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 research on the microstructure of GX2CrNiMoCuN25-6-3-3 and GX2CrNiMoCuN25-6-3 cast steels with
a varying carbon content. The cause for undertaking the research were technological problems with hot cracking in bulk castings of duplex
cast steel with a carbon content of approx. 0.06% and with 23% Cr, 8.5% Ni, 3% Mo and 2.4% Cu. The research has shown
a significant effect of increased carbon content on the ferrite and austenite microstructure morphology, while exceeding the carbon content
of 0.06% results in a change of the shape of primary grains from equiaxial to columnar.
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.
In the high-alloy, ferritic - austenitic (duplex) stainless steels high tendency to cracking, mainly hot-is induced by micro segregation
processes and change of crystallization mechanism in its final stage. The article is a continuation of the problems presented in earlier
papers [1 - 4]. In the range of high temperature cracking appear one mechanism a decohesion - intergranular however, depending on the
chemical composition of the steel, various structural factors decide of the occurrence of hot cracking. The low-carbon and low-alloy cast
steel casting hot cracking cause are type II sulphide, in high carbon tool cast steel secondary cementite mesh and / or ledeburite segregated
at the grain solidified grains boundaries, in the case of Hadfield steel phosphorus - carbide eutectic, which carrier is iron-manganese and
low solubility of phosphorus in high manganese matrix. In duplex cast steel the additional factor increasing the risk of cracking it is very
"rich" chemical composition and related with it processes of precipitation of many secondary phases.
The paper, which is a summary and supplement of previous works and research, presents the results of numerical and physical modeling of the GX2CrNiMoCuN25-6-3 duplex cast steel thin-walled castings production. To obtain thin-walled castings with wall in the thinnest place even below 1 mm was used the centrifugal casting technology and gravity casting. The analyzed technology (centrifugal casting) enables making elements with high surface quality with reduced consumption of batch materials and, as a result, reducing the costs of making a unitary casting. The idea behind the production of cast steel with the use of centrifugal technology was to find a remedy for the problems associated with unsatisfactory castability of the tested alloy.
The technological evaluation of the cast construction was carried out using the Nova Flow & Solid CV 4.3r8 software. Numerical simulations of crystallization and cooling were carried out for a casting without a gating system and sinkhead located in a mold in accordance with the pouring position. It was assumed that the analyzed cast will be made in the sand form with dimensions 250×250×120 mm.
The paper presents the research results concerning the chromium-nickel-molybdenum duplex cast steel GX2CrNiMoCuN 25-6-3-3 grade. The aim of studies was the description of the influence of hyperquenching temperature Tp i.e. 1100, 1125 and 1150℃ on microstructure and mainly mechanical properties i.e. tensile strength UTS, yield strength YS, hardness HB, elongation EL and impact energy KV of duplex cast steel GX2CrNiMoCuN 25-6-3-3 grade. The range of studies included ten melts which were conducted in foundry GZUT S.A. Based on the obtained results was confirmed that application of hyperquenching process guarantees the elimination of brittle s phase in the microstructure of studied duplex cast steel. Moreover on the basis of conducted statistical analysis of the researches results is concluded that with the decrease in hyperquenching temperature increases ductility and amount of austenite, while decreases strength and amount of ferrite in studied duplex cast steel GX2CrNiMoCuN 25-6-3-3 grade.
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.
High-alloy corrosion-resistant ferritic-austenitic steels and cast steels are a group of high potential construction materials. This is
evidenced by the development of new alloys both low alloys grades such as the ASTM 2101 series or high alloy like super or hyper duplex
series 2507 or 2707 [1-5]. The potential of these materials is also presented by the increasing frequency of sintered components made both
from duplex steel powders as well as mixtures of austenitic and ferritic steels [6, 7]. This article is a continuation of the problems presented
in earlier works [5, 8, 9] and its inspiration were technological observed problems related to the production of duplex cast steel.
The analyzed AISI A3 type cast steel is widely used in both wet exhaust gas desulphurisation systems in coal fired power plants as well as
in aggressive working environments. Technological problems such as hot cracking presented in works [5, 8], with are effects of the rich
chemical composition and phenomena occurring during crystallization, must be known to the technologists.
The presented in this work phenomena which occur during the crystallization and cooling of ferritic-austenitic cast steel were investigated
using numerical methods with use of the ThermoCalc and FactSage® software, as well with use of experimental thermal-derivative
analysis.
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.