Strength Of Cast Iron Research Articles

Study of the effect of differentiated cooling modes on the structure and mechanical properties of gray cast iron

The effect of the differential cooling regime on the structure and mechanical properties of gray iron castings is investigated. A technical solution has been developed for the differentiated change in the cooling rate of cast iron castings. An increase in the cooling rate during dendritic crystallization was achieved by blowing the mold with compressed air. To slow down the cooling rate in the interval of eutectic transformation, an exothermic carbon-containing additive, fuel oil M-100, was used. It is shown that the use of controlled cooling can significantly increase the tensile strength of cast iron without introducing additional alloying elements into the composition of cast iron.

Production of High-Quality Castings from Gray Iron by Differentiated Cooling in Iron Mould

The paper considers the possibility of improving the quality of gray cast iron castings by controlling the cooling rate of castings in a mold. It is shown that the use of differentiated cooling can increase tensile strength of cast iron by 12-16%

An Investigation of Effect of Tin (Sn) on Microstructures and Mechanical Properties of Gray Cast Iron

As the tensile strength of gray cast iron is low, it is tried to increase tensile strength by testing various alloying elements. The most preferred of these alloying elements was the copper element. However, it is known that copper increases both hardness and tensile strength by enhancing perlite ratio in microstructure. On the other hand, when tin (Sn) is used in trace amounts compared to copper, it has similar effects on hardness and tensile strength of cast iron. In this study, adding tin element of 0,03-0,06-0,09-0,12-0,15 % by weight in gray cast iron, its effect on tensile strength was investigated and the appearance of the fracture surfaces was examined. It was compared with two different gray cast irons containing 0.4% copper element and free of alloying elements. According to the tensile strength results, the highest tensile strength was observed to be 195 N / mm2 in the specimen number 6 containing 0,12% Sn. The lowest tensile strength was determined as 157 N / mm2 in the specimen number 1 which did not contain alloying elements. In SEM (Scanning Electron Microscopy) images, it is seen that the samples generally exhibit a brittle rupture behaviour. In some of the specimens with the addition of tin and copper, regional ductile rupture behaviours were observed.

Measurement Uncertainty in Tests of Cast Irons

Focusing on heritage structures, various non-destructive tests (NDT) or minor-destructive techniques (MDT) can be applied while the application of destructive testing is limited. The probabilistic models for tensile and compressive strengths of historic cast iron are developed on the basis of destructive tests (DTs) and MDTs, respectively. NDT results are critically compared with DTs. It appears that numerous uncertainties affecting estimated resistance can be treated by statistical approaches along with the semi-probabilistic verification method. Non-destructive hardness tests can hardly be used to estimate strength of cast iron and must be supplemented by destructive tests.

Поліпшення механічних характеристик сірих чавунів термообробкою та обґрунтування її параметрів

The article discusses the technology of heat treatment of gray cast irons in order to improve their mechanical characteristics by implementing a bainitic transformation of the metal matrix. It is proposed to use the environmentally safe technology of hardening “in two waters” to start the process of transformation of austenite of a gray cast iron matrix into bainite without using environmentally harmful baths with molten alloys or salts, and further complete or partial isothermal decomposition of austenite in air furnaces. This not only improves the environmental performance of the process, but also significantly reduces the cost of it. The definition of rational parameters of the process of heat treatment of gray cast irons was carried out using the method of planning and implementing a multifactor experiment. The adequacy of the results obtained as a result of measurements with the implementation of parallel experiments was checked using Student's criterion and satisfied the requirements, and also allowed to discard insignificant members of the regression equation. The regression model of the influence of process parameters on the hardness of thermally hardened cast iron was tested using the Fisher criterion, which showed its adequacy. Experimental studies to determine the factors that determine the strength of gray cast iron hardened to bainite made it possible to establish rational temporal parameters of heat treatment. It is shown that the exposure time in the furnace at 850 °C before cooling and the exposure time in the furnace with a temperature of 400 °C in the process of austenite decomposition should be limited to 30 minutes. The implementation of heat treatment technology with certain parameters to improve the quality of casting, mass produced at the plants of the region, allowed to increase the compressive strength of cast iron by 1.5 times, the surface hardness by 2 times, and the brand of cast iron to increase from SCH20 to SCH25—SCH30. At the same time, it was possible to reduce emissions of vapors of salts, metals and other products of the interaction of melts with the atmosphere.

