The current study investigates the microscale mechanical properties of the constituent phases and their influence on the macroscale properties of multi-phase steels with different microstructural constituents. Two steels, a Transformation Induced Plasticity (TRIP) and an enhanced ductility Dual Phase (DH) steel were produced in a continuous annealing line (CAL). Optical microscopy and EBSD results were utilized for segmentation of microstructural phase constituents. Macroscale mechanical properties were obtained using tensile testing and microscale properties with nanoindentation mapping. The hardness of each constituent is extracted from the hardness maps using a clustering algorithm. TRIP steel shows a homogeneous distribution of retained austenite in ferrite matrix and a small amount of bainite/martensite which is non-banded. In contrast, DH steel shows heterogeneous microstructures where martensite/bainite/retained austenite is found to be banded in the ferrite matrix. Both steels exhibit notable variations in hardness across their constituent phases, which are associated with the resulting microstructural characteristics. Nanoindentation results show that overall hardness/strength in TRIP steel is contributed from ferrite (66 %), retained austenite (33 %) and martensite/bainite (1 %). Whereas in DH steel, it is contributed from ferrite (55 %), mixture of RA, martensite/bainite (∼40 %) and martensite (∼5 %). The macroscopic behavior of TRIP and DH steels was explained and discussed using the rule of mixtures in conjunction with the microscopic properties of individual phases.

Wire arc additive manufacturing (WAAM) is a significant area of interest within the field of additive manufacturing (AM). In the present research, WAAM technology was employed to deposit a Ni-based alloy on a ductile cast iron substrate to fabricate a bimetallic structure of Ni-45 %Fe alloy and ductile cast iron. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), electron back scattered diffraction (EBSD) and X-ray diffraction (XRD) were used to study phase transformations, microstructure and crystallographic texture development in interfacial regions as well as deposited material. The mechanical properties were also studied using micro-hardness and profilometry-based indentation plastometry (PIP) measurements. The results showed that a wide variety of phases are generated within the heat-affected zone (HAZ) and partially melted zone (PMZ). These phases form complex microstructures with single and double shell morphology. The deposited alloy has a face-centred cubic (FCC) structure, with some carbides and graphite that are formed during the solidification of the first deposited layer. The compositional changes were also observed across the interface. The texture of the deposited alloy showed around 30° deviation from 〈100〉 II building direction due to the shape and overlap of the melt pools. The present results provide a better understanding of interface development mechanisms during WAAM of bimetallic structures. The peak of the hardness across the interface was observed in PMZ because of the formation of a martensitic matrix. The PIP measurements showed that the σ_y and the UTS of deposited alloy are lower than the cast iron base metal.

Electrical steels, also known as silicon steels, play an essential role in the generation, transmission, and use of electricity. The magnetic quality of electrical steels and thus the energy efficiency of electromagnetic devices are highly dependent on the thermomechanical processing procedures employed to manufacture the electrical steel sheets. Every processing step, from casting, hot rolling, cold rolling to annealing, introduces a specific microstructure and texture, which influences the microstructure and texture of next processing steps as well as the final magnetic properties. In this paper, both types of electrical steel, i.e., grain-oriented electrical steel (GOES) and non-oriented electrical steel (NOES), are reviewed bearing in mind that NOES has perhaps received less attention till now. The magnetism of ferromagnetic materials and the metallurgical factors that affect the magnetic properties of electrical steels are first briefly discussed. The effect of each thermomechanical processing step on the formation of the microstructure and texture of the final electrical steel sheets is then scrutinised. The status and challenges in optimising the crystallographic texture of electrical steels are discussed. Future directions to the development of energy-efficient and cost-effective electrical steels are pointed out.

This study investigates the subsequent stages of recrystallisation in Interstitial-Free (IF) steel subjected to an unconventional continuous annealing process with a controlled thermal gradient. A cold-rolled steel strip was exposed to varying annealing temperatures along its length, enabling the analysis of microstructural evolution during the course of recrystallisation. The microstructure and stored energy were assessed at various positions along the strip using Electron Backscatter Diffraction (EBSD). The results underscore the significant influence of local misorientation and structural inhomogeneity on orientation selection during recrystallisation. The remaining non-recrystallised volume fraction (NRF) strongly correlates with the average misorientation gradient, obeying a phenomenological power-law correspondence with an exponent of ~3.7. This indicates that the recrystallisation process is highly sensitive to small changes in local orientation gradients. These findings highlight the crucial role of stored energy distribution for texture evolution, particularly during the early stages of recrystallisation in continuous annealing. It is observed that g-fiber grains, in comparison to a-fiber grains, are much more susceptible to grain fragmentation and therefore develop more robust intra-granular misorientation gradients, allowing for successful nucleation events to occur. In the present study, these phenomena are documented in a statistically representative manner. These insights are valuable for optimising thermal processing in interstitial-free (IF) steels.

