Strength Of Cast Iron Research Articles

A Model for the Effect of Microstructure on the Ultimate Tensile Strength of Cast Irons

AbstractThe aim of the present study is to elucidate the influence of individual microstructural parameters, such as pearlite fraction, nodularity, and eutectic cell size, on the tensile strength (UTS) of cast irons. The UTS model was built by integrating the rule of mixtures for each microstructural component, and the UTS was described as a function of the aforementioned factors. The UTS and the required microstructure parameters for the model calculation were obtained experimentally. In the model, two coefficients were introduced to quantify the influence of the eutectic cell size and the interaction terms for the mixed two components. These coefficients were determined through fitting the experimental data, and the model's accuracy was validated using data not included in the fitting process. The results exhibited reasonable agreement, confirming the model's reliability. The model, thus, offers insights into the influence of each microstructural factor on UTS and serves as a guide for designing alloys to achieve the desired UTS through microstructure modifications.

Power Density Analysis of Wind Turbine Main Bearing Units by Holistic Optimization of Material, Manufacturing and Design of the Main Shaft

Given the continuous increases in wind turbine (WT) rated power and size, the nacelle weight and logistic handling costs increases significantly. To support heavier nacelles, stronger towers are needed which again increases material costs, so a need for nacelle power density increase arises. One solution to this problem is to increase the power density of the cast or forged WT main shaft. The power density in cast main shafts is limited by the low tensile strength of cast iron. High tensile strength steels, which theoretically increase power density, are used in state-of-the-art forged main shafts. However, their inner shaft diameter is kept small to reduce drilling costs. Since the loads of WT main shafts are dominated by the bending moments of the rotors, a high section modulus corresponds to a high power density. Material near the centre of the shaft therefore decreases the shaft power density. Hollow forging combines high tensile strength steel with a variable inner shaft diameter, enabling shaft designs with increased power density. Additionally, the use of air-hardening ductile (AHD) steel eliminates the need for costly heat treatment if the wall thickness is thin enough. The paper presents a holistic system model for the predesign of main bearing units (MBU) considering various materials and manufacturing methods. The model enables a feasibility assessment of hollow forged main shafts by comparing the resulting MBU weights across a wide range of WT power ratings. The MBU is selected instead of solely analysing the main shaft to account for the bearing and bearing housing weights, which depend on the main shaft geometry. The results show increased MBU power density of up to 23% for hollow forged shafts compared to forged shafts of the same material. Furthermore, when the shaft is hollow forged from AHD steel, the increase is even greater, up to 52%.

Improving the technology of manufacturing cast brake drums in pink sand molds

The object of research in the paper is the production technology of casting «brake drum» from cast iron of the basic grade SCh20 according to GOST 1412-85 (DSTU EN 1561, EN-GJL-200). The existing problem is that due to the imperfection of the technological processes of manufacturing castings, final internal defects of a shrinking nature are possible. This can lead to a decrease in the strength and operational reliability of the drums, regardless of the chemical composition, which may meet the technical conditions and should provide the specified strength indicators according to the grade of cast iron. Based on the results of 3D modeling, it has been found that with the existing technology of manufacturing brake drum castings in one-time sand molds, final shrinkage defects are formed in the upper part of the casting. To eliminate this problem, a decision is proposed to increase the allowance for mechanical processing on the upper surface of the casting. The possible excess of the mass of the casting and excess consumption of the alloy that will occur when implementing this solution can be compensated by reducing the allowance on other surfaces based on their optimization by the method of dimensional chains and reducing the thickness of the casting wall. For this, a reduction in the carbon content in the alloy is proposed as a factor in increasing the tensile strength of cast iron. On the basis of 90 serial meltings in industrial conditions, the possibility of increasing the strength limit of cast iron by approximately 11 % by reducing the average carbon content in cast iron from 3.45 % to 3.4 % has been proven. The proposed solutions are the essence of improving the production technology of cast brake drums, which are produced by casting in one-time sand molds. The presented study will be useful for machine-building enterprises that have foundries in their structure, where iron is melted for the production of castings.

