Behaviour Of Grey Cast Iron Research Articles

Computational assessment of the microstructure-dependent plasticity of lamellar gray cast iron – Part II: initial yield surfaces and directions

In this paper, the initial multiaxial yield behavior of three different gray cast iron materials with lamellar shaped graphite inclusions is numerically investigated by means of the finite-element method. Therefore, volume elements including the real microstructure of the materials are loaded bi- and triaxially beyond macroscopic yield. The shape of the obtained yield surfaces are compared to the surfaces of four continuum models which, amongst others, are proposed in literature to describe the inelastic behavior of gray cast iron with lamellar shaped graphite inclusions. It is found that the presented continuum models and the macroscopic yield surfaces obtained with microstructure-based finite-element models deviate. Furthermore, the initial inelastic flow direction is computed at the onset of macroscopic yielding. The analysis show that the inelastic flow is normal to the yield surface.

Study on quantitative relation between characteristics of striature bionic coupling unit and wear resistance of gray cast iron

In order to improve the wear resistance of gray cast iron guide rail, striature bionic coupling units of different characteristics were manufactured by laser surface remelting. Wear behavior of gray cast iron with striature bionic coupling units has been studied under dry sliding condition at room temperature using a homemade linear reciprocating wear testing machine. The wear resistance was evaluated by means of weight loss measurement and wear morphology. The results indicated that there is a relationship between weight loss and the area of striature bionic coupling units and α: Δm=Δm0−0.0212S×cosα−0.0241S×sinα.

Effect of Compositional Changes on the Mechanical Behaviour of Grey Cast Iron

The effect of varied alloying elements onthe mirostructure hardness and tensile properties of gray cast iron has been investigated. 0.1wt%, 0.2wt% and 0.3wt% of ferro-silicon inoculants were added to the stream of the iron melt during tapping for uniform dissolution and later poured into prepared sand mould. The cast samples were prepared for metallographic analysis. Hardness and tensile test were determined with standard samples. Mechanical properties are shown to be a function of the matrix, graphite or carbide forms. The increase in inoculants addition increases the carbon equivalent, but the tensile and the hardness properties were found to decrease. Hardness properties decrease from 58.9HRC to 44.70HRC from un-inoculated to 0.3wt% inoculated grey iron respectively

Evaluation of Corrosion Behaviour of Grey Cast Iron and Low Alloy Steel in Cocoa Liquor and Well Water

Corrosion behaviour of cast iron and low alloy steel in cocoa liquor and well water was investigated. The average weight losses of the specimens were measured using digital weighing balance. The results showed that the weight losses of both cast iron and low alloy steel in both media increases with time. Corrosion rate of cast iron in cocoa liquor increases rapidly with time for up to 336 hours (1000 μm/yr), but in well water the rapid rate of corrosion only lasted up to 187 hours (1160 μm/yr) thereafter it continuously dropping until 264 hours (667 μm/yr) after which it remains constant. Low alloy steel corroded faster in cocoa liquor up to 264 hours (200 μm/yr), whereas the initial rapid corrosion rate only lasted up to 168 hours (180 μm/yr) in well water environment. The results revealed that low alloy steel exhibited better corrosion resistance in both media, with cocoa liquor been more aggressive. Thus, low alloy steel will be a better material for piping and pumping system in cocoa processing industries.

Lubricity effect of carbon dioxide used as an environmentally friendly refrigerant in air-conditioning and refrigeration compressors

Abstract Environmental concerns have increased the interest in alternative natural refrigerants for air-conditioning and refrigeration compressors. Carbon dioxide (CO2) or R744 is an attractive candidate to replace harmful hydrofluorocarbon refrigerants, which will need to be replaced in the near future due to their high global warming potential. In this paper the tribological behavior of gray cast iron in the presence of CO2 under unlubricated conditions was investigated. Specifically different regions of the CO2 pressure–temperature (P–T) phase diagram were studied to understand the role of pressure, temperature, CO2 mass, and the chemical interaction of gray cast iron with CO2, focusing on their impact on the friction and wear behavior. It was found that friction decreases significantly when CO2 pressure and temperature approach the gas–liquid transition in the P–T phase diagram, thus exhibiting a form of “superlubricity.” Through X-ray photoelectron spectroscopy it was found that an increase in CO2 pressure causes partial transformation of iron oxides into iron carbonates which have a positive effect on the tribological performance. The thickness of the tribolayer film, formed in the contact zone, was evaluated using Focus Ion Beam and it was found to be of the order of 0.5 μm.

Thermal and mechanical behaviour of grey cast iron and ductile iron castings using magnetic molding and lost foam processes

The magnetic molding process is an extension of lost foam process and uses an expendable pattern surrounded by steel shot bonded together by the action of an induced magnetic field. This paper presents the comparative results obtained from sand mold and magnetic molding processes for grey cast iron and ductile iron castings. Therefore, this paper reviews the factors involved in the production of suitable patterns and the magnetic mold and on the other hand presents the comparative microstructures obtained for grey cast iron and ductile iron castings. This study also describes the advantages and the characteristics of the magnetic molding process. The main factors involved in the magnetic molding process are also discussed.

