Abstract: We elaborated two carbide-free bainitic steels with different microstructures through specific alloy design and austempering process Microstructural characterizations were performed by means of EBSD analysis and in-situ high energy synchrotron diffraction in order to evaluate the phase fractions and the carbon content in the retained austenite, as well as the microtextures These microstructural features were correlated to the tensile properties Both steels exhibited an excellent compromise between high strength (above 1250 MPa), good ductility (uniform elongation up to 14%) and high fracture strain (reduction of area up to 46%) The volume fraction of MA blocks (blocks of retained austenite partially transformed into fresh martensite during the final cooling at room temperature) was a key relevant parameter that strongly influenced the work-hardening at the expense of the damaging processes at high strain

Abstract: In this study, ductile irons with and without 1 wt% copper alloy were austempered to become austempered ductile irons (ADIs). Microstructure, impact toughness, and fracture toughness were evaluated to determine how both the copper alloying and austempering treatments influenced the toughness properties of ductile irons. The results show that, because copper increases the retained austenite content in ADI, the Cu-alloyed ADI has better impact toughness and fracture toughness ( K IC value) than does the unalloyed one. In particular, the impact toughness and the fracture toughness of ADI could be efficiently improved by treating the Cu-alloyed ductile iron at a higher austempering temperature (360 °C) to obtain more retained austenite in its microstructure.

Abstract: The microstructure of transformation induced plasticity (TRIP) steels was characterized by means of electron backscattering diffraction (EBSD) technique to identify and quantify their different microstructures such as ferrite, bainite, and retained austenite. Further, the strain distribution in ferrite and retained austenite was analyzed during deformation. The TRIP steels were annealed by austempering for different durations to investigate the effect of the austempering time on the volume fraction change of the microstructural constituents. The quantitative analysis by EBSD coupled with an image contrast analysis revealed that the amount of retained austenite decreased and the amount of bainite increased with increasing austempering time. The mechanical properties of the TRIP steels were also affected by the austempering time. The maximum elongation was obtained in the sample austempered for 5 min, probably because of the good stability of retained austenite. The strain distribution in bcc and fcc phases during tensile deformation was characterized by evaluating the changes in the average local misorientation of the phases.

Abstract: In this investigation, a new low alloy and low carbon steel with exceptionally high strength and high fracture toughness has been developed. The effect of austempering temperature on the microstructure and mechanical properties of this new steel was examined. The influence of the microstructure on the mechanical properties and the fracture toughness of this steel was also studied. Test results show that the austempering produces a unique microstructure consisting of bainitic ferrite and austenite in this steel. There were significant improvement in mechanical properties and fracture toughness as a result of austempering heat treatments. The mechanical properties as well as the fracture toughness were found to decrease as the austempering temperature increases. On the other hand, the strain hardening rate of steel increases at higher austempering temperature. A linear relationship was observed between strain hardening exponent and the austenitic carbon content.

Abstract: We examined the effects of retained austenite phase on the springback of cold-rolled transformation-induced plasticity (TRIP) steel sheets through a series of V-bending tests. Prior to testing, the intercritically annealed TRIP steel sheets were heat-treated at different austempering temperatures (300, 350 and 400 °C) to obtain three specimens with different retained austenite phase fractions. Results show that the amount of springback in TRIP steel decreased as the fraction of retained austenite phase increased. The amount of springback was reduced by about 30% when the fraction of retained austenite phase increased by 5%. When the area fractions of the retained austenite phase of TRIP steel were less than 3%, we observed micro-cracks in the near-surface points of a V-shaped specimen where compressive and tensile stresses were concentrated. The dependency of material's direction upon springback was very weak in the V-bending test where no constraint such as a blank holder exists during testing.

Abstract: Rolling contact fatigue (RCF) properties of low-temperature bainitic microstructure in the surface layer of a low-carbon steel, obtained by means of carburization and successive lowtemperature austempering were studied. Comparisons were made with those properties of a martensite steel obtained by quenching and tempering. The results showed that the low-temperature bainitic steel exhibits an excellent RCF resistance and reaches a RCF life more than twice that of the martensite steel, presumably as a consequence of the very thin bainite plates (~80 nm in thickness) and the fine-scale dispersion of austenite between the plates. The apparently increased hardness in the surface layer may partly be the cause of the enhanced RCF resistance.