Контроль прочности серого чугуна электрографическим способом

The experimental procedure carried out on a test installation to determine the electrical resistance value in the process of crystallization of cast iron is presented. A scheme of a test installation using a measuring circuit based on the Wheatstone bridge circuit to determine the electrical resistance value of crystallized cast iron is given. Recording measured data over time allowed constructing a graphical dependence of the change in the values of specific electrical resistance during the crystallization of gray cast iron. Experimental data on changes in the values of the specific electrical conductivity of a sample of gray cast iron during crystallization and their relationship to the amount of supercooling of the melt of this alloy are presented. The obtained dependence made it possible to identify on the curve of specific electrical resistivity change under supercooling of cast-iron test sample those areas, which were exposed to the cast-iron melt supercooling. The ratio of the initial and final values of the electrical resistivity under supercooling of cast iron allowed calculating the values of the relative electrical resistivity. Measurements of cast iron strength have shown that they are functionally related to the value of the relative electrical resistivity of gray cast iron, determined by the degree of supercooling of the cast iron melt. The use of this method will make it possible to predict gray cast iron strength and will allow reducing the amount of castings defective in terms of mechanical properties and at the same time increasing foundry production profitability.

Mechanical properties prediction of ductile iron with spherical graphite using multi-scale finite element model

In this paper, using the multi-scale finite element method, the effect of graphite particles on the mechanical behavior of ductile iron has been investigated under tensile loading. For this purpose, taking into account the spherical geometric shape of the graphite phase and considering a specific volume fraction, these spheres are randomly placed in the whole body and a two-component composite material is created. As a next step, a micromechanical model of these materials is developed by defining the mechanical properties of the matrix and graphites as well as their interfaces. The mechanical properties of the matrix are simulated using the Ramberg-Osgood elastic-plastic model. By simulation in ABAQUS software and using nonlinear dynamic analysis, the effects of volume percentages and adhesion of graphite particles with matrix on the direct tensile load-displacement behavior of ductile iron were investigated. The results of experimental tests were used to verify the results of the numerical model. The weight percentage of graphite particles has a significant effect on the tensile strength and elastic modulus of these cast irons. The results show that with the increase in the amount of graphite particles, the tensile strength of cast iron increases up to a certain value and then reverses. With 21% graphite particles, the maximum tensile strength of ductile iron is 601 MPa. Compared with a pure sample of cast iron, the tensile strength increases by approximately 13.4% for this weight percentage of graphite particles.

Estimation of Anomalous Portion in Gray Cast Iron Using Non-Contacting Electromagnetic Sensor

The gray cast iron is used in many mechanical parts due to its excellent damping force, wear resistance and castability. Inspection of the tensile strength of this cast iron is important for quality assurance of the machine products. The areas of reduced tensile strength in the cast iron are defined as abnormal areas in the cast iron. The tensile strength of gray cast iron is affected by its microstructure. The gray cast irons with low tensile strength contain a high percentage of ferrite and a low percentage of pearlite. The electromagnetic properties of the cast iron are affected by the content of these components. In this paper, an electromagnetic sensor is proposed in which the tensile strength of the gray cast iron is measured from changes in these electromagnetic properties. The electromagnetic FEM analysis using a play model method and the verification experiment show that the abnormal part of the tensile strength can be estimated from the difference in the hysteresis magnetic curve and conductivity in the cast iron.

Effect of Mn Content on Fatigue Limit of Various Flake Graphite Cast Irons

In recent years, with the active use of Mn-containing high-tensile strength steels as an automotive body material, it has become increasingly difficult to recycle Mn-containing high tensile strength steel scrap as raw material to produce cast iron, due to the fact that Mn is known as an element promoting the chilling tendency of cast iron melt. Therefore, in this study, the effect of Mn on the fatigue limit of flake graphite cast iron was investigated for the purpose of increasing the strength of cast iron and recycling high tensile strength steel. Flake graphite cast irons with different Mn contents (0.5 mass % and 2.0 mass %, the carbon equivalent corresponding to FC200, FC300 and FC400 of JIS specification (G 5501)) were prepared for plane bending fatigue test.

