Vermicular Graphite Cast Iron Research Articles

High Temperature Oxidation Behavior of High Al-Si Alloyed Vermicular Graphite Cast Iron for Internal Combustion Engine’s Hot-End Exhaust Components

High Temperature Oxidation Behavior of High Al-Si Alloyed Vermicular Graphite Cast Iron for Internal Combustion Engine’s Hot-End Exhaust Components

Surface Residual Stress and Friction Wear Behavior of Vermicular Graphite Cast Iron after Laser Remelting

Surface Residual Stress and Friction Wear Behavior of Vermicular Graphite Cast Iron after Laser Remelting

Characterization on vermicular graphite rate and tensile strength in vermicular graphite cast iron based on nonlinear ultrasonic technique

Ultrasonic techniques have been widely used to detect the percentage of vermicular graphite, defects, etc. in vermicular graphite cast iron. The linear ultrasonic velocity method is the main ultrasonic method for characterizing vermicular graphite rate and tensile strength in the current study, however, it is often easy to misjudge the vermicular graphite rate due to its insignificant variation. This study explores the feasibility of using the nonlinear ultrasonic technique (NUT) to characterize the vermicular graphite rate and tensile strength. Based on the longitudinal critically refracted (LCR) wave detection model, an experimental study to detect the vermicular graphite rate and tensile strength of vermicular graphite cast iron is carried out using the nonlinear ultrasonic harmonic method, and compared with the ultrasonic velocity method. The experiment results show that the relative nonlinear parameter of the LCR wave decreases along with the increase of vermicular graphite rate and increases along with the increase of tensile strength, and it has higher detection sensitivity and resolution than ultrasonic velocity by analyzing the obtained data. The increase in the acoustic nonlinearity parameter (ANP) is related to the increase in the number of grain boundaries in the microstructure. Therefore, the relationship among microstructure, ANP, and mechanical properties of vermicular graphite cast iron can be established, and it’s promising that a new approach might be developed for quickly detecting the vermicular graphite rate and corresponding tensile strength with the NUT.

INVESTIGATION OF MICROSTRUCTURE AND MECHANICAL PROPERTIES PRODUCED BY USING THERMAL ANALYSIS IN THE PRODUCTION OF CAST IRON MATERIAL WITH VERMICULAR GRAPHITE

In this study; microstructure and mechanical properties of Vermicular Graphite Cast Iron (VGCI) material in accordance with EURO6 standard were evaluated by using thermal analysis during the production of engine block. Production of this engine block was performed by ladle metallurgy method with a new production approach suitable for mass production in Erkunt Industry company. Thermal analysis technique was used during production as a production control tool. Samples taken from the block material produced were examined in order to analyze microstructural and mechanical properties. The study results showed that the engine block produced was liable to the standards in terms of chemical composition, structure and mechanical properties. It was determined that the conformity of the microstructure and mechanical properties to the targeted standards can be ensured by using thermal analysis technique. Some foreign (European countries) approvals have been obtained for the material produced.

A New Theoretical Method for Studying Effects of Microstructure on Effective Thermal Conductivity of Vermicular Graphite Cast Iron

To provide the basis for thermal conductivity regulation of vermicular graphite cast iron (VGI), a new theoretical method consisting of shape interpolation, unit cell model and numerical calculation was proposed. Considering the influence of the graphite anisotropy and interfacial contact thermal conductivity (ICTC), the effective thermal conductivity of a series of unit cell models was calculated by numerical calculation based on finite difference. The effects of microstructure on effective thermal conductivity of VGI were studied by shape interpolation. The experimental results were in good agreement with the calculated ones. The effective thermal conductivity of VGI increases in power function with the decrease in graphite shape parameter, and increases linearly with the increase in graphite volume fraction and thermal conductivity of matrix. When the graphite volume fraction increases by 1%, the thermal conductivity of nodular cast iron increases by about 0.18 W/(m·K), while that of gray cast iron increases by about 3 W/(m·K). The thermal conductivity of cast iron has the same sensitivity to the thermal conductivity of matrix regardless of the graphite shape parameter. The thermal conductivity of matrix increased by 15 W/(m·K) and the thermal conductivity of cast iron increased by about 12 W/(m·K). Moreover, the more the graphite shape deviates from the sphere, the greater the enhancement effect of graphite anisotropy on thermal conductivity than the hindrance effect of interface between graphite and matrix. This work can provide guidance for the development of high thermal conductivity VGI and the study of thermal conductivity of composites containing anisotropic dispersed phase particles with complex shapes.

