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Austempering

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Susil K Putatunda – 1st expert on this subject based on the ideXlab platform

  • INFLUENCE OF STEP-DOWN Austempering PROCESS ON THE FRACTURE TOUGHNESS OF AUSTEMPERED DUCTILE IRON
    , 2020
    Co-Authors: Susil K Putatunda, Gowtham A. Bingi

    Abstract:

    Austempered ductile cast iron (ADI) has emerged as a major engineering material in recent years because of its many attractive properties. In this investigation, the influence of a step-down Austempering process on the microstructure and mechanical properties including fracture toughness of an unalloyed ductile cast iron was examined. Compact tension and cylindrical tensile specimens were prepared from unalloyed nodular cast iron as per ASTM standards and were subjected to conventional as well as step-down Austempering process at three different Austempering temperatures. The microstructure and mechanical properties of these samples were evaluated and compared. Test results show that both the step-down and conventional Austempering process resulted in very similar microstructure and mechanical properties in unalloyed ADI. The fracture toughness of the material was found to be influenced by both ferritic cell size (d) and the austenitic carbon ( ). . γ

  • influence of intercritical Austempering on the microstructure and mechanical properties of austempered ductile cast iron adi
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2017
    Co-Authors: Saranya Panneerselvam, Susil K Putatunda, Richard Gundlach, James Boileau

    Abstract:

    Abstract The focus of this investigation was to examine the influence of intercritical Austempering process on the microstructure and mechanical properties of low-alloyed austempered ductile cast iron (ADI). The investigation also examined the influence of intercritical Austempering process on the plane strain fracture toughness of the material. The effect of both austenitization and Austempering temperature on the microstructure and mechanical properties was examined. The microstructural analysis was carried out using optical microscopy, scanning electron microscopy and X-ray diffraction. The test results indicate that by intercritical Austempering it is possible to produce proeutectoid ferrite in the matrix microstructure. Lower austenitizing temperature produces more proeutectoid ferrite in the matrix. Furthermore, the yield, tensile strength and the fracture toughness of the ADI decreases with decrease in austenitizing temperature. A considerable increase in ductility was observed in the samples with higher proeutectoid ferrite content. The fracture surfaces of the ADI samples revealed that dimple ductile fracture produced higher fracture toughness of 60±5 MPa√m in this intercritically austempered ADI.

  • influence of Austempering temperature on the mechanical properties of a low carbon low alloy steel
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2011
    Co-Authors: Susil K Putatunda, Codrick J Martis, James Boileau

    Abstract:

    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.

R Elliott – 2nd expert on this subject based on the ideXlab platform

  • influence of molybdenum on Austempering behaviour of ductile iron part 1 Austempering kinetics and mechanical properties of ductile iron containing 0 13 mo
    Materials Science and Technology, 1999
    Co-Authors: S. Yazdani, R Elliott

    Abstract:

    AbstractMeasurements of the Austempering kinetics and mechanical properties are presented for a ductile iron of composition Fe–3·51C– 2·81Si–0·25Mn–0·39Cu–0·13Mo–0·04Mg (wt-%) for Austempering temperatures of 285, 320, 375, and 400°C after austenitising at 870°C for 120 min. The kinetic studies show that the alloying level is insufficient to cause a significant delay in ausferrite formation in the intercellular boundaries. This implies that the heat treatment processing window is open for all Austempering conditions studied. The mechanical property measurements show that with the correct selection of Austempering temperature all the grades of the ASTM Standard 897M : 1990 and BS EN 1564 : 1997 can be satisfied. The hardenability of the present iron is limited and it is therefore unlikely that these standards will be achieved in thicker section components.

  • use of austenitising temperature in control of Austempering of an mn mo cu alloyed ductile iron
    Materials Science and Technology, 1997
    Co-Authors: R Kazerooni, A Nazarboland, R Elliott

    Abstract:

    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.

  • The Austempering kinetics and mechanical properties of an austempered Cu–Ni–Mo–Mn alloyed ductile iron
    Journal of Materials Science, 1997
    Co-Authors: M Bahmani, R Elliott, N Varahram

    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.

