Scientific papers on cast iron

Micromechanical modelling of constitutive behavior of austempered ductile iron (ADI) at high strain rate

Authors: G. Iannitti, A. Ruggiero, N. Bonora, S. Masaggia, F. Veneri

Università di Cassino e del Lazio Meridionale
Zanardi Fonderie SPA

JOURNAL: Science Direct – Elviser

9th May 2017

n this work, the uniaxial stress-strain response of austenitic ductile iron at high strain rate has been investigated. Traction tests were performed at low (0.001/s) and high rates (740/s and 1200/s) at RT and low temperature. Results showed that the strain rate has a considerable effect on work hardening and ductility. The work hardening seems to be the result of the competition of ferrite and retained austenite behavior under varying combinations of temperature and strain rate. The strain rate was found to increase the material failure strain. Numerical simulations performed with unit cell model indicated that this effect could due to strain localization along inter-spheroids ligaments supported by thermal softening.

Thickness influence on fatigue limit of notched round bars made in as-cast or heat treated ductile iron

Authors: Franco Zanardi, Stefano Masaggia

Zanardi Fonderie SPA

25th November 2020

This work describes the use of a fatigue design procedure in the presence of notch effect, which represents an unconventional extension of Linear Elastic Fracture Mechanics to the U and V notches of whatever opening angle, dimensions and notch tip radius.

Mechanical performance of Nodular Cast Irons after prolonged high-temperature exposure

Authors: Alessandro Morri, Lorella Ceschini, Stefania Toschi, Stefano Masaggia

  • Department of Industrial Engineering, University of Bologna
  • Department of Civil, Chemical, Environmental, and Material Engineering, University of Bologna
  • Zanardi Fonderie S.p.A.

JOURNAL: Journal of materials engineering and performance

4th March 2019

Ductile cast irons (DI) are widely used in industrial applications. Their use is however often limited to components working at room temperature, since prolonged exposure at high temperature can lead to decomposition of both ausferrite and perlite, with a consequent strength reduction. The present paper evaluated the effects of prolonged high temperature exposure on microstructure and residual strength of DI with different matrix, after an isothermal soaking at temperatures between 200 and 600°C. Microstructural analyses highlighted that long-term exposure at temperatures higher than 500°C leads to the complete decomposition of ausferritic and pearlitic matrix microstructures, while hardness tests showed that the hardness is stable up to 500°C for the pearlitic ductile iron, up to 450-500°C for the ausferritic ductile iron and up to 400-450°C for the perferritic ductile iron. Exposure at 500°C for 240 hours induces a reduction of tensile strength of IDI and ADI, respectively of 10 and 25% (for both room and 500°C tensile testing), while has no significant effects on PDI.

Comparison of the low-cycle and medium-cycle fatigue behaviour of ferritic, pearlitic, isothermed and austempered ductile irons

Authors: G. Meneghetti, M. Ricotta, S. Masaggia, B. Atzori

  • University of Padova Department of Industrial Engineering
  • Zanardi Fonderie S.p.A.

JOURNAL: Fatigue & Fracture of Engineering Materials & Structures – FFEMS

18th March 2013

“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.”

Fatigue strength of austempered ductile iron-to-steel dissimilar arc-welded joints

Authors: G. Meneghetti, A. Campagnolo, D. Berto, E. Pullin, S. Masaggia

  • Department of Industrial Engineering, University of Padova
  • Zanardi Fonderie Spa

JOURNAL: Welding in the World

22nd February 2021

Nowadays, the use of different classes of materials in the same structure is increased to keep pace with innovation and high structural performances. In this context, structural components made of different materials need to be joined together and a possible solution is given by arc welding. Dissimilar welded joints must often be able to withstand fatigue loads; however, Design Standards provide fatigue strength categories only for homogeneous welded joints. The aim of the present paper is to compare the fatigue behaviour of EN-GJS-1050 austempered ductile iron-to-S355J2 steel dissimilar joints to the categories of the corresponding homogeneous steel welded joints, as suggested in International Standards and Recommendations. For this purpose, experimental fatigue tests were performed on a selection of dissimilar welded details. First, the microstructure was identified by metallographic analysis; micro-hardness measurements were collected and residual stress profiles were obtained by using the X-ray diffraction technique on a selection of joints. Misalignments were quantified for all specimens. Then, experimental fatigue tests have been performed on a number of joint geometries subject to axial or bending fatigue loadings and tested in the as-welded conditions. The fracture surfaces of the joints have been analysed to locate fatigue crack nucleation sites.

