Abnormal grain growth is a fundamental phenomenon in the processing of grain-oriented electrical steels. The presence of inhibitors, strong texture, and reduced sheet thickness are key factors that contribute to its occurrence. In this work, a grain-oriented electrical steel (Fe-4wt%Si) was obtained using laser powder bed fusion (LPBF) additive manufacturing and subsequent thermomechanical processing. The LPBF-processed slabs were built using scanning strategies without rotation (0 degrees) and with rotations of 45 degrees and 90 degrees between the layers. Subsequently, the slabs were cold rolled to 91 % reduction. Abnormal grain growth occurred during prolonged box annealing at 1200 degrees C, favored by the coarsening of crystalline SiO2-based nanoparticles that acted as inhibitors of normal grain growth. The influence of the scanning strategy on the as-built texture and the magnetic properties after thermomechanical processing was investigated. Very coarse grain sizes, low porosity and reduced thickness contributed positively to the decrease in magnetic losses. The deviation of Goss grains from the ideal orientation was smaller for samples without rotation (0o), indicating that this scanning strategy generates textures closer to the desired ones (Goss and eta fiber). This strategy provided the lowest magnetic losses and the best magnetic properties among the laser scanning strategies investigated.

We followed the microstructural evolution of UNS S32205 duplex stainless steel during cold rolling up to 79% reduction in thickness and at early stages of isothermal annealing at 1080ºC. Qualitative analysis of peak broadening and kernel average misorientation (KAM) parameter obtained by X-ray diffraction (XRD) and electron backscatter diffraction (EBSD), respectively, indicated a higher work hardening of austenite. Strain-induced martensite was not detected within this strain range by using X-ray diffraction and DC-magnetisation measurements. Two particular rolling thickness reductions were chosen for recrystallisation studies; i.e., 43% and 64%. After annealing for 1 min, primary recrystallisation occurred in ferrite (42% of recrystallised grains for 43% cold rolling), whereas austenite only recovered. For a reduction of 64%, the recrystallised fraction of ferrite did not change significantly, while austenite reached a recrystallised fraction of 43%. Full recrystallisation is noticed after annealing for 3 min for both conditions resulting in a bamboo-like grain structure.

AISI 317 L stainless steel replaces 316 L grade in some applications due to its superior mechanical strength and corrosion resistance. Aiming at expanding its applicability to structural applications, ongoing studies are dedicated to overcoming the trade-off between strength and ductility. The stacking fault energy decreases with deformation temperature and favors stacking faulting, (nano)twinning and strain-induced martensite (SIM) formation, resulting in severe microstructural fragmentation. The effect of temperature on deformation behavior of AISI 317 L steel was investigated in samples rolled at room temperature to thickness reductions of 50% and 85% and at 77 K to reductions in thickness of 10% and 50%. The microstructural evolution was followed by scanning electron microscopy, Vickers microhardness, X-ray diffraction, magnetization, electron backscatter diffraction (EBSD) and electron channeling contrast imaging (ECCI). The nucleation sites in the early stages of the transformation sequence gamma -> c -> alpha' were identified in the 10% cryorolled sample. The highest volume fraction of alpha'-martensite reached 45.8% in the cryorolled steel to 50% rolling reduction. Much lower fractions were obtained for samples rolled to 10% reduction at 77 K (2%) and at room temperature to 50% (0.3%) and 85% reductions (1.6%). The texture components after cryorolling were Goss and Brass for austenite; rotated cube, alpha- and gamma- fibers for delta- ferrite and alpha'-martensite. The c-martensite presents the typical texture of hcp metals with a c/a ratio above the ideal value and (0001)- oriented tilted about 21 degrees degrees from the normal direction towards the rolling direction. The results show cryorolling as an effective method for enhancing SIM formation and promoting severe microstructural refinement in AISI 317 L stainless steel.

