Heat Treatment of S.G Cast Iron

S.G Cast iron is defined as a high carbon containing, iron based alloy in which the graphite is present in compact, spherical shapes rather than in the shape of flakes, the latter being typical of gray cast iron . As nodular or spheroidal graphite cast iron, sometimes referred to as ductile iron, constitutes a family of cast irons in which the graphite is present in a nodular or spheroidal form. The graphite nodules are small and constitute only small areas of weakness in a steel-like matrix. Because of this the mechanical properties of ductile irons related directly to the strength and ductility of the matrix present—as is the case of steels. One reason for the phenomenal growth in the use of Ductile Iron castings is the high ratio of performance to cost that they offer the designer and end user. This high value results from many factors, one of which is the control of microstructure and properties that can be achieved in the ascast condition, enabling a high percentage of ferritic and pearlitic structure

Heat treatment of S.G cast iron and its effects

S.G Cast iron is defined as a high carbon containing, iron based alloy in which the graphite is present in compact, spherical shapes rather than in the shape of flakes, the latter being typical of gray cast iron . As nodular or spheroidal graphite cast iron, sometimes referred to as ductile iron,constitutes a family of cast irons in which the graphite is present in a nodular or spheroidal form.The graphite nodules are small and constitute only small areas of weakness in a steel-like matrix. Because of this the mechanical properties of ductile irons related directly to the strength and ductility of the matrix present—as is the case of steels.One reason for the phenomenal growth in the use of Ductile Iron castings is the high ratio of performance to cost that they offer the designer and end user. This high value results from many factors, one of which is the control of microstructure and properties that can be achieved in the ascast condition, enabling a high percentage of ferritic and pearlitic structure.Heat treatment is a valuable and versatile tool for extending both the consistency and range of properties of Ductile Iron castings beyond the limits of those produced in the as-cast condition. Thus, to fully utilize the potential of Ductile Iron castings, the designer should be aware of the wide range of heat treatments available for Ductile Iron, and its response to these heat treatments.The most important heat treatments and their purposes are:Stress relieving - a low-temperature treatment, to reduce or relieve internal stresses remaining after casting Annealing - to improve ductility and toughness, to reduce hardness and to remove carbides Normalizing - to improve strength with some ductility Hardening and tempering - to increase hardness or to give improved strength and higher proof stress ratio Austempering - to yield bainitic structures of high strength, with significant ductility and good wear resistance Surface hardening - by induction, flame,or laser to produce a local wearresistant hard surface1 Although Ductile Iron and steel are superficially similar metallurgically, the high carbon and silicon levels in Ductile Iron result in important differences in their response to heat treatment. The higher carbon levels in Ductile Iron increase hardenability, permitting heavier sections to be heat treated with lower requirements for expensive alloying or severe quenching media.These higher carbon levels can also cause quench cracking due to the formation of higher carbon martensite,and/or the retention of metastable austenite. These undesirable phenomena make the control of composition, austenitizing temperature and quenching conditions more critical in Ductile Iron. Silicon also exerts a strong influence on the response of Ductile Iron to heat treatment. The higher the silicon content, the lower the solubility of carbon in austenite and the more readily carbon is precipitated as graphite during slow cooling to produce a ferritic matrix. Although remaining unchanged in shape, the graphite spheroids in Ductile Iron play a critical role in heat treatment, acting as both a source and sink for carbon. When heated into the austenite temperature range, carbon readily diffuses from the spheroids to saturate the austenite matrix.On slow cooling the carbon returns to the graphite "sinks",reducing the carbon content of the austenite. This availability of excess carbon and the ability to transfer it between the matrix and the nodules makes Ductile Iron easier to heat treat and increases the range of properties that can be obtained by heat treatment.Austempered Ductile Irons (ADI) are the most recently developed materials of the DI family. By adapting the austempering treatment initially introduced for steels to DI, it has been shown that the resulting metallurgical structures provide properties that favorably compare to those of steel while taking advantage of a near-net-shape manufacturing process

