Ductile Iron Grade Research Articles

Microstructure vs. Near-threshold Fatigue Crack Growth Behavior of an Heat-treated Ductile Iron

Perferritic isothermal ductile iron (IDI®) is an intermediate grade between the low-strength grades of austempered ductile iron (ADI) and pearlitic ductile iron (DI) recently developed by Zanardi Fonderie Italy. IDI is produced by heat-treating an unalloyed nodular cast iron. The specific matrix microstructure is called “Perferritic” and consists predominantly of ferrite and pearlite. Compared to the pearlitic grades of nodular ductile iron, IDI combines similar strength with higher toughness as a result of the isothermal heat treatment. In this contribution the fatigue crack growth resistance and Kath of IDI are investigated and correlated to mechanical properties and microstructural features. The threshold Ka was determined using the load shedding technique as per ASTM Standard E-647 using CT specimens extracted from a cast block. Tensile specimens were extracted from the broken CT halves and used to determine the static mechanical properties. A metallographic investigation was carried out to correlate structural features and mechanical properties.DOI: http://dx.doi.org/10.5755/j01.ms.18.1.1336

Drilling performance of green austempered ductile iron (ADI) grade produced by novel manufacturing technology

Machinability study on drilling of green austempered ductile iron (ADI) grade was conducted using a TiAlN-coated tungsten carbide drill. The green ADI grade was produced by a novel manufacturing technology known as continuous casting-heat treatment technology to save energy and time in foundry. However, in spite of good combination of strength, toughness and enhanced wear resistance, the microstructural properties of ADI sometimes lead to machinability issues. The effect of cutting parameters on cutting force coefficients, chip morphology, and surface integrity of the drilled surface were discussed. Results showed that the strength properties of novel ADI are comparable to that of ASTM grade 1 ADI, whereas percent elongation is comparable to that of ASTM grade 2 ADI. Results obtained also showed that the combined effect of cutting speed at its higher values and feed rate at its lower values can result in increasing cutting force coefficients and specific cutting energy. At higher cutting speed, hardness values increases at the subsurface layer of the drilled surface due to plastic deformation.

Effect of laser surface hardening on the microstructure, hardness and residual stresses of austempered ductile iron grades

A study of the laser surface hardening process of two austempered ductile iron grades, with different austempering treatments has been carried out. Hardening was performed with an infrared continuous wave Nd:YAG laser in cylindrical specimens. The microstructure of the laser hardened samples was investigated using an optical microscope, microhardness profiles were measured and surface and radial residual stresses were studied by an X-ray diffractometer. Similar results were achieved for both materials. A coarse martensite with retained austenite structure was found in the treated area, resulting in a wear resistant effective layer of 0.6 mm to 1 mm with a microhardness between 650 HV and 800 HV. Compressive residual stresses have been found at the hardened area being in agreement with the microhardness and microstructural variations observed. The achieved results point out that the laser surface hardening is a suitable method for improving the mechanical properties of austempered ductile irons.

Analysis of Nodular Cast Iron Microstructures for Micromechanical Model Development

Abstract: One of the main factors in determining the different grades of ductile iron is the matrix structure. In the as‐cast condition, the matrix will consist of varying proportions of pearlite and ferrite, and as the amount of pearlite increases, the strength and hardness of the iron also increase. Three different nodular cast irons are here considered and their microstructure characterised in detail using metallographic methods. Then micromechanics models based on the unit cell approach and the finite element method are introduced to describe the actual constitutive response of the materials and the predicted behaviours are compared with experiments.

Contact fatigue resistance of austempered and partially chilled ductile irons

This study reports the results of laboratory tests carried out to evaluate the rolling contact fatigue (RCF) resistance of ductile iron with different treatments. Tests were conducted in a flat washer type RCF apparatus, at loading and lubricating conditions leading to the interaction of surface microasperities, i.e. with specific oil film thickness, λ<1. The microstructures evaluated correspond to different austempered ductile iron (ADI) grades, obtained at different austempering temperatures, and one variant of a partially chilled ductile iron (PCDI). The ADI variants have shown the highest RCF resistance for the lowest austempering temperature evaluated. The PCDI samples, in the as-cast condition, have shown the highest RCF resistance among the different ductile iron variants evaluated. It was observed that nodules play an important role on the nucleation stage of the failure process, and also the reduced nodule size of the PCDI could be responsible for its high RCF life.

