Abstract: An investigation was carried out to examine the influence of microstructure on the plane strain fracture toughness of austempered ductile iron. Austempered ductile iron (ADI) alloyed with nickel, copper, and molybdenum was austenitized and subsequently austempered over a range of temperatures to produce different microstructures. The microstructures were characterized through optical microscopy and X-ray diffraction. Plane strain fracture toughness of all these materials was determined and was correlated with the microstructure. The results of the present investigation indicate that the lower bainitic microstructure results in higher fracture toughness than upper bainitic microstructure. Both volume fraction of retained austenite and its carbon content influence the fracture toughness. The retained austenite content of 25 vol pct was found to provide the optimum fracture toughness. It was further concluded that the carbon content of the retained austenite should be as high as possible to improve fracture toughness.

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

Abstract: Rotating bending fatigue measurements are reported for an austempered ductile iron containing 35 wt% C, 26 wt% Si, 048 wt% Cu, 096 wt% Ni, 027 wt% Mo, and 025 wt% Mn The iron was austenitized at 870, 900 and 950°C and then austempered at 370 and 400°C for times between 30 and 240 min to obtain various austempered microstructures The correlation between fatigue strength and austempered microstructure represented by the parameter XγCγ, where Xγ is the amount of high C austenite and Cγ its C content is examined It is shown that fatigue strength increases as XγCγ increases The highest fatigue strength is obtained with an ausferrite structure; the presence of martensite and/or carbide in the structure reduces the fatigue strength Lower austenitizing temperatures increase the fatigue strength

Abstract: Measurements of austempering kinetics and mechanical properties are presented as a function of austempering time over the range 1–4320 min for different combinations of austempering temperature (275, 315, 370 and 400 °C) and austenitizing temperature (870, 900 and 950 °C) for a ductile iron of composition 3.5% C, 2.6% Si, 0.48% Cu, 0.96% Ni, 0.27% Mo and 0.25% Mn. The austempering kinetics are used to calculate processing windows for the three austenitizing temperatures. The mechanical properties are analysed to show that the processing windows accurately predict the austempering times over which the mechanical properties satisfy the ASTM standard. The analysis shows the role of austenitizing temperature, austempering temperature and time in optimizing the mechanical properties.

Abstract: This study investigates the effect of austenitising temperature (850°C, 900°C, 950°C) and austempering time (0 to 7 h) on the impact energy values of three irons containing increasing silicon contents (2.02%, 2.65%, 3.31%) and around 0.3% manganese, austempered at 360°C. It was shown that increasing the silicon content modifies the Fe-C phase diagram such that (a) a higher solution treatment temperature is required to fully austenitise the iron, and (b) the resulting austenite dissolves less carbon. Increasing the austenitising temperature simultaneously with the silicon content restores a high carbon austenite, a fully ausferritic structure and high impact properties. On the other hand, the low silicon iron austenitised at 950°C results in a microstructure containing a continuous network of intercellular austenite. This is attributed to the manganese whose segregation is more evident in the iron containing 2.02% silicon. For a given silicon content, increasing the austenitising temperature increa...

Abstract: The mass-production considerations in replacing forged and induction-hardened steel crankshafts with ADI are described for a four-cylinder 120 h.p. petrol engine and a single-cylinder diesel engine...

Abstract: The relationship between low-cycle fatigue (LCF) strength of austempered ductile iron (ADI) and cast section size and location was investigated. Uniaxial LCF tests under strain-control were conducted on a number of different grades of ADIs. These ADIs were selected from four positions in Y-block castings with three section sizes (25, 50, and 100 mm in thickness). LCF specimens were cut from specific locations within the castings, austenitized at 1173 K, and then austempered at 573 and 633 K, respectively. Results indicated that LCF strength of ADI degraded with increasing section size due to deteriorated graphite nodule morphology and presence of more microshrinkage pores as a result of the slower solidification rate. The effects of section size, location within the heavy-section casting, and austempering temperatures on the LCF strength of ADI are discussed in terms of the graphite nodule morphology and microshrinkage pores. Fractography with scanning electron microscopy (SEM) was applied to determine the LCF failure mechanisms and fatigue crack propagation modes.

