In the present research work, the influence of heat input rates on microstructures, hot tensile properties, and weld surface hardness number of Super Duplex Stainless Steel 2507 super duplex steels ...and austenitic steels 316L plates were investigated. Pulsed current and constant current modes were used in Tungsten Inert Gas (TIG) welding to join the dissimilar metals using ER2205 as filler. Microstructural studies were revealed at different zones of pulsed and constant current TIG weldments using optical microscopy. The tensile test was conducted at two different temperature conditions (i.e., 27 and 350°C) to investigate the strength of dissimilar weldments. Hardness measurements were made on the weld surface along the transverse direction using Vicker’s hardness tester. The microstructures revealed the formation of inter-granular austenite at the fusion zone with grain boundaries with austenite structures. Due to the constant heat input, a significant microstructural development with high austenite fractions was observed in constant current (CC)-TIG weldment. In comparison to CC-TIG weldments (UTS at 27°C = 600 MPa UTS at 350°C = 456 MPa), higher tensile characteristics were noted in Pulsed Current (PC)-TIG weldments (UTS at 27°C = 695 MPa UTS at 350°C = 475 MPa). The UTS of PC-TIG weldment is improved by 15.8% when compared to CC-TIG weldment due to the controlled heat input rates. PC-TIG weldments exhibited improved hardness numbers in various zones with smaller HAZ widths than CC-TIG weldments.
Solute clustering and G-phase precipitation cause hardening phenomena observed in some low alloy and stainless steels, respectively. Density functional theory was used to investigate the energetic ...driving force for the formation of these precipitates, capturing temperature effects through analysis of the system's configurational and magnetic entropies. It is shown that enrichment of Mn, Ni and Si is thermodynamically favourable compared to the dilute ferrite matrix of a typical A508 low alloy steel. We predict the ordered G-phase to form preferentially rather than a structure with B2-type ordering when the Fe content of the system falls below 10–18 at. %. The B2 → G-phase transformation is predicted to occur spontaneously when vacancies are introduced into the B2 structure in the absence of Fe.
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Efforts are being made worldwide to transform road transport to minimise its contribution to greenhouse gas emissions, with a focus on reducing vehicle mass. Lightweight manganese–aluminium steels ...have gained popularity for this purpose due to their low density and combination of strength and plasticity. In this particular study, the solidification process of five lightweight manganese–aluminium steels with different silicon content was investigated. The steels were fabricated by inductive melting in a vacuum and remelted during further thermal analysis. A reference steel composition (Fe-14Mn-10Al-0.2Si-0.8C) was used, and the remaining four steels contained different amounts of silicon (0.5, 1.0, 2.0 and 4.0 mass%). The impact of silicon on solidification was analysed by thermodynamic calculations (CALPHAD method), differential thermal analysis and optical microscopy. The thermodynamic calculations gave good estimates for the liquidus and austenite liquidus temperatures, but higher solidus temperatures than the experimental results. The presence of silicon decreases the density and lowers the solidus and liquidus temperatures, resulting in a prolonged solidification interval. In addition, the spacing of the secondary dendrite arms decreases, except at a silicon concentration of 0.5 mass%, where an increase was observed compared to the reference steel.
The mechanical behaviour and fracture were studied in a Fe–5Mn–2.5Al–0.2C (in wt-%) Medium Mn steel. Metallographic and magnetic measurements confirm the significant influence of the transformation ...kinetics of the strain-induced martensite on the mechanical properties and strain heterogeneities (Lüders and Portevin-Le Chatelier-like phenomena). An accurate study of isothermal evolutions of the microstructure, associated with atomistic calculations, complements current thermodynamic databases to quantify the nature and volume fraction of phases at different temperatures. A kinetic approach then predicts the influence of annealing conditions on the composition of retained austenite, key parameter for the martensitic transformation kinetics. This supports quantitative modelling of the influence of the intercritical annealing temperature on the ultimate tensile strength for industrial developments of these new grades.
Among various types of stainless steel, 304L and 316L have the most engineering applications. Herein, 304L and 316L powders with similar size distributions and morphologies are used as raw materials ...for selective laser melting (SLM) using the same parameters. It is found that SLM 304L has two phases, γ‐austenite (≈95%) and δ‐ferrite (≈5%) phases, while SLM 316L contains only γ‐austenite phase. The average grain size is found to be 4.9 μm (average grain size of γ‐austenite phase: 5.0 μm; δ‐ferrite: 3.4 μm) for SLM 304L and 16.7 μm for SLM 316L. The small grain size of 304L is attributed to the peritectic reaction during solidification. δ‐ferrite acts as a heterogeneous nucleation site for γ‐austenite. SLM 316L has higher hardness and yield strength than 304L. Results obtained from the comparative study indicate that adding ferrite stabilizer elements (e.g., Cr, Mo, Si, Nb, or Ti) into 316L can lead to peritectic reaction or austenite to ferrite solid phase transformation, which is a possible approach for grain refinement.