Effect of Low Temperatures on Charpy Impact Toughness of Austempered Ductile Irons

Impact properties of standard American Society for Testing Materials (ASTM) grades of austempered ductile iron (ADI) were evaluated at subzero temperatures in unnotched and V-notched conditions and compared with ferritic and pearlitic grades of ductile irons (DIs). It was determined that there is a decrease in impact toughness for all ADI grades when there is a decrease in content of retained austenite and a decrease in test temperature, from room temperature (RT) to −60 °C. However, the difference in impact toughness values was not so noticeable for low retained austenite containing grade 5 ADI at both room and subzero temperatures as it was for ADI grade 1. Furthermore, the difference in impact toughness values of V-notched specimens of ADI grades 1 and 5 tested at −40 °C was minimal. The impact behaviors of ADI grade 5 and ferritic DI were found to be more stable than those of ADI grades 1, 2, 3, and 4 and pearlitic DI when the testing temperature was decreased. The impact toughness of ferritic DI was higher than that of ADI grades 1 and 2 at both −40 °C and −60 °C. The impact properties of ADI grades 4 and 5 were found to be higher than that of pearlitic DI at both −40 °C and −60 °C. The scanning electron microscopy (SEM) study of fracture surfaces revealed mixed ductile and quasicleavage rupture morphology types in all ADI samples tested at both −40 °C and −60 °C. With decreasing content of retained austenite and ductility, the number of quasicleavage facets increased from ADI grade 1–5. It was also found that fracture morphology of ADI did not experience significant changes when the testing temperature decreased. Evaluation of the bending angle was used to support impact-testing data. Designers and users of ADI castings may use the data developed in this research as a reference.

Wear Resistance Properties of Austempered Ductile Iron

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.

NI-ROD 44 WELDING ELECTRODE

Abstract NI-Rod 44 Welding Electrode is a product specifically designed to attain 100% joint efficiency in the common grades of ductile iron while maintaining both strength and ductility through a metallurgically unique nickel-iron-manganese system. This datasheet provides information on composition. Filing Code: FE-112. Producer or source: Inco Alloys International Inc.

Surface laser treatment of ductile irons

The effect of the laser surface treatment of three types of ductile iron (Grades 60-40-18, 80-55-06 and 100-70-03) was studied. Using a continuous CO2 laser with a square 10 mm × 10 mm beam and uniform power density, the effect of beam scan rate at 2.5 and 5 kW power output was investigated. At each power rate, a range of scan rates was used to produce treatments with and without surface melting. The microstructure and hardness of the different zones of the treated material were analysed. It was found that layers of white iron of the same depth were produced in the three test irons when the operating conditions melted the surface material. Surface porosity can be eliminated by melting, although transverse cracks appeared on the surface with this treatment. Surface martensitic hardening produced a layer of uniform hardness only in the case of the grade 100-70-03 ductile iron with a perlitic matrix.

Wear resistance of ductile irons

This study was undertaken to evaluate the wear resistance of different grades of ductile iron as alterna-tives to high- tensile- strength alloyed and inoculated gray irons and bronzes for machine- tool and high-pressure hydraulic components. Special test methods were employed to simulate typical conditions of reciprocating sliding wear with and without abrasive- contaminated lubricant for machine and press guideways. Quantitative relationships were established among wear rate, microstructure and micro-hardness of structural constituents, and nodule size of ductile iron. The frictional wear resistance of duc-tile iron as a bearing material was tested with hardened steel shafts using standard test techniques under continuous rotating movement with lubricant. Lubricated sliding wear tests on specimens and compo-nents for hydraulic equipment and apparatus were carried out on a special rig with reciprocating motion, simulating the working conditions in a piston/cylinder unit in a pressure range from 5 to 32 MPa. Rig and field tests on machine- tool components and units and on hydraulic parts have confirmed the test data.

