Development of high-strength corrosion-resistant austenitic TWIP steels with C+N [Elektronische Ressource] / von Lais Mújica Roncery

Mújica Roncery, Laís

Informations

• Publié par: ruhr-universitat_bochum
• Publié le: 01 janvier 2010
• Nombre de lectures: 20
• Langue: English
• Poids de l'ouvrage: 42 Mo

Extrait

Development of High-Strength
Corrosion-Resistant Austenitic TWIP Steels
with C+N
Dissertation
zur
Erlangung des Grades
Doktor-Ingenieurin
der
Fakultät für Maschinenbau
der Ruhr–Universität Bochum
von
M.Sc. Laís Mújica Roncery
aus Bogotá, Kolumbien
Bochum 2010Dissertation eingereicht am: 07.10.10
Tag der mündlichen Prüfung: 15.11.2010
Erster Referent: Prof. Dr.-Ing. W. Theisen
Zweiter Referent: Prof. em. Dr.-Ing. H. BernsI
Acknowledgments
I would like to express my gratitude to Prof. Dr.-Ing. Anke Kaysser-Pyzalla, for giving me the
opportunity to start the doctorate at Max-Planck Institut für Eisenforschung in the department
Werkstoffdiagnostik und Technologie der Stähle, to Prof. Dr.-Ing. Werner Theisen, for allowing
mecontinuingthePhDworkattheLehrstuhlWerkstofftechnikoftheRuhr-UniversitätBochum
and for his constant support, to Prof. em. Dr.-Ing. Hans Berns, for his invaluable orientation
and advice in several aspects of the dissertation, to Dr.-Ing. Sebastian Weber, who was also a
great advisor during the whole process of the PhD work as group leader in both institutions.
Additionally, I would like to thank to Prof. Dr. Gerhard Inden, Prof. Dr.-Ing. Michael Pohl,
Prof. Dr. Valentin Gavriljuk and Dr. Yu N. Petrov for the fruitful discussion, support and
collaboration in fundamental topics of the thesis.
Because there are not enough pages to name each one of the persons who helped me throughout
the investigations and who accompanied me day by day, here I would like to thank my friends
and colleagues of the Lehrstuhl Werkstofftechnik and the Institut für Werkstoffe at the RUB
and of the WS department at Max-Planck Institut für Eisenforschung.
And last but not least, to those important persons who are the source of my motivation and
joy, my family and Sascha.IIIII
Table of Contents
Nomenclature VII
1 Introduction 1
1.1 State of the Art - Scientific and Technical Aspects . . . . . . . . . . . . . . . . . 1
1.1.1 TRIP and TWIP Steels . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.2 Austenitic Steels with Carbon + Nitrogen . . . . . . . . . . . . . . . . . 3
1.2 Aims and Means of the Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2 Fundamentals 9
2.1 Thermodynamic Equilibrium Calculations . . . . . . . . . . . . . . . . . . . . . 9
2.2 Diffusion Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.3 Nucleation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.4 The Role of Alloying Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.5 Strengthening Mechanisms of Austenitic Steels . . . . . . . . . . . . . . . . . . . 18
2.5.1 Solid Solution Strengthening . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.5.2 Strain Hardening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.5.3 Grain Refinement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.5.4 Dispersion Strengthening . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.5.5 Twinning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.5.6 Stacking Fault Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.6 Corrosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
2.7 Welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3 Methods of Investigation 29
3.1 Thermodynamic Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.1.1 Phase Diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.1.2 Scheil Solidification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30IV Table of Contents
3.1.3 Nucleation of Precipitates . . . . . . . . . . . . . . . . . . . . . . . . . . 30
3.1.4 Stacking Fault Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.2 Thermodynamic - Kinetic Calculations . . . . . . . . . . . . . . . . . . . . . . . 31
3.2.1 Diffusion Annealing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.2.2 Precipitation of Carbides and Nitrides . . . . . . . . . . . . . . . . . . . 31
3.3 Material Manufacture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
3.3.1 Casting, Hot Working and Heat Treatment . . . . . . . . . . . . . . . . . 32
3.3.2 Welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
3.3.3 Optical Emission Spectrometry . . . . . . . . . . . . . . . . . . . . . . . 34
3.4 Mechanical Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3.4.1 Tensile Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3.4.2 Hardness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.4.3 Impact Toughness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.5 Impact Wear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.6 Microstructure Investigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.6.1 Optical Microscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.6.2 Scanning Electron Microscopy . . . . . . . . . . . . . . . . . . . . . . . . 36
3.6.3 X-Ray Diffraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.6.4 Transmission Electron Microscopy . . . . . . . . . . . . . . . . . . . . . . 37
3.7 Chemical Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.7.1 Current Density - Potential Electrochemical Measurement . . . . . . . . 38
3.7.2 Intercrystalline Corrosion . . . . . . . . . . . . . . . . . . . . . . . . . . 38
4 Results 39
4.1 Selection of Suitable Compositions . . . . . . . . . . . . . . . . . . . . . . . . . 39
4.1.1 Isothermal Phase Diagrams . . . . . . . . . . . . . . . . . . . . . . . . . 39
4.1.2 Isoplethal Phase . . . . . . . . . . . . . . . . . . . . . . . . . . 40
4.1.3 Selected Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4.2 Basis for Manufacturing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
4.2.1 Scheil Solidification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
4.2.2 Diffusion Annealing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
4.2.3 Microstructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
4.2.4 Heat Treatment - Precipitation of Carbides and Nitrides . . . . . . . . . 45Table of Contents V
4.3 Stacking Fault Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
4.4 Mechanical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
4.4.1 Tensile Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
4.4.2 Hardness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
4.4.3 Impact Toughness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
4.5 Impact Wear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
4.6 Corrosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
4.6.1 Electrochemical Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
4.6.2 Intercrystalline Corrosion . . . . . . . . . . . . . . . . . . . . . . . . . . 52
4.7 Weldments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
5 Discussion 55
5.1 Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
5.1.1 Austenite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
5.1.2 Decomposition of Austenite . . . . . . . . . . . . . . . . . . . . . . . . . 65
5.2 Effect of Structure on Properties . . . . . . . . . . . . . . . . . . . . . . . . . . 70
5.2.1 Strengthening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
5.2.2 Toughness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
5.2.3 Impact Wear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
5.2.4 Corrosion Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
5.3 Effect of Structure on Manufacturing . . . . . . . . . . . . . . . . . . . . . . . . 85
6 Summary 91
Tables 95
Figures 107
References 168VI Table of ContentsVII
Nomenclature
Abbreviations
TRIP Transformation induced plasticity
TRIP Twinning induced plasticity
SF Stacking fault
SFE Stacking fault energy
PLC Portevin - Le Chatelier
DSA Dynamic strain aging
SEM Scanning electron microscopy
TEM Transmission electron microscopy
EBSD Electron back scattering diffraction
XRD X-Ray diffraction
EDX Energy dispersive X-ray spectrometry
FIB Focused ion beam
DIC Digital image correlation
RD Rolling direction
TD Transverse direction
ND Normal direction
IQ Image quality
IPF Inverse pole figure
ODF Orientation distribution function
LE Local equilibrium
LENP Local non partitioning
PE Paraequilibrium
DBTT Ductile to brittle transition temperatureVIII Nomenclature
FATT Fracture appearance transition temperature
USE Upper shelf energy
LSE Lower shelf energy
SHE Standard hydrogen electrode
IC Intercrystalline corrosion
TTT Time-temperature-transformation (isothermal)
PREN Pitting resistance equiva