Understanding the hot deformation behavior of metallic components produced via additive manufacturing (AM) is crucial, especially for applications in dynamic loads and high temperatures. This research examines the hot compression behavior of a martensitic precipitated hardened stainless steel, known as CX SS, produced through laser powder bed fusion (LPBF). Microstructural evolutions were examined on two sample types—as-built and heat-treated—subjected to hot compression at a constant 1 s⁻¹ strain rate within the temperature range of 300 °C to 650 °C. The impact of microstructural features such as cellular solidification subgrains, nanoscale NiAl precipitates, and the austenite reversion transformation on dynamic recovery (DRV) and dynamic recrystallization (DRX) as mechanisms of restoration is explored using electron backscattered diffraction (EBSD) techniques. A comparison between two sample types revealed that the presence of cellular solidification substructure in the as-built samples delays the restoration mechanism compared to heat-treated samples. Furthermore, LPBF CX specimens in the as-built state and after heat-treatment process exhibit nearly identical deformation behavior at temperatures above 450 °C. This identical deformation behavior is associated with the partial or complete destruction of cells in the as-built samples and the dissolution of NiAl particles in heat-treated ones. The dynamic softening mechanism primarily stems from DRV and partial DRX. Although discontinuous dynamic recrystallization (DDRX) was alleviated in heat-treated samples, the as-built CX SS also showed softening mechanism in form of continuous dynamic recrystallization (CDRX) accompanied by DDRX. A constitutive equation of Arrhenius model, including Zener–Hollomon parameters, evaluated strain accumulation during hot deformation, identifying regions prone to shear bands (SBs), microcracks, and voids.

A systematic experimental study has been carried out to understand ferrite recrystallization during isothermal annealing just below Ac1 in dual phase steels. Three different dual phase microstructures – ferrite-pearlite (FP), ferrite-bainite (FB) and ferrite-martensite (FM) were produced with an identical chemical composition. These samples were subjected to 80 % cold work and subsequently annealed at 725 °C for different soaking durations. The complex interaction between ferrite and secondary constituent/phase during deformation lead to differences in strain partitioning which influenced the kinetics of ferrite recrystallization. The sample with ferrite-martensite (FM) microstructure exhibited faster recrystallization kinetics followed by ferrite-bainite (FB) and ferrite-pearlite (FP). The microstructure and associated hardness evolution starting from cold rolling to annealing for different durations was carefully captured with electron back scattered diffraction (EBSD) and high-speed nanoindentation mapping. Excellent one-to-one correlation between hardness and KAM was observed by coupling EBSD-KAM and nanoindentation mapping. The effect of the secondary constituent/phase on ferrite recrystallization is presented and differences in the recrystallization kinetics are reconciled by correlative characterization. This work lays a foundation to link microstructure to the local mechanical response in dual phase steels and can be gainfully used to characterize multiphase steels and ultimately fine tune the processing.

The combination of mechanical properties (strength, toughness, and crack arrestability) and weldability that is required of steel pipelines has led to the pipeline steel grades that are used today. The only way to control the mechanical properties of these grades is by controlling microstructure and crystallographic texture of the steel plates. In this chapter, descriptions are provided of the microstructure and texture in the most commonly used pipeline steel grades. The composition ranges of these grades are summarized, together with a brief discussion of segregation effects. After a short historical review, the general principles of microstructure and texture formation during the thermomechanically controlled processing of plate and sheet are discussed. These are illustrated with examples taken from the literature and the authors' research. Special attention is paid to texture formation, methods of texture control, and the influence of texture on mechanical properties, anisotropy, and fracture behavior of these microalloyed steels.

