Scanning Electron Microscopy-electron Backscatter Diffraction Research Articles

Thermodynamic instability of polycrystalline tungsten exposed to low-energy hydrogen irradiation

The stability of polycrystalline tungsten (W) exposed to low-energy (120 eV) and large-flux (1.5×1022 ions/m2⋅s) hydrogen (H) irradiation at low-pressure has been evaluated by using scanning electron microscopy-electron backscatter diffraction, energy dispersive spectroscopy, and conductive atomic force microscopy. Both surface degeneration and formation of ultra-fine W crystal grains have been observed during the annealing in the range of 200-900 °C. The thermodynamic stability of irradiated W is significantly affected by the annealing temperature. Our finding suggests that the serious erosion of polycrystalline W by H irradiation results from the thermodynamic instability of irradiated W while the instability is attributed to the strong diffusion of interstitial W atoms under fusion-relevant irradiation conditions. Our calculation confirms the instability of W atoms close to the H clusters, leading to the formation of self-interstitial W atoms in W crystal.

High-Temperature Deformation Behaviour of UNS S32750 Super Duplex Stainless Steel (SDSS) Alloy.

In this study, the high-temperature deformation behaviour of the UNS S32750 Super Duplex Stainless Steel (SDSS) alloy was investigated by means of deformability and microstructure evolution in the (1050-1200) °C temperature (T) range. The deformability of the UNS S32750 SDSS alloy was investigated by the up-setting method using a gravity-drop hammer, with the following deformation energy/impact energy (E∗): 545.2 J, 1021.5 J, 1480.6 J, and 1905.3 J. Data referring to deformation resistance (σc') and mechanical work (A∗) as a function of deformation temperature (T) and deformation energy/impact energy (E∗) were obtained and analysed. It was shown that increasing the deformation temperature leads to an increase in the obtained deformation degree (degree of reduction in height). By analysing the rate of increase in the deformation degree as a function of the applied impact energy, it was shown that the rate of increase in the deformation degree rises with the increase in the applied impact energy. Also, it was observed that the evolution of the deformation resistance (σc') as a function of temperature (T) shows a decreasing tendency while increasing the deformation temperature for all impact energies and that the evolution of the mechanical work (A∗) as a function of temperature (T) shows a decreasing tendency while increasing the deformation temperature for all impact energies. The microstructure evolution of the UNS S32750 SDSS alloy was investigated by X-ray diffraction (XRD) and Scanning Electron Microscopy-Electron Backscatter Diffraction (SEM-EBSD) techniques. It was observed that, in all cases, the microstructure shows intensely deformed grains, strongly elongated in the rolling direction in both ferrite (δ) and austenite (γ) intensely deformed grains. The intensity of grain deformation is increasing with the increase in the applied deformation degree. Also, it was observed that increasing the deformation temperature leads to a strong increase in the weight fraction of the dynamically recrystallised (DRX) ferrite (δ) grains.

In-depth S/TEM observation of Ti–Hf and Ta–Hf-doped Nb3Sn layers

In superconducting Nb3Sn layers with coherence lengths of approximately 3 nm, grain boundaries act as effective pinning sites. Thus, grain refinement is an essential issue that directly affects the superconducting critical characteristics of the Nb3Sn layer. In recent years, Hf addition to Nb3Sn wires co-doped with Ta has attracted notable interest as a method that enables grain refinement down to several tens of nm. In-depth characterization of the Nb3Sn grain morphology in Hf-doping is crucially important to correlate the microstructure with the flux pinning characteristics. In this article, the grain morphologies of Ti–Hf and Ta–Hf-doped Nb3Sn layers were clarified by scanning transmission electron microscopy (STEM) and TEM-based automated crystal orientation mapping (ACOM-TEM). STEM/energy dispersive x-ray spectroscopy (EDS) revealed no significant oxide precipitates in our samples. The grain size distribution was attained by ACOM-TEM. Although Hf-doping attained a grain refinement effect in the Nb3Sn layer in both doping cases, the degree of this effect was relatively small for Ti–Hf. Kernel average misorientation analysis by scanning electron microscopy-electron backscattered diffraction unveiled no appreciable difference between the internal strain states of the Nb-alloy parent phases in Ti–Hf and Ta–Hf. One remarkable new finding through STEM/EDS was the presence of a Cu–Hf compound phase in the Nb3Sn layer. The Cu–Hf compound sounds analogous to the Cu–Ti compounds that form when Nb–47Ti with Cu matrix is heat treated. The STEM/EDS maps revealed a larger amount of Cu flow from the Cu–Sn side along the grain boundaries. The large Cu deposition on the grain boundaries might facilitate grain growth in Nb3Sn. Those findings make a novel contribution to the literature as they provide a deep insight into Nb3Sn phase formation via Hf doping.