“The Role of Microstructure on Tensile Plastic Behavior of Ductile Iron GJS 400 Produced through Di erent Cooling Rates, Part I: Microstructure”

Authors: Giuliano Angella, Dario Ripamonti, Marcin Górny, Stefano Masaggia and Franco Zanardi

  • National Research Council of Italy (CNR)
  • Institute of Condensed Matter Chemistry and Technologies for Energy (ICMATE)
  • Faculty of Foundry Engineering, Department of Cast Alloys and Composites -Engineering, AGH University of Science and Technology
  • Zanardi Fonderie S.p.A.

JOURNAL: MDPI

29th November 2019

A series of samples made of ductile iron GJS 400 was cast with different cooling rates, and their microstructural features were investigated. Quantitative metallography analyses compliant with ASTM E2567-16a and ASTM E112-13 standards were performed in order to describe graphite nodules and ferritic grains. The occurrence of pearlite was associated to segregations described through Energy Dispersive X-ray Spectroscopy (EDS) analyses. Results were related to cooling rates, which were simulated through MAGMASOFT software. This microstructural characterization, which provides the basis for the description and modeling of the tensile properties of GJS 400 alloy, subject of a second part of this investigation, highlights that higher cooling rates refines microstructural features, such as graphite nodule count and average ferritic grain size

“The Role of Microstructure on the Tensile Plastic Behaviour of Ductile Iron GJS 400 Produced through Different Cooling Rates—Part II: Tensile Modelling”

Authors: Giuliano Angella, Riccardo Donnini, Dario Ripamonti, Marcin Górny, Franco Zanardi

  • National Research Council of Italy (CNR), Institute of Condensed Matter Chemistry and Technologies for Energy (ICMATE)
  • Faculty of Foundry Engineering, Department of Cast Alloys and Composites -Engineering, AGH University of Science and Technology
  • Zanardi Fonderie S.p.A.

JOURNAL: MDPI

29th November 2019

Tensile testing on ductile iron GJS 400 with different microstructures produced through four different cooling rates was performed in order to investigate the relevance of the microstructure’s parameters on its plastic behaviour. Tensile flow curve modelling was carried out with the Follansbee and Estrin-Kocks-Mecking approach that allowed for an explicit correlation between plastic behaviour and some microstructure parameters. In the model, the ferritic grain size and volume fraction of pearlite and ferrite gathered in the first part of this investigation were used as inputs, while other parameters, like nodule count and interlamellar spacing in pearlite, were neglected. The model matched very well with the experimental flow curves at high strains, while some mismatch was found only at small strains, which was ascribed to the decohesion between the graphite nodules and the ferritic matrix that occurred just after yielding. It can be concluded that the plastic behaviour of GJS 400 depends mainly on the ferritic grain size and pearlitic volume fraction, and other microstructure parameters can be neglected, primarily because of their high nodularity and few defects.

“Contact Fatigue Strength of Austempered Ductile Iron (ADI) in Gear Applications”

Authors: Fabian Goergen, Dieter Mevissen, Stefano Masaggia, Enrico Veneri, Jens Brimmers, Christian Brecher

  • Laboratory for Machine Tools and Production Engineering (WZL) of RWTH Aachen University
  • Zanardi Fonderie S.p.A.

JOPURNAL: MDPI

20th August 2020

Austempered Ductile Iron (ADI) is widely implemented to achieve lightweight and optimized components in power transmissions (e.g., internal gear in planetary stages), by substituting steel castings or a combination of Ductile Iron and steel-assembled structures. In this paper, the contact fatigue of two ADI grades (ADI J/S900-8; ADI J/S1200-3) is investigated by disk-on-disk tests. The disk-on-disk contact is an analogy model of the tooth contact and represents the tribological conditions at a specific point on the path of contact. The experimental results cover the endurance limit as well as the short time fatigue behavior for both ADI variants. In addition, the pitting characteristics and microstructural changes are analyzed in order to get a further understanding of the fatigue behavior of ADI.

