Microstructure Of Cast Iron Research Articles

Influence of Niobium Addition on Microstructure and Machinability of High Chromium Cast Iron

High Chromium Cast Iron (HCCI) is mostly utilised in environments under severe abrasion and corrosion wear conditions, and research on this material with added niobium obtained positive results regarding wear resistance. The casting process has surface finish and dimensional accuracy limitations compared to machining processes. There are too few studies about HCCI machinability and no one about HCCI with niobium additions. HCCI machinability studies may allow new applications for this material when excellent surface finish and high dimensional accuracy are required. This study analyses the influence of 0.5% Nb addition on the microstructure and machinability of a HCCI alloy with 25.6% Cr and 3.2% C. The samples were heat treated and subsequently machined in dry cutting conditions. Annealing was used to facilitate the pre-machining of the samples, which were later quenched and tempered. Microstructure and hardness were analysed at each stage of the heat treatment. The material was machined after tempered using polycrystalline cubic boron nitride (pcBN) tools. The alloys solidified in the hypereutectic condition. The addition of niobium reduced the hardness and carbide volumetric fraction, increased the service life of the cutting tools in all tests, provided better surface finishing and modified the wear mechanisms.

Influence of Residual Elements Contained in Steel Scrap for the Production of Nodular Cast Iron

Abstract Nodular cast iron is a fundamental material used in engineering. It has unique properties and is one of the most produced materials in the world nowadays. The production of nodular cast iron involves melting of raw materials such as steel scrap, pig iron, machining returns and alloy irons. With the development of increasingly technological steels through the addition of chemical elements to meet a specific application, there is an increasing difficulty in acquiring steel scrap content low alloy for the production of nodular cast iron. The chemical elements present in the steel scrap favor the appearance of unwanted phases and particles. The present study evaluated the effect of the addition of the elements copper, chromium, molybdenum and nickel in levels between 0.50% w and 1.0% w in the formation of nodular cast iron microstructure. While nickel and copper were evenly distributed in the matrix, chromium and molybdenum formed carbides. In addition, chromium strongly favored the formation of perlite in nodular cast iron and molybdenum, the martensite.

Using Computer Microscopy Methods to Control the Microstructure of Malleable Cast Iron Product with Spherical Graphite

The method of identification of objects on images of the microstructure of cast iron with spherical graphite of the correct shape with uniform distribution is presented. Morphological analysis techniques were used to identify shrinkage pores and graphite inclusions in microstructure images. Geometric features of the shape of graphite inclusions were used as methods for identifying graphite, in particular, particle size analysis, which is widely used to identify various objects in computer microscopy. The computer analysis of the image was performed with the program ImageJ. To determine the pores against the background of graphite inclusions, two characteristics were used - the shape and size of the objects themselves. The pores, presented on the image, differ from graphite inclusions by a complex, fractal border and comparatively large areas. For the visualization of the research results, the combination of the graphite part with the calculation and analytical part was used. Such presentation of the results is the most significant and allows to perform the most correct evaluation of the graphitized cast iron microstructure in accordance with GOST 3443-87.

Localized Strain Analysis of Ce- and Mg-Treated Cast Iron under Uniaxial Compression

Cast iron exhibits a wide range of mechanical properties, depending on its microstructural features. The microstructure of cast iron consists of several microconstituents with different elastic-plastic behavior, making the strain non-uniform across the bulk material. To understand the individual effects of these microconstituents on the overall mechanical behavior, local strain analysis using digital image correlation analysis was carried out. Samples with two different compositions (varying cerium, magnesium and silicon) were processed at different solidification velocities in a Bridgman furnace. Sections of the directionally solidified samples were loaded under uniaxial compression to measure global and local strain behavior. Despite the variability of the microstructure, the stress–strain curves obtained by digital image correlation (DIC) were found to react in a well-controlled way to changes in solidification velocity. It was observed that high-strain failure (greater than 15%) was accompanied by local straining of the softer ferritic phase, but during low-strain failure, local straining was not prominent. Higher nodularities, due to higher solidification velocities, raised the compressive strength without affecting the toughness significantly. Higher percentages of carbides led to higher compressive strengths with corresponding losses in ductility. The continuity of the matrix was also found to play an important role in the behavior during compression.

Computer-aided Metals' Microstructure Analysis. Analysis of images featuring sample preparation defects

Authors return to the topic of the article presented at Graphicon-2019 and review the issues of recognizing material microstructure elements, most common problems, recognition errors, and resolving the issues. Authors present methods for reconstructing particle shapes after the removal of image artifacts and separation of touching particles. The article includes examples of applying developed algorithms for analyzing particles present in graphite microstructure in cast iron and for analysis of powder particles. The article also demonstrates the possibilities of applying quantitative analysis methods for images, including defects.