A novel additive manufacturing approach is proposed to produce an electrical steel (Fe-3.5

An anomalous increase in magnetization was investigated in a cold-rolled high-Mn TRIP steel (16.8 wt% Mn) annealed at 350 degrees C for times varying from 5 to 120 min, before the start of austenite reversion (alpha' -> gamma). Besides in-situ and ex-situ magnetic measurements, the full characterization of this phenomenon was also performed with the aid of X-ray diffraction (XRD), Mossbauer spectroscopy, and microstructural characterization using electron backscatter diffraction (EBSD) and atom probe tomography (APT). Based on XRD measurements, the volume fraction of austenite and alpha'-martensite was estimated as a function of annealing time, as well as their lattice strain. Phase quantification confirmed the absence of newly-fresh alpha'-martensite in the material during annealing at 350 degrees C. Short annealing up to 15 min promoted the increase of Ms (saturation magnetization) due to stress relief in alpha'-martensite (Villari effect). Further annealing to 30 min promotes the decrease in Ms driven by short-range solute reorganization within the lattice. After 60 min annealing, the creation of long-range solutedepleted zones (i.e. confined zones highly enriched in Fe) causes a new increase in Ms. In comparison, for 120 min of annealing time, Ms tends to remain unaltered. These findings revealed that short- and long-range chemical fluctuations strongly affect the saturation magnetization of the steel and brought new insights on the use of magnetic probing as a tool for phase quantification in Mn-bearing steels.

A novel additive manufacturing approach is proposed to produce an electrical steel (Fe-3.5%Si) by laser powder bed fusion (LPBF) followed by conventional thermomechanical processing. The aim of this proof-of-concept study is to develop a new processing route for grain-oriented electrical steels from LPBF-processed plates with strong texture and SiO 2 nanoparticles followed by cold rolling and long-term annealing to trigger abnormal grain growth. The slabs were processed with two different scanning strategies; e.g., with (90R) and without 90° rotation (0R) between layers aiming at intensifying the as-built textures near-Goss and/or cube components. The as-built slabs were cold rolled to 83% reduction and annealed for subsequent monitoring of primary recrystallization and abnormal grain growth. Goss or near-Goss nuclei were identified for both strategies after cold rolling. Abnormal grain growth occurred more intensely in samples with a 90° rotation between layers. Goss-oriented grains are bounded by high-angle boundaries with peak misorientations of 50° in 90R and 37.5° in 0R strategy. Porosity in 0R is three times higher than in 90R, while the total fraction of CSL boundaries is similar for both strategies (about 6%). Boundary mobility seems to be higher in 90R, which explains easier grain boundary depinning from oxide nanoparticles than in 0R strategy. In comparison with grain-oriented commercial products, increased total magnetic losses can be explained by thickness effects, porosity and deviation from ideal Goss orientation. Graphical Abstract

Reduced-activation ferritic-martensitic oxide-dispersion-strengthened (RAFM-ODS) Eurofer steel is a potential candidate material for structural applications in fusion reactors. Microstructural stability during long-term exposure at high temperatures is a key issue. Depending on the amount of prior cold-rolling strain and service temperature, important solid-state restoration reactions occur such as recovery, recrystallization and particle coarsening. ODS-Eurofer steel was cold rolled up to 80% reduction in thickness and annealed at 800 degrees C for durations up to 4320 h. Changes in microstructure were tracked by X-ray diffraction measurements using synchrotron radiation in post-mortem specimens to estimate dislocation character and density. The volume fraction of recrystallized grains was estimated using grain orientation spread (GOS) maps from electron backscatter diffraction (EBSD). Most of the softening occur in the first hour of annealing and it seems to be closely related to discontinuous recrystallization where a few special grain boundaries overcome Zener-Smith pinning effects caused by fine and stable Y2O3-based particles. M23C6 carbides undergo coarsening upon annealing and, as a result, extended recovery is the predominant softening mechanism as annealing proceeds, although only about 15% softening is noticed after annealing for 4320 h. Using thermodynamic and kinetic calculations, the results were extrapolated to the predicted service temperature of 650 degrees C. The results suggest that the remarkable microstructural stability of ODS-Eurofer would withstand almost 180 years at high service temperatures without major loss of the mechanical properties of the materials.

