Ductile Iron Components Research Articles

The effects of I-Beam thickness to microstructure and compression load of thin wall ductile iron connecting rod

Lighter automotive components are needed to reduce energy consumption. The manufacturing processes of the components should also consume less energy and be environmentally friendly. Aluminum is a lightweight material, but the manufacturing processes consume a lot of energy. Ductile iron has outstanding design flexibility and applying a thin wall casting technique to the ductile iron components will reduce the weight and make it possible for ductile iron to compete with lightweight materials. The achievement of making a 3 mm I-beam thickness connecting rod which fulfills the design requirement in previous research has encouraged a further reduction in the I-beam thickness. This action is taken to enhance the weight reduction gained from the connecting rod. The aims of this work are to ensure the repeatability resulting from the design of 3 mm I-beam thickness and the ability of the casting design to produce the 2 mm I-beam thickness. Solidification rates in thin wall casting are critical due to the differences in thicknesses in the product. It is also to analyze the effect of I-beam thickness on the compression load. Two types of I-beams, which differ in their thickness, 3 mm and 2 mm, were produced in the foundry scale. All the I-beams were characterized by their microstructure and compression load. The compression load was measured using the tensile method. The results of microstructure observations revealed that the microstructure in I-beam is different from the one in the end rod except for one casting position, while the result of compression load shows a similar value for average compression load between the 3 mm and 2 mm which fulfill the compression load requirement of connecting rod. The casting designs built in this research can produce thin wall ductile iron (TWDI) connecting rods that could stand similar load with the original one.

Research on Ultrasonic Phased Array Detection Technology for Internal Defects of Automobile Ductile Iron Components Based on Computer Technology

With the rapid development of automobile industry, ductile iron component has become one of the most important components, which is the core components in many aspects, such as engine crankshaft, wheel hub, etc., which will be subject to extremely complex loads. Therefore, the crankshaft R region is particularly prone to fatigue cracks, which requires us to continuously strengthen the internal defect detection technology. With the development of detection technology, conventional ultrasonic technology has been unable to meet the needs of society. Through electronic scanning and acoustic beam deflection focusing, we gradually improve the Ultrasonic phased array detection technology (hereinafter referred to as UPADT), which can better realize the detection of automobile ductile iron components. UPADT is a kind of ordered excitation to the beam element, which can realize the deflection and focusing of the sound beam [1]. By combining sector scanning, electron scanning and DDF, we can achieve more beam incident modes, which will have faster detection speed and more accurate sensitivity.

Microcracks Reduction in Laser Hardened Layers of Ductile Iron

A study of surface hardening of Ductile Iron (DI) with and without austempering heat treatment was developed. The chemical composition of the material contains alloying elements such as Cu and Ni, that allow to obtain a Ductile Iron Grade 120-90-02, based on ASTM A536, which was heat treated to be transformed to Austempered Ductile Iron (ADI). Specimens of 10 × 10 × 5 mm3 were obtained for application of surface hardening by Nd:YAG UR laser of 150 W maximum power. The parameters used were advance speed of 0.2 and 0.3 mm/s and power at 105, 120, 135 and 144 W; the departure microstructures were fully pearlitic in the samples without heat treatment, and ausferrite for austempered samples. Microstructural characterization of hardened samples was performed were analyzed and martensite and undissolved carbides were identified in the pearlitic samples, while in ausferrite samples it was found finer martensite without carbides. The depth of hardened surface to different conditions and their respective microhardness were measured. The results indicate that the surface hardening via laser is a suitable method for improving wear resistance by means of hardness increment in critical areas without compromising the core ductility of DI components, but the surface ductility is enhanced when the DI is austempered before the laser hardening, by the reduction of surface microcracks.