Microstructure of electronic-grade polycrystalline silicon core-matrix interface

This paper focuses on the problems encountered in the production process of electronic-grade polycrystalline silicon. It points out that the characterization of electronic-grade polycrystalline silicon is mainly concentrated at the macroscopic scale, with relatively less research at the mesoscopic and microscopic scales. Therefore, we utilize the method of physical polishing to obtain polysilicon characterization samples and then the paper utilizes metallographic microscopy, scanning electron microscopy-electron backscatter diffraction technology, and aberration-corrected transmission electron microscopy technology to observe and characterize the interface region between silicon core and matrix in the deposition process of electronic-grade polycrystalline silicon, providing a full-scale characterization of the interface morphology, grain structure, and orientation distribution from macro to micro. Finally, the paper illustrates the current uncertainties regarding polycrystalline silicon.

Analysis of the mechanical properties and microstructure of titanium surfaces designed by electromagnetic induction nitriding

Nitride has high hardness and excellent wear resistance. It is frequently prepared on a material surface to improve material performance. The nitriding layer can be prepared in different ways, so the bonding strength and microstructure between the nitriding layer and the matrix differ, which will directly affect the surface mechanical properties of the material. In this study, pure titanium (TA1) was nitrided using electromagnetic induction nitriding, and the microstructure of nitriding layer was analysed using x-ray photoelectron spectroscopy (XPS), scanning electron microscopy-electron backscatter diffraction (SEM-EBSD) and scanning electron microscopy-energy-dispersive x-ray spectroscopy (SEM-EDS). In addition, the mechanical properties of the nitriding layer were studied using a nanoindentation and scratch tester. The experimental result shows a 20 μm induction nitriding layer composed of TiN, Ti2N and α(N)-Ti. The compound layer (Ti2N and TiN) was approximately 3 μm. The surface was contaminated with C and O elements, and evident segregation bands were found between the induction nitriding layer and matrix. The induction nitriding layer can considerably improve the wear resistance of titanium alloy, but the bonding force between the induction nitriding layer and matrix decreases owing to the segregation band.

High temperature nano-indentation on the mechanical properties of Zr and Zr–Fe alloys: Experimental and theoretical analysis

In this work, the microstructure and subsurface hardness of pure Zr and Zr-xFe (x = 0.2, 0.4, 0.6) model alloys were investigated at elevated temperatures (298–573 K) by means of scanning electron microscopy-electron backscatter diffraction (SEM-EBSD) analysis, transmission electron microscope (TEM) and high temperature nano-indentation test (HTNIT). Corresponding experimental results indicated that the addition of Fe element could lead to grain refinement for Zr–Fe alloys, and facilitate the formation of second phase particles (SPPs) like Zr3Fe precipitates and spherical particles in the matrix, which were in a close relationship with materials hardening. In order to address the hardness-indentation depth relation of Zr–Fe alloys with temperature effect, a mechanistic model was developed that covered the hardening mechanisms of lattice friction, precipitation hardening and dislocation interaction. Related theoretical analysis showed that all the three hardening mechanisms got weakened at high temperatures, which led to the decrease of materials hardness with increasing temperature. Moreover, the noticeable indentation size effect (ISE) was dominated by the formation of geometrically necessary dislocations (GNDs), and increasing temperature could result in the density decrease of GNDs due to the expansion of the plastic zone at elevated temperatures. With the increase of the indentation depth, the dominant hardening mechanism changed from the contribution of GNDs to that of statistically stored dislocations (SSDs). The results obtained in this work can help comprehend the effect of Fe element on both the microstructure and mechanical properties of Zr–Fe alloys at high temperatures.