The microstructure and mechanical properties were investigated in a 17.48-mm-thick electron beam-welded (EBW) API 5L X65 steel sheet. Electron beam welding has the advantage of joining thick steel parts in a single pass with a high energy conversion efficiency, low heat input and low warpage. The base metal has elongated bands of ferrite interspersed with pearlite colonies aligned along the rolling direction. After welding, a narrow and fine-grained heat affected zone (HAZ) consists of degenerate pearlite and martensite–austenite (M–A) islands. The microstructure of the fusion zone is coarser than the HAZ and more complex, consisting of lower bainite, Widmanstätten ferrite, acicular ferrite, grain boundary ferrite, and small islands of the M–A constituent. These microstructure changes are minimized when EBW is used and do not significantly affect the mechanical properties of the weld. Results of Charpy V-notch tests for weld beads parallel and perpendicular to the rolling direction met the requirements of the API 5L standard. EBW has proven to be a viable alternative for welding thick plates of advanced steels applied in pipeline construction and assembly.

Austenite reversion, i.e., a'-martensite -* gamma phase transformation in UNS S32304 lean duplex steel was investigated. The material was cold rolled to a true strain (e) of 1.61 and subjected to continuous annealing up to 1000 degrees C with a heating rate of 3 degrees C/min. From the dilatometric curve, an unexpected thermal expansion at around 545 degrees C was found within the temperature range where the austenite reversion occurs. Based on this unexpected behavior, additional samples were annealed at the same heating rate until key temperatures. Besides dilatometry, microstructural changes were followed by means of magnetic measurements at room temperature, Vickers microhardness testing, high-resolution electron backscatter diffraction (EBSD), and electron channeling contrast imaging (ECCI). From EBSD data, a protocol was developed to distinguish the different constituents in the material during the austenite reversion, i.e., alpha'-martensite, ferrite, and both reversed and untransformed austenite. The driving force for the austenite reversion was calculated using thermodynamic calculations. The a'martensite -* gamma transformation begins at about 545 degrees C and ends at almost 800 degrees C. In the early beginning, the austenite reversion is governed by a shear mechanism. At higher temperatures, at about 725 degrees C, KAM (kernel average misorientation) distributions and texture of both reversed and untransformed austenite show evidence of a diffusion-controlled austenite reversion mechanism. These results are supported by thermodynamic calculations and microstructural evidence revealed by ECCI.

Warm compression tests were performed for the Mo-based alloy MZ17 (Mo-1.7% wt.-ZrO2). Macroscopic de-formations to about 67% reduction in height were imposed to cylindrical specimens over a wide range of strain rates (from 10-1 to 10 s- 1) at 1000 and 1100 degrees C to investigate the effects of both, the strain rate and deformation temperature on the recrystallization of the alloy. The compression tests were performed under high vacuum (< 5.0 x 10-4 mbar) using a deformation dilatometer followed by fast cooling. Stress-strain curves with very similar shapes can be noticed for all testing conditions. As-deformed microstructures were imaged at the center of the samples where plastic flow is more uniformly distributed using electron backscatter diffraction (EBSD) to distinguish the recovered domains from the recrystallized grains. Electron channeling contrast imaging (ECCI) was used to visualize the dislocation structures. At all tested temperatures and strain rates, only partial recrystallization was detected. The recrystallized volume fraction increases with increasing the strain rate. There is microstructural evidence of three restoration mechanisms acting during warm deformation; i.e., dynamic recovery, dynamic recrystallization and particle stimulated nucleation (PSN), the latter to a minor extent.