The Mechanical Properties of Ductile Iron at Intermediate Temperatures: The Effect of Silicon Content and Pearlite Fraction

The use of ductile irons in thermo-mechanically loaded components is increasing, necessitating more knowledge of material properties at intermediate temperatures. A study of the mechanical properties of ductile irons at intermediate temperatures was conducted, investigating the effect of different pearlite fractions along with silicon content tests in fully ferritic microstructures. The effect of the pearlite fraction and silicon content on tensile and yield strength was measured at different temperatures, from room temperature to 450 °C. Models of tensile and yield strengths were developed based on those measurements. These resulting regression models were tested with data from the literature. Such models can be applied in various design tools, such as FEM calculations and in the optimisation of thermally and cyclic loaded ductile iron components.

Microstructural Adjustment of the Degenerated Graphite Layer in Ductile Iron for Targeted Evaluation on the Fatigue Properties

Graphite degeneration is the most prominent microstructural defect in the casting skin of ductile iron. Induced by either sulfur or oxygen contained in the molding material, its occurrence can be observed in a large range of iron castings, having substantial negative influences on the mechanical properties, especially fatigue resistance. Previous investigations predominately focused on the influence of the degenerated graphite layer, while accompanying changes of the iron matrix were neglected. The superposition of these effects hinders the evaluation of casting skin defects in state-of-the-art design of ductile iron components. The presented solution utilizes an experimental procedure, which enables the production of specimens with specific, individual microstructural configurations in the casting skin. This approach is based on the application of a modified sand core coating. By adding sulfurizing additives to the coating and adjusting its binder content and viscosity, a predominately homogeneous degenerated layer of 0.5 mm thickness was obtained. Using specific heat treatment steps assured a fully ferritic or pearlitic iron matrix, isolating the degenerated layer as the main microstructural defect. Fatigue testing of these specimens will further enable the numerical evaluation of the fatigue resistance in dependence of the casting skin microstructure.

Analytical strength assessments of austempered ductile iron components

Abstract Austempered ductile iron (ADI) is a heat-treated ductile iron with improved tensile strength and toughness. Therefore, ADI is an interesting material for the construction of technical parts. However, for practical use, a strength assessment is necessary. An often-used option for an analytical strength assessment is the FKM-guideline. This guideline includes the strength assessment for steel, cast iron and aluminum materials, but it has not yet been especially investigated for ADI. In this work the use of the guideline for ADI is investigated. On the basis of experimental data, the accuracy of the guideline is examined and the limitations are discussed. Furthermore, the parameters that are used for the calculation in the guideline can be adjusted for the improvement of the accuracy of the strength assessment. In this way in particular, the forecast for shear stresses and the high strength materials can be improved.

Residual Stresses around Individual Graphite Nodules in Ductile Iron: Impact on the Tensile Mechanical Properties

Residual stresses in ferritic ductile iron castings have been studied for decades. However, little attention has traditionally been given to the local residual stresses which may arise in the microstructure as a result of the thermal contraction mismatch between the matrix and the graphite nodules during solid-state cooling. Recent synchrotron X-ray measurements performed by the authors have demonstrated that in the ferritic phase these local stresses can be in the order of 100-150 MPa, hence of the same order of magnitude as the material macroscopic yield stress. This suggests that they might have a significant influence on the mechanical properties of ductile iron components. However, no systematic research appears to have been conducted so far to investigate this aspect. The present work takes a first step in this direction by presenting an integrated theoretical analysis which addresses both the formation of these local residual stresses at the microscopic level and their role during mechanical loading at the macro-scale.

Study on The Effect Of Austempering Temperature On The Structure-Properties Of Thin Wall Austempered Ductile Iron

The Production of thin wall austempered ductile iron components can have strength-to-density ratios that approach those of cast aluminum, making it theoretically possible to apply austempered ductile iron in high strength light weight parts. Short term austempering treatment process was used to obtain thin wall austempered ductile iron castings. The samples of 2 and 3 mm thickness were austenitized at 900 °C for 30 minutes followed by holding at 350°C, 400°C and 450°C inoculated by Ce-Ca-Al-S-O-FeSi at 0.4% for 2, 5 and 10 minutes for each temperature. The austempered samples are comparatively harder than the as-cast ductile iron plates. The hardness also decreases with increase in austempering temperature for a given austempering time for thinner plates and for a thicker plates the hardness is more for the samples treated at 400°C than those treated at 350°C and 450°C for a given austempering time. The Yield strength and the ultimate tensile strength decreased for as-cast ductile iron and increased for thin wall austempered ductile iron samples with increase in plate thickness inoculated by Ce-Ca-Al-S-O-FeSi compare to Zr-Mn-Ca-Al-Ba-FeSi and Sr-Al-Ca-FeSi at 0.4%.