Phase transition and microstructure investigation of perferritic isothermed ductile iron (IDI)

Authors: Martin Landesberger, Robert Koos, Maximilian Erber, Matteo Pernumian, Stefano Masaggia, Markus Hoelzel, Wolfram Volk

  • Technische Universität München
  • Zanardi Fonderie S.p.A.

JOURNAL: International Journal of Cast Metals Research

21st October 2020

Optical analysis, dilatometry as well as neutron diffraction are utilised to investigate the phase transition within ductile iron both in-situ and after the heat treatment process for perferritic isothermed ductile iron (IDI). A suitable annealing temperature is chosen by calculating a phase diagram for the investigated alloy. The phase transition which happens slightly above upper intercritical temperature is followed by neutron diffraction, while dilatometry elucidates the IDI microstructure evolution for cooling rates from 40 to 0.125 K/s. The dilatometry results are visualised in a CCT diagram and further investigated with metallography. An additionally used colour etching method is basis for discussing the formation of the pearlitic/ferritic network. The presence of 2 vol.-% of ferrite was sufficient to achieve the typical IDI microstructure. Finally, the cementite phase volume fractions and crystal structure are evaluated. The lattice constants of ferrite and cementite were independent of the formed microstructure.

Estimation of the fatigue limit of components made of Austempered Ductile Iron weakened by V-shaped notches

Authors: Giovanni Meneghetti, Stefano Masaggia

  • University of Padova, Department of Industrial Engineering
  • Zanardi Fonderie S.p.A.

2012

A fatigue model previously published in the technical literature has been applied to estimate the fatigue limit in presence of V-shaped notches. When the notch tip radius approaches reduced values, the model is based on the mode I notch-stress intensity factor. Conversely, when the notch tip radius is large, the classical approach based on the linear elastic stress concentration factor is matched. The resulting engineering design tool enables one to assess any kind of notch geometry, namely U-shaped and V-shaped notches of whatever notch tip radius and dimension. The well-known scale effect shown by the Kitagawa-Takahashi valid for cracks is included as a particular case. The fatigue model requires two material parameters, namely the plain material fatigue limit and the threshold range of the stress intensity factor for long cracks. The proposed fatigue design procedure has been applied to estimate the fatigue limit of round specimens and a gear made of austempered ductile iron grade 1050. Both specimens and the gears were characterised by the presence a V-notch having a 120° notch opening angle. Theoretical estimation were seen to be in fair agreement with the experimental fatigue test results.

Quiet and light spoked wheel centres made of Austempered Ductile Iron

Authors: Andrea Bracciali, Stefano Masaggia, Gianluca Megna, Enrico Veneri

  • Department of Industrial Engineering, Università di Firenze
  • Zanardi Fonderie S.p.A.

2019

Monobloc wheels are today the main choice of all manufacturers and system operators (trains and metros) thanks to their low weight, simple maintenance and easy approval processes. However, tyred wheels could be competitive again in some situations if a proper redesign is performed, considering that nowadays disk braking is used in almost all vehicles. Both wheel centres and tyres can be manufactured differently in order to eliminate the critical features of their old fashioned design. Materials and shapes can be managed to optimize both mass and maintenance. In this paper, the design process of new wheel centres made of Austempered Ductile Iron (ADI) for a Diesel Multiple Unit (DMU) is described, with particular reference to casting simulations, static and fatigue structural assessment. Mechanical properties of ADI are also introduced and compared to those of steels normally used for railway wheels.

Reclassification of spheroidal graphite ductile cast irons grades according to design needs

Authors: Franco Zanardi, Carlo Mapelli, Silvia Barella

  • Dipartimento di Meccanica, Politecnico di Milano
  • Zanardi Fonderie S.p.A.

