In the case of mining machines, tribocorrosion damage is often observed. This type of consumption is caused by the joint action of mining environment factors such as abrasive and water. The search for methods to counteract tribocorrosion is of great practical importance, but it must be combined with the knowledge of methods of forecasting the value of wear. This paper presents a model of prediction of tribocorrosive wear adapted to corrodible materials – ADI containing Ni and Cu, with the strength class of 800 MPa – and results of a two-stage study on the tribocorrosive wear. Presented results indicate a distinct effect of synergy between friction and corrosion in the total wear of ADI. The tribocorrosion tests confimed the adequacy of the model developed for the ADI.
In this study a group of selected transformation kinetics equations is applied to describe the isothermal ferritic transformation in austempered ductile iron (ADI). A series of dilatometric tests has been carried out on ADI at different temperatures. The obtained experimental data are utilized to determine the parameter values of the considered kinetic equations. It is found that the transformation kinetics models by Starink, Austin and Rickett are substantially more effective at describing the ferritic transformation in ADI than the much celebrated Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation. Furthermore, it is demonstrated that evaluating the kinetic parameters using the least squares method instead of calculating them from vastly used formulas can significantly improve the accuracy of the JMAK model’s predictions.
Studies were carried out to determine the effect of heat treatment parameters on the plastic properties of unalloyed ausferritic ductile iron,
such as the elongation and toughness at ambient temperature and at – 60 °C. The effect of austenitizing temperature (850, 900 and 950°C)
and ausferritizing time (5 - 180 min.) at a temperature of 360°C was also discussed. The next step covered investigations of
a relationship that is believed to exist between the temperature (270, 300, 330, 360 and 390 °C) and time (5, 10, 30, 60, 90, 120, 150, 180,
240 min.) of the austempering treatment and the mechanical properties of unalloyed ausferritic ductile iron, when the austenitizing
temperature is 950°C. The “process window” was calculated for the ADI characterized by high toughness corresponding to the EN-GJS800-10-RT
and EN-GJS-900-8 grades according to EN-PN 1564 and to other high-strength grades included in this standard. Low-alloyed
cast iron with the nodular graphite is an excellent starting material for the technological design of all the ausferritic ductile iron grades
included in the PN-EN-1624 standard. The examined cast iron is characterized by high mechanical properties stable within the entire range
of heat treatment parameters.
The study presented here is related with one of the components of a hybrid decision support system called CAPCAST (Computer Aided Process - CAST), developed under a research project at the Faculty of Metals Engineering and Industrial Computer Science, AGH University of Science and Technology. This is a module for rule generation to serve the knowledge base operating in an expert system. The scope of the system operation involves the selection of technological parameters for the manufacture of machine parts from ductile iron. However, it can be extended to include other materials and technologies.
Austenitization is the first step of heat treatment preceding the isothermal quenching of ductile iron in austempered ductile iron (ADI)
manufacturing. Usually, the starting material for the ADI production is ductile iron with more convenient pearlitic matrix. In this paper we
present the results of research concerning the austenitizing of ductile iron with ferritic matrix, where all carbon dissolved in austenite must
come from graphite nodules. The scope of research includedcarrying out the process of austenitization at 900o
Cusing a variable times
ranging from 5 to 240minutes,and then observations of the microstructure of the samples after different austenitizing times. These were
supplemented with micro-hardness testing. The research showed that the process of saturating austenite with carbon is limited by the rate
of dissolution of carbon from nodular graphite precipitates.
Ductile iron was quenched using two-variant isothermal transformation. The first treatment variant consisted of one-phase austenitization at a temperature tγ = 830, 860 or 900°C, cooling down to an isothermal transformation temperature of 300 or 400°C and holding from 8 to 64 minutes. The second treatment variant consisted of two-phase austenitization. Cast iron was austenitizied at a temperature tγ = 950°C and cooled down to a supercritical temperature tγ’ = 900, 860 or 830°C. Isothermal transformation was conducted under the same conditions as those applied to the first variant. Ferrite cast iron was quenched isothermally. Basic strength (Rp0.2, Rm) and plastic (A5) properties as well as matrix microstructure and hardness were examined. As a result of heat treatment, the following ADI grades were obtained: EN-GJS-800-8, EN-GJS-1200-2 and EN-GJS-1400-1 in accordance with PN–EN 1564:2000 having plasticity of 1.5÷4 times more than minimum requirements specified in the standard.
A mathematical model of austenite - bainite transformation in austempered ductile cast iron has been presented. The model is based on a model developed by Bhadeshia [1, 2] for modelling the bainitic transformation in high-silicon steels with inhibited carbide precipitation. A computer program has been developed that calculates the incubation time, the transformation time at a preset temperature, the TTT diagram and carbon content in unreacted austenite as a function of temperature. Additionally, the program has been provided with a module calculating the free energy of austenite and ferrite as well as the maximum driving force of transformation. Model validation was based on the experimental research and literature data. Experimental studies included the determination of austenite grain size, plotting the TTT diagram and analysis of the effect of heat treatment parameters on the microstructure of ductile iron. The obtained results show a relatively good compatibility between the theoretical calculations and experimental studies. Using the developed program it was possible to examine the effect of austenite grain size on the rate of transformation.
The paper discusses possible applications of the percolation theory in analysis of the microstructure images of polycrystalline materials.
Until now, practical use of this theory in metallographic studies has been an almost unprecedented practice. Observation of structures so
intricate with the help of this tool is far from the current field of its application. Due to the complexity of the problem itself, modern
computer programmes related with the image processing and analysis have been used. To enable practical implementation of the task
previously established, an original software has been created. Based on cluster analysis, it is used for the determination of percolation
phenomena in the examined materials. For comparative testing, two two-phase materials composed of phases of the same type (ADI
matrix and duplex stainless steel) were chosen. Both materials have an austenitic - ferritic structure. The result of metallographic image
analysis using a proprietary PERKOLACJA.EXE computer programme was the determination of the content of individual phases within
the examined area and of the number of clusters formed by these phases. The outcome of the study is statistical information, which
explains and helps in better understanding of the planar images and real spatial arrangement of the examined material structure. The results
obtained are expected to assist future determination of the effect that the internal structure of two-phase materials may have on a
relationship between the spatial structure and mechanical properties.
The objective of studies presented in this publication was structuring of research knowledge about the ADI functional properties and
changes in these properties due to material treatment. The results obtained were an outcome of research on the selection of a format of
knowledge representation that would be useful in further work aiming at the design, application and implementation of an effective system
supporting the decisions of a technologist concerning the choice of a suitable material (ADI in this case) and appropriate treatment process
(if necessary). ALSV(FD) logic allows easy modelling of knowledge, which should let addressees of the target system carry out
knowledge modelling by themselves. The expressiveness of ALSV (FD) logic allows recording the values of attributes from the scope of
the modelled domain regarding ADI, which is undoubtedly an advantage in the context of further use of the logic. Yet, although the logic
by itself does not allow creating the rules of knowledge, it may form a basis for the XTT format that is rule-based notation. The difficulty
in the use of XTT format for knowledge modelling is acceptable, but formalism is not suitable for the discovery of rules, and therefore the
knowledge of technologist is required to determine the impact of process parameters on values that are functional properties of ADI. The
characteristics of ALSV(FD) logic and XTT formalism, described in this article, cover the most important aspects of a broadly discussed,
full evaluation of the applicability of these solutions in the construction of a system supporting the decisions of a technologist.