Increasing the strength of grey cast iron by introducing of dispersed additives into the melt

The basic mechanisms of increasing the strength of alloys, including methods through the introduction of the melt coherent and incoherent crystallizing structural components of the alloy dispersed particles were considered. New data on the influence of ultrafine particles obtained from grinding wastes of tool steels (metal abrasive slime) and proposed as modifying additives on the structure and strength properties of gray cast iron are presented. The prevailing influence of metal component of metal-abrasive sludge on the properties of cast iron is revealed. The optimum amount of additives-modifiers were defined. The increase in the strength of cast iron mid 20 as a result of modification is equal up to 20%

High Temperature Strength of Cast Irons for Cylinder Heads

Hot strength and fracture mechanisms in high quality cast irons were studied, comparing the standard gray iron Grade 300, alloyed with Mo, typically used for cylinder heads in high power engines, with other two materials: one gray iron Grade 300, obtained through graphite refinement and one compacted graphite iron, Grade 450. In these last two materials, the strength increase was obtained by changing the graphite structure, not by hardening the matrix. The experimental results with tensile tests carried out up to 500 °C show that the different strengthening mechanisms, use of Mo or modification of the graphite structure, are both efficient for increasing the strength at room temperature as well as at high temperatures. The CGI has a lower strength reduction with temperature than the gray irons, which shows the significant impact of the compacted graphite shape in reducing the notch effect. These results show the enormous potential of CGI in cylinder heads for high-performance engines.

Strength analysis of lamellar graphite cast iron in the «carbon (C) – carbon equivalent (Ceq)» factor space in the range of C = (3,425-3,563) % and Ceq = (4,214-4,372) %

The object of research is the structural lamellar graphite cast iron, where the carbon equivalent (C eq ) is in the range of (4,214-4,372) % and the carbon content (C) is in the range of (3,425-3,563) %. The aim of research is to describe the distribution of values of tensile strength of cast iron series in the factor space C–C eq at a fixed level of Cr-Ni-Cu-Ti alloyed complex in narrow ranges. To achieve this aim, there are the next objectives. 1. Build a workable analytical description of the impact of the selected input variables on the tensile strength of cast iron. 2. Study the response surface and identify the most informative point of the factor space for further detailed investigation of the microstructure in these points. It is shown that polynomial regression equation provides forecast accuracy, exceeding the accuracy using a linear regression equation in 1,23 times. An existence of a saddle point is revealed on the basis of the canonical transformation of response surface. It is an informative indicator, which suggests that the respective values of the input variables C = 3,492 %, C eq = 4,28 % when the content of alloying elements , form a microstructure that guarantees the value of cast iron tensile strength TS = 203 MPa. In view of the resulting confidence interval, this value with a probability of 95 % is in the range of TS = (193-213) MPa. Metallographic microstructure description in the saddle point is important and can be obtained by the development of modeling results. It is noted that there is a fundamental opportunity to improve accuracy and obtaining more precise description of the response surface – due to numerical building of D-optimal plan or artificial orthogonalization of full factorial experiment , inside the considered in this work

Assessment of Cast-Iron Columns Using Analytical Models

The paper focuses on the assessment of cast-iron columns in industrial heritage structures. For cast-iron structures it is difficult to verify metallurgical composition and processing technology, which directly affect the geometry of cross-sections. The crucial issue of reliability of cast-iron structures is their brittle fracture in tension at higher slenderness ratios. The load carrying capacity of columns is affected by their stability and cast-iron strength in compression and tension. Outcomes of two recently proposed analytical models are compared with extensive experimental data and model uncertainty is quantified. It appears that the model is in a good agreement with experimental data and provides reasonably conservative estimates of load carrying capacity. Outcomes of the study may provide basis for foreseen improvements in calculating buckling coefficient according to ČSN 730038:2014.

Spall behavior of cast iron with varying microstructures

The spall strength of cast iron with varying microstructures has been investigated using plate impact at moderate speed. Stress history measurements were made with manganin stress gauges embedded between the back face of the specimen and a low impedance polycarbonate backing. Five separate cast irons were tested. Four of these consisted of gray cast iron with graphite in flake form, with three classified as Type VII A2 and the fourth containing a bimodal distribution of Types VII A4 and VII D8. The fifth casting consisted of ductile cast iron with graphite in nodular form, classified as Type I, size class 5. The spall strength for the Type VII A2 gray cast irons varied between 40 and 370 MPa, and that of the additional gray cast iron, between 410 and 490 MPa. The spall strength of the ductile cast iron fell within the range of 0.94–1.2 GPa. It is shown that the spall strength is linked to the damage level at the spall plane, where an increased level of tensile stress is required to generate higher levels of damage. Post mortem analysis was performed on the recovered samples, revealing the graphite phase to be the primary factor governing the spall fracture of cast irons, where crack nucleation is directly correlated to the debonding of graphite from the metal matrix. The average length of graphite found within a casting is linked to the material's strength, where strength increases as a function of decreasing length. The morphology and mean free path of graphite precipitates further govern the subsequent coalescence of initiated cracks to form a complete fracture plane. In cases where graphite spacing is large, increased energy level is required to complete the fracture process. A secondary factor governing the spall fracture of cast irons has also been linked to the microstructure of the metal matrix, with pearlite yielding higher spall strengths than free ferrite.

