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Alloy AD730TM is a recently developed Nickel base superalloy for application as turbine disk in modern gas turbines with improved thermal efficiency. Ingot casting followed by open die-forging and then heat treatments are the main manufacturing steps for the production of parts made of this alloy. Solution heat treatment operations are applied at different stages of the manufacturing in order to ease the deformation processing and/or prepare the microstructure for final heat treatment. In this research, the influence of various solution heat treatment schedules on morphology and distribution of the γ′ phase are investigated and documented. The obtained results will contribute to a better understanding of microstructure evolution of AD730TM during solution heat treatments. Differential Thermal Analysis (DTA) is used for the purposes of measurement of temperatures of phase transformations of the alloy. Based on DTA results, three solutionizing temperatures and three holding times were selected for performing and assessing the solution heat treatment process. Optical and electron microscopy were used to study the morphological evolution as well as the coarsening and dissolution of secondary phases at solvus and subsolvus temperatures. The results indicated that precipitate agglomeration and Ostwald ripening are the governing mechanisms during the initial stages and splitting and partial dissolution of γ′ precipitates takes place during subsolvus solution treatments.

With the aim of replacing quenched and tempered forging parts and eliminating by this way costly and time consuming operations; an industrial forging procedure was developed to evaluate the influence of thermomechanical processing parameters on the microstructure and mechanical properties of V and V–Ti microalloyed steels. After austenitization at 1200°C the microalloyed steel billets were forged in a 2500 t mechanical press. Forging was performed in three steps (roll forging, molding and finishing) after which the specimens were cooled according to various schedules in order to study the influence of cooling rate on the tensile, charpy V-notch, impact and hardness values. The variation of ferrite grain size, pearlite colony size, interlamellar spacing, ferrite/pearlite percentage and lath thickness as a function of forging conditions was followed by optical microscopy. The results indicated that by increasing the cooling rate both the strength and toughness increase. Under these conditions the microstructure is mainly composed of non-ferrite/pearlite transformation products. It was also found that under similar forging conditions the Ti-containing microalloy steel leads to a better strength/toughness combination than the V steel. The results are discussed in the framework of classical nucleation theory and the optimum forging conditions to reach the best strength/toughness ratio and microstructure for each steel were determined.

The influences of flow-forming parameters and the state of the microstructure on the quality and mechanical properties of a D6ac steel were studied. The effects of feed rate, the shape of the contact line, the roller angle and the percentage reduction on the elimination of spinning defects such as a wave-like surface, microcracks and bore were studied. Also, the influence of the preheat temperature, the holding time and the cooling rate on the microstructure and mechanical properties of the material was investigated. The experiments were carried out on a 3-roller spinning machine and the optimum conditions for the elimination of the above-mentioned defects were determined. Both optical and electron microscopy were used for the study of the microstructure, and the appropriate heat-treatment leading to the best strength–toughness combination was found. The results obtained are interpreted within the framework of metal working theories and examined critically with existing models.

The influence of reheat temperature, percentage deformation, interpass time and finish rolling temperatures on the microstructure and mechanical properties of AISI 4130 steel were studied. Reheat temperatures of 900, 950, 980, 1050, 1100 and 1200°C were used and reductions per pass of 15, 30, 40, 50 and 60% were employed. Finally, finish rolling temperatures from 500 to 850°C were used. The samples were air cooled after the final pass and the variations of their hardness, tensile and impact properties as a function of thermomechanical treatment parameters were measured and their microstructure studied using both optical and scanning electron microscopy. By a judicious control of thermomechanical treatment it was possible to determine the rolling conditions leading to the optimum combination of strength and toughness. The possible mechanisms responsible for the observed behavior are presented and the results are discussed within the existing models.

High-strength carbon fibers were submitted to various thermochemical treatments in order to obtain a uniform and tough coating of copper particles on their surfaces. After heat treatment in the range 700–1000°C under argon atmosphere they were chemically treated in NaOH, HNO 3 , C 3 H 6 O and HF baths with different concentrations. The last of these solutions was used for the first time in this investigation. The results show that both the thermal and chemical treatments greatly influence the binding quality of copper particles to the fibers which is crucial for a reliable composite material. The results also indicated that heat treatment at 100°C for 2 h and chemical treatment with HF led to a ‘porous’ and groovy surface resulting in a uniform and thin layer of copper after electroplating. Microstructural evolution at different steps was followed by means of optical and scanning electron microscopy and a mechanism for copper growth at the surface of the fibers is proposed. Finally the coated fibers were chopped and sintered with copper powder. The influence of sintering conditions on electrical and thermal conductivities of the composite material was studied and the strength and composition of the interface was examined by the SEM technique.