Heat Treatment Effect on the Microstructure and Tribological Behaviour of a High Chromium Cast Iron with 0.5% of Niobium

Heat Treatment Effect on the Microstructure and Tribological Behaviour of a High Chromium Cast Iron with 0.5% of Niobium

Simplified ResNet approach for data driven prediction of microstructure-fatigue relationship

The heterogeneous microstructure in metallic components results in locally varying fatigue strength. Metal fatigue strongly depends on size and shape of non-metallic inclusions and pores, commonly referred to as defects. Nodular cast iron (NCI) contains graphite inclusions (nodules) whose shape and frequency influence the fatigue strength. Fatigue strength can be simulated by micromechanical finite element models. The drawback of these models are the large computational costs. Therefore, we employ a data-driven machine learning methodology. More precisely, we utilize the simplified residual neural network (SimResNet) which was recently introduced by (Herty et al., 2020) to predict fatigue strength from metallographic data. For the training, we use fatigue data which is simulated with a micromechanical model and the shakedown theorem. The micromechanical models are derived from micrographs of nodular cast iron, respectively. The application of SimResNet shows a good performance to predict fatigue strength obtained through shakedown analysis of nodular cast iron microstructures. We present several test cases. The simplified character of SimResNet enables fast predictions of fatigue by microstructures, even in comparision to classical residual neural networks.

Numerical investigation of the variation of a uniformly dimensioned cast iron property using cooling channels

Cast iron is produced by pouring of smelted metals into a mould, and is differentiated from steel by the carbon content. Different types of cast iron are available, and the properties which are used for distinguishing one from the other are formed based on the chemical composition, liquid treatment, heat treatment, and the cooling rate. The cast iron microstructure is greatly dictated by the graphite size and matrix structure which is primarily influenced by the cooling rate. Cooling rates can make or mar the cast, and are usually varied either with the use of different mould materials or by segmenting the cast. A uniform dimensioned cast with varied properties across its span using the same mould material can be made with the use of cooling channels tailored into the mould. This study seeks to numerically investigate the use of cooling channels to vary the properties of cast iron using the finite element method of solution available in COMSOL Multiphysics. The flow of a cooling fluid through the cooling channels during casting led to different cooling rates across the cast span setting up a temperature differential, an indication of varied properties within it. The cooling rate was observed to be a function of the cooling fluid entry temperature. The properties of a uniformly dimensioned cast iron can be made to vary along its span with the use of a tailored cooling channel in the mould.

The results of the application of thermo-time processing and resonant-pulsating refining in the Siberian region of the Russian Federation

Currently, in the Siberian region of the Russian Federation, thermo-time processing of the melt and the technology of resonant-pulsating refining of metal are widely used. The article highlights the results of the development and implementation of thermo-time processing and resonant-pulsed refining to improve the properties of the metal. Thermo-time treatment, as a rule, is carried out in induction and electric arc furnaces. It was found that thermo-time treatment allows to significantly improve the quality of the metal, improve the mechanical properties of the products. Resonant-pulsating refining combines melt processing with argon purge and vibrational frequency spectrum processing. The impact of this type of metal blowing on the gas content, the microstructure of cast iron, its mechanical properties, and also the operational properties of the products obtained is evaluated. It was established that the strength properties of cast iron increased by 40-65 MPa, hardness increased by 20 to 30 HB, density -by 100-300 Kg/m3. In addition, it should be noted that the use of the technologies presented in the work can significantly reduce the harmful effects of phosphorus. The operational durability of cast iron products has reached the best domestic and foreign indicators. The developed technologies allowed the implementation to achieve the best performance in the industry with minimal cost. These technologies can be widely used in foundries, electric steelmaking and oxygen-converter shops.

Micromechanical modeling of the effect of stress triaxiality on the strain to failure of ductile cast iron

This paper presents modeling of the tensile and failure behavior of different nodular cast iron microstructures under variable stress triaxialities. The model is based on a Representative Volume Element (RVE) approach, which reproduces periodic stochastic distributions of nodules within a 3-D cell. Three cast iron matrices, from fully ferritic to fully pearlitic, are considered as representing the various nodular cast iron classes in relation to strength and ductility. Ductile damage and shear damage models are used for ferrite and pearlite, respectively. Several values of stress triaxiality are applied within the RVE. It is found that numerical results support experimental findings in relation to the local strain distribution and damage initiation and accumulation, reproducing macroscopic tensile responses with good approximation. As highlighted by experiments, triaxiality is found to have a strong effect on material ductility and void volume fraction growth.