CONTINUOUS-CAST 45-12 DUCTILE IRON

Abstract Ductile Iron grade 45-12 produced by continuous casting has consistent density and fine grain structure. It is the softest of the regular grades of ductile iron and it machines at high speeds with good surface finish. This datasheet provides information on composition, physical properties, microstructure, hardness, elasticity, and tensile properties. It also includes information on heat treating, machining, and joining. Filing Code: CI-58. Producer or source: Federal Bronze Products Inc..

A comparison of several analytical techniques for calculating [formula omitted] Curves from load-displacement data and their relation to specimen geometry

Various methods to determine crack growth resistance curves have been compared. Ferritic ductile cast iron (grade 60-40-18) was machined into three different specimen geometries (compact tension, bend bar and Charpy V-notched) which were fatigue precracked and then tested under displacement control at room temperature. Crack resistance curves were generated using the current standard, ASTM E813-81, and a new J-R curve standard, ASTM E1152-87. It was found that R- curves calculated with these two approaches were similar up to approximately 1 to 3 mm of crack extension, at which point the R- curve calculated with ASTM E1152-87 began to drop off. A geometry dependence of the R- curves was observed between the different specimen geometries for both ASTM E813-81 and ASTM E1152-87. The modified J formulation of Ernst was also found to give a geometry dependent R- curve for the ferritic ductile iron.

Approaching austempered ductile iron properties by controlled cooling in the foundry

In a general sense austempered ductile iron (ADI) is a new class of ductile iron that is twice as tough as standard grades of ductile iron at the same strength level. ADI has excellent toughness and wear resistance and has been shown to have superior fatigue properties as well. The unique microstructure developed by austempering ductile iron provides these remarkable engineering properties. This heat treatment is an extra step in the manufacturing process that adds direct and indirect costs. The current capacity of heat-treatment facilities capable of austempering is limited. There is interest in achieving austempered ductile iron (ADI) properties in the foundry, but the cost of adding the elaborate heat-treating facilities required for austempering is high. Acicular irons, where-by high strengths are achieved by transformation on continuous cooling of alloyed irons through the bainitic transformation region, provide one alternative; however, the high ductility and toughness associated with ADI are generally absent in acicular irons. Another alternative is to employ controlled cooling that closely approximates the thermal schedule for austempering. Controlled cooling can be applied either following a hot shakeout or normalizing treatment. This has been done in a laboratory environment. The results of this study will be discussed, and suggestions for pursuit of this technology are given in view of current and emerging foundry processing technologies.

Transformation Behavior in Austempering Nodular Iron

Interest in austempered bainitic ductile irons has increased dramatically in the past few years as more and more successful applications are being reported. The remarkable combination of properties attainable has caused this material to emerge as a new class of ductile iron. Austempered ductile irons achieve strength levels as high as twice those of standard ductile iron grades at the same level of toughness and ductility, see Figure 1. In addition they respond to work-hardening treatments at the surface and thus have exceptionally high bending fatigue strength and wear resistance. These good properties are directly related to the unique bainite-austenite microstructure produced by austempering.

Corrosion of Construction Materials in Clay Environments

ABSTRACTThe corrosion rate and mechanism of construction materials of galleries and casings for boreholes (possibly to be used as consumable overpack of HLW canisters) have been evaluated after a first campaign of corrosion experiments in direct contact with clay, in a humid clay atmosphere and in a gas corrosion chamber. The envisaged construction material is ductile iron (grade 60) and has been tested with and without metallic and organic coatings. The corrosion mechanism is governed by the formation of a rust scale composed of Fe3O4 and C. Preferential attack underneath the surface reaction layer is associated with the progress of a reaction front at the interface between the graphic nodules or flakes and the ferritic or pearlitic structure.Post-corrosion analyses of old gray iron coal mine shafts exposed for 60 and 90 years in well defined conditions are included to validate the use of the results of the short-time tests for very long exposure times.