Influence of FeS2 and FeSi75 in Double-Chamber Sample Cup on Thermal Analysis Curve and Graphite Morphology of Molten Iron

In the production of vermicular graphite cast iron, the allowable range of residual magnesium content in molten iron after treatment is very narrow, amounting to only 0.008%. Therefore, thermal analysis technology was used to quickly evaluate the vermiculation and inoculation level of molten iron at the furnace itself, thus allowing the molten iron to be adjusted in time. The additives in the sample cups play a crucial role in obtaining cooling curves with remarkable characteristics. In this study, either FeS2 or FeSi75 additives were added to one chamber of a double-chamber sample cup made of resin sand, in which the cavities of the double chambers were spherical with diameters of 30 mm. The thermal analysis curves of molten iron in the double-chamber sample cup were acquired using a double channel temperature recorder, and the solidified spherical samples were analyzed quantitatively. The influence of FeS2 or FeSi75 additives on both the cooling curves of molten iron and the graphite morphology were investigated. The experiment’s results indicated that when 0.05% FeS2 is added to one chamber of the sample cup, the cooling curve changes to the solidification pattern of gray cast iron. The continuous increase in the FeS2 additive has little influence on the shape of cooling curves, and the graphite changes form from vermicular to flaked. When the amount of FeS2 is increased from 0.05% to 0.10%, the resulting graphite changes from D-type and E-type to A-type and B-type. When the amount of FeS2 reaches 0.20%, the morphology of graphite is short and thick. With the increase in the amount of FeSi75 additive, the amount of spherical graphite in the sample cup increases gradually, and the vermicularity decreases gradually from 89% to 46%. With the increase in FeSi75 additive from 0 to 0.45%, we observed that the average diameter of graphite decreases from 23 μm to 19 μm and then increases to 22 μm. The eutectic recalescence temperature shows a decreasing trend, and the cooling curve gradually changes from a hypoeutectic to a eutectic pattern. The addition of 0.05% FeS2 or 0.45% FeSi75 to one chamber is more appropriate for a double-chamber sample cup with two spherical cavities with diameters of 30 mm. This lays a foundation for the optimization of additives when using the double-chamber sample cup for thermal analysis of vermicular graphite cast iron.

О теплопроводности высокопрочных чугунов с шаровидным и вермикулярным графитом при изотермической закалке

The results of studies of thermal conductivity of nodular and vermicular graphite cast iron in the temperature range of 25-950 C are presented. It was concluded that up to 700 C, the type of metal matrix, in the temperature range 700, has a significant effect on the distribution of the heat flow...950 C the matrix effect becomes insignificant and graphite is actively connected in the process, in particular the inclusion form

Effects of Vermiculariser, Inoculant and Copper Addition on Microstructure and Corrosion Properties of Vermicular Graphite Cast Iron

In this study, the microstructure and corrosion properties of Vermicular Graphite Cast Iron (VGCI) produced via different methods and parameters were investigated. VGCI was produced from a base ductile iron material using different proportions of vermiculariser and inoculant. Copper was added to a group of samples as an alloying element. The microstructures and corrosion properties of samples were investigated in saltwater media. The effects of production parameters on the microstructure and corrosion behavior were determined. It was observed that as the ratio of vermiculariser applied was increased, the vermicular graphite ratio and vermicularity was also increased. The matrix grain size decreased while the inoculant and pearlite phase ratio increased due to the addition of copper. In electrochemical corrosion studies, VGCI was superior in corrosion resistance compared to SGCI and addition of vermiculariser, inoculants and copper was found effective in improving the corrosion resistance of the VGCI material.

Surface evolution of vermicular cast iron in ultra-high temperature combustion with different single-pulsing duration

The key components in combustion chamber of high power density diesel engines are apt to be damaged rapidly under abnormal combustion. To investigate the surface damage behavior and evolution mechanism of vermicular graphite cast iron in unsteady combustion, a self-developed plasma thermal shock test method was adopted. And the effect of the single-pulsing duration (0.2, 0.5, 5, and 50 s) of combustion on reciprocating thermal shock characteristics was mainly studied. Results showed that as the sample with the longest loading duration (50 s) exhibited the highest mass gain rate (0.05 mg/s), thickness growth rate (0.096 μm/s), roughness (1.889 μm), and hardness (515 HV). The cumulative thickening and spalling of the oxide layer during the plasma impact is the main cause of the changes in ablation rate and surface roughness. And the bainite phase transformation in the heat affected zone increased the hardness of the material.

