Abstract: Low frequency thermal cycling tests were carried out on four types of cast iron (viz., austempered ductile iron, pearlitic ductile iron, compacted/vermicular graphite iron and grey cast iron) at predetermined ranges of thermal cycling temperatures. The specimens were unconstrained.

Abstract: The mechanical properties of transformation induced plasticity (TRIP) steels are strongly affected by the amount of retained austenite and the solute carbon in austenite. In this study, the Rietveld method using neutron diffraction patterns was introduced for determining the weight fraction of retained austenite and the solute carbon content. C–Si–Mn TRIP steels with different austempering temperatures were used. The retained austenite and the carbon content in the austenite of these steel sheets were quantitatively analyzed by neutron diffractions, and their effects on the mechanical properties of the steels were evaluated.

Abstract: Isothermal, successive and up-quenching heat treatments were used to improve the mechanical properties of an AISI 4130 steel. Scanning electron and optical microscopy were used to study the morphology of lower and upper bainite formed by the different heat treatments. Mechanical properties were determined by testing sub-sized tensile and Charpy impact specimens. The results showed that successive austempering improves the mechanical properties compared with continuous cooling and conventional austempering. However, it was shown that the best combination of mechanical properties is achieved when an up-quenching heat treatment is used. The microstructural studies showed that partition of grains by lower bainite is probably the main reason for this improvement.

Abstract: We study gray spherulitic cast iron, its microstructure, hardness ultimate strength in tension, elongation, and impact toughness as functions of the duration of isothermal austenitizing in the bainite region at 350 and 400°C after austenitizing at 900°C. As the temperature of quenching increases from 350 to 400°C, the microstructure of the analyzed cast iron changes from lower to higher bainite and the amount of retained austenite increases (its maximum is attained after 1 h). At the same time, the ultimate strength in tension and hardness decrease, whereas the elongation and fracture toughness increase.

Abstract: In this work, the phases involved in the transformation austenite→ferrite+high-carbon austenite in cast irons were assessed by means of Mossbauer spectroscopy and hardness measurements for samples austempered at five different temperatures between 573 and 673 K with two Mn contents. The C content in the high-carbon austenite was found to have a dependence of t0.40±0.05 on the austempering time t, which evidences that diffusion of carbon has taken place. The kinetic parameter k determined using the Johnson-Mehl-Avrami equation has a maximum of 3.9×10−3 (s−1) at ≈623 K and corroborates that Mn slows the transformation rate.

Abstract: Cast iron with bainitic matrix and globular graphite, so called austempered ductile iron (ADI), allows the substitution of heat-treatable steels. The use of ADI in safety-relevant components requires knowledge of the fracture and fatigue behaviour. Cyclic stress strain behaviour and fatigue life at total strain control and random loading have been investigated at ADI (EN-GJS-1000-5) and pearlitic cast iron (EN-GJS-600-3). In addition fracture mechanic tests at cyclic loading at various stress ratios were carried out.

Abstract: A ductile iron containing 0.6% copper as the main alloying element was austenitized at 850 °C for 120 min and was subsequently austempered for 60 min at austempering temperatures of 270, 330, and 380 °C. The samples were also austempered at 330 °C for austempering times of 30–150 min. The structural parameters for the austempered alloy austenite (Xγ), average carbon content (Cγ), the product XγCγ, and the size of the bainitic ferrite needle (dα) were determined using x-ray diffraction. The effect of austempering temperature and time has been studied with respect to tensile properties such as 0.2% proof stress, ultimate tensile strength (UTS), percentage of elongation, and quality index. These properties have been correlated with the structural parameters of the austempered ductile iron microstructure. Fracture studies have been carried out on the tensile fracture surfaces of the austempered ductile iron (ADI).

Abstract: The machining and heat treatment, employed in the fabrication of ADI parts, produce distortions and residual stresses that can increase the scrap rate. In the present study, dimensional changes, shape distortions and residual stresses due to machining and austempering were determined on internal gears of different chemical compositions, as-cast microstructures and machining-thermal cycle sequences. The influence of chemical composition and as-cast microstructure on dimensional change were found to be in accordance with the predictions obtained by Fuzzy modelling. Shape distortion resulted in an ovalization, whose magnitude depends upon the variation range of the residual stresses due to machining. Whereas residual stresses due to austempering were found to increase when the ovalization increases. The lack of information about the topics here studied, turn these results into a useful contribution to improve the fabrication quality of ADI internal gears. Besides, most of them can be applied to ADI parts in general.

Abstract: An understanding of the kinetics of transformation during austenitization, cooling, and austempering of ductile iron is critical to achieving the desired microstructures and ultimately mechanical properties in austempered ductile iron (ADI). To this end, dilatometry experiments have been carried out to study the austenitization and cooling behavior of an unalloyed ductile iron. When a typical austenitization temperature of 900°C is used, unlike in steels, there is an initial expansion of the specimen, which levels off as the soaking time is increased. This occurs despite the fact that the temperature remains constant. This phenomenon, hitherto unreported, highlights the subtle differences between the austenitization of ductile irons and steels. The initial expansion is attributed to the increase in austenite lattice parameter, arising from the diffusion of carbon from the graphite nodules. The levelling off signals the saturation of austenite with carbon and can therefore be used as an indicator ...