This work investigates the formation of the recrystallisation microstructure and texture of various single-phase ferrite low-carbon steels that were rolled at different temperatures and of which the deformation microstructure was characterized by high resolution electron backscatter diffraction (EBSD). Three cases are considered: (i) cold-rolled interstitial-free (IF) steel, warm-rolled IF steel at 550 °C and warm rolled Fe-Si steel at 900 °C (below the austenitization temperature due to Si). It is well-known that the deformation texture after flat rolling of single-ferrite low carbon steels exhibits the characteristic α/γ-fiber texture, i.e. <110>//Rolling Direction (RD) and <111>//Normal Direction (ND), irrespective of the rolling temperature, as long as there is no concurrent phase transformation. However, different recrystallisation textures appear as a function of the rolling temperature. Generally speaking, the γ-fiber recrystallisation texture is obtained after cold rolling, whereas the θ-fiber components ( <100>//ND) intensify at the expense of the γ-fiber orientations with increasing rolling temperature. Although these phenomena are well-known, the reasons for this behavior in terms of preferential orientation selection remain as yet unclear. In the present paper, recrystallisation microstructures and textures are simulated with a full-field cellular-automaton (CA) description, whereby recrystallisation from its incipient stage is considered as a process of sub-grain coarsening controlled by the well-known physical laws of driving force and kinetics. The simulations integrate in one single model the various conditions that give rise to the observed temperature dependence of the evolving static recrystallisation texture and microstructure. The different rolling temperatures will give rise to different initial microstructures at the onset of recrystallisation with noticeable variations in short-range orientation gradients in γ and θ-fiber orientations, respectively. The mere application of local grain-boundary migration laws on the topology of the deformation structure, without imposing any specific nucleation selection criterion, will properly balance the dominance of γ-fiber grains after cold-rolling and θ-fiber orientations after warm rolling. Finally, the well-known nucleation of Goss orientations ({110}<001>) in shear bands occurring in γ-fiber grains is also simulated in this single conceptual framework.

Wire Arc Additive Manufacturing (WAAM) is a metal Additive Manufacturing (AM) technique that can produce fully dense metallic structures with virtually no porosity and at high productivity, compared to other currently available AM techniques such as Laser Powder Bed Fusion (L-PBF). As development of the technique is still ongoing, monitoring or post-fabrication inspection methods are under active investigation. In this work, we apply Resonant Ultrasound Spectroscopy (RUS) to samples fabricated from two different wires (construction steel and austenitic stainless steel) and quantitatively characterize isotropic and anisotropic elastic behaviour of the obtained dense parts. We find that an isotropic elastic model fits the construction steel samples well. For the 316 L polycrystal however, the isotropic elastic model is unsatisfactory, and an effective orthotropic elastic model is found to fit the resonance data. EBSD and XRD measurements are used to confirm and explain this difference in elastic behaviour between steel grades by the presence of a strong texture in the 316 L samples. Additionally, the texture data measured by EBSD are used to infer single crystal constants from the polycrystal resonance data using the Hill averaging scheme for one of the 316 L samples. We end by discussing the differences between the two elastic models used in the study (orthotropic and texture based) as well as the link between the measured resonances and microstructural descriptions of the samples.

In the present study, the crystallography aspects of the liquid metal embrittlement (LME) phenomenon are investigated in a bi-metallic bronze-stainless steel structure, produced using wire arc additive manufacturing. Most of the LME cracks were found to be propagated along high-angle grain boundaries of the austenitic structure. Surprisingly, it was observed that in some cases, LME cracks propagated transgranularly in austenite grains, which is a rare phenomenon in LME of steels. The Ʃ3-coincidence site lattice (CLS) boundaries showed the highest resistance to LME compared to other CLS types. It was also found that the presence of elongated grains in additively manufactured microstructures can accelerate the LME phenomenon.

Despite the widespread use of laser heat treatment, a fundamental understanding of austenite formation kinetics at high heating rates remains a challenge. This gap is addressed by developing a novel model that uniquely accounts for the initial pearlite colony size and interlamellar spacing as critical input parameters. The model's predictions are validated against experimental observations, where the spatial variation of hardness reveals a distinct two-zone microstructure: a fully austenitized region and a partially transformed intercritical layer. The results show that the relative size of these zones is directly controlled by the initial microstructure. This research provides a crucial insight that austenite formation under rapid heating conditions occurs with negligible superheating, which is essential for optimizing laser processing parameters to achieve a desired microstructure.