Alloys processed by laser powder-bed fusion show distinct microstructures composed of dislocation cells, dispersed nanoparticles, and columnar grains. Upon post-build annealing, such alloys show sluggish recrystallization kinetics compared to the conventionally processed counterpart. To understand this behavior, AISI 316L stainless steel samples were constructed using the island scan strategy. Rhodonite-like (MnSiO 3 ) nanoparticles and dislocation cells are found within weakly-textured grains in the as-built condition. Upon isothermal annealing at 1150 °C (up to 2880 min), the nucleation of recrystallization occurs along the center of the melt pool, where nuclei sites, high stored elastic energy, and local large misorientation are found in the as-built condition. The low value of the Avrami coefficient ( n = 1.16) can be explained based on the non-random distribution of nucleation sites. The local interaction of the recrystallization front with nanoparticles speeds up their coarsening causing the decrease of the Zener-Smith pinning force. This allows the progression of recrystallization in LPBF alloys, although sluggish. These results allow us to understand the progress of recrystallization in LPBF 316L stainless steel, shedding light on the nucleation mechanisms and on the competition between driving and dragging pressures in non-conventional microstructures. They also help to understand the most relevant microstructural aspects applicable for tuning microstructures and designing new LPBF alloys. Graphical abstract

The ultimate goal for structural materials is achieving both high strength and ductility. However, increasing one of these properties usually decrease the other, resulting in the so-called strength-ductility trade-off. According to the Considère criterion, increased strain hardening rates are demanded at higher strains to prevent necking and strain localization. This study reports a novel approach based on strain hardening engineering in a laser powder-bed fusion (LPBF) 304 L stainless steel deformed by tensile testing. The nucleation of αʹ-martensite directly from austenite (γ) was observed without the formation of the intermediate ε-phase. Both fine (11 μm) and coarse (93 μm) grains initially undergo dislocation slip and stacking fault formation in the as-built cellular structure up to a logarithmic strain (ε) of 0.05. Fine austenite grains exhibit αʹ-martensite growing along the extended stacking fault bands (ε > 0.05), while coarse <110> || LD (loading direction) oriented γ-grains primarily accommodate the imposed macroscopic strain via twinning (0.2 > ε > 0.05), followed by martensitic transformation or activation of other twinning systems (ε > 0.2). Deformation twinning is hindered within fine grains due to a (1) higher twinning activation stress and (2) an unfavorable crystallographic orientation. The hierarchical deformation reported for 304 L stainless steel is crucial for component and alloy-for-LPBF design. This study reveals the possibility of using LPBF for strain hardening engineering through grain size control, triggering the hierarchical deformation (and their interaction) in each grain family. As a result, high-strength and ductile alloys may be obtained by exploring this novel processing approach.

The annealing behavior of cold-rolled 317L austenitic stainless steel was investigated. The material was rolled to a true strain (epsilon) of 2.04 and subjected to both stepwise and continuous annealing up to 1000 degrees C, the latter conducted in the presence of an external magnetic field. Electron backscatter diffraction, dilatometry, thermo-dynamic calculations, Vickers microhardness testing, and electron channeling contrast imaging were used to follow the microstructure evolution upon annealing. The microstructure of the cold-rolled steel has about 2.3% of strain-induced alpha'-martensite, 4% of delta ferrite, and austenite as the predominant phase. Eye-shaped defor-mation heterogeneities are also noticeable and contrast with the predominant lamellar structure typical of cold-rolled materials. Microstructure changes were followed by means of magnetic measurements, with emphasis on both Ms (saturation magnetization) and Hc (coercive field) parameters. Our findings confirm the occurrence of austenite reversion, decrease of delta ferrite, and massive sigma phase precipitation for the annealing temper-ature and time intervals herein investigated. At 800 degrees C the steel is almost fully recrystallized, except for the eye-shaped structures, in whose interior precipitation is much less intense. Precipitation of sigma phase occurs preferentially at the delta ferrite lamellae. Magnetization was able to capture the fragmentation of the ferro-magnetic delta ferrite lamellae due to sigma phase precipitation and the changes associated with the decrease of delta ferrite and austenite reversion upon annealing.

