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.

The goal of this paper is to measure the non-wetting to wetting transition temperatures of liquid tin on surfaces of different steel samples in vacuum with residual pressure of 10–8 bar. The experiments were conducted on four steels (C45, S103, CK60 and EN1.4034) of varying compositions using pure tin (99.99%) by the sessile drop method. Non-wetting to wetting transition (contact angle decreasing below 90°) by liquid tin was observed as function of increasing temperature in the range of 820-940 K for low alloyed steels C45, S103 and CK60, while it was considerably higher (around 1130 K) for high chromium EN1.4034 steel. It is concluded that at about the same temperatures, the surfaces of the steel samples are spontaneously deoxidized due to the combined effect of high temperature, low vacuum and C-content of steels. After the oxide layer is removed, the contact angles of liquid tin on steel surfaces were found in the range of 45-80° for low alloyed C45, S103 and CK60 steels and around 20° for high chromium EN1.4034 steel. These relatively high contact angle values compared to other metal/metal couples (such as liquid Cu on steels) are due to the formation of not fully metallic intermetallic compounds (FeSn and FeSn2) at the interface (such do not form in the Cu/Fe system).

The work presents experiment results from the area of copper casting technology and chosen examples of alloyed copper. At present,

copper casting technology is applied in many branches of industrial manufacturing, especially in the sector of construction,

communications, arms and power engineering. Alloyed copper, containing slight additions of different elements and having special

physio-chemical properties, is used in a special range of applications. Copper technology and alloyed copper analyses have been presented,

these materials being used for cast manufacturing for power engineering. The quality of casts has been assessed, based on their

microstructure analysis, chemical content and the cast properties. During the research, special deoxidizing and modifying agents were

applied for copper and chosen examples of alloyed copper; also exemplary samples were tested with the help of metallographic analysis,

electrical conductivity and gaseous impurities research.

Deoxidation of steel with carbon under reduced pressure is often used for increasing the steel purity. Suitable units for this purpose in

foundries are vacuum induction furnaces. Possibilities of increasing the steel purity by deoxidation with carbon in the vacuum induction

furnace were studied for the steel for the petrochemistry of specific composition 25Cr/35Ni. The charge composed of the return material

only was melted in the air. During melting the charge oxidized and the oxidizing slag formed. Chemical composition of steel, morphology,

chemical composition of inclusions in the steel and chemical composition of slag after vacuuming were studied on the basis of samples

taken before and after vacuuming. Temperature and oxygen activity were measured before and after vacuuming. Globular inclusions with

dominant content of silicon and manganese were observed in steel before and after vacuuming. Contents of total oxygen in steel didn’t

change significantly during vacuuming. On the basis of composition of inclusions and measured oxygen activity the activity of Cr2O3

in

inclusions was calculated. A slag sample was taken after vacuuming and equilibrium oxygen activity in steel with regard to the Cr2O3

content in the slag was estimated from the slag composition. Equilibrium oxygen activity in relation to the Cr2O3 content in the slag was

higher than equilibrium activity measured in the steel. For this reason it is not possible, under the studied conditions, to decrease oxygen

content in steel during vacuuming.