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M. Pesci
HA ITALIA S.p.A., Italy
PREVENTING GRAPHITE DEGENERATION WITH FLUORINE-FREE CHEMEX FEEDERS
Abstract
Increasingly, in modern foundries, the application of precise feeders helps designers to prevent porosity in nodular graphite iron castings, ensuring the structural integrity and mechanical performance required by the client. However, at the same time, the metallurgical aspect can be affected by the use of these feeders. Indeed, the presence of abnormal or even degenerated graphite is often found in the surrounding area of sleeves and mini-risers, leading to a loss of mechanical properties to the point of scraping the casting. This study aimed to evaluate the effect of exothermic sleeves, both in terms of graphite morphology in the casting skin, and the presence of a fish-eye defect. The investigation was carried out by comparing different types of feeders, such as insert sleeves and mini-risers. Especially, the graphitic structure was analysed in the presence of CHEMEX’s innovative fluorine-free exothermic material and compared with classical exothermic materials available on the market.
For the implementation of the project, a model plate was designed with cubes featuring different thermal moduli calculated by using NovaFlow&Solid simulation software: 1.6 cm, 1.9 cm and 2.3 cm. The experimental test was carried out in a real foundry by casting standard ductile iron grade EN-GJS-500-7. The entire melting process was monitored by using ATAS MetStar 10.1 adaptive metallurgical process control system based on thermal analysis. It was found that CHEMEX fluorine-free exothermic feeders can guarantee the full integrity of casting skin as well as complete modularity below the feeder’s neck and immediately close to its fracture surface.
Keywords: feeders, degenerated graphite, fish-eye defect, exothermic sleeves, fluorine-free
2.
M. Matejka1, D. Bolibruchová1, A. Sládek1 , R. Podprocká2
1University of Zilina, 2Rosenberg-Slovakia, Slovakia
INTERNAL HOMOGENEITY EVALUATION OF ALSI7MG0.3CU0.5 ALLOY WITH ADDITION OF ZR, TI, AND SR
Abstract
Nowadays, engineering industries are constantly emphasizing the improvement of the material’s properties. One way to improve the properties of the Al alloy is by adding the alloying elements. One of the possibilities is the application of Zr to Al alloys, which has a positive effect on increasing strength, corrosion resistance, and heat resistance. It is most often segregated in the form of intermetallic phases Al3 Zr respectively AlSiZr. Formation occurs during the peritectic reaction at Zr ≥ 0.1 wt. %. The basic morphology Zr of intermetallic phases (dispersoids) is in the form of long needles resp. plates, their size increases with increasing content of Zr. The addition of Zr and Ti to Al-Si alloys results in more intensive grain refinement than when using individual elements alone. Sr together with Zr forms Al3 (Sr1 -xZrx) based phases which can act as crystallization nuclei. The submitted paper focuses on the possibilities of improving the performance of AlSi7Mg0.3Cu0.5 alloy enriched with elements based on Zr, Ti, and Sr, cast into ceramic molds by investment casting technology. The best results were obtained by an alloy with an addition of 0.15 wt. % Zr and 0.2 wt. % Ti. The alloy showed an increase in mechanical properties and a positive character of the precipitated Zr phases in the microstructure.
Keywords: Al-Si-Mg-Cu Alloy, Addition of Zr, Ti, and Sr, Microstructure, Mechanical properties
3.
J. Poklič1,2, A. Nagode1 , P. Mrvar1 , A. Tekavčič2 , M. Petrič1
1Faculty of Natural Sciences and Engineering, University of Ljubljana, 2Kovis Livarna d.o.o., Slovenia
COMPARISON OF IMPACT AND FRACTURE TOUGHNESS OF DUCTILE IRON AND FERRITIC STEEL
Abstract
The aim of the study was to determine the fracture and impact toughness of ductile iron ENGJS-400-18LT and to compare it with the hot-rolled structural steel S235JR+AR at room temperature, 0°C, -20°C and -40°C. Another objective was to determine the temperature interval of the transition from ductile to brittle fracture and to analyse the fracture behaviour of both alloys.
To this end, fracture toughness testing was carried out using a three-point bending test and Charpy impact toughness tests at the abovementioned temperatures for both alloys. Metallographic examination, macroscopic analysis of fracture surfaces and microfractography using a scanning electron microscope (SEM) were also carried out on certain samples.
The impact toughness of S235JR+AR at room temperature is shown to be significantly higher than that of EN-GJS400-18LT, however, drops markedly as the temperature is lowered, so that at -40°C, both alloys exhibit the same impact toughness value. The fracture toughness of EN-GJS-400-18LT is higher than that of S235JR+AR at all temperatures and even increases slightly with temperature.