Influence of compound deoxidation of steel with Al, Zr, rare earth metals, and Ti on properties of heavy castings

Heavy steel castings deoxidized with aluminium are sometimes brittle intercrystalline failed during their service along primary grain boundaries what is initiated by aluminium nitrides and so called conchoidal fractures are formed. The tendency to forming the conchoidal fractures depends in particular on cooling rate (the casting modulus), aluminium and nitrogen contents in steel. During deoxidation, when manufacturing heavy castings, the elements with high affinity to nitrogen, zirconium or titanium, are added to steel that would decrease nitrogen activity by the bond on stable nitrides. The formation of stable nitrides should reduce the tendency of steel to the formation of conchoidal fractures. Deoxidation was thermodynamically analyzed at presence of the mentioned elements. For particular conditions a probable course of deoxidation was estimated at test castings. The deoxidation course was checked by microanalysis of deoxidation products (inclusions). For service and experimental castings the anticipated composition of inclusions was compared. It has been proved that in heavy castings with high aluminium contents in steel under studied conditions neither the addition of zirconium nor of titanium nor of rare earth metals will prevent the formation of conchoidal fractures

Comparison of Methods for Determining the Ferrite Content in Duplex Cast Steels

The paper is concerned with comparing the methods for determining the ferrite content in castings from duplex stainless steels. It uses Schaeffler diagram, empirical formula based calculation, image analysis of metallographic sample, X-ray diffraction and measurement with a feritscope. The influence of wall thickness of the casting on the ferrite content was tested too. The results of the experiments show that the casting thickness of 25 or 60 mm does not have a significant effect on the measured amount of ferrite. The image analysis of metallographic sample and the measurement with the feritscope appear to be the most suitable methods. On the contrary, predictive methods, such as Schaeffler diagram or empirical formula based calculation are only indicative and cannot replace the real measurements. X-ray diffraction seems to be the least suitable measuring method. Values of ferrite content measured in such a way often deviated from the values measured by image analysis and with feritscope

Prediction of Ferrite Content in Austenitic Cr-Ni Steel Castings During Production

Determination of the ferrite content in austenitic steels, which solidified under defined conditions. Ferrite content in austenitic matrix was determined from samples with wall thickness of 60 mm. Measured ferrite contents served to propose the regression equations for the calculation of the ferrite content in steels with Cr content of 18 up to 22 % and Ni of 9 up to 11 %. An additional regression equation was proposed for steels with a higher Ni content. The proposed regression equations have been checked up on the operating melts. In conclusion, the ferrite content in the axis of the casting of wall thickness of 500 mm has been calculated and it was compared to the ferrite determined in the usual way from the cast-on test

Increase of liquid metal utilization during production of bearing circle castings for cement furnaces

In manufacture of super heavy castings for cement furnaces a saving of liquid metal has been achieved by lowering the riser weight. By solidification modelling with the aid of the Niyama criterion a zone in the riser was designated where the occurrence of foundry defects (shrinkage porosity) can be expected. A plate of the material of dimensions ca 700*800*250 mm was taken from the riser. After thermal treatment the samples for making the bars for the static tensile test were taken from it. Based on done tests it has been found out that mechanical characteristics obtained from the static tensile test correlate, besides contraction, in the chosen level of statistical importance of p = 0.01 with carbon content. Neither in the zone of probable occurrence of defects designated by the Niyama criterion during solidification modelling the drop of strength characteristics was observed. Carbon content in a decisive extent influenced the strength characteristics. In case of ductility and contraction the convenient correlations with carbon content were observed from the riser height of 200 mm only. In the height of 400 mm there was already considerable variation of values and some values were lower ones than is demanded by standards

Integration of Virtual Engineering and Additive Manufacturing for Rapid Prototyping of Precision Castings

The present paper is concerned with the practical interconnection between virtual engineering tools and additive model manufacturing technologies and the subsequent production of a ceramic shell by rapid prototyping with the use of Cyclone technology to produce the aluminium casting prototype. Prototypes were developed as part of the student formula project, where several parts originally produced by machining were replaced by castings. The techniques of topological optimization and the combination with the tools of the numerical simulation were used to optimise the virtual prototype before a real production of the first prototype. 3D printing of wax pattern ensured direct and fast assembly of the cluster without any additional operations and troubles during dewaxing. The shell was manufactured in 6 hours thanks to a system of quick-drying of individual layers of ceramic shell. It has been verified that the right combination of individual virtual tools with the rapid prototyping can shorten the development time and delivery of the first prototypes from a few months to a few weeks

Development of a manufacturing technology of compacted graphite iron castings from a cupola furnace

Compacted graphite iron, also known as vermicular cast iron or semiductile cast iron is a modern material, the production of which is increasing globaly. Recently this material has been very often used in automotive industry. This paper reviews some findigs gained during the development of the manufacturing technology of compacted graphite iron under the conditions in Slévárna Heunisch Brno, Ltd. The new technology assumes usage of cupola furnace for melting and is beeing developed for production of castings weighing up to 300 kilograms poured into bentonite sand moulds

Integration of Virtual Engineering and Additive Manufacturing for Rapid Prototyping of Precision Castings

The present paper is concerned with the practical interconnection between virtual engineering tools and additive model manufacturing technologies and the subsequent production of a ceramic shell by rapid prototyping with the use of Cyclone technology to produce the aluminium casting prototype. Prototypes were developed as part of the student formula project, where several parts originally produced by machining were replaced by castings. The techniques of topological optimization and the combination with the tools of the numerical simulation were used to optimise the virtual prototype before a real production of the first prototype. 3D printing of wax pattern ensured direct and fast assembly of the cluster without any additional operations and troubles during dewaxing. The shell was manufactured in 6 hours thanks to a system of quick-drying of individual layers of ceramic shell. It has been verified that the right combination of individual virtual tools with the rapid prototyping can shorten the development time and delivery of the first prototypes from a few months to a few weeks