Влияние комплексного модифицирования на структуру и свойства серого чугуна триботехнического назначения

Introduction. An approach based on the complex modification of cast irons makes it possible to improve its mechanical properties by changing the structure of the metal matrix, as well as the shape of graphite and its distribution. The aim of this work is to study the influence of alloying elements on the structure and mechanical properties of gray cast irons obtained for operation under friction wear conditions. Research methods. The paper describes the process of obtaining complex modified gray cast irons. Fractographic investigation of dynamically destroyed samples is carried out. Structure’s features of SCh35, ChMN-35M and SChKM-45 gray cast irons are studied. Tribological testing under sliding friction conditions is carried out. Results and its discussion. It is established that the complex modification of SCh35 gray cast iron with molybdenum, nickel and vanadium makes it possible to increase its hardness to 295 HB and tensile strength to 470-505 MPa. Alloying with nickel (0.4-0.7 wt.%), molybdenum (0.4-0.7 wt.%) and vanadium (0.2-0.4 wt.%) leads to a decrease in the interlamellar distance of perlite by 2 times, as well as to the metal matrix grain refining. The length of graphite lamellas of modified cast irons is reduced by 3-5 times. An additional effect on the tensile strength of cast iron is due to the alloying of ferrite with molybdenum and vanadium, which is fallen out along the boundaries of graphite inclusions. Alloying of ferrite with molybdenum and vanadium increases the level of its microhardness by 1.4 times in comparison with the α-phase of SCh35 serial cast iron. The results of tribotechnical tests of the designed materials are presented. Conclusions. It is established that the wear of specimens made of SChKM-45 cast iron is approximately 20-30% lower compared to cast iron SCh35 cast iron and 10-15% lower compared to ChMN-35M cast iron. Fractographic studies show that complex alloying with molybdenum, vanadium and nickel, contributing to the refining of pearlite colonies, leads to a decrease of the size of the cleavage facets.

Reserves of resource saving in the manufacture of brake drums of cargo vehicles

The object of research: cast iron grade DSTU EN 1561 (EN-GJL-200), used for the manufacture of brake drums for KrAZ trucks.
 Investigated problem: obtaining the effect of resource saving by minimizing the consumption of alloying elements, while maintaining a given level of mechanical properties of cast iron.
 The main scientific results: experimental and theoretical confirmation of the possibility of reducing the content of Cr introduced into the alloy to increase its strength, as part of the Cr:Ni alloying complex, was obtained. It is shown that a decrease in the Cr content from the upper range (0.34–0.48) % to the lower one (0.21–0.33) % does not affect the ultimate strength of cast iron (σb). The obtained values of σb for both ranges are statistically equal: σb =234MPa, Sσb =16.22 MPa for the upper range of Cr content and σb=240MPa, Sσb=19.86 MPa for the lower range of Cr content, where Sσb is the standard deviation of the tensile strength value. It is established that the hardness (HB) is also unchanged: the obtained values of HB for both ranges are statistically equal: HB213, SHB=9.1 for the upper range of Cr content and HB212, SHB=12 for the lower range of Cr content, where SNB is the standard deviation of hardness. At the same time, it has been statistically proven that the Cr:Ni ratio can be shifted towards lower Cr values – from Cr:Ni=2.2:1 in the existing technology to Cr:Ni=1.76:1 in the ones proposed in this study.
 The area of practical use of the results of the study: the results obtained can be used in machine-building enterprises specializing in the manufacture of hull cast iron parts with a foundry cycle. The adaptation of the proposed results to the actual conditions of the foundry production of implementing organizations will be minimal if they comply with the following criteria: cast iron grade, predominant or minimum casting wall thickness, temperature regime of melting and out-of-furnace treatment, ferroalloys and modifiers used.
 Innovative technological product: iron smelting technology for commercial vehicle brake drum castings that reduces production costs while maintaining a given level of mechanical properties
 The scope of the technological innovative product: technological regimes for producing cast iron for the production of cast brake drums for trucks.

