Revistas
Revista:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE
ISSN:
1073-5623
Año:
2022
Vol.:
53
N°:
7
Págs.:
2586 - 2599
The microstructure evolution of 55VNb microalloyed steel during warm deformation via single pass uniaxial compression was researched, and the effect of deformation conditions on dynamic spheroidisation of cementite lamellae and ferrite conditioning for a range of deformation temperatures (600 degrees C to 700 degrees C) and strain rates (1 to 10 s(-1)) analysed. Cementite lamellae appear to subdivide irrespective of deformation temperature with the ferrite phase penetrating the pattern formed by the cementite crystallites, in turn confirming that the dissolution of this phase during deformation is an important mechanism leading to the break-up of plates and subsequent globulisation. EBSD measurements allowed orientation gradients leading to the final subdivision of the cementite to be determined. Ferrite softening during heavy warm deformation is attributed to dynamic recovery and continuous dynamic recrystallisation, although the evolution of this phase depends, to a great extent, on the region subject to study, as confirmed by local EBSD studies. Misorientation profiles obtained in different regions of ferrite and pearlite enabled the different stages of the microstructural evolution to be monitored for each phase, this being developed via a variety of mechanisms under the same deformation conditions. Finally, the increase in low angle boundary density correlates with the Zenner-Hollomon parameter, and a linear relation between the density of low angle boundaries and steady-state stress estimated for pearlite and ferrite was found, indicating that new boundaries would have been formed dynamically during deformation. High angle boundary density also increases with deformation, although this is almost irrespective of the temperature and strain rate applied.
Autores:
Lukasz Rauch; Krzysztof Bzowski (Autor de correspondencia); Roman Kuziak; et al.
Revista:
METALS
ISSN:
2075-4701
Año:
2019
Vol.:
9
N°:
7
Págs.:
737
The paper presents the design and implementation of a computer system dedicated to the optimization of a hot strip rolling process. The software system proposed here involves the flexible integration of virtual models of various devices used in the process: furnace, descalers, rolling stands, accelerated cooling systems, and coiler. The user can configure an arbitrary sequence of operations and perform simulations for this sequence. The main idea of the system and its implementation details are described in the paper. Besides the computer science part, the material models describing the rolling parameters, microstructure evolution, phase transformations, and product properties are also presented. Effect of precipitation was accounted for various stages of the rolling cycle. Experimental tests were performed to generate data for identification of the models. These include plastometric tests, two-step compression tests, and dilatometric tests. Following this, physical simulations of rolling cycles were performed on Gleeble 3800 to supply data for the verification and validation of the models. Finally, case studies of modern industrial processes were performed, and the selected results are presented.
Autores:
Rauch, L.; Bzowski, K.; Kuziak, R.; et al.
Revista:
METALS
ISSN:
2075-4701
The paper presents the design and implementation of a computer system dedicated to the optimization of a hot strip rolling process. The software system proposed here involves the flexible integration of virtual models of various devices used in the process: furnace, descalers, rolling stands, accelerated cooling systems, and coiler. The user can configure an arbitrary sequence of operations and perform simulations for this sequence. The main idea of the system and its implementation details are described in the paper. Besides the computer science part, the material models describing the rolling parameters, microstructure evolution, phase transformations, and product properties are also presented. Effect of precipitation was accounted for various stages of the rolling cycle. Experimental tests were performed to generate data for identification of the models. These include plastometric tests, two-step compression tests, and dilatometric tests. Following this, physical simulations of rolling cycles were performed on Gleeble 3800 to supply data for the verification and validation of the models. Finally, case studies of modern industrial processes were performed, and the selected results are presented.
Revista:
METALS
ISSN:
2075-4701
Carbide-free bainitic (CFB) steels belong to the family of advanced high strength steels (AHSS) that are struggling to become part of the third-generation steels to be marketed for the automotive industry. The combined effects of the bainitic matrix and the retained austenite confers a significant strength with a remarkable ductility to these steels. However, CFB steels usually show much more complex microstructures that also contain MA (Martensite-Austenite) phase and auto-tempered martensite (ATM). These phases may compromise the ductility of CFB steels. The present work analyzes the substructure evolution during tensile tests in the necking zone, and deepens into the void and crack formation mechanisms and their relationship with the local microstructure. The combination of FEG-SEM imaging, EBSD, and X-ray diffraction has been necessary to characterize the substructure development and damage initiation. The bainite matrix has shown great ductility through the generation of high angle grain boundaries and/or large orientation gradients around voids, which are usually found close to the bainite and MA/auto-tempered martensite interfaces or fragmenting the MA phase. Special attention has been paid to the stability of the retained austenite (RA) during the test, which may eventually be transformed into martensite (Transformation Induced Plasticity, or TRIP effect).