JOURNAL: International Journal of Metalcasting – Springer

2019

The classification of grades inside a material family should be based on the properties required by design procedures. This paper proposes a reclassification of spheroidal graphite ferritic pearlitic and ausferritic (ADI) ductile cast irons grades based on yield strength (YS), strength ratio (SR) UTS/YS and elongation at fracture (EF). In fact, these parameters are fundamental for the static assessment according to the procedures FKM Guideline and BS 7910:2005. Static assessment at room temperature, involving plastic deformation and depending on the wall thickness and stress state triaxiality, is here proposed as the most significant for the material classification. All other properties (e.g., fatigue under cyclic loads, high strain rates and temperature effect, etc.) should be reported with reference to the classification mentioned above. SR and EF control the plastic deformation at the notch tip, where maximum calculated elastic stress is redistributed. Minimum YS is usually assumed as the basic parameter for static and cyclic loading design. Because of the inverse relationship that exists between strength and ductility, Brinell hardness control and material quality index should be adopted as Material Quality Control tools, preventing from a too low EF. Fracture Toughness and its ratio with YS must be considered for preventing brittle fracture due to the presence of flaws. Fracture toughness definitions and available data are not sufficiently consistent for a correct comparison between different material grades. A surrogate Charpy energy measurement is indicated for an indirect estimate of toughness.

Scientific publications on cast iron

“Phase Transition Kinetics in Austempered Ductile Iron (ADI) in Respect of Mo Content”

Authors: Martin Landesberger, Robert Koos, Michael Hofmann, Xiaohu Li, Torben Boll, Winfried Petry and Wolfram Volk

  • Technical University of Munich
  • Institut für Angewandte Materialien—Werkstoffkunde (IAM-WK), Karlsruhe Institute of Technology

JOURNAL: MDPI

26th August 2020

The phase transformation to ausferrite during ADI heat treatment can be significantly influenced by the alloying element Mo. Utilizing neutron diffraction the phase transformation from austenite to ausferrite is monitored in-situ during the heat treatment. In addition to the phase volume fractions, the carbon enrichment of retained austenite is investigated. The results from neutron diffraction are compared to the macroscopic length change from dilatometer measurements. They show that the dilatometer data are only of limited use for the investigation of ausferrite formation. However, they allow to derive the time of maximum carbon accumulation in the retained austenite. In addition, the transformation of austenite during ausferritization was investigated using metallographic methods. Finally, the distribution of the alloying elements in the vicinity of the austenite/ferrite interface zone is shown by atom probe tomography (APT) measurements. C and Mn gets enriched within the interface, while Si concentration is reduced. The Mo concentration in ferrite, interface, and austentite stays at the same level. The delay of austenite decay during Stage II reaction caused by Mo is studied in detail at 400 °C for the initial material as well as for 0.25 wt.-% and 0.50 wt.-% Mo additions.

Effect of casting skin on fatigue properties of CG iron

Authors: S. Boonmee, D. Stefanescu

JOURNAL: International Journal of metalcasting – Springer

2013

Previous studies have demonstrated that the casting skin considerably decreases the tensile strength of compacted graphite (CG) iron. The casting skin is expected to have a more pronounced effect on fatigue properties. This paper explores the effect of nodularity (15, 30 and 40%) and surface condition of the test casting (as-cast, machined, shot blasted) on the bending fatigue of CG iron. A fatigue skin factor was defined as the ratio between the fatigue limit of as-cast-to-machined samples. It was found that the fatigue skin factor increases from 0.68 to 0.85 when nodularity decreases from 40% to 15%. On test castings with 15% nodularity it was found that shot blasting is effective in improving the fatigue limit and in minimizing the effect of the casting skin. A 42.5% increase in the fatigue limit was observed for the as-cast samples after shot blasting. Metallographic examination showed significant plastic deformation on the shot-blasted surface. Microhardness testing revealed that the depth of the work-hardened layer after shot-blasting was approximately 0.8 mm (0.031 in.).

