In this work, the effects of 75 mm thick cast iron, (casting mould YIV) composition (Cu) and heat treatment were investigated on the microstructure and mechanical properties (hardness, elongation, tensile strength, yield strength) of ductile iron castings. As a result of adding Cu, the amount of pearlite is at 80% reduces of amount of ferrite. Normalizing of non-alloy cast iron increases the amount of pearlite to 70%. It also, increases tensile strength (659 MPa) and hardness (248 HB). Studied metallographic crossections were made from the grip sections of the tensile specimens. The structure composition and the characteristics of graphite were determined by computer image analysis. Measurements of graphite of non-alloy cast iron after normalizing and in cooper cast iron indicate the approximate amount of precipitates of graphite and their approximate average diameters. The applied normalizing and the additive alloy (Cu) were established to give comparable mechanical properties and structure of matrix in thick-walled castings.
The paper presents the results of experimental-simulation tests of expansion-shrinkage phenomena occurring in cast iron castings. The tests were based on the standard test for inspecting the tendency of steel-carbon alloys to create compacted discontinuities of the pipe shrinkage type. The cast alloy was a high-silicone ductile iron of GJS - 600 - 10 grade. The validation regarding correctness of prognoses of the shrinkage defects was applied mostly to the simulation code (system) NovaFlow & Solid CV (NFS CV). The obtained results were referred to the results obtained using the Procast system (macro- and micromodel). The analysis of sensitivity of the modules responsible for predicting the shrinkage discontinuities on selected pre-processing parameters was performed, focusing mostly on critical fractions concerning the feeding flows (mass and capillary) and variation of initial temperature of the alloy in the mould and heat transfer coefficient (HTC) on the casting - chill interface.
The paper refers to previous publications of the author, focused on criteria of casting feeding, including the thermal criterion proposed by Niyama. On the basis of this criterion, present in the post-processing of practically all the simulation codes, danger of casting compactness (in the sense of soundness) in form of a microporosity, caused by the shrinkage phenomena, is predicted. The vast majority of publications in this field concerns shrinkage and feeding phenomena in the cast steel castings – these are the alloys, in which parallel expansion phenomenon does not occur as in the cast irons (graphite crystallization). The paper, basing on the simulation-experimental studies, presents problems of usability of a classic, definition-based approach to the Niyama criterion for the cast iron castings, especially of greater massiveness, for prediction of presence of zones of dispersed porosity, with relation to predictions of the shrinkage type defects. The graphite expansion and its influence on shrinkage compensation during solidification of eutectic is also discussed.
The paper presents results of the possibility of adapting the Althoff-Radtke test for High Chromium Cast Iron. The Althoff-Radtke test is a clump attempt used for steel. The Althoff-Radtke test has four different lengths of clamp which qualifies it as a test to quantitatively take into account different kinds of shrinkage ΔL. The length of the slot of the cracked corner and the length of each staple (50 - 350 mm) are the parameters tendency to cast cracks. Castings of white cast iron have a high tendency to hot cracking due to the large range of solidification temperatures, unfavorable kinetics parameters of shrinkage, and especially a lack of expansion before shrinkage. Shrinkage of high chromium white cast iron is similar to the shrinkage of cast steel, and is approximately 2%. Therefore it is important to test susceptibility to hot cracks. Research was carried out under industrial conditions. Four melts were performed, one of the initial chemical composition and the other three modified by different amounts of Fe-Ti, respectively, 0.25%, 0.5% and 0.75% Fe-Ti. The propensity for hot cracking was based on the observation of the dark surface in the corner of the sample. The study shows that the Althoff-Radtke test can be adapted to determine the tendency for hot cracking of high chromium cast iron. It should however be noted that the test results cannot be compared with those for other alloys.
The validation of each simulation code used in foundry domain requires individual approach due to its specificity. This validation can by elaborated on the basis of experimental results or in particular cases by comparison the simulation results from different codes. The article concerns the influence of grey cast iron density curve and different forms of solid fraction curve Fs=f(T) on the formation of shrinkage discontinuities. Solid fraction curves applying Newtonian Thermal Analysis (NTA) were estimated. The experimental and numerical simulation tests were performed on the castings, which were made with Derivative Thermal Analysis (DerTA) standard cups. The numerical tests were realized using NovaFlow&Solid (NF&S), ProCast and Vulcan codes. In this work, the coupled influence of both curves on the dynamics of the shrinkage-expansion phenomena and on shrinkage defects prognosis in grey cast iron castings has been revealed. The final evaluation of the simulation systems usefulness should be based on validation experiment, preceded by comparing the simulation results of available systems which are proposed in given technology.