Specific Distribution of Thermal Effects of Graphite Forming Reactions in High-strength Cast Iron

The dependence of thermal effects of reactions in the formation of inclusions of vermicular and globular graphite is substantiated in the article. The calculation of thermal effects according to the heat of formation of reagents in cast iron and their dependence on the temperature factor is given. The distribution of temperatures and carbon content in the eutectic shell is shown, increasing the compact inclusion of graphite due to diffusing carbon from the melt through the austenitic shell.

SOME FEATURES OF ULTRASONIC TESTING OF CAST IRON OBJECTS WITH FLAKE AND GLOBULAR GRAPHITE USING NORMAL LINEAR PROBES WITH PHASED ARRAYS

Computer modelling of the acoustic characteristics of signals of direct normal probe with phased array (PFR) in the cast iron with flake and globular graphite was performed. As a result the form of acoustic pulses of a longitudinal wave, depending on the passed by wave distance and the values of attenuation coefficient for different models of cast iron was calculated. The main modeled characteristics of the probe include the directivity characteristic and the change in the amplitude of the signal along the acoustic axis. It is shown that the difference in the PFR directivity characteristics for cast iron with flake graphite of different models and steel is due to two factors – significantly lower longitudinal wave velocities in cast iron compared to steel and a decrease in its operating frequency due to attenuation. In this case, for cast iron with globular graphite, a small change in the width of the diagrams is due only to the lower speed of longitudinal waves in cast iron compared to steel. For cast iron with flake graphite model 3, the phenomenon of nonlinear attenuation due to a decrease in the frequency of the maximum of the signal spectrum during the propagation of a longitudinal wave in cast iron with a corresponding decrease in the frequency – dependent attenuation coefficient is established. Evaluation of the nonlinearity of attenuation for cast iron with globular graphite showed that it is very small. The influence of calculation of initial signal delays on the velocity of longitudinal waves in steel on the directivity characteristics in cast iron, decreasing with increasing focus distance, is established. It is shown that for cast iron with flake graphite there are cases when the direction of transmitting of PFR in cast iron is practically absent.

INVESTIGATION OF THE SPECIFICITY OF ULTRASONIC TESTING OF CAST IRON WITH GLOBULAR GRAPHITE USING LONGITUDINAL ELASTIC WAVES

On the basis of the previously developed model for estimating the attenuation coefficient of elastic longitudinal waves in cast iron due to their Rayleigh scattering on graphite inclusions, the influence of such attenuation for cast iron with globular graphite on the characteristics of signals with frequency spectra of different widths depending on the nominal pulse frequencies, cast iron models and the distance traveled by the ultrasonic wave is studied. Computer modeling acoustic channel for environment – cast iron with globular graphite for standard normal probes of two types for studying influence of such environment on characteristics real transmitting and registered signals at the ultrasonic testing. Comparison of results of calculations of spectrums and pulses of registered bottom signals with their experimental values for two samples of cast iron with globular graphite has shown an opportunity of use of the applied settlement model for description of the actual physical phenomena quite adequate for practice. Influence of attenuation of longitudinal waves in cast iron with globular graphite on the directivity characteristic of their radiation is shown on model of cast iron and duration of a pulse. The estimation of the relation of levels of a registered signal and structural noise for various reflectors and characteristics of controllable cast iron has shown performance of recommendations by I. N. Ermolov on reliable detection of a useful signal on a background of noise for thickness, before established experimentally. Features of DGS-diagrams for cast iron with globular graphite, caused by higher, than in steel, attenuation of longitudinal waves and a little smaller speeds of their distribution are marked.

NANOSTRUCTURAL PROCESSES OF MELTING AND MOULDING OF CAST IRON WITH GLOBULAR GRAPHITE

It is shown that melting and molding of cast iron with globular graphite are complex physical and chemical nanostructural processes. The major role in these processes is played by the centers of crystallization of dendrites of graphite, graphite nanocrystals, the dissolved and adsorbed oxygen. The role of the modifying ligature of FeSiMg is reduced generally to essential decrease of concentration of the adsorbed oxygen and an enrichment of fusion by the centers of crystallization of graphite dendrites.

The Study of the Role of Fullerene Black Additive during the Modification of Ductile Cast Iron

The use of fullerene black (FB) as effective modifying additive to cast iron is substantiated by its high potential. Research of nanoadditives to modifier has shown an increase in graphitization degree and the forming of favorable morphology of globular graphite. The results of microstructural analysis and tribological trials have confirmed an improvement of ductile cast iron’s structure and properties when treated with FB-additive.

Tribological Research of Properties of Heat – Treated Cast Irons with Globular Graphite

The contribution deals with the evaluation of tribological properties of materials: isothermally heat-treated cast iron ADI, heat-treated cast iron with globular graphite HTDI with sorbitic structure of the basic metal matrix and heat-treated steel C45. The aim of the research is to gain another knowledge for the application of materials in the condition where the loss of mechanical energy and the loss of material caused by parts wear are being appeared.