Ultra high strength AISI 4130 Steel samples were submitted to various rolling schedules in order to find the rolling conditions leading to the optimum combination of strength and toughness. Reheating temperatures between 900 to 1230°C and reductions between 15 to 90% were employed. Rolling temperatures above Ar3 and also between 620 and 700°C were used and in some experiments annealing was applied to the samples. The influence of the above parameters on the microstructure and mechanical properties of the samples was studied by measuring the variation of their hardness, tensile and impact properties as well as using optical and scanning electron microscopy. The results show that by a judicious control of reheat temperature, percent deformation, interpass time, finish rolling and annealing temperatures it is possible to obtain fine ferrite and nodular colonies of pearlite with small interlammelar spacing. The results are discussed in the frame work of classical nucleation theory and the possible mechanisms which may be responsible for the observed behavior are proposed.

The effect of rolling and annealing parameters on the microstructure and earing of deep drawn Aluminium alloys in the range 0.5 to 3mm thicknesses was studied. 1100 and 1050 Aluminium alloy samples were taken from the mill at different stages of hot and cold rolling as well as at intermediate annealing steps. They were subsequently deep drawn and their earing measured. Also mechanical properties and microstructure of the samples were examined at each stage. The results indicated that by decreasing the finishing temperature the 0 and 90° earing diminishes while 45° earing increases. Also, under appropriate conditions a 1.4% 0 and 90° earing was measures on a 6 mm thick plate after hot rolling. The earing was reduced to about zero when the thickness was brought down to 4mm by cold rolling. For the thicknesseless than 1mm by applying an intermediate annealing at 350°C an almost zero earing was obtained. Finally, it was observed that under all experimental conditions the earing is less for the 1050 alloy than for the 1100.

A creep Deformation Mechanism Map (DMM) of an engineering alloy can be an effective tool for developing physics based prognostics systems. Many classical diffusion based rate equations have been developed for time dependent plastic flow where dislocation glide, dislocation glide-plus-climb and vacancy diffusion driven grain boundary migration (diffusion creep) are rate controlling. Long term creep testing and analysis of complex engineering alloys has shown that power law breakdown phenomenon is related to the dominance of Grain Boundary Sliding (GBS) as opposed to diffusion creep. Rate equations are now available for GBS in complex alloys and, in this paper, a DMM is constructed for Waspaloy (a Nickel-Based Superalloy) and validated by comparison with a collection of experimental data obtained from the literature. The GBS accommodated by wedge type cracking is considered dominant at low homologous temperatures (0.3 to 0.5Tm - temperature in Kelvin) whereas GBS accommodated by power-law or cavitations creep dominates above 0.55Tm.Copyright © 2013 by ASME

Welded structures are examined nondestructively, particularly for critical applications where weld failure can be catastrophic, such as in pressure vessels, load-bearing structural members, and power plants. Ultrasonic Testing (UT) is used in the examination of welds in thinner and thicker gauge materials where the size and location of the flaws are important to detect and interpret. Despite the advantages of the ultrasonic technique, the classification of defects based on ultrasonic signals is still frequently questioned, since the analysis and the identification of defect types depend exclusively on the experience and knowledge of the operator. The problem becomes more acute when high inspection rates, high probability of detection, and low number of false results are required. Thus, the correct classification of the type of flaw present in the material reduces measurement errors, increasing the confidence in the test and consequently the safety of the welded structure during service. In the present study, a new algorithm that allows for the detection and measurement of the length and type of weld defects is proposed. The system is based on a coupled dynamic and static patterns in an A-Scan and uses the defects cited in DIN EN 1713 standard as reference for evaluation. The proposed expert system has been evaluated and validated by examining several specimens containing various types of natural (non-artificial) defects identified in the mentioned standard. The results indicate that, the proposed algorithm has a clear potential in automatic defect detection and presents many advantages to the manual method for defect detection and characterization.Copyright © 2013 by ASME

The high-temperature deformation behavior of the Ni-base superalloy, Waspaloy, using uniaxial isothermal compression testing was investigated at temperatures above the γ′ solvus, 1333 K, 1373 K, 1413 K (1060 C, 1100 C, 1140 C) for constant true strain rates of 0.001, 0.01, 0.1, 1 s -1 and up to a true strain of 0.83. Flow softening and microstructural investigation indicated that dynamic recrystallization took place during deformation. For the investigated conditions, the strain rate sensitivity factor and the activation energy of hot deformation were 0.199 and 462 kJ/mol, respectively. Constitutive equations relating the dynamic recrystallized grain size to the deformation temperature and strain rate were developed and used to predict the grain size and strain rate in linear friction-welded (LFWed) Waspaloy. The predictions were validated against experimental findings and data reported in the literature. It was found that the equations can reliably predict the grain size of LFWed Waspaloy. Furthermore, the estimated strain rate was in agreement with finite element modeling data reported in the literature. © 2013 The Minerals, Metals & Materials Society and ASM International.