Experimental characterization of a Si–Mo–Cr ductile cast iron

High temperature-resistant ductile cast irons behavior is highly interesting for the manufacture of components, such as exhaust manifolds for automotive applications. In the present paper the temperature-dependent static, high cycle and low cycle fatigue behavior of a heat-resistant Si–Mo–Cr ductile cast iron (Fe–2.4C–4.6Si–0.7Mo–1.2Cr) is investigated. Tensile and high cycle fatigue properties, in terms of elastic modulus, yield stress, elongation at break, fatigue limits, and the stress-life Basquin’s curve parameters have been determined at room temperature, 160°C, 500°C and 800°C, thus covering the usual temperature range to which actual components, obtained with this kind of material, are subjected. The alloy showed good monotonic properties at low temperature, but showed to be fragile during fatigue tests, due to the high Silicon content in the alloy. At 500°C mechanical properties are still good, with a 40% decrease with respect to 160°C, and ductility is increased. The last temperature level of 800°C has caused a noticeable drop of the cast iron strength, due to softening and oxidation effects.

Behavior and response of lead-caulked bell–spigot joints in cast iron water mains

The annular space between bell and spigot joints for cast iron pipes installed between 1850 and the early 1960s in North America was typically caulked with lead. Lead was caulked unto place using hand-held or pneumatic hammers and special chisels. Historical anecdotal evidence suggests that some bells may have cracked during caulking, especially if the jointer was over zealous in hammering the lead in place or used pneumatic hammers with excessive pressure to produce a tight joint. This paper examines two mechanistic models, one linear and another non-linear, to estimate the levels of hoop stress induced in the bell as a consequence of lead caulking. Illustrative analyses of lead caulking joints in 16″ and 48″ diameter pipes show that the linear model tends to predict unrealistic high stresses while the non-linear model produced more realistic stresses. Tensile hoop stresses can reach as high as 25% of the tensile strength of cast iron if the joint caulker is over zealous in the hammering action. The non-linear model was also used to reproduce caulking-induced stresses in tests conducted on 20″ diameter pipes by Prior in 1935.

Effect of severe shot peening on microstructure and fatigue strength of cast iron

Effect of nanocrystalline surface obtained by severe plastic deformation on fatigue strength of nodular cast iron has been studied in the paper. Surface nanocrystallization has been applied by means of standard air blast shot peening equipment with particularly severe parameters compared to the usual ones used for similar classes of material. Microscopy observation, microhardness, surface roughness and X-ray diffraction measurements were carried out to characterize the treated surface of differently shot peened specimens. Rotating bending fatigue tests were performed to investigate the effects of process parameters on fatigue behaviour. The results indicate a sensible fatigue strength improvement obtained through application of severe shot peening with respect to conventional shot peening, notwithstanding the specimen’s very high surface roughness due to high energy impacts. The obtained results are critically discussed.

Hydrogen-Induced Ductility Loss in Cast Irons

Effect of hydrogen-charging was investigated with respect to the tensile properties of three types of cast irons: JIS FCD400, FCD450 and FCD700. In this study, hydrogen charging led to a marked ductility loss in all the cast irons. The thermal desorption spectroscopy and the hydrogen microprint technique revealed that, in the hydrogen-charged specimens, most of solute hydrogen was diffusive and mainly segregated at graphite, graphite/matrix interface zone and pearlite. In the fracture process of non-charged specimen, neighboring graphites were interconnected with each other mainly by ductile dimple fracture. On the other hand, in the fracture process of hydrogen-charged specimen, the graphites were interconnected by cracks. The difference in the fracture morphology between the non-charged and the hydrogen-charged specimens is attributed to the presence of diffusive hydrogen in graphite and graphite/matrix interface. During early stage of fracture process in hydrogen-charged specimen, the interspace between graphite and matrix is filled with hydrogen gas, which leads to the ductility loss of matrix in the vicinity of graphite. Even after the initiation of crack from graphite, hydrogen is continuously outgassed from graphite and supplied to the crack tip. Therefore, concerning the hydrogen effect on the strength of cast irons, a role of subsurface graphite as a “local hydrogen supplier” should be taken into consideration.

