Abstract: Austempered irons and steels offer the design engineer alternatives to conventional material/process combinations. Depending on the material and the application, Austempering may provide the following benefits to producers of powertrain components such as gears and shafts: ease of manufacturing, increased bending and/or contact fatigue strength, better wear resistance and enhanced dampening characteristics resulting in lower noise. Austempered materials have been used to improve the performance of powertrain components in numerous applications for a wide range of industries, from gears and shafts to clutch plates and crankshafts. This paper focuses on Austempered solutions for powertrain applications with an emphasis on gear and shaft solutions.

Abstract: The excellent property combination of ADI has opened new horizons for cast iron to replace steel castings and forgings in many engineering applications with considerable cost benefits. Thanks to the extensive research efforts made over the past few years, new processing techniques have opened even more opportunities for this very prospective material to acquire better combinations of strength, ductility, toughness, wear resistance as well as machinability. This review analyses the key features of those novel processing techniques and the resulted new applications of ADI. The survey firstly discusses the possible strengthening mechanism of ADI with special emphasis on the TRIP phenomena, associated with the deformation of ADI. Strength and toughness properties could be improved through the development of: Ausformed ADI; where mechanical processing component was added to the conventional heat treatment as a driving force to accelerate the rate of stage I austempering. Squeeze cast ADI; where superior quality ADI castings were produced through squeeze casting of molten iron in a permanent mold, followed by in‐situ heat treatment of the hot knocked‐out castings in the austenite range followed by normal austempering in a salt bath. Two step austempering to achieve finer ausferrite at higher undercooling during austempering treatment followed by austempering at higher temperature where higher austenitic carbon is promoted. The machinability and ductility of ADI may be considerably enhanced through the development of dual phase microstructures (ferrite+ausferrite or ferrite‐martensite by partial austenitization in the (α+γ+graphite) region followed by normal austempering. The abrasion resistance could be remarkably increased through the development of: Carbidic ADI‐ductile iron containing carbides subsequently austempered to form ausferritic matrix with an engineered amounts of carbides Bainitic/martensitic (B/M) ADI containing less expensive alloying elements such as Si and Mn in the range of 2.5‐3.0% This report discusses as well the recent trials to produce thin‐wall ADI castings.

Abstract: Novel nanostructured high carbon high silicon, carbide-free bainitic steels with very high strength and good ductility have been developed in the recent decade. In this work, an alloy with a high carbon content and no manganese was designed and cast. The prepared samples were heat treated through an austempering process in the range 200–350 °C. Optical and scanning electron microscopes and XRD were used to analyze the microstructures precisely. Bainitic ferrite plates of just a few tens of nanometer thickness were obtained with the hardness of 697±6 HV. It is reasonable to say that the unprecedented hardness values obtained in this work are mostly caused by the extraordinary carbon content of the alloy.

Abstract: Nanostructured bainite was prepared in medium-carbon Si–Al-rich alloy steel by low-temperature austempering of deformation-strengthened supercooled austenite. The deformation strengthening of supercooled austenite can depress the martensite start temperature, allowing austempering at a lower temperature to form nanostructured bainite with high hardness.

Abstract: The effect of reheat temperature on continuous cooling bainite transformation in a low carbon microalloyed steel was investigated using a dilatometer based on welding thermal simulation process. The variation of microstructure was analyzed in detail by means of optical microscope and transmission electron microscope (TEM). The results showed that the morphology of the main microstructure changes from polygonal ferrite to granular bainite with increasing reheat temperature at a given lower cooling rate. For the higher cooling rate, the microstructure is predominantly lath bainite irrespective of the reheat temperature. The specimens with the relatively fine austenite grain size have the lowest bainite start and finish temperatures among the simulated sub-zones of heat affected zone, which is consistent with the result of the bainite lath width size observed using the TEM. Meanwhile, although the prevailing type of impingement mode of transformation is anisotropic growth impingement for all heat treatment processes, the reheat temperature has some influence on the maximum transformation rate and effective activation energy of bainite transformation.