Different thermal fatigue behaviors between gray cast iron and vermicular graphite cast iron

Different thermal fatigue behaviors between gray cast iron and vermicular graphite cast iron

Microstructure and tribological properties of CrAlTiN coating deposited via multi-arc ion plating

Developments in engine technologies have led to reduction in engine volume and increase in engine power. Thus, valve seat ring components in engines should have high wear resistance. In this study, a high-performance coating on the surface of valve seat material was investigated. The CrAlTiN coating was prepared on the surface of vermicular graphite cast iron, a common material of valve seat ring, with a multi-arc ion plating technology. Experimental results showed that the distribution of crystal clusters was relatively uniform as bias voltage increased from − 100 V to − 400 V and large droplets appeared at low bias voltage. As bias voltage increased, the sizes and number of droplets decreased, and pits appeared. The increase of bias voltage was beneficial to the formation of new phase of CrAlTiN coating. At bias voltages of − 300 and − 400 V, the phase composition was mainly TiN, AlN, CrN, and small amounts of Al2O3, Cr2O3, Ti2O3, and Cr. The adhesion, nano-hardness, and elastic modulus of the coating increased and then decreased with increasing bias voltage. When the bias voltage was − 300 V, the maximum adhesion was 61 N, the nano-hardness was 26 GPa, and the elastic modulus was 268 GPa. Moreover, the lowest friction coefficient was observed (0.4). The wear mechanism of CrAlTiN at different bias voltages was abrasive wear.

The Effect of Sulphur Content on the Microstructure of Vermicular Graphite Cast Iron

The Effect of Sulphur Content on the Microstructure of Vermicular Graphite Cast Iron

Growth mechanisms of vermicular graphite in cast iron

To steadily produce high-quality vermicular graphite cast iron (VGI), it is essential to have a deep understanding of the growth mechanism of vermicular graphite. The morphology and microstructure of graphite in VGI were studied using various techniques, including both experimental and theoretical methods. An abnormal graphite structure with an anomalous layer distance of 6.60 Å was observed by transmission electron microscopy (TEM) imaging, which is approximately two times larger than the normal structure (3.40 Å). The theoretical simulations of possible trace elements added (approximately 34 different elements) to the graphite basal planes were studied and analyzed individually to understand the observed phenomenon and their effects on graphite growth. The theoretical calculations (6.56 Å) show good agreement with the experimental results (6.60 Å), which proves that the lattice anomaly is caused by Mg. The abnormal graphite was believed to be the remains of the transition state during the growth of graphite. Based on the investigation, a mechanism is proposed to describe the influence of Mg during the growth process of vermicular graphite.

Influences of dual-phased nanoparticles on microstructure, mechanical properties and wear resistance of vermicular graphite cast iron

Reinforced vermicular graphite cast irons were prepared by using aluminum precursor master alloy containing TiC-TiB2 nanoparticles. It was found that the vermicularity and amount of graphite increased by 15.0% and 16.6%, and grain size decreased by 32.9%. The yield strength, tensile strength and elongation were improved by 10.0%, 6.0% and 26.3% at a temperature of 20 °C, and 11.6%, 6.8% and 22.1% at a temperature of 150 °C. In addition, the wear volume loss was reduced by 18.0% by addition of the nanoparticles.

Research on Laser Cladding Co-Based Alloy on the Surface of Vermicular Graphite Cast Iron

To further improve the hardness of the laser cladding layer on the surface of the vermicular graphite cast iron, the structural parameters of the laser cladding Co-base were designed and optimized, and the properties of the clad layer were evaluated using optical microscopy (OM), scanning electron microscopy (SEM), energy spectroscopy (EDS), X-ray diffractometer (XRD), electrochemical workstation, and friction wear equipment. The results show that the average hardness of the molten layer of Ni and Co-based composite cladding layer is 504 HV0.5, which is 0.64 times that of the Co-based cladding layer due to the combined factors of Ni-Cr-Fe equivalent to the dilution of the Ni-based cladding layer to the Co-based cladding layer. Due to the potential difference of the Ni, Cr, and Co elements on the surface of the cladding layer, the self-corrosion potential of the Ni and Co-based composite cladding layer is 1.08 times that of the Co-based cladding layer, and the self-corrosion current density is 0.51 times. Laser cladding Co-based cladding layer has high corrosion resistance. Under the influence of plastic deformation and oxidative wear of the cladding layer of the Ni and Co-based composite cladding layer, the wear amount of the cladding layer of the Ni and Co-based composite cladding layer is less.

Ultrasonic flaw detection spectrogram characterization of vermicular graphite cast iron engine cylinder head

The defects formed in the manufacture of the vermicular graphite cast iron engine cylinder head seriously affect the operation of the engine, which is necessary to detect. Ultrasonic testing is a non-destructive testing method that has the advantages of quick response, high resolution, and high security. In this paper, various types of specimens are prepared corresponding to different types of actual defects in the vermicular iron cylinder head. An ultrasonic A-scan system was built to test the specimens. The short-time Fourier transform, the continuous wavelet transform, the empirical wavelet transform, and the empirical modal decomposition were adopted to transform the signals into spectrograms which were further analyzed to reveal the inherent features of defects. The results show that the short-time Fourier transform can be used to distinguish all the common defects comparing to other methods. Comparing to the time-domain waveforms, the transformed spectrograms provide clear time-frequency distribution and highlight the inherent characteristics of the signal.