Surface laser treatment of cast irons: A Review

Heat treatments are frequently used to modify the microstructure and mechanical properties of materials according to the requirements of their applications. Laser surface treatment (LST) has become a relevant technique due to the high control of the parameters and localization involved in surface modification. It allows for the rapid transformation of the microstructure near the surface, resulting in minimal distortion of the workpiece bulk. LST encompasses, in turn, laser surface melting and laser surface hardening techniques. Many of the works devoted to studying the effects of LST in cast iron are diverse and spread in several scientific communities. This work aims to review the main experimental aspects involved in the LST treatment of four cast-iron groups: gray (lamellar) cast iron, pearlitic ductile (nodular) iron, austempered ductile iron, and ferritic ductile iron. The effects of key experimental parameters, such as laser power, scanning velocity, and interaction time, on the microstructure, composition, hardness, and wear are presented, discussed, and overviewed. Finally, we highlight the main scientific and technological challenges regarding LST applied to cast irons.Fil: Catalán, Néstor. Pontificia Universidad Catolica de Chile. Escuela de Ingeniería. Departamento de Ingeniería Mecanica y Metalurgica; ChileFil: Ramos Moore, Esteban. Pontificia Universidad Católica de Chile. Facultad de Física; ChileFil: Boccardo, Adrian Dante. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados en Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Estudios Avanzados en Ingeniería y Tecnología; ArgentinaFil: Celentano, Diego Javier. Pontificia Universidad Catolica de Chile. Escuela de Ingeniería. Departamento de Ingeniería Mecanica y Metalurgica; Chil

Microstructural Analysis of Austempered Ductile Iron Castings

A ustempered ductile iron ADI castings have a wide range of application areas in engineering designs due to their promising mechanical properties and lower cost. ADI has very good strength and toughness values at the same time its ductility is relatively high compared to most of the other cast irons. These promising mechanical properties originate from combination of specific graphite and matrix microstructure. The size, shape and fraction of graphite as well as the matrix microstructure influences the mechanical properties. In this paper the efforts regarding to a localization project of ADI is presented. In a more detailed manner, the first locally produced ADI which cannot satisfy the mechanical properties stated in ISO 17804 is compared with the original sample which is conform with the standard. The two pieces are inspected by mechanically and microstructurally by means of which necessary actions are detected for the local production. In other words the relation between the macro mechanical properties and the microstructural conditions are tried to be clarifie

Development Of Spheroidal Graphite Cast Iron For Nuclear Fuel Transport Cask

In the present work SG iron specimens with carbon equivalent (%CE) ranging from 4.12 - 4.36, has been subjected to annealing, normalizing, quench & tempering, austempering and DMS treatment to obtain different matrix microstructure and microconstituent. Optical microscopy is observed for microstructure, phase volume fraction, nodularity, and nodule count for each of the as-cast and heat treat specimens. XRD analysis is done to validate the phases present in each specimen as well as to determine the amount of carbon dissolution in respective phases. Mechanical properties such as tensile strength, % elongation, Vicker’s hardness, and impact strength are measured by conducting necessary test following ASTM standards. Failure mechanisms involved in static and dynamic loading are investigated observing the fracture surfaces after tensile and impact test respectively, under Scanning Electron Microscope. The corrosion behavior of as-cast and heat treated specimens, (in sea water) is also studied. Specimens are immersed completely in sea water at room temperature and pressure, and the weight difference is recorded at regular intervals, for twelve weeks. The mechanical properties showed a quite good relationship with microconstituents for respective as-cast and heat treated specimens. The as-cast specimens show graphite spheroids within ferritic matrix resulted in increased ductility and impact strength (with increasing ferrite volume fraction) caused by increasing Si content. Annealing treatment led to the presence of completely ferritic matrix for every alloy consequently increasing ductility and impact toughness as compared to as-cast matrices. On the other hand specimens which underwent quenching & tempering treatment show the highest strength and hardness due to the tempered martensitic matrix, among all other heat treatment processes. Strength and ductility values of normalized austempered and DMS-treated specimens are intermediate to those of lowest strength value for annealed specimen and higher elongation value and that of highest strength and lowest elongation value for the quenched & tempered specimens. It is observed that the elongation increases with increased nodularity can be attributed to increases amount of Mg and Ce, whereas nodule count increases the hardness of respective as-cast and heat treated specimens. The increase of hardness may be due to increase of Ni and Cr content which provides strength to ferrite via solid solution strengthening (for ferritic specimens). Normalizing treatment produced a ferritic/pearlitic matrix and showed increased UTS and hardness with increased pearlite content. Austempered heat treatment resulted in coarse upper bainitic matrix leading to suitable combination of strength and ductility, whereas matrix consists of martensite and ferrite are obtained by DMS treatment. The failure mode for the soft ferritic matrix is observed to be ductile in nature caused by microvoid coalescence, and that of other matrices are mostly brittle signified by the presence of low energy stress paths (River marking) and cleavage facets. Mechanical properties of SG iron alloys studied in current research, found to be well above the recommended properties for fabrication of nuclear fuel cask, (in as-cast as well as heat treated conditions) and hence can successfully be used for the desired purpose

Design of Heat Treatment for Production of Austempered Ductile Iron (ADI) With Targeted Automotive Applications