Revista:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
ISSN:
0921-5093
Año:
2017
Vol.:
691
Págs.:
42 - 50
Annealing after cold rolling brings about the activation of recovery and recrystallization in microalloyed steels. The importance of recovery has been most often associated with its effects on the recrystallization kinetics. However, recovery has gained particular importance as an alternative heat treatment under the name "back annealing" or "recovery annealing". In the present work, various annealing treatments were applied to a Nbmicroalloyed steel in the range of temperatures and times where recrystallization is not complete. As a consequence, a large set of tensile strength-ductility pairs was obtained, even for conditions in which recrystallization was avoided. Through non-destructive magnetic coercive field measurements, recovery and partial recrystallization were monitored for each annealing treatment. Magnetic softening is significantly greater than mechanical softening. The variation in recovery in terms of temperature and time is highly affected by the presence of Nb in solution in the hot band (before cold rolling). At low recovery annealing temperatures, 350-450 degrees C, Nb solute drag on dislocations is the main mechanism that controls recovery, whereas at 550 degrees C, Nb strain induced precipitation leads to a recovery plateau in terms of coercive field.
Autores:
Bzowski, K.; Kitowski, J.; Kuziak, R.; et al.
Revista:
COMPUTER METHODS IN MATERIALS SCIENCE
ISSN:
1641-8581
Año:
2017
Vol.:
17
N°:
4
Págs.:
225 - 246
The paper describes the material database, which was developed and included in the VirtRoll computer system dedicated to the design of optimal hot strip rolling technologies. The structure and functionalities of the database are described in the first part of the paper. The integration between the database and the system through the Scalarm platform is described next. Following chapters are dedicated to generation of material data, which are included in the database. These data are coefficients in material models, which include flow stress models, microstructure evolution models, phase transformation models and mechanical properties models. Several models of various complexity and various predictive capabilities were chosen for each mentioned phenomenon. All are mean field models to allow fast simulation of the whole manufacturing chain. Modern steel grades were selected as the case studies. Experimental tests performed to generate the data composed plastometric tests, stress relaxation tests and dilatometric tests. Inverse analysis was applied to determine the coefficients in the model. Discussion of results focused on validation and on new aspects of models recapitulates the paper.
Revista:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE
ISSN:
1073-5623
Año:
2017
Vol.:
48A
N°:
6
Págs.:
2943 - 2948
Very often Nb contributes to the strength of a microalloyed steel beyond the expected level due to the grain size strengthening resulting from thermomechanical processing. Two different mechanisms are behind this phenomenon, and both of them have to do with the amount of Nb remaining in the solution after hot rolling. The first of them is the increase of the hardenability of the steel due to Nb, and the second one is the fine precipitation of NbC in ferrite. The contribution of the precipitates to the work hardening of two thermally and thermomechanically processed microalloyed steels is addressed in this work and this contribution has been integrated into previously developed models by the authors for ferrite-pearlite microstructures. An L (eff) is considered through the effective spacing associated to the different obstacles and their interactions with the moving dislocations. The model obtained shows good agreement with the experimental tensile curves from the end of yield point elongation to the onset of necking. (C) The Minerals, Metals & Materials Society and ASM International 2017
Revista:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE
ISSN:
1073-5623
Año:
2016
Vol.:
47A
N°:
6
Págs.:
3150 - 3164
Boron is added to steels to increase hardenability, substituting of more expensive elements. Moreover, B acts as a recrystallization delaying element when it is in solid solution. However, B can interact with N and/or C to form nitrides and carbides at high temperatures, limiting its effect on both phase transformation and recrystallization. On the other hand, other elements like Nb and Ti are added due to the retarding effect that they exert on the austenite softening processes, which results in pancaked austenite grains and refined room microstructures. In B steels, Nb and Ti are also used to prevent B precipitation. However, the complex interaction between these elements and its effect on the austenite microstructure evolution during hot working has not been investigated in detail. The present work is focused on the effect the B exerts on recrystallization when added to microalloyed steels. Although B on its own leads to retarded static recrystallization kinetics, when Nb is added a large delay in the static recrystallization times is observed in the 1273 K to 1373 K (1000 A degrees C to 1100 A degrees C) temperature range. The effect is larger than that predicted by a model developed for Nb-microalloyed steels, which is attributed to a synergistic effect of both elements. However, this effect is not so prominent for Nb-Ti-B steels. The complex effect of the composition on recrystallization kinetics is explained as a competition between the solute drag and precipitation pinning phenomena. The effect of the microalloying elements is quantified, and a new model for the predictions of recrystallization kinetics that accounts for the B and Nb+B synergetic effects is proposed.