Strain-induced alpha '-martensite and austenite reversion in a cold rolled UNS S32304 lean duplex steel were tracked by means of magnetic measurements, with emphasis on both M-s (saturation magnetization) and H-c (coercive field) parameters. Grain-averaged quality metrics derived from EBSD (electron backscatter diffraction) analysis were also used to distinguish the phases during austenite reversion. The material was cold rolled to a true strain (epsilon) of 1.61 and subjected to isothermal and continuous annealing, the latter conducted in the presence of an external magnetic field. The evolution of the alpha '-martensite fraction upon straining and after isothermal annealing was monitored by coupling the Ms values and thermodynamic simulations, as well as from EBSD analysis. For the isothermally annealed material (epsilon = 1.61), the overall behavior of Ms and hardness displayed similar trends with a strong decrease for temperatures higher than 500 degrees C, suggesting austenite reversion. Results confirmed the occurrence of austenite reversion for the temperature interval investigated here. At 800 degrees C, austenite reversion is complete, and the steel is fully recrystallized. Besides, from the EBSD analysis, evidence of ferrite transformation into austenite was rather noticeable, in accordance with thermodynamic simulations and magnetic probing. Complementary electron channeling contrast imaging (ECCI) revealed that precipitation reactions mainly occur in the recrystallized austenite at 700 and 800 degrees C. The Hc behavior of both, the strained and annealed conditions was inferred to be mostly driven by microstructural changes in ferrite.

Non-oriented (NO) silicon steel is used in magnetic cores of electrical machines due to its good magnetic and electric properties, such as high electric resistivity, high permeability, low coercive field, and low power losses. However, the noise and vibration, caused by magnetostriction, may lead to early failure of the equipment. Since the stator core is submitted to compressive stresses due to the shrinking fitting, positive values of magnetostriction are not appropriate. Fe-Ti alloys have low negative magnetostriction values making them strong candidates for replacing Fe-Si alloys. In this work, Fe-3wt.%Ti alloy was cold rolled down to 0.3 mm of thickness and annealed for 48 h at 850 degrees C. Magnetization showed to be 7 kA/m (0.09 T) higher than Fe-Si, and the magnetostriction is lower than 1 ppm up to 1.5 T while for Fe-Si is higher than 1 ppm for <0.25 T. Microstructure and texture were evaluated to explain the magnetic properties. The magnetic properties of Fe-3wt.%Ti are better than commercial non-oriented Fe-Si and could be an alternative to improve the performance of electrical motors.

Alloys manufactured by laser powder-bed fusion have intrinsic and hierarchical microstructural features inherited from the fast solidification (up to 10(4) K/s) and subsequent thermal cycles. This creates epitaxed grains, dislocation cell structures, and second-phase oxide nanoparticles. Epitaxed grains follow a pattern where finer grains are found in the melt pool centerline along the laser track. Upon further annealing, this characteristic microstructure has pronounced consequences on the recrystallization mechanisms and thus on grain topology. By changing the scanning strategy, we control the emerging grain patterns in a representative alloy (AISI 316L austenitic stainless steel) by creating linear strings for unidirectional scans, while a chessboard grain pattern arises by applying a 90 degrees-rotation between layers. Upon post-processing annealing (at 1150 degrees C from 15 min to 8 h), we study the relationship between the as-built and recrystallized microstructures. Recrystallization starts with fine nuclei in regions with high dislocation density along the melt pool centerlines, resulting in early-stage linear impingement (linearly clustered nucleation), as revealed by microstructural path analysis. Recrystallization is sluggish, due to dynamic Zener-Smith pinning. This effect leads to jerky boundary motion due to periodic pinning and depinning from oxide particles, caused by their gradual coarsening. Lower nuclei number density slows kinetics for the case of unidirectional scanning, while twinning aids in the nucleation of grains with mobile grain boundaries. Our findings show that changes in the laser scanning strategy are a suitable design tool for tailoring recrystallization and thus microstructure.