Abstract: In the present study the fatigue strength of austempered ductile irons with dual matrix structures (ADI with DMS) has been studied for an unalloyed ductile cast iron. For this purpose, specimens were intercritically austenitized (partially austenitized) in two phase region (α + γ ) at various temperatures (810°C, 820°C and 830°C) for 20 minutes and then quenched into salt bath held at austempering temperature of 315°C and 375°C for 120 minutes and then air cooled to room temperature to obtain various ausferrite volume fractions and their morphologies. Conventionally austempered specimens (austempered from 900°C) with fully ausferritic matrix and unalloyed as cast specimens having ferrit + pearlite structures were also tested for a comparison. Rotating bending fatigue test were carried out an the experimental results showed that, in ADI with DMS, volume fraction of ausferrite and continuity of ausferritic structure along intercellular boundaries play important role in determining fatigue strength. The fatigue strength of these specimens increases with increasing ausferrite volume fraction. The fatigue strength was correlated with the ausferrite volume fraction and high carbon austenite and its carbon content. Conventionally austempered specimens exhibited much greater fatigue strength than ADI with DMS specimens.

Abstract: The research described in this article is a fragment in the series of published works trying to determine the applicability of new materials for parts of the mining machinery. Tests were carried out on the – very popular in mining applications – 36HMN steel and three types of the austempered ductile iron, using special stand for the controlled abrasion testing of samples subjected to the effect of loose abrasive. Tests carried out with the use of corundum showed the competitive properties of cast iron as compared with the examined steel. Microscopic evaluation, hardness measurements and magnetic tests showed that the surface layer of austempered ductile iron undergoes a strong work hardening, resulting in abrasion wear indices superior to those of the steel for heavy-duty use.

Abstract: The mechanical properties of steel decide its applicability for a particular condition. Heat treatment processes are commonly used to enhance the required properties of steel. The present work aims at experimentally investigating the effect of austempering and martempering on AISI 52100 steel. Different tests like microstructure analysis, hardness test, impact test, and wear test are carried out after heat treatment process. It was found that annealed steel was least hard and more wear prone, while martempered steel was hardest and least vulnerable to wear. Austempered steel had the highest impact strength and it is increased with soaking time up to certain level. Least wear rate is observed in martempered sample both in abrasion and dry sliding. However, least friction coefficient is shown by annealed samples.

Abstract: microstructure of the metal matrix of the cast iron was obtained without any thermal treatment (unwrought) by a suitable composition of alloy additives. It was shown that by adding molybdenum, chromium, nickel and copper it is possible to obtain in the cast iron metal matrix consisting of upper bainite, its mixture with lower bainite or ausferrite in the casts with the wall thickness of 3 25 mm. The process of cast iron crystallization is presented and described with the help of the thermal and derivative analysis (TDA) curves. It also shows the thermal eects

Abstract: In this paper, the fatigue behaviour of some ductile irons for structural applications is analysed in terms of strain–life, stress–life and cyclic stress–strain curves. Push–pull, strain-controlled fatigue tests were carried out on ferritic, pearlitic, isothermed and austempered ductile irons. The same tests were executed on a structural steel for comparison purposes. The experimental data were processed according to the common practice as well as to a recent procedure proposed by the authors, which ensures the compatibility conditions are satisfied in a strict sense. Conversely, if the common practice is applied, compatibility conditions are satisfied only approximately. Finally, the results of the experimental fatigue tests on the different materials are compared and discussed in view of application to structural components.

Abstract: Peculiarities of the bainite structure formed in low-carbon steel 07G2NDMBT during isothermal austenite decomposition, namely, the sizes of crystallites, their mutual orientation, and the presence of cementite precipitates, are considered The temperature range of the formation of bainite with the subgrain structure was determined The size of the austenite grain and degree of hot deformation were found to affect the transformation of bainite that occurs upon subsequent cooling and the submicrocrystalline bainite structure We studied the structure and mechanical properties of a rolled sheet 16 mm thick, which was subjected to thermomechanical treatment (TMT) under plant conditions in accordance with optimum regimes It was shown that the high structure dispersion of the steel subjected to TMT is due to not only the formation of bainite with the subgrain structure, but also the partial transfer of crystal-structure defects from hot-rolled austenite to the final bainite structure