Abstract: Much interest has been focused on austempered ductile iron (ADI) because of its superior mechanical properties, which might be improved by further control of microstructure. It has so far been assumed that segregation of alloying elements in the intercellular region just delays bainitic reaction in these regions. However, the existence of bainite-free regions (UAV) even after 10,000 minutes at test temperature, e.g., 375 C, indicates something intrinsic to the mechanism of bainitic transformation. The bainitic transformation start (B{sub s}) temperature is a function of alloying elements; segregation of alloying elements can also alter the B{sub s} temperature. In other words, B{sub s} temperature in the region near graphite should be different from the intercellular region. Therefore, the intercellular region with higher concentration of alloying elements such as Mn should have a lower B{sub s} temperature, which leads to formation of UAV even after a long high-temperature austempering time (hereafter, this stable UAV will be named as the minimum UAV value). To examine this concept, theoretical and experimental procedures were employed.

Abstract: Measurements of ultimate tensile strength, 0.2% proof strength, elongation, unnotched Charpy impact energy, and austempering kinetics are presented as a function of austempering time over the range 1–4320 min and for an austempering temperature of 375°C after austenitising at 950, 920, 870, 840, and 800°C for a ductile iron of composition Fe-3.39C-2.56Si-0.37Mn-0.25 Mo-0.29Cu-0.04Mg. These measurements are analysed to relate microstructure and mechanical properties, and to define processing windows for the different austenitising temperatures. It is shown that decreasing the austenitising temperature accelerates the stage I reaction and can be used to open a processing window that is closed at a higher austenitising temperature. The introduction of ferrite into the austempered structure, through control of the austenitising temperature, can be used to influence the mechanical properties of the austempered iron. Decreasing the austenitising temperature reduces the iron hardenability.

Abstract: Measurements of ultimate tensile strength, 0.2% proof strength, elongation and unnotched Charpy impact energy are presented as a function of austempering time in the range from 1 to 4320 minutes for austempering temperatures of 400, 375 and 285 °C and austenitising temperatures of 870, 920 and 950 °C for a ductile iron of composition 3.39%C, 2.56% Si, 0.25% Mo, 0.29% Cu, 0.37% Mn and 0.04% Mg. Austempering kinetic measurements are presented for the various austenitising and austempering temperatures. These measurements are analysed to relate microstructure and mechanical properties and to define processing windows for the different austempering conditions. The analysis suggests a new definition for the closure time of the processing window. The newly defined processing windows are consistent with mechanical property observations in the present iron and a previously studied iron with the same base composition but containing 0.67% Mn.

Abstract: Measurements of ultimate tensile strength, 0.2% proof strength, elongation, and impact energy are presented as afunction of austempering time in the range 1 to 4320 minfor austempering temperatures of 350, 375 and 400°C and austenitising temperatures of 870 and 920°C in a ductile iron of composition Fe-3.49C-2.33Si-0.42Mn-0.25Cu-0.23Mo-O.035Mg. With an austenitising temperature of 920°C, the mechanical properties satisfy the ASTM A897M: 1990 austempered ductile iron (ADI) standard at an austempering temperature of 350°C but not at 375 and 400°C. This is consistent with the predictions from the austempering kinetic measurements of an open processing window at 350°C and a closed window at 375 and 400°C. The mechanical properties measured with an austenitising temperature of 870°C satisfy the standard at 350 and 375°C but not at 400°C. This is consistent with the predictions from austempering kinetic measurements of an open window at 350 and 375°C and a closed window at 400°C. Decreasing the austenit...

Abstract: Measurements of the solute distribution between nodules and of the tensile properties at two different levels in a 25 mm keel block of a ductile iron of composition 3.39%C, 2.56%Si, 0.25%Mo, 0.29%C...

