Severe Plastic Deformation of Ferritic and Austenitic Steels

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$dissertation global and local fracture properties of metal matrix ...$

Danksagung Mein Dank gilt natürlich auch meine Mitstreitern/innen Andrea, Marianne, Kurt, Peter, Woidl, Martin, Robert, Joachim und vielen mehr. Meiner Studienkollegin und Diplomandin Doris wünsche ich für Ihre weitere Zukunft alles Gute. Mein Dank gilt auch der gesamten Familie Pippan. Eure uneingeschränkte Leidenschaft zum Kletter- und Skisport hat mich von Beginn an fasziniert. Durch Euch konnte ich abseits der Wissenschaft die landschaftlichen Reize der Steiermark kennen lernen. Ich danke Euch, Reinhard und Siegrid, das Ihr mir das ermöglich habt. Auch möchte ich mich für die Möglichkeit der regen Konferenzteilnahme bedanken. Einige der vielen Ziele werden mir noch sehr lange in Erinnerung bleiben. Dazu gehören die Aufenthalte in Florida (TMS 2007), Jeju (Rex&GG III, Südkorea 2007), Nürnberg (Euromat 2007), Dresden (APNFM 2008), Goslar (NanoSPD4 2008) und Berlin (Thermec 2009) oder St. Thomas (Plasticity09, US Virgin Islands 2009). Die zahlreichen Abfahrten entlang des “weißen Ringes“ (Metallkunde Kolloquium, Arlberg 2008, 2009) und die Vielzahl an Skitouren in den Wölzer Tauern (NFNmeeting, Planneralm 2007-2009) bleiben mir wohl unvergessliche Erlebnisse. Mein besonderer Dank gilt meiner Familie, meinen Eltern Reingard und Walter, meinen Geschwistern Anna, Christoph und Elisabeth sowie meinen Großeltern Annemarie und Reinhard. Danke für Euren Rückhalt und für Euer Vertrauen, ohne deren ich nicht so weit gekommen wäre. VI Leoben, September 2009
Abstract Abstract The effect of severe plastic deformation on technical relevant steels is of great interest because they have been found to exhibit excellent properties over their coarse grained counterparts. The methods to obtain small scaled microstructures are known for a long time but in recent years a lot of effort is put in research, development and processing of high performance nanostructured materials. In order to explore the unusual structure-property relationship, to improve and make use of the properties and behaviors of nanocrystalline materials more and more research activities have been focused on bulk nanostructured materials. Meanwhile a variety of synthesis techniques have been developed whereby High Pressure Torsion (HPT) is one of the most promising methods for the production of brittle and hard to deform engineering materials. The present work is assigned to the fundamental understanding of severe plastic deformation of ferritic and austenitic single phase steels with respect to the processing temperature. The two types of steel have been chosen as examples for mechanical and magnetic application, respectively. In the first part the microstructural refinement of typical soft magnetic steels such as Fe-3wt% Si and Fe-17wt% Co is studied in detail by transmission electron microscopy. The physical properties of the aforementioned steels are examined particularly with regard to the coercive force Hc and the saturation magnetization Ms. In several studies before it is shown that the grain size substantially affects the magnetic properties of soft magnetic materials. A dramatic decrease in Hc is observed when the grain size D is in the order of the Bloch wall thickness (D smaller than around 100 nm). The most common process which is used in industry for the production of nanocrystalline materials is based on rapid cooling followed by a controlled annealing procedure. In the present work HPT was used to produce nanocrystalline soft magnetic materials by the inherent fragmentation of the initial microstructure. It is shown that different deformation temperatures and subsequent VII
Page 1: Severe Plastic Deformation of Ferri
Page 4 and 5: Affidavit IV I declare in lieu of o
Page 8 and 9: Abstract thermal treatments for sho
Page 10 and 11: Kurzfassung Das großtechnisch am w
Page 12 and 13: Contents IV.4 Evolution of the Micr
Page 14 and 15: Chapter I SPD provide several benef
Page 16 and 17: Chapter I I.3 Principle of High Pre
Page 18 and 19: Chapter I Fig. 1.3: The big HPT too
Page 20 and 21: Chapter I behaviour. Slip dissoluti
Page 22 and 23: Chapter II Fig. 2.1: Steady-state m
Page 24 and 25: Chapter II Fig. 2.4: In-situ torque
Page 26 and 27: Chapter II 14
Page 28 and 29: Chapter III 16 Fe C Cr Cu Ni Co Si
Page 30 and 31: Chapter III III.2 Magnetic Properti
Page 32 and 33: Chapter III cooling-down process to
Page 34 and 35: Chapter III Ring Method The SQUID a
Page 36 and 37: Chapter III independent on the appl
Page 38 and 39: Chapter III 26
Page 40 and 41: Chapter IV The effect of Mn on aust
Page 42 and 43: Chapter IV the designations denote
Page 44 and 45: Chapter IV Fig. 4.4: In-situ torque
Page 46 and 47: Chapter IV Fig. 4.5: a) Microstruct
Page 48 and 49: Chapter IV TEM studies. Transmissio
Page 50 and 51: Chapter IV conditions such as the a
Page 52 and 53: Chapter IV the average grain size i
Page 54 and 55: Chapter IV 42 For each processing t
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Chapter V substructure-free, fully
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Chapter V (I) High local stresses o
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Chapter V Fig. 5.4: Stress-strain c
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Chapter V Fig. 5.6: SSRT fracture s
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Chapter V (III) A high hydrogen abs
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Conclusions discontinuous dynamic r
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Conclusions From the technical poin
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Appendix 58
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Appendix VII.2 HR-TEM microstructur
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Appendix VII.4 SSRT fracture surfac
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Appendix Fig A.9: Higher magnificat
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Appendix VII.5 Microstructures foll
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List of Appended Papers Paper E S.
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Paper A 1. Introduction Over the la
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Paper A transmission electron micro
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Paper A Fig. 4: BSE images of HPT d
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Paper A Fig. 7: SEM images of HPT d
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Paper A temperatures and it seems t
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Abstract Paper B iIIiB Tailoring th
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Fig. 1: Dimensions and orientation
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Paper B evaluated to quantify the s
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Paper B grained metallic materials
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Paper C iIIiC Using Ring Samples to
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Paper C All sets of samples were de
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Paper C Therefore the rings for the
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Paper C (iv) The stress distributio
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Paper D 1. Introduction Metals and
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Paper D Fig. 2: Sequence of microgr
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Paper D approximately 0.4 µm; a se
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Paper D behaviour was studied in-si
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Paper E 1. Introduction Recrystalli
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Paper E consist of a substructure w
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Paper E the centre to the edge afte
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Paper E suspended. This indicates t
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Paper F 1. Introduction Over the pa
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Paper F F - 4 Fig. 1: Schematic ill
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Paper F Fig. 2 demonstrates the rad
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Paper F strains the initial coarse
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Paper F Fig. 6: a) TEM micrograph o
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Paper F Fig. 7: Sequence of TEM mic
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Paper F Fig. 7g represents the micr
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Paper F 4. Discussion The present s
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Paper F Ad iii) It is well known th
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Paper F 5. Conclusions A deformatio
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Severe Plastic Deformation of Ferritic and Austenitic Steels

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