Thermal fatigue behavior of gray cast iron with striated biomimetic non-smooth surface

In order to enhance thermal fatigue resistance of brake drum materials, gray cast iron samples with biomimetic non-smooth surface were processed by laser to imitate the alternately soft and hard structure of shell nacreous layer. The key feature of this biomimetic non-smooth surface is that some parallel striations with various spacing distribute on the smooth surface of sample. With self-controlled thermal fatigue test method, the thermal fatigue behaviors of smooth and non-smooth samples were investigated and compared. The results indicated that biomimetic non-smooth surface had a beneficial effect on improving thermal fatigue resistance of samples, and the resistance of non-smooth sample which has smaller spacing of striations is the best in the experiment. Function of non-smooth unit such as the resistance to initiation and propagation of thermal crack is the main reason for improved thermal fatigue property of gray cast iron.

Effects of the exposure to corrosive salts on the frictional behavior of gray cast iron and a titanium-based metal matrix composite

The introduction of increasingly corrosive road-deicing chemicals has created significant and costly problems for the trucking industry. From a tribological perspective, corrosion of the sliding surfaces of brakes after exposure to road salts can create oxide scales that affect friction. This paper describes experiments on the effects of exposure to sodium chloride and magnesium chloride sprays on the transient frictional behavior of cast iron and a titanium-based composite sliding against a commercial brake lining material. Corrosion scales on cast iron, whose compositions were analyzed by several methods, initially act as abrasive third-bodies. Then they become crushed, spread out, and behave as a solid lubricant. Owing to its greater corrosion resistance, the titanium composite remained scale-free and its frictional response was markedly different. No corrosion scales were formed on the titanium composite after aggressive exposure to salts; however, a reduction in friction was still observed. Unlike the crystalline sodium chloride deposits that tended to remain dry, hygroscopic magnesium chloride deposits absorbed ambient moisture from the air, liquefied, and retained a persistent lubricating effect on the titanium surfaces.

Effects of surface shape on thermal fatigue resistance of biomimetic non-smooth cast iron

According to the principle of bionics, the experimental samples with a biomimetic non-smooth surface were manufactured using a laser. Three kinds of shapes including ‘spot’, ‘striation’ and ‘lattice’, were chosen for forming the non-smooth surface. With the self-controlled thermal fatigue test method, the thermal fatigue behavior of smooth and non-smooth samples was investigated and compared. The results indicated that the biomimetic non-smooth surface had a beneficial effect on improving the thermal fatigue behavior of gray cast iron, and that the non-smooth sample with the lattice shape had the highest resistance to thermal fatigue. Compared to the base material, the non-smooth unit zone was characterized by the alteration of microstructure. The lack of the graphite phase, the enhancing of mechanical properties in the unit zone and the effects of thermal crack deflection are the main reasons for improving the thermal fatigue resistance of gray cast iron with the biomimetic non-smooth surface.

A STUDY ON THE FAILURE ANALYSIS OF CAST IRON BRAKE BLOCKS THAT ARE USED FOR RAILWAY APPLICATIONS

In order to clarify the cracking and failure behavior of gray cast iron brake blocks that are used for the railway applications, macro- and micro observations regarding the cracks and the micro-structure of the used brake blocks were examined. Three brake blocks, which have different degrees of hot spots and cracking during the actual application, were selected for testing. In addition, a thermal-mechanical coupled finite element analysis (FEA) was applied to calculate the temperature and the stress field in the brake blocks during braking. As a result, it was observed that surface cracks were initiated at the hot spots and propagated into the matrix. From the observation of dispersed graphites close to the crack path, it can be said that the deterioration of materials due to the frictional heat of braking made it easy to initiate cracks at the hot spot. The hardness of the brake block was recommended to be under 85 by the Rockwell B scale in order to prevent hot spots and crack initiation. From the FEA, the procedure for the occurrence of hot spots and cracks was successfully simulated by assuming the surface roughness on the slid surface of the brake block.

Construction of Equations of State for Semi-Brittle Materials by the Triaxial Test Data

The results are cited for the experimental and theoretical investigations into elasto-plastic behavior of gray cast iron. The constitutive equations are established for this material with allowance for internal friction and dilatancy.

Wear in metal/silicon nitride sliding pairs

Ball-on-rotating disc tests were conducted to assess the relative wear behaviour of various disc materials in contact with silicon nitride under lubricated environment at room temperature high load and high speed conditions. Some selected tests were also performed under unlubricated conditions for comparison. The discs were made of grey cast iron, Al-bronze, bronze, aluminium and stainless steel. The lubricant was commercial additive free mineral base oil having a viscosity grade of 68. The applied normal load ranged between 16 and 300 N. The sliding speed changed from 0.5 to 4.0 m/s. The behaviour of grey cast iron and Al-bronze in sliding contact with silicon was characterised by a decrease in wear with an increase in sliding speed. Bronze and aluminium experienced very high wear rates as sliding speed increased. Stainless steel exhibited high wear and also caused significant damage to silicon nitride. Severity of wear between stainless steel and silicon nitride increased with the speed. High wear occurred at both low and high sliding speeds, which were accompanied by high wear track temperatures on the disc surface. This phenomenon resulted in considerable wear on both mating surfaces.