Ingot forging processes often consist of several successive deformation steps with high interpass times, during which metadynamic recrystallization (MDRX) occurs. Two-stage isothermal compression tests were carried out at 1150°C and 1200°C with strain rates of 0.25-2s −1 and interpass times of 5-25s. Based on the experimental results, a material model for MDRX is proposed. The constitutive model was implemented in Forge NxT 1.1 ® software to simulate the multistage compression. Results from the material model are consistent with the numerical analysis and experimental results.

The Ni-base superalloy, Waspaloy, was linear friction welded (LFWed) under various processing parameters and then subjected to a post weld heat treatment (PWHT). Tensile testing integrated with the optical image correlation Aramis® system indicated that there is a critical axial shortening value (2 mm) below which LFWed and post weld heat treated (PWHTed) Waspaloy exhibited weak integrity. At and above this critical shortening, the yield strength and ultimate tensile stress (UTS) values were more or less the same as for the parent material. However, total elongation continued to increase with axial shortening even above the critical value due to decrease in width of thermo-mechanically affected zone (TMAZ). The sample with the highest axial shortening (4.9 mm) exhibited an elongation 91% of the parent material elongation. According to Aramis® data, the mixture rule can be used reliably to determine the contribution of TMAZ to the tensile elongation of PWHTed Waspaloy. Microstructure characterization across the weld in the as-LFWed and PWHTed conditions was carried out to correlate the process parameters and microstructural changes that affect the tensile properties. Weak integrity at axial shortening below 2 mm was mainly due to lack of bonding and/or presence of oxides at the weld interface. In the as-welded condition, a loss in hardness was observed, and related to the extensive dissolution of strengthening phase (γ′) in the weld area. The applied PWHT restored the hardness in the weld region.

Fusion welding of nickel-base superalloys is often associated with fusion zone solidification cracking and/or liquation induced heat affected zone (HAZ) cracking. As an alternative joining technology, linear friction welding (LFW) was used in the current study to join the nickel-base superalloy, WASPALOY. Under the experimental conditions used in the present investigation, the temperature data recorded by inserting thermocouples at different locations from the weld interface indicated that the temperature in the weld area reached up to 1280 °C, which is at least 50 °C below the melting point of the bulk alloy. However, this temperature is well above the liquation temperature of the low melting point components in the alloy (1245 °C). As a result, liquation may occur in linear friction welded (LFWed) WASPALOY. The occurrence of liquation and/or microcracking was investigated using optical microscopy (OM), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) X-ray mapping. The high pressure applied during the oscillation and forge phases of the LFW process and the resulting γ grain refinement contributed in preventing liquation and microcracking in the weldments. Furthermore, according to the SEM and X-ray mapping results, LFW altered the chemical composition, morphology and size of the γ′ precipitates at a location of 2 mm from the weld interface. It was determined that γ′ coalescence at 2 mm from the weld interface played a role in decreasing the microhardness (by 30%) relative to the base metal.

Friction stir welding (FSWing) induces residual stresses and distortions in welded structures. Such residual stresses reduce the fatigue life of welded components, while the induced distortions prevent the welding of large or thin components. In the present study, needle peening was used to induce additional residual stresses in 2.3-mm thick (FSWed) aluminum alloy (AA) 2024-T3 sheets. This was done with the objective to counterbalance the welding-induced stresses and thus reduce the overall stresses and distortions. The needle peening process, which stems from shot peening, consists of hammering a surface using cylindrical spherical ended shots sliding back and forth in a treatment head. An instrumented needle peening machine was used to carry out peening on as-received (or bare) and bead-on-plate FSWed AA2024-T3 material. In both cases, the width of the peening area corresponded to that of a typical weld. The influence of the peening process parameters such as needle size, applied power and travel speed on the surface quality and magnitude of the induced distortions were evaluated. The results indicate that, by increasing the needle diameter from 1.2 mm to 2.0 mm, the peening-induced deflection on bare sheet material increased by an average value of 27% while the roughness average, Ra, decreased by an average value of 47%. It was also found that a surface finish qualitatively similar to that of conventional shot peening could be obtained by using appropriate needle peening trajectories. Finally, needle peening with an applied power of 10% was sufficient for eliminating 37% of the welding-induced transverse curvature and 82% of the welding-induced longitudinal curvature.

