Microstructure and Mechanical Properties of Welded Joints of 1.4462 Duplex Steel Made by the K-TIG Method

K-TIG (Keyhole Tungsten Inert Gas) method is a new, emerging welding technology that offers a significant acceleration of the joining process, even for very thick plates. However, its potential for welding of certain materials is still unknown. Particularly challenging are duplex steels as this technology does not allow the use of a filler material, which is crucial for these steels and for weld joint microstructure adjustment. In order to demonstrate the suitability of this technology for single-pass welding of 1.4462 duplex steel detailed studies of the microstructure of the weld joints obtained for different linear energies were carried out and discussed with respect to their mechanical properties. According to the results obtained, the heat-affected zone (HAZ) shows a microstructure similar to the HAZ of duplex steel welded with the traditional TIG multi-pass methods. However, the weld, due to the lack of filler material, had a microstructure different to that typical for duplex steel welded joints and was also characterized by an increased content of ferrite. However, all joints, both in terms of microstructure and mechanical properties, met the requirements of the relevant standards. Moreover, the K-TIG process can be carried out in the linear energy range typical of duplex steel welding, although further optimization is needed.

Influence of the Addition of Ni on as-Cast Microstructure of Duplex Fe-Mn-Al-C Lightweight Steel

Lightweight Fe-Mn-Al-C steels have low density, and high mechanical properties, which makes them a possibility for weight reduction in vehicles for road transport. In steel production, as-cast microstructure is an important parameter for further processing. The as-cast microstructure of five lightweight duplex steels was investigated: Fe-15Mn-10Al-0.8C, Fe-15Mn-10Al-1.7Ni-0.8C, Fe-15Mn-10Al-3.9Ni-0.8C, Fe-15Mn-10Al-5.6Ni-0.8C and Fe-15Mn-10Al-8.6Ni-0.8C. The influence of Ni was analysed through thermodynamic calculations and microstructural characterization. The samples were analysed through an optical and electron microscopy. The base microstructure of the studied steel consists of ferrite and austenite. Further investigation showed that the decomposition of austenite was accompanied by the formation of kappa carbides and the B2 ordered phase. The addition of Ni prevented the formation of a lamellar kappa ferrite morphology, but at 5.6 wt.% Ni, the decomposition of austenite was most severe, resulting in a large amount of kappa carbides and a B2 ordered phase.

Possibilities to Use Physical Simulations When Studying the Distribution of Residual Stresses in the HAZ of Duplex Steels Welds

Dual phase steels combine very good corrosion resistance with relatively high values of mechanical properties. In addition, they can maintain good plastic properties and toughness at both room temperature and lower temperatures as well. Despite all the advantages mentioned above, their utility properties can be reduced by technological processing, especially by the application of the temperature cycles. As a result, in the material remain residual stresses with local stress peaks, which are quite problematic especially during cyclic loading. Moreover, determining the level and especially the distribution of such residual stresses is very difficult for duplex steels both due to the structure duality and in light of the very small width of the heat-affected zone (HAZ). This is why the paper presents the possibilities of using physical simulations to study the effect of temperature cycles in residual stresses’ magnitude and distribution, where it is possible to study the HAZ in more detail as well as on a much larger sample width due to the utilization of special samples. In the thermal–mechanical simulator Gleeble 3500, temperature-stress cycles were applied to testing samples, generating stress fields with local peaks in the testing samples. In addition, the supplied steel X2CrMnNiN21-5-1 had different phase rations in the individual directions. Therefore, as the residual stresses were measured in several directions and at the same time, it was possible to safely confirm the suitability of the used measurement method. Moreover, the effect of the stress and strain on the change of partial phases’ ratios was observed. It has been experimentally confirmed that annealing temperatures of at least 700 °C are required to eliminate local stress peaks after welding. However, an annealing temperature of 550 °C seems to be optimal to maintain sufficient mechanical properties.

Duplex Steels Used in Building Structures and Their Resistance to Chloride Corrosion

Welded structures made of duplex steels are used in building applications due to their resistance to local corrosion attack initiated by chlorides. In this paper, the material and technological factors determining the corrosion resistance are discussed in detail. Furthermore, recommendations are formulated that allow, in the opinion of the authors, to obtain a maximum corrosion resistance for welded joints. The practical aspects of corrosion resistance testing are also discussed, based on the results of qualification tests. This work is of a review character. The conclusions and practical recommendations are intended for contractors and investors of various types of structures made of the duplex steel. The recommendations concern the selection and use of duplex steels, including the issues of metallurgy, welding techniques, and corrosion protection.

Stochastic evaluation of stress and strain distributions in duplex steel

Austenite–ferrite duplex steels generally consist of two differently textured polycrystalline phases with different glide mechanisms. For estimating the effective mechanical behavior of heterogeneous materials, there exist well established approaches, two of which are the classes of mean-field and full-field methods. In this work, the local fields resulting from these different approaches are compared using analytical calculations and full-field simulations. Duplex steels of various textures measured using X-ray diffraction are considered. Special emphasis is given to the influence of the crystallographic texture on the stress and strain distributions.

PROSPECTS OF APPLICATION OF TUBES MADE OF DUPLEX STEELS OF A NEW GENERATION IN THE HEAT EXCHANGING EQUIPMENT OF NUCLEAR POWER PLANTS

Prospects of using tubes produced by Centravis Production Ukraine JSC of ferritic-austenitic (duplex) steels of a new generation according to the developed innovative technology in the heat exchanging equipment of nuclear power plants (NPP) were scientifically substantiated based on analysis of scientific and technical literature and the results obtained in comprehensive studies. Comparative corrosion studies of the tubes made of austenitic Cr-Ni and Cr-Ni-Mo steels and 02Cr22Ni5NМo3 (UNS S 31803) duplex steel have shown a substantially improved resistance of the latter to intercrystalline, pit and crevice corrosion, corrosion cracking and erosion. Presence of special low-energy γ-γ, α-α grain boundaries and α-γ interphase boundaries characterized by an increased corrosion resistance and a contribution to the growth of steel durability as a whole was found for the first time in the structure of ferritic-austenitic steels.

Electrochemical Data on the Effect of Extreme Temperatures on 2101 Duplex Steel Corrosion Performance in Chloride-Sulphate Environment

The detrimental outcome of heat treatment operation at 1200oC on 2101 duplex stainless steel was studied in 2 M H2SO4/0%-1.75% NaCl by potentiodynamic polarization, open circuit potential measurement and optical microscopy analysis. Result reveal the processes heightened the corrosion vulnerability of the duplex alloy with maximum corrosion rate result of 11.3 mm/y at 0.5% NaCl for the annealed steel (A2101ST), followed by quenched steel (Q2101ST) with corrosion rate value of 9.03 mm/y. These values were significantly lower than the peak corrosion rate of the as received steel (ASR2101ST) at 5.785 mm/y. The corrosion rate of all the duplex steels generally decreased beyond 0.5% NaCl. ASR2101ST sustained it passivation characteristics till 1.75% NaCl due to the resilience of its oxide protective film while the passive film of Q2101ST and A2101ST were completely destroyed due to alteration in the metallurgical configuration of the heat treated duplex steels. While the surface of ASR2101ST mildly deteriorated, severe intergranular and pitting corrosion was observed on Q2101ST and the surface of A2101ST was marginally pitted in the presence of SO42- ions. In Cl-/SO4 ion solution ASR2101ST showed an etched morphology with ferrite and austenite phases appearing in addition to superficial pitting. Q2101ST and A2101ST were severely deteriorated in the solution.