Revista:
KEY ENGINEERING MATERIALS
ISSN:
1013-9826
Año:
2016
Vol.:
716
Págs.:
281 - 290
Revista:
TRATER PRESS
ISSN:
1888-4423
Año:
2015
N°:
46
Págs.:
30 - 39
Revista:
REVISTA DE METALURGIA
ISSN:
0034-8570
One of the major challenges in the development of new steel grades is to get increasingly high strength combined with a low ductile brittle transition temperature and a high upper shelf energy. This requires the appropriate microstructural design. Toughness in steels is controlled by different microstructural constituents. Some of them, like inclusions, are intrinsic while others happening at different microstructural scales relate to processing conditions. A series of empirical equations express the transition temperature as a sum of contributions from substitutional solutes, free nitrogen, carbides, pearlite, grain size and eventually precipitation strengthening. Aimed at developing a methodology that could be applied to high strength steels, microstructures with a selected degree of complexity were produced at laboratory in a Nb-microalloyed steel. As a result a model has been developed that consistently predicts the Charpy curves for ferrite-pearlite, bainitic and quenched and tempered microstructures using as input data microstructural parameters. This model becomes a good tool for microstructural design.
Revista:
MATERIALS SCIENCE FORUM
ISSN:
0255-5476
Año:
2014
Vol.:
783-786
Págs.:
783 - 788
Revista:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
ISSN:
0921-5093
Año:
2013
Vol.:
568
Págs.:
206 - 211
Different recrystallization models are now available in the literature for plain carbon and microalloyed steels. However, the attempts made to unify these models have been unsuccessful due to the considerable scatter in experimental results that support the corresponding equations. In fact, kinetics results can be separated into different groups depending on the testing procedure. In order to cope with this problem and improve the reliability of the different models, the different methods that are currently applied at laboratory need to be re-analyzed. The present work concentrates on the determination of recrystallization/softening kinetics of austenite from torsion tests. To this purpose the softening results obtained by the application of double hit torsion tests to two Nb microalloyed steels and the fraction recrystallized as determined by metallography have been subjected to a direct and an inverse analysis that takes into account the specificity of the torsion test. (C) 2013 Elsevier B.V. All rights reserved.
Revista:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
ISSN:
0921-5093
Año:
2013
Vol.:
578
Págs.:
174 - 180
Although a lot of data are available in the literature on the recrystallization behavior of plain carbon and microalloyed steels, comparisons are often difficult to make due to the effect of different experimental techniques and the type of tests used to obtain these data. Few systematic comparisons can be found in the literature to correlate the different techniques and methods. A previous paper by the present authors concentrates on the analysis of torsion methods. The present study focuses on the recrystallization kinetics determined by using double hit and stress relaxation tests in plane strain compression mode. The specificity of the test and the strain distribution across the section has been incorporated into the analysis, by means of finite element methods. A good correlation has been obtained between the kinetics for stress relaxation and double hit tests. However, some rules should be respected in order to determine the true reaystallization/softening kinetics comparable with those obtained for other deformation modes like torsion. (C) 2013 Elsevier B.V. All rights reserved.
Revista:
JOURNAL OF MATERIALS SCIENCE
ISSN:
0022-2461
Año:
2013
Vol.:
48
N°:
4
Págs.:
1480-1491
A strain reversal applied for both under hot and cold workings produces a microstructural transient which manifests in different ways and at different scales. The evolution of the dislocation network during strain reversal is the result of the competition between two mechanisms. The first mechanism corresponds to the partial untangling and recovery of previously created dislocation network and the second one is associated to the build-up compatible with the current deformation condition. This study proposes a phenomenological formulation based on an effective equivalent strain concept to describe, in a simple way, the several experimental manifestations of the microstructural transient at grain and intragranular scales and its effect on the static recrystallisation kinetics.