International audience; The effects of pre- and post-weld heat treatments on the butt joint quality of 3.18-mm thick Inconel 718 alloy were studied using a 4 kW continuous wave Nd:YAG laser system and 0.89-mm filler wire with the composition of the parent metal. Two pre-weld conditions, i.e., solution treated, or solution treated and aged, were investigated. The welds were then characterized in the as-welded condition and after two post-weld heat treatments: (i) aged, or (ii) solution treated and aged. The welding quality was evaluated in terms of joint geometries, defects, microstructure, hardness, and tensile properties. HAZ liquation cracking is frequently observed in the laser welded Inconel 718 alloy. Inconel 718 alloy can be welded in pre-weld solution treated, or solution treated and aged conditions using high power Nd:YAG laser. Post-weld aging treatment is enough to strengthen the welds and thus post-weld solution treatment is not necessary for strength recovery

Annealed Ti–6Al–4V alloy sheets with 1 and 2 mm thickness are welded using a 4 kW Nd:YAG laser system. The effects of welding speed on surface morphology and shape, welding defects, microstructure, hardness and tensile properties are investigated. Weld joints without or with minor cracks, porosity and shape defects were obtained indicating that high-power Nd:YAG laser welding is a suitable method for Ti–6Al–4V alloy. The fusion zone consists mainly of acicular α′ martensite leading to an increase of approximately 20% in hardness compared with that in the base metal. The heat-affected zone consists of a mixture of α′ martensite and primary α phases. Significant gradients of microstructures and hardness are obtained over the narrow heat-affected zone. The laser welded joints have similar or slightly higher joint strength but there is a significant decrease in ductility. The loss of ductility is related to the presence of micropores and aluminum oxide inclusions.

The effect of welding speed ranging from 5 to 30 mm/s on 2-mm butt joint quality of friction stir welded AZ31B-H24 magnesium alloy was investigated to determine defects, microstructures, hardness and tensile properties. High welding speed over a wide range can be used to weld this material at high tool revolution rates indicating the great potential of this technique for magnesium alloys. Equiaxed grains were observed in the stir and thermo-mechanically-affected zones. The grain size in the stir zone decreases with increasing welding speed due to lower heat input. Higher welding speeds produce slightly higher hardness in the stir zone. The yield strength increases with increasing welding speed. The tensile strength increases first with increasing welding speed but remains constant from 15 to 30 mm/s. A Hall–Petch linear relationship between yield strength and inverse square root of grain size in the stir zone illustrates the strong relationship between these parameters.

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Electron beam (EB) weldments of 17-4 precipitation hardening (PH) martensitic stainless steel (SS) consisted of a series of distinct yet very narrow heat-affected zones (HAZ) with different microstructural characteristics (composition, fraction and/or size of precipitates, phases and grains). Considering the limited size of each HAZ, shear punch testing (SPT) offers a practical solution for evaluating the mechanical and fracture properties of individual regions within the weldment. This paper describes the use of SPT to determine the variation in the tensile strength (yield and maximum), ductility and strain hardening properties of different regions of the weldment and relate them to the microstructural gradient observed in each of them.

International Conference on Aerospace Materials- Beijing International Materials Week 2006 From 6/25/2006 To 3/30/2006., Beijing, China, available, unclassified, unlimited

The use of electron beam technology for freeforming 321 SS was investigated using 347 SS solid wire and BNi-2 brazing paste as filler materials. The electron beam freeforming (EBFF) studies involved examining the effect of processing parameters on the characteristics of the line build-ups. Specifically, the effective growth rate and the dimensional features (height-to-width ratio) of the build-ups were found to be dependent on the beam energy and the filler material conditions (e.g. wire feed rate and the number of re-melting passes). The EBFF work indicated that build-ups with either filler material could be deposited on 321 SS using an optimized processing window that resulted in properties comparable to technical data available for 347 SS and BNi-2., available, unclassified, unlimited