Jianghuai Yang – 3rd expert on this subject based on the ideXlab platform

  • effect of microstructure on abrasion wear behavior of austempered ductile cast iron adi processed by a novel two step Austempering process
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2005
    Co-Authors: Jianghuai Yang, Susil K Putatunda

    Abstract:

    Abstract An investigation was carried out to examine the influence of a novel two-step Austempering process on microstructural parameters and the abrasion wear resistance of austempered ductile cast iron (ADI). Two batches of cylindrical pin specimens were prepared from an alloyed nodular ductile cast iron and were initially austenitized at 927 °C (1700 °F) for 2 h. The first batch of samples was austempered by the conventional single-step Austempering process at five different temperatures, e.g., 288 °C (550 °F), 316 °C (600 °F), 343 °C (650 °F), 371 °C (700 °F), and 385 °C (725 °F) for 2 h, whereas the second batch of samples were processed by the two-step Austempering process. These samples were initially quenched in a salt bath maintained at 260 °C (500 °F) and then the temperature of the salt bath was raised to interfacial Austempering temperatures316 °C, 343 °C, 371 °C and 385 °C. These samples were austempered at these temperatures for 2 h. The test results show that this two-step Austempering process has resulted in significant improvement in microstructural parameters (such as higher volume fraction of austenite, X γ , higher carbon content in austenite, C γ , finer ferritic cell size, d , as well as higher total carbon in the matrix, X γ C γ ). Two-step process has also resulted in significant improvement in abrasion wear resistance in ADI, compared to the conventional single-step Austempering process.

  • near threshold fatigue crack growth behavior of austempered ductile cast iron adi processed by a novel two step Austempering process
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2005
    Co-Authors: Jianghuai Yang, Susil K Putatunda

    Abstract:

    Abstract The influence of a novel two-step Austempering process on the microstructure and the near threshold fatigue crack growth behavior of austempered ductile cast iron (ADI) were investigated. Cylindrical tensile and compact tension (CT) specimens (for fatigue threshold tests) were prepared from an alloyed nodular ductile cast iron as per ASTM standards and were austempered by both the conventional single-step and the novel two-step Austempering processes at four different temperatures. The near threshold fatigue crack growth behavior of these samples was examined in room temperature and ambient atmosphere. Tests results indicate this two-step Austempering process has resulted in higher hardness, higher yield and tensile strengths for ADI but higher near threshold fatigue crack growth rate and lower fatigue threshold, as compared to the conventional single-step Austempering process. Results also demonstrate that fatigue crack growth behavior of ADI in the near threshold region is influenced by microstructural parameters, such as volume fraction of austenite ( X γ ), carbon content in austenite ( C γ ), ferritic cell size ( d ) as well as total austenitic carbon, X γ C γ . SEM fractographs in all samples exhibit a combination of mechanisms, i.e. ductile striation with quasi-cleavage facet around graphite nodules.

  • influence of a novel two step Austempering process on the strain hardening behavior of austempered ductile cast iron adi
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2004
    Co-Authors: Jianghuai Yang, Susil K Putatunda

    Abstract:

    Abstract An investigation was carried out to examine the influence of a novel two-step Austempering process on the strain-hardening behavior of austempered ductile cast iron (ADI). Strain-hardening exponent ( n value) of specimens austempered by conventional single-step Austempering process as well as the novel two-step process were determined over the entire plastic deformation regions of the stress–strain curves. Optical microscopy and X-ray diffraction analysis were performed to examine mechanisms of strain-hardening behavior in ADI under monotonic (tensile) loading. Test results show that this novel two-step process has resulted in improved microstructural variables in the ADI matrix, and higher hardness, yield strength and tensile strengths, but lower ductility and strain-hardening exponent values compared to the conventional single-step Austempering process. Test results also indicate that strain-hardening exponent of ADI is a function of amount and morphology of microstructural constituents and interaction intensities between carbon atoms and dislocations in the matrix.