Revista:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
ISSN:
0921-5093
Año:
2013
Vol.:
571
Págs.:
57 - 67
The present work relies on the production of selected microstructures through the application of thermal and thermomechanical laboratory tests, followed by mechanical testing and microstructural characterisation. The relations that link the microstructure parameters and the tensile properties have already been discussed and extended from ferrite-pearlite to high strength microstructures in a previous work. Using these results as a starting point, the present work goes a step forward and develops a methodology to consistently incorporate the effect of mesotexture (EBSD) into the existing relations that link the Charpy impact toughness to the microstructure. The result is an extension of the existing equation for the FATT from ferrite-pearlite to high strength microstructures (bainite, tempered martensite). The upper shelf energy for the Nb-microalloyed steel under consideration correlates linearly with the sum of the different terms of the FATT equation (solutes, grain boundary carbides, pearlite and precipitation/dislocations strengthening) excepting the grain size. (C) 2013 Elsevier B.V. All rights reserved.
Revista:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
ISSN:
0921-5093
Año:
2013
Vol.:
561
Págs.:
40 - 51
A series of available equations allows the yield and the tensile strength of low carbon ferrite-pearlite microstructures to be expressed as a function of the optical grain size, steel composition and interstitials in solution. Over the years, as the complexity of steel microstructures has increased, some additional terms have been added to account for precipitation and forest dislocation contributions. In theory, this opens the door for an extension of these equations to bainitic microstructures. Nevertheless, there is a series of difficulties that needs to be overcome in order to improve prediction accuracy. In the present work, different microstructures (ferrite-pearlite, bainite, quenched, and quenched and tempered) were produced and tension tested in a C-Mn-Nb steel. Optical microscopy and EBSD (Electron Back Scattered Diffraction) were applied and the results were compared as a function of the tolerance angle. Based on this work, an adaptation to Pickering's equation is proposed, including its extension to other microstructures rather than ferrite-pearlite. (C) 2012 Elsevier B.V. All rights reserved.
Revista:
MATERIALS SCIENCE FORUM
ISSN:
0255-5476
Año:
2012
Vol.:
715-716
Págs.:
643 - 648
A reversion of the strain produces a modification of the static recrystallization kinetics. Initially, the reversion increases the recrystallization time, that reaches a maximum at a certain strain, and decreases again for increasing reverse strains. This transient on recrystallization kinetics develops over a strain interval similar to that of the microstructural and stress-strain transients. At strains beyond the transient, the reversion can be regarded as a shift on the strain axis. However, at the authors knowledge there is no formulation able to describe the material behaviour during the transient. The present work introduces an equivalent strain concept based on the substructural dissolution/build-up processes taking place as a result of the strain reversal. This formulation allows including the effect of the strain path on recrystallization models.
Revista:
STEEL RESEARCH INTERNATIONAL
ISSN:
1611-3683
Año:
2012
N°:
Special Feature Metal Forming 2012
Págs.:
1147 - 1150
In an authors ¿ previous work a new model that allows reproducing accurately the mechanical transient behaviour in two-stage strain reversal has been presented. This model, based on the isotropic and kinematic hardening concepts, takes advantage of the definition of an equivalent effective strain. This equivalent effective strain has been supposed to control the isotropic stress evolution. Meanwhile, a phenomenological approach has been adopted for the evolution of the kinematic stress to describe the Bauschinger effect. Now the exten-sion of the model to cyclic strain reversal is undertaken in order to assess its applicability. Taking into account some physically reasonable assumptions, the model can be generalised without extra parameters. Some multipass strain reversal torsion tests have been performed in a CMn steel. The experimental results of these tests and the predictions of the model have been compared and a good fitting has been achieved
Revista:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE
ISSN:
1073-5623
Año:
2012
Vol.:
43A
N°:
12
Págs.:
4553 - 4570
While the role of Nb during the processing of austenite is quite clear, what happens in subsequent stages to the concentration of this element left in solution is subject to some debate. In particular, some uncertainty still subsists concerning the eventual homogeneous precipitation in Nb supersaturated polygonal ferrite. The present work was aimed at clarifying the precipitation sequence of Nb during coiling, through a systematic work and a careful selection of the processing conditions in order to produce different scenarios concerning the initial state of Nb. A Nb-microalloyed steel was thermomechanically processed in the laboratory followed by simulated coiling at different temperatures in the 873 K to 1023 K (600 A degrees C to 750 A degrees C) range. Transmission electron microscopy (TEM) showed interphase precipitation of NbC at high coiling temperatures, while at 873 K (600 A degrees C), homogeneous general precipitation took place in ferrite and followed a Baker-Nutting orientation relationship.