Increasing the mechanical properties of structural cast iron for machine-building parts by combined Mn – Al alloying

The object of research in this work was cast iron for machine-building parts, alloyed with Al. The possibility of improving the mechanical properties of cast iron by choosing the optimal Mn – Al combinations, depending on the carbon content in the cast iron, was determined. The study was carried out on the basis of available retrospective data of serial industrial melts by constructing the regression equation for the ultimate strength of cast iron in the three-factor space of the input variables C – Mn – Al. The optimization problem was solved by the ridge analysis method after reducing the dimension of the factor space by fixing the carbon content at three levels: C = 3 %, C = 3.3 %, and C = 3.6 %.
 It was found that the maximum values of the ultimate strength are achieved at the minimum level of carbon content (C = 3%) and are in the range of values close to 300 MPa. In this case, the Al content is in the range (2.4–2.6) %, and the Mn content is about 0.82 %. With an increase in the carbon content, there is a tendency to a decrease in the content of Mn and Al in the alloy, which is necessary to ensure the ultimate strength close to 300 MPa. The results of the ridge analysis of the response surface also showed that at the upper limit of the carbon content (C = 3.6%), it is not possible to reach the ultimate strength of 300 MPa in the existing range of Mn and Al variation.
 All solutions are verified for the following ranges of input variables C = (2.94–3.66) %, Mn = (0.5–1.1) %, Al = (1.7–2.9) %.
 Graphical-analytical descriptions of the optimal Mn – Al ratios are obtained, depending on the actual content of carbon in the alloy, which make it possible to purposefully select the optimal melting modes by controlling the tensile strength of the alloy

Research on improving durability of high-strength spheroidal graphite cast iron gears by nitriding heat treatment

The vibration damping property of high-strength spheroidal graphite cast iron is higher than that of steel materials, and it is possible to reduce gear meshing vibration, which is effective in reducing noise in gear devices. This material is significantly stronger than conventional spheroidal graphite cast iron. However, the problem is that the fatigue strength is inferior at the as-cast material level compared to conventional railway gear materials. Gas nitriding can significantly improve the fatigue strength of cast iron. In this study, we report the results of material fatigue test and improvement of nitriding heat treatment property by adding alloying elements in order to determine the optimum gas nitriding treatment conditions for cast iron gears. Furthermore, we manufactured the nitriding gear for railway vehicles and this noise performance was evaluated by rotation test. The thermal strain of the gear due to the nitriding heat treatment is less than that of carburizing, and the noise is reduced by about 2 dB on average compared to the conventional material tooth grinding gear.

Study of Factors Affecting Tensile Strength of Grey Cast Iron

Tensile strength of a material is the capacity of material to withstand tensile force without failure. Tensile strength is important mechanical property of material which gives direction to use it for proposed application safely. It is very important parameter considered in designing sound product. Grey cast iron carries properties like high compressive strength, castable, good machinability, good abrasion resistance, high thermal conductivity, resist to expand under high temperature. Tensile strength of grey cast depends mainly on carbon content, steel scrap % used, inoculation, graphite morphology, cooling time. Present paper summarizes study of factors affecting tensile strength of grey cast iron. With the study of factors affecting the tensile strength of cast iron it is very helpful to achieve required tensile strength by controlling the factors affecting strength of the material. While studying and experimenting on the behavior of tensile strength, clear idea comes into the picture how the strength is affected.

On uniqueness of thermophysical properties and prospects of cast iron with vermicular graphite for internal combustion engines

The article is devoted to the problem of implementation new cast irons into mechanical engineering, namely, cast iron with vermicular graphite (CGI) for the manufacture of parts for engines operating under thermomechanical stress. The article presents the results of the analysis of the CGI modern situation. It is shown that the serial production of engineering products in the world began relatively recently due to the development of reliable technology of cast iron modifying for vermicular graphite (VG) only by the end of the XX century. The use of CGI in mechanical engineering in Russia is extremely limited mainly because of outdated inaccurate and even erroneous information about its properties. The data of own research of microstructure, thermal conductivity and strength of cast iron obtained with the use of modern methods and techniques of control are presented. It is shown that the thermal conductivity of CGI may significantly differ within the grades regulated by the obsolete domestic standard GOST 28394-89 which, inter alia, requires reworking for this reason. All investigated microstructures of CGI have thermal conductivity in the temperature interval from 22 °C to 300 °C varying within no more than 5 %. At high and irregular share of sphere graphite (SG) with temperature growth thermal conductivity can grow a little, with decrease of SG share its growth slows down, and since ~200 ºС it starts to fall. At a high share of VG more than 90 % the thermal conductivity starts to fall from ~100 °С, but by 300 °С the fall is no more than 10 %, which is much less than the fall in the same temperature range of the thermal conductivity of lamellar graphite iron (GI) more than 30 %. The difference in thermal conductivities between the perlitic gray cast iron and CGI with a low and medium share of SG already at temperatures higher than 200 °C becomes commensurate with the error of measurement, and at 300 °C practically disappears. At the same time, in the presence of a high SG share in the structure of CGI its thermal conductivity at 300 °С remains considerably lower than that of the perlitic gray cast iron, the difference being ~30 %.