Grey relational analysis coupled with principal component analysis to optimize the machining process of ductile iron.

The strict specifications for specific applications of the ductile iron casting must qualify the defined standards with limiting tensile strength and the correct material composition limits. The undesired combinations of properties are reported during casting of ductile iron components because of the graphite presence as spheroids rather than as flakes. The design specific grades of ductile Iron comprising desired matrix microstructure can be produced by controlling the matrix microstructure with alloy additions around the graphite either by heat treatment or as-cast. The present research investigates the machinability of ductile iron grade EN-GJS-500-7and the development of model and optimized design for the major machining characteristic indexes viz. metal removal rate, cutting forces and surface roughness in turning process. The cutting parameters selected are cutting speed, feed rate and depth of cut. The grey relational analysis adopting grey relational grades as performance index is used to determine the optimal combination of cutting parameters. The set of experiments on the basis of response surface methodology (RSM) are employed in preparing the objective model to study the effect of the main turning parameters. Further principal component analysis is applied to calculate the weighting values corresponding to the selected machining characteristic indexes in order to determine their relative importance during the process. The results obtained from the confirmation experiments revealed that grey relational analysis coupled with principal component analysis is an appropriate approach and thus proposed to be a useful tool to improve the cutting performance in turning process.

Modelling and simulations of ductile iron solidification- induced variations in mechanical behaviour on component and microstructural level

The mechanical behaviour and performance of a ductile iron component is highly dependent on the local variations in solidification conditions during the casting process. Here we show a framework which combine a previously developed closed chain of simulations for cast components with a micro-scale Finite Element Method (FEM) simulation of the behaviour and performance of the microstructure. A casting process simulation, including modelling of solidification and mechanical material characterization, provides the basis for a macro-scale FEM analysis of the component. A critical region is identified to which the micro-scale FEM simulation of a representative microstructure, generated using X-ray tomography, is applied. The mechanical behaviour of the different microstructural phases are determined using a surrogate model based optimisation routine and experimental data. It is discussed that the approach enables a link between solidification- and microstructure-models and simulations of as well component as microstructural behaviour, and can contribute with new understanding regarding the behaviour and performance of different microstructural phases and morphologies in industrial ductile iron components in service.

The effects of local variations in mechanical behaviour – Numerical investigation of a ductile iron component

The effects of incorporating local mechanical behaviour into a structural analysis of a cast ductile iron component are investigated. A recently presented simulation strategy, the closed chain of simulations for cast components, is applied to incorporate local behaviour predicted by a casting process simulation into a Finite Element Method (FEM) structural analysis, and the effects of the strategy on predicted component behaviour and simulation time are evaluated. The results are compared to using a homogeneous material description. A material reduction method is investigated, and the effects of material reduction and number of linearization points are evaluated.The results show that local mechanical behaviour may significantly affect the predicted behaviour of the component, and a homogeneous material description fails to express the stress–strain distribution caused by the local variations in mechanical behaviour in the component. The material reduction method is able to accurately describe this effect while only slightly increasing the simulation time. It is proposed that local variations in mechanical behaviour are important to consider in structural analyses of the mechanical behaviour of ductile iron components.

