Microstructure Of Ductile Cast Iron Research Articles

On the role of residual austenite in improving the complex of properties of ductile cast iron

This article is analyzing the prospects and ways to expand the field of applying ductile cast iron-high-strength cast iron in technology. Ductile cast iron occupies a special place among structural materials. With the same level of mechanical properties, having less specific weight than steel, it provides less weight of products in comparison with steel. This reduces the consumption of raw materials and energy resources in the manufacture and operation of machines and mechanisms. There is a positive effect both in terms of economy and ecology. In addition, ductile cast iron has better casting properties than steel. In recent years, scientists and engineers have focused their efforts on finding new ways to improve the complex of mechanical and operational properties of ductile cast iron. This will make it possible to expand the field of their application and obtain additional advantages. A very effective direction – obtaining bainite matrix and a great amount of stable austenite in the structure of ductile cast iron by heat treatment allows to realize martensitic transformation in the most loaded parts during their operation and thereby increases adaptability. In this case, in addition to the traditional type of heat treatment - one-stage isothermal hardening, the technology of two-stage isothermal hardening is actively implemented, which allows for providing more dispersed ferrite and more stable austenite in the structure. A fundamentally new approach to obtaining the favorable microstructure of ductile cast iron is the organization of a foundry and heat treatment complex that makes it possible to obtain the ferrite-austenite mixture in the structure of ductile cast iron directly from the cast state, bypassing a separate heat treatment operation

ASSESSING THE VOLUME FRACTIONS OF THE PHASES, NODULARITY AND NODULE COUNT OF SPHEROIDAL GRAPHITE CAST IRON USING IMAGEJ SOFTWARE

In this study, a simple method for assessing the microstructure of ductile cast iron by using a freeware digital image processing software is described. The method is applied to three different ductile iron grades to assess their ferrite, pearlite and graphite volume fractions as well as graphite nodularity, nodule count, nodule size. All specimens were found to show good nodularity (~ 88 % by area) with different graphite average size and perimeter morphology. The amount of graphite was also found to be similar (11±2 % by area) in all specimens. On the other hand, ferrite percentages were found as 85.8, 57.1, and 52.5 % respectively for ASTM A536 grades 60-40-18, 65-45-12, and 80-55-06. It was also found that among these three grades, the higher the pearlite content, the higher the hardness. The agreement with the standards confirms that quantitative metallography through image processing is a powerful tool in order to estimate the mechanical properties of cast irons.

Determination of susceptibility of cast iron with a predetermined chemical composition to shape properties and microstructure through bainitic transformation

.The problem of nanostructuring cast iron is hardly ever reported on scientific reports. Most of the research is undertaken in terms of steel nanostructurization. Bhadeshia states that to obtain a fragmented matrix of steel, the carbon content in the matrix must be at the level of 0.6% C. It should be noted that the carbon in the ferrite-pearlite matrix meets this condition, because the content of this element in the matrix is within the range of 0.7-0.9%. The authors of this work have attempted to evaluate the ability to shape the properties and microstructure of ductile cast iron as a result of not fully completed bainitic transformation, compared to the standard process of obtaining ADI cast iron. The tested material was characterized by a higher degree of alloying elements compared to the basic chemical composition of ADI cast iron. The aim of the work was to maximize the fragmentation of the cast iron microstructure by selecting a low temperature of isothermal transformation, i.e. 40°C above Ms temperature in the lower bainite range. The JMatPro program was used to determine the isothermal transformation temperature. Heat-treated cast iron was subjected to dilatometer tests to compare the results obtained from the computer program, microstructure research and hardness tests. Heat-treated cast iron was subjected to dilatometer tests to compare the results obtained from the computer program, microstructure research and hardness tests.

Sintered Fe-Mo-Si-C alloys with ductile cast iron microstructure

Sintered Fe-Mo-Si-C alloys, produced by admixing 4.0 wt.% silicon carbide to two different pre-alloyed powders with compositions of Fe-0.85Mo and Fe-1.5Mo, sintering at 1250 °C for 45 minutes and cooling in a vacuum furnace, showed a microstructure similar to that of a ductile cast iron. The microstructure of the sintered alloys was characterized by the bull’s eye structure consisting of a black particle surrounded by ferrite shell and harder shell of pearlite/bainite, respectively. With the influence of alloying element content in the pre-alloyed powders, the proportion of the harder shell, particularly the bainite fraction, increased with increasing molybdenum content. Due to the matrix hardenability via bainite formation by the molybdenum influence, tensile strength of the sintered alloys increased but elongation decreased with increasing molybdenum content.