Proračun jačine pitinga kod materijala od livenog gvožđa i legura bakra

An attempt is made to predict the pitting strength of cast iron and copper alloy materials from their compressive yield or compressive proof strength for a reliability of 99% at 107 load cycles. The compressive yield or compressive proof strength is related to the tensile strength of ductile cast iron and copper alloy materials by a proportionality factor. Two proportionality factors are used for brittle cast iron materials. The pitting strength formulation incorporates a nominal design factor at 99% reliability which is estimated from a probabilistic model based on the lognormal probability density function. Pitting strength estimates from the predictions are compared with those of American Gear Manufacturers Association (AGMA) estimates and data from other sources. The predicted values for gray cast irons had variances in the range of -11.28% to 25%. Ductile cast iron pitting strength estimates deviated from those of AGMA by -30.28% to 1.73% and 16.76% to 36.34% for Austempered ductile irons. The variances obtained for cast bronze were from 11.17% and 14.73%, but the sample size was small. These variances appear to be reasonable due to the many factors that can influence pitting resistance. Since pitting strength data for many grades of cast iron and copper alloys are not available (especially in the public domain), they may be estimated by the expressions developed in this study for initial design sizing. Also, the pitting strength of new cast iron and copper alloy materials could likewise be estimated for initial design sizing. This will eliminate long and costly contact fatigue testing at the initial design phases, which of course is necessary for design validation.

О РЕЗУЛЬТАТАХ ТЕРМОУСТАЛОСТНЫХ ИСПЫТАНИЙ ЧУГУНА И ОЦЕНКЕ ЕГО ДОЛГОВЕЧНОСТИ

The article notes that at present, despite numerous studies of thermal fatigue, the thermal fatigue strength of cast irons due to stresses in parts made of this material requires additional study. Issues of thermal fatigue strength are especially relevant for such heat-stressed parts of internal combustion engines of autotractor diesel engines as the cylinder head. Of particular importance for these parts in their design and restoration is the ability to predict thermal fatigue strength, which is the main criterion that determines their durability. The article describes an approach to solving the problem of predicting the thermal fatigue strength of cast iron parts based on the data on their stress state and the results of thermal fatigue testing of samples on a specially designed and manufactured installation. The setup consists of two massive plates mounted on racks, between which a sample with a hole was rigidly installed. During the tests, the sample was heated by a special annular furnace to a temperature of 550°C for two minutes, and then cooled with running water through the central hole. A sample bounded on both sides during heating and thermal expansion accumulated residual tensile stresses as a result of relaxation processes and, upon reaching critical values and the appearance of fatigue defects in the form of cracks, ruptured. The proposed mode quite accurately repeats the operating conditions of the heat-receiving surface of the cylinder heads in the area of the intervalve jumpers when changing the operating mode at rated power and subsequent engine shutdown. As a result of the tests, the curves of the number of cycles to failure depending on the achieved stresses were obtained and their approximation was carried out. On the basis of approximating expressions and dependences of "limited durability" under low-cycle loading of parts, the thermal fatigue strength of a part made of cast iron can be predicted when its stress state changes as a result of design changes or after restoration.