Study on high-cycle fatigue fracture mechanism and strength prediction of RuT450

Fatigue failure is the most common failure mode of structural materials. In this study, the high-cycle fatigue properties at different temperatures, fracture surface morphologies and corresponding damage mechanisms of a widely used vermicular graphite cast iron RuT450 were investigated. It is found that the fatigue strength values are 150 MPa, 143 MPa and 108 MPa for room temperature, 400 °C and 500 °C, respectively. The decrease rate of fatigue strength is affected by the change of morphology. At high temperature, the proportion of pearlite decreases and graphite becomes blunt. In general, the cracks initiate from the graphite phase boundary and propagate through the pearlite lamellae. In addition, according to the change of matrix micro-structure and crack growth processes under different temperature conditions, and by the quantitative analysis of micro-structure, the effect of temperature can be transformed into related parameters of matrix. Based on the changes, a fatigue strength prediction model for vermicular graphite cast iron at different temperatures was proposed, which predicts the trend well.

Study on thermal fatigue behaviors of two kinds of vermicular graphite cast irons

Abstract Due to the good thermal stability and mechanical properties, vermicular graphite cast iron is widely used to make industry components. Many of them are inevitably impacted by alternating temperature load. Therefore, two kinds of vermicular graphite cast irons, RuT400 and RuT450, were employed to study the features of thermal fatigue crack initiation and propagation in different temperature ranges. And the relationship between the length of thermal fatigue crack and number of cycles were also analyzed. It can be found that the thermal fatigue properties between the two materials are obviously different because of different microstructures. At present testing temperatures, RuT450 has higher pearlite content, lower thermal crack growth rate, higher transition temperature. The grain boundary slide temperature of ferrite and transition temperature of pearlite have important influences on the thermal fatigue cracks of two kinds of vermicular graphite cast irons.

Intelligent recognition of defects in vermicular graphite cast iron engine cylinder head by ultrasonic testing

To detect and intelligently identify the defects of the vermicular cast iron cylinder head, defective casting samples were made corresponding to each type of the actual defects. We setup the ultrasonic testing system to examine the defective samples. The detected defect signals were processed to obtain the characteristic spectrograms of the defects, which were further sorted and classified into a sample database. An algorithm based on a convolutional neural network was proposed to identify the defects intelligently. A convolutional neural network model was established. The network structure and parameters were optimized. It shows that a neural network with 3×3 convolution kernel dimension, 3 convolution layers, 20 convolution kernels in each layer and a learning rate of 0.0005 can effectively identify the spectrograms of the defects. The results show that the identification accuracy of the proposed algorithm is 97.14%. The model meets the practical requirements of cylinder head defect detection. The detection efficiency has improved significantly.

Effect of h-BN on the turning performance of high-strength vermicular graphite cast iron

Hexagonal boron nitride (h-BN) is an excellent solid lubricant that can be used to improve the processability of difficult-to-cut materials. We tried to solve the processing difficulty of vermicular graphite cast iron (VGI) by adding 0.0144 wt% of h-BN micro-powders into VGI (tensile strength Rm ≥ 450 MPa). Then, we use coated cemented carbide tools (CCC tools, coatings TiC + Al2O3) to carry out the turning test on VGI. By analyzing the maximum wear maxVB of the flank face, the wear morphology characteristics of rake face, and the residue on rake face, the wear mechanisms of the tool are studied. Finally, the role of h-BN in the processing process is assumed and the Gray-Markov model of maxVB is modeled. It can be found that: when v = 100~200 m/min, the tool life of cutting VGI with h-BN (sample A) was twice that of cutting VGI without h-BN (sample B). In particular, when v = 200 m/min, the tool life of cutting sample A is as high as 8 min. It is shown that h-BN can make CCC tools have the same advantages as PCBN tools in cutting VGI. In cutting sample A, the wear mechanisms of rake face are abrasive wear, adhesive wear, and oxidation wear, and adhesive wear is the main cause of tool failure. Given the cutting speed, when t ≥ 2 min, the adhesive wear of the rake face in cutting sample A is slighter than that in cutting sample B. h-BN can effectively reduce the adhesive wear. The error of maxVB predicted by Gray-Markov model is Δ ≤ 1.25%, which can be used to analyze and predict the tool wear of VGI with h-BN.