Micro-structural characterisation and mould-filling behaviour of grey cast iron stirred in the semi-solid state

This paper reports progress made in semi-solid processing of cast iron, the development of globular microstructure in various grades of iron and improvements in the mechanical properties of cast products. An explanation on the filling mechanism and flow behaviour of semi-solid slurry into a cylindrical sand mould cavity is presented based on the theory of solid feeding, interdendritic liquid flow and mass feeding. Results of analysis on fill-volume, macro- and micro-structural features are discussed for the components made by pouring the semi-solid slurry at a low solid fraction of less than 0.15 into sand moulds. In the case of the cast components, a microstructure with highly globular primary particles is observed. Precipitated graphite appears globular as opposed to the flaky structure common in castings produced under conventional methods. Vickers hardness results show hardness values higher than those of conventional castings and a decreasing pattern is observed from the edge to the centre of components while the values increase with decreasing cross-sectional thickness of specimens.

Influence of surface roughness on friction and scuffing behaviour of cast iron under sparse lubrication

Friction and scuffing behaviour of grey cast iron as influenced by the surface roughness under sparse lubrication conditions is studied. The studies are carried out on a three-shoe-on-disc machine under the conditions of parallel sliding. The experiments were conducted at three oil supply rates of 0.10, 0.22 and 0.36 μg/cm 2 per contact obtained through a mist oiling system and with specimens of cast iron shoes of different roughness values, Ra, between 0.04 and 2.0 μm against a 0.55% C steel disc. In a step load procedure, the friction torque at the end of each load step and the scuffing load are the major parameters measured. Results of friction and scuffing behaviour as a function of roughness and oil supply rates have been discussed.

Modelling of the deformation behaviour of flake graphite iron under multi-axial cyclic loading

A model based on continuum theory for describing the cyclic deformation behaviour of grey cast iron under multi-axial loading is presented and compared with test results obtained from strain-controlled tension/torsion tests. The unsymmetrical stress-strain response of cast irons under tension and compression is modelled by taking into account the opening and closing of graphite flakes, the bulk stress of cast iron being directly related to the internal stress acting on the steel matrix. Predictions are compared with experimental results obtained from proportional and non-proportional biaxial tests. The method is simple yet able to describe the essential features of the deformation of grey cast iron, and can be easily integrated with existing elasto-plastic constitutive models.

Evaluation of the Mechanical Behaviour of Grey Cast Iron by Means of the Wedge-penetration Test

The maximum load in a wedge-penetration test is used to obtain the tensile strength of grey cast iron. This strength is internationally employed to classify the quality of these materials. In the present work, it is shown that a characteristic force-displacement curve can be associated with either the wedge-penetration test or the tensile test. This curve reveals a similar behaviour of the material during both tests. The newly-defined curve could be the basis of an easier and cheaper method to evaluate the fracture development of grey cast iron.

Relationship between Penetration and Solidification Behavior of Gray Cast Iron

Relationship between Penetration and Solidification Behavior of Gray Cast Iron

Wear tests of grey cast iron against ceramics

The rolling wear of grey cast iron, partially stabilized zirconia, SiC and Si 3N 4 against themselves in unlubricated contact was performed at room temperature. The wear behaviour of grey cast iron against each of the above ceramics was also examined, both unlubricated and lubricated with methanol at room temperature. It was found that the wear life, defined as the onset of severe wear, was highest for the wear of silicon carbide against itself and was approximately ten times that compared with the other materials in this study. The hardness of the ceramics had a strong influence on the wear of grey cast iron in unlubricated contact. The thermal conductivity of the ceramics also influenced the wear of grey cast iron in combination with ceramics when lubricated with methanol.

The role of the matrix graphite interaction in the tensile behaviour of grey cast iron

In grey case iron solidified by continuous casting, strain mechanisms appear to be the main contributions to the non-linearity of the recorded stress-strain curve of tensile test. A simple rheological model is presented here based on the localized plastic strain of the matrix and the progressive microcracking of the graphite flakes. In this model, graphite phase and metallic matrix are present in the form of elements submitted to simplified strain processes. A load-elongation behaviour of the model give a qualitative description of the macroscopical tensile behaviour of grey cast iron. This model shows that the presence of the graphite flakes has some effect in the tensile behaviour of the material. It would be possible to obtain quantitative information on the role of a given microstructural parameter concerning different strain mechanisms in grey cast iron submitted to tensile test.

The low-cycle fatigue behaviour of grey cast iron and its application to fatigue problems in diesel engine cylinder liners

Cracking of cast iron cylinder liners in some large railway diesel engines is identified as a high strain fatigue problem. A series of low-cycle fatigue tests on three cast irons is reported. An improved material, in which the cooling rate in the critical region of the cylinder liner is slower than normal, has been produced and is shown to be clearly superior to two cast irons used extensively in service. This superiority is due to an improved resistance to both fatigue crack initiation and propagation.