Microstructures analysis and quantitative strengthening evaluation of powder metallurgy Ti–Fe binary extruded alloys with (α+β)-dual-phase

Abstract In this study, Fe, one of the inexpensive β-phase stabilizers, was employed to fabricate Ti alloys by the powder metallurgy route. The formation mechanism of unique microstructures and texture of the extruded Ti–Fe alloy was elucidated through scanning electron microscopy-electron backscatter diffraction (SEM-EBSD) and transmission electron microscopy-energy-dispersive X-ray spectroscopy (TEM-EDS). For the Ti–Fe alloys consolidated from the pre-mixed pure Ti powder and Fe particles by spark plasma sintering and following hot extrusion, the additive Fe atoms existed as solid solution atoms in β-Ti phase. The increment in the Fe content was effective in increasing the β-Ti phase volume fraction and refining the α-Ti grains. The mean α-Ti grain size of Ti-4 wt.% Fe alloy was 1.27 μm, which was about ten times less than that of the pure Ti material (12.42 μm). The α and β phases of the extruded Ti-1–4 wt.% Fe material were aligned in parallel to the extrusion direction, and they suppressed the grain growth of each other. Although yield stress (YS) and tensile strength (TS) remarkably increased to 1093 MPa and 1183 MPa, respectively, with an increase in the Fe content, a large elongation of 28–38% was obtained in the extruded Ti–Fe alloys. These tensile properties were favorable compared to the commercial Ti-6 wt.% Al-4 wt.% V alloy. The dominant strengthening factors for the Ti–Fe alloys were α-Ti grain refinement and β-Ti hard phase dispersion. In the case of 4 wt% Fe addition, 50% of the YS increment was due to the latter strengthening mechanism.

In-situ observation of abnormal grain growth in a low-alloyed carbon steel using SEM-EBSD

Because abnormal grain growth (AGG) degrades mechanical properties of industrial polycrystalline materials such as steel, understanding and controlling AGG are important. In this study, AGG of Al-Nb-microalloyed low-carbon steel was investigated at 1100°C using in-situ scanning electron microscopy-electron backscatter diffraction (SEM-EBSD). Owing to the pinning particles of AlN and Nb(C,N), fine austenite grains formed initially, and AGG appeared owing to the dissolution of the pinning particles at high temperatures. Relatively large grains invaded the surrounding smaller grains with a size ratio of approximately 0.3, resulting in AGG. We developed the in-situ observation method to investigate the AGG of the carburization process using a diffusion couple of high- and low-carbon steels. The carbon diffusion into the low-carbon steel from the high-carbon steel enhanced the grain growth of the low-carbon steel. Although the detailed mechanism is still unclear, we clearly showed that carburization can reduce the pinning force. When focusing on the misorientation of the grain boundary, grain boundaries with misorientation angles of 50–59° remained during AGG, which is explained by their lower mobility owing to their lower grain boundary energy. These results suggest that the difference in grain-boundary mobility can induce duplex grain growth with a bimodal distribution, resulting in AGG.

Influence of ageing treatment temperature and duration on σ-phase precipitation and mechanical properties of UNS S32750 SDSS alloy