Abstract: An investigation was carried out to examine the influence of structural and mechanical properties on wear behavior of austempered ductile iron (ADI). Ductile iron (DI) samples were austenitized at 900 °C for 60 min and subsequently austempered for 60 min at three temperatures: 270, 330, and 380 °C. Microstructures of the as-cast DI and ADIs were characterized using optical and scanning microscopy, respectively. The structural parameters, volume fraction of austenite, carbon content of austenite, and ferrite particle size were determined using x-ray diffraction technique. Mechanical properties including Vicker’s hardness, 0.2% proof strength, ultimate tensile strength, ductility, and strain hardening coefficient were determined. Wear tests were carried out under dry sliding conditions using pin-on-disk machine with a linear speed of 2.4 m/s. Normal load and sliding distance were 45 N and 1.7 × 104 m, respectively. ADI developed at higher austempering temperature has large amounts of austenite, which contribute toward improvement in the wear resistance through stress-induced martensitic transformation, and strain hardening of austenite. Wear rate was found to depend on 0.2% proof strength, ductility, austenite content, and its carbon content. Study of worn surfaces and nature of wear debris revealed that the fine ausferrite structure in ADIs undergoes oxidational wear, but the coarse ausferrite structure undergoes adhesion, delamination, and mild abrasion too.

Abstract: Among industrial alloys, cast irons have the most variable characteristics with the lowest price; of these groups, ADIs have been attracted in industry because of their favorite properties to be replaced by forged steels. One of these properties is their desirable wear behavior. The predominant wear mechanism in ADIs is delamination of spherical graphites to oval ones, crack propagation from stress concentration centers and producing larger cavities by pulling off graphites due to plastic deformation. There are different methods for improvement wear resistance in these materials such as; reducing austempering temperature, increasing hardness of surfaces in contact, increasing the fineness of ausferritic matrix, work hardening of ferrite phase, increasing the amount of high-carbon retained austenite at ambient temperature. Another way for reaching this purpose is the production of carbidic austempered ductile irons (CADI) with implementation of carbidizing alloying elements and or by chills. KEYWORD: Austempered Ductile Iron (ADI), Wear properties, Relative Wear Resistance (RWR), Delamination Mechanism.

Abstract: The invention relates to a heat treatment process of austempered ductile iron grinding balls. For quenching treatment on the austempered ductile iron grinding balls, the heat treatment process comprises the following steps: immediately immersing cast iron grinding balls coming out of a casting production line into isothermal quenching oil and controlling the temperature of the isothermal quenching oil in the range from 70 DEG C to 110 DEG C; and staying in the quenching oil for 3-12 minutes, wherein the surface temperature of the cast iron grinding balls out of oil after isothermal quenching ranges from 200 DEG C to 270 DEG C. For tempering treatment on the austempered ductile iron grinding balls, the heat treatment process comprises the following steps: immediately delivering the cast iron grinding balls out of oil into a tempering furnace, and controlling the temperature of isothermal tempering in the range from 260 DEG C to 320 DEG C and the time of isothermal tempering in the range from 220 minutes to 320 minutes, thereby obtaining the austempered ductile iron grinding balls. The isothermal quenching oil is used as a quenching medium instead of a salt bath, and therefore, salt bath pollution is avoided; the production cost is low, and the obtained austempered ductile iron grinding balls are good in hardness which ranges from 50 HRC to 58 HRC.

Abstract: Recent interest in the development of austempered ductile cast irons has resulted in considerable study of the physical metallurgy and mechanical properties of these high strength, high toughness cast irons. Equally important is the identification of process control and quality assurance factors to achieve the desired properties successfully and consistently. In this study, aspects of austempered ductile iron quality control are reviewed including the production of quality ductile iron that will respond to austempering heat treatments, heat treatment process control variables to achieve the desired properties, and non-destructive techniques for quality assurance. A distinction is made between austempered ductile irons transformed at high temperatures and austempered/bainitic ductile irons transformed at low temperatures. Austempering response is a complex interaction between all heat treatment variables and chemical composition on a macroscopic and microscopic level. Alloying elements are essential to provide sufficient hardenability (or austemperability) for heavy section heat treatment. Austenitizing temperature as well as austempering time and temperature affect the transformation response for a given alloy. In addition, segregation causes a non-uniform transformation response within the material on a microscopic level. In many cases the final properties of austempered ductile iron can be directly related to the amount of stabilized (retained) austenite present in the final structure. Non-destructive techniques to measure stabilized austenite are discussed and evaluated. Problems associated with dimensional control for critical tolerance components are highlighted.