The Effects of Austempering Temperature and Time on Mechanical Properties of Ductile Cast Iron Grade FCD450

The purpose of the study was to inspect microstructure, mechanical properties and impact toughness of ductile cast iron grade FCD450 produced by austempering process. The study focused on austempering parameter, which effected impact toughness of material at low temperature. The FCD450 was initially temperature austenized at 885°C (1625˚F) for 2 hours. Austempering was carried out at three different temperatures of 271°C (520˚F), 313°C (560˚F) and 357°C (675˚F). The austempering temperature were varied at 1.5, 2.5 and 3.5 hours. X-ray diffraction was showed that the austempered ductile cast iron (ADI) microstructure consists of austenite and ferrite. The results showed that when austempered at 357°C (675˚F) for 2.5 hours has highest hardness and impact energy at low temperature. The dimple ductile fracture of ADI fracture surfaces was revealed by scanning electron microscope (SEM).

Effect of Nitrogen Addition on Microstructure and Mechanical Properties of As-Cast High-Chromium Cast Iron Containing Niobium

This work was conducted to study the effect of four different nitrogen additions on as-cast microstructure, hardness and impact toughness as well as abrasion wear resistance of high-Cr cast iron containing niobium. The results showed that as nitrogen content increased, the austenitic dendrites matrix became less elongated and the eutectic M7C3 carbides were gradually refined in size. EDS analysis demonstrated that N element preferentially accumulated in the NbC particles and substitute part of C to form Nb nitrides (NbN) or Nb cabonitrides Nb(C,N). Such nitrides or carbonitride particles were relatively hard compared to matrix and eutectic carbides resulting in an increase in hardness with increasing N content. The optimum toughness (12 J) was obtained for the iron containing 0.093 wt%N with an enhancement of 33%. The wear resistance increased with increasing N addition, in which the maximum wear resistance was reported for the alloy containing 0.15 wt% N. There was an enhancement in wear resistance of 47% by adding 0.15 wt%N to HCCI at low applied load (30 N), and it decreased to 17.5% at high applied load (60 N). Hence, the highest wear resistance and moderate toughness of HCCI could be achieved by adding 0.15 wt%N.

Effect of cast iron microstructure on adherence of an epoxy protection

ABSTRACT To study the influence of the microstructure of cast iron on the adhesion of an epoxy coating, ferritic, pearlitic and austempered samples were prepared in as-received, polished and oxidised states. A pull-off test (dry adhesion) was performed before immersing in water while the cross-cut test was made after 24 days of exposition in distilled water (wet adhesion). X-rays were combined with optical microscopy (LOM) and scanning electron microscopy (SEM) for surface analysis. The adhesion of the epoxy coating on the cast iron surface firstly depends on the roughness of the surface; polished samples showed high adherence by comparison with as-received samples. On the oxidised samples, the surface oxide significantly improves the adhesion of the coating in both dry and wet states for all three sample microstructure. The presence of carbide in the structure was observed to decrease adherence.

Influence of Niobium Content on the Mechanical Properties and Abrasion Wear Resistance of Heat-Treated High-Chromium Cast Iron

The effect of niobium addition up to 3.4 wt% on the microstructure and mechanical properties of heat-treated high-Cr cast iron containing 13.5 wt% Cr was investigated. Niobium addition caused small hard NbC particles to precipitate within the proeutectic austenite which impede the development of austenite dendrite growth resulting in structure refinement. This austenitic matrix upon heat treatment changed to mainly martensitic one with some retained austenite and reinforced with small amounts of secondary carbides of M7C3 type. It was found that the hardness increased with increasing Nb content due to structure refinement and precipitation of hard NbC particles. These particles caused a depletion of carbon in the austenite matrix and thus most of the austenite was transformed to martensite upon heat treatment. The highest impact value was obtained for the base alloy without Nb addition which could be attributed to the high amount of retained austenite. The high-Cr cast iron alloyed with Nb in the range of 1.55–3.4 wt% showed an increase in hardness without any deterioration in toughness. The wear resistance was significantly enhanced by the presence of hard NbC particles up to 2.52 wt% Nb. Exceeding this optimum amount of addition leads to agglomeration of NbC particles and hence deterioration of the wear resistance through three body abrasion wear mechanism.