Abstract: Concern about the fuel economy of automobiles has stimulated the development of bainitic steels. A high strength to weight ratio together with good ductility may be achieved by this endeavour if a number of metallurgical issues can be resolved. Strong bainitic steels are alloyed with silicon in order to avoid the deleterious effect of cementite which otherwise forms in association with bainite. This strengthens the steels and also enhances the toughness because the carbon that is usually precipitated as brittle cementite instead partitions into the residual austenite, allowing the latter to be retained. The amount of retained austenite in the steel can, in principle, be optimised by heat treatment. Substantial work has, in the past, been carried out on the nature of the bainite transformation. However, this is not the case when it comes to the decomposition of the retained austenite during tempering. This is important because applications such as the galvannealing of automotive steel involves subjecting it to temperatures as high at 475◦C. The goal of the work initiated in this thesis was to gain a detailed understanding of the thermal decomposition of retained austenite. Systematic characterisation experiments have been undertaken to demonstrate the progress of the tempering process as a function of time and temperature. High resolution dilatometry was carried out to distinguish quantitatively between the two competing processes of austenite decomposition and tempering of martensite. Based on these studies a new theory has been proposed for the decomposition of retained austenite during and after the tempering process. In essence, the austenite is rendered unstable to martensitic transformation during cooling from the tempering temperature even though the fraction of precipitation is minute. The evolution of microstructure during the progress of tempering has been captured using in situ transmission electron microscopy. This study provides strong evidence of the austenite decomposition model. The fact that the process does not involve nucleation of new ferrite, but rather the growth of existing ferrite at the expense of austenite, has been confirmed by direct observation. High-energy synchrotron X-ray radiation has been used for in situ experiments which revealed the structural changes during the tempering process with a particular focus on the change in lattice parameters and carbon content of the film and blocky types of austenite. More importantly, it verified the instability of the austenite to the cooling process. The tempering behavior of Mn and Ni-containing bainitic steels has been compared and it has observed that the process is faster in the latter case. These experiments provided critical data in the validation of kinetic theory. The non-uniform strains and dislocation densities were estimated from X-ray measurements during the progress of tempering process. An attempt has been made to predict the overall transformation kinetics of the decomposition of retained austenite subjected to the tempering treatment, based on the simultaneous transformations of ferrite and cementite. This helped confirm that it is not tenable to argue that new ferrite forms by reconstructive nucleation and growth during tempering.

Abstract: The invention discloses a method for manufacturing an austempered ductile iron (ADI) front axle of a heavy truck by sand casting. By the method, nickel molybdenum copper austempered ductile iron (ADI) front axle of the heavy truck is produced by a furane resin sand molding process, and the problems that the internal density and the performance reliability of ADI products are difficult to guarantee and the mechanical properties of the ADI products are low are solved. The method has the following steps of: firstly, casting a blank of the nickel molybdenum copper alloyed spheroidal graphite cast iron front axle by the furane resin sand molding process; secondly, performing the surface shot peening strengthening and isothermal quenching heat treatment; and finally machining the front axle parts. By the method, casting is replaced by forging, and the iron is replaced by steel, the comprehensive mechanical properties are obviously higher than those of common spheroidal graphite cast iron and forged steel, the weight of truck parts is reduced, the investment of heavy forging equipment and dies is saved, the cost is reduced, the production cycle is shortened, energy is saved, the emission is reduced, and the economic benefit and the social benefit are obvious.

Abstract: The microstructure and properties of austempered ductile iron with carbides was studied to increase the abrasive resistance of ADI. It was proven that the austempering temperature influences greatly the microstructure, impact toughness, hardness and abrasion resistance of CADI. With increase of austempering temperature, the acicular ferrite becomes thicker and bigger, the impact toughness rises, and the hardness decreases. But there is a complicated effect of austempering temperature on wet abrasion resistance. In addition, the CADI grinding balls were cast and the field testing was performed. The CADI ball is one third of abrasion loss of low chromium cast iron, zero rate of breakage and no loosing round.

Abstract: In this paper, ductile irons with different microstructures were machined in a group of experiments using standard testing procedure and the effect of microstructure on the machinability was investigated. Bars (diameter 90 mm x 320 mm) of ferritic/pearlitic, tempered martensitic, and lower ausferritic microstructures were produced by various heat treatments and then tested to evaluate their machinability. Five groups of ductile iron specimens with various microstructures were tested following ISO 3685: 1993 (E) standard. Specimens were subjected to dry cutting; cutting force, flank wear width, and surface roughness were measured to compare the machining performances. In addition, further turning tests were conducted on the specimens of austempered microstructure at various feed rates (while keeping the cutting speed and depth of cut constant), and both surface roughness and cutting force values were recorded. The influence of feed rate on the machinability of austempered ductile iron was investigated and a correlation between feed rate and machinability, in terms of cutting force and surface roughness, was established. Not only the tangential cutting force component but also the feed force component was taken into consideration in these tests.

