The examined material comprised two grades of corrosion-resistant cast steel, namely GX2CrNiMoN25-6-3 and GX2CrNiMoCuN25-6-3-

3, used for example in elements of systems of wet flue gas desulphurisation in power industry. The operating conditions in media heated

up to 70°C and containing Cl- and SO4 ions and solid particles produce high erosive and corrosive wear.The work proposes an application

of the σ phase as a component of precipitation strengthening mechanism in order to increase the functional properties of the material.

The paper presents the results of examination of the kinetics of σ phase precipitation at a temperature of 800°C and at times ranging from

30 to 180 minutes. Changes in the morphology of precipitates of the σ phase were determined using the value of shape factor R.

Resistance to erosion-corrosion wear of duplex cast steel was correlated with the kinetics of sigma phase precipitating.

The paper presents the results of investigation into the technological possibility of making light-section castings of GX2CrNiMoN25-6-3

cast steel. For making castings with a wall thickness in the thinnest place as small as below 1 mm, the centrifugal casting technology was

employed. The technology under consideration enables items with high surface quality to be obtained, while providing a reduced

consumption of the charge materials and, as a result, a reduction in the costs of unit casting production.

The paper presents the results of examination concerning optimization of the σ phase precipitates with respect to the functional properties of ferritic-austenitic cast steel. The examined material comprised two grades of corrosion-resistant cast steel, namely GX2CrNiMoN25-6-3 and GX2CrNiMoCuN25-6-3-3, used for example in elements of systems of wet flue gas desulphurisation in power industry. The operating conditions in media heated up to 70°C and containing Cl- and SO4 ions and solid particles produce high erosive and corrosive wear. The work proposes an application of the σ phase as a component of precipitation strengthening mechanism in order to increase the functional properties of the material. Morphology and quantities of σ phase precipitates were determined, as well as its influence on the erosion and corrosion wear resistance. It was shown that annealing at 800°C or 900°C significantly improves tribological properties as compared with the supersaturated state, and the best erosion and corrosion wear resistance achieved due to the ferrite decomposition δ → γ’ + σ was exhibited in the case of annealing at the temperature of 800°C for 3 hours.

The investigations were inspired with the problem of cracking of steel castings during the production process. A single mechanism

of decohesion – the intergranular one – occurs in the case of hot cracking, while a variety of structural factors is decisive for hot cracking

initiation, depending on chemical composition of the cast steel. The low-carbon and low-alloyed steel castings crack due to the presence

of the type II sulphides, the cause of cracking of the high-carbon tool cast steels is the net of secondary cementite and/or ledeburite

precipitated along the boundaries of solidified grains. Also the brittle phosphor and carbide eutectics precipitated in the final stage

solidification are responsible for cracking of castings made of Hadfield steel. The examination of mechanical properties at 1050°C

revealed low or very low strength of high-carbon cast steels.