Abstract: In the present work, austempering is carried out for three different grades (Unalloyed, copper alloyed and Nickel alloyed) of ductile iron. After that the variation of mechanical properties (Hardness, Tensile strength and Elongation) and microstructure of the austempered ductile iron (ADI) with alloying elements (Copper and Nickel) and austempering process variables (austempering temperature and austempering time) were studied. It is found that, with increasing austempering time hardness, tensile strength and elongation are increasing but with increasing austempering temperature hardness and tensile strength are decreasing and elongation increasing. Austempered ductile iron with alloying element (Cu or Ni) is showing some improved mechanical properties such that: higher strength, hardness and lower elongation, than the unalloyed austempered ductile iron. In Microstructure, higher ferrite fraction is observed for higher austempering time and higher austenite fraction is observed for higher austempering temperature, for all the three grades of austempered ductile iron.

Abstract: The use of austempered ductile iron obtained by heat treating spheroidal-graphite cast iron is very important in the gear industry. However the nature of the bainitic structure, which is used to improve wear resistance, has never been fully identified. The aims of this study were: - to optimize the upper bainitic structures in S. G. cast irons (usually called austempered ductile iron or A. D. I.) to have the best abrasive wear resistance at room temperature. - to study the influence of the solidification cell characteristics upon these optimized structures. - to determine the evolution of the microstructures during the abrasion test. Results clearly indicate the primordial influence of the retained austenitic phase. A high percentage of retained austenite promotes a high abrasive wear resistance. The analysis of the results shows that this austenitic phase is heterogeneous. The best abrasive wear resistance is associated with the lowest hardness value. During abrasion, austenite at or near the surface is gradually and partly transformed to martensite.

Abstract: This research is focused on using nitriding to enhance the wear resistance of austempered ductile iron (ADI), ductile iron (DI), and gray iron (GI). Three gas nitriding processes, namely “Gas nitriding + nitrogen cooled down to 800 o F” (Blue), “Gas nitriding + cooled down to 300 o F” (Gray), and “Gas nitriding + oil quenched” (Oil) were used. This study was carried out through optical metallography, roughness measurements, microhardness, and SEM. The ball-ondisc wear tests were conducted under lubricated conditions. It was found that COF for all materials in all nitrided conditions was small (<0.045). The best wear performance was seen for ADI processed using the Gray and Oil gas nitriding processes. These processes produced a compound layer thickness of 4– 6μm, a low surface roughness (0.8–1.3 μm, Ra) and a high surface microhardness (1800–2200 HV). The wear rate decreased with increasing surface microhardness and decreasing surface roughness.

Abstract: The invention relates to a carbide-carrying austempered ductile iron and a quenching technology thereof. Cr and B are added to an Mn-Si alloy, the carbide amount is properly increased, and inoculating deterioration treatment is carried out by using RE-B, so the carbide becomes a fine uniformly-distributed agglomerate to improve the hardness, the abrasion resistance, the hardenability and the toughness; and the addition of Sn and the increase of the Si amount are carried out to improve the potential of a matrix electrode, and the added Sn and the increased Si form a surface passivating film together with Cr to improve the corrosion resistance. The quenching technology of the carbide-carrying austempered ductile iron is step austempering and is characterized in that an austempered workpiece undergoes first-step austempering by using grading quenching oil to avoid the generation of pearlite, and then second-step austempering is carried out at a proper temperature in an air isothermal furnace to obtain a proper amount of fine lower bainite, increase the amount of tempered martensite, and improve the hardness and the abrasion resistance, so the carbide-carrying austempered ductile iron having the advantages of high strength and hardness, appropriate toughness, strong abrasion and corrosion resistances, good processing properties, easy precision guarantee and low cost is obtained.