IntroductionSuper-Duplex Stainless Steeles (SDSS) proved an excellent potential for its use in many chemical and offshore applications due to their both high mechanical properties and a high corrosion resistance in chloride ion solutions. ObjectivesThis study evaluates the influence of ageing treatment temperature and duration on σ-phase precipitation and mechanical properties of UNS S32750 SDSS alloy. MethodsThe influence of ageing treatment on microstructural features was analysed by SEM-EBSD (Scanning Electron Microscopy - Electron Backscatter Diffraction) technique, while on mechanical properties by tensile and impact testing techniques. ResultsThe obtained results show that for the short duration ageing treatments the σ-phase nucleates, within the δ-phase matrix, at the δ/γ grains boundary by the δ → σ precipitation, while for long duration ageing treatments the σ-phase nucleates, within the δ-phase matrix, at the δ/δ grains boundary, or in other favourable nucleation sites, due to the eutectoid decomposition δ → σ + γ2. Experimental data showed that at low temperatures, i.e. 780 °C, in order to induce the precipitation of σ-phase, the minimum incubation time is situated close to 20 min, and that increasing treatment temperature decreases the minimum incubation time, with at 850 °C and 920 °C the σ-phase being firstly detected at 5 min. The σ-phase precipitation shows the highest precipitation kinetics at 850 °C, when the maximum weight-fraction is obtained for each treatment duration when compared with ageing treatments performed at 780 °C and 920 °C. ConclusionAll presented data brings valuable insight into the σ-phase precipitation phenomena and its influence on UNS S32750 SDSS alloy’s exhibited mechanical properties and, also, can provide researchers and industrial steel processors a guide regarding the selection of optimal ageing treatment parameters to avoid/minimise the embrittlement induced by the precipitation of deleterious σ-phase.

Microstructure Characterization of Massive Ferrite in Laser-Weldments of Interstitial-Free Steels

Laser welding, which is known for its precision and high welding rate, offers a high-cooling-rate processing environment. In this study, laser welding was applied to interstitial-free steel plates with phosphorous additions of 0.002 and 0.009 wt%. After laser welding was performed and the weldment was cooled by protective gas, massive ferrite was produced. The base metal, heat affected zone, and weld region were observed and compared by optical microscopy (OM). It was found that increasing the phosphorous content led to refinement of the grain size of the massive ferrite. In addition, the allotriomorphic ferrite in the base metal and the massive ferrite in the weld were characterized and analyzed under scanning electron microscopy–electron backscatter diffraction (SEM-EBSD). The substructures of massive ferrite in OM can be resolved to be low-angle sub-boundaries in kernel average misorientation (KAM) analysis conducted on SEM. Furthermore, TEM analysis revealed that the substructures of massive ferrite were associated with the dislocation cell structures; it is presumed that during the growth of massive ferrite, the rapid migration of incoherent boundaries generated a high dislocation density, and subsequent cooling led to auto-tempering.

Influence of ageing treatment on microstructural and mechanical properties of a solution treated UNS S32750/EN 1.4410/F53 Super Duplex Stainless Steel (SDSS) alloy

In this present study, the influence of isothermal ageing temperature and ageing duration on microstructural and mechanical properties of a solution treated UNS S32750 Super Duplex Stainless Steel (SDSS) alloy, was investigated by SEM-EBSD (Scanning Electron Microscopy-Electron Backscatter Diffraction) microscopy, tensile and, impact testing techniques. Isothermal ageing treatments, performed at temperatures between 400°C and 600°C and, treatment durations of 3h and, 120h, were applied to a commercial UNS S32750 SDSS alloy. Microstructural characteristics, such as: distribution and morphology of constituent phases, distribution maps of grain's modal orientation (MO) and, obtained mechanical properties were analyzed. The applied isothermal ageing treatments did not induce any significant changes in relation to phase's morphology, grain-size and, MO distribution. Obtained results show that the microstructure consists of elongated γ-phase grains within δ-phase matrix, showing a grain-size close to (45–48) μm in the case of δ-phase, (22–24) μm in the case of γ-phase and, (1.6–2.1) μm in the case of γ2-phase. Significant changes were noticed in the case of mechanical properties (ultimate tensile strength, 0.2 yield strength and, elongation to fracture) due to precipitation of secondary phases. The most influential secondary phase is the R-phase, observed in the case of isothermal ageing treatment performed at 600°C with a treatment duration of 120h (A3.2 state). The A3.2 state, in comparison with solution treated (ST) state, showed a reduction in elongation to fracture of approx. 62% and, an increase in ultimate tensile strength and, respectively, 0.2 yield strength of approx. 24% and, respectively, approx. 16%.