ON THE POSSIBILITY OF APPLYING A NEW PARAMETER OF THE PRIMARY STRUCTURE OF GRAY CAST IRON TO EVALUATE THE STRENGTH OF CASTINGS

The possibility of evaluating the strength of pearlite gray cast iron with lamellar graphite using the ratio of the area of the interdendritic eutectic phase to the perimeter of the primary austenite dendritic crystals was investigated. It is found that this parameter increases from 15,1 to 39,3 as the ultimate tensile strength of cast iron decreases from 300 to 180 MPa. The correlation coefficient for this relationship was 0.9.

Extrema of micro-hardness in fully pearlitic compacted graphite cast iron

ABSTRACT For improving the mechanical strength of cast irons, a fully pearlitic matrix is sought by alloying with tin, copper and manganese. This applies in particular to the compacted graphite irons considered here. While average macro- and micro-hardness values were similar for the four fully pearlitic alloys under study, it was found that high copper and low tin content showed some very high maximum micro-hardness values, significantly higher than the corresponding mean. Such values may be seen as hard points in the material that would certainly impair machinability. Discussion of the reasons for these extreme values opens directions for further studies.

Failures of the Cast-Iron Columns of Historic Buildings—Case Studies

Selected technical problems related to the rehabilitation of cast-iron columns in structures from the turn of the 19th and 20th century are discussed in the paper. Lack of contemporary standard regulations related to the design of cast-iron structures is a significant problem in the design works and experimental investigations on cast-iron columns are frequently required. The paper presents results of the tests concerning principal properties of cast-iron—strength and deformability. The historical design principles are discussed in the light of the results of experimental investigations. As it was demonstrated, the actual load-carrying capacities of cast-iron columns may exceed by several times the values resulting from the 20th century design rules. The conservatism of the design principles resulted, however, from the material uncertainties—lack of homogeneity and hidden defects of the cast-iron. Selected examples of failures of cast-iron columns from 19th-century structures such as post-industrial buildings and engineering structures are discussed. They resulted from errors made during adaptation works. The reasons for these failures and considered methods of repairing the structures are presented.

Pearlite Refining Strategies for Hypoeutectic Gray Cast Iron

Pearlite refining is one of the most used methods to increase the strength of cast irons, and it can be achieved using different strategies. In this work, three strategies to obtain pearlite refining were applied to a given hypoeutectic gray cast iron centrifuged in a coated steel mold: (1) increasing the Cu, Mo and Cr contents; (2) intensifying the cooling rate of the metallic mold; and (3) cooling of the cast iron with forced air. Strategies 2 and 3 aimed to increase the cooling rate during the eutectoid reaction. Then, four experiments were conducted: a reference experiment and other three applying separately the strategies above. Materials samples were characterized by optical metallography, chemical analyses, microhardness, pearlite interlamellar spacing measurements and tensile tests. The metallographic examination did not show any important change in the graphite morphology. The pearlite interlamellar spacing and microhardness were computed as distribution curves from at least thirty measurements in the materials matrices. These curves showed a decrease in pearlite interlamellar spacing and an increase in pearlite microhardness for the three materials in which the pearlite refining strategies were applied as compared to the reference material. The mean pearlite interlamellar spacings were reduced from 0.10 μm for the reference material to 0.07 μm, 0.08 μm and 0.08 μm for the materials in which strategies 1, 2 and 3 were applied, respectively. The UTS increased from 378 MPa for the reference material to 423 MPa, 418 MPa and 390 MPa for the strategies 1, 2 and 3, respectively.

Increase of strength of cast-iron cylinder liners of engines of road construction vehicles

Cylinder liners made of gray cast iron are quite widespread in the design of engines of road construction vehicles. The negative properties of this structural material include relatively low strength and high fragility. This increases the probability of both manufacturing and operational defects. Therefore, improving the performance of the considered parts is an urgent problem. A promising direction in this case is the use of chemical-and-thermal treatment. The aim of the work is to study the effect of chemical-and-thermal treatment of gray cast iron on strength. The paper investigates the strength of cast iron subjected to chemical-and-thermal treatment (thermal diffusion surface alloying). On the basis of experimental studies, the effect of the thickness of the hardened layer on the strength was studied. A numerical model is created in the Ansys software. The effect of the hardened layer on the strength of cylinder liners of engines of road-building vehicles is investigated.