Parts produced by laser powder-bed fusion (LPBF) show unique microstructures consisting of dislocation structures and an oxide nanoparticle dispersion usually embedded in epitaxially-grown grains. Thermomechanical processing is an alternative to enhance the microstructure of such materials. However, the deformation mechanisms and the resulting microstructures following annealing are not yet well understood, hindering further microstructure control. We apply cold rolling and subsequent annealing in AISI 316L stainless steel processed by LPBF and perform an in-depth microstructural characterization to understand the origin of abnormal growth and how to avoid it. Upon deformation, mechanical twinning occurs. Early plastic instabilities arise due to the fine substructure with high defect density, resulting in profuse shear banding. Such shear bands carry most of the subsequent deformation, reducing the volume fraction of oxide particles along these regions due to enhanced particle dissolution via cracking/fragmentation. Upon annealing, the cold-rolled specimens show abnormal <110> || ND grains nucleating at shear bands. The earlier recrystallization onset and fragmented particle dissolution in shear bands result in a local lower Zener pinning and generate a size advantage for <110> || ND grains. Based on this investigation, abnormal growth may be triggered by shear bands in cold-rolled and annealed LPBF alloys for grain boundary engineering. Our results suggest that avoiding shear banding (and the consequent particle fragmentation) inhibits abnormal grain growth, thus yielding a more uniform and fine-grained microstructure.

The 15-5PH (UNS S 15500) stainless steel combines high mechanical strength, ductility, and good corrosion resistance for aircraft and aerospace applications. This set of properties and its high added-value applications make it an excellent choice for additive manufacturing processes such as laser powder-bed fusion (LPBF). However, there is a need to understand the complex microstructure developed in LPBF-processed parts, which may show particularities such as columnar solidification, preferential orientation, different kinds of porosities, chemical segregation along the melt pools, metastable phases, and oxide nanoinclusions. We report the microstructural characterization of LPBF-processed 15-5PH stainless steel in the as-built condition and after aging. Low porosity (<1%), high hardness (420 HV0.1), and a large amount of retained austenite (15%) were found in the as-built samples. The microstructure shows the usual "fish scale"-like morphology. Grain size and hardness vary depending on the location within the melt pools. Reconstruction of the parent grains from EBSD maps indicates a microstructural refinement due to in situ reaustenitization of parts of the previous consolidated layers, where these heat-affected zones are harder and present larger amounts of retained austenite. After aging, as-built samples were harder and more resistant to overaging than annealed or wrought counterparts. Transmission electron microscopy reveals a large amount of nanometric crystalline silicon-oxide inclusions, indexed as cristobalite. The combination of fine-grained martensite, coherent Cu-rich clusters, nanometric oxide particles, and retained austenite makes LPBF-processed 15-5PH stainless steel a very promising material for high-end structural applications.

This work reports the behavior of annealed commercially pure cold-drawn thin iron wires. Primary recrystallization is complete after holding for 180 s at 1123 K. After recrystallization, grain growth takes place within the central region but not close to the surface. For annealing times up to 14400 s, the grain size distribution broadens and the texture strengthens. The resulting texture is intense along the direction <110> parallel to the wiredrawing direction (WD). For longer times, abnormal grain growth takes place. The center of the wire is the preferred place for abnormal grain growth. By contrast, the grains closer to the surface do not experience any growth, and abnormal grains cannot consume them. Throughout the microstructure, one finds AlN and MnS particles. Close to the wire surface, there is a significantly higher particle density than in the center. We discuss mechanisms for the onset of abnormal grain growth, considering particle pinning and crystallographic texture. We observed two kinds of abnormal grains. Most abnormal grains belonged to the <110 > // WD fiber texture component, whereas a minority did not. We propose two mechanisms of abnormal grain growth initiation. The first mechanism explains the initiation of the abnormal grains with the assistance of the texture. The second mechanism associates the formation of a candidate abnormal grain to the topological path of the largest grains during normal grain growth preceding the onset of abnormal grain growth.