Influence of isochronal treatments on microstructure and mechanical properties of solution treated UNS S32750 SDSS alloy specimens

In this study, the influence of isochronal treatments performed at temperatures between 700 °C and 1060 °C and, with a treatment duration of 15 min, on microstructure and mechanical properties of a solution treated UNS S32750 Super Duplex Stainless Steel (SDSS) alloy was investigated by SEM-EBSD (Scanning Electron Microscopy-Electron Backscatter Diffraction), tensile testing and, impact testing techniques. Microstructural characteristics, such as: constituent phases, weight fraction, grain-size, morphology and, obtained mechanical properties, such as: absorbed energy, ultimate tensile strength, yield strength and, elongation to fracture were analysed. The isochronal treatments induced changes in relation to alloy’s constituent phases morphology, grain-size and, precipitation of secondary phases. Obtained results show that the microstructure consists of elongated γ-phase grains, due to prior hot-deformation, in a δ-phase matrix. Also, within the δ-phase matrix, secondary phases can precipitate during isochronal treatments. The following secondary phases were identified: γ2-phase, σ-phase and, χ-phase. Changes were observed, also, in recorded mechanical properties, due to precipitation of deleterious secondary phases. The most influential precipitated secondary phase is the σ-phase, which was observed in samples treated at temperatures between 780 °C and 1000 °C and, induced decrease in alloy’s absorbed energy and elongation to fracture, both reaching minimum values, close to 3.3 [J] and, respectively 9 [%].

Influence of Aging Treatment on Microstructure and Tensile Properties of a Hot Deformed UNS S32750 Super Duplex Stainless Steel (SDSS) Alloy

In this present study, the influence of isothermal aging temperature and duration on microstructural and mechanical properties of a hot-deformed UNS S32750 super duplex stainless steel (SDSS) alloy was investigated by SEM-EBSD (scanning electron microscopy-electron backscatter diffraction) and tensile testing techniques. An isothermal aging treatment, at temperatures between 400 and 600 °C and treatment duration between 3 and 120 h, was applied to a commercial UNS S32750 SDSS alloy. Microstructural characteristics of all thermomechanical (TM) processed states, such as distribution and morphology of constituent phases, grain’s modal orientation (MO), and obtained mechanical properties were analysed correlated with the TM processing conditions. The obtained experimental results show that the constituent phases, in all TM processed states, are represented by elongated γ-phase grains within the δ-phase matrix. The R-phase was observed in the case of aging treatment performed at 600 °C for 120 h. Within the δ-phase matrix, dynamically recrystallized grains were identified as a result of applying hot deformation and isothermal aging treatments. Also, it was observed that aging treatment parameters can significantly influence the mechanical behaviour exhibited by the UNS S32750 SDSS alloy, in terms of elongation to fracture and absorbed energy during impact testing.

Towards micro- and nanostructured AlZnCu alloys cast from commercial-purity metals

Structural and composition modification of high-zinc aluminum alloys refines their microstructural scale from a few millimeters to a few micrometers. In a series of studies, high-aluminum Al–30Zn alloys were doped with (2–20) wt.% Cu, 1 wt% Mn and small (∼100 ppm) Ti addition. The alloys’ microstructure has been studied using SEM/EBSD (scanning electron microscopy/electron backscatter diffraction) and LM (light microscopy) techniques. A small addition of Ti introduced with Al-3 wt.% Ti-0.15 wt% C (TiCAl) master alloy decreases the grain diameter in the high-aluminum zinc alloys from 1500–2000 μm to 100–200 μm. The high-zinc, high-copper alloy (Al–30Zn–20Cu) cast into a steel mold shows microstructure refinement to 2–5 μm. The observed refinement should improve the ductility of the examined alloys while preserving other properties discussed in the paper.