Abstract: A numerical description relating microstructure to elastic and plastic deformation behavior would make it possible to simulate the mechanical behavior of complex cast components with tailored material properties Limited work and data, however, have been published regarding the connection between microstructure and plastic behavior of austempered ductile irons (ADIs) In the current work, the effects of austempering temperature and austempering time on the strength coefficient and the strain hardening exponent of the Hollomon equation were investigated for two ADI alloys The results show that the plastic behavior is highly dependent on the combination of austempering temperature and austempering time It was found that as the austempering temperature increases, both the strength coefficient and the strain hardening exponent initially decrease, but after reaching a minimum at the critical austempering temperature, they show a plateau or an increase The effect of the austempering time on the plastic behavior depends on the austempering temperature At low austempering temperatures, the strength coefficient and the strain hardening exponent decrease with increased austempering time, whereas at higher austempering temperatures, they show little time dependence These relations are explained by the microstructural transformations that take place during the austempering heat treatment

Abstract: The newly developed multiphase transformation-induced plasticity (TRIP) steels are of interest for industrial applications because of their excellent combination of high strength and ductility. Their performance can be successfully controlled by designing an optimum balance in the volume fractions of ferrite, bainite and retained austenite. The characteristics of the retained austenite are considered to be the main key to achieving the desired final properties. Against this background, the effects of retained austenite characteristics, such as volume fraction, carbon concentration, size and shape, on the behaviour of TRIP steels have been studied. The crystallographic orientation of the retained austenite was measured by electron backscattered diffraction (EBSD). The effect of initial cold-rolling reduction on the microtexture development of the retained austenite was studied on an aluminium-containing TRIP steel. The results show that, by increasing the cold-rolling reduction before the final austempering, the main components of the face-centred cubic phase, i.e. copper, brass and Goss, dominate the texture of the retained austenite. In contrast, the copper and Goss components of the retained austenite are absent in the texture of lightly deformed sheets. The features of the preferred orientation of the retained austenite are discussed and explained in terms of the annealing texture of the recrystallized ferrite and bainite.

Abstract: Fil: Colombo, Diego Alejandro. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnologia de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingenieria. Instituto de Investigaciones en Ciencia y Tecnologia de Materiales; Argentina

Abstract: The paper deals with some factors influencing micro structure and mechanical properties of austempered ductile iron (ADI). Final structure and properties of ADI are obtained by exactly controlled process of heat treatment of nodular cas t iron. In dependence on transformation temperature, various matrixes can be obtained (i.e. mixture of bainite with retained austenite), containing various content of retained austenite an d consequently mechanical properties of ADI are changed. The influence of conditions of isother mal heat treatment on microstructure and mechanical properties of austempered ductile iron, especially different temperature of isothermal transformation of austenite and different holding t ime at this temperature, is shown in the paper.

Abstract: Purpose – The aim of this paper is to study the effect of heat treatment temperature and time on the corrosion behavior of ductile iron in 0.5 M NaCl and 0.5 M H2SO4.Design/methodology/approach – Ductile iron samples of known composition were austenized at temperatures 800°C and 850°C, and austempered at 300°C and 350°C for periods of 30, 45 and 60 min to convert them to austempered ductile iron (ADI). The corrosion behavior of these ADI samples in 0.5 M NaCl and H2SO4 was measured using the conventional weight loss method. The metallographic examination of the samples was carried out to study the morphology of their corroded surfaces.Findings – Ductile iron is susceptible to corrosion in both acidic and chloride media, while attack by acid media is mainly at the grain boundaries, that from the chloride is pitting. The corrosion behavior of the material is affected by the compositional structures of the materials as well as the austempering temperature and time it was subjected to.Practical implications –...

Abstract: The effect of compound modification and various kinds of heat treatment on microstructure and mechanical properties of the low chromium white cast iron was studied.The results showed that,after modification,the carbide morphology in cast iron has been greatly improved;the annealed modified cast iron is suitable for machining;both martensitic quenching and austempering can cause the hardness and the impact toughness of modified cast iron increase greatly.