The accuracy of simulated recrystallisation textures is essential for predicting the formability of steel sheets. In a continuum modelling approach, this texture can be effectively calculated in two stages: nucleation and growth. However, the precision of the final texture depends heavily on the accuracy of the nucleation texture simulation. This paper presents a nucleation texture model that combines the strain-induced boundary migration (SIBM) mechanism with a traditional oriented nucleation model. The results indicate that the SIBM mechanism promotes the nucleation of low-stored energy grains and enhances the nucleation texture compared to using the oriented nucleation model alone. The findings suggest that the accuracy of nucleation texture could be improved by setting a minimum stored energy threshold for grains that nucleate during the early stages of recrystallisation.

Cup drawing is a benchmark experiment frequently used to validate anisotropic constitutive models and multiscale crystal plasticity codes for yield locus prediction. Earing of the cup rim and thickness variation along the cup wall are sensitive to plastic anisotropy. This test was implemented on an industrial forming press and applied to 85 mm diameter disks of commercial AA1100, AA3103, and AA5005 alloy sheet. Cup geometry was determined using a laser probe coordinate measurement machine (CMM). Finite element models (FEM) were developed with ABAQUS Explicit software and a user-defined subroutine for the anisotropic yield locus based on the hierarchical multiscale model (HMS). As the coordinate cloud produced by the CMM is unrelated to the nodes of the deformed FEM-mesh, both were fitted to a polynomial-Fourier series expansion. After cleaning and correction of the CMM data, point-by-point comparison can be performed between model and experiment. For AA1100, the position of the ears was correctly identified but their magnitude was underestimated. Excellent coincidence was found for AA5005, with strong ears at 0 and 90°. The small ears at -30° and 30° and secondary ears at 90° were correctly predicted for AA3013.

This study explores the evolution of solidification microstructure of a laser powder bed fusion (L-PBF) martensitic stainless steel during solution annealing and aging. Quasi in-situ experiments using electron backscatter diffraction (EBSD) revealed that the finer, more equiaxed microstructure below the melt pool was susceptible to recrystallization and grain growth during solution annealing. The two distinct solidification microstructures below and inside the melt pool converged into a uniform grain morphology after solution annealing and aging processes. Graphical Abstract: (Figure presented.)

Rolling and annealing is a crucial technology to produce electrical steel sheets. This technology is not just aimed to control the geometry of steel sheets but more importantly to enhance the magnetic properties of the final products via appropriate microstructure and crystallographic texture. In this study, the evolution of microstructures and textures of an Fe-1.2 wt.% Si alloy through the entire processing route (from reheating, warm rolling to annealing) is monitored by electron back-scatter diffraction. Plastic flows of the material during conventional and asymmetric rolling are analyzed in detail based on geometric parameters of the rolling gaps. Deformation textures are accurately predicted by the full-constraint Taylor and advanced Lamel (ALAMEL) crystal plasticity models. The development of recrystallization textures is accounted for by the plastically stored energy in deformed crystals, which in turn is approximated by the plastically dissipated power (i.e., the Taylor factor) as predicted by the full constraint Taylor model. Although asymmetric warm rolling does not produce an improved texture or microstructure for electrical steels, the present study provides useful information on the evolution of the recrystallization microstructure and texture in steels with a complex strain history after asymmetric warm rolling.

This study investigates the sub-structure of IF steel in three conditions: cold rolled, statically recovered, and warm rolled. After both cold and warm rolling, the steel exhibits the typical 〈110〉//RD and 〈111〉//ND fiber textures. Considering the short-range misorientation gradient ∆θ/∆x to assess locally stored energy variations, it was observed that 〈111〉//ND grains exhibit significantly higher gradients than 〈001〉//ND grains in all conditions. In the statically recovered conditions, the ∆θ/∆x values are significantly reduced compared to the cold rolled condition, but these values are significantly higher than those of the dynamically recovered after warm rolling. The strongly reduced orientation gradients in the 〈111〉//ND grains after warm rolling may reduce the nucleation potency of these orientations in the ensuing recrystallization. This study enhances our knowledge of deformation microstructure as a function of rolling temperature and is relevant in explaining reported differences in annealing textures during static recrystallization after cold vs warm rolling.

