Formation of ultrafine-grained microstructure in HSLA steel profiles by linear flow splitting

Bohn, Tilman; Bruder, Enrico; Müller, Clemens

doi:10.1007/s10853-008-2682-2

Cited by 21 publications

(15 citation statements)

References 15 publications

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“…During subsequent steps the splitting roll drives further into the sheet whereas the width of the supporting rolls is reduced so that the thickness of the flanges is kept constant. [6,7,9,13] Fig. 1.…”

Section: Linear Flow Splitting (Lfs)mentioning

confidence: 99%

“…In the present case of ferrite steels with minimum grain dimensions (pancake thickness) of around 80 -100 nm [9] being deformed at room temperature and at strain rates which are typically in the order of 1 -10 s -1 [13], it is relatively save to rule out significant contributions from diffusional processes. The extreme texture intensities of bcc rolling components that have been observed near the split surface [14] are also a strong indicator in this respect, though shear components may also occur under certain feed rates and lubrication conditions [23].…”

Section: Materials Flow and Deformation Mechanisms In Lfsmentioning

confidence: 99%

“…In contrast to conventional SPD processes their primary objective is not the generation of UFG microstructures while retaining the initial shape of the workpiece but the production of branched profiles from plain sheet metal [6][7][8]. However, since LFS and LBS induce severe strains under high hydrostatic compressive stresses they generate UFG microstructures by the same mechanisms [9]. Due to the fact that the deformation is confined to a small volume which exhibits steep strain gradients and maximum strain levels at the surface, LFS and LBS are rather Surface Severe Plastic Deformation (S²PD) processes such as surface mechanical grinding [10], or gradation rolling [11] than bulk SPD processes like equal-channel angular extrusion [12].…”

mentioning

confidence: 99%

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Integral sheet metal design via severe plastic deformation – state of the art and future challenges

Bruder

Kaune

Müller

2014

IOP Conf. Ser.: Mater. Sci. Eng.

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Abstract. The innovative forming processes Linear Flow Splitting (LFS) and Linear Bend Splitting (LBS) were developed to facilitate the continuous production of branched profiles with tailored sheet thickness by inducing severe plastic strain. In contrast to most SPD processes the stress state in LFS and LBS is very complex and plastic deformation is confined to limited volumes which results in steep strain gradients and consequently ultrafine grained (UFG) gradient microstructures. Even though the processes have been commercialized, the increased lightweight potential that originates from the local grain refinement remains mostly idle since it is neither fully understood nor easily assessable yet. The present work shows the state of the art for the LFS and LBS processes and compares the microstructures and distribution of mechanical properties for different steels processed with different LFS parameters. The data is used to identify characteristic manufacturing induced properties that are insensitive to processing parameters. Based on the experimental results a material flow model for the processing zone is proposed which is discussed with respect to the current understanding of plasticity at severe strains.Keywords: Surface Severe Plastic Deformation, Work Hardening, Linear Flow Splitting, Linear Bend Splitting, Gradient Microstructures IntroductionThe use of Severe Plastic Deformation (SPD) as top down approach to refine microstructures of metals and alloys to the submicron range has been investigated extensively during the last decades [1][2][3]. Aside from the scientific interest in fundamental research on plasticity phenomena at large strains, there is also a strong technological interest in these processes which is driven by the exceptional mechanical properties that are associated with the presence of ultrafine grained (UFG) microstructures [1]. Even though high strength materials are needed for a wide range of commercial applications where lightweight design is mandatory, the commercial success of SPD processes is rather limited so far [4]. The main reason for this are most likely the high processing costs of the predominantly discontinuous SPD processes but there is also a strong competition from materials based on modern alloy design and thermo-mechanical processing [5]. However, the Linear Flow Splitting (LFS) and Linear Bend Splitting (LBS) processes that are reviewed in the present paper demonstrate that UFG microstructures by SPD and commercial success in mass markets are no antagonisms. The LFS and LBS processes also referred to as split profiling and split bending have an exceptional position in the field of SPD. In contrast to conventional SPD processes their primary objective is not the generation of UFG microstructures while retaining the initial shape of the workpiece but the production of branched profiles from plain sheet metal [6][7][8]. However, since LFS and LBS induce severe strains under high hydrostatic compressive stresses they generate UFG microstructures by the same mechanisms [9]...

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Section: Linear Flow Splitting (Lfs)mentioning

confidence: 99%

Section: Materials Flow and Deformation Mechanisms In Lfsmentioning

confidence: 99%

mentioning

confidence: 99%

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Integral sheet metal design via severe plastic deformation – state of the art and future challenges

Bruder

Kaune

Müller

2014

IOP Conf. Ser.: Mater. Sci. Eng.

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“…The material used in this investigation is the HSLA steel of the grade ZStE 500 with an average hardness measured to 196 HV0.05 [3]. UFG-microstructures are generated in the flange by the process.…”

Section: Flange Propertiesmentioning

confidence: 99%

“…The flange zone where no further deformation takes place represents the microstructural evolution of the previous splitting steps. This steady-state in the process zone results in that the microstructural and property gradients are only limited to the direction perpendicular to the flange surface [3].…”

Section: Ufg Microstructuresmentioning

confidence: 99%

Further processing of ultrafine-grain materials

2010

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Linear flow splitting enables the production of bifurcated profiles out of sheet metal. Included in the Collaborative Research Centre (SFB) 666 the new roll forming procedure uses obtuse angled splitting rolls and supporting rolls to increase the surface of the band edge. High hydrostatic stresses in the deformed zone lead to an elevated formability of the high strength steel ZStE 500. As a result of the process, the flanges consist partially of an UltraFine-Grain microstructure (UFG). Produced parts are characterized by increased stiffness and high surface hardness. The new structure influences the formability in an extensive way. The investigations presented in this paper discuss the further processing of the flanges from linear flow split profiles. Therefore three point bending tests and roll forming experiments are carried out. A finite element analysis to characterize the damage is set up as well.

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Formability of Ultrafine Grained Metals Produced by Severe Plastic Deformation–An Overview

Bruder

2018

Adv Eng Mater

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Severe plastic deformation (SPD) techniques have attracted considerable attention due to their capability to refine the grain size of metals and alloys down to the ultrafine grained (UFG) regime. A characteristic feature of SPD processes is that they generate semi-finished parts such as rods or sheets, which require further shaping in order to become marketable products. One approach for the shaping of SPD processed materials is the use of metal forming processes, which can be a challenge with regard to the low work hardening rate and tendency to strain localizations of most UFG metals. This article summarizes the current state of knowledge on the formability and forming behavior of UFG metals under different loading scenarios, discussing both limitations and application potential. Furthermore, the interaction between microstructural aspects and the formability, such as the occurrence of strain localizations during and the role of heat treatments are also addressed. Given that the formability of UFG metals has received far less attention than other aspects so far, this work also aims at identifying apparent contradictions as well as scientific and technological questions that need to be addressed in future to expand the current knowledge of the field.

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Formation of ultrafine-grained microstructure in HSLA steel profiles by linear flow splitting

Cited by 21 publications

References 15 publications

Integral sheet metal design via severe plastic deformation – state of the art and future challenges

Integral sheet metal design via severe plastic deformation – state of the art and future challenges

Further processing of ultrafine-grain materials

Formability of Ultrafine Grained Metals Produced by Severe Plastic Deformation–An Overview

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