304L and 316L have similar compositions. However, a selective laser melted 304L and 316L show a significant difference in grain size and morphology. Their microstructures and mechanical properties are compared using a scanning electron microscope, electron backscattered diffraction, nanohardness, and tensile tests. This comparative study proposed a method for grain refinement and microstructure tuning in additive manufacturing.
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.
The application of duplex steels is constantly increasing due to their excellent combination of high strength and fracture toughness complemented with superior resistance to localized chemical ...corrosion and stress corrosion. Since ultrafine-grained and nanocrystalline metals have shown improved mechanical and physical properties compared to their coarse grain counterparts, a further optimization of duplex steels could be realized by an additional nano-structuring process. Therefore, in the present study, a conventional duplex steel (X2CrNiMoN22-5-3) was deformed by high pressure torsion (HPT). The evolution of the microstructure and hardness upon deformation was examined. Special attention was devoted to the change of fracture toughness induced by HPT. In order to take grain shape changes during deformation into account, specimens with different orientations with respect to the principal shear deformation direction were tested. A pronounced anisotropy in the crack propagation behavior depending on the specimen orientation combined with an exceptional increase of strength was discovered.
The evolution of microstructure and texture during isothermal annealing of a heavily warm-rolled duplex steel (DSS) was studied. For this purpose a DSS steel was hot rolled, homogenized at 1448 K and ...subsequently warm-rolled to 90% reduction in thickness at 698 K and 898 K. This was followed by isothermal annealing at 1448 K for different time intervals up to 7200 seconds. Lamellar microstructure with alternate arrangement of deformed ferrite and austenite bands was observed in the as warm-rolled condition. The ferrite in DSS warm-rolled at 698 K showed much stronger α-fiber (Rolling direction (RD)// ) than γ-fiber (Normal direction (ND)// ) as compared to the ferrite in DSS warm-rolled at 898 K. The austenite in warm-rolled DSS showed a predominantly pure metal (or copper type) texture. Upon annealing the lamellar morphology of the as warm-rolled structure transformed into a bamboo type morphology for short annealing time but finally broke down with increasing isothermal annealing time due to mutual interpenetration of the two phases. Retention of deformation texture components and presence of annealing twins in austenite indicated discontinuous recrystallization. Despite differences of texture in the as warm-rolled condition the ferrite in annealed DSS showed much stronger α-fiber as compared to γ-fiber due to strong recovery behavior of ferrite during annealing. The texture evolution in the two phases was not affected by the presence of the other phase while grain growth was significantly restricted due to the presence of the other phase.
Recently, low-density Fe–Mn–Al–C steels have attracted attention because of their low density with excellent combinations of strength and ductility. They can be divided into three categories: ...ferritic steels, duplex steels and austenitic steels, depending on the microstructure. The solidification of five duplex low-density steels was investigated. Five steels 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 were produced in a vacuum induction furnace under Ar atmosphere and remelted in a simultaneous thermal analyser (NETZSCH STA 449 C Jupiter). The influence of Ni on the solidification process was analysed using thermodynamic calculations and differential scanning calorimetry. The samples were analysed by light microscopy. The thermodynamic modelling was performed with commercial software Thermo-Calc using the CALPHAD method. The Thermo-Calc calculations show a better agreement for the liquidus temperatures at lower Ni additions, while the higher Ni additions show a better agreement for the solidus temperatures. The Ni additions slightly increase the density, reduce the distance of the secondary dendrite arms and lower both the solidus and liquidus temperatures, but do not influence the solidification interval.
In many industrial applications, metallic materials are exposed to harsh operating conditions. Due to a combination of chemical and thermal stresses, the constructional and functional materials are ...degraded, and their utility properties are lost. These undesirable events are of a physicochemical nature and are commonly known as ‘corrosion’. In this Special Issue Book, 3 reviews and 18 original research papers focused on the complex relationships between the microstructure, phase constitution, and corrosion behavior of metallic materials are collected. Both high temperature and low temperature corrosion studies are included as they investigate the physicochemical processes at the material interfaces. Furthermore, possibilities for increasing the corrosion resistance of metallic materials are studied by means of surface modification and application of protective layers. This Special Issue Book, Microstructure and Corrosion Behavior of Advanced Alloys, displays the diversity and complexity of modern corrosion research. It is hoped that it will become a valuable source of reference for corrosion scientists.
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