Austemperability of intercritically austempered ductile iron (IADI)

Authors: Ricardo Aristizabal-Sierra, Kathy Hayrynen, Robin Foley, John Griffin, Charles Andrew Monroe

Conference: 118th Metalcasting Congress

JOURNAL: American Foundry Society

2014

Step block castings of IADI were produced with thicknesses of 0.6 in. (1.6 cm), 1 in. (2.5 cm), and 2 in. (5.1 cm). A ‘low alloy’ (Cu = 0.7 wt%) and a ‘high alloy’ iron (Cu=0.7 wt%, Ni = 0.7 wt%) were produced. Two intercritical austenitization temperatures were tested for each alloy. No pearlite was detected in any of the 0.6 in. (1.6 cm) thickness sections. In the 1 in. (2.5 cm) samples, no pearlite was found in the high alloy conditions while a small amount of pearlite was found in the two low alloy conditions. At a section thickness of 2 in. (5.1 cm) there was significant amounts of pearlite and ferrite in all the conditions tested. Ferrite increased with decreased austenitization temperature and increased section thickness. Tensile properties in the 0.6 in. (1.6 cm) step blocks were higher than those seen at other thicknesses. The coarser as-cast structure obtained in thicker sections gives some deterioration in properties, but austemperability limits in the samples also contributed to these differences.

Cast Iron: History and Application

Author: Andrew Ruble Department of Materials Science & Engineering University of Washington

This module introduces cast iron along with its varieties and applications. Cast iron, like steel, is composed primarily of iron and carbon. However, cast iron’s composition is near 4% weight carbon, which along with 1-3% weight of silicon, greatly affects the microstructure of the iron and carbon, causing graphite, a crystalline form of carbon, to form instead of cementite (Fe3C). Cast iron is divided into many groups and three are touched upon in this module: gray iron with graphite flakes, ductile iron with spherical graphite, and compacted graphite iron with wormlike graphite. A discussion of properties follows and includes a hands-on activity that demonstrates the vibration damping of cast Iron.

Fatigue crack tip damaging micromechanisms in pearlitic ductile cast irons

Authors: Francesco Iacoviello, Vittorio Di Cocco, Mauro Cavallini

JOURNAL: Frattura ed Integrità Strutturale

24th June 2014

In the last years, damaging micromechanisms in ductile cast irons (DCIs) were widely investigated: DCI microstructure (ranging from ferritic–pearlitic DCIs to austempered ones), graphite elements morphology (shape, dimension and distributions) and loading
conditions were the main investigated parameters. Focusing on the role played by the graphite nodules, they were considered merely as voids embedded in a metal matrix. Recent analysis underlined that the nodules role in the DCIs damage evolution is more complicated and is influenced by the matrix microstructure. In this work, the crack tip damaging micromechanisms in a pearlitic DCI is investigated considering both fatigue loading conditions and the effects of overloads, focusing the interaction between the crack and the investigated DCI microstructure (pearlitic matrix and graphite nodules). On the basis of experimental results, the applicability of ASTM E399 standard on the characterization of fatigue crack propagation resistance in pearlitic DCIs is critically re-analyzed

In-situ measurement of phase transformation kinetics in austempered ductile iron/h3>

Authors: Leopold Meier, Michael Hofmann, Patrick Saal, Wolfram Volk, Hartmut Hoffmann

Technische Universität München

JOURNAL: ScienceDirect – Elsevier

10th September 2013

Austempered ductile iron (ADI) alloyed with 0.42% Mn and 0.72% Cu was heat treated in a mirror furnace and the phase transitions were studied in-situ by neutron diffraction. The heat treatment consisted of austenitisation at 920 °C and isothermal austempering at 400 °C, 350 °C and 300 °C, respectively. Due to the growth of ferrite platelets, the austenite content decreases rapidly at all temperatures within the first 15–20 min and reaches a stable plateau after 35 min (400 °C) to 80 min (300 °C). The carbon content of the residual austenite, which was monitored and characterised by the change of the lattice parameter, increases up to 1.6 wt.% caused by redistribution from the newly formed ferrite. While at higher austempering temperatures this takes place almost parallel to the phase transformation, at 300 °C the redistribution of carbon to austenite lags behind considerably. Furthermore the neutron data revealed an austenite peak asymmetry during austempering which is attributed to successive phase transformation. It results temporarily in two fractions of austenite, an initial low-carbon and an enriched high-carbon modification.