In an industrial context, selecting an appropriate crystal plasticity (CP) model that balances efficiency and accuracy when modelling deformation texture (DT) is crucial. This study compared DTs in IF-steel after undergoing cold rolling reductions using different CP models for two input texture scenarios. Three mean-field (MFCP) models were utilised in their most basic configurations, without considering grain fragmentation or strain hardening, in addition to a dislocation-density-based full-field (FFCP) model. The study quantitatively compared the results from the MFCP models with those from the FFCP models. Furthermore, all CP model results were compared with experimental textures obtained from electron back-scatter diffraction (EBSD) experiments. The findings revealed that certain MFCP models could predict deformation textures as accurately as the FFCP models. Notably, one of the MFCP models exhibited a superior match with experimental textures for cold rolling reductions at 60%. Upon closer examination of specific crystallographic components, it was observed that MFCP models tended to predict a stronger {111}〈211〉 component, while the full-field model favours the {111}〈011〉 component. It is crucial to emphasise the importance of quantifying the texture within individual grains when assessing the macro-level deformation texture in rolling simulations.

This study examines the interface layer between a high-strength low-alloy steel and an overlaying austenitic stainless steel as deposited through wire arc additive manufacturing in a bi-metal block. By utilizing optical and electron microscopy techniques, and accompanied by phenomenological and thermodynamic modeling, the work elucidates on the nature of the distinct microstructural features at a new level of detail. Results showcase martensite in the form of a band along the fusion line of the first dissimilar layer, as well as in segregated islands. Within the same bead, yet away from the fusion line, an austenite matrix is identified alongside a large phase fraction of primary ferrite and sparse bainite. These findings enhance our understanding of the nature of the heterogeneous microstructure at the interface of a bi-metal build and establish empirical evidence for future modeling of microstructural development. Supplementary characterization reveals the impact of these microstructural heterogeneities on bulk mechanical performance. Hardness indents exhibit varied results along the interface, peaking at martensite islands with values up to 370HV_0.2, surpassing the neighboring matrix by 50%. Under quasi-static tensile loading, bi-metallic specimens display strain partitioning along the fusion boundary, as confirmed by Digital Image Correlation. When compared to the adjoining stainless steel, the diluted interface layer exhibits superior strength (σ_y: 411 MPa) and comparable ductility (24%), leading to necking and failure away from this region. These results help predict the structural performance of bi-metal parts, and build a base for further research in more intricate loading scenarios, such as crack propagation processes.

The phase transformations, microstructure and properties of two Medium-Mn processed via quenching and partitioning steels were compared in this contribution and a new strategy for controlling mechanical properties by introducing and controlling cold-worked ferrite prior to heat treatment is proposed. It was found that during heating, the recovery and recrystallization of cold-worked ferrite compete with austenitization, thereby inhibiting the coarsening of austenite. The cold-worked ferrite interface will significantly delay the austenitization kinetics during the partitioning local equilibrium stage compared to martensite. These results lead to a diverse parent austenite, as well as a refined martensite substructure. As a result, the randomly distributed variants increase the number of effective grain boundaries, thus enhancing yield strength. The intercritical annealing process at a temperature of 860 °C resulted in the formation of fresh martensite-retained austenite (M/RA) constituents exhibiting a remarkably fine (<2 μm) and uniform grain morphology. Such microstructure yielded substantial improvement in both the strength and ductility of the steel. The proposed treatment led to excellent elongation (24%) at fracture, combined with very high ultimate tensile strength and yield strength of 1345 MPa and 1163 MPa, respectively, of the steel, resulting in a product of strength and elongation that exceed 32 GPa%.

While the grain size effect (GSE) is universally observed in polycrystalline metals and alloys, extended dislocation pileups (DPUs) at grain boundaries (GBs) are rarely observed. Although this discrepancy was noticed over 50 years ago, DPUs are still widely accepted as the explanation for the GSE, often expressed as the Hall-Petch (HP) relationship. To provide a quantitative assessment of the pileup hypothesis, four classical pileup models were compared to three sets of numerical calculations, spanning a grain size range from 25 nm to 25mm. To do so, the stress field and Peach-Köhler force for short dislocation segments and circular dislocation loops were calculated as closed-form expressions and simplified to the case of pileups. Published values for the Hall-Petch constant provide the reference for estimating the critical tip stress for transmission of plastic strain from one grain to its neighbour. The results are compared in terms of consistency between models and between models and experiments. Different assumptions on the pileup geometry induce important variations in the results. Tendencies found in the numerical models resemble the trends marked in compilations of experimental results; predicted values for dislocation density and plastic shear upon yielding disagree with commonly accepted values. Added to the scarceness of experimental observation, the analysis indicates that DPUs play a role in polycrystal plasticity but do not consistently explain the GSE.