TWIP and Fracture Behavior in the Superalloy 625 at Room and Cryogenic Temperatures

In this study an austenitic nickel base alloy (Alloy 625) with medium to high stacking fault energy was tensile tested at room temperature and at cryogenic temperature, -196°C, to investigate if twinning was involved in the fracture process. Fracture surfaces and microstructure were characterized using scanning electron microscopy and texture was evaluated with scanning electron microscopy-electron backscatter diffraction at three positions along the tensile test specimens. Features where investigated with electron channelling contrast imaging. At room temperature the predominant deformation mechanism is slip and at cryogenic temperature slip is followed by deformation twinning. At room temperature deformation twinning will make an extra deformation contribution in the localized necking region compared to the cryogenic temperature case where deformation twins already are distributed in the microstructure and in this case will hinder the dislocations to move freely and instead cause stress field build up at the twin boundaries and subsequent microcrack and void formation.

Surface damages of polycrystalline W and La2O3-doped W induced by high-flux He plasma irradiation

In this study, polycrystalline tungsten (W) and three oxide dispersed strengthened W with 0.1 vol %, 1.0 vol % and 5.0 vol % lanthanum trioxide (La2O3) were irradiated with low-energy (200 eV) and high-flux (5.8 × 1021 or 1.4 × 1022 ions/m2⋅s) He+ ions at elevated temperature. After He+ irradiation at a fluence of 3.0 × 1025/m2, their surface damages were observed by scanning electron microscopy, energy dispersive spectroscopy, scanning electron microscopy-electron backscatter diffraction, and conductive atomic force microscopy. Micron-sized holes were formed on the surface of W alloys after He+ irradiation at 1100 K. Analysis shows that the La2O3 grains doped in W were sputtered preferentially by the high-flux He+ ions when compared with the W grains. For irradiation at 1550 K, W nano-fuzz was formed at the surfaces of both polycrystalline W and La2O3-doped W. The thickness of the fuzz layers formed at the surface of La2O3-doped W is 40% lower than the one of polycrystalline W. The presence of La2O3 could suppress the diffusion and coalescence of He atoms inside W, which plays an important role in the growth of nanostructures fuzz.

Physical characterization of uranium oxide pellets and powder applied in the Nuclear Forensics International Technical Working Group Collaborative Materials Exercise 4

Physical characterization is one of the most broad and important categories of techniques to apply in a nuclear forensic examination. Physical characterization techniques vary from simple weighing and dimensional measurements to complex sample preparation and scanning electron microscopy-electron backscatter diffraction analysis. This paper reports on the physical characterization conducted by several international laboratories participating in the fourth Collaborative Materials Exercise, organized by the Nuclear Forensics International Technical Working Group. Methods include a range of physical measurements, microscopy-based observations, and profilometry. The value of these results for addressing key investigative questions concerning two uranium dioxide pellets and a uranium dioxide powder is discussed.

Crystallographic features of the martensitic transformation and their impact on variant organization in the intermetallic compound Ni50Mn38Sb12 studied by SEM/EBSD.

The mechanical and magnetic properties of Ni-Mn-Sb intermetallic compounds are closely related to the martensitic transformation and martensite variant organization. However, studies of these issues are very limited. Thus, a thorough crystallographic investigation of the martensitic transformation orientation relationship (OR), the transformation deformation and their impact on the variant organization of an Ni50Mn38Sb12 alloy using scanning electron microscopy/electron backscatter diffraction (SEM/EBSD) was conducted in this work. It is shown that the martensite variants are hierarchically organized into plates, each possessing four distinct twin-related variants, and the plates into plate colonies, each containing four distinct plates delimited by compatible and incompatible plate interfaces. Such a characteristic organization is produced by the martensitic transformation. It is revealed that the transformation obeys the Pitsch relation ({0[Formula: see text]}A // {2[Formula: see text]}M and 〈0[Formula: see text]1〉A // 〈[Formula: see text]2〉M; the subscripts A and M refer to austenite and martensite, respectively). The type I twinning plane K1 of the intra-plate variants and the compatible plate interface plane correspond to the respective orientation relationship planes {0[Formula: see text]}A and {0[Formula: see text]}A of austenite. The three {0[Formula: see text]}A planes possessed by each pair of compatible plates, one corresponding to the compatible plate interface and the other two to the variants in the two plates, are interrelated by 60° and belong to a single 〈11[Formula: see text]〉A axis zone. The {0[Formula: see text]}A planes representing the two pairs of compatible plates in each plate colony belong to two 〈11[Formula: see text]〉A axis zones having one {0[Formula: see text]}A plane in common. This common plane defines the compatible plate interfaces of the two pairs of plates. The transformation strains to form the variants in the compatible plates are compatible and demonstrate an edge-to-edge character. Thus, such plates should nucleate and grow simultaneously. On the other hand, the strains to form the variants in the incompatible plates are incompatible, so they nucleate and grow separately until they meet during the transformation. The results of the present work provide comprehensive information on the martensitic transformation of Ni-Mn-Sb intermetallic compounds and its impact on martensite variant organization.