A New Approach to Modeling the Ductile Cast Iron Microstructure for a Finite Element Analysis

In this article, a methodology for the generation of geometric models representing the microstructure of a ductile cast iron (DCI) is presented. This methodology is based on a series of image processing algorithms to extract the graphite nodules contours and the utilization of the Bezier curves to smooth the geometric models curves. For the contours obtained by the image processing stage and generated geometric models, the circularity is calculated using the circular shape factor index, in order to analyze the induced error through the discretization process by the image processing stage and the variation of the circularity as the design parameters of the geometric modeling change. On the other hand, the design parameters effect of the geometric models on the stress behavior in the microstructure, through a finite element analysis, is also analyzed. It is shown that as the Bezier curve degree increases, the circularity of the geometric models decreases, thus increasing the maximum stresses produced in the DCI microstructure. Further, it is also found that the number of interpolation points has a significant effect on the mechanical properties when the Bezier curves degrees are equal to 10 and 12 than for the lower degrees.

Numerical investigation of low cycle fatigue mechanism in nodular cast iron

The failure mechanism in ductile cast iron under static loading is nucleation, growth, and coalescence of voids. It is known from the literature that elastic–plastic porous materials under strain controlled cyclic loading show an increase of void volume fraction called void ratchetting effect. From this observation, we suggest that void ratchetting is the relevant mechanism for low cycle fatigue in nodular cast iron as well. The low cycle fatigue process in the microstructure of ductile cast iron has been simulated cycle by cycle using unit cell models. The strain-life approach for fatigue is followed in this work. The matrix material behavior is modeled as an elastic–plastic one. From the simulations, void ratchetting is identified as a potential mechanism of low cycle fatigue in nodular cast iron which finally leads to failure. The lifetime of different load ratio and different matrix material behavior is extracted from the simulations. The simulated strain-life curves are compared with experimental data from literature.

Influence of Boron on Crystallization and Microstructure of Ductile Cast Iron

AbstractThe objective of the research was to determine the influence of boron on the crystallization process and microstructure of ductile cast iron. In the case of ductile cast iron it is a vital issue because even as little as trace presence of boron changes the properties of ductile cast iron in a significant way. With the use of a new ATD-4 (TDA) tester and CRYSTALDIGRPAH converter it was possible to measure the crystallization process parameters of the same alloy with four different contents of boron in one mould. Four samples with different boron contents were extracted, their microhardness was measured and quantitative analysis of microstructure was conducted. Obtained results allowed to state that with increasing content of boron the amount of graphite precipitates decreases, the amount of pearlite precipitates increases, the shape of graphite precipitates deteriorates and hardness increases. It is also planned to perform additional testings with boron contents between previously tested values.

Automatic quantitative analysis of microstructure of ductile cast iron using digital image processing

Ductile cast iron is preferred as nodular iron or spheroidal graphite iron. Ductile cast iron contains graphite in form of discrete nodules and matrix of ferrite and perlite. In order to determine the mechanical properties, one needs to determine volume of phases in matrix and nodularity in the microstructure of metal sample. Manual methods available for this, are time consuming and accuracy depends on expertize. The paper proposes a novel method for automatic quantitative analysis of microstructure of Ferritic Pearlitic Ductile Iron which calculates volume of phases and nodularity of that sample. This gives results within a very short time (approximately 5 sec) with 98% accuracy for volume phases of matrices and 90% of accuracy for nodule detection and analysis which are in the range of standard specified for SG 500/7 and validated by metallurgist.

Numerical Analysis of Stress States for Graphitic Cast Iron Structures

The presented work is focused on the analysis of stress distribution around the graphitic particles in microstructure of ductile cast iron with the spheroidal shape of graphite (SGCI) and grey cast iron with the lamellar shape of graphite (LGCI). The analysis was made with help of the finite element method in the software system ADINA.v.8.6.2. On the basis of the real structure, the finite element method was used for creation of the model which was subsequently used for calculation of the distribution of stress in the material structure. The input data for numerical analysis were obtained on the basis of evaluation of the structure with help of image analysis. The numerical analysis proved that graphitic particles in the matrix cause the accumulation of stress and the distribution of given stress depends on the shape of the graphitic particles.

Effect of room-temperature compression on microstructure of ductile cast iron subjected to hot plastic deformation

The change in the microstructure of ductile cast iron subjected to hot plastic deformation has been investigated after the fracture of the samples induced by compression (upset forging) at room temperature. It has been shown that compression-induced tangential stresses cause shear deformation, which results in the shear fracture of test samples at an angle of 40°–50° to the longitudinal axis of a sample. It has been established that the fracture is accompanied by the formation of a narrow zone of severe plastic deformation of ductile cast iron, which is located on both sides of the major fracture. In this zone, the initial microstructure undergoes significant changes due to the plastic flow of the matrix and graphite inclusions.

Effect of hot plastic deformation on microstructural changes in cast iron with globular graphite

The effect of hot plastic deformation on the transformation of the primary (cast) microstructure of ductile cast iron with globular graphite (ductile cast iron) has been investigated. The results of metallographic (with the use of light and scanning electron microscopes) and electron microprobe analyses of experimental cast iron samples in the cast and deformed states have been discussed. It has been shown that an increase in the degree of plastic deformation from 20 to 80% brings significant microstructural changes in both the pearlitic-ferritic matrix and graphite inclusions of cast iron.