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It is well known that the presence of large heterogeneous textured regions in forged near alpha titanium alloys could lead to large variations of mechanical properties when fatigue and creep cycles are applied at room temperature. On the other hand, experimental studies and microtexture investigations are complex to set up, lengthy and costly, and one cannot expect to understand the alloy behavior by relying only on empirical approaches. Hence, numerical methods are excellent alternatives for analyzing the influence of microscopic and macroscopic heterogeneities on mechanical properties in shorter times and with minimum need for experimentation. In the present investigation, a cellular automata (CA) method was used to simulate the effect of texture heterogeneities, on both local and global mechanical properties. A 2D array of cells was used and the stresses and strains developed in various heterogeneous regions were evaluated using the Eshelby theory. Using the CA method, various types of microstructures were modeled and compared with each other to quantify the influence of processing parameters on mechanical properties. The results predict, and are used to explain, the experimentally phenomena observed in creep responses during cold fatigue/creep tests of near alpha titanium samples., available, unclassified, unlimited

The bimodal microstructure of a IMI 834 billet was studied. It presents sharp textured regions called macrozones in which the main texture component of α s colonies of hcp symmetry, inherited from β grains of bcc structure is such as the c axes coincide with those of the α p grains characterised by one single texture component. This feature is the result of a variant selection. Analysis and simulations suggest that elastic anisotropy could be decisive for the selection.

Processing conditions for manufacturing Ti–6Al–4V components by welding using an electron beam source are known to influence the transformation microstructure in the narrow fusion and heat-affected zones of the weld region. This work examined the effect of multiple-sequence welding on the characteristics of the transformed beta microstructure, using laser scanning confocal microscopy to resolve the Widmanstatten alpha–beta structure in the fusion zone. The evolution in the alpha interlamellar spacing and plate thickness with processing was then related to microhardness measurements in the weld region.

A continuous wave 4 kW Nd:YAG laser system was used to weld 2-mm butt joints of sand-cast ZE41A-T5 magnesium alloys at a power of 2.5 kW, welding speed of 6.0 m/min, and defocusing distance from − 2 to + 3 mm for the material in the machined surface conditions. It was found that the adjustment of defocusing distance greatly influences the establishment of conduction or keyhole mode welding. Conduction welding is obtained at a power density of 4.0 × 10⁵ W/cm². Keyhole welding is reached at a threshold irradiance of 1.5 × 10⁶ W/cm². The fusion zone consists of refined equiaxed grains formed through cellular growth in the Zr-containing magnesium alloys. The partially melted zone is rather narrow, only a few grains wide. No grain growth or coarsening but softening is observed in the heat affected zone (HAZ). The weld defects observed include three main types: imperfect shape, cavities, and weld cracks. The mechanisms of their formations are discussed. In addition, the original cast quality was found to have a significant influence on the formation of defects such as underfill, surface depression, porosity, and burn-through during laser welding., Canadian Metallurgical Quarterly.

Regions with sharp hexagonal close-packed (hcp) local textures, named macrozones, have been observed in an IMI 834 billet and analyzed in relation to the bimodal alloy microstructure. They are clearly related to regions with primary αp grains oriented around a main texture component. The resulting αp microtexture is discussed considering heterogeneous deformation and globularization of initial packets of αp lamellae. Within an hcp macrozone, several prior β grain orientations were present at high temperature. The β phase developed no sharp texture heterogeneities during α/β working. Clusters of β grains sharing close orientations and containing small grains with high angle boundaries were observed. This β microtexture can result from severe α/β deformation of initially large prior grains, associated with continuous dynamic recrystallization. By cooling, the αs colonies inherited from the β grains and surrounding the αp grains display several texture components with the main one matching that of the αp phase. This connection seems to be due to a variant selection influenced by the presence of αp grains.

The presence of hcp regions with grains having relatively close orientations has been reported in commercial near alpha titanium billets (IMI 834, Ti 6246, etc). The size of these textured regions (called macrozones) is significantly larger than the average grain size of the microstructure observed after thermomechanical processing. The elongated shape of these large hcp regions suggests that they are eventually related to large prior b grains that pancaked during the ingot break down process. In this contribution, Orientation Image Microscopy was used to study the relationship between the hcp local microtexture heterogeneities and the prior b orientations. Specifically, the orientations of the primary (equiaxed) ap grains and the secondary (lamellar) as colonies produced after the transformation of the b phase were discriminated from OIM maps. Furthermore, from the as inherited OIM map, it was possible to reconstruct the corresponding b OIM map over large regions. The analysis showed that the large hcp macrozones observed in the as received material are not related to corresponding bcc macrozones. However, within an hcp macrozone, various clusters of b grains with similar orientations can be found. In such coherent regions, randomly orientated b grains were also observed, which could be related to microstructural changes during deformation (continuous dynamic recrystallization) as suggested by hot deformation results., available, unclassified, unlimited