Abstract: An attempt has been made to assess the grinding wear behaviour of austempered ductile iron (ADI) as media material in comminution of Kudremukh haematite iron ore in a ball mill Spheroidal graphite (SG) iron balls were austenitised at 900°C for one hour and austempered at 280°C and 380°C for different time durations These materials were characterized by measuring hardness, carrying out X-ray diffraction analysis, studying microstructures using scanning electron microscope (SEM) Grinding wear behaviour of ADI was assessed during wet grinding at different pH of the mineral slurry The wear resistance of ADI was compared with that of forged En 31 steel balls under similar grinding conditions It was found that ADI balls austempered at 280°C for 30 minutes which contains lower bainite registered superior wear resistance It was also noted that the wear resistance of ADI was more at higher pH range of the slurry

Abstract: Microstructures and mechanical properties for medium carbon steels including practical spring steels austempered at 400°C and 300°C were investigated. The larger strain was applied, the larger the fraction of retained austenite became martensite through strain induced transformation. 0.2% proof stress was increased by the increase of the fraction of bainitic ferrite. Uniform elongation was increased by increasing the fraction of retained austenite. Good strength–ductility balance with tensile stress over 1800 MPa for high strength spring was achieved in austempered SUP12 at 300°C composed of three phases of retained austenite, martensite and lower bainite.

Abstract: This study presents the novel processing technique known as continuous casting-heat treatment processes to produce Austempered Ductile Iron (ADI) which is a new class of ductile iron. ADI is characterized by improved mechanical properties but has low machinability as compared to other cast irons and steel of similar strength. The novel technique is developed by the integration of casting (in die casting) and heat treatment processes in foundry to save cost energy and time. Specimens just after casting were austenitized at 930 deg. C for 90 min and then austempered in fluidized bed at 380 deg. C for 90 and 120 min. Hence, the effect of austempering time on the morphology of retained austenite and mechanical properties of the material were examined and compared with conventionally produced ADI. Drilling tests were then carried out to evaluate the machinability of ADI in terms of cutting forces, chip micro-hardness, chip morphology and surface roughness. The mechanical properties of ADI austempered for 120 min have found to be better as compare to the ADI austempered for 90 min.

Abstract: Austempered Ductile Iron (ADI) can offer an excellent combination of low cost, design flexibility, good machinability, high strength-to-weight ratio, good toughness, good wear resistance and fatigue strength. Although ADI has found quite wide application in some industries, its use in automotive parts production has been limited. The properties of ADI can be tailored by changing the heat treatment schedule. In this research a Ni-Cu-Mo ADI was subjected to heat treatment schedules involving various austenitizing and austempering process times and temperatures. The mechanical (hardness, toughness) and tribological (scuffing) properties were determined and they were related to both the microstructures and the heat treatment procedures. The highest scuffing resistance is obtained in ADI with a feathery ausferrite microstructure. Such a microstructure also produces the highest toughness but hardness values are only at the Grade I or II levels.

Abstract: A method by which properties of a component (18) formed of a ductile iron alloy and having thick sections can be promoted with an austempering process. The method entails casting a ductile iron alloy containing iron, carbon, silicon and alloying constituents. The casting is solidified at a rate that inhibits segregation of the alloying constituents to grain boundaries of the casting, and so that the casting contains graphite nodules having a count of greater than 100 nodules per mm 2 . The casting is then austempered by heating to an austenitization temperature to yield a microstructure having a single-phase matrix of austenite that contains carbon, and then quenching the casting to an austempering temperature. The casting is held at the austempering temperature for a duration sufficient to yield a microstructure whose matrix is mostly ausferrite and essentially free of martensite and pearlite.

Abstract: The needs of material that consumed low of energy during its production and saved energy during its used enhance the use of austempered ductile Iron (ADI), especially when ADI is made as thin wall austempered ductile Iron (TWADI). This research is conducted to see effect of thin wall ductile iron (TWDI) chemical composition to microstructure, UTS, and elongation of TWADI. TWDI plates were produced by vertical casting. The dimension of the plate is 150 × 75 mm with the thickness of 1 mm. Number of plate produced in 1 mould are 5. The difference of the plates lay on its position during the pouring. Chemical composition was checked before the liquid treatment process. All the plates then austempered in fluidized bed furnace with austenisation temperature 960 °C for 30 min and austempered temperature 350 °C for 10 min. This research found that the chemical composition of TWDI did not prevent austempering process to increase the ultimate tensile strength (UTS) and elongation.

Abstract: Effect of cementite precipitation on the extend of bainite transformation in fe-cr-c steel Analytical calculations and experimental measurements of volume fraction of bainitic ferrite and volume of the untransformed austenite indicate that there is a necessity of carbides precipitation. A consequence of the precipitation of cementite during austempering is that the growth of bainitic ferrite can continue to larger extent and that the resulting microstructure is not an ausferrite but it is a mixture of bainitic ferrite, retained austenite and carbides.