Characterization and Design of Enhanced Ductile Irons

Author: Dr.-Ing. Martin Landesberger

UNIVERSITA’: Technische Universität München

15th June 2022

The present work addresses the heat treatment of ductile cast iron, which increases mechanical properties of this material class significantly. To fully realize this potential, a profound understanding of the phase transformation processes and the resulting microstructures during heat treatment is necessary. Depending on the selected temperature levels and holding times, very different microstructures are formed in ductile iron castings. The distribution of carbon (C) embedded in the iron matrix is decisive here. In heat treatment to isothermed perferritic ductile iron (IDI), C takes a major role in formation of the pearlitic-ferritic network, while in austempered ductile iron (ADI) it ensures the stability of the austenite at room temperature and enables the formation of acicular ferrite. In ADI, the acicular ferrite, together with the retained austenite, forms the ausferritic microstructure, which can be adjusted to varying degrees of fineness depending on the temperature control. The heat treatments of ductile iron to IDI and ADI consist of an isothermal annealing at high temperature, which is continued isothermally between 250 °C and 425 °C after quenching in a salt melt. Finally, the material is cooled to room temperature. The main difference is the high temperature stage. While ADI is completely austenitized at approx. 900 °C, IDI is adjusted to a mixed structure of austenite and ferrite. This is done by annealing IDI at about 820 °C within the critical interval. Once a sufficient understanding of the phase transformation for different alloys is obtained, the mechanical properties can be tailored to specific applications, especially for ADI. To avoid pearlite formation during the quenching process, in ADI the use of Cu, Ni and Mo is necessary. IDI offers itself as a low-cost alternative to ADI due to a low alloying element demand, if properties are required that are intermediate between pearlitic cast iron grades and ADI. Using various in-situ and ex-situ methods, this work provides a fundamental contribution to process understanding in the production of the two enhanced cast irons. Dilatometry as well as neutron diffraction allow direct observation of the transformation processes as well as the enrichment of the austenite with C. After deriving suitable heat treatment temperatures and holding times, both methods are opposed. The characterization of the phase transformation kinetics of IDI is followed by a detailed investigation of the influence of Mo on the expression of the process window of ADI heat treatment. Extensive metallographic investigations provide information on the decay of retained austenite and the associated formation of carbides when the process window is exceeded. Further information on the characteristics of the ausferritic microstructure was obtained by means of electron backscatter diffraction measurements. Finally, atom probe tomography is used to localize the C and further alloying elements within the ausferrite microstructure at the atomic level. The methods are then utilized for designing an technical ADI alloy to be used in components subjected to cyclic loading. Tensile strength, hardness, Charpy impact energy, and cyclic material properties are determined for 300 °C, 350 °C, and 400 °C temperature levels. For the 350 °C stage, the isothermal holding time is optimized to ensure a production in the most energy-efficient and resource-saving way possible.

Dissertations performed in Zanardi Foundries SpA

Sliding-rolling behavior of ADI, IDI and 42CrMo4 QT+Ni

Student: Giuliari

2013

In this work the dry sliding-rolling behavior of austempered ductile irons (ADI) is studied. The study involves six types of cast irons, produced by the Zanardi Fonderie S.p.A., and a nitrided steels, used for comparison purpose. The study of the sliding-rolling behavior is addressed to simulate the tribological damage that occurs in different systems such as gears, cam shafts and rocker arms. Dry conditions were used to better analyze the role of the microstructure of austempered nodular cast irons because they are often used in tribological applications where the antagonisti is of the same material, in steel or copper alloy. Cast irons and steel were tested in dry sliding-rolling conditions (10% sliding) using the disc-on-disc configuration, by means of an Amsler tribometer. By so doing it is possible to obtain the wear curve for comparing the performance of the different materials. Furthermore, the evolution of the friction coefficient is recorded during each test, in order to understand the influence of the graphite and to identify possible transitions in wear mechanism. All specimens were subjected to metallographic analysis, in order to follow the surface damage progression, by means of scanning electron microscope inspection of the wear paths; furthermore, possible cracks formation can be observed on cross section samples normal to wear paths by means of an optical microscope.