Abstract: Ductile iron specimens of ∼3.5 mass% C and ∼2.8 mass% Si were austempered at 420°C for 0.5 h∼24 h. These upper bainitic austempered ductile iron (ADI) specimens were 90°-eroded by Al 2 O 3 particles of ∼275 μm grit size under the average particle velocity of 73 m.s - 1 to understand phase transformation at the erosion surface. According to the experimental results, the retained austenite content and the carbon content of bainitic ferrite decreases through phase transformation during erosion. After erosion, the retained austenite and the high carbon content bainitic ferrite form s-carbide, another carbide and ferrite. The other austempering carbide of the remaining matrix also transforms into e-carbide in the erosion process.

Abstract: The effect of austenitising temperature on the transformation kinetics of Fe-3.2C-2.68Si-0.07Mn-0.022P-0.003S-0.02Cu0.12Cr-0.8Ni-0.25Mo [mass fractions] ductile iron was investigated. X-ray diffraction and optical microscopy were used to determine the transformation kinetics during the austempering at 350 °C after austenitising at 850 °C, 900 °C and 930 °C for 120 min. The stage I reaction of austempering occurs in two steps, first in eutectic cells and than in the intercellular area. Decreasing the austenitising temperature is shown to increase the driving force for the stage I reaction but to have little effect on the stage II reaction. By lower austenitising temperature the rate of transformation is greater, a more uniform microstructure is obtained, while the austemperability is smaller. These changes shift the processing window for Ni-Mo ductile iron for selected austenitising temperature.

Abstract: A new type of high strength steel containing a significant amount of stable retained austenite was obtained by austempering immediately after intercritical annealing. This sort of low carbon steel only contains alloying elements of silicon and manganese rather than nickel and chromium. Its mechanical properties were enhanced considerably due to strain-induced martensite transformation and transformation-induced plasticity (TRIP) of retained austenite when it was strained at temperatures between Ms and Md, because retained austenite was moderately stabilized due to carbon enrichment by austempering. Austempering was carried out at different temperatures and 400 ℃ was found to be optimal. Tensile strength, total elongation and strength-ductility balance reached the maximum values and the product of tensile strength and total elongation exceeded 30 135 MPa % when the TRIP steel was held at 400 ℃ and strained at 350 ℃.

Abstract: The acicular ferrite in austempered ductile iron(ADI)matrix around graphite was corroded preferentially in wet condition,promoting crack origination and propagation and resulting in the disappearance of ADI fatigue limit.ADI fatigue strength was gradually reduced with increasing the time of test and was reduced by 50% in wet condition at 107 cycles compared with the fatigue limit in dry condition.The fatigue strength variation of ferritic ductile iron in wet condition was similar to that of ADI.The ferritic ductile iron,however,has better corrosion resistance so that the fatigue strength was lowered only by 10% in wet condition at 107 cycles compared with the fatigue limit in dry condition.On the other hand,the fatigue limits of A DI and ferritic ductile iron were dropped by 32% and 25% in tap water dipping 480h/dry condition respectively compared with those in dry condition.The reduction of fatigue limit was attributed to corrosion pits formation correlated with stress concentration,resulting in origination and propagation of fatigue crack.

Abstract: Thanks to its good comprehensive mechanical properties, Austempered Ductile Iron (ADI) has found a wide application in advanced countries. The techniques of austempering and the factors of affect properties of ADI were introduced. And then, based on the reality of our country, the paper gives a brief study on the prospect of ADI in China.

Abstract: The present study examined the effects of heat treatment and the addition of Cu-Ni alloy on the corrosion resistance of the matrix of spheroidal graphite cast iron in aqueous environments. Test materials of white cast iron and carbon steel were used for comparison with spheroidal graphite cast iron. The alloy spheroidal graphite cast iron that added Cu and Ni was prepared. The spheroidal graphite cast iron was subjected to three kinds of heat treatment to adjust the matrix: annealing, oil quenching, and austemper heat treatment. In electrochemical tests, measurements of corrosion electrode potential and cathode and anode polarization were used. The following was clarified from the relationship between the electrode potential and current density of each of the materials in each of the solution. The alloy spheroidal graphite cast iron had a high corrosion electrode potential owing to the addition of Cu-Ni, and tended to have a low corrosion current density. This demonstrates that in any of the materials having a matrix adjusted by heat treatment, the addition of Cu-Ni increased the corrosion resistance. The corrosion current density was highest in a sulfuric acid environment.

Abstract: Austempered ductile iron is a newly developed engineering material with a favorable combination of comprehensive mechanical properties Its properties, such as good comprehensive mechanical properties ,high fatigue strength, good fiction and wear characteristics are included The application of ADI at home and abroad was presented as well