Вплив технологічних параметрів ЛГМ-процесу на мікроструктуру сірого чавуну, модифікованого дисперсним феросиліцієм у порожнині ливарної форми

Вплив технологічних параметрів ЛГМ-процесу на мікроструктуру сірого чавуну, модифікованого дисперсним феросиліцієм у порожнині ливарної форми

Scientific and technological bases of ladle processing by resonant-pulsating refining

Currently, the technology of resonant-pulsating metal refining (RPR) becomes more widely used for refining cast iron and steel. The paper highlights the stages of development of resonant-pulsating refining to improve the quality of products and presents the results of physical and mathematical modeling of metal refining with nitrogen and argon. It is established that physical modeling gives a good qualitative picture of the processes of metal blowing in the ladle by tuyeres of various designs. Mathematical modeling allows us to quantify the optimal parameters of blowing with argon and nitrogen in ladles of different capacities, depending on the ladle size and on diameters of tuyere and pulsator. The influence of this type of metal blowing on gas content, microstructure of cast iron, its mechanical and performance properties of products made of it was evaluated. It was found that the strength properties of cast iron increased from 91 - 105 to 130 - 170 MPa, the hardness increased from 137 - 150 to 163 - 182 HB, and the density also increased from 6890 - 6900 to 7000 - 7200 Kg/m 3 . In addition, it should be noted that the use of the presented technology can significantly reduce the harmful effects of phosphorus. The operational stability of products made of blast-furnace cast iron has reached the best domestic and foreign indicators. This technology has also proved to be effective in continuous casting of steel on high-grade casters. It made it possible to achieve the best performance in the industry with minimal costs during implementation. The developed technology is easy to implement on existing steel non-furnace processing units and on continuous steel casting machines. It can be widely used in foundries, electric steelmaking and oxygen-converter shops.

Distance map based micromechanical analysis of the impact of matrix heterogeneities on the yield stress of nodular cast iron

A method to construct 3D representative volume element (RVE) models of the nodular cast iron microstructure that accounts for the presence of heterogeneities in the matrix is proposed. The main advantage is the possibility to generate a wide spectrum of realistic distributions of the matrix heterogeneities in a simple and fast way. The method takes advantage of the fact that the spatial distribution of some of the matrix heterogeneities is intrinsically connected to the distribution of the graphite nodules, due to the nature of the solidification process. Accordingly, the graphite morphology is reconstructed first via X-ray computed tomography and subsequently used to estimate the distribution of the pearlite and of the Si micro-segregation – considered as case studies – by means of dedicated distance functions. The obtained 3D models are used to show that the spatial variation in the matrix plastic properties associated with the Si micro-segregation is not expected to influence the material yielding behavior significantly. In addition, it is shown that when the matrix pearlite content increases for a fixed overall C concentration, the corresponding decrease in the nodules’ volume fraction can account for as much as 1/3 of the obtained increment in the material macroscopic proof stress.

Ductile Cast Iron Microstructure Adjustment by Means of Heat Treatment

Ductile Cast Iron Microstructure Adjustment by Means of Heat Treatment

Mechanical behavior and microstructure of hypereutectic high chromium cast iron: the combined effects of tungsten, manganese and molybdenum additions

The combined effects of W, Mn and Mo additions on the microstructure and properties of a hypereutectic high chromium cast iron (HCCI) were studied. The results indicated that W was distributed uniformly in the matrix and carbides. The W and Mo addition promoted the formation of M2C and M6C carbides. When 13wt.% Mn was added to the samples, the solubility of Mn in the matrix increased the stability of the austenite phase and improved the toughness of the materials. Moreover, Mn and Cr form the M7C3 carbides in hypereutectic HCCI. A large number of (Fe, Mn)3C carbides were produced in the matrix during the later stage of solidification, which significantly improved the wear resistance of the matrix. When the amount of W, Mn and Mo added was 6wt.%, 15wt.% and 4.2wt.%, respectively, the HCCI exhibited the best performance herein. The addition of 6wt.% W led to an increase in the average hardness of the samples and the microhardness of carbides of up to 57.5 HRC and 1680 HV, respectively. Similarly, it is worth mentioning that the impact toughness of the 6% W sample reached 6.35J/cm2, and the mass loss of the Cr16 and 0% W samples was 1.43 and 1.23 times that of the 6% W sample, respectively. The wear resistance of the 6% W sample showed no significant change before and after heat treatment. The combination of W, Mn and Mo simultaneously improved the wear resistance and impact toughness of the hypereutectic HCCI.

Microstructure and Hardness of Gray Cast Iron as a Product of Solidification in Permanent Mold

Molds of metal are widely used in the casting process. The cooling rate in solidification of castings product with metal molds on the outer side and inner side is different. Therefore, sizes and types of phase will be also different. This study aims to investigate the microstructure andhardness of gray cast iron. To realize this research, the gray cast iron melting process was carried out in an induction furnace. Melted gray cast iron was poured into a Ferro Casting Ductile mold that has been through a preheating process at a temperature of 300 o C. The gray cast iron is then tested for composition, microstructure and hardness. The test results show that the part containing morecementite phase will be harder.