This work deals with the problem of intermetallic phases in cast standard duplex steel ASTM A890 Gr 4A (generally known as 2205). The investigated steel was subjected to isothermal heat treatment in the range from 595 °C to 900 °C and in the duration from 15 minutes to 245 hours, and was also investigated in terms of anisothermal (natural) cooling after casting into the mould. The precipitation starts at grain boundaries with a consistent ferrite transformation. The work is focused on the precipitation of the sigma phase (σ) and the chi phase (χ). Examination of the microstructure was conducted using light and scanning electron microscopy. Their statistical analysis was carried out using the results of the investigations of precipitation processes in the microstructure, both within the grains and at the grain boundaries. To illustrate this impact, the surface area of precipitates was evaluated. The percentage of these intermetallic phases was calculated by measuring their area using a computer image analysis system. Based on their observations, a combined time-temperature transformation (TTT) diagram with continuous cooling transformation (CCT) curves was created.

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 S304H steel is used in the construction of pressure components of boilers with supercritical operating parameters. The paper presents the results of the research on the microstructure after ageing for 20,000 hours at 650 and 700°C. The microstructure examination was performed using scanning and transmission electron microscopy. The precipitates were identifies using transmission electron microscopy. The influence of ageing time on microstructure changes and the precipitation process of the tested steel is described. The presented research results are an element of material characteristics of the new generation of steel, which are used in the design work of pressure devices of steam boilers and in diagnostic work during operation.

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.