As a relatively new solid-state joining process, friction stir welding (FSW) may provide a feasible approach to join dissimilar materials such as Mg to Al alloys. In this work, the effects of selected process parameters including work-piece placement, pin tilting angle, and pin location on the quality of dissimilar AA 2024-T3 to AZ31B-H24 butt joints were investigated for the first time. Sound butt joints with low distortion and no solidification cavities or cracks were successfully obtained indicating the potential of FSW to join dissimilar Al to Mg alloys.

A cellular automaton model is proposed to describe the creep behaviour of Ti alloys. The technique is a well-known mathematical method that has been recently used to simulate the mechanical behaviour of materials identified by a discrete number of sites, called cells, organised in a two- or three-dimensional lattice. The creep behaviours of various types of microstructures with different crystallographic textures were simulated. The results can explain the large discrepancy obtained in the creep responses of the titanium samples subjected to similar loading conditions.

The tool geometry in friction stir welding (FSW) is a critical parameter to produce reliable and consistent joints, especially when it comes to joining dissimilar alloys with different mechanical and thermal properties. The aim of the present work is to investigate the effect of FSW tool design on the mechanical characteristic of as-welded AA2198(T3)-AA2024(T3) joints. Three shoulder profiles (flat, spiral, and fan) and five different pin profiles (tapered cylindrical, straight cylindrical, threaded cylindrical, cone and square) were tested. A visual inspection and metallographic characterization were conducted to evaluate the sound state of the joint. Tensile tests and scanning electron microscopy combined with energy-dispersive X-ray spectroscopy were used to assess the mechanical properties of the different joints in regard to fractographic analyses and local chemical composition. Significant flash was produced for flat shoulder configurations. FSW tools with fan or with spiral shoulders prevent the formation of the flash defect. Lack of penetration (LOP) and kissing bond defects were avoided by tapering the tip of the pin with a diameter greater than or equal to the plate thickness. The tapered cylindrical pin with a fan shoulder was the optimal tool design configuration for mechanical properties.

The present work investigated the effect of strain reversal during high pressure torsion on the evolution of microstructure, texture and hardness properties of two different materials with different dynamic recovery behavior, namely, high purity (99%) Aluminum (2N-Al) and Aluminum-Magnesium (Al-2.5%Mg) alloy. In the two aluminum alloys subjected to different routes, the evolution of the ultrafine structure followed same trend. At lower strain level, sub grains with prominent LAGBs network were observed and at higher strains, ultrafine equiaxed grains separated by HAGBs were observed throughout the disk. The texture evolution in monotonically and strain reversal processed 2N-Al and Al-2.5%Mg showed presence of typical torsion texture components at different strain levels. The strength of the components was observed to follow different trends depending on the processing routes.

The bainitic ferrite plate thickness is the main parameter that controls the strength of this type of microstructures. Such thickness has been proved to mainly depend on the austenite yield strength, the driving force for the transformation and the transformation temperature. However, no research has focused on how these parameters evolve throughout the transformation and how this evolution can affect the outcome. In this study, thermal and thermomechanical treatments have been performed in three selected steels. The treatments have been designed in such a way that all the mentioned parameters are comparable, aiming to obtain similar microstructures in terms of bainitic ferrite plate thickness. However, significant differences have been found among the microstructures, with variations in plate thickness larger than 100 nm. These results indicate that there might be other factors that take part in the scale of bainitic microstructures. To explain these differences and based on the kinetics of the transformation and on the carbon content of austenite at the end of the transformation, a possible explanation has been proposed., Richard Huizenga at the Department of Materials Science and Engineering of the Delft University of Technology is acknowledged for the X-ray analysis. The authors gratefully acknowledge the support for this work by the European Research Fund for Coal and Steel under the Contracts RFCS-2015-709607 & RFCS-2019-899482 and by the Program Atracción de talento investigador (Consejería de Educación, Juventud y Deporte, Comunidad de Madrid), under the fellowship 2016-T2/IND-1693. They also acknowledge the support provided by the subsequent laboratories belonging to CENIM: X-Ray Diffraction, Metallography and Phase Transformations. The financial and equipment support from National Science and Engineering Research Council (NSERC) Canada is acknowledged by M. Jahazi and M. Zorgani acknowledges the scholarship provided by the Lybian government for his PhD studies.