Abstract: At the present time the structure of granular bainite is widely used in heat treatment. The novel technologies include spheroidizing treatment of rolled stock from steel 20Kh2NACh. The composition of the steel provides a structure of granular bainite in rolled strips up to 10 mm wide with their cooling in still air from the temperature attained at the end of hot rolling. After a high-temperature tempering of the strips for 4 h the granular bainite transforms into granular pearlite which is optimum for cold forging. The available published data on the structure of granular bainite are insufficient for explaining the causes of the accelerated transformation. In this connection, it is interesting to investigate the phase composition, the microstructure, and the transformation mechanism of granular bainite.

Abstract: Measurements of the austempering kinetics and mechanical properties of an alloy ductile iron after single and stepped austempering treatments following austenitising at 920°C are presented. The kinetic and tensile data are analysed to show how the thermal and mechanical stability of the austenite phase vary with austempering treatment. Both the thermal and mechanical instability of the austenite phase are shown to limit the ductility achieved in single austempering treatments at 375 and 400°C to such an extent that the Charpy impact energy fails to satisfy the ASTM standard A897M: 1990. Stepped austempering treatment improves both the thermal and mechanical stability of the austenite phase and increases the impact energy to such an extent that the ASTM standard is satisfied over a wide range of austempering conditions. A well defined relationship is shown to exist between impact energy and the austenite carbon content for different austempering treatments after austenitising at 920°C.

Abstract: Measurements of the retained austenite content, average austenite C content, UTS, 0.2% proof strength, elongation, and unnotched Charpy impact energy are reported for the stepped austempering treatment (870°C for 120 min; 375°C for 120 min; 285°C)as a function of austempering time at 285°C for a ductile iron of composition Fe–3.5 C–2.64Si–0.67n–0.007P–0.013S–0.25Mo–0.25Cu–0.04Mg (wt-%). These measurements are compared with previous measurements for single and stepped austempering treatments. The comparison shows that stepped austempering treatments can be used to improve elongation and impact energy obtained in single treatments in the high Mn ductile iron. Control over the austenitising and first step austempering temperatures can be used to change the relative improvements in elongation and impact energy. The austempering time required to achieve these improvements is much longer than that used in a single step treatment.

Abstract: Austempered ductile cast iron (ADI) has emerged as a major engineering material in recent years. In addition to high strength and relatively light weight (compared to steel), it has high ductility, good wear resistance and good damping capacity. It has many potential applications such as automotive components (e.g. crank shafts and gear boxes) as well as aircraft components (landing gears). In many structural applications, (e.g. aircraft landing gear) it is often required that the material be hardened at the surface while the interior of the material must remain soft or ductile. The higher hardness at the surface layer imparts excellent wear resistance while the soft inner core provides higher toughness and fracture resistance. The conventional methods of surface hardening such as carburizing and nitriding or shot peening have several limitations, e.g. retained austenite, massive carbide formations and insufficient case depth. In recent years, there has been significant interest in use of laser i...

Abstract: Manganese is known as an inexpensive element and a potent promoter of hardenabilty in ductile iron but it also segregates severely and encourages the formation of carbides in the matrix. Thus, it is suggested that when the Mn content is high, attempts should be made to minimise the Mn segregation. In the present work the effect of solidification rate and homogenisation treatment on the severity of segregation of Mn and Si in several types of wear resistant high Mn ductile iron was investigated. It is demonstrated that increasing the solidification rate, leading to a high nodule count, decreases not only the heterogeneity of these elements but also the carbide content.

Abstract: A method of manufacturing a plate-type track shoe. The method involves casting or obtaining a cast, plate-type track shoe which has been made from a suitably high quality ductile iron and heating the plate-type track shoe to a desired austentizing temperature within a range of about 1450° F.-1750° F. for up to about six hours to austentize the ductile iron. The plate-type track shoe is then rapidly cooled to a desired austempering temperature within a range of about 450° F.-800° F. and maintained at the desired austempering temperature for up to about 6 hours to isothermally produce a plate-type track shoe having an ausferrite microstructure. The plate-type track shoe is then cooled, washed, and optionally coated with a rust inhibitor and/or coated or painted. The process produces austempered plate-type track shoes which have high strength, excellent durability, and which are less costly to produce, per pound, than comparable parts manufactured from formed steel. Additionally, the cast feature allows surface features and indicia to be incorporated which is not possible with roll formed steel track plates. Most importantly, the process of the present invention enables specific, desired quantities of track shoes to be produced, which would not be possible with parts formed from steel, where an entire heat of rolled steel would have to be purchased and used, thus requiring the manufacture and inventorying of a very large quantity of track shoes.