This research is on austempered ductile iron (ADI), which offers an excellent combination of low cost, design flexibility, good machinability, high strength-to-weight ratio, good toughness, good wear resistance and fatigue strength. While ADI has found quite wide application in some industries, its use in automotive parts production has been limited. ADI obtains its excellent properties through the development of a high carbon austenite+ferrite microstructure referred to as ausferrite. The properties of ADI can be tailored by changing the heat treatment schedule. In this research a special chemistry Ni-Mo-Cu ADI was subjected to heat treatment schedules. Mechanical properties (hardness, tensile strength, and toughness), tribological properties (scuffing and surface deformation) and microstructural studies were conducted. Feathery ausferrite microstructure produced by high austempering temperature and long time gave very good tribological properties. While martensitic microstructure produces by low austempering temperature and short time gave very high hardness. Heat treatment recommendations were made based on the targeted automotive applications

Study of SG iron and its tribological behaviour

Erosive wear tests were performed on different alloys composition of SG iron using air jet erosion test rig. Erosion damage was measured by the removed material volume at impact angles 30¢ª, 45¢ª and 60¢ª. The effect of impact angle, standoff distance and pressure in wear features of specimens were discussed as mechanism of erosive wear by using the taguchi¡¯s analysis. The objective was to investigate which design parameter significantly affects the erosion wear. It was found that the pressure and impact angle is the most powerful factor influencing the erosion wear rate. The surface morphology shows erosion mechanism of the spheroidal graphite at the surface deforms gradually, lips are produced in the direction of the blast, and they extend, and finally drop off. This process of growth, extension, and dropping off is repeated, but life spans are different depending on the material. The basic mechanism of the erosion damage is at first the plastic transformation near the surface due to the impacts. In this study we deal with determination of crystallite-size distribution and microstrain measurement of SG iron by the means of x-ray diffraction line broadening method. XRD analysis shows that only ferrite phase is present mainly in all samples of SG iron. It was shown that nodular cast iron has excellent erosion resistance and it is expected to find wide applications as a wear-resistant material. Nodular cast iron (SG iron) shows the highest wear resistance probably due to its graphite morphology which controls crack propagation and thermal conductivity

Effect of Processing Parameters on Properties of Alloyed Austempered Ductile Iron

Ever since its discovery in 1948, the use of ductile iron is increasing continuously, this is due to the combination of its various excellent mechanical properties of the material. Extensive research is being carried out to develop even better properties. Austempered ductile iron is the most recent development in the area of ductile iron or S.G. iron. This is formed by an isothermal heat treatment of the ductile iron. The newly developed austempered ductile iron is now replacing steel in many fields so it is becoming very important to study various aspects of this material. In the present work the effect of Copper and Nickel as alloying element along with the process variables (austempering temperature and austempering time) on the properties (Hardness, Tensile strength and Elongation) and microstructure of ductile iron has been studied. 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 higher strength, hardness and lower elongation than the unalloyed austempered ductile iron. In microstructure ferrite is increasing with increasing austempering time and austenite is increasing with increasing austempering temperature in all the Cu alloyed, Ni alloyed and unalloyed grades

Liuoslujitetun pallografiittivaluraudan mekaanisten ominaisuuksien parantaminen austemperoimalla

