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.

Oxygen is an element that is first purposely brought into the steel melt to remove some unwanted elements or to reduce their concentration

(oxidation). In the made cast steel there is on the contrary necessary to reduce the oxygen content with the use of deoxidation to such a

level in order to avoid a reaction with carbon with the formation of CO bubbles. Concentration of oxygen in steel before casting is given,

in particular, by the manner of metallurgical processing and the used deoxidation process. Oxygen is found in molten steels both as

chemically bound in the form of oxides and in the form of oxygen dissolved in the solution – the melt. Chemical composition

of the melt strongly influences the activity of oxygen dissolved in the melt and further on the composition of oxidic inclusions forming in

the melt during the reaction with oxygen. In the Fe-C-Cr-Ni based alloys in the reaction with oxygen greatly participates also chrome,

whose products are often in solid state and they are the cause of forming such defects as e.g. oxidic films.

The research was concerned with the influence of chemical composition of austenitic steels on their mechanical properties. Resulting properties of castings from austenitic steels are significantly influenced by the solidification time that affects the size of the primary grain as well as the layout of elements within the dendrite and its parts with regard to the last solidification points in the interdendritic melt. During solidification an intensive segregation of all admixtures occurs in the melt, which causes a whole range of serious metallurgical defects and it has also a significant influence on subsequent precipitation of carbides and intermetallic phases. Chemical heterogeneity then affects the structure and mechanical properties of the casting. In a planned experiment, we cast melted steels containing 18 to 28 % Cr and 8 to 28 % Ni with variable carbon and nitrogen contents. Testing the tensile strength of the cast specimens we could determine the Rp0.2, Rm, and A5 values. The dependence of the mechanical properties on the chemical content was described by regression equations. The planned experiment results allow us to control the chemical content for the given austenitic steel quality to achieve the required values of the mechanical properties.

An analysis has been carried out of the influence of annealing time at the preheating temperature of 650 °C on the change in hardness and alloy structure of lamellar graphite cast iron in the working as well as in the laboratory conditions. This preheat temperature is common during reclaiming welding of castings with complex shapes. The changes in unalloyed cast iron EN-GJL 200 to EN-GJL 300 according to ISO 1690 standard and cast iron with low amount of elements such as Sn, Cu, Cr, and Mo and their combinations were assessed. It was found that the cast iron of higher strength grades has better hardness and structural stability. Cast iron alloyed with chromium or its combinations has the highest stability. In unalloyed cast iron, a partial degradation of pearlite occurs; in alloyed cast iron the structural changes are not conclusive.

For the EN GX4CrNi13-4 martensitic stainless steel, research was conducted to investigate the impact of the quenching intensity and the content of nickel on the mechanical properties and amount of retained austenite. It was found that the amount of retained austenite significantly increases with growing nickel concentration. On the other hand, the cooling rate at quenching makes a difference only if the cooling is intensive, then amount of retained austenite decrease. A higher nickel content improves the mechanical properties. With more intensive cooling, the tensile strength decreases while the yield strength increases. The ductility is not significantly affected by the cooling intensity.