Abstract: Measurements of the average austenite carbon content, retained austenite content, unreacted austenite content, and mechanical properties are reportedfor various austempering heat treatments of an alloyed ductile iron of composition (wt-%) Fe-3.39C-2.56Si-0.37Mn-0.25Mo-0.29Cu-0.04Mg. It is shown that a stepped austempering treatment can be used to considerably increase the ductility of the alloy compared with a single heat treatment and to extend the austempering time interval over which the ASTM standard can be satisfied. Decreasing the second step austempering temperature accelerates the stage I reaction during the second step treatment but produces little change in the mechanical properties of the alloy used in the present work. Decreasing the first step austempering time to 375°C accelerates the stage I reaction in the second step treatment but slightly decreases the maximum impact energy and increases the austempering time at which it is achieved.

Abstract: PROBLEM TO BE SOLVED: To provide a method and an equipment for solid forming austempering treatment, capable of performing quenching at sufficient cooling velocity without causing distortion even in the case of a relatively thick material to be treated and also capable of securing desired austempering temp. SOLUTION: A material to be treated is heated to a temp. in the austenite region (not lower than the A point). Then, the material to be treated is quenched while holding this material to be treated between forming heat treatment dies having a temp. set at the temp. T1 lower than the desired austempering temp. T2 . Subsequently, the forming heat treatment dies are heated to the austempering temp. T2 and the material to be treated is held at the austempering temp. T2 , and bainitic transformation is allowed to occur.

Abstract: Bainitic reaction kinetics in ductile iron contained according to Ukrainian standard (weight %) 3.60-3.80 carbon, 2.60-2.80 Si, ∼ 0.12 Mn, ∼ 0.60 Cu and additionally alloyed by Mo (0.15-0.20) has been studied. It was found that the overall transformation kinetics becomes slower as transformation temperature increase. This is because more intensive redistribution of carbon into austenite at higher temperatures. Two austenites wlith different carbon content have been fixed and kinetics of their lattices parameters has been studied.

Abstract: PROBLEM TO BE SOLVED: To manufacture a vehicle member at low costs with high productivity by forming the teeth part of a gear or the like or the contacting part of a sliding surface or the like in the outer periphery part of the stock or the inner periphery part of a hole consisting of a ferritic spherical graphite cast iron and applying an austempering treatment to the whole including this contacting part. SOLUTION: A flywheel stock 1 is formed with the spherical graphite cast iron containing C, Si, Mn, P, S Mg, thereafter a heat treatment is applied to make ferritic. Thereafter, required places of the boss part and clutch plate sliding and contacting part or the like of the fly wheel stock 1 are machined and then the gear is plastically formed in a ring-like gear part 5 to make the flywheel. And the austempering treatment is applied to the whole flywheel within a heat treatment furnace. This treatment is executed by heating at 850-920 deg.C for 0.5-2.0 hour, thereafter heating at 370-400 deg.C for 0.5-2.5 hour and cooling by air. After this treatment, shot peening is applied to the ring-like gear part 5 to improve the strength of the dedendum if necessary.

Abstract: Procedures related to the preparation of samples for Mossbauer spectroscopy studies of phase transformations in metals research are discussed in examples of works undertaken by the authors; (i) determination of austempering kinetics of compacted graphite cast irons, (ii) CEMS studies aimed at finding suitable polishing treatments that reproduce the bulk phase proportions, (iii) CEMS investigations on samples polished by spark planing, and (iv) the research of surface processes produced by laser melting treatments.