Based on the Calculation and Analysis of the Separator of the Strength of the Cast Iron Base

Pressure component of the magnetic base with gray cast iron strength analysis methods and intensity conditions the calculation there are obvious flaws and inadequacies. Test, analysis of this issue, the introduction of the internal friction, calculate and analyze the effective value of the internal friction angle φ to obtain a more accurate, more in line with the actual strength conditions

Investigation into the Spall Strength of Cast Iron

Abstract The spall strength of cast iron has been investigated by means of planar plate impact experiments conducted in a vacuum. A single stage gas gun was utilized to drive projectiles to velocities between 100 and 300 m/sec, resulting in low to moderate shock loading of the cast iron specimens. Measurement of the stress histories were made with the use of commercial manganin stress gauges that were imbedded between the back face of the cast iron specimen and a low impedance backing of polycarbonate. Spall strength values were calculated utilizing the measured peak stress and minimum stress pullback signals captured in the stress history. Spall Strength values were found to vary between 0.98 and 1.45 GPa for the cast iron tested. Post-Mortem analysis of recovered specimen has provided insight into the evolution of spall failure in cast iron and shed light on the varying nature of the spall strength values calculated. It was determined that the lower bound of strength values was associated with small scale micro-failure, while the upper bound values corresponded to complete spall fracture.

Investigation into the Spall Strength of Cast Iron

Abstract The spall strength of cast iron has been investigated by means of planar plate impact experiments conducted in a vacuum. A single stage gas gun was utilized to drive projectiles to velocities between 100 and 300 m/sec, resulting in low to moderate shock loading of the cast iron specimens. Measurement of the stress histories were made with the use of commercial manganin stress gauges that were imbedded between the back face of the cast iron specimen and a low impedance backing of polycarbonate. Spall strength values were calculated utilizing the measured peak stress and minimum stress pullback signals captured in the stress history. Spall Strength values were found to vary between 0.98 and 1.45 GPa for the cast iron tested. Post-Mortem analysis of recovered specimen has provided insight into the evolution of spall failure in cast iron and shed light on the varying nature of the spall strength values calculated. It was determined that the lower bound of strength values was associated with small scale micro-failure, while the upper bound values corresponded to complete spall fracture.

Investigation into the Spall Strength of Cast Iron

Abstract The spall strength of cast iron has been investigated by means of planar plate impact experiments conducted in a vacuum. A single stage gas gun was utilized to drive projectiles to velocities between 100 and 300 m/sec, resulting in low to moderate shock loading of the cast iron specimens. Measurement of the stress histories were made with the use of commercial manganin stress gauges that were imbedded between the back face of the cast iron specimen and a low impedance backing of polycarbonate. Spall strength values were calculated utilizing the measured peak stress and minimum stress pullback signals captured in the stress history. Spall Strength values were found to vary between 0.98 and 1.45 GPa for the cast iron tested. Post-Mortem analysis of recovered specimen has provided insight into the evolution of spall failure in cast iron and shed light on the varying nature of the spall strength values calculated. It was determined that the lower bound of strength values was associated with small scale micro-failure, while the upper bound values corresponded to complete spall fracture.

The Influence of Microstructure and Chemical Composition on the Strength of Cast Iron Used for Railway Vehicles

Generally, the shape of graphite and the contents of elements strongly affect the tensile strength of cast iron. In this study, hardness tests and tensile tests for the two types of gray cast iron were carried out. The test results showed the similarity in the hardness but considerable difference in the tensile strength between two materials. Microstructure analysis and chemical analysis were conducted to determine the cause for the difference in the tensile strength between the two types of cast iron. The experimental results showed differences in the microstructure and chemical composition between the two materials. B-type brake disk material(B-type) that had higher tensile strength includes flake, vermicular and spheroidal graphite, whereas A-type brake disk material (A-type) included only flake graphite in the structure. Nodularity of graphite in the B-type was higher than that in the A-type. Also, the B-type had the higher Si content and lower Mn content. In addition, the B-type had Cu, while the A-type did not. Therefore, we concluded that the difference in the strength between the two types of cast iron was due to the difference in the shape of the graphite and the contents of Cu in the cast irons.

Continuous Laser Process of Welding and Heat Treatment for Joining Cast Iron and Stainless Steel

Continuous process of welding and heat treatment using a laser is proposed. The process begins with the welding stage where the laser irradiates in pulse mode at the optimized power so as to minimize the heat affected zone (HAZ). Next, to improve the mechanical characteristics of the HAZ. The temperature during the heat treatment is controlled by the laser power, the scanning speed, and the number of laser scans. Therefore this is a continuous process completed in a short time. This process is applied in the joining of dissimilar materials (spheroidal graphite cast iron and ferritic stainless steel) that are used in the exhaust components of automobile engines. Observations of the weld specimen with a microscope showed the formation of high carbon hardened martensite in the HAZ of the cast iron. The ratio of the welding joint strength to the spheroidal graphite cast iron strength was 69% (343MPa). Then using the heat treatment, the martensite was transformed into troosetite. After the continuous processing (1 laser scan) the joint strength became 82% (408MPa). The trial weld of the car engine exhaust part passed the thermal fatigue test of the engine bench test.