Revista:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE
ISSN:
1073-5623
Año:
2012
Vol.:
43A
N°:
12
Págs.:
4571 - 4586
Often, Nb contributes to the strength of a microalloyed steel beyond the expected level because of the grain size strengthening resulting from thermomechanical processing. Two different mechanisms are behind this phenomenon, and both of them have to do with the amount of Nb remaining in solution after hot rolling. The first of them is the increase of the hardenability of the steel as a result of Nb, and the second one is the fine precipitation of NbC in ferrite. Three Nb microalloyed steels were thermomechanically processed in the laboratory and coiled at different temperatures to investigate the effect of Nb content on the tensile properties. The extra strength was linearly related to the Nb remaining in solution after the hot working. The maximum contribution from Nb was reached for a coiling temperature of 873 K (600 A degrees C).
Revista:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE
ISSN:
1073-5623
Año:
2011
Vol.:
42A
N°:
9
Págs.:
2633 - 2642
A strain reversal produces microstructural and mechanical transients that cannot be described with conventional models applicable under monotonic deformation conditions. State-of-the-art models incorporating plastic strain path effects are polarized into continuum constitutive models of cyclic plasticity and multiscale constitutive approaches extrapolating crystallographic hardening models for monocrystals to polycrystals. The present work proposes a model midway between these two approaches that describes the mechanical transient through a combined kinematic-isotropic hardening model and the microstructural transient and its effect on the subsequent static recrystallization kinetics. The incorporation of an effective strain concept makes the link among the different submodels and allows for the first time an accurate reproduction with a reduced number of parameters both for mechanical and microstructural experimental data during the transient following a strain reversal.
Autores:
Rancel, L.; Gomez, M.; Medina, S.; et al.
Revista:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
ISSN:
0921-5093
Año:
2011
Vol.:
530
Págs.:
21 - 27
For a bainitic steel of C = 0.38%, the bainitic packet size measured by OM is about 3.5 times larger than that measured by EBSD with a 15 degrees grain boundary misorientation. This ratio is used to calculate the effective surface energy given by Griffith's model for cleavage fracture. Average ferrite lath width and cementite carbide width values are also measured. Following the general form of Griffith's equation, the effective surface area of cleavage fracture gamma(p) is determined for each microstructural unit. It is concluded that the bainite packet size determined by EBSD with a 15 degrees misorientation angle criterion is the microstructural parameter that controls cleavage crack propagation. Given the relationship between the average unit crack path (UCP) and the bainitic packet size, it is concluded that the effective surface energy of cleavage fracture (gamma(p)) is between 71.6 and 82.6 J m(-2). (C) 2011 Elsevier B.V. All rights reserved.
Revista:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
ISSN:
0921-5093
Año:
2010
Vol.:
527
N°:
42494
Págs.:
934 - 940
Multipass torsion tests were performed on an Nb-microalloyed steel at decreasing temperatures so as to analyze the effect of strain reversal - in the strain accumulation region - on the gamma -> alpha transformation kinetics. Strain reversal involved a significant delay in the start of the transformation as well as a microstructural transient compared to monotonic strain conditions. However, after several passes with no reversal performed within the inter-critical temperature region, both types of tests led to similar microstructures. (C) 2009 Elsevier B.V. All rights reserved.
Revista:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE
ISSN:
1073-5623
Año:
2010
Vol.:
41A
N°:
4
Págs.:
985 - 993
The efficacy of some magnetic inductive parameters and of the maximum differential permeability derived from magnetic hysteresis loop measurements is studied in terms of nondestructively monitoring recovery and the onset and the progress of recrystallization in a cold-rolled low carbon steel. The remnant induction, which is known to be affected by the dislocation density, proved useful to monitor recovery, whereas the induction values measured at higher magnetic fields are not sensitive enough. In order to differentiate between contributions from crystal orientation and from changes in microstructure, the effect of texture evolution during recrystallization is analyzed in terms of the average magnetocrystalline energy. All the magnetic inductive parameters considered have proven to be able to characterize the recrystallized fraction when the usual weakening in the intensity of alpha fiber components and the enhancement of gamma fiber components took place during recrystallization.