Dilatometric study of austempering heat treatment of nodular cast iron

Student: Marco dal Molin

University: Università degli studi di Trento

Thesis supervisor: Straffellini Giovanni e Pellizzari Massimo

2013

Cast iron is one of the most used metallic materials for industrial applications due to its excellent castability, which makes possible to obtain even very large casting of complex shape by means of classic green sand process. However, cast iron has always been considered a “”poor”” material, suitable only for low stress demanding applications. In fact, cast iron contains graphite particles which favor brittle fracture; therefore, all plastic deformations processes that strengthen the matarial by work hardening, such as forging and rolling, cannot be applied. Nor is it possible to take advantage through recrystallization processes induced by plastic deformation. On the other hand, the typical solidification structure of cast iron is characterized by the inevitable presence of segregation of the alloy elements and inhomogeneities that affect the final properties. Mechanical properties improvement can be obtained by heat treating the cast iron, in order to modify the microstructure of the matrix. The austempering treatment, in particular, is one of the most interesting processes, thanks to the excellent mechanical properties of the ausferritic matrix obtained.

Determination of austempering process window of austempered ductile iron as the silicon content varies./h3>

Student: Elena Pullin

University: Università degli Studi di Padova

Thesis supervisor: Prof. Giovanni Meneghetti

Thesis supervisor of Zanardi Fonderie: Ing. Stefano Masaggia

2015

This thesis work concern the microstructural and mechanical characterization of three nodular cast iron, having different silicon content, which have been subjected to austempering heat treatment for improving strength and toughness properties. The objective of the research was to evaluate the effect of an industrial heat treatment on final microstructure and mechanical properties, in order to identify the so-called optimal process window for ADI production. For this purpose, the effect of the temperatures and times of the austenitization and austempering phases on ausferrite formation has been analyzed; then, microstructural evidence and the corresponding mechanical properties have been cross-checked to define the optimum process parameters for the best compromise between mechanical strenght and toughness.

Mechanical performance of Nodular Cast Irons after prolonged high temperature exposure

Student: Valentina Catellani

University: Università di Bologna

Thesis supervisor: Chiar.mo Prof. Alessandro Morri

Thesis supervisor of Zanardi Fonderie: Ing. Stefano Masaggia

2017

Cast irons are used for severl applications such as hydraulic, pneumatic, architecture, machine tools and automotive. Nodular cast irons, in particular, are characterized by superior mechanical properties than other classes of cast irons, good ductility, fatigue resistance and impact strength, as well as excellent castability. Despite cast irons are also used for high temperature applications , the data available in literature on their mechanical behavior after prolonged exposure to high temperature are very limited, thus limiting their diffusion in competition with Q&T steels. The aim of this work is to evaluate the effect of prolonged exposure to high temperatures on microstructure and mechanical properties on four different of nodular cast irons produced by Zanardi Fonderie. The materials examined are an austempered ductile iron (ADI 1050), a pearlitic ductile iron (GJS/800-2), a perferritic ductile iron (IDI800) and a ferritic ductile iron (GJS/400-18). After a controlled degradation in experimental furnace, all materials have been subjected subjected to hardness measurement and tensile tests, both at room temperature and at 500°C; furthermore, a complete microstructural characterization using optical and scanning electron microscopy has been carried out. The data obtained have been analyzed and commented in comparison with previous research activities.

“Development of local approaches for fatigue life prediction of Austempered Ductile Iron-to-Steel dissimilar joints”

Student: Elena Pullin

University: Università degli Studi di Padova

Thesis supervisor: Prof. Giovanni Meneghetti

Thesis supervisor of Zanardi Fonderie: Ing. Stefano Masaggia

13th December 2019

Nowadays, the use of dierent classes of materials in the same structure is increased to keep pace with innovation and high-performance requirements for products. In this context, structural components made of dierent materials need to be joined together and a possible solution for metals is given by arcwelding technologies. As dissimilar welded joints must be able to withstand high cyclic loads under service conditions, the present contribution aims to compare the fatigue behaviour of Austempered Ductile Iron-to-S355J2 steel dissimilar joints to the categories of the corresponding homogeneous steel welded joints, suggested in International Standards and Recommendations. First, metallographic analyses, micro-hardness measurements and residual stresses proles were obtained on a selection of joints. Angular and linear misalignments were quantied for all specimens. Then, experimental fatigue tests were carried out on the dissimilar welded details. Finally, experimental data were re-analysed in terms of local approaches to explicitly take into consideration stress concentrations and provide the best level of accuracy for the fatigue assessment of the welded structures.