Effect of Boron on the Strength and Toughness of Direct-Quenched Low-Carbon Niobium Bearing Ultra-High-Strength Martensitic Steel

The effect of boron on the microstructures and mechanical properties of laboratory-control-rolled and direct-quenched 6-mm-thick steels containing 0.08 wt pct C and 0.02 wt pct Nb were studied. The boron contents were 24 ppm and a residual amount of 4 ppm. Two different finish rolling temperatures (FRTs) of 1093 K and 1193 K (820 °C and 920 °C) were used in the hot rolling trials to obtain different levels of pancaked austenite prior to DQ. Continuous cooling transformation (CCT) diagrams were constructed to reveal the effect of boron on the transformation behavior of these steels. Microstructural characterization was carried out using various microscopy techniques, such as light optical microscopy (LOM) and scanning electron microscopy-electron backscatter diffraction (SEM-EBSD). The resultant microstructures after hot rolling were mixtures of autotempered martensite and lower bainite (LB), having yield strengths in the range 918 to 1067 MPa with total elongations to fracture higher than 10 pct. The lower FRT of 1093 K (820 °C) produced better combinations of strength and toughness as a consequence of a higher degree of pancaking in the austenite. Removal of boron lowered the 34 J/cm2 Charpy-V impact toughness transition temperature from 206 K to 158 K (−67 °C to −115 °C) when the finishing rolling temperature of 1093 K (820 °C) was used without any loss in the strength values compared to the boron-bearing steel. This was due to the finer and more uniform grain structure in the boron-free steel. Contrary to expectations, the difference was not caused by the formation of borocarbide precipitates, as verified by transmission electron microscopy (TEM) investigations, but through the grain coarsening effect of boron.

Influence of Solution Treatment Temperature on Microstructural Properties of an Industrially Forged UNS S32750/1.4410/F53 Super Duplex Stainless Steel (SDSS) Alloy

In this present study, the influence of solution annealing temperature on microstructural properties of a forged Super Duplex Stainless Steel (SDSS) was investigated by SEM-BSE (Scanning Electron Microscopy-Backscattered Electrons) and SEM-EBSD (Scanning Electron Microscopy-Electron Backscatter Diffraction) techniques. A brief solution treatment was applied to the forged super duplex alloy, at different temperatures between 800 °C and 1100 °C, with a constant holding time of 0.6 ks (10 min). Microstructural characteristics such as nature, weight fraction, distribution and morphology of constituent phases, average grain-size and grain misorientation were analysed in relation to the solution annealing temperature. Experimental results have shown that the constituent phases in the SDSS alloy are δ-Fe, γ-Fe and σ (Cr-Fe) and that their properties are influenced by the solution treatment temperature. SEM examinations revealed microstructural modifications induced by the Cr rich precipitates along the δ/γ and δ/δ grain boundaries, which may significantly affect the toughness and the corrosion resistance of the alloy. Solution annealing at 1100 °C led to complete dissolution of σ (Cr-Fe) phase, the microstructure being formed of primary δ-Fe and γ-Fe. The orientation relationship between δ/δ, γ/γ and δ/γ grains was determined by electron back scattering diffraction (EBSD). Both primary constituent phase’s microhardness and global microhardness were determined.