This thesis studies the mechanical properties of solid solution strengthened spheroidal graphite cast iron after austempering heat treatment. Austempering heat treatment consists of three stages: austenitising, quenching and austempering. In the end the microstructure should consist of austenite and ferrite needles, generally called ausferrite. This unique material is called austempered ductile iron (ADI). With successful heat treatment the casting gains better mechanical properties. Aim in the experimental part of this thesis is to find a suitable combination of austenitising and austempering processes to improve the mechanical properties of the used samples with less alloying or even to develop a new austempered material. Inspected samples are solid solution strengthened irons with a silicon content that is 1–1.8% higher than usual. Silicon changes the phase boundaries and therefore samples require tailored heat treatment. Different parameters of heat treatment are tested, with starting values based on existing literature. Methods used to test the resulting material include Vickers and Brinell hardness tests, microstructure analysis and tensile test. The properties of solid solution strengthened ductile iron grades GJS-500-14 and GJS-600-10 are investigated and grade GJS-500-7 is used as a reference material. First, different austenitising temperatures were tested, and the microstructure and hardness of the samples are analysed to select the austenitising temperature. Second, components were austenitised in the selected temperature and then austempered for different times and at different temperatures in molten salt bath. Finally, the optimised combination of heat treatments is tested with tension test bars. The austenitising tests showed 950°C to be a good austenitising temperature for the solid solution strengthened materials due to higher silicon content. For reference grade GJS-500-7 normal temperature 860°C was used. In the second stage, austempering temperature 310°C with one hour austempering time was selected for further investigations. Tensile strength tests show that with this tailored heat treatment GJS-500-14 gained approximately 30% better yield and tensile strength compared to GJS-500-7, but elongation was 13% lower. Heat-treated GJS-600-10 gained 22% better yield strength and 30% better tensile strength with 25% lower elongation. Hardness increased 20% in both materials compared to GJS-500-7. When comparing the studied solid solution strengthened grades to standardised ADI, the elongation was doubled with the same strength values. Combining these grades with the proposed heat treatment creates a material, which has potential for a novel austempered grade with example values GJS-1300-950-7.Tämän diplomityön tarkoituksena oli liuoslujitetun pallografiittivaluraudan mekaanisten ominaisuuksien tutkiminen austemperoinnin jälkeen. Tähän lämpökäsittelyyn kuuluu kolme vaihetta: austenitointi, sammutus ja austemperointi. Käsittelyssä mikrorakenne muuttuu austeniitiksi ja ferriittineulasiksi, mitä kutsutaan ausferriitiksi ja itse materiaalia ADI:ksi (Austempered Ductile Iron). Onnistuneen lämpökäsittelyn tuloksena valutuotteen mekaaniset ominaisuudet paranevat. Kokeellisen osuuden tavoitteena on löytää sopivin austenoinnin ja austemperoinnin yhdistelmä ja saavuttaa samat mekaaniset ominaisuudet niukemmalla seostuksella, tai jopa löytää uusi austemperoitu materiaali. Tässä työssä tutkitaan liuoslujitettua pallografiittirautaa, jonka piipitoisuus on 1–1,8 % normaalia suurempi. Pii muuttaa faasirajoja ja edellyttää lämpökäsittelyn räätälöimistä. Testattavat lämpötilat ja ajat lämpökäsittelyihin valitaan kirjallisuuden perusteella. Materiaalia tutkitaan Vickers ja Brinell kovuuskokeilla sekä mikrorakennekuvien ja vetokokeen avulla. Liuoslujitetuttujen rautalaatujen GJS-500-14 ja GJS-600-10 ominaisuuksia halutaan tutkia, ja GJS-500-7 toimii vertailukohteena. Ensin testataan eri austenitoinnin lämpötiloja ja sen jälkeen austemperoinnin eri aikoja ja lämpötiloja suolakylvyssä. Lopuksi, näiden lämpökäsittelyiden parasta yhdistelmää testataan vetosauvoilla. Austenitointitestit osoittivat, että liuoslujitetuille korkeamman piipitoisuuden materiaaleille sopiva lämpötila on 950°C, mutta GJS-500-7 kannattaa austenitoida normaalissa 860°C:n lämpötilassa. Toisessa vaiheessa valittiin seuraavia austemperointeja varten lämpötilaksi 310°C ja ajaksi yksi tunti. Vetotulokset osoittavat että räätälöidyn lämpökäsittelyn avulla materiaalin GJS-500-14 myötö- ja murtolujuus paranevat noin 30% verrattuna materiaaliin GJS-500-7, mutta venymä pienenee 13%. Lämpökäsitelty GJS-600-10 puolestaan saavuttaa 22% paremman myötölujuuden ja 30% paremman murtolujuuden sekä 25% pienemmän venymän kuin GJS-500-7. Molempien liuoslujitettujen materiaalien kovuus oli 20% suurempi referenssimateriaaliin nähden. Verrattaessa lämpökäsiteltyjä liuoslujitettuja materiaaleja standardoituihin ADI-laatuihin venymä on jopa kaksi kertaa parempi samoilla lujuuden arvoilla. Lämpökäsittelemällä liuoslujitettua valurautaa saadaan materiaali, joka on potentiaalinen uusi ADI-laatu esimerkiksi ominaisuusarvoilla GJS-1300-950-7

Effect of copper on austempering behavior of ductile iron

Even since its discovery in 1948, the use of ductile iron is increasing continuously, this is due to the combination of its various excellent mechanical properties. Excessive amount of research is being carried out to develop even better properties. Austempererd ductile iron is the most recent development in the area of ductile iron or S.G. ron. This is formed by an isothermal heat treatment of the ductile iron. The newly developed austempered ductile iron is now replacing steel in many fields so it has becoming very important to various aspects of this material. In the present work the effect of copper along with the process variables (austempering temperature and austempering time) on the properties (Hardness, Tensile strength and Elongation) and microstructure of ductile iron is studied. 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 copper is showing some higher strength, hardness and lower elongation than the austempered ductile iron without copper. In microstructure ferrite is increasing with increasing austempering time and austenite is increasing with increasing austempering temperature in both the grades