Casting and stress-strain simulations of a cast ductile iron component using microstructure based mechanical behavior

The industrial demand for increased component performance with concurrent reductions in component weight, development times and verifications using physical prototypes drives the need to use the full potential of casting and Finite Element Method (FEM) simulations to correctly predict the mechanical behavior of cast components in service. The mechanical behavior of the component is determined by the casting process, and factors as component geometry and casting process parameters are known to affect solidification and microstructure formation throughout the component and cause local variations in mechanical behavior as well as residual stresses. Though residual stresses are known to be an important factor in the mechanical behavior of the component, the importance of local mechanical behavior is not well established and the material is typically considered homogeneous throughout the component. This paper deals with the influence of solidification and solid state transformation on microstructure formation and the effect of local microstructure variations on the mechanical behavior of the cast component in service. The current work aims to investigate the coupling between simulation of solidification, microstructure and local variations in mechanical behavior and stress-strain simulation. This is done by performing several simulations of a ductile iron component using a recently developed simulation strategy, a closed chain of simulations for cast components, able to predict and describe the local variations in not only elastic but also plastic behavior throughout the component by using microstructural parameters determined by simulations of microstructural evolution in the component during the casting process. In addition the residual stresses are considered. The results show that the FEM simulation results are significantly affected by including microstructure based mechanical behavior. When the applied load is low and the component is subjected to stress levels well below the yield strength of the material, the residual stresses highly affect the simulation results while the effect of local material behavior is low. As the applied load increases and the stress level in the component approaches and passes the yield strength, the effect of residual stresses diminishes while the effect of local mechanical behavior increases. In particular the predicted strain level is heavily affected by the use of local mechanical behavior. It is proposed that it is important to include both local mechanical behavior and residual stresses in stress-strain simulations to predict the true mechanical behavior of the component.

Incorporating predicted local mechanical behaviour of cast components into finite element simulations

A software which enables the incorporation of local variations in both elastic and plastic mechanical behaviour predicted by a casting process simulation into a Finite Element Method (FEM) simulation is presented. The software uses a piecewise linearization of the Hollomon or the Ludwigson equation to characterize plastic mechanical behaviour of the material on an element level throughout a component. The accuracy obtained in the linearization is investigated, and the performance of the software is studied using different input parameters. The applicability of the software is verified and demonstrated on a ductile iron component, and a simulation strategy for cast components denoted a closed chain of simulations for cast components is discussed.

Effect of Residual Stress in Ductile Iron Component on its Natural Frequency

In the paper four components of ductile iron cast in different stress status, including the cast status, the status of vibratory stress relief and the status of thermal stress relief with 3 months of the natural stress relief and 10 years of the natural stress relief, are selected.X-ray diffraction method is used to measure residual stress and experimental modal analysis is for measuring natural frequency. A quantitative relation between residual stress in ductile iron cast component and its natural frequency variation is obtained. Thus we provide a reference for using natural frequency to evaluate the macroscopic residual stress of ductile iron material component. The results show that the peak value variation of macro residual stress in ductile iron component have a logarithmic relation to its natural frequency variation, and same as the mean value variation in macro-residual stress and its natural frequency variation.

Wear Resistance of Powder Hard Metal Inserted Ductile Iron

A continuous effort is being devoted to study the feasibility of improving the wear resistance of ductile iron components through an insertion of a hard metal powder layer during the casting process. Tests have been run to evaluate the wear resistance of the inserted material, compared to a non inserted ductile iron. The tests have been run in accordance with ASTM G65-94, which specifies the so-called rubber wheel test. Three different kinds of material have been tested: a non inserted ductile iron, an inserted ductile iron in the as-cast state and an inserted ductile iron with a rectified surface. The tests have been run gradually; each test piece has been taken out from the test apparatus and weighted at different intervals, from 200 to 6400 wheel revolutions (or 0.1 to 4.4 km of sliding distance); the results obtained show that the non inserted ductile iron presents a loss of weight fifty percent higher than the inserted material. The analysis of the surface of the test pieces after the wear tests has been run under stereo and scanning electron microscopy. The non inserted ductile iron test piece surface has shown an uniform waviness with a wavelength around half a millimeter and under higher magnification much finer wear marks have been observed. The inserted ductile iron test piece surface has shown the same relief with half a millimeter wavelength but a significant difference has been noticed: the fine wear marks have been observed in the metallic matrix of the insert but they stop in the neighborhood of the tungsten carbide particles, leading the authors to propose that these hard particles remained unchanged until the metallic matrix supporting them has been sufficiently removed to cause the respective extraction; this behavior should explain the smaller weight loss rate of the inserted material.