardened layer, which was found to improve wear resistance. • Austempering heat treatment of ductile iron was investigated. • Materials were characterized by XRD, SEM-EBSD and shot-peened. • Shot-peening led to martensite from the original ausferrite microstructure. • Dry-sliding tests revealed negative influence of shot-peening on wear behavior. [ABSTRACT FROM AUTHOR]